Etiology of Cephalosporium stripe in relation to the expression of resistance in cultivars of winter
wheat (Triticum aestivum L.)
by Joseph Brian Morton
A thesis submitted in partial fulfillment of the requirements for the degree of DOCTOR OF
PHILOSOPHY in Plant Pathology
Montana State University
© Copyright by Joseph Brian Morton (1979)
Abstract:
Systemic spread of the vascular pathogen, Cephalosporium gramineum was characterized relative to
anatomical and developmental features of its winter wheat (Triticum aestivum L.) host. The pattern of
foliar chlorotic striping and the distribution of fungal cells in vascular bundles within consecutive
nodes were examined at various growth stages of winter wheat. Pathogen movement appeared to be
restricted by xyIem maturation gradients between internodes, within nodes, and within leaves.
Restriction of symptom development above that imposed by maturation gradients was exhibited by the
winter wheat cultivar Crest LRC 40, This response was attributed to increased gelation and gummo-sis
within the xyIem and/or to inhibition of fungal speculation. A descriptive model was developed that
related pathogen invasion and colonization to symptom expression. All evidence suggested that this
pathogen is incapable of actively penetrating living cells at any time during the disease cycle. The
number and pattern of vascular bundles in different winter wheat cultivars and the temporal association
between pathogen colonization and symptom induction formed the basis for a disease index rating
system. Leaves were quantitatively rated on a scale of one to eleven, with one denoting one stripe per
leaf and eleven denoting complete chlorosis. Both the movement and distribution of C. gramineum and
the disease index rating system have practical implications in a germplasm development program. The
first emphasizes the need to separate rate of disease development from rate of host development in
evaluating winter wheat genotypes. The second provides a valuable tool for monitoring symptom
expression within and among plants of different genotypes.
The pattern of stripe formation on Cephalosporium gramineum infected flag leaves of the susceptible
winter wheat cultivar Marias was closely correlated with depression of relative water content,
conductance, net photosynthesis, and chlorophyll content. All measurements were made in the field
from paired healthy and infected plants. Regression analysis indicated that all four physiological
parameters were interrelated, providing evidence that stripe formation coincides with localized
restriction of lateral water movement, reduction in transpiration rate, suppressed photosynthetic
activity, and loss of chlorophyll. Chlorosis around colonized vascular bundles is therefore attributed to
effects of localized water deficits rather than a diffusible toxin. Highly significant correlations between
all four parameters and the disease index suggested that visual scoring of infected leaves is an accurate
indicator of physiological effects of symptom expression. The influence of pathogenesis on vegetative
and reproductive growth patterns was followed throughout the ontogeny of three winter wheat
cultivars, Marias, Crest LRC 40, and P.I. 278212. Internode elonaation was inhibited, but leaf
exnansion remained unaffected by disease. Differential responses between stem and leaves was
ascribed to the relationship between pathogen movement and host xyIem maturation gradients. Spikelet
number was unaltered, seed number was reduced in Marias and P, I . 278212, and thousand kernel
weight was sharply reduced in Marias and P. I . 278212 but only moderateIy reduced in Crest LRC 40.
Thus, the effects of this disease are not pronounced until after anthesis during grain filling. Duration of
photosynthesis, as measured by averaging COg exchange of ten flag leaves of each cuI -tivar over a 35
day period after anthesis, appeared to play a major role in seed weight reduction. Both Marias and P.I.
278212 are highly susceptible to Cephalosporium stripe based on reduction in seed weight, whereas
Crest LRC 40 is more resistant.
Seven winter wheat cultivars representing established varieties, as well as selections from the USDA
World Collection, were examined to identify possible phenotypes expressing resistance to
Cephalosporium gramineum. Two types of resistance were observed: (l) exclusion of the pathogen
such that successful colonization was prevented and (2) restriction of systemic spread of the pathogen
following successful colonization of the host. The former was expressed as a reduction in the
percentage of diseased plants. The latter was expressed as a reduction in the percentage of diseased
tillers per infected plant and also as a reduction in the rate and severity of disease development. Both
types of resistance were expressed independently. P.I. 278212 exhibited a low infection percentage, but
was rapidly and completely invaded after successful ingress. Crest LRC 40, on the other hand,
demonstrated a high percentage of diseased plants, but showed restricted infection between tillers and a
moderate rate of systemic invasion. Each phenotype may be identified and evaluated separately if
seeding rates are set to permit recognition of individual plants. Maximum resistance would be attained
if both types of resistance were incorporated into a single agronomical Iy desirable genotype. Infection
among plants occurred only in soils undergoing frost-heaving, suggesting that root breakage was
essential for ingress of the fungus into the host. Differential responses between cultivars to pathogen
exclusion could not be attributed to gross changes in either propagule levels in the soil or root mass.
Cumulative effects of microhabitat interactions between the soil-root interface or differential responses
to woundhealing are suggested as possible explanations for dissimilarities between cultivars. ETIOLOGY OF CEPHALOSPORIUM STRIPE IN RELATION TO
THE EXPRESSION OF RESISTANCE IN CULTIVARS OF
WINTER WHEAT ( TRITICUM AESTIVUM L . )
by
JOSEPH BRIAN MORTON
A t h e s i s s u b m it t e d in p a r t i a l f u l f i l l m e n t
o f t h e r e q u ir e m e n t s f o r t h e deg ree
of
DOCTOR OF PHILOSOPHY
in
P l a n t P a th o lo g y
Approved:
C h a ir p e r s o n ,
G ra d u a te Committee
Head, M a jo r D epartm ent
G ra d u a te Dean
MONTANA STATE UNIVERSITY
Bozeman, Montana
J u ly ,
1979
ACKNOWLEDGMENTS
I wo u ld
lik e
the f o l l o w i n g
Dr.
t o e x t e n d my s i n c e r e g r a t i t u d e and a p p r e c i a t i o n t o
people :
Don E. M a t h r e ,
f o r h is p ro fe s s io n a l guidance,
ideas,
patience,
\
and f r i e n d s h i p w h i l e s e r v i n g as my m a j o r p r o f e s s o r t h r o u g h o u t t h e c o u r s e
of th is
study.
The members o f my t h e s i s c o m m i t t e e .
C a rro ll,
Dr.
A l l e n T a y l o r , and Dr.
Dr.
E.L,
I . K. M i l l s ,
S h ar p , Dr. T.W.
for th e ir
t i m e and
in va lua b le a d v ic e .
Dr.
A . L.
Scharen, f o r h elp
i n t h e d ev e lo p me nt and a p p l i c a t i o n o f
a p o r t a b l e c l o s e d s yst em f o r m e a s ur i n g CC^ exchange in t h e f i e l d .
Ro b er t J o h n s t o n ,
obstacles during t h i s
f o r his assistance
i n o v er com ing numerous
study.
L o r i e Ewing and R i c k R u f f ,
f o r s u p p o r t i n g my r e s e a r c h e f f o r t s w i t h
t h e i r h ar d w o r k and e n t h u s i a s m .
The Montana A g r i c u l t u r a l
Department,
fo r providing fin a n c ia l
My f a m i l y ,
educational
E x p e r i m e n t S t a t i o n and t h e P l a n t P a t h o l o g y
a id w i t h a re search a s s i sta.ntshi p .
f o r t h e i r s u p p o r t and encouragement d u r i n g my f o r m a t i v e
years.
My w i f e ,
S o n ja , f o r her w i l l i n g
s a c rific e ,
u nd e rs ta n d in g , love,
and moral s u p p o r t o v e r t h e p a s t f o u r y e a r s .
My d a u g h t e r ,
me o f what
E l i s e , f o r h er
I once was and wh at
i n n o ce n ce and c u r i o s i t y , w h i c h remi nds
I s h o u l d be.
TABLE OF CONTENTS
Page
VITA . ................................. ................................................................................................
ACKNOWLEDGMENTS. ■. .
Ii
. . ........................................................................................
TABLE OF CONTENTS.............................................. ...
I 11
. . .............................
iv
LIST OF T A B L E S .......................
LIST OF' FIGURES.
vi
............................................................ ............................................. v i I i
ABSTRACT................................................................................................................... •
INTRODUCTION...........................................................
CHAPTER ONE:
x
I
RELATIONSHIP BETWEEN FOLIAR SYMPTOM DEVELOPMENT
AND THE MOVEMENT AND DISTRIBUTION OF CEPHALOSPORIUM GRAM I NEUM THROUGHOUT THE ONTOGENY OF .
I TS WINTER WHEAT (TRI Tl CUM AESTI VUM L . ) HOST . . .
5
I n t r o d u c t i o n ..............................................
6
M a t e r i a l s and Methods
8
..........................................
R e s u l t s . . . . , .................................................................................................
10
Discuss? o n ..................................................................................
30
L ite ra tu re
38
CHAPTER TWO:
C ite d .
PHYSIOLOGICAL EFFECTS OF CEPHALOSPORIUM STRIPE
ON GROWTH AND YIELD OF WINTER WHEAT ( TRIT.I CUM
AESTIVUM L , ) CUL TI V A R S ............................................................
41
I n t r o d u c t i o n ............................................................
42
M a t e r i a l s and Methods
44
.........................................
R e s u l t s ....................... .... ....................................................................
D i s c u s s i o n .......................
• • • •
52
62
V
Page
L ite ra tu re
CHAPTER THREE:
C i t e d .................................................................................................
69
IDENTIFICATION OF RESISTANCE TO CEPHALOSPORIUM
STRIPE IN SELECTED WINTER WHEAT ( TRITICUM
AESTIVUM L . ) CULTIVARS......................................... / . . . .
73
Introd u ction .
......................................................................................................
M a t e r i a l s and Methods
..........................................
74
77
R e s u l t s .......................
80
Di scuss i o n .......................
95
L iteratu re
C i t e d ................................................................................................
SUMMARY AND CONCLUSIONS..................................................................
102
10
vi
LIST OF TABLES
Tab I e
I- 1
Page
R e l a t i o n s h i p between f o l i a r s t r i p i n g p a t t e r n s and
movement o f C e ph al o s po r i um gramineum i n c o n s e c u t i v e
le av es o f i n f e c t e d M a ri a s w i n t e r wheat p l a n t s a t
d i f f e r e n t d e v e l o p m e n t a l g r o w t h s t a g e s ..............................................
16
1-2
D i s t r i b u t i o n o f C e p h a l os p or i u m gramineum in each
b u n d l e t y p e w i t h i n c o n s e c u t i v e nodes o f two w i n t e r
wheat c u l t i v a r s a t d i f f e r e n t g r o w t h s t a g e s ..................................... 25
I -3
R e a c t i o n o f t wo w i n t e r wheat c u l t i v a r s t o i n f e c t i o n
by C e p h a l os p or i u m gramineum as r e l a t e d t o a c c u m u l a t i o n
o f g e l s , c o n i d i a , and m y c e l i a w i t h i n t h e lumina o f
i n f e c t e d v a s c u l a r b u n d l e s .....................................................................
Il-I
11-2
.
29
C o r r e l a t i o n s between n e t p h o t o s y n t h e s i s , r e l a t i v e w a t e r
c o n t e n t , c o n d u c t a n c e , and c h l o r o p h y l l c o n t e n t i n Ce p ha l os p o r i u m gramineum i n f e c t e d f l a g l e av es o f t h e s u s c e p t i b l e
w i n t e r wheat c u l t i v a r M a r i a s . ................................................................
54
Percent r e d u c t io n w it h re sp ect t o h e a lt h y c o n t r o l s o f
c o n s e c u t i v e i n t e r n o d e l e n g t h s o f w i n t e r wheat s i n f e c t e d
w i t h C e p h a l os p or i u m gramineum ................... ..........................................
56
I 1-3
E f f e c t o f C e p h a l os p or i u m gramineum i n f e c t i o n on l e a f
a r e as o f t h r e e w i n t e r wheat c u l t i v a r s . ..........................................57
11-4
The e f f e c t s o f C e ph al o s po r i um s t r i p e symptom d ev el op men t
on w i n t e r wheat y i e l d components and t h e i r r e l a t i o n s h i p
t o the d u r a t i o n o f p h o to s y n th e s is o f f l a g leaves f o l l o w i n g
a n t h e s i s. ................................................... ...................................................... ....
Ill-I
11 1-2
I I I -3
58
D i f f e r e n t i a l res pon se s o f s e l e c t e d w i n t e r wheat c u l t i v a r s
t o t he i n c i d e n c e o f i n f e c t i o n by Ce p ha l os po r iu m gramineum
..
81
E ffect o f in fe c tio n
h e i g h t and y i e l d o f
.
85
by C e p h a l o s p o r i urn, gramineum on
t h r e e w i n t e r wheat c u l t i v a r s i n
E f fe c t o f d i f f e r e n t s o i l environments r e l a t i n g
i n j u r y o r b reakage on t he p e r
w i t h C e p h a l os p or i u m gramineum
1978.
to root
90
vii
T a bl e
I I 1-4
I I 1-5
Page
E f f e c t o f d i f f e r e n t i n o c u l a t i o n p r o c e d u r e s in t h e
• f i e l d on t h e p e r c e n t a g e o f t i l l e r s i n f e c t e d w i t h
CephalOspori um gramineum among t h r e e w i n t e r wheat
c u l t i v a r s in 1978 . . ! ..................................................................... ....
.
E f f e c t o f C e ph al o s po r i um gramineum i n o cu lu m d e n s i t y
on i n f e c t i o n o f t h r e e w i n t e r wheat c u l t i v a r s o f
d i f f e r i n g s u s c e p t i b i l i t y .............................................................................. 94
92
v ii i
LIST OF FIGURES
Figure
I -1
1-2
1-3
1-4
1-5
Ir6
I I- 1
11-2
Il-B
11-4
Page
C h l o r o t i c s t r i p i n g p a t t e r n on a C e p h a l o s p o r i urn
gramineum i n f e c t e d w i n t e r wheat l e a f and an i l l u s ­
t r a t i o n o f a t r a n s v e r s e s e c t i o n o f t h a t l e a f showing
the d i s t r i b u t i o n o f v a s c u la r bundles c o lo n iz e d . . . . . .
11
The p a t h o l o g i c a l e f f e c t s , o f v a s c u l a r b un dl e c o l o n i z a ­
t i o n by C e p h a l os p or i u m gramineum i n i n f e c t e d w i n t e r
wheat l e a v e s ......................................................................................................
13
I l l u s t r a t i o n o f t h e v a s c u l a r b u n d l e t y p e s and t h e i r
c o u r s e t h r o u g h a w i n t e r wheat node ...................................................
18
L ig h t microgra phs o f c r o s s - s e c t ions through a w i n t e r
wheat node i n f e c t e d w i t h C e ph al o s po r i um g r a m i neum,
showing v a s c u l a r b un d l e t y p e s and t h e i r d i s t r i b u t i o n a t
l e v e l s A-C i n d i c a t e d by a r r o w s i n F i g u r e 1 - 3 ............................
19
I l l u s t r a t i o n o f x y Iem m a t u r a t i o n g r a d i e n t s i n a w i n t e r
wheat p l a n t ..........................................................................................................
21
L i g h t m i c r o g r a p h s showing x y Iem d i f f e r e n t i a t i o n i n
response t o a m a t u r a t i o n g r a d i e n t i n t h e stem o f a
w i n t e r wheat p l a n t . . . . . .
............................................................
24
P l e x i g l a s s t u b u l a r chamber f o r m e a s ur i n g c arbon d i o x i d e
exchange i n w i n t e r wheat l e a v es i n t h e f i e l d ............................
47
P o l y u r e t h a n e foam d e v i c e f o r s a t u r a t i n g 1.5 cm X 1 .5 cm
segments c u t f r o m h e a l t h y and Ce p ha l os po r iu m g r a m i neum
i n f e c t e d w i n t e r wheat le a ve s ................................................................
50
The r e l a t i o n s h i p between s t r i p e f o r m a t i o n in C e p ha l o s p o r i u m gramineum i n f e c t e d f l a g le a ve s and n e t p h o t o ­
s y n t h e s i s , r e l a t i v e w a t e r c o n t e n t , c o n d u c t a n c e , and
c h l o r o p h y l l c o n t e n t , ...................................................................................
53
R e l a t i o n s h i p between s t r i p e f o r m a t i o n and n et p h o t o ­
s y n t h e s i s i n C e p h a l o s p o r i urn gramineum i n f e c t e d f l a g
l e a v es o f t h r e e w i n t e r wheat c u l t i v a r s ..........................................
60
ix
Figure
Page
Ill-I
The r a t e o f f o l i a r s t r i p e f o r m a t i o n on t h e u pp e r f o u r
le a ve s o f p r i m a r y t i l l e r s f r o m t h r e e w i n t e r wheat .
c u l t i v a r s i n f e c t e d w i t h C e ph al o s po r i um g r ami neu m....................... 83
I I 1-2
The d i f f e r e n t i a l , r espons es o f t h r e e w i n t e r wheat
c u l t i v a r s t o i n f e c t i o n by Cephal o s p o r I urn gramineum
one month a f t e r h ea d i ng . . . ................................................................. 84
X
ABSTRACT
S y s t e m i c s pr ead o f t h e v a s c u l a r p a t h o g e n , C e p h a l os p or i u m gramineum
was c h a r a c t e r i z e d r e l a t i v e t o a n a t o m i c a l and d e v e l o p m e n t a l f e a t u r e s o f
i t s w i n t e r wheat (T r i t i cum a e s t i v u m L . ) h o s t .
The p a t t e r n o f f o l i a r
c h l o r o t i c s t r i p i n g and t h e d i s t r i b u t i o n o f f u n g a l c e l l s in v a s c u l a r
b u n d l e s w i t h i n c o n s e c u t i v e nodes were examined a t v a r i o u s g r o w t h st ag e s
o f w i n t e r w h e a t . . Pathogen movement a pp ear ed t o be r e s t r i c t e d by x y Iem
m a t u r a t i o n g r a d i e n t s between i n t e r n o d e s , w i t h i n n o d e s , and w i t h i n
leaves.
R e s t r i c t i o n o f symptom d ev e lo p me nt above t h a t imposed by
m a t u r a t i o n g r a d i e n t s was e x h i b i t e d by t h e w i n t e r wheat c u l t i v a r Cr es t
LRC 40,
T h i s r e s p on s e was a t t r i b u t e d t o i n c r e a s e d g e l a t i o n and gummos i s w i t h i n t h e x y Iem a n d / o r t o i n h i b i t i o n o f f u n g a l s p o r u l a t i o n .
A
d e s c r i p t i v e model was d e v e l o p e d t h a t r e l a t e d pathogen i n v a s i o n and
c o l o n i z a t i o n t o symptom e x p r e s s i o n .
Al I e v i d e n c e s u g g e st e d t h a t t h i s
pat hog en i s i n c a p a b l e o f a c t i v e l y p e n e t r a t i n g l i v i n g c e l l s a t any t i m e
d u rin g the d isease c y c l e .
The number and p a t t e r n o f v a s c u l a r b u n dl e s
i n d i f f e r e n t w i n t e r wheat c u l t i v a r s and t h e t e m po r al a s s o c i a t i o n
between p at hogen c o l o n i z a t i o n and symptom i n d u c t i o n formed t h e b a s i s
f o r a d i s e a s e i n d ex r a t i n g s yst em.
Leaves were q u a n t i t a t i v e l y r a t e d on
a s c a l e o f one t o e l e v e n , w i t h one d e n o t i n g one s t r i p e p e r l e a f and
ele ven d e n o tin g complete c h l o r o s i s .
Both t h e movement and d i s t r i b u t i o n
o f Cy gramineum and t h e d i s e a s e i n d e x r a t i n g system have p r a c t i c a l
i m p l i c a t i o n s i n a germplasm dev el op men t p r ogr am.
The f i r s t emphasizes
t h e need t o s e p a r a t e r a t e o f d i s e a s e d ev el op men t f ro m r a t e o f h o s t
d e v e lo p me nt i n e v a l u a t i n g w i n t e r wheat g e n o t y p e s .
The second p r o v i d e s
a v a l u a b l e t o o l f o r m o n i t o r i n g symptom e x p r e s s i o n w i t h i n and among
p la n t s o f d i f f e r e n t genotypes.
The p a t t e r n o f s t r i p e f o r m a t i o n on Ce p ha l os po r iu m gramineum i n f e c ­
t ed f l a g l e a v es o f t h e s u s c e p t i b l e w i n t e r wheat c u l t i v a r M a r i a s was
c l o s e l y c o r r e l a t e d w i t h d e p r e s s i o n o f r e l a t i v e w a t e r c o n t e n t , conduc­
t a n c e , n e t p h o t o s y n t h e s i s , and c h l o r o p h y l l c o n t e n t .
Al I measurements
were made in t h e f i e l d f r o m p a i r e d h e a l t h y and i n f e c t e d p l a n t s .
Reg­
r e s s i o n a n a l y s i s i n d i c a t e d t h a t a l l f o u r p h y s i o l o g i c a l p a r a m e t e r s were
i n t e r r e l a t e d , p r o v i d i n g evidence t h a t s t r i p e fo r m a tio n c o in c id e s w it h
l o c a l i z e d r e s t r i c t i o n o f l a t e r a l w a t e r movement, r e d u c t i o n i n t r a n s ­
p i r a t i o n r a t e , su pp r es s ed p h o t o s y n t h e t i c a c t i v i t y , and l o s s o f c h l o r o ­
p h y ll.
C h l o r o s i s ar ound c o l o n i z e d v a s c u l a r bun dl es i s t h e r e f o r e
a t t r i b u t e d . t o e f f e c t s o f l o c a l i z e d w a t e r d e f i c i t s r a t h e r t han a d i f ­
fu sib le toxin.
H i g h l y s i g n i f i c a n t c o r r e l a t i o n s between a l l f o u r p a r a ­
m e t e r s and t h e d i s e a s e i n d e x s u gg est ed t h a t v i s u a l s c o r i n g o f i n f e c t e d
l e av es i s an a c c u r a t e i n d i c a t o r o f p h y s i o l o g i c a l e f f e c t s o f symptom
expression.
The i n f l u e n c e o f p a t h o g e n e s i s on v e g e t a t i v e and r e p r o ­
d u c t i v e g r o w t h p a t t e r n s was f o l l o w e d t h r o u g h o u t t h e o n t o g e n y o f t h r e e
xi
w i n t e r wheat c u l t i v a r s , M a r i a s , C r e s t LRC hO, and P . I . 278212.
Internode e l o n a a t i on was i n h i b i t e d , b u t l e a f e x o a n s i o n re ma in ed u n a f f e c t e d '
by d i s e a s e .
D i f f e r e n t i a l r esponses between stem and l e av es was
a s c r i b e d t o t h e r e l a t i o n s h i p between p at hogen movement and h o s t x y Iem
m aturation g ra d ie n ts .
S p i k e l e t number was u n a l t e r e d , seed number was
reduced i n M a r i a s and P , I . 278212, and t ho usan d k e r n e l w e i g h t was
s h a r p l y reduced i n M a r i a s and P . I . 278212 b u t o n l y m o d e r a t e I y reduced
i n C r e s t LRC 40.
Thus, t h e e f f e c t s o f t h i s d i s e a s e a r e n o t pronounced
u n t i l a f t e r a nthesis during gra in f i l l i n g .
Duration o f pho tosyn th esis,
as measured by a v e r a g i n g COg exchange o f t e n f l a g le a ve s o f each c u I t i v a r o v e r a 35 day p e r i o d a f t e r a n t h e s i s , appeared t o p l a y a m a jo r
r o l e in seed w e i g h t r e d u c t i o n .
Both M a r i a s and P . I . 278212 a r e h i g h l y
s u s c e p t i b l e t o C e p h a l os p or i u m s t r i p e based on r e d u c t i o n i n seed w e i g h t ,
whereas C r e s t LRC 40 i s more r e s i s t a n t .
Seven w i n t e r wheat c u l t i v a r s r e p r e s e n t i n g e s t a b l i s h e d v a r i e t i e s , .
as w e l l as s e l e c t i o n s f r o m t h e USDA World C o l l e c t i o n , were examined t o
i d e n t i f y p o s s i b l e p h e n ot y p es e x p r e s s i n g r e s i s t a n c e t o Ce p ha l os po r iu m
g rami n eum. Two t y p e s o f r e s i s t a n c e were o b s e r v e d : ( l ) e x c l u s i o n o f t he
pat hog en such t h a t s u c c e s s f u l c o l o n i z a t i o n was p r e v e n t e d and (2) r e s ­
t r i c t i o n o f s y s t e m i c s p re ad o f t h e pat hog en f o l l o w i n g s u c c e s s f u l
c o l o n i z a t i o n o f the h o s t.
The f o r m e r was e x p r e s s e d as a r e d u c t i o n i n
the percentage o f diseased p l a n t s .
The l a t t e r was e x p r e s s e d as a
r e d u c t i o n in t h e p e r c e n t a g e o f d i s e a s e d t i l l e r s p e r i n f e c t e d p l a n t and
a l s o as a r e d u c t i o n i n t h e r a t e and s e v e r i t y o f d i s e a s e d e v e l o p m e n t .
Both t y p e s o f r e s i s t a n c e were e x p r e s s e d i n d e p e n d e n t l y .
P . I . 278212
e x h i b i t e d a low i n f e c t i o n p e r c e n t a g e , b u t was r a p i d l y and c o m p l e t e l y
in va de d a f t e r s u c c e s s f u l i n g r e s s . . C r e s t LRC 40, on t h e o t h e r h an d ,
d e m o n s t r a t e d a h i g h p e r c e n t a g e o f d i s e a s e d p l a n t s , b u t showed r e s t r i c ­
t e d i n f e c t i o n between t i l l e r s and a mod er at e r a t e o f s y s t e m i c i n v a s i o n .
Each p he no ty p e may be i d e n t i f i e d and e v a l u a t e d s e p a r a t e l y i f s e e d in g
ra te s are s e t t o p e rm it r e c o g n i t i o n o f i n d i v i d u a l p l a n t s .
Maximum
r e s i s t a n c e w o u l d be a t t a i n e d i f b ot h t y p e s o f r e s i s t a n c e were i n c o r p o ­
ra te d i n t o a s i n g l e agronomical I y d e s i r a b l e genotype.
I n f e c t i o n among
p l a n t s o c c u r r e d o n l y in s o i l s u n d e r g o i n g f r o s t - h e a v i n g , s u g g e s t i n g
t h a t r o o t b r ea ka g e was e s s e n t i a l f o r i n g r e s s o f t h e f u n g u s i n t o t he
host.
D i f f e r e n t i a l r e sp on se s between c u l t i v a r s t o p a th og e n e x c l u s i o n
c o u l d n o t be a t t r i b u t e d t o g r o s s changes in e i t h e r p r o p a g u l e l e v e l s in
t he s o i l o r r o o t mass.
Cumulative e f f e c t s o f m i c r o h a b i t a t i n t e r a c t i o n s
between t h e s o i l - r o o t i n t e r f a c e o r d i f f e r e n t i a l resp on se s t o wound­
h e a l i n g a r e su gg e st ed as p o s s i b l e e x p l a n a t i o n s f o r d i s s i m i l a r i t i e s
between c u l t i v a r s .
INTRODUCTION
C e p ha l o s p o r i u m gra mi neu m, c a u s a l a g e n t o f C e p h a l o s p o r i u m s t r i p e ,
i s t h e o n l y f u n g a l v a s c u l a r p at hogen o f w i n t e r w h e a t .
Consequently,
s t u d y o f t h e f u n g u s , t h e w i n t e r wheat h o s t , and most o f a l l ,
the h o s t-
p at hogen
and
in te ra ctio n
epidem iological
r e la t io n s h ip s o f t h i s disease.
The P a t h o g e n ,
c o n ce r ne d
d isease
(I)
is re q u ir e d t o c h a r a c t e r i z e e t i o l o g i c a l
its
Most s t u d i e s on t h e b i o l o g y o f (X gramineum have
m orphological, c u l t u r a l ,
i n c i d e n c e and d e v e l o p m e n t , and
in h a b it p la nt
residues
in t h e s o i l .
(2)
and n u t r i t i o n a l
its a b ilit y
The f i r s t a f f e c t s
hab it to
t o c o l o n i z e and
the pathogen's
c a p a c i t y t o s p o r u l a t e and in va de t h e h o s t ' s v a s c u l a r n e t w o r k .
second
in f lu e n c e s the pathogen's o v e r w in t e r i n g a b i l i t y , which determines
inoculum p o t e n t i a l
£.
The
in the s o i l
f r o m one g r o w i n g season t o t h e n e x t .
gramineum i s an i m p e r f e c t f un g us b e l o n g i n g t o t h e o r d e r
M o n i l i a l e s and. t h e f a m i l y Moni I i a c e a e .
sp eculating s tr u c tu r e s ,
c lu s te rs of h yaline ,
the t i p s .
This c l a s s i f i c a t i o n
i s based on
in which c o n id io p h o re s are se pa ra te w it h
l oose
o n e - c e l led c o n i d i a pro du ce d i n a s l i m e , m a t r i x at
More r e c e n t l y ,
Hymenula c e r e a l i s E l l .
h owev er,
this
f un g us has been renamed
& Ev. o f t he f a m i l y T u b e r c u l a r i a c e a e because i t
p ro du c es c o n i d i o ph or es packed t i g h t l y
c e r ta in environmental c o n d itio n s .
in t h e l a b o r a t o r y as w e l l
together
i n t o a s p d r o d o c h i urn u nd e r
This f r u i t i n g
s t r u c t u r e can d e v e l o p
as i n t h e f i e l d .
Cy gramineum grows s l o w l y on a s o l i d medium, w i t h
p e r a t u r e f o r s p e c u l a t i o n a round
15°C.
In a s i m p l e
t h e optimum tem­
l i q u i d medium
2
c o n s i s t i n g o f g l u c o s e , NaNO^, and KgPO^, a bundant c o n i d i a I p r o l i f e r a t i o n
o c c u r s by f i s s i o n
In i t s
sol I .
and b u d d i n g .
s a p r o p h y t i c p has e,
Other fu n g i
C^. gramineum is a poo r c o m p e t i t o r i n t h e
such as I r I c h o d e r m a s p . , Peni c i l l i u m
Fu s ar i um culmorurrt a r e much more e f f i c i e n t
Hence,
su rviva l
of
g e n t upon s y s t e m i c
A fte r
s p . , and
c o lo n iz e rs o f p la n t residues.
gramineum between seasons i n t h e s o i l
in v a s io n o f the host d u r in g
its
is c o n t i n ­
p a ra sitic
phase.
i n g r e s s , c o n i d i a move p a s s i v e l y w i t h t h e t r a n s p i r a t i o n a l
In t h i s way, £ .
gramineum e v e n t u a l l y c o l o n i z e s a l l
stream.
t i s s u e s o f t he w i n t e r
whe at p l a n t , f r o m t h e cul m and l e av es t o t h e glumes, and awns o f t h e
head.
which
S in ce Cephal o s p o r i urn s t r i p e
is a sim ple
i n t e r e s t disease
in
i n f e c t i o n o f p l a n t s o c c u r s o n l y once d u r i n g t h e g r o w i n g season,
i t must r e l y upon t h e s t r a w , s t u b b l e , and c h a f f r e m a i n i n g a f t e r h a r v e s t
for
i n o c u l u m c a r r y o v e r and d i s s e m i n a t i o n .
The h o s t
range o f C_. g r a m j neum i s q u i t e broad w i t h i n
G r a mi n e ae , when a r t i f i c i a l
in o cula tio ns w ith
are employed.
co n d itio n s,
Under f i e l d
the fa m ily
liq u id co n!d ia l
suspensions
h o w e v e r , w i n t e r wheat
is the
most common h o s t .
B a r l e y , o a t s , and r y e a l s o have been r e p o r t e d t o be
n a tu ra lly
in some a r e a s .
infected
The H o s t .
it
The c o n d i t i o n s under w h i c h w i n t e r wheat
p a r t i c u la r l y susceptible to
i s grown make
i n f e c t i o n by £ . gra mi neu m.
sown c r o p and e s t a b l i s h e s some t i l l e r s
and a d v e n t i t i o u s
p r i o r t o o n s e t o f dormancy i n t h e w i n t e r .
It
is a f a l l -
r o o t g rowt h
V e r n a l i z a t i o n , which occurs
3
d u r in g the w i n t e r months, is a p r e r e q u i s i t e f o r f l o w e r i n g .
spring,
f r o s t - h e a v i n g c o n d i t i o n s c o i n c i d e w i t h high
the s o i l .
a ro un d
Thus,
in fectio u s
In t h e
i n o c ul u m l e v e l s
in
p r o p a g u I es o f iC. gram?neurn a r e p r e s e n t
i n f e c t i o n s i t e s c r e a t e d by r o o t b r eak ag e o r w o u n d i n g .
Spring-
sown c r o p s do n o t e n c o u n t e r t h e s e c o n d i t i o n s , and hence escape i n f e c t i o n
The H o s t - P a t h o g e n
t o pat hog en
or
In te ra c tio n .
Most o b s e r v a t i o n s on h o s t r esponse
i n v a s i o n have been made e i t h e r
late
i n n o n - v e r n a I i ze d w i n t e r wheat s e e d l i n g s .
events o c c u r rin g
in t h e i n f e c t e d
c h l o r o t i c and n e c r o t i c s t r i p i n g
in t h e i n f e c t i o n
In b o t h
instances, only
le a ve s were examined e x t e n s i v e l y .
of
The
le a ve s and l e a f s h e a t h s , s e v er e
s t u n t i n g , and b l i g h t e d heads a r e symptoms a t t r i b u t e d
water d e f i c i t s .
p rocess
Accumulations o f fun g al c e l l s ,
to
im position o f
gums, and g e l s were
s u g g e s t e d as t h e causq o f v a s c u l a r d y s f u n c t i o n , w h i c h i n t u r n p r e v e n t e d
the v e r t i c a l
and l a t e r a l
tra n s p o rt of w ater.
The s t u d y o f h o s t r esponses i n r e l a t i o n
t o d i f f e r e n c e s o bse rv ed
between w i n t e r wheat c u l t i v a r s
has been l i m i t e d t o w h i t e head c o u n t s
infected
W h i l e t h e s e p a r am e te r s showed t h a t d i f ­
fe re n tia l
sp ecific
rows and y i e l d
data.
re sp on s es between c u l t i v a r s e x i s t e d ,
in
they d id hot reveal the
phenomena t h a t caused t h e s e d i s p a r i t i e s .
The o v e r a l l
purpose o f t h i s
t h e s i s was t o
i d e n t i f y and e v a l u a t e
p h e n o t y p i c res pon se s o f s e l e c t e d w i n t e r wheat c u l t i v a r s w h i c h responded
d iffe re n tia lly
to
in fe c tio n
by C_. gram! neum.
In so d o i n g ,
i t was
■necessary t o f o l l o w d i s e a s e d ev e lo p me nt t h r o u g h o u t t h e o nt o g e n y o f t h e
4
host.
T h i s a pp ro ac h p r o v i d e d t h e o p p o r t u n i t y t o examine c l o s e l y t h e
dyna mi c n a t u r e o f t h e h o s t - p a t h o g e n
i n t e r a c t i o n o v e r t i m e a g a i n s t t he
bac kg ro und o f d i f f e r e n t h o s t g e n o t y p e s .
C h a p t e r one r e l a t e s m i c r o s c o p i c movement and d i s t r i b u t i o n o f
gramineum w i t h m a c r o s c o p i c f o l i a r symptom d eve lo pmen t t h r o u g h o u t t he
o n t o g e n y o f two d i f f e r e n t i a l l y
C h a p t e r two r e l a t e s f o l i a r
r e s p o n d i n g w i n t e r wheat c u l t i v a r s .
symptom d ev e lo pmen t w i t h p h y s i o l o g i c a l
e f f e c t s o f p a t h o g e n e s i s on g r o w t h and y i e l d o f t h r e e d i f f e r e n t i a l l y
r e s p o n d i n g w i n t e r wheat c u l t i v a r s .
C h a p t e r t h r e e r e - e x a m i n e s t h e r o l e o f r o o t wound in g on pathogen
ingress,
id e n tifie s
o f resistance,
t h r e e p h e n o t y p i c r esponses a t t r i b u t e d
and e v a l u a t e s . d e p l o y m e n t o f t h i s
pl as m d e v e lo p me nt p r ogr am.
resistance
t o two t y pe s
in a germ-
CHAPTER I
RELATIONSHIP BETWEEN FOLIAR SYMPTOM DEVELOPMENT AND THE
MOVEMENT AND DISTRIBUTION OF CEPHALOSPORIUM GRAM I NEUM
THROUGHOUT THE ONTOGENY OF. ITS WINTER WHEAT
(TRITICUM AESTIVUM L . ) HOST
6
!NTRODUCTtON
Ce p ha t os p or turn gramineum N i s i kado & I k a t a
& Ev.),
a fa c u lta tiv e
o n ly reported fungal
s trip e .
tal
s o i l - b o r n e p a t h o g e n ,, i s t h e c a u s a l a g e n t o f t h e
v a s c u la r d isease o f w i n t e r wheat,
I t has a w i d e h o s t range w i t h i n
conditions
re s tric t
The pat hogen e n t e r s
(= Hymenula ce r e a l i s Et I .
in fe c tio n
C e p h a l o s p o r i um
t h e Gra mi ne ae , b u t e n v i r o n m e n ­
t o f a l l - s o w n c r o ps o r p e r e n n i a l s
(4,15)
t h e v a s c u l a r syst em o f t h e r o o t s t h r o u g h wounds made
by f r o s t h e a v i n g o f t h e s o i l
o r by wir ewor ms
(4,19).
Subsequently, th e .
f un g us moves s y s t e m i c a l I y t h r o u g h t h e v a s c u l a r n e t w o r k and i s c o n f i n e d
there u n t il
the host
d i s e a s e d e v e lo p me nt
con i d ia
i s m o ri b u nd
The r a t e and e x t e n t o f
is d ep endent upon t h e movement and m u l t i p l i c a t i o n
of
in t h e x y Iem ( 4 , 2 1 ) .
Symptoms a p p e a r i n i t i a l l y
on le av es and l e a f s h e a t h s .
re su lts
(21,22).
in c h lo ro s is
as d i s c r e t e n e c r o t i c o r c h l o r o t i c s t r i p e s
U ltim ate ly,
and n e c r o s i s o f a l l
b l i g h t i n g o f t he heads
(3,4,12).
symptoms become more e x t e n s i v e
coalescence o f these s t r i p e s
f o l i a r t i s s u e f o l l o w e d by
Nodal d i s c o l o r a t i o n a p p e a r s as f o l i a r
(3).
C o l o n i z e d v a s c u l a r b u n d l e s a r e d i s c o l o r e d and become o c c l u d e d w i t h
c o n id ia , m ycelia,
and g e l s
(3,4,20,21).
I n t e r r u p t i o n o f the la t e r a l
f l o w o f w a t e r has been s u g g e s t e d as t h e cause o f s t r i p e
20,21).
W h i l e t he e v e n t s
p o r t are u n re s o lv e d ,
cedes f o l i a r
it
le a din g t o
impairment o f
form ation
(16,
l a t e r a l water tr a n s ­
i s known t h a t c o l o n i z a t i o n by t h e pat hogen p r e ­
symptom d ev e l o p m e n t
(2 1).
In a d d i t i o n t o o c c l u s i o n by t h e
7
f un g us and b y - p r o d u c t s o f t h e h o s t - p a t h o g e n
r i d e pro du ce d by
gram?neum i n c u l t u r e has been h y p o t h e s i z e d as a
major c o n t r i b u t o r t o v a s c u la r d y s f u n c t i o n
To d a t e ,
i n t e r a c t io n , a polysaccha­
(16,20).
s t u d i e s o f t h e r e l a t i o n s h i p between p at hog en l o c a l i z a t i o n
and f o l i a r symptom e x p r e s s i o n have i n v o l v e d a n a l y s i s o f
fie ld -g ro w n plants
la te
inoculated seedlings
l ea ves a r e o b v i o u s
s till
l e a v es f r o m
i n t h e season o r f r o m n o n - v e r n a I i z e d , wound-
i n t h e g r een hou se
(20,21).
Even t ho ugh
infected
i n d i c a t i o n s o f the host-p a tho g en i n t e r a c t i o n ,
re p re s e n t o n ly a p o r t i o n o f the
they
i n t e g r a t e d v a s c u la r network w i t h i n
t h e e n t i r e p l a n t body.
F u r t h e r m o r e , a n o n - v e r n a I i zed w i n t e r wheat p l a n t
i s an a t y p i c a l
and c h e m i c a l e n v i r o n m e n t f o r
physical
C_. g r ami n eu m, s i n c e
(in fe c tio n n orm ally occurs
in the s p r in g
occurred.
t h e r e f o r e , we examined d i s e a s e d evel opment
In t h i s
study,
l ong a f t e r v e r n a l i z a t i o n has
Cy g r a m i neum i n f e c t e d w i n t e r wheat und er n a t u r a l
co n tro lle d
inoculum l e v e l s .
were f o l l o w e d
wheat.
To a i d
in r e l a t i o n
The r a t e and d i s t r i b u t i o n
t o the developmental
In s e l e c t i n g
in r e l a t i o n
c o n d i t i o n s usin g
o f t h e pat hogen
g r o wt h s t a g e s o f w i n t e r
r e s i s t a n t g e n o t y p e s f o r an o ng o i ng germplasm
d ev e lo p me nt progr am ( 1 2 ) , a s t a n d a r d i z e d d i s e a s e
based on a n a t o m i c a l
fie ld
in
f e a t u r e s o f a wheat
i n d e x r a t i n g system
l e a f and on p a t t e r n s o f movement
t o symptom e x p r e s s i o n was a l s o d e v e l o p e d .
8
MATERIALS AND METHODS
H isto lo gical
processing.
p re p a rin g excis ed
scopic analyses
g la c ia l
le a f,
(9).
St an d ar d p a r a f f i n methods were .used in
node, and i n t e r n o d e segments f o r
The segments Were f i x e d
a c e tic acid-ethanol
5 =5: 90 v : v : v )
graded s e r i e s o f t e r t i a r y - b u t y l
(P araplast,
so lu tion
S c ie n tific
(3 0:69:1
alcohol
Products),
v:v:v)
lig h t.m ic ro ­
i n FAA (40% f o r m a l d e h y d e -
f o r 48 h o u r s , d e h y d r a t e d i n a
s o l u t i o n s , embedded i n p a r a f f i n
softened
in a g l y c e r o l - w a t e r - T w e e n 20
f o r 5 d a y s , and f i n a l l y
frozen
in d ry
ice t o
,
p r e v e n t t e a r i n g o f t h e p a r a f f i n away f r o m t h e t i s s u e segments d u r i n g
sectioning.
Transverse s e c tio n s
820 M i c r o t o m e
(American O p t i c a l )
Haupt's adhesive
sections
(2% g e l a t i n ) .
in x y le n e ,
Fa st Green
10-11 uM t h i c k were c u t w i t h a Model
and p l a c e d on g l a s s s l i d e s c o a t e d w i t h
A fte r d isso lvin g
the p a r a f f i n
t h e y were s t a i n e d w i t h S a f r a n i n
f rom t h e
(1.0% a q u e ou s ) and
(0.5% e t h a n o l ) .
F i e l d p l a n t i n g and i n o c u l a t i o n p r o c e d u r e s .
s t u d y were p l a n t e d
Al I c u l t i v a r s
i n a randomized b l o c k d e s i g n w i t h
a t t h e Montana A g r i c u l t u r a l
Each w i n t e r wheat
i n e a r l y September a t a r a t e o f 200 seeds p e r row.
E arly p la n tin g f a c i l i t a t e d
grams o f o a t k e r n e l s
lum s o u r c e w i t h
four re p lic a tio n s
E x p e r i m e n t S t a t i o n nea r Bozeman, Montana.
The rows were 3 * I m long and spaced 3 0. 5 cm a p a r t .
l i n e was p l a n t e d
in t h i s
r o o t g r o w t h w h i c h maximi zed i n f e c t i o n .
Twenty
i n f e s t e d w i t h £'. g r a m ineum were added as an i n o c u ­
t h e seed
spring c o in c id e n t w ith
(11).
I n o c u la t i o n occurre d n a t u r a l Iy in the
f r o s t heaving.
I
P lant m a t e r ia ls .
The d i s e a s e
i n d e x r a t i n g syst em f o r mea sur ing
symptom s e v e r i t y was d e v e l o p e d u s i n g s i x w i n t e r wheat c u l t i v a r s whi ch
demonstrated d i f f e r e n t i a l
neum.
Marias
tib le ,
Winalta
(C .l.
yie ld
re sp on s es when i n f e c t e d w i t h
17595) and Lancer
(C .l.
( C . 1.
gram?-
135^7) were h i g h l y s u s c e p ­
13670) and C r e s t L i n e Row Component
(LRC) 40
(MT 7579) were i n t e r m e d i a t e , and P . I . 094424 and P . I . 278212 were
re sista nt
(12).
M a r i a s and C r e s t LRC 40 were used t o compare t h e move­
ment and d i s t r i b u t i o n
ted t i l l e r s .
o f (X gramineum w i th symptom e x p r e s s i o n
in
in fe c­
10
RESULTS
Di se ase
i n d e x r a t i n g sy st em f o r e v a l u a t i n g symptom s e v e r i t y .
s yst em f o r r a t i n g 'symptom s e v e r i t y was d e v e l o pe d f o r a l l
A
w i n t e r wheat
l e a v es r e g a r d l e s s o f t h e i r p o s i t i o n on a p l a n t o r g e n o t y p i c . b a c k g r o u n d .
Ten l e a v es f r o m each o f s i x c u l t i v a r s
ferent
l o c a t i o n s on p r i m a r y t i l l e r s
d iffe re n t s trip in g
ch lo ro sis.
were s e l e c t e d ra n do ml y f ro m d i f -
a t headin g.
p a t t e r n r a n g i n g f ro m one d i s c r e t e s t r i p e t o c o m p l et e
Leaves were p h o t o gr a p he d on a s l i d e - v i e w i n g b o x , wh ich
provided the b a c k l ig h t
i l l u m i n a t i o n necessary t o d i s t i n g u i s h t r a n s l u c e n t
a p p e a r i n g v e i n s f r o m t h e more opaque l a m i n a .
w ith c h lo r o tic s trip e s
c o u l d be i d e n t i f i e d
q u e n t l y examined f o r
(I)
s trip in g
P atrick
ca te g orie s.
A se g­
p r o c e s s i n g and s u bs e ­
i d e n t i f i c a t i o n o f vascular
gramineum and t h e i r d i s t r i b u t i o n
r e l a t i v e to the
leaves.
l e a f v a s c u la r bundles
The o r d e r o f e a r l i e s t
l a t e s t m a t u r i n g and o f
to
t h e median b u n d l e , t h e
(Figure 1-1).
l e a f were i d e n t i f i e d
bundle
1-1)
( 1 3 , 1 4 ) c l a s s i f i e d wheat
in t e r m e d ia t e bundles
la te ra l
and (2)
p a t t e r n bn i n t a c t
s m a lle s t bundles were:
each
(Figure
a n a t o m i c a l c o m p ar i s on s o f v a s c u l a r b u n d l e
d i s t r i b u t i o n between c u l t i v a r s ,
b u n d l e s c o l o n i z e d by £ .
Hence, v e i n s a s s o c i a t e d
re a dily
ment o f each l e a f was e x c i s e d f o r h i s t o l o g i c a l
external
Each l e a f e x h i b i t e d a
In t h i s
la te ra l
i n t o three
largest to
b u n d l e s , and t h e
s t u d y , t h e b u n d l e t ypes
and t h e number o f each d e t e r m i n e d .
in
Five
b u n d l e s were o b s e r v e d c o n s i s t e n t l y on each s i d e o f t h e median
in a l l
c u ltiv a rs .
The number o f
interm ediates
ranged f ro m 33 t o
L5
Figure
14
1-1.
13
y
12
LI
M
LI
L2
j
L3
U
C h l o r o t i c s t r i p i n g p a t t e r n on a C e p ha l o sp or i um gramineum
i n f e c t e d w i n t e r wheat l e a f and an i l l u s t r a t i o n o f a t r a n s ­
v e r s e s e c t i o n o f t h a t l e a f showing t he d i s t r i b u t i o n o f
v a s c u la r bundles c o lo n iz e d .
M = median v e i n , L = l a t e r a l
v e i n , and I = i n t e r m e d i a t e v e i n .
Ten l a t e r a l b un dl es were
al ways o b s e r v e d i n a l l wheat l ea ves examined.
12
k3 p e r l e a f between c u l t i v a r s
as w e l l as between le aves w i t h i n each
cu ltiv a r.
The d i s t r i b u t i o n
o f c o l o n i z e d v a s c u l a r b u n dl e s was c l o s e l y r e l a t e d
t o the p a tte r n o f e x te r n a l s t r i p i n g .
Small q u a n t i t i e s o f t h e f un gus
in
v a s c u l a r b u n d l e s o f b o t h t h e stem and l e a v e s produced no v i s i b l e damage
t o surrounding tis s u e s .
ruption of p ro to p la sts
With
incre ased pro pagule
l e v e l s , h ow ev e r, d i s ­
in phloem and m e s o p h y l V c e l Is b o r d e r i n g t h e
v a s c u l a r b u n dl e s
was
concomitant w ith
i n c r e a s e d c o l o n i z a t i o n by t h e f un gus and a pp ear an ce o f
c e l l u l a r degeneration
bundle s.
detected
(Figure
I-2A-C).
in r e g i o n s p r o x i m a l
Gels and gums appeared
t o the in f e c t e d v a s c u la r
A marked d e c r e a s e i n c h l o r o p l a s t numbers w i t h i n a f f e c t e d meso­
p hy l I c e l l s was a s s o c i a t e d w i t h e x t e r n a l m a n i f e s t a t i o n s o f c h l o r o t i c
s trip e s .
Zones o f t i s s u e d i s r u p t i o n c o a l e s c e d when a d j a c e n t v a s c u l a r
b u n dl e s were c o l o n i z e d .
Each s t r i p e a pp ear ed t o r e s u l t
caused by f u n g a l c o l o n i z a t i o n .
an i n d i c a t i o n
from l o c a l i z e d v a s c u l a r d y s fu n c t io n
Hence, t h e s t r i p i n g
o f the e x te n t o f system ic
throughout the
l e a f v a s c u la r system.
i n f e c t i o n by £ . gramineum
The d i s e a s e
s pr ead o f t h e s e c h l o r o t i c s t r i p e s on a l e a f .
was c h os en ,
since a l l
ten
ve in s.
la te ra l
a b l e between
wheat
p a t t e r n was used as
index q u a n t i f i e d the
A range o f one t o e l e v e n
l ea ves possessed a s i n g l e median v e i n and
The i n t e r m e d i a t e b u n d l e s , b e i n g numerous and v a r i ­
l e a v e s , were n o t
d ia te s adjacent to a la te r a l
included.
However, s i n c e t h e i n t e r m e ­
b u n d l e became i n f e c t e d soon a f t e r
X
Figure
1-2.
The p a t h o l o g i c a l e f f e c t s o f v a s c u l a r b u n d l e c o l o n i z a t i o n by
C e p h a l o s p o r i u m gramineum i n i n f e c t e d w i n t e r wheat l e a v e s .
A)
An u n i n f e c t e d v a s c u l a r b u n d l e .
B)
An i n f e c t e d v a s c u l a r b undl e
in the e a r l y stages o f c o l o n i z a t i o n .
Some me s op hy l l d e t e r i o r a ­
t i o n is e v id e n t (a rro w ).
C)
An i n f e c t e d v a s c u l a r b undl e in
l a t e stages o f c o l o n i z a t i o n .
E x t e n s i v e d e t e r i o r a t i o n o f phloem
( a r r o w ) and s u r r o u n d i n g me so ph y ll c e l l s .
Bars r e p r e s e n t 50
mi c r o n s .
14
c o l o n i z a t i o n o f the
w i t h "the l a t e r a l
la te ra l,
bundle .
s trip e s
in du ce d by them were r e p r e s e n t e d
A s c o r e o f one deno te d a s i n g l e s t r i p e on a
l e a f , which corresponded t o in v a s io n o f a s i n g l e
adjacent
in term ediates.
A score o f ele ven
which corresponded t o fungal
establishm ent
la te ra l
b u n d l e and
in d ic a t e d complete c h l o r o s i s ,
in. mo st ,
if
not a l l ,
vascular
bundles o f a l e a f .
S y s t e m i c movement o f C. gramineum between c o n s e c u t i v e n o d e s .
A node
i s t h e o n l y r e g i o n o f t h e wh eat stem where l e a f t r a c e s
intercon n ect to
form a v a s c u l a r continuum w it h
the r e s t o f the p l a n t .
As s u c h ,
c ritic a l
s y s t e m i c movement o f t h e f u n g us a c r o p e -
ta lly
region f o r successful
in the p l a n t .
Each s u c c e s s i v e node r e p r e s e n t s a t e m p o r a l
both w i t h
respect, t o th e e x t e n t o f
lo p me nt .
Consequently,
it
is a
gradient
i n f e c t i o n and t h e e x t e n t o f h o s t deve­
t h e f o c u s o f a t t e n t i o n was on c o n s e c u t i v e nodes
o f w i n t e r wheat culms a t v a r i o u s d e v e l o p m e n t a l g r o w t h s t a g e s . .
F ifty
r andoml y s e l e c t e d d i s e a s e d p l a n t s o f t h e s u s c e p t i b l e c u l t i v a r
M a r i a s were t agged
began.
i n t h e s p r i n g when stem e l o n g a t i o n o f t h e main t i l l e r s
O b s e r v a t i o n s were r e s t r i c t e d
penultim ate
t o the developmental
l e a f emergence and a n t h e s i s
A t each o f f i v e
F e ek e ' s s c a l e ,
s t a g e s . between
(P ee ke ' s s c a l e 7 - 5 t o
10. 5)
( 10 ) .
c o l l e c t i o n d a t e s c o r r e s p o n d i n g t o a change o f 0 . 5 on t h e
t e n main t i l l e r s
were h a r v e s t e d and t h e upp er f o u r le a ve s
o f each r a t e d f o r symptom s e v e r i t y .
Each l e a f and i t s
node o f a t t a c h ­
ment were t h e n e x c i s e d and c u l t u r e d on a c i d i f i e d
cornmeal
(Difco)
Each nodal
t o t e s t f o r t h e p r e s en c e o f t h e f u n g u s .
agar
(HCMA).
segment
15
e x t en de d f r o m t h e apex o f t h e i n t e r n o d a l
i n t o t h e p.uI v j n u s above t h e node.
segment t o d i f f e r e n t i a t e
it
la cu na bel ow t h e node t o midway
T h i s was termed t he n o d e - p u l v i n u s
f r o m t h e p u l v i n u s - i n t e r n o d e s egment , w h ic h
c o n s i s t e d o f t h e r e m a i n d e r o f t h e p u l v i n u s and 0 . 5 cm o f t h e
above.
internode
Both segments were e x c i s e d f r o m t h e upp er two v i s i b l e
nodes a t
each g r o w t h s t a g e and c u l t u r e d on HCMA t o d e t e r m i n e t h e l e a d i n g edge o f
f u n g a l advancement.
A l t h o u g h t h e crowns o f a l l
tille rs
examined were in va de d s y s t e m i -
c a l l y by Cy gramineum as d e t e r m i n e d by b o t h v i s u a l
iso la tio n
f r o m t h e l o w er mo s t l e a v e s ,
b l i g h t i n g and f u n g a l
t h e r a t e o f movement t h r o u g h o u t t h e
e n tire t i l l e r
a p p a r e n t l y was a f f e c t e d by t h e s t a g e o f h o s t dev el op men t
( T a b le - 1-1).
At growth stage 7-5,
as t h e f o u r t h
node
t h e f un gus had advanced o n l y as f a r
( t h e node i m m e d i a t e l y above t he c r o w n ) .
nodes were v i s i b l e a t t h a t t i m e ,
the t h i r d
being in a j u v e n i l e stage o f
d ev e lo p me nt as j u d g e d by t h e d i a m e t e r o f stem and p u l v i n u s .
had p r o g r e s s e d
i n t o the t h i r d
second node was v i s i b l e ,
p ul v i n u s segment s;
The f un gus
node by g r o w t h s t a g e 8 , a t w h i c h t i m e t h e
but s t i l l
ment c o n t i n u e d t h r o u g h t o t h e f l a g
Resistance t o fu n g a l
Onl y two
i mmat ure.
node
T h i s p a t t e r n o f a dvance­
(node I i n T a b l e
advancement was o b s e r v e d i n
1-1).
immat ure node­
For e x am p le , a t g r o w t h s t a g e 9 . 5 , when t h e head was
a l m o s t r eady t o emerge f r o m t h e " b o o t " ,
t h e f un gus was i s o l a t e d f ro m
o n l y one edge o f t h e f l a g n o d e - p u l v i nus segment .
t h e p u l v i n u s edge o f t h e segment.
In a d d i t i o n ,
I t d i d n o t emerge f r o m
t h e f un g us was n ot
16
TABLE 1-1.
R e l a t i o n s h i p between f o l i a r s t r i p i n g p a t t e r n s and
movement o f C e p h a l o s p o r i u m gramineum i n c o n s e c u t i v e
le a ve s o f i n f e c t e d M a r i a s w i n t e r wheat p l a n t s a t
d I f f e r e n t developmental growth stag e s .
a/
S e v e r i t y Score—
Feekes s c a l e —^
8.5
9.5
I
O
O
O
O
2
O
3
O
1.7*
4
2.3*
9.4*
%
8.0
O
7-5.
O
Leaf-/
10.5
1 .4 *-/
2.0*
4.4*
. 4.1*
6 .9*
10.1*
9-9*
10.8*
11.0*
a/
— Each v a l u e r e s p r e s e n t s t h e mean o f t e n t i l l e r s a t each
growth s ta g e .
Each l e a f was a s s i g n e d a s e v e r i t y s c o r e
based on t h e number o f s t r i p e s v i s i b l e on a s c a l e f r o m
one t o e l e v e n . I = one s t r i p e / l e a f , 11 = t o t a l l y b l i g h t e d
leaf.
— Each g r o w t h s t a g e is r e p r e s e n t e d by t h e Feekes s c a l e , wh ich
p a r t i t i o n s w i n t e r wheat d ev e l o p m e n t i n t o a n u m e r i c a l s c a l e
f r o m I t o 11.
— Leaf I re p re s e n ts the f l a g l e a f , l e a f , 2 the p e n u lt im a t e
l e a f , l e a f . 3 t h e t h i r d l e a f b el o w t he f l a g , and l e a f 4
th e f o u r t h l e a f below the f l a g .
—^ A s t e r i s k i n d i c a t e s s u c c e s s f u l i s o l a t i o n o f t h e f un g us
f r o m . n o d e s c u l t u r e d on a c i d cornmeal a g a r .
1.7
detected
in t h e p u l v i n u s - i n t e r n o d e segment above t h e f l a g
To examine t h i s
phenomenon more c l o s e l y > a n a t o m i c a l
t h e node and p u l v i n u s and t he p a t t e r n
r e g i o n s were s t u d i e d .
o f f u n g a l movement w i t h i n
S erial
s e c t i o n s were c u t f rom
t h e base o f each node t o midway t h r o u g h t h e p u l v i n u s .
by m i c r o s c o p i c
t h e se
o f M a r i a s a t each g r o w t h s t a g e and
processed f o r h i s t o l o g i c a l e x a m in a tio n .
in n o d e - p u l v i n u s
features of
S u c c e s s i v e nodes and l e av es o f a t t a c h m e n t were
e x c is e d from s i x p rim a ry t i l l e r s
fungus
node.
Presence o f t h e
r e g i o n s and l e a v e s o f a t t a c h m e n t was e s t a b l i s h e d
id e n tific a tio n
o f c o n i d ia , m yce lia , gel a ccum ula tio ns, or
any c o m b i n a t i o n o f t h e t h r e e .
A node i s composed o f v a s c u l a r b u n d l e s and i n t e r c o n n e c t i n g x y Iem
strands
from the
l e a f o f a t t a c h m e n t as w e l l
im m ed ia tely above.
P atrick
node a c c o r d i n g t o t h e i r
m orphological
and
(13) c l a s s i f i e d
le a f of o r ig in .
c h a ra c te ris tic s ,
(3) p a t t e r n
as f r o m t h e t wo l eaves
v a s c u la r bundles
They can be i d e n t i f i e d by ( I )
(2) p o s i t i o n
re la tiv e
t o o th e r bundles,
o f b r a n c h i n g t h r o u g h t h e node ( F i g u r e s . 1-3,
o f the v a s c u l a r bundles o r i g i n a t i n g
i n each
in t h e
1-4).
l e a f o f attachm ent
Al I
(desig­
n a t e d L) a r e c o n t i n u o u s and n o n - b r a n c h i n g t h r o u g h t h e n od e, a l t h o u g h
"b ridg in g
s t ra n d s " fuse w it h
th e ir d is tin c tiv e
them.
They a r e r e a d i l y d i s t i n g u i s h e d by
s i z e and shape w i t h i n
bundles o r i g i n a t i n g
in the
the node,
l e a f above l e a f
Lateral
vascular
L (designated. L I) are c o n t i ­
nuous t h r o u g h t h e node and f u s e w i t h o t h e r x y Iem t r a c e s o n l y n ea r t h e
base o f t h e node.
They a r e
id e n tifie d
by t h e i r autonomy r e l a t i v e
to
18
Figure
I - 3.
I l l u s t r a t i o n o f t he v a s c u l a r b u n d l e t y pe s and t h e i r c our se
t h r o u g h a w i n t e r wheat node.
Redrawn f r o m P a t r i c k ( 1 3 ) .
L = l a t e r a l and i n t e r m e d i a t e b u n d l e s f r o m l e a f o f a t t a c h m e n t
( L A ) , LI = l a t e r a l b u n d l e s f r o m l e a f above LA, L2 = l a t e r a l
b u n d l e s o f second l e a f above LA, BS = b r i d g i n g s t r a n d n e t ­
w o r k , PP = p i t h p l e x u s .
A-C r e f e r t o r e g i o n s o f t h e node
shown i n c r o s s - s e c t i o n i n F i g u r e 1-4.
Fig ure
1-4.
L i g h t m i c r o g r a p h s o f c r o s s - s e c t i o n s t h r o u g h a w i n t e r wheat node i n f e c t e d
w i t h C e p h a l o s p o r i u m gra mi neu m, showing v a s c u l a r b u n d l e t y pe s and t h e i r
d i s t r i b u t i o n a t l e v e l s A-C i n d i c a t e d by a r r o w s i n F i g u r e I ~ 3 . L = l a t e r a l
bun dl es f r o m l e a f o f a t t a c h m e n t , LI = l a t e r a l b u n d l e s f ro m l e a f above l e a f
o f a t t a c h m e n t , L2 = l a t e r a l b un d le s f r o m second l e a f above l e a f o f a t t a c h ­
ment, I I = i n t e r m e d i a t e b un d le s f rom l e a f above l e a f o f a t t a c h m e n t , BS =
b r i d g i n g s t r a n d n e t w o r k , PP = p i t h p l e x u s .
Arrows i n d i c a t e c o l o n i z a t i o n
by C e p h a l o s p o r i u m gramineum.
Bars r e p r e s e n t 50 m i c r o n s .
20
o t h e r b u n d l e s and t h e " b r i d g i n g
le a f traces to
the
interconnect
l e a f above LI
l e a f and stem b u n d l e s !
(designated
since they fuse w it h
strand network" th a t
L2) were d i f f i c u l t
l i n k s with, e n t e r in g
L a t e r a l bundles o f
to d is tin g u is h
re a d ily,
t he " b r i d g i n g . s t r a n d n e t w o r k " and t h e p i t h p l e x u s
n e a r t h e t o p o f t h e node.
The p i t h
plexus connects w it h
s t r a n d s , making t h e x y Iem n e t w o r k c o n t i n u o u s among a l l
the b rid g in g
v a s c u l a r b un d le s
w i t h i n t h e node ( 1 3 ) .
. When £ . gramlneum was i d e n t i f i e d
it
in a s p e c i f i c bundle
o f t e n c o u l d be t r a c e d t o t h e same b u n dl e
node above.
For e x am p le ,
if
in one n o d e ,
in t h e node b e l o w and t he
t h e f u n g us was o b s e rv e d in a l a t e r a l
bundle
in a node,
i t w o u l d be f ound a l s o
strand
in t h e node b el o w and in an L b u n d l e
LI
in an L2 o r p o s s i b l y a l i n k i n g
In t h e node a b o ve .
Thus,
v e r t i c a l movement o f t h e f u n g us was f o l l o w e d f r o m one node t o t h e n e xt
a t each g r o w t h s t a g e .
related
I t s d i s t r i b u t i o n w i t h i n each node c o u l d t hen be
to d is tr ib u tio n
in o t h e r nodes.
S y s t e m i c advancement o f C_. gramjneum a t . v a r i o u s g r o w t h s t a g e s was
c l o s e l y a s s o c i a t e d w i t h x yl e m m a t u r a t i o n g r a d i e n t s between nodes, x y Iem
strand d i f f e r e n t i a t i o n w it h in
w ith in
le a ves,
fashion, e .g.
nodes, and x yl e m s t r a n d d i f f e r e n t i a t i o n
The g r a s s stem m a t ur e s v e r t i c a l l y
in a m u l t InodaI
b a s i p e t a l Iy- f r o m t h e t o p o f one node t o t h e t o p of. the.
node i m m e d i a t e l y bel ow ( F i g u r e
b a s i p e t a l Iy from the t i p
I -5 A ) (17).
t o t h e base . o f t h e
median b u n d l e d e v e l o p i n g f i r s t ,
The l e a f a t each node ma tur es
le a f sheath, w ith
f o l l o w e d by t he l a t e r a l
t he
b u n d l e s , and
21
Figure
l _ 5-
I l l u s t r a t i o n o f x y Iem m a t u r a t i o n g r a d i e n t s i n a w i n t e r wheat
p l a n t . A)
V e r t i c a l m a t u r a t i o n g r a d i e n t s i n t he i n t e r n o d a I
regions.
B)
V e r t i c a l m a t u r a t i o n g r a d i e n t s w i t h i n t he f l a g
n o d e - l e a f j u n c t i o n o f t he p u l v i n u s .
S i x phases a r e r e p r e ­
s e n t e d , I = f l a g l e a f e me rg en c e, 6 = f u l l m a t u r i t y o f a l l
t is s u e s a f t e r heading.
Both A and B were redrawn f ro m P r a t t
(1 7).
F i l l e d a re as i n d i c a t e immature t i s s u e s .
C)
Redrawn
f rom P a t r i c k ( 1 4 ) , t h i s shows t h e sequence o f v a s c u l a r
b u n d l e d i f f e r e n t i a t i o n w i t h i n a node.
L = l a t e r a l b un dl es
o f l e a f o f a t t a c h m e n t , LI = l a t e r a l b un dl es f r o m l e a f above
l e a f o f a tt a c h m e n t , I l = in t e r m e d ia t e bundles from le a f
above l e a f o f a t t a c h m e n t , L2 = l a t e r a l b u n d l e s f r o m second
l e a f above l e a f o f a t t a c h m e n t , BS = b r i d g i n g s t r a n d n e t w o r k ,
PP = p i t h p l e x u s .
22
f i n a l l y by t h e s m a l l e r
m a t ur e between nodes
the p u l v in u s a t
in te r m e d ia te bundles
(14).
i s t h e stem p o r t i o n a t t h e a r e a o f
t he n o d e - l e a f j u n c t i o n .
n um erically p a r titio n e d
into, f i v e
phases
sequence f o r d i f f e r e n t b u n d l e t y p e s
is
in itia te d
m a tu r e f i r s t
b rid ging
firs t
at
(Figure
The p i t h
o t h e r x y l e m s t r a n d s and i s
t h e x yl em s t r a n d s
leadin g
I - 5 B ) (17) . M a t u r a t i o n
The L,
L I , and L2 b u n dl e s
d iffe re n tia tio n
plexus develops
l a s t t o mature (Figu re
£ . gramineum c o n s i s t e n t l y
in to
The d i f f e r e n t i a t i o n
interconnected u n t i l
strand network.
insertion
i s t h e same t h r o u g h t h e node, b u t
t h e node b a s e .
b u t are n o t
region t o
T h i s m a t u r a t i o n sequence i s
o f x y Iem s t r a n d s w i t h i n a node i s acropet.a I .
it
The l a s t
o f t he
independently o f t h e .
I - 5 C ) ( 14 ) .
i n v a de d nodes o n l y a f t e r m a t u r a t i o n o f
i n t o them.
Moreover, the fungus demonstrated
s e le c tiv ity
f o r b u n d l e t y p e s dependent upon t h e i r sequence o f d e v e l o p ­
ment w i t h i n
each node.
The o r d e r o f
in g re s s fo llo w e d c l o s e l y the o rd e r
of d iffe re n tia tio n .
Fungal p r b p a g u I es were f i r s t
( - 5B )
o f t he v e r t i c a l
detected
i n nodes a t phase 5 ( F i g u r e
m aturation g r a d ie n t.
This stage o f d i f f e r e n t i a ­
t i o n was c h a r a c t e r i z e d most o f t e n
growth stage 8 .5 ,
tio n
and node I a t g r o w t h s t a g e 9 . 5 .
o f these n ode-puIv in u s
among b u n d l e t y p e s .
The L,
m a t u r e t h r o u g h t h e node.
p ith
i n node 3 a t g r o w t h s t a g e 8 , node 2 a t
segments v e r i f i e d
LI,
e xa mi na ­
the m a t u r a t io n g r a d ie n t
and L2 b u n d l e s appeared t o be f u l l y
Much o f t he b r i d g i n g
p l e x u s , h ow eve r, were s t i l l
H isto lo g ica l
ju v e n ile .
s t r a n d n e t w o r k and t h e
A l t h o u g h much o f t h e
23
c y t o p l a s m o f t h e s e v e s s e l s had d i s a p p e a r e d ,
Iig n ifie d .
In t he v a s c u l a r b u n d l e s o f t h e stem in t he p u l v i n u s ,
me tax yl em e l e m e n t s were s t i l l
e l e m e n t s had l o s t
becoming
t h e c e l l w a l l s were n ot
lig n ifie d
u n d i f f e r e n t i a t e d whereas t h e p r o t o x y Iem
t h e i r p r o t o p l a s m i c c o n t e n t s and t h e c e l l w a l l s were
(Figure
I- 6 ) .
C o n i d i a and o c c a s i o n a l l y m y c e l i a were d e t e c t e d o n l y
b u n d l e s o f t h e s e n odes.
LI o r L2 b u n d l e s .
network,
node.
u n til
The f u n g us was n e v e r f ou n d
I n t e r e s t i n g l y , £.
i n t he
large L
R a r e l y were any s i g n s o f t h e f u n g us e v i d e n t
the p i t h p le x u s ,
a ll
t he
i n t he b r i d g i n g
in
strand
o r v a s c u l a r b u n d l e s o f t h e stem above t he
gramjneum was n e v e r f ou nd
o f th e vessel elements w i t h i n
i n v a s c u l a r b u n dl e s
them had f u l l y m a t u r e d .
The p a t t e r n o f p at h og en d i s t r i b u t i o n
f r o m f u l l y m a t u r e nodes
into
d e v e l o p i n g nodes above a t each g r o w t h s t a g e o f w i n t e r wh e at dev el op men t
illu s tra te s
the
t he r e s t r i c t i v e
influ en ce
la te r a l m aturation g ra die n ts
growth stage
lin k in g
(Table
1-2).
10.5 i s e x t e n s i v e l y c o l o n i z e d
strands.
i t was a b l e t o
inv ade a l l
in to a ll
r e s t r i c t i o n s were
For e x a m p l e , node 3 a t
in a l l
Once t h e f un g us had p e n e t r a t e d
s u c c e s s fu lly colonized a l l
channels
imposed by b o t h t h e v e r t i c a l and
bundles
in t h e node.
b u n d l e t y p e s and
in t o the p i t h
plexus,
A f t e r t h e f un g us had
o f t h e b u n d l e t y p e s , i t was a f f o r d e d open
o f t h e b u n d l es o f node 2 d i r e c t l y a b o ve .
imposed on v e r t i c a l
s h o u l d have in va de d most o r a l l
or
o f t h e L,
I f no
l a t e r a l movement, t h e f un gus
LI,
L2 b u n d l e s ,
the b r i d g i n g
s t r a n d n e t w o r k , and t h e p i t h p l e x u s o f node 2 c o n c u r r e n t l y .
Only some
2k
Figure
1-6.
L i g h t m i c r o g r a p h s showing x y Iem d i f f e r e n t i a t i o n in
response t o a m a t u r a t i o n g r a d i e n t i n t he stem o f a
w i n t e r wheat p l a n t .
B r i g h t - f i e l d o p t i c s o f A) mat ur e
and C) immature v a s c u l a r b u n d l e s i n t h e stem o f t he
pulvinus.
F l u o r e s c e n t o p t i c s o f B) t h e same mat ur e
and D) t he same immature v a s c u l a r b un d le s showing
the e x te n t o f l i g n i f i c a t i o n in vessel c e l l w a l l s .
Bars r e p r e s e n t 50 m i c r o n s .
25
TABLE 1-2.
D i s t r i b u t i o n o f C e ph a i o s p o r i u m gramineum in each b u n d l e
t y p e w i t h i n c o n s e c u t i v e nodes o f two w i n t e r wheat
c u I t i vars at d i f f e r e n t growth stages.
Pr o p o r t i o n o f Bundles Col oni zed—^
MARIAS
CREST LRC 40
Bundle Type—^
Growth Stage
(Peekes s c a l e )
LI
L'
7- 5
NODE
1.7
U
6 BS
0.8
0
Bundle Type
PP
L
LI
.
1.2
0.2
0
0
0
0
O
0
0
0
O
0
0
0
8.5
NODE 4
2.0
I .2
NODE 3
.1.5
O
NODE 3
NODE 2
NODE I
’
'
'
0
0 . 7
'
L2 S BS
0 '
PP
0
0
0
0
0
0
0
0
0
0
6
0
0
1.3
0.8
0.3
0
0.5
0
0
1.0
0.2
0
0
NODE 2
0
0
0
0
0
0
0
0
NODE I
0
0 '
0
0
0
0 .
0
0
2. 1
I .2
2. 1
1.5
0.5
1.5
0.5
■ VO
' 0. 5
0.3
0
0.3
0
0
0
9-5
NODE 4
"
0
3 . 2
2 . 5
NODE 3 ■
2 . 3
2. 1
NODE 2' ■
1.2
0.8
0
0
0
0
0
0
0
0
' 4.0
3- 5
3. 2
2.2
2 . 5
1.8
1.3
1.0
NODE 3
3- 9
3.3
2.7
2.0
1.5
1.0
1.0
0.2
NODE 2
2.0
1.7
1.2
0.3
I .0
1.0
I .0
0
NODE I
!•I
0.4
0
0
0.2
0.2
0
NODE I
10. 5
NODE 4
.
0.2
0 '
'
0 ,
—^ P r o p o r t i o n o f v a s c u l a r bundl es col on I zed w i t h i n each bundl e t ype.
Each
v al ue r e p r e s e n t s t he mean o f 6 t i l l e r s . ' I = 0-25% bundles c o l o n i z e d ,
2 = 25-50% bundl es c o l o n i z e d , 3 “ 50-75% bundles c o l o n i z e d , 4 f 75"100%
bundl es c o l o n i z e d .
—^Bundles i d e n t i f i e d by l e a f o f o r i g i n in r e l a t i o n t o each n ode .
L = late­
r a l bundl es o f l e a f above l e a f o f i n s e r t i o n , L2 = l a t e r a l bundl es o f the
second l e a f above l e a f o f i n s e r t i o n , BS - b r i dg i ng s t r a nd n e t wor k , com­
p r i s e d o f I n t e r m e d i a t e bundl es from the l e a f above l e a f o f i n s e r t i o n ,
PP “ p i t h p l e x u s , a r i s i n g I nde pe nde nt l y w i t h i n the node.
-^Node 4 Is the
lowermost node and node
I i s t he f l a g node.
26
o f t h e L,
L I , and L2 b u n d l e s and t h e b r i d g i n g s t r a n d s
we re c o l o n i z e d ,
pathogen.
h o w ev e r , and t h e p i t h
A dd itio n al
node 2 and t h e f l a g
sp arsely colonized
l i n k e d t o them
p l e x u s was c o m p l e t e l y f r e e o f t h e
c o n s t r a i n t was i n e v i d e n c e f o r t h e b u n d l e s between
node (node I ) ,
in t h e
la tte r.
fo r only several
Consequently,
moving up an i n f e c t e d stem i n a s e q u e n t i a l
nodes and between t h e b u n d l e t y p e s
L b u n d l e s were
t h e f un g us was observed
temporal
p a t t e r n between
in each node r a t h e r t h a n
in a r a p i d ,
unordered p ro g r e s s io n .
The p a t t e r n o f p at hogen d i s t r i b u t i o n
ween nodes was m i r r o r e d m a c r o s c o p i c a I I y
t i on ( T a b l e
I - 1) .
o b s e rv e d h i s t o l o g i c a l l y b e t ­
in t h e p a t t e r n o f s t r i p e f o r m a - .
At each c o n s e c u t i v e g r o w t h s t a g e a f t e r 7 - 5 ,
t he
a v e r a g e number o f s t r i p e s on., le aves a t t a c h e d t o r e c e n t l y mat ur ed nodes d i d n o t exceed t wo s t r i p e s , whereas t h e
le aves
i m m e d i a t e l y bel ow
a v er a ge d between f o u r and t en s t r i p e s .
Leaves f u r t h e r down t h e stem
were u s u a l l y c o m p l e t e l y b l i g h t e d .
Thus,
t h e movement and d i s t r i b u t i o n
associated w ith
wheat p l a n t s .
t h e x y Iem m a t u r a t i o n g r a d i e n t s
LI,
lim ited
by t h e b a s i p e t a l
between nodes; movement between v a s c u l a r b un dl e
i s r e s t r i c t e d by t h e a c r o p e t a I and l a t e r a l d i f f e r e n t i a t i o n
L2,
bundles
ra l,
o f developing w in te r
V e r t i c a l movement i n t h e stem i s
m aturation g ra d ie n t
types
o f C_. gramineum i s c l o s e l y
bridging strands,
and p i t h
p l e x u s ; and movement w i t h i n
i s r e g u l a t e d by t h e s e q u e n t i a l
d iffe re n tia tio n
and i n t e r m e d i a t e b u n d l e s o r i g i n a t i n g
in the
L,
the L
o f med ian ,
leaves.
of
la te ­
27
D iffe re n tia l
r e sp on se s o f t wo c u l t i v a r s
M a r i a s and C r e s t LRC 40 were compared w i t h
t o s pread o f C. g r ami neu m.
r e s p e c t t o t h e r a t e o f symp­
tom e x p r e s s i o n t h r o u g h o u t t h e i r g r o w t h and d e v e l o p m e n t .
was chosen because i t
C r e s t LRC 40
appeared t o possess some mechanism by which
complete b l i g h t i n g
of a ll
l ea ves o c c u r r e d
t h e same t i m e span
( Ch a p t e r 3 ) .
l a t e r t ha n i n M a r i a s w i t h i n
Consequently, h i s t o l o g i c a l
studies
s i m i l a r t o t h o s e p e r f o r m e d on M a r i a s were co nd u ct ed t o d e t e r m i n e any
v i s u a l d i s s i m i l a r i t i e s which might c h a r a c t e r i z e t h i s
phenomenon.
Iden­
tic a l
sample s i z e s and h a r v e s t i n g d a t e s were u s e d , s i n c e b o t h M a r i a s and
Crest
LRC 40 have t h e same h e a d i n g
d iffe re n t
observed
bundletypes o f Crest
in M a r i a s ,
but
its
dates.
The f un g us
LRC 4 0 1s nodes
rate of
invasion
in t h e
in va de d t h e
same sequence
lagged c o n s i d e r a b l y
( Ta b le
1- 2 ) .
To d i s c e r n d i f f e r e n c e s
c o n !d ia l, m yce lia l,
and g e l
in h o s t re sp on s e t o pat hogen c o l o n i z a t i o n ,
a c c u m u l a t i o n s were q u a n t i f i e d
in c o lo n iz e d
v a s c u l a r b u n d l e s by r a t i n g each on a s c a l e o f one t o t h r e e
trace
(1-30% v e s s e l s / b u n d l e f i l l e d ) ,
fille d ),
and abundant
number o f v e s s e l s
m od er at e
(30-70% v e s s e l s / b u n d l e
(70-100% v e s s e l s / b u n d l e f i l l e d )
LI b u n d l e s upward t o
ever observed in
i n f e c t e d v e s s e l s , r u l i n g them o u t as
139 i n
L bundle s.
Onl y t h os e nodes a t v a r i o u s g r o w t h s t a ge s
had p r o g r e s s e d
q ua n tities.
The
i n each v a s c u l a r b u n d l e w i t h i n a node ranged f rom a
minimum o f 24 in
response.
in d ica tin g
i n t o t h e LI and L2 b u n d l e s ,
No t y l o s e s
were
a s i g n i f i c a n t host
in w h i c h t h e f un gus
b u t had n o t y e t
i nvaded t he
28
p ith
p l e x u s , were s c o r e d .
S ubstantial d iffe re n c e s
appear ed t o e x i s t
between M a r i a s and C r e s t LRC 40 ( T a b l e
M a r i a s was assumed t o
p at h og en movement,
g r e a t e r gel
tio n
l a c k any c a p a c i t y f o r a c t i v e
then Crest
production,
o f both.
in c o n i d i a , m y c e l i a , and g e l a c c u m u l a t i o n s
1-3).
re s tric tio n of
LRC 40 possessed t h e a b i l i t y
i n h i b i t con i d i a I
If
p ro life ra tio n ,
to e l i c i t
o r a combina­
29
TABLE I - 3 .
R e a c t i o n o f two w i n t e r wheat c u l t i v a r s t o
i n f e c t i o n by C e ph al o s po r i um gramineum as
re la te d to accumulation of g e ls , c o n id ia ,
and m y c e l i a w i t h i n t he lumi na o f i n f e c t e d
V ascular bundles.
E x t e n t o f A c c u m u l a t i o n —^
. C u ltiva r
Gels
Coni d i a
Myce I i a
Marias
1.0
2.4
1.1
C r e s t LRC hO
2.2
I .2
1 .8
a/
— Each v a l u e r e p r e s e n t s t h e mean o f 42 nodes.
Readings
o f a l l L and LI b u n dl e s in each node were a v e r a g e d .
Only nodes in w h i c h
gram? neum had n o t y e t p r o g r e s ­
sed i n t o t h e p i t h p l e x u s were s c o r e d .
I = trace
amounts (1-30% v e s s e l s / b u n d l e ) , 2 ■= moder at e amounts
(30-70% v e s s e l s / b u n d l e ) , and 3 = abundant amounts
(70-100% v e s s e l s / b u n d l e ) .
30
DISCUSSION
Al I h o s t - p a t h o g e n
i n t e r a c t i o n s may be c h a r a c t e r i z e d
components o f t h e d i s e a s e p y ra mi d s i n g l y and t o g e t h e r
by e x am in i ng
(2).
This study
p l a c e d e q u a l emphasis on p a t h o l o g i c a l e f f e c t s o f . C. gramineum on t he
h o s t and on p h y s i o l o g i c a l and m o r p h o l o g i c a l e f f e c t s o f t h e w i n t e r wheat
h o s t on p at h og en movement.
The t e m p o r a l
r e l a t i o n s h i p between t h e s e two
components was i n v e s t i g a t e d by f o l l o w i n g d i s e a s e d ev e l o p m e n t d u r i n g t h e
ontogeny o f
i n f e c t e d wheat p l a n t s .
Both d i s e a s e d e ve l o pm en t and h o s t
d ev e lo p me nt a r e i n i t i a t e d w i t h i n a s i m i l a r t i m e f r a m e , s i n c e f i e l d
in fe c tio n
i n Montana o c c u r s a t one t i m e - - i n
causes r o o t b r e ak a ge
(4,15).
f o r p a s s i v e e n t r y o f co nT d ia
concomitant w ith
i n t o t he
between
roots.
i n d u c t i o n o f stem e l o n g a t i o n
reports
Hence, d i s e a s e o n s e t
by £ .
g r ami neu m.
is
in w i n t e r w h e a t . .
th a t p athological e ffe c ts
i n f e c t e d v a s c u la r bundles d id not occur u n t i l
colonization
heaving
The exposed x yl e m e l e m e n t s p r o v i d e s i t e s
Our s t u d y c o n f i r m e d e a r l i e r
and a ro un d
t he s p r i n g when s o i l
Consequently, a s e q u e n tia l
in
a f t e r abundant
re la tio n sh ip
.
i n v a s i o n and c o l o n i z a t i o n by t h e pat hog en and f o l i a r symptom
e x p r e s s i o n was o b s e r v e d .
The f ungus was d e t e c t e d p r i o r t o e x t e r n a l
symptom d e v e l o p m e n t , b u t c h l o r o t i c s t r i p i n g was r a r e l y v i s i b l e
l a r re g ion s devoid o f the fungus.
in v a s c u ­
I m p ai r m en t o f l a t e r a l w a t e r t r a n s p o r t
re su ltin g
f r o m v a s c u l a r d y s f u n c t i o n has been p o s t u l a t e d as t h e mechanism
o f strip e
form ation
(16,20,21).
Phloem and m e s o p h y l l d e t e r i o r a t i o n
w i t h i n and a round a b u n d a n t l y c o l o n i z e d , v a s c u l a r b u n d l es c o u l d be a
31
m anifestation o f
l o c a l i z e d w a t e r s t r e s s caused by r e s i s t a n c e t o w a t e r
movement t o t h e s e c e l l s .
As a d j a c e n t v a s c u l a r bun dl es became i n f e c t e d ,.
the regio ns o f t i s s u e d eg e ne ra tio n o v erlap p ed .
b un dl es were c o l o n i z e d ,
the
U l t i m a t e l y , when a l l
l e a f became b l i g h t e d .
T h i s p a t t e r n o f pat hogen movement i n r e l a t i o n
f ormed t h e b a s i s
f o r a disease
f ro m one t o e l e v e n p e r
node and i n t o
tool
its
le a f,
i n d ex r a t i n g s ys t em .
in d ic a te d the e x te n t o f
le a f of attachm ent.
fo r v is u a lly m onitoring
t o symptom e x p r e s s i o n
This disease
Each s t r i p e ,
rangin g
i n f e c t i o n through a
i n d e x may be a u s e f u l
t h e r a t e and e x t e n t o f p at h og en s pread up­
ward t h r o u g h an . i n f e c t e d w i n t e r wheat p l a n t .
Individual
r e a d i n g s may
t hen be e x t en de d t o a p o p u l a t i o n o f p l a n t s w i t h i n a s i n g l e c u l t i v a r
evaluating d i f f e r e n t i a l
plants
r esponses between g en ot yp es as w e l l as s e l e c t i n g
f ro m a s e g r e g a t i n g p o p u l a t i o n .
Many e l e m e n t s o f t h e £ .
unique
gram! neum-w i n t e r wheat i n t e r a c t i o n a r e
in c o m p a r i s o n t o o t h e r v a s c u l a r p a t h o g e n - h o s t
r e s p e c t t o t h e h o s t , w i n t e r wheat
it
d iffe rs
s ig n ific a n tly
which are s u s c e p t i b l e
o f wh eat
in teractio n s.
With
i s an a n n u a l , her ba ce ou s mo nocot , and
f r o m Woody monocots such as banana and d i c o t s
t o o t h e r v a s c u l a r pathogens.
The v a s c u l a r b u n d l e s
l a c k a cambium f o r s e c o n d a r y g r o w t h and t h u s r e ma in as d i s c r e t e
bundles o f f i x e d s iz e s except
intercon n ectin g netw ork.
in t h e n od al
T r ac e s f r o m t h e
ched t h r o u g h t h e node and i n t o t h e
in t h e
for
r e g i o n s , w he re t h e y f orm an
l e a f o f a t t a c h m e n t pass u n b r a n ­
in te r n p d e below.
The v a s c u l a r b u n d l e s
l e a f are o f s i m i l a r s iz e s t o t h e i r c o u n t e r p a r t s
in t h e stem. T h u s ,
32
movement o f t h e f un gus f r o m s e v e r a l
in to the le a f re s u lts
tio n .
in
v a s c u l a r bun dl es
localized s trip e s
in t h e stem upward
in t h e r e g i o n s o f c o l o n i z a ­
No v i s i b l e e x t e r n a l e v i d e n c e o f p h y s i o l o g i c a l
w a t e r s t r e s s was f ou nd
In d i c o t s ,
d i s o r d e r caused by
in asymptomatic re g ion s o f the
le a f.
on t h e o t h e r h a n d , t h e p e t i o l e b u n d l e s b r a nc h f rom t h e
i n t e r c o n n e c t i n g v a s c u l a r n e t w o r k o f t h e stem and a r e much s m a l l e r i n .
size .
Whereas
lo ca lize d occlusion
flow s i g n i f i c a n t l y ,
in almost a t o t a l
i n stem bun dl es does n o t a l t e r w a t e r
extensive d ysfu n ctio n
c u t o f f o f water flow
diseases a s s o c ia te d w i t h
i n t h e p e t l o l a r b u n d l es r e s u l t s
(6,7).
Consequently, v a s c u la r
these p la n t s o f t e n e x h i b i t g e n e r a liz e d w i l t i n g
r a t h e r t ha n d i s c r e t e c h l o r o t i c p a t t e r n s a round
W i n t e r wheat
z a tio n period to
is a l s o d i s t i n c t i v e
in itia te
flow ering.
in
its
in f e c t e d bundles (7 ).
requirem ent f o r a v e r n a l i ­
In co mp ar i ng symptom d evel opment
w i t h i n w o u n d - i n o c u l a t e d v e r n a l i z e d and non-verna.l i zed w i n t e r wheat
plants,
Bruehl
form ation.
(4) o b s e r v e d t h a t t h e
He s u g g e st e d t h a t " i t
p a r tic u la r ly a ctive
ment".
u n til
l a t t e r were r e s i s t a n t
is probable th a t
w i n t e r wheat was e v i d e n t o n l y
While Weise's
d e v e lo p me nt w i t h i n m a t u r i n g
re g a rd in g events
l eaves
the
is s i m i l a r
le a f , d id not
o n t o g e n y on d i s e a s e d e v e l o p m e n t .
i s not
stage o f d ev e lo p ­
form ation
in t h e m a t u r e o u t e r
(21) o b s e r v a t i o n s
o f only a s p e c i f i c organ,
t h e f un gus
t h e h o s t passes a c e r t a i n
In o u r s t u d i e s , we f ou nd t h a t s t r i p e
to s tr ip e
in n o n - y e r n a I i zed
l eaves
( C ha pt e r 3 ) .
l e a d i n g t o symptom
t o o u r s , h is exam inatio n
r e f l e c t the
imp act o f h o s t
33
The u n i qu e n a t u r e o f _C. q r a m l neum as a p l a n t pat hogen was d i s c o ­
v e re d a f t e r s t u d y i n g t h e m ut ua l
movement.
i n t e r a c t i o n o f h o s t o n t o g e n y and pathogen
The speed o f f u n g a l g r o wt h and s p e c u l a t i o n ,
fu n c tio n o f vessels
t h e s t r u c t u r e and
in t h e p l a n t , and t h e speed o f h o s t response a l l
i n t e r a c t e d t o d e t e r m i n e t h e r a t e and e x t e n t o f s y s t e m i c
the h ig h ly s u s c e p tib le c u l t i v a r Marias,
in v a s c u l a r b u n d l e s
of d iffe re n tia tio n
are
liv in g
c e lls .
liv in g c e lls
c a l Iy a c t i v e p r o t o p l a s t s .
S i nc e t h e f un gus c o u l d n o t be
i n w h ic h any o f t h e i n d i v i d u a l
elements r e t a i n e d p r o to p la s m ic components,
c a p a b ility to p a ra s itiz e
In
s y s t e m i c movement was r e s t r i c t e d
by t h e s t a g e o f v a s c u l a r d i f f e r e n t i a t i o n .
detected
in fe c tio n .
i t apparently
V es se l s
vessel
l a c k e d any
in t h e i r j u v e n i l e stage
since they contain
in t a c t , m etaboli-
In t he m a t u r e s t a t e , h ow ev e r,
t h e y become
d e v o i d o f t h e p r o t o p l a s m and n u c l e u s and t hu s may be c o n s i d e r e d as non­
liv in g
c e lls .
The pat hog en was a b l e t o
inva de t h e s e n o n - l i v i n g v e s s e l s
re a d ily .
O t he r a s p e c t s o f d i s e a s e e t i o l o g y s u b s t a n t i a t e t h e i n a b i l i t y o f j X
gramineum t o p e n e t r a t e
liv in g
c e lls .
These i n c l u d e t h e p a t h o g e n ' s
requirem ent f o r
r o o t w ou nd in g f o r s u c c e s s f u l
p re s en c e w i t h i n
t h e xylem u n t i l
a fte r a ll
i n g r e s s and i t s
other plant
tissues
re s tric te d
lose
b io lo g ic a l a c t iv it y .
Bateman ( I )
gories:
n utrients
r e c e n t l y p a r t i t i o n e d p l a n t pat hogens
p a ra s itic ,
p e r t h o p h y t i c , and s a p r o p h y t i c .
f ro m l i v i n g c e l l s
d ire c tly ,
i n t o three ca te ­
The f i r s t o b t a i n s
t h e second d e r i v e s
its
f ood f rom
34
c e lls
k ille d
in advance o f c o l o n i z a t i o n , and t h e t h i r d
from n o n - l i v i n g c e l l s a f t e r c o l o n i z a t i o n .
seeks i t s
f ood
The p a r a s i t i c h a b i t o f C_.
gramineum does n ot f i t
i n t o any o f t h e s e c o n v e n i e n t d i v i s i o n s .
this
c h a r a c t e r i s t i c s common t o bot h p e. rt h o p h y t e s and
pat hog en e x h i b i t s
saprophytes,
an i n t e g r a l
since
it
p a r a s t izes f u n c t i o n a l l y n o n - l i v i n g c e l l s
part of a liv in g
s ys t e m .
Rather,
t h a t are
Although o t h e r v a s c u la r pathogens,
n o t a b l y Fusar ium and V e r t i c i I l i u m , a r e a l s o r e s t r i c t e d
t o x y Iem t h r o u g h ­
out the
t o penetrate
liv in g
l i f e t i m e o f the h o s t ,
ce lls
o f the ro o t to
A d e s c r i p t i v e model
t h e y possess t h e a b i l i t y
in itia te
f o r £.
in fe c tio n
(8,18).
gramineum movement and d i s t r i b u t i o n
t h r o u g h a node and above i n t o t h e stem and l e a f of. a t t a c h m e n t
is presen­
t ed h e r e based upon t h e e v i d e n c e f o r d e v e l o p m e n t a l sequence o f b u n d l e
t y pe s w i t h i n each n o d e , t he m a t u r a t i o n g r a d i e n t between n od es , and t h e
sequence o f
node.
i n v a s i o n among b u n d l e t y p e s a f t e r
As a node d e v e l o p s ^
L bundles w i t h i n which a l l
t h e f u n g us g a i n s
in itia l
ingress
ingress f i r s t
in to a
i n t o the
la rge
o f t h e v e s s e l e l eme nt s a r e f u l l y m a t u r e .
The
f un gus s u b s e q u e n t l y moves i n t o t h e LI b u n d l e s nea r t h e base o f t h e node
a f t e r m a t u r a t i o n o f t he b r i d g i n g s t r a n d n e t w o r k w h i c h
w it h th e L bundle s.
interconnects
them
W i th t h e a c r o p e t a I m a t u r a t i o n o f a d d i t i o n a l b r i d ­
ging s t r a n d s ,
t h e f un g us g a i n s access t o t h e L2 b u n d l e s n ea r t h e apex
o f t h e node.
S i n ce t h e p i t h
bundle ty p e s ,
c o n t a c t must be made w i t h
f un gus can i n v a de i t .
plexus develops
A f t e r successful
in dep e nd e ntly o f a l l
other
the b r id g i n g s tra n d s b efo re the
c o lo n iz a t io n o f the p it h
plexus,
35
t h e f u n g us has r e ady access t o a l l
o t h e r v a s c u l a r b u n d l e s and l i n k i n g
s t r a n d s t h o u g h o u t t h e node w h i c h u l t i m a t e l y
invasion.
strip e s
M a c r o s c o p i c a 11y, t h i s
(L b u n d l e s ) on l e a v e s ,
the a djace n t
leads t o c o m p l e t e s y s t e m i c
s e q u e nc e - a pp ea r s as
tin g
a ll
discrete
f o l l o w e d by s l o w l y w i d e n i n g s t r i p e s as
i n t e r m e d i a t e b u n d l e s become i n v a d e d .
S t r i p e s may c o a l e s c e
d ep e n d i n g upong t h e p a t t e r n o f L b u n d l e c o l o n i z a t i o n
tu a lly ,
in itia l
i n t h e node.
Even­
l a t e r a l and i n t e r m e d i a t e b u n d l e s become c o l o n i z e d and b l i g h ­
occurs.
T h i s sequence i s r e p e a t e d . i n each node and l e a f o f a t t a c h ­
ment as t h e f u n g us moves upward in t h e p l a n t .
T h i s model has
d ev e lo p me nt p r ogr am.
im p o rta n t p r a c t i c a l
app lica tio n
t o a germplasm
Because p f t h e c l o s e t e m p o r a l a s s o c i a t i o n between
symptom e x p r e s s i o n and xyl em m a t u r a t i o n g r a d i e n t s , a l l
p r oge ny
for
lines
r e q u i r e c l o s e m o n i t o r i n g o f h e a d i n g d a t e s so t h a t s e l e c t i o n
] a t e - m a t u r i n g g e n o ty p es
d iffe re n tia l
p a r e n t a l and
is
not f a v o r e d .
Furthermore, s e le c ti o n
for
res pon se s t o symptom d eve lo pmen t i s e f f e c t i v e o n l y a f t e r
h e a d i n g , s i n c e symptoms dp n o t a pp ear on t h e f l a g
leaf u n til
head
emergence.
The r a t e o f s y s t e m i c s p r ea d o f £ . gramineum may be a f f e c t e d a t two
le v e ls .
cessful
The f i r s t ,
in g res s
which
is
related
i n t o new t e r r i t o r y ,
t o the c a p a b i l i t y
f o r gaining suc­
i s gove rn ed by t h e r a t e o f g rowt h
and m a t u r a t i o n o f x yl e m t i s s u e as . d i s c u s s e d above f o r M a r i a s .
s ec on d , w h i c h
is re la te d
^ o . the a b i l i t y
The
o f t h e pathogen t o overcome h o s t
I
defenses a f t e r
successful
ingress,
is gove rn ed by g e n e t i c d i f f e r e n c e s
36
between w i n t e r wheat c u l t i v a r s .
in C r e s t
Such an i n t e r a c t i o n appear ed t o e x i s t
LRC 40, w h i c h d e l a y e d c o m p l e t e s y s t e m i c
i n f e c t i o n by t he f un gus
much l o n g e r t h a n d i d M a r i a s .
Two resp on se s w h i c h c o u l d e l i c i t
cal
blockage o f v e r t i c a l
gums, and g e l s ,
and (2)
s lo ws s p e c u l a t i o n .
and/or
this
t he s y n t h e s i s o f an i n h i b i t o r y
The f i r s t
t h e s e h o s t - v a s c u l a r p at hogen
in v e s s e l s
to M arias.
the
(7).
in te ra c tio n s ,
in f e c t e d w it h £.
However, u n l i k e most o f
no t y l o s e s o r v e s s e l c o l l a p s e
gramineum ( 5 , 7 ) .
in
Mo r e o v e r ,
in advance o f c o n ! d i a l
in fecte d vessels.
LRC 40 e x h i b i t e d
It
i n c r e a s e d g e l a t i o n and gummosis as compared
is p o s s i b le t h a t these r e a c t i o n s precluded o r retarde d
l a t e r a l movement o f con i d ia f ro m c o l o n i z e d
b r i d g i n g s t r a n d n e t w o r k and p i t h
s pr ead
s u b s t a n c e which
b u t o c c u r r e d s i m u l t a n e o u s l y w i t h o r su bsequent t o f u n g u a l
p ro life ra tio n
Cr e s t
the p h y s i ­
has been i m p l i c a t e d as a r e s i s t a n c e
b o t h g e l a t i o n and gummosis were r a r e l y d e t e c t e d
invasion,
(l)
l a t e r a l movement o f con i d i a by t y l o s e s ,
mechanism in s e v e r a l v a s c u l a r d i s e a s e s
were o b s e r v e d
r e a c t i o n are
in to a l l
L and LI b u n d l e s
p l e x u s , w h ic h would
bundles o f a node.
lim it
in to the
systemic
Movement o f £ . g r a m i neum i n t o t h i s
i n t e r c o n n e c t i n g n e t w o r k o f x y Iem s t r a n d s
lagged c o n s i d e r a b l y
b ehi nd t h e
maturation g ra d ie n t.
The a p p a r e n t
in h ib itio n
of co n id ia l
p r o l i f e r a t i o n w it h in colonized
b u n d l e s o f C r e s t LRC 40 s u g g e s t e d an i n t e r a c t i o n a t t h e m o l e c u l a r
P o s s i b l y , a t o x i c compound i s s y n t h e s i z e d by t h e c u l t l v a r w h ic h
le ve l.
in h ib its
37
s p o r u l a t i on s u f f i c i e n t l y
to retard
system ic
in fe c tio n .
b o t h o f t h e s e phenomena may be r e s p o n s i b l e f o r
m i c i n v a s i o n by £ .
chemical
analyses
t he r e t a r d a t i o n o f s y s t e
gram? neum,. each must be s u b j e c t e d
to determine t h e i r r e l a t i v e
S i nc e e i t h e r o r
roles
to rigorous b io ­
in pathogenesis.
LITERATURE CITED
39
1.
Bateman, D.F. 1978. The dynamic n a t u r e o f d i s e a s e . In " P l a n t
D i s e a s e : An Advanced T r e a t i s e " ( J . G . H o r s f a l l and E. B. C o w l i n g ,
e d s . ) V o l . 3. pp. 53-83,,
Academic P re s s . New Y o r k .
2.
B r o w n i ng , J 1. A. , M.D. Simons, and E. T o r r e s . 1977. Managing h o s t
g enes : E p i d e m i o l o g i c and g e n e t i c c o n c e p t s . In " P l a n t Di se ase:
An Advanced T r e a t i s e " ( J . G . H o r s f a l l and E. B. C o w l i n g , e d s . )
V o l . 2. pp. 1 9 1 - 2 1 2 J Academic P r e s s . New Y o r k .
3.
B r u e h l , G.Wi 1956. P r e m a t u r i t y b l i g h t phase o f C e pha lo spo ri um
s t r i p e d i s e a s e o f w h e a t . P l a n t D i s . Rep. 4 0 : 2 3 7 - 2 4 1 .
4.
B r u e h l , G.W. 1957- C e p ha l o sp or i um s t r i p e d i s e a s e o f w h e a t .
p ath olog y 47:641-649.
5.
Chambers, H. L.
o f tomato.
6.
Dimohd, A. E. 1966. P r e s s u r e and f l o w r e l a t i o n s in v a s c u l a r b un d le s
o f the tomato p l a n t . P la n t P h y s i o l. 41:119-131.
7.
Dimond, A . E . 1970.
syndrome. Ann.
8.
G a r b e r , R.H. and B.R. Houst on. 1966. P e n e t r a t i o n and d evel opment o f
V e r t i c i l i i u m a l b o - a t r u m i n t h e c o t t o n p l a n t . P h y t o p a t h o l o g y 5 6:
1121 - 1126 .
9.
Je ns en , W.A. 1962. B o t a n i c a l H i s t o c h e m i s t r y - P r i n c i p l e s and P r a c ­
t i c e . W.H. Freeman and Co., San F r a n c i s c o and London.
Phyto­
and M . E. Corden. 1 9 6 3 . Semeiography o f Fusar ium w i l t
P hyto p ath olog y 53:1006-1010.
B i o p h y s i c s and b i o c h e m i s t r y o f t h e v a s c u l a r w i l t
Rev. P h y t o p a t h . 8 : 3 0 1 - 3 2 2 .
10.
L a r g e , E.C. 1954. Growth s t a g e s i n c e r e a l s - - ! I l u s t r a t i o n o f t he
Feekes s c a l e . P l a n t P a t h o l o g y 3 : 1 2 8 - 1 2 9 .
11.
M a t h r e , D.E. and R.H. J o h n s t o n . 1975- C e pha lo spo ri um s t r i p e o f
w i n t e r w h e a t : Pr oc ed ur es f o r d e t e r m i n i n g h o s t r e s p o n s e . Crop
S c i . 15:591-594.
12.
M a t h r e , D . E . , R.H. J o h n s t o n , and C.F. McGuire. 1977. Ce pha lo spo ri um
s t r i p e o f w i n t e r w h e a t : Pathogen v i r u l e n c e , s o u r c e s o f r e s i s ­
t a n c e , and e f f e c t on g r a i n q u a l i t y . P h y t o p a t h o l o g y 6 7 :1 14 2 -1 14 8
13.
P a t r i c k , J.W. 1972. V a s c u l a r system o f t he stem o f t h e wheat p l a n t .
I . M a t ur e s t a t e . A u s t . J . B o t . 2 0 : 4 9 - 6 3 .
40
14.
P a t r i c k , J.W, 1972. V a s c u l a r syst em o f t h e stem o f t h e wheat p l a n t .
I I . De vel opment. A u s t . J . B o t . 2 0 : 6 5 - 7 8 .
15•
P o o l , R . A . F , and . E. L . Sharp. 1969 . Some e n v i r o n m e n t a l and c u l t u r a l
f a c t o r s a f f e c t i n g C e p h a l o s p o r i urn s t r i p e o f w i n t e r w h e a t . P l a n t
D i s . Rep. 5 3 : 8 9 8 - 9 0 2 .
16.
P o o l , R . A . F . and E . L . Sharp. 1969. P o s s i b l e a s s o c i a t i o n o f a
p o l y s a c c h a r i d e and an a n t i b i o t i c w i t h t h e d i s e a s e c y c l e o f
C e p h a l o s p o r i u m gra mi neu m. P h y t o p a t h o l o g y . 5 9 : 1763- 1764.
17.
P r a t t , H. 1948. H i s t o - p h y s i o l o g i c a I
g e n e s i s . B o t . Rev. 1 4 : 6 0 3 - 6 4 3 .
18.
R i s h b e t h , J . 1955• Fu s ar i um w i l t o f bananas in J a m a i c a . I . Some
o b s e r v a t i o n s on t h e e p i d e m i o l o g y o f t h e d i s e a s e . A n n . B o t .
g r a d i e n t s and p l a n t o r g a n o ­
19 : 293- 328 .
19.
S l o p e , D. B. and R. B a r d n e r . 1965• C e p ha l o s p o r i u m s t r i p e o f wheat
and r o o t damage by i n s e c t s . P l a n t P a t h o l o g y . 14 : 1 8 4 - 1 8 7 .
20.
S p a l d i n g , D . H . , G.W. B r u e h I , and R . J . F o s t e r . 1961. P o s s i b l e r o l e
o f p e c t i n o l y t i c enzymes and p o l y s a c c h a r i d e in p a t h o g e n e s i s by
Cephal o s p o r i u m gramineum in w h e a t . P h y t o p a t h o l o g y 53=227- 235.
21.
Wei s e , M . V . 1972. C o l o n i z a t i o n o f wheat s e e d l i n g s by C e p h a l o s p o r i urn
gramineum i n r e l a t i o n t o symptom d ev e l o p m en t . P h y t o p a t h o l o g y
6 2 : 1013- 1018 .
.22.
Weis e , M.V. and R.V. R a v e n s c r o f t . 1978. S p o r o d o c h i urn d ev el opment
and c o n i d i u m p r o d u c t i o n i n C e p ha i o s p o r i u m g r ami n eu m. P hy t o p a ­
th o lo g y 6 8 : 3 9 5 - 4 0 1.
CHAPTER I I
PHYSIOLOGICAL EFFECTS OF CEPHALOSPORIUM STRIPE ON GROWTH AND
YIELD OF WINTER WHEAT (TRITICUM AESTIVUM L .) CU LTI VARS
42
INTRODUCTION
A lte ra tio n
tio n
o f water r e la t io n s
has been i m p l i c a t e d
b lig hte d
(5,6) .
Al I o f t h e d i s e a s e symptoms, w h i c h
l ea ves and h e a d s , s t u n t e d p l a n t s ,
a r e r e sp on se s t h a t can be a t t r i b u t e d
(14,21).
include
and g r e a t I y red uce d y i e l d s ,
to d is ru p tio n
in w a t e r economy
Di seas es o f w i n t e r wheat caused by r o o t and c r o w n - i n f e c t i n g
have o c c a s i o n a l l y been c o n f u s e d w i t h C e ph al o s po r i um s t r i p e
because o f t h e i r
men t
in te ra c­
between t h e v a s c u l a r p a t h o g e n , C e ph al o s po r i um g ra mi n eu m, and i t s
w i n t e r wheat h o s t
fungi
in the
(2,5,22) .
d e fic its
re se mb lan ce t o t he w h i t e head s t a g e o f d i s e a s e d e v e l o p
In such i n s t a n c e s , symptoms were a s s o c i a t e d w i t h w a t e r
imposed as a r e s u l t o f s e v e r e
Most a t t e m p t s a t d e f i n i n g
s p o r i u m s t r i p e - w i n t e r wheat
in fe c tio n
(22).
t h e d i s e a s e p h y s i o l o g y o f t h e Ce p ha l o-
i n t e r a c t i o n have been i n d i r e c t .
h i s t o l o g i c a l l y e v a l u a t e d pat hog en movement r e l a t i v e
develo pment.
pr eceded
He o b s e r v e d t h a t
Weise
(31)
t o f o l i a r symptom
i n v a s i o n and c o l o n i z a t i o n by t h e f un gus
inductio n o f f o l i a r s t r ip e s .
Mo re o ve r
(Chapter I ) ,
there
seemed t o be an a s s o c i a t i o n between t h e a ppear ance o f gums and g e l s ,
wh i ch a c c u m u l a t e d as f u n g a l
d isru p tio n
co lo n iza tio n
o f phloem w i t h i n v a s c u l a r b u n d l e s and mesophyI I c e l l s
rounding the v a s c u l a r bundle s.
c e ll
collapse
excised
became more e x t e n s i v e ,
in t h e s e r e g i o n s .
infected
sur­
S t r i p e s appeared in c o n j u n c t i o n w i t h
E x a m i n a t i o n o f e o s i n dye t r a n s p o r t
l e a v es r e v e a l e d t h a t b o t h v e r t i c a l and l a t e r a l
l o c a t i o n o f w a t e r were i n h i b i t e d
and t h e
in s y m p t o m a t i c r e g i o n s
(27,31)•
in
trans­
Some
43
i n v e s t i g a t o r s have s u g g e s t e d t h a t a c c u m u l a t i o n s o f a low m o l e c u l a r w e i g h t
p o l y s a c c h a r i d e pro du ce d by C_. gramineum in c u l t u r e
s trip e
form ation
Gramin in A,
o f action
(24,27).
is re s p o n s ib le f o r
Ot he rs have i m p l i c a t e d a t e t r o n i c a c i d t o x i n ,
in v a s c u l a r b r o w n i n g , a l t h o u g h t h e y do n o t p o s t u l a t e a mode
( 18.).
The o n l y a t t e m p t t o d i r e c t l y
on t h e w a t e r r e l a t i o n s
o f w i n t e r wheat
co nd u ct ed by S p a l d i n g , e t a I
content o f a l l
determine the e f f e c t s
(27).
infecte d w ith
o f pathogenesis
C_. gramineum was
They measured t h e r e l a t i v e m o i s t u r e
r e g i o n s o f w i n t e r wheat s h o o t s a f t e r h e a d i n g and found
t h a t d e s i c c a t i o n was more p ronounced
T heir study, w h ile s u b s ta n tia tin g
in d i s e a s e d t ha n i n h e a l t h y t i s s u e s .
th a t water d e f i c i t s
are
p a th o g e n e s is , d id not e v a lu a t e the p h y s i o l o g i c a l e f f e c t s
d e fic its
o f these w a te r
on t h e h o s t t h r o u g h o u t d i s e a s e d ev el op men t o r d e t e r m i n e w h e t h e r
t h e d i s e a s e syndrome was due w h o l l y o r
The p u r po s e o f t h i s
determine i t s a p p l i c a t i o n
in p a r t t o w a t e r s t r e s s .
i n v e s t i g a t i o n was t o o b t a i n a more c o m p r e he n si v e
a n a l y s i s o f disease p h y s io lo g y
e ffe cts
i nduced d u r i n g
in r e l a t i o n
to se le ctio n
t o symptom e x p r e s s i o n and t o
f o r disease r e s is t a n c e .
o f p a t h o g e n e s i s on p l a n t m e t a b o l i c p r o c e s s e s ,
patterns,
e longation
The
on p l a n t g rowt h
and u l t i m a t e l y on y i e l d components f ro m t h e o n s e t o f stem
through the g r a i n f i l l i n g
d iffe re n tia lly
p e r i o d were examined
r e s p o n d i n g w i n t e r whe at c u l t i v a r s .
in s e v e r a l
44
MATERIALS AND METHODS
Three w i n t e r wheat c u l t i v a r s ,
Component
M a ri a s
(LRC) 40 (MT 7 5 7 9 ) , and P . l .
( C . I . 17595) , C r e s t
Li ne Row
278212 were used i n t h i s s t u d y .
They we re p l a n t e d
i n e a r l y S e p t e m b e r , 1978 a t t h e Montana A g r i c u l t u r a l
E x p er i m en t S t a t i o n
n e a r Bozeman, Montana i n a randomized b l o c k d e s i g n
w ith four re p lic a tio n s .
Each c u l t i v a r was seeded in p a i r e d rows 3.1 m
lo ng and spaced 7 1 cm a p a r t .
nels
infeste d w ith
To on,e row was added 20 grams o f o a t k e r ­
C^ g r a m ! neum (20) s i m u l t a n e o u s l y w i t h
t h e seed.
A
s e e d i n g r a t e o f 200 seeds p e r row was used t o maxi mi ze t h e number o f
in fe c te d seedlings.
In t he s p r i n g , d i s e a s e d p l a n t s we re i d e n t i f i e d
each row by s t r i p i n g
on l o we r l ea ves and l e a f s h ea t h s and t h e main t i l ­
l e r s were t a g g e d .
Each row was t h i n n e d m a n u a l l y u n t i l
15 cm a p a r t .
Seedlings
in
in fe c te d plants
were spaced a t
least
in a d j a c e n t ch eck rows
were s i m i l a r l y
t h i n n e d so t h a t e v e r y i n f e c t e d p l a n t was p a i r e d w i t h a
healthy p la n t.
R e lative w ater content
chlo rop h yll
(RWC), c o n d u c t a n c e , n e t p h o t o s y n t h e s i s , and
c o n t e n t were measured t o e v a l u a t e t he p h y s i o l o g i c a l
re la tio n ­
s h i p s between w a t e r s t r e s s and symptom e x p r e s s i o n a t v a r i o u s degrees o f
s trip in g
on f l a g
l eaves o f d i s e a s e d w i n t e r whe at p l a n t s .
t a n c e were used as
in d icato rs
o f t o t a l water p o te n tia l
tra n s p iratio na l
beh a vio r.
of water stre ss
in a l e a f and t h e
RWC and c o n d uc ­
t h e f o r m e r b e i n g a measure
l a t t e r b e i n g a measure o f
Net p h o t o s y n t h e s i s and c h l o r o p h y l l
were used as i n d i c a t o r s o f t o t a l
photoassim ila to r y a c t i v i t y .
content
For each
45
infected fla g
a ll
le a f, a healthy fla g
l e a f was sampled c o n c u r r e n t l y .
f o u r p a r a m e t e r s c o u l d he e x p r e s s e d as p e r c e n t o f c o n t r o l
out environmental
the f i e l d .
factors
Im p lic it
t o ca nc e l
common t o bot h h e a l t h y and d i s e a s e d p l a n t s
in
in t he r e s u l t s , t h e r e f o r e , was t h e a s s um pt io n t h a t
o bs er ve d d i f f e r e n c e s a r e caused p r i m a r i l y by p a t h o l o g i c a l
Symptom s e v e r i t y
Thus,
(number o f s t r i p e s p e r
r e s p on s e s .
l e a f ) was based on a d i s e a s e
i n d e x r a t i n g s yst em p r e v i o u s l y d e s c r i b e d
(Chapter
I).
Leaves w e re sampled between 9 a.m. and noon on c a l m , c l e a r d ay s. On
each s a m p l i n g d a t e ,
between t e n and f i f t e e n
le av es were e v a l u a t e d .
The l e av es ranged
s t r i p e t o complete c h l o r o s i s .
r a t i n g were a n a l y z e d f o r a l l
i n f e c t e d and h e a l t h y f l a g
in symptom s e v e r i t y
U ltim a te ly ,
t en
four p hysiolo g ica l
f ro m one
l e av es o f each s e v e r i t y
parameters.
For one
sample p o p u l a t i o n , measurements were made i n t h e f o l l o w i n g s e q u e n c e : Net
p h o t o s y n t h e s i s , c o n d u c t a n c e , and r e l a t i v e w a t e r c o n t e n t .
c o n t e n t was d e t e r m i n e d f r o m a d i f f e r e n t ,
Chlorophyll
though equal s i z e d ,
sample
p o p u l a t i o n , s i n c e RWC d e t e r m i n a t i o n s we re d e s t r u c t i v e .
Net p h o t o s y n t h e s i s .
le a ve s
in t h e f i e l d
Carbon d i o x i d e
f l u x was measured on a t t a c h e d
u s i n g a p o r t a b l e c l o s e d syst em a da pt ed f ro m a t e c h ­
n i q u e d e v e l o p e d by C l e g g , e t a I ( 9 ) •
ThS sample chamber was c o n s t r u c t e d
o f t u b u l a r p l e x i g l a s s w i t h a d i a m e t e r o f 2 . 6 cm and a l e n g t h o f
The i n t e r n a l
volume t o t a l l e d
ves s e a l e d by c l o s e d - c e l l
100 cmX
insulation
b o t h h a l v e s were clamped t o g e t h e r ,
19 cm.
The chamber c o n s i s t e d o f two h a l ­
tape
a tig h t
(Figure
Il-I).
T h us , when
s e a l was o b t a i n e d .
Glass
46
t u b i n g 0 . 6 cm X 2 . 5 cm was a t t a c h e d t o two p o r t a l s p o s i t i o n e d
in t h e
u pp e r h a l f o f t h e t u b e and s e a l e d o f f by r u b b e r serum b o t t l e caps.
samples were t a k en
in p l a s t i c s y rin g e s
t h e t wo g l a s s t u b e s .
(B*D m u l t i f i t ,
10 m l )
Gas
inserted
in
The sample chamber was mounted a t one end i n a
b u r e t clamp h o l d e r a t t a c h e d t o a m e t a l
ringstand.
The a n g l e o f t h e
sample chamber was c o n t i n u a l l y a d j u s t e d so t h a t t h e l e a f b l a d e was p o s i ­
t io n e d p e r p e n d ic u la r t o the su n 's
incident
rays.
Wi th b o t h h a l v e s o f
t h e chamber clamped t i g h t l y a t one e n d , t h e r e was a s u f f i c i e n t gap t o
i n s e r t a l e a f from the o p p o s ite e n d ,
ted p r i o r
in itia l
to sealing
COg l e v e l s
le a f w ith in
around t h e
w ith a s e lf - c lo s in g
m i n u t e s , a second
the
le a f.
A 10 ml a l i q u o t o f gas was c o l l e c ­
t h e sample chamber t o r e p r e s e n t
The chamber was t h e n clamped s h u t
s p r i n g b r a s s t e s t t u b e w i r e c l a m p , and a f t e r two
10 ml a l i q u o t o f gas was t a k e n f r o m w i t h i n
t h e chamber.
The h a l v e s o f t h e chamber were l e f t open a few m i n u t e s between
measurements t o a l l o w e q u i l i b r a t i o n w i t h a mb i en t a i r .
lin g ,
t h e s y r i n g e s were s t o r e d f o r 2 - 3 h o u r s
u n til
t h e y c o u l d be t r a n s f e r r e d
in je cted
The gas samples were
A c a r r i e r gas o f known COg c o n c e n t r a t i o n
was passed t h r o u g h t h e s yst em a t a r a t e o f
11/min.
column packed w i t h d r r e r i t e was i n s e r t e d between t h e
IR a n a l y z e r .
200 u l / l
shaded c o n t a i n e r
i n t o a Beckman IR 215 I n f r a r e d Gas A n a l y z e r t o d e t e r m i n e t h e i r
COg c o n c e n t r a t i o n s .
the
A f t e r gas samp­
in a c o o l ,
t o the l a b o r a t o r y .
leaf
The IR a n a l y z e r was c a l i b r a t e d
COg u s i n g s t a n d a r d gases a t
170 u l / l
A s ix
(320 u l / l )
i nch d r y i n g
in je ctio n
s i t e and
t o read f r o m 0 t o
and 320 u l / l .
47
Figure
I 1-1.
P l e x i g l a s s t u b u l a r chamber f o r m e a su r i ng c ar bon
d i o x i d e exchange i n w i n t e r wheat l e av es i n t h e
fie ld .
Two gas samples were c o l l e c t e d i n p l a s t i c
10 ml s y r i n g e s a t t h e b e g i n n i n g and end o f a two
m i n u t e i n t e r v a l and b r o u g h t back t o t he l a b o r a t o r y
f o r i n j e c t i o n i n t o an IR gas a n a l y z e r .
48
D iffe re n tia l
CC^ c o n c e n t r a t i o n s were r e c o r d e d as peaks on a Beckman
Model 9.3500 R e c o r d e r .
tia l
CO2 a s s i m i l a t i o n
In c o n v e r t i n g
Peak h e i g h t s were measured t o d e t e r m i n e d i f f e r e n ­
r a t e s between p a i r e d h e a l t h y and d i s e a s e d
u l/1
COg t o mgCOg/dmZ/hr,
e stim a te d using the f o r m u la ,
w i d t h o f t he
Conductance.
w ith a d if fu s iv e
Nebraska) .
v a ria tio n
D iffu sive
l e a f a r e a measurements were
.905 L X W where L =
l e a f midway f r o m t h e t i p
leaf
l e n g t h and W =
(16).
r e s is t a n c e t o w a te r vapor
p o r o m e t e r (Model
leaves.
LI 6 0 ,
l o s s was measured
Lamda I n s t r u m e n t s
Co., L in c o ln ,
The recommended p r e c a u t i o n s were o bse r ve d t o r educe s a m p l i n g
(17) •
t h es e s t u d i e s .
n e a r t h e b a se ,
The w i d e a p e r t u r e v a p o r cup ( 1 X 2
cm) was used in
Th re e r e a d i n g s were t a k e n f ro m t h e a d a x i a I l e a f s u r f a c e ,
in t h e m i d d l e , and n ea r t h e t i p .
an e s t i m a t i o n o f o v e r a l l
d iffu s iv e
The mean r e p r e s e n t e d
r e s i s t a n c e f o r each l e a f .
Readings
were made a f t e r c o m p l e t i o n o f p h o t o s y n t h e t i c measur ement s, wh ich a l l o w e d
at
l e a s t 30 m i n u t e s
fo r a le a f to re turn
to a steady-state c o n d itio n .
Leaf c o n d u c t a n c e , w h i c h was p r e f e r r e d
because o f
its
water content,
d ire c t
c o rre la tio n w ith
and t r a n s p i r a t i o n
red,
the
leaf d iffu s iv e
A fte r d iffu s iv e
l ea ves were s e ver ed bel ow t h e
• p a i r e d w i t h an i n f e c t e d
sealed t o g e t h e r
le a f,
in a s m a l l
resistance
net p h o to s y n th e s is ,
r a t e , was c a l c u l a t e d
C = I Z r gd where r gd i s t h e a d a x i a l
R e la tive water c o n te n t;
to d if fu s iv e
Iig u le .
and b o t h e x c i s e d
re la tive
from the fo rm u la ,
resistance.
r e s i s t a n c e had been measu­
A healthy
l e a f was
le a ve s we re i m m e d i a t e l y
p l a s t i c b ag , w h i c h was p l a c e d on i c e
in a
kS
chest c o o le r.
In t h e
laboratory,
a s p e c i f i c sequence f o r h a n d l i n g each l e a f was
employed t o m i n i m i z e s a m p l i n g e r r o r .
bag a t a t i m e ,
the
infected
e n c l o s e d chamber l i n e d w i t h
Only one l e a f was removed f rom t h e
leaf f i r s t .
Removal t o o k p l a c e w i t h i n an
s a t u r a t e d paper t o w e l s t o m a i n t a i n h i g h
hum idity.
Four
1.5 cm segments were c u t f r o m each
tem plate.
One segment was f r o m t h e b a s a l
r e g i o n , and one f ro m n e a r t h e t i p
region,
l e a f using a p r e - c u t
two f r o m t h e m i d d l e
o f each l e a f .
Each l e a f s e g m e n t ' s f r e s h w e i g h t was d e t e r m i n e d
e x c i s i o n and s u b s e q u e n t l y wedged between two s t r i p s
o p e n - c e l l e d p o l y u r e t h a n e foam.
fie d
f r o m Cat sky
le a f discs.
It
T h is apparatus
(8) t o w o r k w i t h s q u a r e wheat
im mediately a f t e r
o f w ater-saturated
(Figure
l e a f segments
c o n s is te d o f a square p l e x i g l a s s
At 2 cm i n t e r v a l s ,
deep t r o u g h was c u t f o r p o s i t i o n i n g
the
l e a f segments.
a 1.5 cm X I cm
A fte r
in se rtio n
l e a f segmen ts, an opaque s q ua r e p i e c e o f g l a s s 0 . 5 cm t h i c k was
c e n t e r e d o v e r t h e foam.
that a l l
w ater.
instead o f
t r a y which enclosed a
2 . 5 cm l a y e r o f p o l y u r e t h a n e foam.
of a ll
I 1-2) was mo di ­
c u t edges o f t h e
It
s u p p l i e d enough downward p r e s s u r e t o e n s u r e
l e a f segments we re in d i r e c t c o n t a c t w i t h
The e n t i r e a p p a r a t u s was t h en p l a c e d
in a c l e a r p l a s t i c chamber
c o n t a i n i n g 2 . 5 cm o f w a t e r and s e a l e d w i t h a I i d t o m a i n t a i n h i g h r e l a ­
t iv e hum idity.
The l e a f segments we re i n c u b a t e d a t room t e m p e r a t u r e
under i l l u m i n a t i o n o f 350 e r g s / c m ^ f o r t h r e e h o u r s .
T u r g o r w e i g h t was o b t a i n e d by removal o f each segment w i t h
fla t
50
Figure
I 1-2.
P o l y u r e t h a n e foam d e v i c e f o r s a t u r a t i n g 1.5 cm
X 1.5 cm segments c u t f r o m h e a l t h y and CephaI o s p o r i urn gramineum i n f e c t e d w i n t e r wheat l e a v e s .
51
tipped fo rc e p s , pressing
it
between s i x
p a p e r f o r 30 s e c o n d s , and w e i g h i n g
it.
l a y e r s o f Whatman No.
I filte r
L ea f segments were i n c u b a t e d a t
70°C in a m e c h a n i c a l l y c o n v e c t e d d r y i n g oven f o r 24 hours and d r y
weights determined.
R e l a t i v e w a t e r c o n t e n t was computed u s i n g t h e f o r m u l a :
(Fr esh Wei ght - Dry Weig h t ) / ( T u r g o r W ei g ht - Dry W e i g h t ) .
Chlorophyll
content.
C h l o r o p h y l l was e x t r a c t e d f r o m a s e p a r a t e
p o p u l a t i o n o f p a i r e d h e a l t h y and d i s e a s e d
d ur e
(l).
Optical d en sity
l eaves u s i n g A r n o n 1s p r o c e ­
readings o f the c h l o r o p h y l l - a c e t o n e superna­
t a n t were o b t a i n e d f r o m a Beckman Model 25 Scanning S p e c t r o p h o t o m e t e r .
;
C hlorophyll
c o n t e n t was computed as m i l l i g r a m s
of ch lo rop h yll
l e a f area.
L e a f a re a was e s t i m a t e d as. d e s c r i b e d above.
per u n i t
52
RESULTS
C e p ha l o s p o r i u m gramineum i n f e c t e d f l a g
generalized w i l t i n g
reductions
typical
l eaves d i d n o t e x h i b i t
o f o th e r v a s c u la r diseases
in w a t e r c o n t e n t , w a ter vapor d i f f u s i o n ,
ch lo ro p h yll
c o n t e n t were
( 11) .
COg u p t a k e , and
I i n e a rly c o rre la te d w ith successive
in t h e number o f c h l o r o t i c s t r i p e s
p er
infected
Rather,
le a f
(Figure
increases
11-3). This
and t h e h i g h l y s i g n i f i c a n t c o r r e l a t i o n s
between a l l
w ith
I I - 1) s u g g e st e d t h a t t h e e f f e c t s
respect
t o symptom s e v e r i t y
of vascular dysfunction
le d t o
(Table
lo c a liz e d water d e f i c i t s
r e g i o n s a round h e a v i l y c o l o n i z e d v a s c u l a r b u n d l e s .
o f the
o f t h e p ar amet er s
le a f continued t o fu n c tio n
i n t he
N o n - i nvaded p o r t i o n s
i n a nor mal m a n ne r .
No change i n n e t p h o t o s y n t h e s i s was obs er ve d u n t i l
symptoms a p p e a r e d .
only
a fte r fo lia r
The c o mp en sa ti o n p o i n t , where COg u p t a k e
i s b a l a n ce d
by COg e v o l u t i o n , was a t t a i n e d when g r e a t e r t han 90% o f t he v a s c u l a r
bundles
in a l e a f were c o l o n i z e d .
In c o m p l e t e l y b l i g h t e d
exchange was e x p r e s s e d as a n e g a t i v e v a l u e .
increased,
it
re sp ira tory a c t iv it y
rose
leaves,
COg
Thus, as symptom s e v e r i t y
in r e l a t i o n
to photosynthesis u n t i l
predominated.
The consequences o f w a t e r i m b a l a n c e , a l o n g w i t h t h e d e p r e s s i o n o f
p h o t o s y n t h e s i s , can s i g n i f i c a n t l y
yie ld
growth
p o te n tia l.
include
i n h i b i t p l a n t g rowt h p a t t e r n s and
Responses w h ic h measure t h e s e e f f e c t s on v e g e t a t i v e
i n t e r n o d e e l o n g a t i o n and l e a f e x p a n s i o n .
cative of a lte ra tio n s
in r e p r o d u c t i v e d eve lo pmen t
Responses i n d i ­
i n c l u d e t h e number o f
53
The r e l a t i o n s h i p between s t r i p e f o r m a t i o n in
C e p h a l o s p o r i u m gramineum i n f e c t e d f l a g l ea ves
and n e t p h o t o s y n t h e s i s , r e l a t i v e w a t e r c o n t e n t ,
c o n d u c t a n c e , and c h l o r o p h y l l c o n t e n t .
Symptom
s e v e r i t y was based on t he number o f s t r i p e s p er
le a f.
I = one s t r i p e p e r l e a f , 11 = c o m pl e t e
ch lo rosis.
Each p o i n t i s t h e mean o f t e n l e a v e s .
O
O
</>O
(PERCENT OF CONTROL)
NET PHOTOSYNTHESIS
ing/dm2/hr
Il-].
I
I
I
I
4 I
I
SYMPTOM SEVERITY
I 4 .4 : r 4 4
I
1 4 -1
I
I
I I
SYMPTOM SEVERITY
t
PERCENT OF CONTROL)
RELATIVE WATER CONTENT
percent
Fig ure
TABLE I 1 -1.
C o r r e l a t i o n s between n et p h o t o s y n t h e s i s ,
r e l a t i v e w a t e r c o n t e n t , c o n d u c t a n c e , and
c h l o r o p h y l l c o n t e n t in C e p h a I o s p o r i urn
gramineum i n f e c t e d f l a g l e a v es o f t h e
s u s c e p t i b l e w i n t e r wheat c u l t i v a r M a r i a s .
C o r r e l a t i o n C o e f f i c i e n t —^
I
I
I
J
I
CD
CO
D
VO
LO
Co
C
CTv
O
B
CO
I
I
&
———
.96
. 97
------- —
—— —
.96
—^ C a l c u l a t e d f ro m t h e mean v a l u e s r e p r e s e n t e d
F i g u r e 11-2.
in
—^ A = n e t p h o t o s y n t h e s i s , B = r e l a t i v e w a t e r c o n t e n t ,
C = c o n d u c t a n c e , and D = c h l o r o p h y l l c o n t e n t .
55
spikelets
formed p e r h e a d , t h e number o f f l o r e t s
and t h e e x t e n t o f g r a i n
fe rtiliz e d
per head,
fillin g .
I n t e r n o d e e l o n g a t i o n was s e v e r e l y r e s t r i c t e d c o n t i n u o u s l y t h r o u g h ­
o u t d ev el op men t o f t h e two c u l t i v a r s
M a r i a s and P . I . 278212
( Ta b le
11-2).
S t u n t i n g was more pronounced d u r i n g e l o n g a t i o n o f t h e i n t e r n o d e between
t h e p e n u l t i m a t e and f l a g nodes and o f t h e p e d u n c l e , s u g g e s t i n g t h a t t h e
cumulative e ff e c t s
o f d i s e a s e were most s e v e r e d u r i n g head emergence.
The re sp on se o f C r e s t
o f p at hogen s p r e a d .
effects
vars
LRC 40 r e f l e c t e d a more moder at e
U n l i k e stem e l o n g a t i o n ,
o f p a t h o g e n e s i s oh l e a f a re as
( Ta b l e
in crease
in ra te
t h e r e were no s i g n i f i c a n t
i n any o f t h e w i n t e r wheat c u l t i ­
I |-3 )•
The heads o f t w e n t y p r i m a r y t i l l e r s
o f each c u l t i v a r were examined
t o d e t e r m i n e t h e e f f e c t s o f d i s e a s e d ev el op men t on t h e y i e l d component s,
s p ike lets/h ea d ,
g r a i n s / h e a d , and g r a i n w e i g h t
(t ho us a nd k e r n e l w e i g h t ) /
head.
No change i n s p i k e l e t number among t h e t h r e e c u l t i v a r s
t h a t t h e movement o f £ .
indicated
gramineum had n o t p r o g r e s s e d enough i n t h e e a r l y
s t a g e s o f v e g e t a t i v e g r o w t h t o evoke a s t r e s s e d c o n d i t i o n
(Table
I 1-4).
By t h e t i m e o f f l o w e r i n g , h ow eve r, d i s e a s e s e v e r i t y had i n c r e a s e d
s u ffic ie n tly
to
impose w a t e r s t r e s s on l a t e m a t u r i n g f l o r e t s
nea r t h e apex and base o f t h e heads.
was a r e d u c t i o n
grain
fillin g
located
The most d r a m a t i c e f f e c t observed
in g r a in w e ig ht a t p l a n t m a t u r i t y .
T hus, t h e p e r i o d o f
between f l o w e r i n g and senescence appeared t o be most
.
£
56
TABLE 11- 2.
Percent r e d u c t io n w it h respect t o h e a lt h y c o n t r o l s
o f c o n s e c u t i v e i n t e r n o d e l e n g t h s o f w i n t e r wheats
i n f e c t e d w i t h Cephal o s p p r i urn gramineum.
I n t e r n o d e —^
C u ltiva r
Marias
Crest
P .l.
LRC 40
278212
1-4
1-3
1-2
1-1
35^
34
32
42
41
37
4
6
11
17
16
11
28
28
27
47
40
35
Peduncl e
Mean
— I n t e r n o d e s a r e numbered f ro m b el ow t h e f l a g node ( I - 1) down- .
wa r d .
—^ Mean p e r c e n t r e d u c t i o n f ro m h e a l t h y c o n t r o l s based on a sample
s i z e o f 50 p r i m a r y t i l l e r s o f each c u l t i v a r .
57
TABLE 11-3,
E f f e c t o f C e p ha l o s p o r i u m gramineum i n f e c t i o n on
l e a f a r e as o f t h r e e w i n t e r wheat c u l t i v a r s .
L ea f Area
' Fl ag Lea f
C ultJvar
Marias
Crest
P .l.
LRC 40
278212
(cm^)—^
P e n u l t i m a t e Leaf
Infected
Hea I t h y
Infected
Hea I t h y
23.3
2 3. 9
19-3
17.1
18.0
2 0. 5
20.8
33. 5
. 34.1
30. 8
31. 6 .
.
21.2
N o n - s i g n i f l e a n t d i f f e r e n c e s were
—^The mean o f t e n l e a v e s .
o bse r ve d a t P = .05 u s i n g a p a i r e d T - t e s t f o r a l l c o m p a r i sons between h e a l t h y and i n f e c t e d l e a v e s .
58
TABLE I 1-4.
The e f f e c t s o f C e ph a l o s p o r i u m s t r i p e symptom d evel opment
on w i n t e r whe at y i e l d components and t h e i r r e l a t i o n s h i p
t o t h e d u r a t i o n o f p h o t o s y n t h e s i s o f f l a g l e av es f o l l o w i n g
anthesis.
P e r c e n t o f H e a l t h y C o n t r o l —^
Ma r ia s
Crest
LRC 40
P. 1. 278212
S p ike le ts/
Head
Seeds/
Head
Thousand
K er n el W t .
C/
IOOa-
96b
31a
35a
100a.
100a
65b
72b
100a
O
Ln
CO
C ultiva r
33a
27a
Duration o f ,
P h o t o s y n t h e s i s—
"^Mean o f 20 p r i m a r y t i l l e r s .
^ M e a n p e r c e n t n e t p h o t o s y n t h e s i s o v e r a 35 day p e r i o d f o l l o w i n g
a n t h e s i s f r o m t h e d a t a p r e s e n t e d i n F i g u r e 11 - 4 .
~ For each c o l u mn , v a l u e s w i t h t h e same l e t t e r a r e n o t s i g n i f i c a n t l y
d i f f e r e n t a t P - . 0 5 , a c c o r d i n g t o Dunc an' s m u l t i p l e range t e s t .
59
s e r i o u s l y a f f e c t e d by p a t h o g e n e s i s .
d ev el op men t t h a t symptom e x p r e s s i o n
peduncle,
It
is d u r in g t h i s
i s m a n i f e s t e d on t h e f l a g
le a f,
the
and t h e head ( C h a p t e r 3 ) .
To m o n i t o r t he r a t e o f p h o t o s y n t h e t i c
i n c r e a s i n g symptom s e v e r i t y ,
in tervals
stage o f p la n t
from the f l a g
wheat c u l t i v a r
impairment
f o r 35 days f o l l o w i n g a n t h e s i s .
t e d a s h ar p d e c l i n e
damage.
o f each w i n t e r
Measurements were then
Both M a r i a s and P . I . 278212 e x h i b i ­
in p h o t o s y n t h e t ic a c t i v i t y concomitant w it h
increase
in c h l o r o t i c s t r i p e s
headin g,
t he f l a g
to
n e t p h o t o s y n t h e s i s was measured a t f i v e day
l ea ves o f t en p r i m a r y t i l l e r s
t e r m i n a t e d because o f h a i l
in r e l a t i o n
(Figure
11-4).
the
By t h r e e weeks a f t e r
l e av es were c o m p l e t e l y b l i g h t e d and p h o t o s y n t h e s i s
was t o t a l l y s u p p r e s s e d .
The f l a g
l e av es o f Cr es t
t i n u e d t o show p h o t o s y n t h e t i c a c t i v i t y ,
although b l i g h t i n g e v e n tu a lly occurred.
visu a l
in d exin g o f s t r i p e
tia te s
the c lo s e c o r r e l a t i o n
F i gure
I l-j.
LRC 4 0, h ow ev e r, co n­
even 35 days a f t e r h e a d i n g ,
The c l o s e a s s o c i a t i o n between
d ev el opment and n e t p h o t o s y n t h e s i s s u b s t a n ­
between t h e two p a r a m e t e r s
illu s tra te d
The d u r a t i o n o f p h o t o s y n t h a t e p r o d u c t i o n by t h e f l a g
c u l t i v a r was e s t i m a t e d by a v e r a g i n g t h e d e c l i n e
o v e r t h e 35 day p e r i o d
(Figure
I 1-4).
in
l e av es o f each
in net pho tos y n th es is
CO2 exchange was assumed t o be
z e r o a f t e r c o m p l e t e f o l i a r b l i g h t i n g o c c u r r e d , even t hough t h e r e were
i n d i c a t i o n s o f some r e s i d u a l
g ra in -fillin g
re sp ira to ry a c tiv it y .
Much o f t h e
lack
in d i s e a s e d p l a n t s as compared w i t h h e a l t h y ones can be
in
60
Figure
11-4.
R e l a t i o n s h i p between s t r i p e f o r m a t i o n and n e t p h o t o ­
s y n t h e s i s i n C e p h a l o s p o r i u m gramineum i n f e c t e d f l a g
le a ve s o f t h r e e w i n t e r wheat c u l t i v a r s .
Ten leaves
o f each c u l t I v a r were m o n i t o r e d f o r 35 days a f t e r
heading.
Symptom s e v e r i t y was s c o re d by t he number
o f s t r i p e s p er l e a f . I = one s t r i p e p e r l e a f , 11 =
complete c h l o r o s i s .
V e r t i c a l bar s r e p r e s e n t one
standard d e v ia tio n .
MARIAS
CREST LRC 40
P.1.278212
DAYS
AFTER
H E A D IN G
61
p r o b a b l y be a t t r i b u t e d
flow ering
( Ta b l e
11-4).
t o the e f f e c t s
o f d i s e a s e d ev el op men t a f t e r
62
DISCUSSION
Disease-in duced p l a n t w a te r d e f i c i t s
in the t o t a l
p la nt water p o te n tia l
may be g e n e r a t e d by a l t e r a t i o n
e ith e r d ire c tly ,
i n c r e a s e d r e s i s t a n c e t o w a t e r movement w i t h i n
tern, o r
as
i n t h e case o f
the w a te r c o nd u c ting s y s -
i n d i r e c t l y as i n t h e case o f t o x i n - i n d u c e d changes
p e r m e a b i l i t y , wh ic h a l t e r
solute p o te n tia ls w ith in a ffe c te d c e lls
While v a s c u la r d y s f u n c t i o n
im plicated
in membrane
(12).
in Cv g ram?neum i n f e c t e d p l a n t s has been
in d i s e a s e s y m p t om a t ol o gy
( 6 , 2 4 , 2 7 , 3 1 ) , a t o x i n , G ra mi ni n A,
a l s o has been s u g g e s t e d as a cause o f symptom d e v e l o p m e n t .
G ra mi n in A
caused v a s c u l a r d i s c o l o r a t i o n and some c h l o r o s i s when i t was a d m i n i s ­
tered to healthy plants
( 18 ) .
The r e s u l t s o f t h i s
major r o l e
s t u d y s u g g e s t t h a t a t o x i n does n o t p l a y a
in disease development.
The l i n e a r
symptom e x p r e s s i o n and n e t p h o t o s y n t h e s i s ,
c o n d u c t a n c e , and c h l o r o p h y l l c o n t e n t ,
co rre la tion s
form ation,
r e l a t i o n s h i p s between
r e l a t i v e water c o n te n t,
as w e l l as t h e s i g n i f i c a n t
between t h e f o u r p a r a m e t e r s t h r o u g h o u t p r o g r e s s i v e s t r i p e
in d ica te
t h a t o n l y pronounced
lo ca lize d e ffe c ts
develop
a round e x t e n s i v e l y c o l o n i z e d v a s c u l a r b u n d l e s .
The d e c l i n e
i n RWC and c o n d u c t a n c e , w h i c h
by s t o m a t a I r e g u l a t i o n
stress.
(4,12,28),
indicated
is c o n t r o l l e d p r i m a r i l y
lo ca lize d
i n t e r n a l water
S i n c e b o t h o f t h e s e p a r a m e t e r s we re s i m i l a r l y a f f e c t e d by
disease development,
t h e main f a c t o r c a u s i n g w a t e r d e f i c i t s
be reduced w a t e r s u p p l y .
A d iffu s ib le
toxin
appeared t o
t h a t a l t e r e d membrane
63
p e r m e a b i l i t y wo ul d have r e s u l t e d
i n a poo r c o r r e l a t i o n between RWC and
c o n d u c t a n c e due t o abnormal s t o m at a I o pe n i ng o r c l o s u r e
remai ns u n c l e a r ,
It
h oweve r, w h e t h e r t h e d e c r ea s e i n c o nd u c t a n c e immedi­
a t e l y pre ced ed o r o c c u r r e d s i m u l t a n e o u s l y w i t h
sm all
(12,28).
temporal d i f f e r e n c e s a s s o c ia te d w i t h
c h l o r o t i c s t r i p e were d i f f i c u l t
increased c o n c u r r e n t l y w i t h
to d e te c t.
the d e c l i n e
the drop
in RWC,. s i n c e
t h e appearance o f each new
If d iffu s iv e
resistance
in RWC, t o x i n a c t i v i t y c o n f i n e d
t o t h e r e g i o n a ro un d each c o l o n i z e d v a s c u l a r b u n d l e c a n n o t be r u l e d out .
com pletely.
It
i s d o u b t f u l , h ow ev e r,
t e t r o n i c acid d e r iv a t iv e
s p e c ia lly
fungal
re s tric te d .
c e lls ,
ch lorosis
gels,
(Chapter
saccharide
t h e low m o l e c u l a r w e i g h t
i s o l a t e d by Kobayashi
and Ui
(18) would be so
The t e m p o r a l a s s o c i a t i o n between a c c u m u l a t i o n o f
and gums w i t h
I,
that
i n t e r n a l c e l l c o l l a p s e and e x t e r n a l
3 1) s u gg e s t s t h a t t h e
low m o l e c u l a r w e i g h t p o l y ­
i s o l a t e d f r o m c u l t u r e e x t r a c t s o f JC. gramineum wo u ld be a
more l o g i c a l
incita.nt o f r e s t r ic t e d
l a t e r a l w a t e r movement
(24,27).
Net p h o t o s y n t h e s i s can be s u p p re s se d by p a t h o g e n - i n d u c e d w a t e r
d e fic its
in two w a y s .
t a n c e , w h ic h r e s t r i c t s
The f i r s t
i n v o l v e s an i n c r e a s e
in s t om at a I r e s i s ­
b ot h t h e o u t wa r d d i f f u s i o n o f w a t e r va po r and t h e
u p ta k e o f c ar bon d i o x i d e
(4,28).
The second i n v o l v e s
lo ca lize d d is ru p ­
t i o n o f c h l o r o p l a s t s , w h i c h woul d e f f e c t i v e l y a l t e r t h e p h o t o c h e m i c a l
m a c h i n e r y o f a l e a f such t h a t t h e H i l l
re a ction,
photophosphorylation,
and t h e r e d u c t i v e p e n t o s e p ho sp ha te c y c l e a r e i n h i b i t e d
the h i g h l y s i g n i f i c a n t c o r r e l a t i o n s
(4).
Based on
between n e t p h o t o s y n t h e s i s ,
RWC,
64
c o n d u c t a n c e , and c h l o r o p h y l l
b ot h r esponses a r e
sis
content w ith
involved.
L aw l o r
re spect t o s t r i p e
form ation,
(19) d e t e r m i n e d t h a t p h o t o s y n t h e ­
i n wheat may be c o m p l e t e l y s u pp r e s s e d a t a w a t e r p o t e n t i a l
-.18 b a r s .
Th us,
l o c a l i z e d w a t e r s t r e s s due t o b l o c k a g e o f
o f only
la te r a l water
t r a n s p o r t o u t o f c o l o n i z e d v e s s e l s c o u l d be r e s p o n s i b l e f o r t h e d rop
in p h o t o s y n t h e t i c a c t i v i t y .
The l i n e a r r e l a t i o n s h i p s between symptom s e v e r i t y and t he f o u r
physiolo g ica l
parameters p ro v id e d
between s u c c e s s i v e
i n d i r e c t e v i d e n c e t h a t an i n t e r a c t i o n
le a ve s was n o t a s i g n i f i c a n t h o s t r e s p o n s e .
p e n u l t i m a t e and f l a g
le a ve s o f
15 p r i m a r y t i l l e r s
c u l t i v a r M a r i a s were examined f o r d e c l i n e
in r e l a t i o n
t o symptom s e v e r i t y .
Both
o f the s u s c e p tib le
in n e t p h o t o s y n t h e s i s and RWC
l e av es responded as p r e d i c t e d
from the r e l a t i o n s h i p s
shown i n F i g u r e
in dep e nd e ntly o f o t h e r
l eaves on a d i s e a s e d t i l l e r .
o f water
n ot y e t
in t h e culm was e v i d e n t l y n o t
i nvaded o r
The
I I -3.
Th us , each
im pa ire d ,
in t h e e a r l y s t a g e s o f
l e a f responded
V e r t i c a l movement
since w i l t i n g
i n l eaves
i n f e c t i o n was n o t o b s e r v e d .
Such a r es pon se r u l e s o u t h i g h m o l e c u l a r w e i g h t s u b s t a n c e s as c o n t r i b u ­
t o r y t o w ar d w a t e r i mb a la nc e i n t h i s
h o s t - v a s c u l a r pat hogen
s i n c e t h e e x t r e m e l y s h o r t v e s s e l e le me nt s
in t h e nodal
unpub I , o b s e r v . ) wo u ld g r e a t l y f a c i l i t a t e
a w iltin g
t h a t o b s e rv e d i n elm t r e e s t r e a t e d w i t h
produced by C e r a t o c y s t i s u Imi
The c o l l e c t i v e
in te ra ctio n ,
regio ns
r es pon se s i m i l a r t o
the high m o le c u la r w e ig ht t o x i n
(3 0).
d is ru p tiv e e ffe cts
(Morton,
o f C e p h a l o s p o r i urn s t r i p e
65
d ev e lo p me nt on t h e p h y s i o l o g i c a l
ra te ly re fle cte d
in t h e
t h a t the disease
i n d e x r a t i n g system i s a v a l i d
disease s e v e r i t y .
le a f's
p r o c e s s e s o f a wheat
l e a f were a c c u ­
symptom s e v e r i t y s c o r e .
This
indicates
in d ic a to r o f visual
In co mp ar i ng n e t p h o t o s y n t h e s i s w i t h symptom d eve ­
lopment c o n c u r r e n t l y
in th r e e c u l t i v a r s ,
the c lo s e r e l a t i o n s h i p th a t
e x i s t e d between t h e p h y s i o l o g i c a l measurements and v i s u a l
scoring of
symptom e x p r e s s i o n makes e i t h e r method s u i t a b l e f o r d e l i n e a t i n g c u l t i v a r
d iffe re n c e s
in d isease s e v e r i t y .
t o C e p h a l o s p o r i urn s t r i p e ,
to
involved
Rather, a d i r e c t v is u a l
h ea d i ng s u f f i c e s
resistance
t h e r e f o r e , does n o t r e q u i r e t h e more complex
and t i m e - c o n s u m i n g p r o c e d u r e s
p onses,
E v a l u a t i o n o f germplasm f o r
i n me a su r in g p h y s i o l o g i c a l
res­
s c o r i n g o f symptom s e v e r i t y a f t e r
to accurately r e f le c t
t h e h o s t ' s p h e n o t y p i c response
in fe c tio n .
M o n i t o r i n g d i s e a s e d ev el opment a t s e v e r a l
s t a g e s o f h o s t d e v e lo p me nt was u s e f u l
e f f e c t s o f pathogenesis.
e ffe cts
on l e a f e x p a n s i o n ,
elongation.
in p a r t i t i o n i n g
the p h y s i o l o g i c a l
y e t caused a s e v er e r e d u c t i o n
Both would have responded s i m i l a r l y
r esponses e l i c i t e d
ontogenetic
I n v a s i o n by £ . gramineum p r odu ce d no v i s i b l e
(11) o r g e n e r a l i z e d w a t e r s t r e s s
in
in terno d e
i f hormone imbal ances
( 4 , 1 1 ) were i n v o l v e d .
The d i f f e r e n t i a l
i n t h e stem and l e av es may be a t t r i b u t e d
t e m p o r a l and s p a c i a I
t o the
r e l a t i o n s h i p between pathogen movement and h o s t
x y Iem m a t u r a t i o n g r a d i e n t s
node j u n c t i o n
sequential
(Chapter l ) .
re ac he s m a t u r i t y ,
the
By t h e t i m e x y Iem i n a l e a f -
l e a f has c o m p l e t e l y e x p a n d e d .
Thus,
66
t h e p at hogen i s e f f e c t i v e l y
p r e v e n t e d f r o m i n v a d i n g t he
has a t t a i n e d maximum s i z e .
I f the e f f e c t s
host w a te r balance r e s u l t
movement,
then th e re
t h e pat hogen
from lo c a l i z e d
le a f.
la te ra l
water stress-induced
Undoubtedly,
re s tric tio n
in t h a t
t o be imposed by
its
period o f e lo n g a tio n ,
i n t e r n o d e may be caused by c u m u l a t i v e
l o c a l i z e d e f f e c t s a round c o l o n i z e d v a s c u l a r b un d le s
source-sink
re la tio n sh ip s
i n v o l v i n g t he p a r t i t i o n i n g o f
p h o t oa s s i m i t a t e s between l ea ves and i n t e r n o d e s d u r i n g t h e i r
p e r i o d s o f d om in an t g r o w t h a l s o p l a y a r o l e
between p l a n t organs
o f water
Pathogen i n v a s i o n o f stem v a s c u l a r
b un d le s above a node, h ow ev e r, o c c u r s d u r i n g
so t h a t reduced g r o w t h
it
o f pat hogen c o l o n i z a t i o n on
i s no o p p o r t u n i t y f o r w a t e r s t r e s s
in a d e v e l o p i n g
le a f before
(23).
Ip f a c t ,
this
respective
in the d i f f e r e n t i a l
response
co m p etitio n f o r photosynthate
may be more r e s p o n s i b l e f o r t h e s e v e r e r e d u c t i o n
in e lo n g a t i o n o f the
uppermost I n t e r n q d e and p e d u n c l e t h an pat hog en c o l o n i z a t i o n o f t h e stem.
For t h e f i r s t
15 days a f t e r a n t h e s i s ,
t o 50% o f a s s i m i l a t e s
so r a p i d l y
fla g
le a f
from the f l a g
the top
le a f
i n t e r n o d e competes f o r up
(7)•
in a s u s c e p t i b l e c u l t i v a r t h a t a f t e r
is s t i l l
F o lia r s trip in g
increases
15 d a y s , o n l y
10% o f t h e
a c t i v e l y p h o to s y n th e s i z i n g , thereby s e v e r e ly reducing
t h e s u p p l y o f p h o t o s y n t h a t e t o b o t h t h e t o p i n t e r n o d e and t o t h e ped­
uncle.
The mod er at e re sp on s e by C r e s t LRC 40 may be due in p a r t t o
co lonization
o f fewer bundles
t o more l e a f a re a a c t i v e l y
weeks a f t e r h e a d i n g .
in t h e
internodal
r e g i o n s and a l s o in p a r t
producing p ho to s y n th a te d u r in g
the f i r s t
few
67
The e f f e c t o f C e p h a l o s p o r i u m s t r i p e
o f head d ev el op men t p i n p o i n t e d t h e p e r i o d
severely a ffe c te d y ie ld
p o te n tia l.
i n f e c t i o n on d i f f e r e n t s t a g e s
i n which, p a t h o g e n e s i s most
F u l l e x p r e s s i o n o f s p i k e l e t number
p e r head i s c o n t i n g e n t upon t h e d u r a t i o n o f p h o t o s y n t h e t i c area oh
l o we r
l ea ves
(.10).
The i n a b i l i t y
nent su pported v is u a l
and d i s t r i b u t i o n was
o f d i s e a s e t o a l t e r t h i s y i e l d compo­
and h i s t o l o g i c a l
e v i d e n c e t h a t pat hog en movement
lin k e d t o host m a t u r a t io n g r a d ie n t s
(Chapter I ) .
S o u r c e - s i n k r e l a t i o n s h i p s between c o n s e c u t i v e l y e x p a n d i n g
t h e d i f f e r e n t i a t i n g head a p p a r e n t l y k e p t apace w i t h s t r i p e
l eaves and
form ation.
Complete g e n e t i c e x p r e s s i o n o f g r a i n number p e r head i s dependent upon
successful
s e lf-fe rtiliz a tio n
o f each m a t u r e f l o r e t .
S i nc e f l o r e t deve­
lopment p r o g r e s s e s f r o m t h e m i d d l e o f t h e head t o w a r d each end ( 3 ) , t h e
l o c a t i o n o f any a b o r t i v e f l o r e t s
i s an i n d i c a t o r o f t h e s t a g e d u r i n g
f l o w e r i n g a t wh i ch d e t r i m e n t a l e f f e c t s
Re d u c t i o n
o f pathogenesis are f e l t
t he most
i n seed number o c c u r r e d o n l y a t b o t h ends o f t h e h eads,
in d i­
c a t i n g t h a t w a t e r s t r e s s caused by d i s e a s e was i n t r o d u c e d o n l y d u r i n g
late anthesis.
Substantial
r e d u c t i o n o f c a r b o h y d r a t e s t o r a g e in t he
g r a i n s o f each d i s e a s e d head s u g g es t ed t h a t t h e most s e v e r e e f f e c t s
of
p a t h o g e n e s i s a r e e x p r es s ed between f l o w e r i n g and se ne sc e nc e , when g r a i n
fillin g
takes p la c e .
that y ie ld
d e ve l o pm en t
This v e r i f i e d e a r l i e r re p o r ts which concluded
reduction
resulted
f ro m p a t h o l o g i c a l
(15,25).
The f l a g
le a f,
resp on se s
late
in host
p e d u n c l e , and head c o n t r i b u t e up t o
80.% t o c a r b o h y d r a t e p r o d u c t i o n f o r g r a i n f i l l i n g
( 1 3 , 2 9 ) , most o f w h i c h
68
accumulates w i t h i n
s u rp ris in g ,
the f i r s t
therefore,
t a n t w i t h an i n c r e a s e
f o u r weeks a f t e r a n t h e s i s
It
is not
t h a t t h e d e c r e a s e in n e t p h o t o s y n t h e s i s c o nco mi ­
in f o l i a r s t r i p i n g o f diseased f l a g
l a r g e l y re s p o n s ib le f o r the d ra m a tic d e c l i n e
o f two s u s c e p t i b l e c u l t i v a r s .
In a d d i t i o n ,
t h e head was u n d o u b t e d l y a f f e c t e d a l o n g w i t h
s is ,
(26).
le a ve s was
i n t ho usan d k e r n e l w e i g h t
transport o f assim ilates to
in h ib itio n
o f photosynthe­
b ot h f r o m t h e s t a n d p o i n t o f reduced c a r b o h y d r a t e s y n t h e s i s and a l s o
because o f e x t e n s i v e phloem d i s r u p t i o n
i n c o l o n i z e d v a s c u l a r bun dl es
(Chapter I ) .
Seed w e i g h t r e d u c t i o n
Consequently,
when s c r e e n i n g
i s v i s u a l l y m a n i f e s t e d as reduced seed s i z e .
seed s i z e may be a u s e f u l
se le ction t o o l,
p a rtic u la rly
large bulk o r re c u rre n t s e le c tio n p o p u la tio n s .
on t h e b a s i s o f seed s i z e c o u l d be an e f f e c t i v e ,
i d e n t i f y i n g and e v a l u a t i n g
wheat germplasm.
S electing
y e t s i m p l e , means o f
r e s i s t a n c e t o Ce p ha l so po r iu m s t r i p e
in w i n t e r
LITERATURE CITED
70
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A r n o n , D . 1 . 19 ^ 9 . ' Copper enzymes i n i s o l a t e d c h l o r o p l a s t s . P o l y p h e n o l o x i d a s e in Beta v u l g a r i s . P l a n t P h y s i o l . 2 4 : 1 - 1 5 ,
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A s h e r , M . J . C . 1972., E f f e c t o f O ph i o b o l u s g r a m i n i s i n f e c t i o n on
g r o w t h o f whe at and b a r l e y . Ann. A p p l . B i o l . 7 0 : 2 1 5 - 2 2 3 .
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Bingham, J . 1966. V a r i e t a l r espons e i n wheat t o w a t e r s u p p l y i n t h e
f i e l d , and male s t e r i l i t y caused by a p e r i o d o f d r o u g h t in a
g l a s s h o u s e e x p e r i m e n t . A nn . A pp I . B i o l . 5 7 : 3 6 5 - 3 7 7 .
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Boy er , J . S . 1973. Response o f m e t a b o l i s m t o low w a t e r p o t e n t i a l s
p l a n t s . P h y t o p a t h o l o g y 63= 46 6- 47 2.
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Brueh I , G.W. 1956. P r e m a t u r i t y b l i g h t phase o f C e p h a l o s p o r i urn
s t r i p e d i s e a s e o f w h e a t . P l a n t D i s . Rep. 4 0 : 2 3 7 - 2 4 1 .
6.
B r u e h I , G.W. 1957. Cephal o s p o r i urn s t r i p e d i s e a s e o f w h e a t . P h y t o ­
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C a r r , D . J . and I . F . Ward I aw. 1965. The s u p p l y o f p h o t o s y n t h e t i c
a s s i m i l a t e t o t h e g r a i n f r o m t h e f l a g l e a f and e a r o f w h e a t .
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C a t s k y , J . I 96 0 . D e t e r m i n a t i o n o f w a t e r d e f i c i t
from l e a f b la de s , B i o l . P l a n t . 2 :7 6 -7 8 .
9.
C l e g g , M . D . , C. Y. S u l l i v a n , and J . D. East i n . 1978. A s e n s i t i v e
t e c h n i q u e f o r t h e r a p i d measurement o f c ar bon d i o x i d e c o n ce n ­
t r a t i o n s . P la nt P h y s io l. 62:924-926.
in
in d i s c s c u t o u t
10.
D a v i d s on , J . L. 1965. Some e f f e c t s o f l e a f a re a c o n t r o l
o f w h e a t . A u s t . J . A g r i c . Res. 1 6: 7 21 -7 31•
on t h e y i e l d
11.
Dimond, A . E. 1970. B i o p h y s i c s and b i o c h e m i s t r y o f t h e v a s c u l a r w i l t
syndrome. Ann. Rev. P h y t o p a t h . 8 : 3 0 1 - 3 2 2 .
12.
Duniway, J. M. 1976. Wat er s t r e s s a n d . I m b a l a n c e . In " P h y s i o l o g i c a l
P l a n t P a t h o l o g y " (R. H e i t e f u s s and P.H. W i l l i a m s , e d s . ) V o l . 4.
p p . 4 3 0 -4 4 9. S p r i n g e r - V e r l a g . B e r l i n , H e i d e l b e r g , New Yor k.
13.
Evans-, L . T . 1975. The p h y s i o l o g i c a l b a s i s o f c r o p y i e l d . In "Crop
P h y s I o l o g y - - S o m e Case H i s t o r i e s " ( L . T . E vans, e d . ) pp, 327 -3 55.
Cambridge U n i v e r s i t y P r e s s .
71
14.
G a t e s , C.T. 1968. Wat er d e f i c i t s and g r o wt h o f her ba ce ou s p l a n t s .
In " W a t e r D e f i c i t s and P l a n t G r o w t h " ( I . I . K o z l o w s k i , e d . )
V o l . 2. p p . 13 5 - 1 9 0 . Academic P r e s s . New Yor k and London.
15-
J o h n s t o n , R.H. and D.E. Math r e . 1972. E f f e c t o f i n f e c t i o n by Cepha l o s p o r i u m gramlneum on w i n t e r w h e a t . Crop S c i . 1 2 : 8 1 7- 8 1 9.
16.
Kemp, C. D. I 9 6 0 . Methods o f e s t i m a t i n g t h e l e a f a r e a s o f g ra s se s
f r o m l i n e a r measurement s. Ann. B o t . N.S. 2 4 : 4 9 1 - 4 9 9 .
17•
Kanemasu , E . T . , G.W. T h u r t e l I , and C. B. Ta nn e r. 1969. D esi gn,
c a l i b r a t i o n , and f i e l d use o f a st omat a I d i f f u s i o n p o r o m e t e r .
■P l a n t P h y s i o l . 4 4 : 8 8 1 - 8 8 5 .
18.
K o b a y a s h i , K. and T. LU. 1979• P h y t o t o x i c i t y and a n t i m i c r o b i a l
a c t i v i t y o f G r a m i n i n A, p roduced by C e ph al o s po r i um gramineum,
t h e c a u s a l a g e n t o f Cephal o s p o r i u m s t r i p e d i s e a s e o f w h e a t .
P h y s i o l. P la n t Path. 14:129-133,
19-
L a w l o r , D.W. 1976. Wa ter s t r e s s in du ce d changes i n p h o t o s y n t h e s i s ,
p h o t o r e s p i r a t i o n , r e s p i r a t i o n , and CO2 c o mp en s at i on c o n c e n t r a ­
t i o n o f w h e a t . P h o t o s y n t h e t i c a 1 0 :3 72 - 38 7-
20.
Math r e , D.E. and R.H. J o h n s t o n . 1975. C e p h a l o s p o r i urn s t r i p e o f
w i n t e r w h e a t : P ro ced ur es f o r d e t e r m i n i n g h o s t r e s p o n s e . Crop
S c i . 15:591-594.
21.
Math r e , D. E . , R.H. J o h n s t o n , and C. F. McGui re. 1977. C e p h a l o s p o r i urn
s t r i p e o f w i n t e r w h e a t : Pat hogen v i r u l e n c e , s o u r c e s o f r e s i s ­
t a n c e , and e f f e c t o f g r a i n q u a l i t y . P h y t o p a t h o l o g y 67 : 11 4 2 - 1 148
22.
P a p e n d i c k , R . I . and R . J . Cook, 1974. P l a n t w a t e r s t r e s s and d e v e l o p
ment o f F u s a r i urn f o o t r o t in wheat s u b j e c t e d t o d i f f e r e n t c u l ­
t u r a l p r a c t i c e s . Phytopathology 64:358-363•
23.
P a t r i c k , J.W. 1972. D i s t r i b u t i o n o f a s s i m i l a t e d u r i n g stem e l o n g a ­
t i o n in wheat. A u s t . J . B i o l . S c i . 25:455-467.
24.
P o o l , R . A . F . and E . L . Sharp. 1969. P o s s i b l e a s s o c i a t i o n o f a p o l y ­
s a c c h a r i d e and an a n t i b i o t i c w i t h t h e d i s e a s e c y c l e o f Cephalos p o r i u m g r ami n eu m. P h y t o p a t h o l o g y 5 9 : 1 7 6 3 - 1 7 6 4 .
25.
R i c h a r d s o n , M . J. and W.J. Re n n i e . 1970. An e s t i m a t e o f t h e l os s o f .
y i e l d caused by C e p h a l o s p o r i urn gramineum i n w h e a t . P I . P a t h .
19:138-140.
72
26.
Shen, K .M. , Y. K. Shen5 and H . C. Y i n . 1959. D i s t r i b u t i o n and
a c c u m u l a t i o n o f a s s i m i l a t e s i n wheat d u r i n g r i p e n i n g . S c i . Res.
(Peking) 3:437-440.
27.
S p a l d i n g , D . H . , G.W. Brueh I , and R. J . F o s t e r . 1961. P o s s i b l e r o l e
o f p e c t i n o l y t I c enzymes and p o l y s a c c h a r i d e in p a t h o g e n e s i s by
C e ph a l o s p o r i u m gramineum i n w h e a t . P h y t o p a t h o l o g y 5 3 : 2 2 7 - 2 3 5 .
28.
S l a y t e r , R . 0. 1967. P l a n t - W a t e r R e l a t i o n s h i p s .
Yor k and London.
29.
T h o r n e , G. N, 1965. P h o t o s y n t h e s i s o f e a r s and f l a g
and b a r l e y . Ann. B o t . N. S. 2 9 : 3 1 7 - 3 2 9 .
30.
Van Al f e n , N.K. and N,C. T u r n e r . 1975. I n f l u e n c e o f a C e r a t o c y s t i s
UImi t o x i n on w a t e r r e l a t i o n s o f elm (UTmus a m e r i c a n a ) . P l a n t
P h y s io l. 55:312-316.
31.
Weis e , M.V. 1972. C o l o n i z a t i o n o f wheat s e e d l i n g s by C e p h a l o s p o r i urn
gramineum in r e l a t i o n t o symptom d e v e l o p m e n t . P h y t o p a t h o l o g y
6 2 : 1013- 1018 .
>
Academic P re s s . New
l e a v e s o f wheat
CHAPTER I I I
IDENTIFICATION OF RESISTANCE TO CEPHALOSPORIUM STRIPE IN
SELECTED WINTER WHEAT (TRITI CUM AESTI VUM L . )
CUL T I VARS
74
INTRODUCTION
One o f t h e most p o t e n t i a l l y damaging pathogens- o f w i n t e r wheat
(T r i t ?cum a e s t i vum L . ) , e s p e c i a l l y
in r e g i o n s p r a c t i c i n g m o n o c u l t u r e ,
C e p ha l o s p o r i u m gramineum, t h e c a us a l a g e n t o f Cephal o s p o r i urn s t r i p e .
p ote ntia l
b lig hte d
greater
f o r economi c d e s t r u c t i o n
is r e f l e c t e d
Its
in s t u n t e d p l a n t s ,
l e a v es and h e a ds , and reduced y i e l d s , w h i c h can reach 50% o r
(10,18). £.
gramineum i s a f a c u l t a t i v e s o i l - b o r n e p a r a s i t e ,
w h i c h o v e r w i n t e r s as a s a p r o p h y t e w i t h i n
over from the p re v io u s crop
the s o i l
(3,4,2 2 ,2 3 ).
infected plant
Here i t
resid ues c a r r i e d
can r emai n v i a b l e
in
f o r up t o t wo y e a r s by p r o d u c i n g a b r o a d - s p e c t r u m a n t i f u n g a l
a n tib io tic
(4).
Current c o n tro l
p r o c e d u r e s have been o r i e n t e d t owar d
crop r o t a t i o n ,
refuse d e s tru c tio n ,
t o r educe s o i l
inoculum le v e ls
and d e e p - p l o w i n g , a l l
(3,11,17,24).
mizes r o o t g r o w t h and hence i n f e c t i o n s i t e s
a l s o has been recommended ( 1 1 , 1 7 ) .
al ways d e p e n d a b l e , h ow ev e r,
d itio n s
is
f o r successful
fa c to rs w ith
o f which serve
Late p l a n t i n g , wh ich m i n i ­
a v a i l a b l e t o t h e p a th og e n,
These c u l t u r a l
p r a c t i c e s a r e n ot
s i n c e t h e y r e l y upon f a v o r a b l e c l i m a t i c c o n ­
i m p l e m e n t a t i o n and a r e
respect to a lte r n a te c ro p s .
i n f l u e n c e d by economic
The most e f f e c t i v e and d e s i ­
r a b l e c o n t r o l method wo u ld be p l a n t i n g o f r e s i s t a n t v a r i e t i e s .
D iffe re n tia l
Japan
(.24).
m aterials
h o s t s u s c e p t i b i l i t y was f i r s t
However,
planted
not ed by w o r k e r s
in
t h e i r o b s e r v a t i o n s were based on w i n t e r wheat
in n a t u r a l l y
l e nc e l e v e l s were unknown.
i n f e s t e d f i e l d s where i n o c u l u m and v i r u ­
In t h e U n i t e d S t a t e s , B r u e h l
(3)
id e n tifie d
75
f o u r v a r i e t i e s as r e s i s t a n t
inoculations o f a liq u id
t o C e p h a l o s p o r i um s t r i p e u s i n g hypo der mi c
coni d i a l
suspension
cr own , b u t t h e y p r o ve d t o be s u s c e p t i b l e
o f natural
U n til
e spe cia lly
in fe c tio n
in f e s t e d w it h jX
over
(12).
t o assess
in the f i e l d .
f o r a d d i t i o n o f a d e fin e d q u a n t i t y o f oat kernels
gramineum i s o l a t e s o f known v i r u l e n c e w i t h t h e seed a t
M a th r e and J o h n s t o n
(14) used t h i s
1000 h a r d red w i n t e r wheat c u l t i v a r s
g r o w i n g areas o f t h e w o r l d .
high or
und er c o n d i t i o n s
inoculum, g e n o ty p ic d i f f e r e n c e s ,
l a r g e p o p u l a t i o n s , were d i f f i c u l t
This tec h n iq ue c a l l e d
p la ntin g
in t h e f i e l d
(1 9).
t h e d e v e lo p me nt o f o a t k e r n e l
in
i n t o wheat culms above t h e
f r o m t h e m a j o r w i n t e r wheat
A l t h o u g h most o f t h e s e c u l t i v a r s were o f
interm ediate s u s c e p t i b i l i t y ,
t a n c e were d i s c o v e r e d .
i n o c ul u m t o screen
some p r o m i s i n g s o u r c e s o f r e s i s ­
None o f t h e c u l t i v a r s
tested,
t h o u g h , were
immune t o t h e d i s e a s e .
The m a j o r c r i t e r i o n
fo r evaluating s u s c e p t ib ilit y
s t r i p e has been r e d u c t i o n
in y i e l d
p o te n tia l
have i n c l u d e d g e n e r a l v i s u a l d i s e a s e r e a d i n g s
e arly
t o C e p h a l o s p o r i um
(3,10,14,24).
Other t e s t s
( 3 , 2 4 ) , disease readings
i n h o s t d e v e lo p me nt me a su r in g the. p r o p o r t i o n o f d i s e a s e d t i l l e r s '
( 1 2 , 1 4 ) , and r e a d i n g s
late
w h i t e heads
These p a r a m e t e r s p r o v i d e d
(12,14).
d iffe re n tia te c u ltiv a rs
reme s u s c e p t i b i l i t y
c rite ria
d id not
I n f o r m a t io n necessary t o
a c r o s s a g raded s e r i e s w h ic h e x t en de d f ro m e x t ­
t o high
reveal
in h o s t d ev e lo pmen t me asur i ng t h e number o f
resistance
(3,12,14,24).
However, t h e se
t h e s p e c i f i c p h e n o t y p i c r e s p o n s e ( s ) e x p r e s s e d by
76
each g e n o t y p e w h i c h ,
cation o f c u I t iv a r s
if
r e c o g n i z e d , m i g h t a l l o w more d i s c r e t e c l a s s ! f i
in to su scep tib le ,
i n t e r m e d i a t e , and r e s i s t a n t c a t e
gories.
The pur po se o f t h i s w o r k was t o i d e n t i f y
a c t i o n o f Cephal o s p o r i urn s t r i p e
wheat c u l t i v a r s .
in r e l a t i o n
t he t y pe s and c a u s a t i v e
resistance e l i c i t e d
by s e l e c t e d w i n t e r
P h e n o t y p i c e x p r e s s i o n s o f r e s i s t a n c e were e v a l u a t e d
t o im p o rta nt f a c e t s o f the h ost-pathogen
t h e i r v a l u e as s e l e c t i o n t o o l s
i n t e r a c t i o n and
i n a germplasm d ev e lo p me nt pro gr am.
77
MATERIALS AND METHODS
The seven h a r d red w i n t e r wheat c u l t W a r s chosen f o r t h i s s t u d y
varied
in t h e i r s u s c e p t i b i l i t y
a gr o n o m i c c h a r a c t e r i s t i c s .
27595) and L anc er
(C .l.
t o C e p h a l os p or i u m s t r i p e and i n t h e i r
Based on y i e l d
r e d u c t io n s , Marias
23547) were r a t e d as h i g h l y s u s c e p t i b l e , W i n a l t a
13670) and C . l . 07638 were r a t e d as i n t e r m e d i a t e ,
(C .l.
Component
(LRC) 40 (MT 7579)
re sista n t,
and P . l .
Crest
Unl es s o t h e r w i s e s p e c i f i e d , a l l
re sista nt
E xp e r i m e n t S t a t i o n nea r Bozeman, Montana.
were p l a n t e d
in e a r l y
September o f
(1 4).
t e s t s were c o n d uc t ed a t t h e Montana
A g ricu ltu ra l
The c u l t i v a r s
1977 and 1978 a t a s e e d i n g r a t e o f
Each row was spaced 3 0. 5 cm a p a r t .
p l o t experim ental design w ith
L i n e Row
and P . l . 094424 were r a t e d as m o d e r a t e l y
278212 was r a t e d as h i g h l y
200 seeds per 3.1 m row.
(C .l.
f o u r r e p l i c a t i o n s was u sed ,
t r e a t m e n t s c o m p r i s e d t h e main p l o t s
and t h e c u l t i v a r s
A s p lit
in which
made up t h e s u b ­
p lo ts.
I no c ul u m c o n s i s t e d o f e i t h e r
co nidia l
suspensio n.
in f e s t e d oat ke rn els or a l i q u i d
The f o r m e r was p r e p a r e d by i n o c u l a t i n g a u t o c l a v e d
oat kernels w ith a concentrated c o n id ia l
s u s p e ns i o n o f £ . grami neum,
i n c u b a t i n g them f o r 2~3 weeks, and t he n a l l o w i n g
The o a t k e r n e l s were added s i m u l t a n e o u s l y w i t h
p la ntin g .
The l i q u i d
them t o a i r - d r y
(12).
t he seed a t t h e t i m e o f
i n o c ul u m was p r e p a r e d by g r o wi n g t h e f un g us
shake c u l t u r e composed o f m o d i f i e d E c k e r t ' s medium ( 2 0 ) .
in
One' l i t e r o f
IO^ c o n i d i a / m l was added t o each s i d e o f a 3-1 m row by d i r e c t l y
pourin g
78
the
i n o c ul u m i n t o a s o i l
sharp k n i f e .
T h u s , t wo l i t e r s
P opulations o f £.
tio n
s lic e a fte r cu ttin g
of
gramineum i n f i e l d
from the rh iz o s p h e re o f M a ria s ,
s o i l were q u a n t i f i e d by d i l u ­
(21).
Blendor w i t h
d ilu te d
to
Soil
samples were
C r e s t LRC hO, and P . I . 278212.
S i x r e p l i c a t e s were o b t a i n e d f r o m s i x d i f f e r e n t
mized b l o c k d e s i g n .
o f the roots w ith a
i n o c ul u m were added t o each row.
p l a t i n g on s e l e c t i v e gr een wheat a g a r
co lle cte d
a ll
rows p l a n t e d
Twenty gram subsamples were a g i t a t e d
in a rando­
in a Waring
2Q0 mis o f d i s t i l l e d w a t e r f o r 20 seconds and s u b s e q u e n t l y
10~3 and 10~4.
Colony c o u n t s were read a f t e r 5 days i n c u b a ­
t i o n a t 22°C.
P h e n o t y p i c e x p r e s s i o n o f r e s i s t a n c e t o C e p h a l o s p o r i urn s t r i p e was
scored a c c ordin g t o
(I)
t h e number o f t i l l e r s
symptoms 30 days a f t e r h e a d i n g ,
(2)
p er row e x h i b i t i n g
t h e number o f t i l l e r s
e x h i b i t i n g d i s e a s e symptoms 30 days a f t e r h e a d i n g , and
s e v e r i t y o f d i s e a s e symptoms a t p e r i o d i c
heading.
in te rva ls
per p l a n t
(3) t h e r a t e and
b e f o r e and a f t e r
Symptom s e v e r i t y Was r a t e d on a s c a l e o f one t o e l e v e n , w i t h
one d e n o t i n g a s i n g l e s t r i p e on a l e a f and e l e v e n
ch lo rosis
(Chapter I ) .
To i d e n t i f y
i n d i c a t i n g c o m p l et e
r e sp on se s w i t h i n
i n o c u l a t e d rows we re t h i n n e d m a n u a l l y
e ffe cts
disease
in d ivid u a l
pla nts,
i n t h e s p r i n g so t h a t m i t i g a t i n g
o f d i f f e r e n t s e e d i n g r a t e s were p r e v e n t e d :
Root g r o w t h o f M a r i a s ,
Cr e s t LRC 40, and P . I . 278212 was measured by
displacement
i n w a t e r and by d r y w e i g h t .
S i n g l e seeds o f each c u l t i v a r
were p l a n t e d
in a s a n d y - l o a m s o i l c o n t a i n e d w i t h i n
P olyvinyl c h lo rid e
79
p i p e s e c t i o n s 3 0. 5 cm lo ng and 3 • 8 cm i n d i a m e t e r .
f i v e p l a n t s each were a r r a n g e d
p i p e s e c t i o n s were e n c l o s e d
Four r e p l i c a t i o n s o f
i n a randomized b l o c k d e s i g n .
in a r e c t a n g u l a r - s h a p e d e n c l o s u r e ,
The 60
the
f l o o r s and s i d e s o f w h i c h c o n s i s t e d o f 2 . 5 cm w i d e s t y r a f o a m t o remove
temperature e f f e c t s
a ro un d t h e edges.
The p l a n t s were grown f o r 60 days
i n an e n v i r o n m e n t a l g r o w t h chamber a t 5 /2 0 ^ 0
photoperiod
w hite
( d a r k / l i g h t ) w i t h a 12 h o u r
( 3 . 8 X IO^ e r g s / c m ^ / s e c combined i n c a n d e s c e n t and c o o l ,
fluorescent
lig h t).
A f t e r two m o n t h s , t h e s o i l
and r o o t s were
removed f r o m t h e p i p e s e c t i o n s by a p p l y i n g g e n t l e p r e s s u r e t o one end.
Much o f t h e s o i l was f i r s t
removed by c a r e f u l w a sh ing w i t h w a t e r , a f t e r
w h i c h t h e r o o t s were soaked in 0.05% sodi um h exa met aphosphat e f o r f i v e
d ay s .
surface
C al ci um c h l o r i d e was t he n added u n t i l
(H. F e r g u s o n , p e r s o n a l comm.).
a g a i n by a g i t a t i o n
the ro o ts
flo ate d
t o t he
The r o o t s were c o l l e c t e d , washed
i n w a t e r , and t h en p l a c e d
in a w a t e r - f i l l e d
separa­
t o r y f u n n e l w h i c h was c o n n ec t ed t o a 10 ml p i p e t t e by r u b b e r t u b i n g .
This allo w e d the d e t e r m i n a t io n o f r o o t displacement
w e i g h t s were o b t a i n e d a f t e r
70°C f o r two weeks.
in c u b a tin g the ro o ts
in w a t e r .
Dry
in a d r y i n g oven a t
80
RESULTS
• Phenotypic e x p re s s io n o f r e s i s t a n c e .
sporium s t r i p e
The m a n i f e s t a t i o n s o f Ce pha lo -
r e s i s t a n c e were examined on a p o p u l a t i o n b a s i s
e x c l u s i o n between p l a n t s ) as w e l l as on an i n d i v i d u a l
gen r e s t r i c t i o n w i t h i n
p la n ts).
demonstrated a d i f f e r e n t i a l
w ith in
i n o c u l a t e d rows
(Table
I I I - 1) .
in t h i s
(patho­
study,
in cid en ce o f diseased t i l l e r s
A l t h o u g h an a l m o s t t w o - f o l d d i f - .
ference
in t h e number o f
between
1977 and 1978, t h e c o m p a r a t i v e d i f f e r e n c e s between c u l t i v a r s
r emai ned t h e same.
infecte d
p la n t basis
The c u l t i v a r s examined
r esponse t o t h e
(pathogen
tille rs
was obs er ve d f o r each c u l t i v a r
M a r i a s and Lancer were c l a s s i f i e d as s u s c e p t i b l e .
C r e s t LRC hO and W i n a l t a were i n t e r m e d i a t e , and C. I . 0 7638, P . I . O S h h lb ,
and P . I . 278212 were r e s i s t a n t b o t h y e a r s .
Thus, environ m e n tal e f f e c t s
on i n f e c t i o n between p l a n t s d i d n o t o b s c u r e
in h e re n t g e n e t i c d i f f e r e n c e s
between c u l t i v a r s .
F i v e c u l t i v a r s were employed t o examine r esponses w i t h i n
i n f e c t i o n by
for
g r a m ! neum.
t he i n c i d e n c e o f
T h i r t y p l a n t s o f each c u l t i v a r were r a t e d
i n f e c t i o n among t i l l e r s
o f in d ivid ua l
p l a n t s . Crest
LRC 40 was t he o n l y c u l t i v a r w h i c h possessed t h e c a p a b i l i t y
s y s te m !c in v a s io n o f a l l
a ll
o f the c u l t i v a r s ,
spacing e f f e c t s .
plants to
tille rs
w i t h i n each p l a n t
la te developing t i l l e r s
Some o f t h e s e t i l l e r s
(T a bl e
t o pre vent
I I I - 1) .
o c c u r r e d because o f
d i d n o t e x p r e s s d i s e a s e symptoms,
w h i c h c o u l d a c c o u n t f o r much o f t h e v a r i a t i o n among c u l t i v a r s .
the s i g n i f i c a n t
reduction
in d i s e a s e
. In
i n c i d e n c e among t i l l e r s
However,
w ith in
81
TABLE I l l - J . .
D i f f e r e n t i a l r esponses o f s e l e c t e d w i n t e r whe at c u l t i v a r s
t o t h e i n c i d e n c e o f i n f e c t i o n by Cephal o s p o r i urn gramineum
Pathogen E x c l u s i o n
D i seased Ti I l e r s / R c w —/
C u l t i var
1977
Pathogen R e s t r i c t i o n
Diseased T i l l e r s / P l a n t
1978
1978
Ma ri as
42a-/
77a
99a
L anc er
45a
—
—
26b
53b
66b
25b
49b
96a
Crest
LRC kO
Winalta
C. I .
07638
—
15c
P . I . 094424
9c
27c
93a
P . I . 278212
5c
15c
90a
a/
— V al ue s a r e r e p r e s e n t e d as mean p e r c e n t a g e s o f h e a l t h y c o n t r o l s a c r o s s
four re p lic a tio n s .
— For each c o l u m n , v a l u e s w i t h t h e same l e t t e r a r e n o t s i g n i f i c a n t l y
d i f f e r e n t a t P = . 0 5 , a c c o r d i n g t o Duncan's m u l t i p l e range t e s t .
82
p la n t s o f Crest
LRC 40. c a n n o t be a t t r i b u t e d
s i n c e many o f t h e e a r l i e r m a t u r i n g t i l l e r s
to t h i s environmental e f f e c t *
were a l s o d i s e a s e - f r e e .
Three r e p r e s e n t a t i v e c u l t i v a r s were s e l e c t e d t o examine responses
w ith in
p l a n t s which could
symptom e x p r e s s i o n .
le ad t o a r e d u c t i o n
i n t he r a t e and e x t e n t o f
M a r i a s and P . I . 278212 were chosen because t h e y
r e p r e s e n t e d t h e e x tr e me s o f r e s i s t a n c e t o p at hogen e x c l u s i o n between
pla nts.
Crest
reaction to
it
LRC 40 was s e l e c t e d , n o t o n l y because o f
i n f e c t i o n between p l a n t s ,
re s tric ts
a f t e r heading
s trip e
f o r m a t i o n on f l a g
q u a n tify accurately,
d ev el op men t w i t h i n
b u t a l s o because o f e v i d e n c e t h a t
l e a v es d u r i n g t h e f i r s t
month
h o s t re sp on s e were more d i f f i c u l t
symptom s e v e r i t y
(Figure
infected p la n t s .
The r a t e o f s t r i p e f o r m a t i o n was
leaves o f p r i m a r y t i l l e r s
f ro m t h r e e weeks p r i o r t o head in g u n t i l
I I I- 1 ).
The s e v e r i t y
two weeks a f t e r
i n f e c t e d p l a n t s o f each c u l t i v a r one month a f t e r
readings
f o r t h e uppermost f o u r
le aves o f a l l
t i I I e r s w i t h i n each p l a n t were a v e r a g e d , so t h a t a mean s e v e r i t y
was o b t a i n e d f o r each p l a n t
(Table
(Figure
I I 1-2).
ra tin g
Measurement o f h e i g h t
p e r f o r m a n c e in r e l a t i o n t o h e a l t h y c o n t r o l s p r o v i d e d
in d ia tio n s o f d if f e r e n t ia l
c u ltiv a rs
for
The e x t e n t o f symptom d ev el op men t was d e t e r ­
mined by s c o r i n g t h i r t y
r e d u c t i o n and y i e l d
to
v a r i e d a pp ro ache s were t aken t o f o l l o w symptom
m o n i t o r e d by s c o r i n g t h e uppermost f o u r
heading.
interm ediate
(Chapter 2 ).
S i nc e t h e dynamics o f t h i s
heading
its
I I 1-2).
r esponses t o d i s e a s e s e v e r i t y between
83
Figure
M I-1 .
The r a t e o f f o l i a r s t r i p e f o r m a t i o n on t h e upper f o u r
l e av es o f p r i m a r y t i l l e r s f r o m t h r e e w i n t e r wheat c u l t i yaps i n f e c t e d w i t h C e p ha l o s p o r i u m gramineum.
Symptoms
were q u a n t i f i e d u s i n g a s e v e r i t y i n d ex m e a s u r i n g t he
number o f s t r i p e s p e r l e a f . I = one s t r i p e p e r l e a f ,
11 = c o m p l e t e c h l o r o s i s .
Leaves numbered f r o m f l a g l e a f
( L i ) downward t o f o u r t h l e a f ( L 4 ) . A = M a r i a s , B = C r e s t
LRC 40, C = P . l . 278212.
Days before — Headlag — Days after
Figure
I I 1-2.
The d i f f e r e n t i a l r esponses o f t h r e e w i n t e r wheat
c u l t i v a r s t o i n f e c t i o n by Cephal o s p o r i u m gramineum
one month a f t e r h e a d i n g .
The uppermost f o u r l eaves
o f a l l t i l l e r s w i t h i n each o f 30 p l a n t s / c u l t i v a r
were s c o r e d f o r symptom s e v e r i t y .
These r e a d i n g s
were aver ag ed i n t o a mean s e v e r i t y s c o r e f o r each
p la n t.
S e v e r i t y was based on t h e number o f s t r i p e s
p er l e a f .
I = one s t r i p e p e r l e a f , 11 = c o m pl e t e
ch lo ro sis.
A = M a r i a s , B = C r e s t LRC hO, C = P. I .
278212.
30-
I
0
1
I
1
I
3
<
«
5
I
I
I
7
SYMPTOM SEVERITY
I
9
I
I
11
n
85
TABLE I I 1-2.
E f f e c t ' o f i n f e c t i o n by C e p h a i o s p o r ?um
gramineum on h e i g h t and y i e l d o f t h r e e
w i n t e r wheat c u l t i v a r s i n 1978.
P e r c e n t R e d u c t i o n —^
C u ltiva r
Height
Y ield
Ma ri as
3 7 a -/
73a
C r e s t LRC 40
I lb
34b
P . I . 278212
35a
79a
/
— Mean p e r c e n t a g e s w i t h r e s p e c t t o h e a l t h y
c o n t r o l s across f o u r r e p l i c a t i o n s .
Ten
heads f r o m i n f e c t e d main t i l l e r s were
h a r v e s t e d w i t h i n each r e p l i c a t i o n .
L /
— For each c o lu mn , v a l u e s w i t h t h e same
l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t a t
P = . 0 5 , a c c o r d i n g t o Duncan' s m u l t i p l e
range t e s t .
86
A fte r successful
P .l.
i n v a s i o n o f t h e h o s t o c c u r r e d , b o t h M a r i a s and
278212 were e q u a l l y s u s c e p t i b l e t o r a p i d s y s t e m i c movement o f C_.
g r a m m e urn t h r o u g h o u t t h e v a s c u l a r n e t w o r k .
headin g, th e f l a g
le a ve s o f t h e p r i m a r y t i l l e r s
b ot h c u l t i v a r s were n e a r l y b l i g h t e d .
red i n a l l
other t i l l e r s
total
a v er ag e s e v e r i t y
b lig h tin g .
Crest
In M a r i a s , 29 o u t o f t h e 30
The r e m a i n i n g p l a n t was a l m o s t as
ra tin g of
10.
P .l.
278212 d i f ­
f r o m M a r i a s , as 93% o f t h e i n f e c t e d p l a n t s had
r a t i n g s between 9 and 11.
suffered su b sta n tia l
infected plants o f
o f t h e s e p l a n t s , as e v i d e n c e d by t h e e x t e n t o f
h e a v i l y a f f e c t e d , w i t h a mean s e v e r i t y
fered only s l i g h t l y
of
A s i m i l a r temporal p a t t e r n o c c u r­
symptom d e v e l o p m e n t a month a f t e r h e a d i n g .
plants e x h ib ite d
By f o u r t e e n days a f t e r
h e i g h t and y i e l d
Both o f t h es e c u l t i v a r s
reductions.
LRC 4 0, on t h e o t h e r h a n d , l i m i t e d
t h e r a t e o f symptom e x p r e s ­
sio n t o the e x t e n t t h a t o n ly the
l owermost
b lig h te d
Both t h e p e n u l t i m a t e and f l a g
14 days a f t e r h e a d i n g .
a v er ag ed s e v e r i t y s c o r e s o f l e s s t h an 5,
h a l f o f each
of s trip e
in d ica tin g tha t
l e a f expressed f o l i a r c h l o r o s i s .
f o r m a t i o n on t h e f o u r t h
the fo u rth
le aves o f p r i m a r y t i l l e r s
leaves
l e s s t ha n
In te re stin g ly,
t h e speed
l e a f was s i m i l a r t o t h a t o bse r ve d on
l ea ves o f t h e two s u s c e p t i b l e c u l t i v a r s .
gen moved up t h e p l a n t d i d
were
lo c a liz in g
Onl y as t h e p a t h o ­
responses become more e f f e c t i v e .
The e x t e n t o f d i s e a s e d eve lo pmen t i n a l l
tille rs
o f Crest
LRC bO a month
a f t e r h e a d i n g was a l s o g r e a t l y reduced as compared t o M a r i a s and P . l .
278212.
Most o f t h e p l a n t s d i s p l a y e d mean s e v e r i t y r a t i n g s between 3
87
and 6.
In p a r t ,
these
l o w e r s c o r e s were due t o t he s i g n i f i c a n t number
o f d i s e a s e - f r e e t i l l e r s w i t h i n each p l a n t .
The moder at e r espons e by
Crest
fu r th e r substantiated th is
LRC 40 t o h e i g h t and y i e l d
c u ltiv a r's
tolerance
t o the p h y s i o l o g i c a l e f f e c t s
Mechanisms o f r e s i s t a n c e .
involved
study.
reductions
o f pathogenesis.
Two t y p e s o f r e s i s t a n c e a p p e a r t o be
in t h e e x p r e s s i o n o f t h e t h r e e p henot ypes
The f i r s t ,
successful
which
id e n tifie d
in t h i s
i s e x e m p l i f i e d by P . I . 278212, p r e v e n t s t h e
i n v a s i o n and c o l o n i z a t i o n o f t h e fungus, i n a bo v e - g r o u n d
vascular tissu es.
It
i s termed pat hogen e x c l u s i o n .
The s e c o n d , which
i s e x e m p l i f i e d by C r e s t LRC 40, c o n f i n e s t h e pathogen among t i l l e r s
in d iv id u a l
p l a n t s and i n h i b i t s
l a r network, a f t e r
t h e fungus has i n i t i a t e d
pat hog en r e s t r i c t i o n .
or
in h ib itio n
presented
g r o wt h and s p e c u l a t i o n w i t h i n
H isto lo gical
between p l a n t s may be due w h o l l y o r
successful
dence o f
p a t h o g e n , e x c l u s i o n o f t h e fungus
in p a r t
t o s o i 1-rhizo sph e re -p ath og e n
i n t o t h e h o s t was r e - e x a m i n e d .
i n f e c t i o n between p l a n t s o f M a r i a s ,
regimes b ot h
pat hogen movement was
t h e r o l e o f r o o t wou nd in g as a p r e r e q u i s i t e f o r
i n g r e s s o f t h e fungus
278212 was e v a l u a t e d
i s termed
I.
S i nc e £ . gramineum i s a s o i l - b o r n e
T h us ,
It
the vascu­
e v i d e n c e t h a t g e l a t i o n , gummosis,
o f speculation a c t i v i t y c u r t a i l
in Ch a pt e r
in teractio n s.
pathogenesis.
of
in s o i l s
Cr e s t
In c i­
LRC 40, and P . I .
subjected t o d i f f e r e n t environmental
in t h e g reenhous e and in t h e f i e l d .
The i n f l u e n c e o f s o i l m i c r o f l o r a on i n f e c t i o n
in a c o n t r o l l e d
88
environment
in w h i c h me c h a n i c a l
by t r a n s p o r t i n g s o i l
r o o t bre ak ag e d i d n o t o c c u r was s t u d i e d ,
from the f i e l d
i t was- h e a t - s t e r i l i z e d .
i n t o t h e g r e e n h o u s e , where h a l f o f
The t h r e e w i n t e r wheat c u l t i v a r s we re p l a n t e d
in a r andomi zed d e s i g n w i t h i n each s o i l
cations.
t r e a t m e n t ' b lock w i t h
To a p p r o x i m a t e s e e d i n g and i n o c u l u m r a t e s
four r e p li­
in the f i e l d ,
seeds and 7 grams o f i n f e s t e d o a t k e r n e l s were added t o g e t h e r
I m e t e r row.
o b s e rv e d
In n e i t h e r s o i l
(Table
I I 1-3).
t r e a t m e n t was any s u b s t a n t i a l
Hence, t h e s o i l s
tested
in t h i s
70
i n each
in fe ctio n
s tu d y d id not
a p p e a r t o c o n t a i n m i c r o o r g a n i s m s c a p a b l e o f p r o m o t i n g i n f e c t i o n by .£.
gram? neum.
The p o s s i b i l i t y
o f r o o t damage due t o s o i l
e l i m i n a t e d by s p r i n g p l a n t i n g .
s p rin g wheat,
a rtific ia lly
A p ril o f
man.
L em hi , w h i c h
Marias,
heaving
i n t h e f i e l d was
C r e s t LRC 40, P . I . 278212, and a
i s s u s c e p t i b l e t o C e p h a l o s p o r i urn s t r i p e when
i n o c u l a t e d , were p l a n t e d w i t h
1977 a t t h e Montana A g r i c u l t u r a l
A randomized b l o c k d e s i g n w i t h
four
oat kernel
inoculum in mid-
Ex pe r ime nt S t a t i o n n ea r Boze­
r e p l i c a t i o n s was u s e d .
Soil
assays o f r h i z o s ph e re p r o p a g u l e l e v e l s • i n d i c a t e d t h a t p o p u l a t i o n s o f
up t o 5 X IO^ co ni d .i a p e r gram o f s o i l were p r e s e n t d u r i n g t h e f i r s t
month a f t e r p l a n t i n g .
Even w i t h
2% i n f e c t i o n was e v i d e n t .
these hig h
ino cul um l e v e l s ,
The w i n t e r wh eat c u l t i v a r s ,
being
l es s t han
in a non-
v e r n a l i z e d c o n d i t i o n , e x p r e s s e d symptoms o n l y on t h e o u t e r , o l d e r
o f t h e few p l a n t s
l eaves
t h a t became d i s e a s e d . .
To s u b s t a n t i a t e t h e above f i n d i n g s
under c o n d i t i o n s where v e r n a l i -
89
c o l o n i z a t i o n wo u ld o c c u r , t h e t h r e e w i n t e r wheat c u l t i v a r s were p l a n t e d
w it h oat kernel
i n o c ul u m i n e a r l y September o f 1977 a t Bozeman, Montana
where s e v er e w i n t e r c o n d i t i o n s a s s u r e d a de qua te r o o t b r eak ag e in t he
s p r in g from s o i l
f r o s t h e a v i n g ; and a t D a v i s ,
C a lifo rn ia
i n November o f
1977, where a m i l d w i n t e r d i d n o t c r e a t e t h e s o i l - f r e e z i n g
required f o r s o il
extensive
conditions
heaving but d id a l l o w f o r p l a n t v e r n a l i z a t i o n .
While
i n f e c t i o n between p l a n t s was o b s e r v e d among c u l t i v a r s a t
Bozeman, no i n f e c t i o n was a p p a r e n t a t Da vi s
tha t so il
(Ta bl e
f r o s t h e a v i n g causes r o o t b r e a k a g e ,
dence t h a t
r o o t wou nd in g
ill-3 ).
Assuming
t he se d a t a p r o v i d e e v i ­
is necessary f o r s u c c es s fu l
p a t h o g e n e s i s by C_.
g r a m irieum.
This being the case,
t wo mechanisms a r e e n v i s i o n e d w h i c h m i g h t
a f f e c t t h e number o f p l a n t s e x p r e s s i n g d i s e a s e symptoms:
and s t r u c t u r a l
chemical
the
The f i r s t woul d a f f e c t t h e number o f p o t e n t i a l
in t h e r o o t s a v a i l a b l e
inoculum p o t e n t i a l
H isto lo gical
in t h e
in fectio n
t o t h e p a t h o g e n , and t h e second wo u ld a l t e r
i n t h e s o i l a ro un d t h e r o o t s .
exam ina tio n o f ro o t c r o s s - s e c t i o n s usin g standard
embed di ng , s e c t i o n i n g , and s t a i n i n g p r o c e d u r e s
s ur e me nt s o f r o o t mass by d i s p l a c e m e n t
reveal
physical
in r o o t m o r p h o l o g y o r number, and (2) b i o ­
i n t e r a c t i o n s between t h e h o s t and f u n g a l p r o p a g u l e s
rhizosphere.
site s
d iffe re n ce s
(I)
any l a r g e d i f f e r e n c e s
g r o w t h between M a r i a s ,
Crest
( C h a p t e r 1 , 9 ) and mea­
i n w a t e r and d r y w e i g h t d i d n o t
in g r o s s anatomy o r
in t h e e x t e n t o f r o o t
LRC 40, and P . I . 278212.
The number o f
90
TABLE I I I - ] .
E f f e c t o f d i f f e r e n t s o i l environments r e l a t i n g
i n j u r y o r b r eak ag e on t h e p e r c e n t a g e o f p l a n t s
w i t h C e p ha l o s p o r i u m gra mi neu m.
to root
infected
% D is ea sed T i I I e r s /Row—
Win t e r Wheat
Test
C r e s t LRC *fO
P . I . 278212
Lemhi ■
' %
%
%
% '
2
I
O
O
I
O
I
I
I
O
O
2
Fall planted,
Bozeman, Mont.
77
53
15
—
Fal I p l a n t e d ,
D av is ,. C a l i f .
O
O
O
--
GREENHOUSE
S t e r iIe Soil
N o n - s t e r i Ie s o i I
FIELD
Spring p l a n t e d ,
Bozeman, Mont.
Ma ri as
S p r i n g Wheat
.
—^ Va l u e s a r e r e p r e s e n t e d as mean p e r c e n t a g e s o f f o u r r e p l i c a t i o n s .
91
roots
the
produced by p l a n t s o f each c u l t i v a r were n o t c o u n t e d d i r e c t l y ,
l a c k o f any d i s s i m i l a r i t i e s
physical d iffe re n c e s
ro le
i n r o o t g r o wt h p a t t e r n s do n o t p l a y a s i g n i f i c a n t
i n f e c t i o n p e r c e n t a g e s between p l a n t s .
To d e t e r m i n e
if
oat kernel
these c u l t Iv ars e x h i b i t e d a d i f f e r e n t i a l
ro o t breakage,
inoculated
in fe c tio n
and f r o m o a t k e r n e l
wound in g had o c c u r r e d .
the o th e r
( Ta b le
i n o c u l a t e d rows
I noculum l e v e l s
in the s p r in g a f t e r n a t u r a l
c u ltiv a rs
in the s p r in g ,
root
regardless o f p h y s i­
i n t h e r h i zo sp he r e o f M a r i a s , C r e s t
are hig h under n a t u r a l
in t h e f a l l
fie ld
conditions
f r o m 4 X IO^ t o
LRC 40, and
and s p r i n g , when p r o p a g u l e
(22).
levels
Wheat i n each row was
20 grams o f i n f e s t e d o a t k e r n e l s .
d i f f e r e n c e s between c u l t i v a r s
d is p a ritie s
o f t h e r o o t s were
le ngth o r r o o t t e n s i l e s t r e n g t h .
P . I . 278212 were m o n i t o r e d
le ve ls varied
i n w h ic h a l l
I I 1 - 4 ) , d e m o n s t r a t i n g t h a t maximum r o o t br eakage
such as r o o t
ino cula te d w ith
r o o t wou nd in g in t h e
N e i t h e r t r e a t m e n t d i f f e r e d s u b s t a n t i a l l y f rom
p r o b a b l y o c c u r r e d among a l l
factors
response
p e r c e n t a g e s we re o b t a i n e d f rom
rows exposed o n l y t o n a t u r a l
m anually severed w i t h a sharp k n i f e
cal
r o o t mass wo u ld su gg est t h a t
in a f f e c t i n g
t o mechanical
fie ld
in t o t a l
Although propagule
I X IO^ p e r gram o f s o i l ,
no a p p r e c i a b l e
were o b s e rv e d which c o u l d a c c o u n t f o r t he
i n p at h og en e x c l u s i o n between p l a n t s .
The e f f e c t o f v a r i o u s
r esponses t o
qua n tities of
but
i n o c u l u m l e v e l s on d i f f e r e n t i a l
c u ltiv a r
i n f e c t i o n between p l a n t s was examined by a d d i n g known
i n f e s t e d o a t k e r n e l s as an i n o c ul u m s o u r c e t o s o i l w i t h
92
TABLE I I 1-4.
E f f e c t o f d i f f e r e n t i n o c u l a t i o n p r o c e d u r e s in
t h e f i e l d on t h e p e r c e n t a g e o f t i l l e r s i n f e c ­
t e d w i t h C e p h a l o s p o r i u m gramineum among t h r e e
w i n t e r wheat c u l t i v a r s in 1978.
Percent
C u ltiva r
Ma r ia s
Crest
LRC 40
P . I . 2/8212
a/
In fe c tio n -
N a t u r a l wound in g—^ Root s l i c e
oat kernels
& oat kernels
^ Root s l i c e £—
l i q u i d ino cul um
75
79.
76
48
52
77
21
17
76
a/
— Mean p e r c e n t a g e s o f t i l l e r s
rep I i c a t io n s .
i n f e c t e d p e r row a c r o s s f o u r
—^ Rows i n o c u l a t e d w i t h 20 grams o f i n f e s t e d o a t k e r n e l s .
Wounding due s o l e l y t o s o i l f r o s t h e a v i n g i n t h e s p r i n g .
— Rows i n o c u l a t e d w i t h 20 grams o f i n f e s t e d o a t k e r n e l s .
In
a d d i t i o n t o r o o t b r eak ag e f r o m s o i l h e a v i n g , r o o t s were
s e ver ed on b o t h s i d e s o f each row w i t h a s h a r p k n i f e i n l a t e
March.
No a d d i t i o n a l i n o cu lu m was added.
d/
'
— U n i n o c u l a t e d rows s l i c e d on b ot h s i d e s i n l a t e March w i t h a
sharp k n i f e .
I m m e d i a t e l y a f t e r s e v e r i n g r o o t s , two l i t e r s
o f IO^ c o n i d i a / m l were poured i n t o t h e s o i l s l i c e .
93
no p r e v i o u s h i s t o r y o f c r o p p i n g t o w i n t e r w h e a t .
natural
Under c o n d i t i o n s o f
r o o t w o u n d i n g , a p o s i t i v e c o r r e l a t i o n e x i s t e d between
d e n s i t y and t h e p e r c e n t a g e o f t i l l e r s
The d i f f e r e n t i a l
i n f e c t e d p e r row ( T a b l e
responses- between c u l t i v a r s ,
i n oc ul um
I I 1-5).
h owever, d i d n o t change.
The same r e sp on se s we re n ot e d when two i s o l a t e s o f t h e f un gus were used,
one o f m i l d v i r u l e n c e
#17).
( i s o l a t e #5) and one o f h i g h v i r u l e n c e
Thus, an i n o c u l u m d e n s i t y o f 20 grams o f o a t k e r n e l s p e r 3 . I m
row, w h i c h p roduced up t o
sp rin g,
I X IO^ p r o p a g u l e s p e r gram o f s o i l
in t h e
c a nn o t o v e r r i d e t h e r e s i s t a n c e mechanism a f f e c t i n g pathogen-
exclusion.
Only when two l i t e r s
c o n i d i a / m l were added
of
(Tab Ie
I 11-4).
liq u id
inoc ul um c o n c e n t r a t e d t o
IO^
immediately a f t e r m anually s e v e r in g the roots
i n t h e s p r i n g was t h e d i f f e r e n t i a l
ted
( isolate.
re sp on se between c u l t i v a r s o b l i t e r a ­
Sb
TABLE 111-5.
E f f e c t o f C e p h a l os p or i u m gramineum
i n o c u l u m d e n s i t y on i n f e c t i o n o f t h r e e
w i n t e r wheat c u l t I v a r s o f d i f f e r i n g
s u s c e p tib iIity .
% Diseased T i I I e r s / R o w ^
I noculum D e n s i t y —^
C u ltiva r
Ma ri as
CreSt
LRC 40
P. I . 278212
5 gms
10 gms
20 gms
39
57
73
30
38
50
14
18
24
a/
— Mean p e r c e n t a g e s o f f o u r r e p l i c a t i o n s ,
h/
— The q u a n t i t y o f o a t k e r n e l s i n f e s t e d w i t h C_.
gramineum a p p l ied w i t h t h e seed t o a 3 « I m row.
95
DISCUSSION
Three p h e n o t y p i c r e sp on se s t o C e p h a l o s p o r Ium s t r i p e by s e l e c t e d
w i n t e r wheat c u I t i v a r s were i d e n t i f i e d
e x p r e s s e d as a r e d u c t i o n
tio n .
Soil
co n d itio n s,
in teract
number o f d i s e a s e d t i l l e r s
w i t h i n p l a n t s and t h e t h i r d
pathogen, e .g .
a ll
severely b lig h te d .
entry,
e.g.
re sista n t
it
i n g r e s s such t h a t t he
Based on t h e d i f f e r e n t i a l
types o f r e s i s ­
P . I . 278212 i s h i g h l y r e s i s t a n t
t o exclu de the pathogen, e . g .
become i n f e c t e d , y e t
re duce s t h e r a t e
t h e e x c l u s i o n and r e s t r i c t i o n
i n d e p e n d e n t o f each o t h e r .
in the
Both o f t h e s e l a t t e r responses
is r e s t r i c t e d w i t h i n the h o s t.
its a b ility
in a popula ­
The second causes a r e d u c t i o n
in te r a c tio n s a f t e r successful
res pon se s among c u l t i v a r s ,
tance are
is
i n a manner w h ic h e x c l u d e s t h e p a t h o ­
and s e v e r i t y o f d i s e a s e d e v e l o p m e n t .
pat hog en
The f i r s t
t h e r o o t sys tem o f t h e h o s t , and i n f e c t i o u s
i n t o the h o s t .
involve, h o s t-fu n g u s
study.
i n t h e number o f d i s e a s e d p l a n t s
p r o p a g u Ies o f t h e f u n g us
gen f r o m i n g r e s s
in t h i s
in
a low p e r c e n t a g e o f p l a n t s
i s h i g h l y s u s c e p t i b l e t o s y s t e m i c movement o f t h e
tille rs /p la n t
Crest
become d i s e a s e d and i n f e c t e d p l a n t s a r e
LRC 40, however,
i s s u s c e p t i b l e t o pathogen
most o f t h e p l a n t s become i n f e c t e d , b u t
it
is moderately
t o s y s t e m i c movement o f t h e p a t h o g e n , e . g . . low p e r c e n t a g e o f
tille rs /p la n t
become i n f e c t e d and t he
le a ve s and heads o f d i s e a s e d p l a n t s
are o n l y m oderately b l i g h t e d .
In h e a y i l y seeded rows , t h e p e r c e n t a g e o f t i l l e r s
re fle cte d
the percentage o f p la n ts
infected
i n a row
in f e c t e d / r o w f o r those c u l t i v a r s
in
96
which, most o r a l l
case, o f C r e s t
o f the t i l l e r s
LRC 40,
though,
re fle c te d d iffe re n ces to
tille rs
i n t e r m e d i a t e between
i n f e c t i o n by C r e s t LRC 40 may a c t u a l l y be a
in d i s t i n g u i s h i n g
reductions
In o r d e r t o e f f e c t i v e l y d i f f e r e n t i a t e
CU I t i v g r s
b ut between
response, w h i c h was b i a s e d t o w ar d a more r e s i s t a n t phenot ype
because o f e r r o r s
that
T h e r e f o r e , the
In t he
infecte d/row
i n f e c t i o n n o t o n l y between p l a n t s ,
p l a n t r e a c t i o n t o p at hogen
pla nt,
the percentage o f t i l l e r s
o f each p l a n t as w e l l .
susceptible
in each p l a n t were d i s e a s e d .
such a s C r e s t
LRC 4 0,
in d i s e a s e d t i l l e r s
a ll
t h r e e p he not yp es
per
in
l o we r s e e d i n g r a t e s a r e r e q u i r e d so
i n d i v i d u a l p l a n t s c o u l d be d i s c r i m i n a t e d .
T h i s wo u l d p a r t i t i o n
p at h og en e x c l u s i o n re sp on s es f ro m p at h og en r e s t r i c t i o n
r e s p on s e s .
R e s i s t a n c e , as m a n i f e s t e d by low i n f e c t i o n p e r c e n t a g e s between
p l a n t s , was f i r s t
wheat p l a n t
c ia lly
a ttrib u te d
(13).
S e v e r a l c u l t i v a r s , w h i c h were r e s i s t a n t when a r t i f i ­
in o c u la t e d through the r o o t s , expressed s u s c e p t i b i l i t y a f t e r
stem i n o c u l a t i o n s .
w ith
t o r o o t a n d / o r crown r e g i o n s o f t h e w i n t e r
Reductions
In i n f e c t i o n p e r c e n t a g e s ,
reduced i n o cu lu m d e n s i t i e s ,
in j u r y and/or reductions
factors
Mat hr e and J o h n s t o n
period fo llo w in g
root
g re s s i n t o the ro o ts
in ju ry
Resistance t o
i n r o o t mass do n o t a pp ear t o be m a j o r
i n f l u e n c i n g t h e number o f p o t e n t i a l
t o the fungus.
concomitant
f u r t h e r in d ic a t e d t h a t the f a c t o r ( s )
g o v e r n i n g r e s i s t a n c e was i n h e r e n t t o t h e r o o t s o r c r o wn .
root
.
in fe c tio n s ite s a vailab le
(13) d e t e r m i n e d t h a t t h e optimum
in w h i c h c o n i d i a can s u c c e s s f u l l y g a i n
i s one day.
P o s s i b l y , c u l t i v a r s may respond
in ­
97.
t o the
rate o f wound-healing,
i n f e c t i o n by c l o s i n g o f f
levels
thus a f f e c t i n g
in fe ctio n s ite s .
in cid ence o f ro o t
O t i e n o (15) o b s e r v e d h i g h
o f c o n i d i a p r o x i m a l t o r o o t s and r o o t h a i r s p r i o r
o f s e e d l i n g s g e r m i n a t e d on p e t r i
la r
the
to
in fe ctio n
p l a t e c u l t u r e s o f C_. g r amj neu m. S i m i ­
l o c a l i z e d p o c k e t s o f c o n i d i a were o b s e r v e d n e x t t o r o o t s c o l l e c t e d
in the f i e l d
e a rly
d is trib u tio n
of
If
d iffe re d
c u ltiv a rs
in the s p rin g
in fectio u s
(Morton, unpublished o b s e r v . ) .
p r o p a g u Ies c o u l d be a l t e r e d
This
s ig n ific a n tly
in t h e i r c a p a c i t y t o s y n t h e s i z e t h e m u c i l a g i n o u s
c o a t i n g a round t h e r o o t s , w h i c h m i g h t s e r v e t o c o n c e n t r a t e propagul.es
around p o t e n t i a l
in fe ctio n
site s.
The a b i l i t y
pensions t o o v e r r id e the r e s is t a n c e
be a t t r i b u t e d
of
liq u id
coni d i a l
sus­
re sp on s e t o pat hog en e x c l u s i o n c o u l d
t o high c o n c e n tr a t io n s o f propagules
v i c i n i t y o f ro o ts a t the tim e o f wounding.
in t h e
While t h i s
immediate
study f a i le d
d e l i n e a t e m a j o r changes i n t h e s o i I - r o o t - p a t h o g e n
in te ra ctio n ,
r e s u l t s do n o t
lo ca lize d e ffe c ts
r u l e o u t s m a l l e r , more s i g n i f i c a n t
w ith in m icrohabitats
Reduction
observed o n ly
in t h e p e r c e n t a g e o f t i l l e r s
va s c u la r network
the
in te rfa c e .
i n f e c t e d w i t h i n p l a n t s was
i n C r e s t LRC 40, w h i c h was a l s o u n i q u e
r e s tric t v e rtic a l
types
in and a r ou nd t h e s o i l - r o o t
to
in
its
a b ility
to
and l a t e r a l movement o f C.. gramineum t h r o u g h o u t i t s
(Chapter I ) .
I f t h e c l o s e a s s o c i a t i o n between pheno-
i s more t h e c i r c u m s t a n t i a l ,
down movement o f t h e f un gus
t h e n t h e same r esponses w h i c h s l o w
i n t h e culms and l ea ves o f
infected t i l l e r s
m i g h t a l s o be r e s p o n s i b l e f o r r e t a r d i n g s y s t e m i c i n v a s i o n o f t h e f un g us
98
between t i l l e r s .
L im itin g
i n v a s i o n between t i l l e r s
l o o s e l y a n a lagous t o t h e d w a r f b u n t
in te ra c tio n ,
in w h i c h r e s i s t a n c e
(Ti I l e t l a
o f a p l a n t may be
c o n t r o y e r s a ) - w i n t e r wheat
i s e x p r e s s e d by i n a b i l i t y o f t h e f un gus
t o s u c c e s s f u l l y c o l o n i z e the. g r o w i n g p o i n t b e f o r e t h e o n s e t o f stem
e longation
(6).
in te ra c tio n ,
tille r
In t h e cas-e o f t h e C e p h a l o s p o r |um s t r i p e - w i n t e r wheat
t h e f u n g u s may need t o e n t e r t h e v a s c u l a r s yst em o f each
p r i o r t o a r e s t r i c t i v e host response,
t e r wheat p l a n t
The crown r e g i o n o f a w i n ­
i s a c ompl ex a g g r e g a t i o n o f compressed nodes. ( 1 6 ) , w h ic h
t h e f u n g u s must t r a v e r s e
i n o r d e r t o i n v a de d e v e l o p i n g t i l l e r s .
complex l i n k a g e s and s h o r t v e s s e l e l e m en t s would
movement and d i s t r i b u t i o n
impose a d d i t i o n a l
D iffe re n tia l
p l a n t s and t o
in t h e m s e l v e s .
i n f l u e n c e pat hogen
An a c t i v e h o s t re sp on s e would
b a r r i e r s t o the pathogen.
r e sp on se s between c u l t i v a r s t o p e r c e n t a g e o f d i s e a s e d
l o c a l i z a t i o n o f pat hog en movement have been i d e n t i f i e d
other vascular w i l t
diseases
(1,8).
It
i s d o u b t f u l , h o w ev e r , t h a t
mechanisms r e g u l a t i n g p h e n o t y p i c resp on se s a r e t h e same.
v a s c u l a r p at hogens o f her ba ce ou s a nn u al s , such as
and V e r t i c i n i u m
s yst em o f t h e i r
d ev el op men t
in
the
Whereas o t h e r
Fusar lum oxysporum
d a h lia e , are capable o f a c t i v e l y p e n e t r a t i n g the ro o t
r e s p e c t iv e hosts at d i f f e r e n t o n to g e n e tic stages o f
(7), £.
s ys tem o n l y a f t e r
spring.
The
it
gramineum p a s s i v e l y e n t e r s t h e w i n t e r wheat r o o t
has been i n j u r e d by s o i l
h e a vi n g c o n d i t i o n s
in the
None o f t h e r e sp on se s r e l a t e d t o h y p e r a u x i n y such as t y l o s e s
fo rm a tio n , vessel c o lla p s e , o r c e l l
p ro life ra tio n
(.2,5) have been
.
99
o b s e r v e d i n t h e v a s c u l a r n e t w o r k o f w i n t e r wheat p l a n t s
C_. gram?neum,
Such s i g n i f i c a n t d i f f e r e n c e s
e tio lo g y - suggest t h a t
in v a r i o u s f a c e t s o f d i s e a s e
C e p h a l os p or i u m s t r i p e c a nn ot be compared r e a d i l y
w ith o th e r v a s c u la r diseases.
nisms a n d /o r th e
infecte d w ith
It
follo w s,
therefore,
t h a t t h e mecha­
i n h e r i t a n c e o f r e s i s t a n c e may a l s o n o t be co mp ar a bl e .
Many a s p e c t s o f C e p h a l o s p o r i u m s t r i p e e t i o l o g y have r e l e v a n c e t o
germplasm e v a l u a t i o n ,
Y ield
e s p e cia lly
in the c o n t e x t o f s e l e c t i o n
r e d u c t i o n s have o f t e n been measured by h a r v e s t i n g a l l
w ith in
in d ivid u a l
rows
(10,12,14).
infected w ith in
o f symptom d e v e l o p m e n t .
t o a s i n g l e measurement.
ded a t a g i v e n t i m e
p l a n t s , and a l t e r a t i o n s
E arly v is u a l
(12,14).
I).
o f h ea d i ng d a t e s ,
re sista n t
d i s e a s e r e a d i n g s have been r e c o r ­
in m a t u r a t io n
to
regardless o f s u s c e p t i b i l i t y
i n v a s i o n by £ .
l a t e r maturing P . l .
to
2 /8 212 a r e e q u a l l y
gramineum a f t e r s u c c e s s f u l
When symptom s e v e r i t y
the
head in g
r a t e s , which are c l o s e l y
For e x a m p l e , M a r i a s and P . l .
s u s c e p tib le to systemic
t i o n has o c c u r r e d .
lumped t o g e t h e r i n ­
T h is s c o r in g procedure f a i l e d
symptom d e v e l o p m e n t ,
(Chapter
percentage o f
i n t h e r a t e and s e v e r i t y
Al I o f t h e s e p he not yp es a r e
account f o r these d i f f e r e n c e s
d isease
infected,
in th e f i e l d w i t h o u t regard t o d i f f e r e n t i a l
d a t e s between c u l t i v a r s
associated w ith
plants
T h i s p r o c e d u r e o b s cu r e s p h e n o t y p i c
d i f f e r e n c e s e x p r e s s e d as p e r c e n t a g e o f p l a n t s
tille rs
procedures.
in fe c­
i s e v a l u a t e d w i t h o u t knowledge
2 / 82 12 wo u ld a pp ear t o be more
t h an t h e e a r l i e r m a t u r i n g M a r i a s .
p r o gr a m , t h i s wo u ld have, t wo m a j o r d r a w b a c k s .
In a germplasm d evel opment
F irs t,
i t wo ul d o b s c u r e
100
g e n o t y p i c d i f f e r e n c e s a s c r i b e d s o l e l y t o an a c t i v e h o s t
t o t h a t e x h i b i t e d by C r e s t LF^C MO...
tio n of
r esponse s i m i l a r
S e c o n d l y , . i t wo ul d f a v o r t h e s e l e c ­
l a t e m a t u r i n g c u l t i v a r s a t t h e expense, o f t h e more a g r o n o m i c a l I y
p re fe ra b le e a r l y maturing c u l t i v a r s .
r a l weeks a f t e r h e a d i n g
( 1 2 , 1 4 ) more a c c u r a t e l y r e f l e c t g e n o t y p i c d i f ­
f e r e n c e s in h o s t r esponse t o d i s e a s e
The i d e n t i f i c a t i o n
The w h i t e head r e a d i n g s made s eve ­
i n c i d e n c e between p l a n t s .
o f d i s t i n c t p h e n o t y p i c responses t o
i n f e c t i o n by
C. gramineum e s t a b l i s h e s t h e g r o un d w o r k w i t h w h i c h p a r e n t a l m a t e r i a l s
and s u bs e q u e n t s e g r e g a t i n g p o p u l a t i o n s may be more c a r e f u l l y screened
f o r d i f f e r e n t m anifestations o f resistance.
p at hogen r e s t r i c t i o n ,
being
Both pathogen e x c l u s i o n and
i n d e p e n d e n t l y e x p r e s s e d , m i g h t be e f f e c t i v e l y
combined t o p r o d u c e a s u p e r i o r g e n o t y p e w i t h
p r e v e n t , as w e l l as c h e c k ,
I f t h i s goal
separately.
t h e maximum p o t e n t i a l
to
i n f e c t i o n by £ . gra mi neu m.
i s t o be a t t a i n e d ,
To examine d i s e a s e
each p he not yp e must be r e c o g n i z e d
i n c i d e n c e between p l a n t s , w h i t e head
c o u n t s o r t a l l y s o f t h e number o f d i s e a s e d p l a n t s p er row must be made.
Disease i n c i d e n c e between t i l l e r s
w ith in
i n f e c t e d p l a n t s , h ow ev er , must
be enumerat ed on s p a c e - p l a n t e d m a t e r i a l s .
s h o u l d be a p p r a i s e d a t
symptoms, a r e f u l l y
cuItiv a r
l e a s t one month a f t e r h e a d i n g , when d i s e a s e
expressed.
Y i e l d p e r f o r m a n c e may be used t o measure
r e s p o n s e s t o symptom s e v e r i t y ,
w i t h i n a row are. exami ne d.
would
Both o f t h e s e phenot ypes
but only i f
More d e f i n i t i v e
in fe c te d plants
gaug in g o f t h i s
phenot ype
i n c l u d e e v a l u a t i o n o f seed s i z e , w h i c h r e f l e c t s t h e e x t e n t o f
101
g ra in -fillin g
a f t e r a n t h e s i s , ■h e i g h t r e d u c t i o n , o r the. r a t e o f sym p to m
d e ve l o pm en t on f l a g
Ma thr e
(unpub.
l e a v es u s i n g a d i s e a s e
re su lts)
i n d ex r a t i n g sys tem.
o b s e r v e d up t o 90% i n f e c t i o n
in
inoculated
rows p l a n t e d t o a s u s c e p t i b l e ' c u l t i ' v a r a t a s e e d i n g r a t e o f a p p r o x i m a t e l y
50 seed s p e r 3.1 m row,
s u g g e s t i n g t h a t reduced s e e d i n g r a t e s a r e n o t
m i t i g a t i n g with, re s p ec t t o
space-planting,
i n f e c t i o n between p l a n t s .
id e n tific a tio n
crossing.
In a d d i t i o n ,
Screening f o r p a r e n t a l m a t e r ia ls
so t h a t p he not yp es a r e w e l l d e f i n e d p r i o r t o
p e d i g r e e a n a l y s i s and e a r l y g e n e r a t i o n t e s t i n g
c u r r e n t l y employed a t Montana S t a t e U n i v e r s i t y
s p a c e - p l a n t e d p r o ge n y r o w s .
app ro ac h
(12,14) n e c e s s it a te s
Th er e i s some q u e s t i o n w h e t h e r such an
i s t h e most e f f e c t i v e method f o r
increasing re s is ta n c e ,
s i n c e t h e g e n e t i c s o f C e p ha l o s p o r i u m s t r i p e
I f resistance
by
o f each p he no ty p e and e v a l u a t i o n o f
c u 1 1 i v a r re sp on s es a r e f a c i l i t a t e d .
requires s p ace -p lq ntin g ,
Therefore,
is q u a n t i t a t i v e l y expressed,
h ow ev e r,
i n h e r i t a n c e a r e unknown.
t he n
o f p r o ge n y p o p u l a t i o n s may be more r e l i a b l e .
la t e r generation te s tin g
In such a p r o gr a m , some
s e l e c t i o n p r e s s u r e may be a p p l i e d on e a r l i e r b u l k p r oge ny p o p u l a t i o n s
by s c r e e n i n g f o r seed s i z e , w h i c h s e l e c t s f o r d i s e a s e - f r e e p l a n t s as
w ell
as p l a n t s more t o l e r a n t t o d i s e a s e d e v e l o p m e n t .
T h i s a pproach
would keep p o p u l a t i o n s manageable o v e r a number o f s e l f I ng g e n e r a t i o n s .
S c r e e n i n g f o r seed s i z e may a l s o be e f f e c t i v e
p r ogr am,
should s t a b l e , g e n e tic m a l e - s t e r i l e
developed which co uld f a c i l i t a t e
in a r e c u r r e n t s e l e c t i o n
so ur c es
out-crossing.
i n w i n t e r wheat be
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t o m a t o e s . p h y t o p a t h o l o g y 6 4 : 4 5 5 t-4 6 I .
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}0M
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105
SUMMARY AND CONCLUSIONS
The e t i o l o g y , o f Cephal o s p o r i u m s t r i p e was examined t h r o u g h o u t t h e
d e v e l o p m e n t a l g r o w t h s t a g e s o f seven w i n t e r wheat c u l t ! v a r s , w h ic h were
d iffe re n tia te d
on t h e b a s i s o f t h e i n f l u e n c e each had on v a r i o u s s t a g e s
o f the disease c y c l e .
The maximum e x p r e s s i o n o f d i s e a s e symptoms i s
g ov er ne d by o p t i m a l c o n d i t on s f o r t wo b i o t i c
component s, t h e h o s t and
t h e p a t h o g e n , and f o r t wo a b i o t i c c o m p on e n t s , t h e s o i l and t h e a tm os ­
phere.
Thus,
s p e c ia lly
t h e d i s e a s e c y c l e may be p a r t i t i o n e d
i n t o t wo s e t s o f
spring w ith in
in teractio n s.
t h e r h i z o s p h e r e and i s
the h o s t- p a th o g e n - s o il
s y st em .
takes p la ce in e a r l y
i n f l u e n c e d by e v e n t s s u r r o u n d i n g
The second t a k e s p l a c e t h r o u g h o u t t h e
r e m a i n d e r o f t h e g r o w i n g season w i t h i n
the host-pathogen
The f i r s t
t e m p o r a l l y and
t h e p l a n t and i s
i n f l u e n c e d by
in te ra c tio n .
E x c l u s i o n o f t h e p a t h o g e n , such t h a t t h e p e r c e n t a g e o f d i s e a s e d
p l a n t s p e r row i s r e d u c e d ,
i s a t y p e o f r e s i s t a n c e w h ic h may be i n t r i ­
c a t e l y a s s o c i a t e d w i t h e ve nt s in t h e h o s t - p a t h o g e n - s o i l s ys t e m .
mass, w h i c h w o u l d a f f e c t
p a t h o g e n , and p r d p a g u l e
t h e number o f
leve ls
Root
i n f e c t i o n s it e s a v a i l a b l e to the
in t h e r h j z o s p h e r e , w h i c h wo u l d a f f e c t
i n o c ul u m p o t e n t i a l , were n o t s i g n i f i c a n t l y d i f f e r e n t between c u l t ! v a r s .
These r e s u l t s ,
h ow ev e r, do n o t r u l e o u t t h e p o s s i b i l i t y
n ib le d if fe r e n t ia l
or
leve ls
in the v i c i n i t y
Any i n f l u e n c e on e v e n t s a s s o c i a t e d w i t h
“j
l e ss d i s c e r ­
res pon se s such as t h e r a t e o f w o u n d - h e a l i n g
l o c a l i z e d propagule
face.
of
o f the r o o t - s o i l
in r o o t s
in te r­
ro o t breakage, which
is
106
e ssen tia l
for
a ffe c t this
i n g r e s s o f t h e p at hog en
type o f re s is ta n c e .
i n t o t h e r o o t s y s t e m , would, a l s o
Of t h e c u I t i v a r s e x a m i n e d , R , I . 278212,
P . I . 094424, and C. I . 07638 were r e s i s t a n t t o d i s e a s e by e x c l u d i n g t h e
p at hogen w h i l e M a r i a s ,
Lancer,
Crest
LRC 40, and W i n a l t a were su s ce p­
tib le .
R e s t r i c t i o n o f t h e p a t h o g e n , such t h a t e i t h e r d i s e a s e
among t i l l e r s
o f in fe c te d plants
i s reduced o r t h e r a t e and s e v e r i t y o f
symptom e x p r e s s i o n
is c u r t a i l e d ,
c i a t e d w i t h events
in t h e h o s t - p a t h o g e n s ys t e m .
s y s t e m i c movement o f Cr
network.
liv in g
nal
re p re s e n ts a type o f re s is t a n c e asso­
In a l l
c u ltiv a rs ,
the
gramineum was l i m i t e d by m a t u r a t i o n o f t h e x y Iem
At no t i m e was t h e fungus o b s e r v e d p e n e t r a t i n g
vessel ele ments.
in cid en ce
In t h e case o f C r e s t
i mmat ure,
LRC 4 0, h o w ev e r , a d d i t i o ­
c u r t a i l m e n t o f t h e pat hog en was e v i d e n t between t i l l e r s ,
up t h e Culm, and l a t e r a l l y
in the leaves.
This a c t i v e host
v e rtic a lly
response
was t h o u g h t t o r e s u l t e i t h e r f ro m l o c a l i z a t i o n o f f u n g a l c e l l s
t i o n o r gummosis, f r o m i n h i b i t i o n
o f coni d i a l
p ro life ra tio n ,
by g e l a ­
or a combi­
n a t i o n o f t h e s e two phenomena.
Cr
gram? neum i n va d e s t h e v a r i o u s v a s c u l a r b u n d l e t y p e s o f each
node and i t s
le a f o f attachment
pattern o f co lo n iza tio n
is v i s u a l l y appare nt
The pat hog en was r a r e l y o b s e r v e d
symptoms.
fe ra tio n
i n t h e same s e q u e nc e .
This r e p e t i t i v e
in f o l i a r s t r i p e
form ation.
in V a s c u l a r b u n dl e s e x h i b i t i n g no
Hence, c h l o r o t i c s t r i p e s were c l o s e l y a s s o c i a t e d w i t h p r o l i ­
o f the fungus w i t h i n
c o lo n iz e d v a s c u la r bundle s.
Reduction
in
107
r e l a t i v e w a t e r c o n t e n t , c o n d u c t a n c e , n e t p h o t o s y n t h e s i s , and c h l o r o p h y l l
c o n t e n t were d i r e c t l y
co rre la ted w ith s t r ip e
t h i s d a t a suggests- t h a t f u n g a l
form ation.
Taken t o g e t h e r ,
c o l o n i z a t i o n and p r o l i f e r a t i o n
in te ra cts
w i t h t h e h o s t t o cause l o c a l i z e d v a s c u l a r d y s f u n c t i o n a ro un d and w i t h i n
in f e c t e d b u n d le s , which
in t u r n
in h ib its
the p h y s i o l o g i c a l a c t i v i t y o f
a d j a c e n t phloem and mesophy11 c e l l s .
t h e dev el op men t o f a d i s e a s e
i n d e x r a t i n g s ys t em , w h i c h q u a n t i f i e d
t h e number o f c h l o r o t i c s t r i p e s on a l e a f a t a g i v e n t i m e , a l l o w e d
experimental
a c tiv ity
of
r e l a t i o n s h i p s between symptom dev el op men t and p h y s i o l o g i c a l
infected
le a ve s t o be m o n i t o r e d t h r o u g h o u t t h e o n t o g e n y o f
the h o s t p l a n t s .
Id e n tific a tio n
o f t h e two t y p e s o f r e s i s t a n c e t o Cephal o s p o r i urn
s t r i p e and t h e i r s u b se q ue n t e f f e c t s on t h e h o s t - p a t h o g e n
have i m p o r t a n t a p p l i c a t i o n s
in teractio n
i n a germplasm dev el op men t p r o gr a m.
Exclu­
s i o n o f t h e p at hogen and r e s t r i c t i o n o f t h e pat hogen a r e i n d e p e n d e n t l y
e x p r e s s e d among c u l t i v a r s .
influence at d i f f e r e n t
This
is not s u r p r i s i n g
if
times d u r in g th e disease c y c le .
each e x e r t s
its
Each phenot ype
s h o u l d be r e c o g n i z e d and e v a l u a t e d s e p a r a t e l y when s c r e e n i n g f o r p a r e n ­
tal
m a te ria ls,
but selected together
i n s e g r e g a t i n g p o p u l a t i o n s so t h a t
b o t h t y p e s o f r e s i s t a n c e a r e combined t o g e t h e r
i n t o a s i n g l e genotype.
F o l i a r symptom e x p r e s s i o n p r o v i d e s a p o w e r f u l s e l e c t i o n
evaluating a l l
physiological
p h e n o ty p ic responses, s in c e i t
s t a t e o f the
leaf.
tool
for
accurately r e fle c ts
t he
T h u s , more c o m p l i c a t e d and t i m e
108
consuming measurements o f p h y s i o l o g i c a l a c t i v i t y
and w a t e r d e f i c i t s
such as p h o t o s y n t h e s i s
are unnecessary.
S e l e c t i o n p r o c e d u r e s must be used w h i c h r e c o g n i z e t h a t t h e r a t e o f
symptom d e v e lo p me nt i s a f f e c t e d , n o t o n l y by a c t i v e
resistance
to the
p at hogen movement, b u t by t h e h o s t ' s m a t u r a t i o n g r a d i e n t s as w e l l .
R e c o r d i n g h e a d i n g d a t e s and making s e l e c t i o n s a t a s t a n d a r d i z e d
a f t e r h e a d i n g wo u ld e n s u r e t h a t t h e m i t i g a t i n g
d ev e lo p me nt a r e removed f r o m c o n s i d e r a t i o n .
in terval
in flu e n c e s o f host
cop. 2
M o r t o n , Joseph B
Etiology of eephalosporium stripe in rela­
tion to the expression of
resistance ...
ISSUED TO
H
i !
'