878
Resistance of graft-compatible and graft-incompatible Pseudotsuga menziesii
rooted cuttings to Phellinus weirii
1
JAMES A. ENTRY
Department of Forest Science, Oregon State University, Corvallis, OR 97331, U .S .A .
AND NAN C. VANCE AND DONALD L. COPES Pacific Northwest Research Station, Forestry Sciences Laboratory, 3200 Jefferson Way, Corwillis, OR 97331, U.S.A.
Received June 23, 1993
Accepted October 12, 1993
ENTRY, J.A., VANCE, N.C., and CoPES, D.L. 1994. Resistance of graft-compatible and graft-incompatible
menziesii rooted cuttings to Phellinus weirii. Can. J. For. Res. 24: 878-881.
Pseudotsuga
One-year-old rooted cuttings taken from 23- and 26-year-old graft-compatible and graft-incompatible Pseudotsuga
menziesii (Mirb.) Franco were inoculated with one of three isolates of Phellinus weirii. After 20 months in a green­
house, infection frequency and severity were significantly greater in the graft-incompatible cuttings. Cellulose con­
centration in the root tissue was higher in graft-incompatible than graft-compatible cuttings. Concentrations of
lignin, phenolic compounds, and tannins were higher in graft-compatible than graft-incompatible cuttings. Cellulose
concentration had a positive linear correlation (r2 = 0.84) with the P. weirii infection rating. The concentration of
phenolic compounds and lignin in secondary root tissues was negatively correlated with the infection rating (r2 = 0.73
and 0.84, respectively). The lignin/cellulose and phenolic/cellulose ratios were negatively correlated with the infec­
tion rating of P. weirii infection in a linear relationship (r2 = 0.82 and 0.77, respectively). W hite-rot fungi cannot
use tree defense compounds, such as lignin and phenolics, as the sole energy source; an alternate energy source
is necessary to degrade these compounds. The lignin/cellulose and phenolic/cellulose ratios in the roots may be
important measurements to explain the host-pathogen response of P. weirii infection.
ENTRY, J.A., VANCE, N.C., et COPES, D.L. 1994. Resistance of graft-compatible and graft-incompatible
menziesii rooted cuttings to Phellinus weirii. Can. J. For. Res. 24 : 878-881.
Pseudotsuga
Des boutures racinees d'un an prelevees sur des Pseudotsuga menziesii ll.ges de 23 et 26 ans compatibles et
incompatibles au greffage furent inoculees avec un des trois isolats de P hellinus weirii. Apres 20 mois en serre, Ia
frequence et Ia severite de !'infection etaient significativement plus elevees chez les boutures incompatibles au
greffage. La concentration de cellulose dans les racines etait plus elevee chez les boutures incompatibles au greffage
que chez les boutures compatibles au greffage. La concentration de lignine, de composes phenoliques et de tannins
etait plus elevee chez les boutures incompatibles au greffage que chez les boutures compatibles au greffage. La
concentration de cellulose etait positivement et lineairement correlee (r2 = 0,84) avec le degre d'infection par
P. weirii. La concentration de composes phenoliques et de lignine dans les racines secondaires etait positivement cor­
relee (r2 = 0,73 et 0,84, respectivement) avec le degre d'infection. Les ratios lignine/cellulose et phenols/cellulose
etaient negativement correles (r2 = 0,82 et 0,77, respectivement) avec le degre d'infection par P. weirii selon une rela­
tion lineaire. Les champignons de carie blanche ne peuvent utiliser les composes impliques dans les mecanismes de
defense chez les arbres, tels Ia lignine et les phenols, comme seule source d'energie. Une autre source d'energie est
necessaire pour degrader ces composes. Les ratios lignine/cellulose et phenols/cellulose dans les racines pourraient
etre des indices importants pour expliquer les reactions hote-pathogene dans le cas de !'infection par P. weirii.
Introduction Phellinus weh·ii (Murr.) Gilb., the fungus that causes lam­
inated root rot, is one of the most damaging forest tree dis­
eases in the Pacific Northwest and has been estimated to 6 3
cause timber losses of 4 .4 X l 0 m ·year -J (Nelson et a!.
1981). The disease spreads when uninfected roots contact
roots of infected trees or stumps (Wallis and Reynolds 1965;
Nelson 1980). Phellinus weirii can remain infective in buried
stumps and roots for as long as 50 years (Hansen 1979).
Phellinus weirii can infect nearly all c onifers, but some
species are more susceptible than others. Pse udotsuga
menziesii (Mirb.) Franco is highly susceptible.
Graft unions of compatible trees show less cell necrosis,
suberization, and walling off of cells of different genotypes
than graft unions of incompatible clones, which are char­
acterized by a strong, well-defined cell necrosis and walling­
off process (Copes
1970). We hypothesized suberization
and the walling-off process to be disease resistance processes
1Author to whom all correspondence should be addressed.
Printed in Cnnndn I lmprimC llU Conadn
(Vance et a!.
1980). The mechanism responsible for internal
menziesii may be ini­
graft-incompatibility symptoms in P.
tiated by the same cellular process that protects trees from
disease. Teasdale et a!. ( 1974) found disease resistance and
cellular-incompatibility responses in other plants to be sim­
ilar processes. If the mechanism is the same, clones clas­
sified as graft incompatible may be more resistant to fungal
diseases than graft-compatible clones because of their abil­
ity to initiate a stronger suberization reaction in cells attacked
by the fungus. The objective of this study is to determine
(i) if rooted cuttings of graft-compatible P. menziesii clones
are more susceptible to P. weirii than rooted cuttings of
graft-incompatible clones and (ii) to determine if there are
differences in tree defense compounds between the com­
patible and incompatible clones that might account for dif­
ferences in resistance to P.
weirii infection.
Methods
Seedling growing conditions
In 1987, cuttings of five highly graft-compatible and five highly
graft-incompatible P. menziesii clones of Willamette Valley and
879
ENTRY ET AL.
Siuslaw National Forest origin (Copes 1981) were rooted at the
USDA Pacific Northwest Forestry Sciences Laboratory, Corvallis,
Oreg., using propagation procedures described in Copes (1970).
Cuttings were taken from 23- to 26-year-old trees. In October
1989, cuttings were transplanted into 500-mL potting contain­
ers containing equal volumes of perlite, vermiculite, and peat
moss. Cuttings were grown in a temperature controlled green­
house for 20 months (October 1989 to June 1991) and watered
daily. Average photon flux density at summer maximum (measured
2
June 23, 1987, from 11:00-17:00) was 700 11mol·rn- ·s-1, and
average day:night temperatures were 24:23°C. Cuttings were
fertilized quarterly with Arnon's solution (Arnon and Hoagland
1940). At potting, the seedlings were inoculated with P. weirii as
described below.
Study design
The study was arranged in a split-plot factorial design. Main
plots were graft-compatible and graft-incompatible clones.
Subplots were P. menziesii clones and P. weirii isolates. A total
of 240 cuttings included 210 cuttings inoculated with P. weirii plus
30 uninoculated controls. There were 115 cuttings in each main
plot treatment. Each of the 10 P. menziesii clones was inoculated
separately with each of the three P. weirii isolates and replicated
seven times. There was one control for each P. menziesii clone X
P. weirii isolate, e.g., three control inoculations per clone.
Inoculation of cuttings
Three P. weirii isolates were grown on 3% malt agar. Isolates
MPTR and WC5 were donated by Everett M. Hansen, Department
of Botany, Oregon State University, Corvallis, and were isolated
by Pete Angwin (Angwin 1989). Isolate MP l was obtained from
Earl Nelson, Pacific Northwest Research Station, Corvallis,
Oreg., and was isolated from a P. weirii infected stump on Mary's
Peak, Oregon.
Ten blocks of Alnus rubra Bong., 3 em in diameter X 10 em
long, were washed, and placed in each 0.89-L container with
50 mL of malt extract broth medium. The blocks and broth
medium were autoclaved at 123°C for 60 min at 140 kPa and
left to cool. Three 20 rom diameter fungal plugs from 3% malt
agar colonized by one of the P. weirii isolates were placed on each
block (30 in each 0.89-L. container) of A. mbra under a laminar
flow hood. Blocks were incubated for 6 months. All blocks used
for inoculation were well colonized by P. weirii.
Inoculation procedures followed the method described by
Hansen (1986). A. P. weirii colonized block was fastened with
two 0.5 em wide rubber bands to the primary root of each cut­
ting. Uncolonized A. mbra blocks were attached in similar fash­
ion to the primary roots of the controls. Care was taken not to
wound roots.
Twenty months after inoculation, cuttings were removed from
the containers and roots carefully washed with tap water and
then distilled water. Root sections from five roots, approximately
2.5 em long, were excised from each cutting and surface disin­
fected by immersion in 3% Hz02 for 10 min and in LpH (Vestal
Laboratories, St. Louis, Mo.) for I 0 min. The root sections were
placed on Goldfarb's medium (Goldfarb 1986) in separate 60-mL
test tubes.· Inoculum blocks were split in half and assayed for
P. weirii using the same procedure described above. Phellinus
weirii was recovered from each inoculum block after immer­
sion in 3% H202 for 10 min and for 10 min in LpH, then placed
in Goldfarb's medium in test tubes. Identification of P. weirii
was confirmed by the presence of setal hyphae.
Each cutting was rated by (i) infection rating and (ii) infection
percentage (percentage of roots infected). Infection ratings were
scored as 0, living and uninfected; 1, living and infected; and
2, dead and infected. Infection percentage was scored as 1, infected
or 0, uninfected. A cutting was considered infected if P. weirii was
successfully recovered frorn root tissue in test tubes. Infection per­
centage was computed from the number of cuttings infected with
P. weirii divided by the total number of cuttings.
TABLE I. Comparison of Phellinus weirii inoculated cuttings
of graft-compatible and graft-incompatible 32-month-old
P. menziesii clones and controls for root, shoot, and total
biomass and shoot/root ratio
Biomass (g dry weight/
Graft compatibility
Shoot
Root
Total
Shoot/root
Inoculated
Graft compatible
Graft incompatible
2.28a
1.48b
1.90a
! .23b
4.18a
2.68b
1.23a
1.18a
Uninoculated controls
Graft compatible
Graft incompatible
2.42a
I.52b
2.06a
1.3 l b
4.48a
2.83b
1.17a
1.16a
Nam:
In each column, values followed by the same letter are not significantly dif­
ferent (p >
0.05)
as determined by Fisher's protected least significant difference test.
Biomass analysis
At harvest, all cuttings were dried at 80°C for 48 h. After
reisolation procedures, oven-dry weights of each root and shoot
were recorded separately and then added to determine total dry
weight of each tree. Shoot/root ratios were calculated by divid­
ing shoot dry weight by root dry weight.
Fresh secondary root tissue of uninoculated control cuttings
of each P. menziesii clone was dried at 70°C for 48 h and ground
to <I rnm mesh. A 0.2-g subsample was used for carbon frac­
tionation analysis following the method of McClaugherty et a!.
(1985) and Ryan et a!. (1990). Soluble waxes, fats, and oils were
removed using a series of dichloromethane washes (Technical
Association of the Pulp and Paper Industry 1976), and water­
soluble phenolics were removed with hot water (Technical Asso­
ciation of the Pulp and Paper Industry 1981). Cellulose and
lignin were determined using the methods described in Effland
(1977) and measured using the Polin-Denis procedure (Allen
et a!. 1974). Hot water extractable tannins were measured using
methods described by Allen et a!. (1974).
Statistical analysis
All data, except that for infection percentages, were normally
distributed. Log transformations of infection ratings and infection
percentage were performed to normalize data. Data were sub­
jected to analysis of variance for split-plot factorial experiments
(SAS Institute Inc. 1982). Residuals were equally distributed
with constant variance. Contrasts on preplanned comparisons
among individual treatment means were computed with Fisher's
protected least significant difference (LSD) test at p :<:; 0.05.
Because ANOVAs for all data did not indicate significance in
the interactions of graft compatibility X P. menziesii clone X
P. weirii isolate, P. weirii X graft compatibility, or P. weirii X
P. menziesii clone, only differences between graft-compatible
and graft-incompatible cuttings will be discussed (Snedecor and
Cochran 1980; Steel and Torrie 1980). All means are presented
in the text as untransformed numbers. Correlations from regres­
sion by least squares were analyzed using P. weirii infection
rating or infection percentage as they (dependent) variables and
root biochemical parameters as the x (independent) variables
based on 21 replicates.
Results
Twenty months after inoculation, shoot, root, and total
biomass were significantly
(p
<
0.05) greater in graft­
compatible than graft-incompatible cuttings (Table 1). How­
ever, there was no significant difference in shoot, root, total
biomass, and shoot/root ratios between
P. weirii inoculated
cuttings and controls (of either graft type).
Cellulose concentrations were higher in secondary root
tissue of graft-incompatible than graft-compatible cuttings
880
CAN. J. F OR.
RES.
VOL. 24, 1994
TABLE 2. Biochemical analyses of secondary roots of uninoculated graft-compatible and
graft-incompatible P. menziesii cuttings
Graft compatibility
Cellulose"
Lignin"
Phenolicsb
Tanninsc
Cellulose/
lignin"
Graft compatible
Graft incompatible
32.58b
45.63a
37.07a
31.69b
20.69a
12.5Gb
0.50a
0.38b
0.88b
1.43a
Nom: In each column, values followed by the same letter are not significantly different
protected least significant difference test.
(p
>
Cellulose/
phen )ic"
1.57b 3.65a 0.05) as detennined by Fisher's
"Percent dry weight of root tissue.
6Equivalent phenol units per gram root tissue.
''Equivalent tannin units per gram root tissue.
"Percent cellulose per gram root tissue I percent lignin per gram root tissue,
'Percent cellulose per gram root tissue I equivalent phenol units per gram root tissue.
TABLE 3. Infection of 32-month-old graft-compatible and graft­
incompatible P. menziesii cuttings 20 months after inoculation
with three separate P. weirii isolates
Graft compatibility
Infection
percentage
Mean
infection
rating
Percentage of
trees living
Graft compatible
Graft incompatible
39b
74a
0.76b
1.47a
63a 36b NoTE: All interactions of the variables and P. weirii isolate were not significant
in the ANOVA (p > 0.05). Graft compatibility was the only significant variable. In each
column, values followed by the same letter are not significantly different as detcmlined
by Fisher's protected least significant difference test
(p
>
0.05).
whereas concentrations of lignin, phenolic compounds, and
tannins were lower (Table
2). The lignin/cellulose and phenolic/
cellulose ratios were higher in secondary root tissue of graft­
compatible than graft-incompatible cuttings.
Twenty months after inoculation, both infection percent­
TABLE 4. Coefficients of determination (r2)
of infection percentage and infection rating
by P. weirii with biochemical parameters
measured in root tissue of 32-month - o l d
cuttings f r o m graft-compatible a n d graftincompatible P. menziesii (n = 21)
Parameter
Infection
percentage
Infection
rating
Cellulose
Lignin
Phenolics
Tannins
Lignin/cellulose
Phenolic/cellulose
Tannin/cellulose
Root biomass
Total biomass
0.84*
0.75
0.73*
0.21
0.76*
0.83*
0.46
0.03
0.04
0.84*
0.84
0.73*
0.20
0.82*
0.77*
0.45
O.G3
0.05
•Indicates significance nt
0.001.
age and infection rating were higher in the graft-incompatible
cuttings. A significantly greater percentage (p $ 0.05) of
graft-compatible cuttings tested survived (Table 3). For the
10 clones, there was no correlation between infection per­
phenolic ratios were lower in the more resistant graft­
compatible cuttings, indicating proportionally less substrate
centage or infection ratings and root, shoot, or total biomass.
more carbon allocated to tree defense as lignin, phenolics, and
pounds in secondary toot tissue of P. men zies ii cuttings
The concentration of cellulose, lignin, and phenolic com­
tannins. The cellulose/lignin and cellulose/phenolic ratio
correlated linearly with the percentage of trees infected and
were linearly correlated with infection percentage and with
the infection rating (Table 4). The concentration of cellu­
the infection ratings. Several studies have found that lignin
can only be metabolized when an alternate carbon source
lose was positively correlated and phenolic compounds and
such as cellulose, hemicellulose, or sugars is present (Kirk
et a!. 1976; Ulmer et a!. 1983; Leatham 1986; Otjen and
Blanchette 1985; Leisola et a!. 1983).
lignin were negatively correlated. Lignin/cellulose and
phenolic/cellulose ratios were negatively correlated with
both infection rating and infection percentage (Table
4).
Discussion
Thirty-two months after rooting, the graft-compatible cut­
(cellulose) available for fungal metabolism and growth and
These results indicate that infection may be related to the
amount of energy available from the cometabo!ized sub­
strate (cellulose) in relation to host defense compounds
(lignin and phenolics). If infection is to occur, P. weirii
tings were larger than graft-incompatible cuttings. The infec­
must grow from the inoculum block and colonize the host
tion percentage and the infection rating were higher in the
root. The energy base (inoculum block) was the same for
smaller, graft-incompatible cuttings. This may be related to
size. However, when analyzed across all data, root or total
biomass did not correlate with P. weirii infection percentage
cellulose and phenolics/cellulose were related to P. weirii
of the infection rating (Table
4), indicating that seedling
all inoculations, suggesting the concentrations of lignin/
infection. Entry et al. ( 199 1) found that Armillaria ostoyae
(Romagn.) Herink infection was related to the ratios of
size was not a significant factor in P. weirii infection.
The concentration of cellulose, an energy source most
energy from sugars : energy required for lignin degrada­
1988; Kirk
infection. Graft-incompatible cuttings may allocate more
fungi require to degrade lignin (Blanchette et al.
and Farrell
1987), was higher in the more infected graft­
incompatible cuttings. The concentrations of tree defense
tion. Similar energy relationships may also influence P. weirii
carbon to cellulose and less carbon to the shikimic acid
compounds, such as lignin, phenolics, and tannins (Vance
et a!. 1980), were higher in the more resistant graft­
pathway that produces defense compounds such as phenolics
and lignin. The relationship between lignin/cellulose and
phenolic/cellulose and P. weirii is linear. The correlation
compatible cuttings. The cellulose/lignin and cellulose/
between phenolic/sugar and lignin/sugar in root bark tissue
ENTRY ET AL. and A.
ostoyae infection was also linear (Entry et al. 1992).
Although more work is necessary, the lignin/cellulose and
phenolic/cellulose ratios in roots may be useful measure­
ments to predict the susceptibility of trees to infection by
P. weirii. Presently, there is no method of measuring tree
susceptibility to P. weirii attack, other than susceptibility
ratings among various western conifers (Hadfield 1985;
Hadfield et al. 1986). The phenolic/cellulose an d lignin/
cellulose ratios may provide dependable parameters of
host resistance to P. weirii.
One objective of this study was to determine if g r af t ­
incompatible P. menziesii clones were more resistant to
P. w eirii than graft-compatible clones. Surprisingly, study
results indicated that the reverse was true. Clones with the
lowest ability to form compatible grafts with other P. men­
ziesii types were the least able to resist P. weirii attack. The
process responsible for graft r ejec tion apparently is not the
same for regulating P. weirii resista nce . Graft-compatibility
status may become a criterion for evaluating P. weirii resis­
tance to P. menziesii.
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