AN ABSTRACT OF THE THESIS OF
Danai Boonyakiat
in
for the degree of
Horticulture
Title:
Master of Science
presented on j
July 16, 1980.
Factors Affecting Storage of Yellow Globe Danvers Onions:
Abscisic Acid During Maturation and Storage and Phenolic
Substances Inhibitory to Botrytis allii and Botrytis cinerea
Abstract approved:
_
n
f
.
Daryl G. Richardson
;
Free abscisic acid (ABA) in Yellow Globe Danvers onion tissues was
determined during maturation and storage.
The amount of ABA in leaf
tissue reached a maximum (1.81 ng/gm dry weight) at 40% top fall.
Neck
tissue ABA reached a maximum (0.33 ng/gm dry weight) at 60-70% top fall.
ABA of bulb tissue slightly increased during maturation, then declined
and remained steady (0.21 ng/gm dry weight) during storage with a slight
increase again after 5 month storage.
onion bulbs began to sprout.
Bulb tissue ABA decreased when
Some preliminary data indicates that bulb
ABA concentration may be positively related to respiration rate.
A
study of phenolic constituents in bulb inner and dry outer scales,
found that major phenolics are quercetin 0 and 26,750 yg/gm dry weight;
chlorogenic acid 416.7 and 937.5 yg/gm dry weight; catechin 458.3 and
812.5 yg/gm dry weight; catechol 41.7 and 312.5 yg/gm dry weight;
caffeic acid 141.7 and 62.5 yg/gm dry weight; and arbutin trace and
absent in inner scale and outer scale, respectively.
Mycelial growth and spore germination of ji. allii and B^. cinerea
::were inhibited by catechol concentration above 50 ug/1.
The mechanism
of inhibition appears to be different in the two species of Botrytis.
Preliminary study on bulb weight loss at 3 different storage temperatures: 0°, 10° and 20oC showed that weight loss was 3, 5 and 10%,
respectively, after 6 months storage.
Onions with dry outer scales
removed developed new dry outer scales in 4 weeks at room temperature,
and room temperature with air circulation.
Factors Affecting Storage of Yellow Globe Danvers Onion:
Abscisic Acid During Maturation and Storage
and Phenolic Substances Inhibitory to
Botrytis allii and Botfytis cinerea
by
Danai Boonyakiat
A THESIS
submitted to
Oregon State University
in partial fulfillment of
the requirements for the
degree of
Master of Science
Completed July 16, 1980
Commencement June 1981
APPROVED:
Associate^rofessor of Horticulture in charge of major
v v "jr v
Head of Department of Horticulture
Dean of Graduate School
AJ-
Date thesis is presented
July 16, 1980
Typed by Larky Hansen for
Danai Boonyakiat
ACKNOWLEDGMENTS
I would like to extend thanks to Dr. Daryl G. Richardson and Dr.
Mary Powelson for their aid and guidance throughout my program and to
Carol Standley for her very competent technical assistance.
I would
like to extend special thanks to the Anandhamahidol Foundation for
support during my graduate program.
TABLE OF CONTENTS
I.
II.
III.
IV.
V.
VI.
VII.
Introduction
1
Literature Review
2
Free Abscisic Acid Concentration in Onion Tissues
During Maturation and Storage: Abscisic Acid and
Respiration Rate
16
Materials and Methods
17
Results and Discussion
21
A Simple Method for Characterization and Quantitation
of Onion Phenolic Compounds
26
Materials and Methods
28
Results and Discussion
30
Effect of Catechol on Mycelial Growth and Spore
Germination of Botrytis allii and jB. cinerea
3A
Literature Review
35
Materials and Methods
37
Results and Discussion
39
Effect of Storage Temperatures on Monthly and Cumulative Weight Loss of Onion
51
Dry Outer Scale Regeneration
57
Bibliography
59
Appendix
71
LIST OF FIGURES
Figure
1
2
3
Percentage sprouting and hormonal changes of onion bulbs
cultivar Rijnsburger.stored at 5-80C
12a
ABA concentration in Yellow Globe Danvers onion tissues
during maturation and storage
24a
A.
Regression line of respiration rate and ABA concentration of eight onionrvarieties
25a
Regression line of respiration rate and ABA concentration of five onion varieties
25a
Peak area weight relative to individual phenolic standards
at various concentrations
33a
Spore germination of Botrytis allii over time at 20 C
relative to catechol concentration in the medium
47a
Spore germination of B^. cinefea over time at 20 C
relative to catechol concentration in the medium
48a
Colony diameter of B^. allii (after 4 days) and j5.
ciherea (after 2 days) incubated at 20oC relative to
catechol concentration in the medium
49a
Cumulative percent weight loss during 6 months storage
of Yellow Globe Danvers onions
54a
Percent weight loss per month during 6 months storage
of Yellow Globe Danvers onions
55a
B.
4
5
6
7
8
9
Page
LIST OF TABLES
Table
1
2
3
4
5
6
Page
Comparison of respiration rate and ABA.concentration of
eight onion varieties after 1 month storage at 0oC
23
Rf values of authentic standards and the major phenolic
compounds in onion scales
29
The concentrations of extractable phenolic compounds in
onion inner and outer scale tissues
32
The effect of catechol concentration on percent of spore
germination of B^. allii after 15 hrs and IS. ciherea
after 8 hrs incubation at 20oC
44
The effect of catechol concentration on colony diameter
of B^. allii and 15. cinerea after 4 and 2 days, respectively, incubated at 20oC
45
Slope of regression line for different concentrations of
catechol and B^. allii and B^. cinerea spore germination
46
LIST OF APPENDICES
Appendix
Page
1
Flow diagram for free ABA extraction from onion tissue
71
2
Free ABA concentration in onion tissues during maturation and storage
72
Comparison of respiration rate of eight onion varieties
after 8 months storage at 0oC
73
ABA concentration and respiration rate of eight onion
varities after 1 month storage at 0oC
74
IR spectrum of unknown phenolic with Rf = 0.86 in BAW
and Rf = 0.74 in 2% acetic acid
75
3
4
5
6
7
A.
Unknown
B.
Protocatechuic acid
C.
Catechol
D.
Catechol sample
Chemical structures of major phenolics constituents of
Yellow Globe Danvers onion
76
Comparison of respiration rate of eight onion varieties
after 8 months storage at 0oC
78
Factors Affecting Storage of Yellow Globe Danvers Onion:
Abscisic Acid During Maturation and Storage
and Phenolic Substances Inhibitory to
Botrytis allii and Botrytis cinerea
INTRODUCTION
The serious problems for storage onions are sprouting and storage
diseases.
Sprouting reduces onion storage life and diseases cause
substantial storage losses for the growers.
These studies examine the
conditions that may help control onion sprouting and neck rot disease.
Abscisic acid (ABA) may be involved in controlling sprouting and
catechol, a plant phenolic compound, may inhibit growth of neck rot
fungus.
These studies characterize:
ABA concentration in onion
tissues during maturation and storage; 8 onion varieties with respect
to ABA content, sprout elongation, and respiration rate; the effect of
storage temperatures on weight loss; a preliminary experiment on dry
outer scale regeneration; individual quantities of the major phenolic
concentrations in onion inner and dry outer scales; and finally, the
effect of catechol on radial growth and spore germination of Botrytis
allii (onion neck rot fungus) and Botrytis cinerea (grey mold fungus).
LITERATURE REVIEW
Onion (Allium cepa L.) is an economically important crop throughout much of the world (47, 48).
lily family (Liliaceae) (47) .
The genus Allium is placed in the
The onion has a complex life cycle.
It
is generally a biennial, although some forms, such as the tree onions
are perennials (48).
Growth in the first year is normally vegetative
with a day-length induced bulb formation (6, 47).
day and short-day types.
There are both long-
The Yellow Globe Danvers and Sweet Spanish
varieties grown in Oregon are long-day types.
In the second year,
flower production is stimulated by environmental factors.
When these
are favorable, the shoot apex ceases to produce leaf primordia and
initiates the inflorescence (6, 7, 47).
The onset of bulbing is controlled by conditions of day-length
and temperature and characterized by a rapid elongation of leaves
due to an extension of the neck region of the sheath.
When the leaf
sheaths are swollen as a result of cell expansion rather than cell
division, new.leaf blades cea.se to form.
to swell to form storage tissue (6, 7).
The scale leaves continue
At the center of the bulb,
the last 5-6 leaves are initials during the growing season and will
renew growth as shoot sprouts after the resting period has ended in
storage or as overwintering bulbs (47).
As bulbing progresses, leaf
blades cease to emerge and the older leaves begin to become senescent
from the tip downwards.
Maturation is characterized by a loss of
turgidity in the upper part of the sheath causing the top to fall down
while still green due to softening of the neck region.
Older leaf
blades and roots die off as maturity progresses (1, 6, 7, 47, 48, 88).
A.
Varieties.
There are two general types of onions grown in the United States
as
dry bulbs, the pungent type and the mild type.
inantly long day types.
class:
Both are predom-
Four distinct colors are recognized in each
red, white, yellow and brown (47, 48, 88).
The pungent type
can store longer than the mild type (45).
B.
Chemical constituents.
Onion bulbs consist of a number of carbohydrates in the dry matter,
protein constitutes 1.4% and fat 0.2%.
In 100 gm of raw bulb tissues
there were 50 international units of vitamin A, 0.03 gm of thiamine,
0.04 mg of riboflavin, 0.02 mg of niacin, and 9.0 mg of ascorbic acid
(47).
A characteristic of most members of Allium sp. is their onion or
allinaceous odor which is attributable to organic sulphur compounds
(47).
Volatile compounds that impart the flavour and odor of Allium spp
arise from odorless precursors (S-alkenyl-L-cysteine sulphoxides) which
yield equimolar quantities of thiopropanol-S-oxide, pyruvate and
ammonia.
Thiopropanol-S-oxide is the lachrymatory (tear-inducing)
factor of fresh onions.
This breaks down rapidly in the cut or bruised
tissue to yield a mixture of volatile disulphides and thiosulphonates
that are responsible for odor and flavour.
The concentration of
flavour components in onions is increased by subjecting the growing
plants to water stress and can be reduced by growth in sulphur deficient
conditions (6, 7).
It is interesting to note that these compounds
which are responsible for allinaceous odors and flavours are formed only
4
after the onion has been cut or injured.
Heating and freeze-drying,
which destroy or suppress enzymatic changes, reduce the formation of
onion odor (47).
C.
Curing.
The objectives of curing onions are to encouraged the development
of natural dormancy, seal the neck and outer scales to prevent diseases
and to form intact dry outer scales to reduce the respiration rate of
bulbs (47, 85, 91, 98).
A properly cured onion has a dried shrunken
neck and several intact dry outer scales.
The weight loss during the
curing period should not normally be more than 5%.
The curing period
normally takes about 6-14 days under natural conditions (66).
the curing period the scale color is developed (42).
During
The scale color
of onions after harvest is affected by temperature and humidity during
the curing period.
The optimum tempefature for artificial curing is
about 240-320C for 2-3 weeks with relative humidity about 50-70%
(42, 47).
The curing period is very important for long storage and
long distance shipping.
Field curing can be accomplished when the
production area is not subjected to rainfall in the harvest period
(91).
After onions have been lifted, onions lie in windrows 10 days
or longer until the tops are quite dry (46, 47, 98).
The dry outer
scales contain natural sprout inhibitors that are necessary for extended storage periods (98).
Onions that were not cured before storage
had increased neck rot during the storage period (91).
Onions cured
with tops intact generally lose water from the neck and foliage more
rapidly than those that are topped at lifting (61).
D.
Storage.
The storability of onion bulbs is limited by weight loss, storage
diseases and sprouting (1).
Once curing is accomplished, optimum
temperature for storage of onions is at or near 0 C and RH between
60-70%.
If relative humidity rises above 80% root growth is promoted
and decay may also increase.
Storage temperatures about 10-15 C
increase sprouting by accelerating the breaking of dormancy (1, 42, 46)
Under storage conditions onions lose water and dry matter and serious
losses due to storage rots, sprouting and rooting can occur (46, 47).
There are many kinds of storage but the most common methods are bulk
storage and pallet box storage (66) ..
Ventilation is very important in
storage of onions, since ventilation removes heat and moisture which
are by-products of respiration and transpiration (85).
Onions which
were overmature or were excessively dried in storage caused larger
numbers of green "peeler" onions, loose scales, and are variable in
color.
tion.
This problem is prevented by proper management of air circulaIf air circulation is inadequate to remove moisture and to re-
duce temperature from respiration the entire lot of onions may be lost
due to sprouting and rots (44).
Respiration rate declines immediately after harvest.
Respiration
rates of dormant onion bulbs are very low compared with those of other
stored vegetables and fruit.
Carbon dioxide evolution measured on the
same apparatus at 10 C was 8 mg (XL kg
and 34 mg CO
kg
hr
hr
for onion and 18, 31
for stored beet root, carrot and cauliflower
heads respectively (87, 98).
Respiration rates slowly increase as the
bulbs remain in storage and begin to sprout (99).
But even though the
6
respiration rate of onion bulbs is much lower than that of most vegetable crops, the loss of dry matter can be important, because onions
are often stored for long periods (47, 99).
relative weight loss due to CO
(See calculations of
and moisture loss p. 52 ).
Factors affecting dormancy and storage life.
1.
Genetic factors:
Onions of the globe type are noted for greatest storability while
the Bermuda type can be stored only for a period of 1 to 2 months.
The Spanish types appear intermediate in storage potential (47, 62, 88).
There is a positive correlation between the length of the growing season and length of storage life in the comparison of cultivars.
Char-
acteristics which vary among cultivars have been shown to influence
storability include differences in dry matter content, growth inhibitor
content, rate of respiration, rate of moisture loss, outer scale quality and rate of maturation (6, 86, 102).
Cultivars containing higher dry matter can store longer than those
with low dry matter.
This may be related to metabolic substrate
reserves (6, 7, 29, 73).
A low rate of respiration reflects high storage potential (80, 81).
Ward and Tucker (99, 100) have suggested that the low respiration rate
of dormant bulbs and the very small rise in respiration observed with
increasing temerpatures may indicate that respiration is controlled by
the dormancy system.
Cultivars that have good quality of dried outer scales can be
stored longer.
Quality of dried outer scales refers to the number.
7
thickness, color and completeness of the scales.
Intact dried outer
scales reduce respiratory gas exchange and also reduce moisture loss
from the bulb.
Intact scales also prevent infection by pathogens (6,
47).
2.
Conditions during the growing season:
Onion storage behavior is affected by the conditions under which
the crop is grown.
Onions that are grown on soils with high organic
matter have poorer keeping quality than those grown on lower organic
matter soils.
This loss of keeping quality is thought to be due to
the effects of organic soils in delaying bulb maturation through the
retention of both nitrogen and soil moisture (31, 33).
Drinkwater,
et al. (26) found non-irrigated onions matured faster than onions receiving heavy and frequent irrigation.
However weight loss during
storage was greater in non-irrigated onions than in onions from irrigated treatments.
The effect of various levels of N and K on keeping
quality is not clear'.
However applications of N without K tend to
decrease the keeping quality (53).
Increasing rates of P fertiliza-
tion increased number and thickness of dried outer scales of onion,
which should improve storage life.
good scale quality (52).
Copper is essential for color and
Leaf diseases, premature topping, and prema-
ture desiccation may increase decay, shorten dormancy and storage life.
Bulbs grown under shaded conditions sprouted sooner than onions grown
under full light (6, 7).
Topping generally resulted in physiological
shrinkage and generally more rot loss and total loss.
Topping flush
with the bulbs usually resulted in an increased shrivelling of the
8
bulbs but rotting was generally less than for bulbs receiving topping
with longer residual stems (38)•
3.
Storage temperature and humidity:
The most influential storage factor is temperature.
The ideal
temperature of onion storage is about 0 C or near 0 C with 60-70%
relative humidity (66).
Both low temperatures (0-2.5 C) and high
temperatures (25-30 C) have been found to extend dormancy and storage
life (7, 64, 63).
Bulbs from the lower storage temperatures had the
lowest weight loss and generally a more desirable appearance (104).
Dormancy disappears most rapidly at temperatures in the range 10-12 C
(7, 64).
Onion bulbs stored at 0 C or 30 C had rates of leaf initia-
tion about half that observed for storage at 15 C.
slowest at 0
storage at 10
Sprouts emerged
and 30 C whereas most rapid emergence occurred after
and 15 C (1).
Because the rate of respiration rises
with increasing temperature a lower storage temperature is generally
more desirable due to slower consumption of stored metabolites and reduced loss of moisture (90).
Storage temperatures also affect seed
production for the following growing season.
onions stored at 7.5
Jones (46) found that
and 11-12 C were the earliest to produce seed
stems and also the first to bloom when compared with other temperatures.
than 7.5
stalks.
Mother bulbs stored at either higher or lower1 temperatures
and 11-12 C produced many vegetative bulbs and few seed
Storage of onions at a temperature near the freezing point,
but which does not freeze the bulbs, reduced the losses from growth
and decay during storage (12).
Temperatures in the range 0-20 C show onion (cultivar 'Rijnsburger') respiration rate to be linearly related to temperature, the mean
increase of respiration rate is 0.55 mg CO
kg
Relative humidity should be held between 65-75%.
humidity encourages root growth and decay.
hr
C
(96, 97).
Too high relative
On the other hand with
relative humidity lower than 50%, the bulbs become too dry and dry
outer scales shed, leaving the edible scales exposed to environment
(80, 101).
Air circulation must be sufficient to prevent heat accumulation in
the onions and to remove moisture from within piles, bins or sacks.
Air circulation about 2 cfm of air per cubic foot of onion at 1 1/4
inches of static pressure is sufficient for curing.
After curing,
1 cfm of air per cubic foot of onions is recommended for storage
ventilation and circulation (66).
The usefulness of CA storage for onions is still questionable.
On balance 5% CO
and 5% 0
seems capable of reducing losses from
sprouting, root growth and other disorders.
But increasing the CO
to 10% induces a disorder that resembles the translucent scale defect
(81).
4.
Growth Regulators:
In recent years many growth substances have been used to prevent
or delay sprouting in stored onions.
Pre-harvest application of
maleic hydrazide, properly applied in the field is the most effective
method of preventing sprouting in stored onions (43, 44, 45, 47).
method of using maleic hydrazide is to apply 2-3 lbs/acre when the
The
10
plant is nearly mature and tops begin to fall but are still green
(47).
Application of maleic hydrazide is usually 10-14 days before
normal lifting.
Overmature bulbs in the field or bulbs cured before
applying maleic hydrazide did not respond to maleic hydrazide very
well (41, 43, 44).
Maleic hydrazide treated onions did not have normal
mitotic cell division, the cells enlarged without cell division although many prominent nuclei were observed.
When untreated onions
were sprouting, treated onions were beginning to show cell enlargement
at the apex (44).
In maleic hydrazide treated bulbs, endogesnous growth promoters
remained at low levels and inhibitors persisted at a high level
longer than in untreated bulbs (44).
Regrowth in untreated bulbs was
characterized by formation of sheath and leaf initials and rapid cell
division.
All growth promoters were at high levels of activity and
inhibitors were absent.
But maleic hydrazide treated bulb tissues
did not develop into organs.
Growth promoting activities were at low
levels, while inhibitor activity was still high (13, 87).
Injection with 1 ml of 100 ppm maleic hydrazide during bulb formation prevented sprouting and the effect could not be reversed by
injection of equal quantities of IAA, GA or kinetin (44, 87).
The application of maleic hydrazide will reduce or prevent sprouting in most varieties, but it will not make a poor keeping variety equal
to a good keeping variety (45).
Onions go into a rest period during the fall and early winter.
During the rest period, onions will not respond to rapid changes of
environment.
Onions treated with maleic hydrazide go into the normal
11
rest period but do not come out of it.
When onions have completed
the rest period, they enter the dormant period.
This dormancy is the
physiologic internal type; during this dormancy onion bulbs will respond to changes of environment, slowly in the early dormancy and
rapidly as dormancy is lost.
In early dormancy for most storage
varieties, the shoot sprout will be found in the lower half of the
bulb.
And in late dormancy onion shoot sprouts extend into the upper
two thirds of the bulbs, the basal plate is swollen and the scales
around the base are cracked.
When cut transversely the basal plate
shows several conspicuous rings of tan to dark brown root primordia.
In the case of onions properly treated with maleic hydrazide these
characteristics are not apparent (7, 43, 44).
Maleic hydrazide prolongs dormancy by effects on nucleic acid
synthesis and cell division rather than by a direct effect on the level
of natural growth inhibitors and growth promoters in the bulb (7).
The
effects of maleic hydrazide were not overcome by application of auxin,
gibberellin or kinetin or their combination (2).
Maleic hydrazide does not, however, inhibit all expansion as
onions treated with 0, 0.33, 0.67, and 1.0 gallon maleic hydrazide per
acre at 10%, 25%, 50% and 75% top fall stages all had the same yield
and bulb size distribution (Richardson 1978 unpublished data).
Dormancy and sprouting are under control of the balance between
endogenous growth inhibitors and promoters.
Growth inhibitors are pro-
duced in the leaves and then translocated into the bulb during maturation.
Early removal of thn leaves prior to harvest or early chemical
(desiccation) of leaves can shorten the dormancy period (7, 15, 24).
12
In the resting stage, growth inhibitors were shown (Figure 1) to
be present in the study by Thomas and Isenberg (87).
In the dormancy
stage inhibitors decreased gradually until the onset of sprouting.
Auxin and gibberellins increased around the beginning of the sprouting
period, but auxin activity preceded gibberellin.
They suggested that
inhibition was controlled by interactions between natural auxins and
inhibitors but sprout extension may be controlled by natural gibberellin.
Cytokinin activity also increased prior to sprouting.
Cytokinin
may be necessary to stimulate rapid cell division before shoot extension.
It is possible that auxin affects cell permeability enabling
the translocation of food reserves which are necessary for sprout
growth (87).
Long dormant period varieties contain higher amounts of inhibitor
than short dormant period varieties.
In a study of dormancy of shoot
apices, it was found that kinetin and sucrose were very effective in
promoting growth of shoot apices.
of the excised shoot apices.
1618 but not ABA.
AMO 1618 and ABA can reduce growth
But sucrose overcomes the effect of AMO
Kinetin has slightly counteracted the effect of ABA
and AMO 1618 (63, 64).
Aung and Peterson (7) have shown that both dormant and sprouting
bulbs contain free gibberellin-like substances.
The total gibberellin
of dormant bulbs was greater than that of sprouting bulbs.
This seeming
contradiction was explained by the degrees of onion bulb dormancy lie in
the modes of mobilization and/or utilization patterns of gibberellin by
the bulb in response to external stimuli.
The lesser amount of gibber-
ellin in growth while the converse may be the case with dormant bulbs.
12a
Figure 1.
Hormcnal regulation of onion bulb donnancy
49
Hormone activity
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I-ig. i. Percentage sprouting and hormonal changes of onion bulbs cv. Rijnsburgcr stored at
s-s-c
FROM,
Thomas, T. H. and F. M. Isenberg. Hormone physiology
of. onion tulbs during dormancy. Experimental Horticulture No. 23. (85)
13
Perhaps the high level of bound gibberellin and low level of free
fraction are associated with sprouting while the high level of free
gibberellin and low level of bound are associated with dormancy.
Greater amounts of growth inhibitors can be extracted from late
compared to a medium maturing onion bulbs and this suggests that the
earliness of sprouting in onion may be associated with a decrease in
the concentration of growth inhibitors (50).
Applications of ABA to maturing onions induced early senescence of
the leaves and prolonged the rest period of bulbs.
This effect was
partially overcome with the application of gibberellins, auxins, and
cytokinins, and totally overcome by applying a mixture of the three
hormones (2).
Pre-harvest spray applications of NAA and 2,4,5-T can stimulate
early sprouting in stored bulbs.
The injection of leaf blades during
bulb formation with 1 ml of 100 ppm IAA, GA and kinetin either singly
or together can reduce storage life due to sprouting (2, 7).
In the case of rooting, exogenously applied ABA at 10
inhibits the growth of onion roots.
Concentrations of 10
M or 10
M
M inhibit
90% growth after 48 hours, and 10_ M inhibit 50% of growth after 48
hours (89).
In the cortical area of onion roots between 3-4 mm from
the root tip, roots treated by ABA have smaller cells and are 2.6 times
shorter than untreated ABA roots.
ABA treated cells show that the
thickness of the longitudinal cell wall is greater than the untreated
cell (78).
Levy et al. (56) found that adding ethephon to the growth medium
caused swelling of leaf bases but ethephon also caused retarded leaf
14
growth and a reduction in the final size of bulbs.
Ethephon induced
bulbing of short day, intermediate, and long day onion cultivars under
non-inductive short day conditions (57, 60).
E.
Storage diseases.
Important onion storage diseases are neck rot caused by Botrytis
allii and bacterial soft rot caused by Erwinia carotovora (45).
In-
fected seeds have been shown to be a major source of B^. allii in the
onion crop.
Benomyl applied to seed samples containing 1, 10 and 20%
infection reduced the average neck rot percentage in stored bulbs from
26.2 to 3.8% (67, 68).
Seed dressing of benomyl (applied as a dry pow-
der or as a slurry) virtually eliminated infection from the seeds and
produced crops of healthy onions which remained free of neck rot during
storage (68).
15. cinerea can cause brown stain symptoms on dry outer
scales (22).
Walker (93, 94, 92) indicated that Botrytis spp can cause
serious diseases in storage for onion besides B^. allii such as B_.
squamosa, 1$. cinerea and B^. byssoidea.
Pseudomonas cepacia Burkh.
was described by Burkholder as capable of causing decay of onion bulbs
(94).
tissue.
Kawamoto (49) found that P^. cepacia infected only wounded onion
Irwin (40) described the most prevalent symptom which appeared
in infected plants as a wilting and chlorosis of two or more lower
leaves which is followed closely by appearance of elongated lesions
emerging from the neck and extending up the adaxial side of one or more
young leaves.
Soft rots of onion in Lake Labish area are caused by
P^. cepacia, I\ eichorii and Erwinia spp (40).
Bruising during lifting,
curing and storing onions and failure to cure onions before placing
15
them in storage increased neck rot and other diseases in storage (91).
Fusarium basal rot caused by Fusarium sp is soil borne and is thought to
invade through basal wounds or through old root scars (94).
Walker and
Maude (96) found the occurrence of Gliocladium roseum on mycelia and
sclerotia of ]$. allii and in culture G^. roseum produced substances
inhibitory to the growth of j5. allii.
Storage diseases are incited by prolonged periods of high relative
humidity and presence of water on plant surfaces with high temperature
(47).
16
FREE ABSCISIC ACID CONCENTRATION IN ONION TISSUES
DURING MATURATION AND STORAGE: ABSCISIC ACID AND RESPIRATION RATE
D. Boonyakiat and D. G. Richardson
2
Department of Horticulture, Oregon State University, Corvallis OR 97331.
Additional index words,
Abstract.
dormancy, Allium cepa
Free abscisic acid (ABA) in yellow Globe Danvers onion tis-
sues was determined during maturation and storage.
The amount of ABA
in leaf tissue reached a maximum (1.81 ng/gm dry weight) at 40% top fall
and then declined rapidly.
Neck tissue ABA reached a maximum (0.33
ng/gm dry weight) at 60-70% top fall, then declined as the neck tissues
dried.
ABA of bulb tissue increased to 0.31 ng/gm dry weight at 60-70%
top fall, then declined and remained steady (0.21 ng/gm dry weight)
during storage with a slight increase again after 5 months storage.
Bulb tissue ABA decreased slightly when onion bulbs began to sprout.Some preliminary data indicates that bulb ABA concentration may be
positively related to respiration rate.
The amount of abscisic acid (ABA) in onion tissues during top
fall and storage has riot been fully characterized with respect to dormancy and respiration.
Mahotiere (63) found that 1 he concentration of
inhibitors of onion variety MSU 4535 which is a long dormant period is
higher than "Downing's Yellow Globe" which is an intermediate dormant
Received for publication
, 1980. Oregon Agricultural
Experiment Station Tech. Paper Nb._
. From the M.S. dissertation of the senior author.
2
Graduate Student and Associate Professor of Horticulture, respectively.
17
type.
He indicated the inhibitor resembled abscisic acid (ABA) but
was not ABA itself.
Earlier research (2, 7, 15, 24, 87) referred to
inhibitors (implying ABA) to correspond to dormancy of onion.
Leopold
(55) indicated that ABA was associated with changes in dormancy of buds
and seeds of trees and that ABA could be increased by osmotic stress
and mineral deficiencies.
Thomas and Isenberg (87) found that a
growth inhibitor was present in onions but this decreased gradually
until just before the onset of sprouting.
IAA content increased to a
very high level before the onions showed visible signs of swelling of
the leaf bases, then fell off rapidly after 5-7 days (24).
of IAA increased again before sprouting in storage (86).
The level
It seems that
dormancy is controlled by a balance of ABA levels and other growth
regulators such as IAA, gibberellins and cytokinins (87) rather than
by a single hormone.
The inhibitor in the bulb was later identified as
ABA by Stow (83).
The objectives of these studies are:
to determine the amount of
ABA in onion tissues with respect to dormancy during maturation and
storage, and to compare 8 onion varieties with respect to ABA and
respiration.
Materials and Methods
Extractions of free abscisic acid from freshly harvested Yellow
Globe Danvers leaves, neck and bulb tissues were begun in August 1979.
The method was based on that of Powell et al. (75).
Fresh onion tissue
were frozen and lyophilized in a Virtis Uni-trap model 10-100 freeze
dryer.
Five grams of lyophilized onion tissue was added to 50 ml of
18
methanol and ground at high speed for 2 minutes by Sorval omni-mixer
and the methanol solution was separated from the tissue residue by
suction filtration through Whatman no. 1 filter paper.
The residue
was washed with small amounts of methanol until the rinse was clear.
Radioactive 1-C
14
-cis, cis - ABA 100 pi containing 10
4
dpm dissolved
in ethanol was added as an internal standard.
Powell's method was modified by partitioning against 50 ml of
ethyl acetate 3 times instead of methylene chloride in the final extraction of the acidified (pH 2.5) aqueous phase.
This procedure was
found to be more rapid and to produce higher recoveries of free ABA
in Douglas-fir needles (W. K. Ferrell et_ al., manuscript in preparation) .
The aqueous phase was discarded and the ethyl acetate was taken
to dryness by rotary vacuum evaporator.
The residue was taken up in
2 ml of ethyl acetate and transferred into a small test tube and dried
by a stream of air.
The residue was esterified by adding ether-diazo-
methane generated from Diazald (Aldrich Chemical Co. Inc., Milwaukie,
Wise), dried in an air stream and diluted with 400 yl ethyl acetate.
The methyl esterified ABA was separated and quantitated by injecting
0.5 ul into a 5750 Hewlett-Packard gas chromatograph equipped with a
122 cm x .02 cm glass column charged with 2% Epon Resin 1001 liquid
phase on chromosorb WAW-DMCS 80/100 support (Analabs Inc., 80 Republic
Dr., New Haven, Conn.) with oven at 205 C, injector heater 215 C and
electron capture detector 290 C.
Nitrogen carrier gas flow was 25 ml/
min.
Extraction losses were monitored by the recovery of internal
standard 1-C
14
-cis, cis-ABA.
The methyl esterified ABA and internal
19
standard were then injected (0.5 yl) into the GLC for analysis and the
remainder of the sample was quantitatively transferred (toluene rinse)
to a liquid scintillation vial and 12 ml of 4 gm of Omnifluor in 1000
ml of toluene was added for counting in order to calculate extraction
efficiency.
Percent recovery was calculated by converting cpm (counts
per minute) read by Beckman LS 7500 (Irvine, Ca.) liquid scintillation
counter to dpm (disintegrations per minute) by the formula:
,
dpm =
Then dpm of 1-C
with dpm of 1-C
14
14
cpm x 100
Hr
TT-.—:
counting efficiency
-cis, cis-ABA in the sample extract was compared
-cis, cis-ABA standard added initially.
The respiration rate of onion hybrid XP-H667 was lowest (7.83 mg
C0„ kg
hr
) and significantly different (P_<.05) from the other 7
hybrids and varieties.
There were no significant differences in
respiration rate among XP-H742 Sapporo Yellow Globe, Autumn Beauty,
XP-W207 and XP-H348.
The onion variety Yellow Globe Danvers had the
highest respiration rate but was not significantly different from XPW209, XP-H348, XP-H195 (Table 1).
The concentration of ABA in variety XP-H195 was lowest but there
was no significant difference (P<^05) between XP-H742, Sapporo Yellow
Globe, Autumn Beauty, XP-H667, and Yellow Globe Danvers.
Onion variety
XP-H348 contained the greatest amount of ABA but this level of ABA
was not significantly different from variety XP-H207 (Table 1).
The correlation between the level of ABA in onion bulb and respiration rate was very low (r = -0.02) Fig. 3A.
This data suggests no
relationship between amount of ABA and respiration rates of onion.
20
However, it is very interesting that when the data for XP-H195, Yellow
Globe Danvers and XP-H667 were excluded, the very high ( r = 0.99)
correlation coefficiency for the remaining 5 onion varieties
respira-
tion rate and ABA data indicates (Fig. 3B) that ABA may in fact have a
relationship to respiration rate of onion.
The number of samples
in this study may however, be too small to strongly support such a
conclusion, but the possible involvement is intriguing.
Further study
is clearly needed to elucidate the strength of interaction between ABA
and respiration rate.
Eight varieties of onion were used;
XP-H702 (Sweet Spanish type),
SP-H667 (Danvers type. Sweet Spanish background), XP-H195 (Yellow Globe
Danvers, Ontario Pink root resistance) obtained from Asgrow Seed Company, Autumn Beauty, XP-W207 and XP-H348 obtained from Crookham Seed
Company, Sapporo Yellow Globe obtained from Takii Seed Company and
Yellow Globe Danvers from Salem area.
All of these onions were grown
under the same cultural practices in the same field.
The method for C09 determination in respiration studies followed
the Claypool and Keefer method (25) except a Beckman model 865 Infrared gas analyzer was used to quantify C0_ rather than the methylene
blue dye reduction solution.
Onion bulbs were weighed to about 1 kg
and put in 1 gallon glass jars fitted with flow through tubes, flow
rate was adjusted to 50 ml/min and read daily by flowmeter.
The res-
piration rate of each variety consisted of 9 observations.
Following the respiration studies, onion bulbs were removed from
the jar to determine the ABA content as described previously.
21
Results and Discussion
Based on 1-C
14
-cis, cis-ABA recoveries, the average extraction
efficiency was found to be 75% with a range from 71% to 80%.
The
following ABA results are reported as adjusted values due to the 75%
extraction efficiency.
Adjusted free ABA was calculated by:
adjusted
ABA =
J
jL—
0.75
The concentration of ABA in leaf samples increased dramatically as
onion top fall progressed and ABA reached the highest concentration
(1.81 ng/g dry weight at 50% top fall) (August 30).
ABA concentration
in the leaves then decreased very rapidly after top fall when onion
leaves were senescing but had not yet dried.
Levels of ABA in leaves
thereafter decreased gradually to 0.53 ng/gm dry weight on September
10, 0.22 ng/gm dry weight on September 20, and 0.01 ng/gm dry weight on
October 1.
ABA content in completely dried leaves was very low
(Figure 2).
The ABA concentration in the neck tissue reached its maximum
(0.33 ng/gm dry weight) at 60-70% top fall, then ABA levels decreased
gradually to 0.27 ng/gm dry weight on September 20 and 0.15 ng/gm
dry weight on October 1 (Figure 2).
In onion bulbs the amount of ABA was lowest at the onset of top
fall (0.04 ng/gm dry weight) when compared with ABA concentrations in
leaf and neck tissues.
ABA in the bulbs, increased to 0.31 ng/gm dry
weight at about 60-70% top fall and thereafter decreased to 0.21 ng/gm
dry weight during the curing period and stayed at this level until
November.
Although no radio-tracer experiments were used to confirm
22
movement of ABA to the bulb following the decrease in leaf ABA, there
is the suggestion that there may have been ABA translocation from the
leaves to the bulb.
ABA apparently has very weak effect on dormancy
of onion, perhaps because onion bulbs contain other inhibitors and all
of them may affect dormancy of onion by synergistic effects.
Kato
(50) indicated that onion bulbs also contain a growth inhibitor called
allyl sulphide.
Some plants have phenolic inhibitors such as p-couma-
rin and chlorogenic acid (55).
Bulb tissue ABA reached maximum amount (0.31 ng/gm dry weight)
after leaf ABA was declining and could be explained as ABA translocated
from leaves.
The concentration of free ABA which declined during
storage could be due to free ABA being bound as abscisyl-3-glucopyranoside.
Bound ABA might then be released as free ABA which could
correspond to the second peak in February which declined again as
sprouting occurred.
23
Table 1.
Comparison of respiration rate and ABA concentration of
eight onion varieties after 1 month storage at 0 C.
Respiration rate
ABA7
Varieties
mg of CO /kg/hr
ng/g dry wt.
XP-H667
7.83 a
0..33 b
XP-H742
9.74 b
0,.24 a
'Sapporo Yellow Globe1
9.73 b
0..27 a
'Autumn Beauty'
9.98 b
0..32 b
XP-W207
10.70 be
0..46 c
XP-H348
10.80 be
0,.49 c
XP-H195
11.49 c
0,.23 a
12.55 c
0..25 a
'Yellow Globe Danvers'
Mean separation by Duncan's New Multiple Range Test (P=0.05)values
sharing the same letter are not significantly different.
x: n=9 for respiration rates
y: n=3 for ABA determinations
24
Figure 2.
ABA concentration in Yellow Globe Danvers onion tissues
during maturation and storage.
BULB
• LEAF
o NECK
D
o SPROUT
09
C
H
(0
8/20
8/30
9/10
9/20
10/1
ll/l
DATE
25
Figure 3A.
Regression line of respiration rates and ABA concentrations
of eight onion varieties.
3B.
Regression line of respiration rates and ABA concentrations
of five onion varieties.
25a
13 I*
*
Figure 3A
R«-.02
5cr
a.
CO
UJ
01
UJ
_j
CD
<
9
cr
8
21
1.6
VARIABLE
2
O
36
26
ABA
Figure 3B
12-2
©
R=.99
6
•
£IIS
™"
Q.
CO
UJ
cr
UJ
_i
CD
<
114
5 106
*■
-
-
•
>
•
•
18
.2 2
.2.7
VARIABLE
.32
ABA
.36
26
A SIMPLE METHOD FOR CHARACTERIZATION AND QUANTITATION
OF ONION PHENOLIC COMPOUNDS
D. Boonyakiat and D. G. Richardson
Department of Horticulture, Oregon State University, Corvallis OR 97331.
Additional index words;
caffeic acid, catechin, catechol, chlorogenic
acid, quercetin, fungal inhibitors.
Abstract.
A study of phenolic constituents in onion bulb inner and
dry outer scales was performed by a method combining paper chromatography and Densicord recorder trace to densitometrically measure the
amount of phenolics.
Major phenolic constituents (yg/g dry weight)
found in inner and outer dry scales respectively were quercetin 0 and
26,750, catechin 458 and 812, catechol 41 and 312, caffeic acid 141
and 62, and a minor phenolic (arbutin or quercetin glucoside) trace
and absent.
There has been interest for some time in the possible involvement
of phenolic compounds in mechanisms associated with plant resistance
to fungal pathogens.
Walker's pioneering work (92, 95, 97) on phenolic
compounds relative to onion smudge resistance has attracted some
interest, but there have been few follow-up studies aimed at specific
pehnolic compounds which are found in tissues relative to their effects
on fungal spore germination or hyphal growth.
studied the effect of phenolics:
Clark and Lorbeer (22)
Quercetin, protocatechuic acid and
catechol on mycelial growth and spore germination of Botrytis cinerea
Graduate Student and Associate Professor of Horticulture, respectively. Received for publication
, 1980. Oregon Agriculture Experiment Station Tech. Paper No.
. From
the M.S. dissertation of the senior author.
27
and
Colletotrichum circinans.
Pappelis (72) found chlorogenic
acid to be fungistatic for 13. allii.
A preliminary study (C.E. Bubl, unpublished research notes) indicated
qualitative differences in chlorogenic acid, catechol and quercetin
with respect to their inhibitory activities on 15. allii mycelial
growth.
Although no concentrations were specified, quercetin was not
inhibitory, whereas chlorogenic acid was progressively inhibitory comparing a low and a high concentration, and catechol had a very strong
inhibition at the single concentration used.
It was decided therefore
to attempt to further characterize the concentrations of individual
phenolic constituents which might possess anti-fungal properties.
Although the method described by Anderson and Todd (4) has been
used to quantify total phenols in tobacco tissue by binding to polyvinyl
pyrrollidone (PVP) no information is available as to the quantitative
nature of this technique relative to individual phenolic types, which
are known to exhibit different binding properties with PVP.
Since
chlorogenic acid was used as the standard and quercetin is the major
phenolic in onion dry outer scales, there is a reasonable question as
to whether the PVP binding method gives an accurate estimate of individual phenolic concentrations.
Attempts to elute individual phenolic
compounds from paper for quantitation leads to losses, either from
binding or to differential oxidations.
While there are limitations,
the method is fairly simple, rapid and gives reasonable accuracy provided suitable standards are available.
28
Materials and Methods
Dried outer scales and dried inner scales of stored Yellow Globe
Danvers onion bulb tissue were ground to pass a 40 mesh screen.
One
gram of ground tissues were extracted by enclosing the sample in a
filter paper envelope held by a steel clip and placed in a 50 ml
conical flask containing 20 ml of gently boiling absolute methanol
for 10 minutes.
The envelope containing the sample was transferred
to a Soxhlet apparatus and extracted with additional methanol for 18
hours.
The methanol extracts were combined, concentrated, and adjusted
to 25 ml final volume (18, 19).
Known standards; quercetin, chloro-
genic acid, catechol, catechin, caffeic acid, protocatechuic acid and
arbutin (Sigma Chemical Company, St. Louis, Mo.), and portions of
extract were paper chromatographed on 7.5 x 45 cm Whatman No. 1 in
n-butanol:
acetic acid:
water (BAW) (4:1:2.2 v/v/v) as one elution
system or by 2% acetic acid as a second system.
Spots on chromatograms
were marked under ultraviolet light of 266 nm, before and after spraying
with a visualization reagent according to Bhatia et^ al. (9).
Sprayed
chromatograms were placed in a 70 C hot air oven for 5 minutes and Rf's
of unknown spots were compared to Rf's of standards (Table 2).
An
unknown was tentatively assigned as arbutin based on the identical
chromatographic behavior in two solvent systems compared with authentic
arbutin.
There is the possibility that the compound in question could
also be one or more of the glucosides of quercetin.
Standard concentrations of catechol, catechin, chlorogenic acid
and caffeic acid were spotted on 7.5 cm x 45 cm Whatman No. 1 paper at
29
Table 2.
Rf values of authentic standards and the major phenolic
compounds in onion scales.
2% acetic acid
B A W
1.
Catechin
0.41
0.72
2.
Catechol
0.74
0.91
3.
Chlorogenic ac:id
0.58
0.59
4.
Caffeic acid
0.31
0.74
5.
Quercetin
0.01
0.87
6.
Arbutin
0.86
0.74
30
5, 10, 25, 50, 100 yg.
Four hundred yl extract (equal to 16 mg dry
weight) of inner and dry outer scales of onion were spotted between
the standards.
Phenolic compounds were separated by descending chroma-
tography in 2% acetic acid (18, 19).
Paper chromatograms were sprayed
with Bhatia's visualization reagent (9), then were cut into 23 x 3 cm
strips.
The amount of phenolic compound in each spot was densitome-
trically measured by Densicord recorder trace (Photovolt Corp., New
York City).
The area under the recorder trace peak for each spot was
cut out and weighed as this was proportional to the concentration used.
Standard curves for each phenolic compound were developed from the
relation between weight of area under peak and the concentration applied
(Fig. 4).
The amounts of the individual phenolics in onion samples
were then estimated by comparison to the standard curve for that particular phenolic substance.
Quercetin and onion phenolic extracts were spotted in the same
amount as above but quercetin was separated by descending chromatography
in (BAW) n-butanol, acetic acid, and water (40:10:22 v:v:v).
The con-
centration of quercetin in the onion tissues was estimated by the same
method as above.
Results arid Discussion
The approximate amounts of major phenolics found per gram of onion
dry outer scales are:
quercetin 26,750 yg, chlorogenic acid 937.5 yg,
catechin 812.5 yg, catechol 312.5 yg and caffeic acid 62.5 yg.
The
inner scales of onion contain the approximate amounts of the following
phenolic compounds per gram dry weight:
catechin 458.3 yg, chlorogenic
31
acid 416.7 yg, caffeic acid 141.7 yg and catechol 81.7 yg.
No querce-
tin was detected in the inner scales (Table 3).
Jones (47) indicated that the major phenolic in dry outer scales
of a brown onion was quercetin at about 4% on a dry weight basis.
The
Yellow Globe Danvers variety used here had 2.6% quercetin on a dry
weight basis.
K. P. Link et al. (58, 59) found 0.01% or less of onion
outer scale dry weight was catechol, whereas 0.03% were found for
Yellow Globe Danvers in this study.
Pappelis (72) found chlorogenic
acid synthesis was induced in exposed bulb scales of onions in the
ambient atmosphere at 25 C for 48 hours.
both the exposed and unexposed tissues.
Caffeic acid was present in
He reported 18 mg of chloro-
genic acid per gram fresh weight and this amount was fungistatic for
13. allii.
About 8 mg of caffeic acid was contained per gram fresh
tissue, but this level of caffeic acid stimulated the germination of
B. allii spores.
Clark et al. (22) studied the role of phenolics in
Botrytis brown stain of onion.
They found only catechol inhibited
growth of 15. cinerea and Colletotrichum circihans.
Quercetin had no
effect on these fungi.
The inhibitory effects of catechol concentrations on spore germination and growth of Botrytis allii, and B^. cinerea are described in
Boonyakiat Thesis (10).
The amounts found in this study should be
more than adequate for protection of onions from.neck rot disease.in
storage.
The dried outer scales of onions contain a higher concentra-
tion than inner scales of all phenolic compounds except caffeic acid.
This may explain why the dry outer scales protect the bulb from the invasion of Botrytis spp. and possibly other fungal pathogens.
32
Table 3.
The concentrations of extractable phenolic compounds in
onion inner and outer scale tissues.
outer scale
inner scale
(yg/gm dry wt.)
(yg/gm dry wt.)
1.
Catechin
812.5
458.3
2.
Catechol
312.5
41.7
3.
Chlorogenic acid
937.5
416.7
4.
Caffeic acid
62.5
141.7
5.
Quercetin
6.
Arbutin (on the glycosides of quercetin)
26,750.0
absent
0
trace
33
Figure 4.
Peak area weight relative to individual phenolic standards
at various concentrations.
o CATECHIN
- CAFFEIC ACID
r1
CATECHOL
• CHLOROGENIC
A QUERCETIN
ACID
6"
S.4
<
u
<
a
Q.
.1
0
IO
20
30
40
50
CONCENTRATION
60
70
80
( jjg )
u>
34
EFFECT OF CATECHOL ON MYCELIAL GROWTH AND SPORE GERMINATION
OF BOTRYTIS ALLII AND BOTRYTIS CINEREA1
2
3
4
D. Boonyakiat , M. L. Powelson and D. G. Richardson
Department of Horticulture and Department of Botany and Plant Pathology,
Oregon State University, Corvallis OR 97331.
Additional index words:
Allium cepa, neck rot, onion phenolics, onion
disease resistance.
Abstract. Catechol, a naturally occurring phenolic constituent of onions
exhibits inhibition of the neck rot organism, Botrytis allii and may be
inhibitory to other pathogens.
Mycelial growth of ]5. allii and B^.
ciherea were progressively inhibited by catechol concentrations above
50 and 100 Ug/1 respectively.
Spore germination of B^. allii was in-
hibited by catechol concentrations above 150 Pg/l and 50 yg/1 in the
case of B^. ciherea.
The mechanism of response to catechol inhibition
appears to be different in the two species of Botrytis.
Catechol has
a greater effect on the length of time for maximum germination of
B.* allii than for B^. cinerea.
High concentrations (400 yg catechol/1)
provided a clue in that visual oxidation of phenolics occurred in the
presence of B. cinerea but not in the presence of B. allii.
Received for .publication
Experiment Station Tech. Paper No.
tion of the senior author.
2
Graduate Student in Department of
3
Assistant Professor in Department
4
Associate Professor in Department
;
1980. Oregon Agricultural
. From the M.S. dissertaHorticulture.
of Botany and Plant Pathology.
of Horticulture.
35
Literature Review
Neck rot caused by Botrytis allii Munn. has been identified in
many countries as one of the major bulb-destroying diseases of stored
onions (93, 94, 97).
after harvest.
The disease is found most commonly on the bulbs
Initial bulb symptoms are characterized as having a
soft and watery texture.
As the disease progresses this area enlarges,
turns tan to brown and finally dark brown.
At advanced stages of
disease the tissue becomes spongy or corky and the bulb is light in
weight.
Mycelia often develop on the surface of the bulbs or between
decayed bulb scales and black sclerotia can be observed on the surface
of the rotted tissues (93, 94).
Onion bulbs have been reported to contain the phenolic compounds
4,-glucocide, 3,4,-diglucoside and y^'-diglucosides of quercetin (36).
Onion bulbs also contain protocatechuic acid approximately 1000 yg/gm of
the dry scales and catechol, 1000-2000 yg/gm dry weight of scales
(58, 59).
Pappelis et al., 1976 found that onions exposed to 25 C
for 48 hrs in ambient atmosphere resulted in the accumulation of about
18 mg of chlorogenic acid per gram fresh weight.
to be fungistatic to ]J. allii (22).
This amount, was found
About 8 mg of caf feic acid was
also found per gram fresh weight but at this level caffeic acid stimulated the germination of B^. allii spores (72) .
Other phenolic com-
pounds in onion scales were phloroglucinol, a methyl ester of protocatechuic acid, and ferulic acid from fleshy scales (47).
Onion varieties resistant to the smudge disease caused by Colletotrichum circinans accumulated anthocyanins and simple phenolics such as
protocatechuic acid and catechol in the dried outer scales of red
36
pigmented varieties.
Protocatechuic acid and catechol inhibit germina-
tion and penetration of fungi (28).
Protocatechuic acid and catechol,
two water soluble phenolic compounds present in dry outer scales of
colored onions are not present in the scales of the white varieties.
These two phenolics inhibit the infection by C. circinans and are toxic
to fungi at dilutions up to about 1-3000 (5, 37, 47, 58, 59).
Clark
and Lorbeer (1974) indicated, that catechol inhibited growth of both B^.
cinerea and C^. circinans.
Mycelial growth of these two fungi was not
inhibited by protocatechuic acid or quercetin at concentrations up to
600 yg/ml.
In vivo, crushed, pigmented yellow onion scales inhibited
germination of conidia of jB. cinerea and C^. circinans (22) .
Onion,
leaves, inoculated with spores of 15. allii, exhibited a sharp increase
in flavonoids and chlorogenic acids, especially in the epidermal cells
(84).
Owen et_ al., 1949 (71) found a relationship between pungency
(which refers to strong, odor of onion) and disease resistance in the
onion.
An abundance of moisture in the air greatly increased the
occurrence of neck rot.
The diseases were more severe on mild varie-
ties than pungent ones.
1$. cinerea is the causal organism for brown stain symptoms on
onion bulbs (21) .
Ellerbrook e^t al. (27) indicated that both _B. cinerea
and 15. allii caused flower blighting and seed yield losses of 98 and
47% respectively.
Wukasch ^t al. (103) found that ozone injured leaves
of onions are more susceptible to B^. cinerea infection.
15. cinerea
also caused lesions on onion leaves and produced a cavity within each
lesion as a result of collapse and separation of mesophyll and epidermal
36a
cells (23).
Phenolic compounds have been implicated in resistance to other
diseases.
Byrde (16) indicated that there is strong evidence to suggest
that the resistance to brown rot of certain high tannin varieties of
apples increases as a result of reduced activity of fungal macerating
enzymes by oxidized polyphenols produced by the fruit which are most
effective in inactivating the pectolytic enzymes of Sclerotihia fructigena.
The oxidation products may be expected to have the ability to
precipitate pectolytic enzyme of the fungus which are necessary for
its pathogenicity.
The young roots of potatoes resistant to Verticillium alboatrum
contain higher levels of chlorogenic acid than the susceptible varieties (74).
Chlorogenic acid content in the roots of resistant varieties
of potatoes is approximately five times higher than susceptible ones.
Roots of both resistant and susceptible varieties lose their ability
to synthesize chlorogenic acid when they age (71).
Glomerella perennans, (syn. G^. cingulata), which causes bitter rot
of stored apples, is a major source of wastage in some years (39).
Chlorogenic acid had been shown to inhabit spore germination of this
fungus in culture.
Apples containing higher chlorogenic acid level in
the peel were more resistant to G. perennans.
Anthocyanins, a group
of compounds normally present in the peel of the apple variety Cox's
Orange Pippin, also inhibited the germination of spores of (J. perennans
(39).
A study of the role of oxidized polyphenols by Byrde et al. in
1969 (16) suggested that polyphenols in apple fruits form a defense
mechanism against the brown rot disease caused by Sclerotihia
37
fructigena.
Polyphenols were oxidized by most enzymes of the fungus,
which are necessary for its pathogenicity (16).
In some cases phenolic compounds are localized in non-living
"protective layers" of plant organs and play a fungistatic role in preventing further infection from fungi.
An example is the wax covering of
apple leaves which contains soluble acidic constituents, including
phenolics.
These compounds reportedly play a role in resistance to
powdery mildew (28).
Phenolic compounds also play a role in the hypersensitive reaction.
The appearance of a hypersensitive reaction is a consequence of the
disturbance of the balance between oxidative and reductive processes
of polyphenol compounds.
The result is an excessive oxidation of poly-
phenol compounds and a breakdown of cellular structure related to
necrosis (30).
In the case of viruses, phenolics influence resistance of plants
to virus mostly by the hypersensitive reaction.
In some cases, tannic
acid in raspberry probably inactivates most viruses by clumping the
viruses particles into complexes which are largely uninfective (17).
Materials and Methods
Cultures;
A culture of 3. allii isolated from diseased Yellow
Globe Danvers onion (Allium cepa L.) and B^. ciherea isolated from bean
pods (Phaseolus vulgaris) were maintained on potato dextrose agar.
Spores and mycelia were obtained by incubating the cultures in the
dark for 10 days at 20OC.
Basal medium:
The basal medium consisted of 20 g agar; 5 g
38
dextrose; 5 g peptone; 1.0 g KH
distilled water (22).
PO ; 0.5 g Mg SO -IE 0 and 1000 ml of
Stock solutions of catechol and the other pheno-
lic compounds (Sigma Chem. Co. and Eastman Kodak Company, Rochester,
N.Y.) were added to molten media (50 C) to achieve final concentrations
in the medium of 0, 50, 100, 150, 200, 250, 300, 350 or 400 pg/liter.
Radial growth and spore germination of Botrytis spp were evaluated
relative to catechol concentrations.
From the margins of five day old
cultures of B^. allii and IJ. cinerea, 4 mm diameter plugs were cut with
a cork borer.
Plugs were placed upside down onto the phenolic test
agars and the 9 cm diam. petri dishes were incubated in darkness at
20 C.
Two measurements of radial growth per plate were made each day
thereafter until the colony on the control plate covered the entire
plate.
This was 5 days for 13. allii and 3 days for B^. cinerea.
Each
concentration treatment consisted of 23 plates as replicates.
Spores from ten day old B^. allii and B^. cinerea cultures were harvested in water and the final spore concentration was adjusted to 10
conidia per ml.
3
This suspension was sprayed onto agar media which con-
tained the different concentrations of catechol.
Plates were incubated
in the dark at 20 C according to the optimum conditions described (20).
(Microscopic examination at 100X was used to assess germination of
spores).
A spore was considered germinated if the germination tube
was longer than the width of the spore.
Counts were made at 4, 6, 8,
9, 12, 15, 18 and 24 hrs. for B. allii and 4, 6, 8, 9, 12, 15 for B.
cinerea.
Each treatment consisted of 4 replications.
Statistic analysis:
Radial growth and spore germination test data
were analyzed by using a one-way analysis of variance as described by
39
Steel and Torrie (82).
The Student Newman-Keul's test was used to
determine significant differences between treatments.
Results arid Discussion
Extent of mycelial growth after A days incubation of _B. allii
steadily decreased as the concentration of catechol increased (Figure
7).
Every concentration of catechol significantly reduced radial growth
of 15. allii when compared with the control (Table 5).
Each treatment
also differed significantly from the others except for the 200 yg/1 and
250 yg/1 treatments.
Mycelial growth of _B. cinerea in all treatments except the 50 yg/1
treatment differed significantly (P<0.5) from the control (Table 5).
One hundred yg/1 of catechol had statistically the same effect on
mycelial growth of 15. cinerea as 150 yg/1 of catechol.
Similarly, no
significant difference was found between the 200 and 250 yg/1 treatments.
At 400 yg/1 of catechol, no mycelial growth was observed for B^.
cinerea in 2 of the 23 observations and in 5 observations where some
mycelial growth had occurred a deep brown to black color was observed
in the media.
Slopes of the regression lines for colony size for both fungi and
different concentrations of catechol were significantly different
(p=0.005) (Figure 7).
Mycelial growth of both species of Botrytis was
2
negatively correlated (R =.90) with increasing concentrations of
catechol.
Mycelial growth of 15. cinerea was more vigorous than that of B^.
allii as IJ. cinerea grew to the edge of the 9 cm plates in 3 days
40
compared to 5 days for 15. allii.
In an earlier study, Clark and Lorbeer
(22) reported that catechol concentrations of 50 yg/1 to 500 yg/1
steadily reduced mycelial growth of 15. cihefea.
In our experiment,
however, 50 yg/1 of catechol inhibited growth of j3. allii but not 13.
cinerea.
At 100 yg/1 catechol 15. ciherea mycelial growth was slightly
inhibited after 2 days.
Clark and Lorbeer (22) studied the effect of
different concentrations of catechol, protocatechuic acid and quercetin
on growth of 13. cinerea.
Only catechol inhibited growth whereas con-
centrations of protocatechuic acid and quercetin up to 500 yg/1 did
not inhibit mycelial growth of this fungus.
The reason that some
observations on mycelial growth of jB. cinerea showed deep brown color
may be due to the reaction of oxidative enzymes on phenolics present
in the medium.
Whether oxidations can be conclusively ascribed to the
action of fungal enzymes on the phenolics is yet to be determined.
Approximately 8% of the conidia of 13. allii began to germinate
during the first 2-4 hours of incubation for control cultures and after
15 hrs of incubation 90% of the spores had germinated.
Percent germi-
nation of B. allii spores after 15 hrs incubation on media containing
50 and 100 yg/1 of catechol was not significantly different from the
control (Table 4).
However, with all other treatments the percent
spore germination was significantly reduced after 15 hrs incubation
when compared with the control.
With the highest experimental concen-
tration of catechol (400 yg/1) only 20 percent of the spores had germinated after 15 hrs of incubation.
About 77% of the conidia of 13. cinerea began to germinate after
2-4 hours incubation on control media.
After 8 hrs of incubation.
41
spore germination of 1J. cinerea was 90 percent in the control (Figure
5) .
All catechol treatments of B^. cinerea spore germination were sig-
nificantly different (P=.05) from the control.
However there were no
significant differences in germination between treatments of 50 u.g/1 "
and 100 yg/1 of catechol; between 150 yg/1 and 200 yg/1; 250 yg/1,
300 yg/1, and 350 yg/1 concentrations.
The effect of increasing catechol concentration on inhibiting
spore germination of both Botrytis allii and Botrytis cinerea is readily
evident in Table 4.
Although there are some spore germinations which
are not significantly different than spore germination of adjacent
catechol treatments, nevertheless, the trend of inhibition is clear.
For all experimental concentrations of catechol at 20 C, rates of
spore germination of B^. cinerea were faster than that of B^. allii.
The
rate of spore germination of 15. allii reached over 90% at 15 hrs incubation on PDA without catechol, whereas it took only 8 hrs for that
of 15. cinerea.
On 400 yg/1 of catechol after 15 hrs incubation, spore
germination of 15. allii was only 19 percent compared to 49 percent for
B. cinerea.
This may suggest that catechol affects the length of time
for maximum germination of B^. allii more than it directly affects B^.
cinerea spores.
In order to try to determine whether the nature of inhibition
mechanisms might be the same or different, regression lines of percent
spore germination over time for 15. allii at different concentrations
of catechol were compared using analysis of covariance.
The slope of
each regression line was compared with all others using the t-test
following the method of Neter (70).
The slope of the regression line
42
for 0 yg/1 of catechol was not found to be significantly different
(p=.05) from that of 50 yg/1.
However slopes of the regression lines
for 100, 150, 200, and 250 yg/1 catechol differed from the control but
not from each other.
The slopes of the regression line of 400 yg/1
catechol differed significantly (P=.05) from all other treatments
(Table 6, Figure 5).
In the case of 15. cinerea, there were no significant differences
among the slopes of the regression lines for spore germination and different concentrations of catechol even though there were significant
differences in percent of spore germination at different concentrations
of catechol after 8 hrs incubation (Table 6, Figure 6).
The effect of varying catechol concentrations on 15. allii and jB.
cinerea mycelial growth as determined by regression analysis suggests
that they probably differ in the mechanisms by which they react to
catechol in their environments.
The calculation of slope data was
used in order to ask the question as to whether both species of Botrytis were reacting to catechol via the same mechanism and it appears
from the data that they are not.
The differences (if, indeed they are
real) in mechanisms are beyond the scope of this study, although the
high concentration (400 yg catechol/1) may have provided a clue in
that substantial oxidation of phenolics occurred in the case of Botrytis cinerea but not in the case of Botrytis allii.
Concentrations of catechol greater than 150 yg/1 inhibited spore
germination of both 15. allii and B^. cinerea after incubation of 15
and 8 hrs respectively.
This raises an interesting hypothesis with
respect to the nature of resistance to neck rot in those resistant
43
onion varieites which contain catechol greater than some critical
concentration in the dry outer scales or neck tissues as they are
cured.
Since there are many more hosts that 1$. cinerea attacks, this
may indicate that 13. cinerea may.be better adapted to react to diverse
environments including media containing catechol than is Botrytis allii
which has a narrower host range.
The early study by Clark et^ al. (22) incidated that the number of
B^. cinerea colonies was reduced with concentration ranging from 350450 yg/1 of catechol and spore germination was completely inhibited
at 500 yg/1.
Crushed pigmented yellow onion scales contain compounds
which inhibit spore germination of 1$. cinerea.
Protocatechuic acid and
quercetin up to 500 yg/1 reportedly had no effect on inhibiting spore
germination of ]$. cinerea.
It' is likely that onion scales have several
phenolic compounds which may act additively or synergistically to
inhibit various pathogens.
Onion cultivars that contain high levels
of catechol may be expected to resist infection by .B. allii and 15.
cinerea.
The amounts of catechol in the inner and outer scales
(Table 3) are 41.7 and 312.5 yg/1 dry wt. respectively in the onion
variety Yellow Globe Danvers.
The outer scale amounts appear to be
quite sufficient to inhibit infection by IS. allii, but the inner scale
concentrations may be only marginally effective.
44
Table 4.
The effect of catechol concentration on percent of spore
germination of .B. allii after 15 hrs and B^. cinefea after 8
hrs incubation at 20oC.*
percent spore germination
catechol concentration (yg/1)
B. allii
B^. cinefea
0
92.60 a
91.50 a
50
90.40 a
68.18 b
100
88.53 a
67.49 b
150
74.93 b
61.00 c
200
66.90 c
58.60 c
250
64.90 c
33.57 d
300
46.45 d
33.57 d
350
44.65 d
29.72 d
400
19.65 e
4.81 e
* values followed by the same letter are not significantly different according to Student-Newman-Kuel's test (P<0.05).
45
Table 5.
The effect of catechol concentration on colony diameter of
Botrytis allii and B^ ciherea after 4 and 2 days respectively,
incubated at 20 C.
Mycelial growth (mm)
B. allii
B. cinerea
0
57.15 a
81.,4 a
50
45.98 b
79.,9 a
100
38.44 c
68..6 b
150
34.96 d
60..7 be
200
31.04 e
60..7 c
250
31.04 e
51..3 e
300
26.89 f
38,.6 d
350
24.28 g
33..8 e
400
20.63 h
25,.7 f
Catechol concentration (yg/1)
*Values followed by the same letter are not significantly different
according to Student-Newman-Kuel's test (P<0.05).
46
Table 6.
Slope of regression line for different concentrations of
catechol and 1$. allii and B^. cirierea spore germination.*
Catechol concentration (ug/1)
B^. allii (slope)
15. cinerea (slope)
0
8.6 a
1.53 a
50
8.2 a
1.38 a
100
6.0 b
1.41 a
150
5.8 b
1.49 a
200
5.2 b
1.42 a
250
5.0 b
1.10 a
300
4.1 c
1.10 a
350
4.5 c
0.85 a
400
3.6 d
0.88 a
* Values followed by the same letter are not significantly different according to Student-Newman-Kuel's test (P^0.05).
47
Figure 5.
Spore germination of Botrytis allii over time at 20 C
relative to catechol concentration in the medium.
47a
Figure 5.
I
I
_i
2
^~ ~_ ^oi
**•_ "^CT
_ a>
_
C oi o> c»
- - oo c
In omo
om
—~wcvjfO
D» * • c D 0
!
o«
Oi
- o
in
o
ro v
D
!
I
I
OOOOOOOOOOO
ocT>oor^c£>»o^-tocvi
N0llVNIWa3£)
%
—
48
Figure 6.
Spore germination of I[. cinerea over time at 20oC relative
to catechol concentration in the medium.
48a
Figure 6,
_J
2 C ~ ~ "^ ^ ■"* -^ ~
2 OoOOO O 0
O
OOc inOiOQ in
um — — CJCVIIO ro
D# * • c DO D ©
t
I
!
I
ooooooooooo
oa>cDh-c0ir5^rrooj
N0!1VNMU39
%
—
49
Figure 7.
Colony diameter of 1$. allii (after 4 days) and 15. cirierea
(after 2 days) incubated at 20oC relative to catechol concentration in the medium.
COLONY
DIAMETER (cm)
' L aanSxa
e6<7
50
Preliminary Experiment
'Weight Loss Over Time at 3 Storage Temperatures'
51
EFFECT OF STORAGE TEMPERATURES ON WEIGHT LOSS
Field cured Yellow Glove Danvers onions from the Lake Labish area
near Salem, Oregon were placed in cold storage rooms at 0 , 10 , and
20 C.
Fifteen onion bulbs were individually weighed on October 15,
1979 and stored at each temperature.
The same onion bulbs were removed
to be weighed every month until April 15, 1980.
Split plot analysis
of variance was performed to determine the difference of weight loss
between treatments by the method described in Steel and Torrie (82).
Effect of storage temperature on weight loss.
Onion bulbs stored for six months at 20 C, 10 C and 0 C had weight
losses of 10%, 5%, and 3% respectively (Figure 8).
Onion bulbs stored
at 20 C had 5 layers of paper-like dry outer scales compared with 3
layers of dry outer scales on onions stored at 10
or 0 C.
Cumulative
weight losses at 20 C, 10 C and 0 C were significantly different at
0.05 level both by temperature and by sampling date (Figure 9).
Weight loss (shrinkage) in storage of onions is due to respiration
losses of carbon as CO
and transpiration losses of water and other
volatiles (46, 47, 66).
Brewster (6, 7) indicated that within the
o
o
range 0 -20 C onion bulb respiration rate was linearly related to
temperature.
Ward and Tucker (100) reported a mean increase of 0.55 mg
C0„ Kg
C
h
and the data of Robinson et al. (79) show an increase
of about 0.3 CO /Kg/h/ C.
Onion bulbs stored at low temperature (-1
to +2 C) and high temperatures (25
to 30 C) have longer storage lives
than those stored at 12 -16 C, but onions stored at high temperatures
52
were subjected to more storage diseases (2, 7).
Onions stored from
30 -35 C yield satisfactory onions for the fresh market, but their
external color may be less attractive than bulbs from cold storage.
Most cultivars of onions can not be stored effectively between 5 C
and 20 C because development of sprouting and decay are most rapid in
this range (80, 81).
At 0 C and 25
to 30 C temperatures are expected
to delay and prevent progress of inflorescence initiation.
Tempera-
tures of 9 -13 C appeared most favorable for flower initiation.
Storage at 25 C to 30 C after floral initiation can promote reversion
from a floral to a vegetative condition (8).
The results of this
study indicate that onions are best stored at low temperature (0 C).
There was no incidence of rotting for the onion bulbs stored at 10
and 20 C.
Likely explanations are that relative humidity was not
suitable for pathogens or onion bulbs were free from pathogens from the
field.
Previous work cited above, showed that at 0 C onions can be
stored longer with less weight loss and with lower incidence of diseases.
The dramatic increase in weight loss in the 10 C storage at
the 5th month was likely due to excessive sprouting evident at that
temperature which did not occur in the 20 C or 0 C stored onions
(Figure 9).
Relative weight losses for this study at 20 C
Assume 8-10 mg CO
kg
hr
is the respiration rate.
So after six months, respiration rate = 6 months x 30 day/month x
24 hrs/day x 8-10 mg C02./kg/hr
= 43,200 mg/kg
53
This is about 4.32% at 20OC
4.32%. as. CO
10% weight loss
= 43% loss in respiration
lost in transpiration = 57%
54
Figure 8.
Cumulative percent weight loss during 6 month storage of
Yellow Globe Danvers onions.
54a
Figure 8.
O
CSJ
O
CD
<0
^-
oJ
SSOl 1H9I3M% "3AllVlffWnO
55
Figure 9.
Percent weight loss per month during 6 month storage of
Yellow Globe Danvers onions.
55a
Figure 9.
-
to
-
w
-
<3Z
O
IO
-
oo
H1N0IN y3d
*-
SS0-I1H9I3M%
o
CsJ
56
Preliminary Experiment
"Dry Outer Scales Regeneration"
57
DRY OUTER SCALES REGENERATION
A preliminary experiment attempted to determine the development of
dried outer scales as affected by different temperatures and air velocity conditions.
Dried outer scales of onion were removed until
fleshy scales were exposed.
Peeled onions were placed in portable
food dehydrators set at 40OC and 50 FPM of air, 350C and 50 FPM of
air, 30OC and 50 FPM of air and 20OC and 50 FPM of air.
Other onions
were dipped in chloroform for 1 minute or in 100 ppm ethephon for 5
minutes and placed in room temperature on the lab bench.
Another
treatment merely left the peeled onions at room temperature.
Evalua-
tion of scale regeneration was made after peeled onions had been
exposed to the above conditions for 4 weeks.
Each treatment consisted
of 5 observations.
Dry outer scale regeneration:
A preliminary study.
Room temperature and room temperature with air circulation promoted the best scale development in 4 weeks.
At 40 C, 35 C, and 30 C
onion bulbs appeared cooked, becoming soft and shrunken within 2 weeks.
Dipping onion bulbs in chloroform in an effort to accelerate moisture
loss from the outer scales by altering cuticular wax structures caused
the basal plate to dry and split, and fungal attack occurred by the
end of 4 weeks.
Ethrel at 100 ppm had no effect on scale development.
Further study for dry outer scale regeneration should be done, because
the occasional seasonal variation in curing results in losses from
"bald" or "skinned" onions which do not store well and are unacceptable
in the market.
58
Leaving onions cure in tjie field too long can result in loss
of outer wrapper-scales and cause bald onions in storage (98).
Similarly increased risk of rain can.lead to storage rot problems (91).
Irrigations which are continued after the onions have matured may allow
rot organisms in the soil to separate the dry wrapper-scales from the
root plate and these scales fall off during harvest and result in many
bald onions (98).
Intact dry outer scales of onion reduce respiration
rate, see appendix 2, prevent moisture loss from the bulb, and prevent
the entry of pathogens (66).
Quality of the outer dried leaf scales
of onion refers to the number, thickness, color and completeness of
the scales.
hr
kg
Rate of onion respiration is increased about 10 mg CO
by removal of dry outer scales from the bulbs.
Onions with
cracked or missing scales are more subject to weight loss (6).
Again
earlier work has indicated that dry outer scales of onion provide
benefits for storage life of onions.
Determining the best methods for
development of dry outer scales on "bald" or "peeler" onions would
represent substantial reductions in losses to onion growers and packers.
59
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APPENDICES
71
Appendix 1.
Flow diagram for free ABA extraction from onion tissue.
equivalent of 5g ground tissue in CH OH
3
i
Filtrate
10 DPM14C-ABA-
-25 ml of Na HCO3
buffer at pH 8.0
CH OH
evaporated off
Partitioned against
CH„C10 3 x 50 ml.
2 2^
3,
discard
CH2C12
. aqueous fraction
pH adjusted
to 2.5
I
Partitioned against
CH Cl
3 x 50 ml
J:
discard aqueous fraction
I
CH Cl
2
fraction
^
Partitioned against KaOH
buffer Ph 10 3 x 50 ml
JT
discard CH Cl
VK
aqueous fraction
pH adjusted to 2.5
Partitioned against
Ethyl acetate 3 x 50 ml.
^
discard aqueous fraction
14
count of C
ABA
for % recovery
^
Taken to dryness and methyl
esterification by diazomethane
Injection of esterified ABA into GLC
72
Appendix 2.
Sampling date
Free ABA concentration (ng/g dry weight) in onion tissues
during maturation and storage.
Approximately % top fall
Foliage
Neck
Bulb
Aug. 20, 79
0
0.37
0.15
. 0.04
Aug. 30, 79
40
1.81
0.27
0.17
Sept. 10, 79
60
0.53
0.33
0.31
Sept. 20, 79
100
0.28
0.27
0.21
0.01
0.15
0.20
Oct. 1, 79
Nov. 1, 79
0.25
Jan. 1, 80
0.15
Feb. 1, 80
0.53
Mar. 1, 80
0.45
Apr. 1, 80
0.28
Apr. 1, 80
sprout
0.24
73
Appendix 3.
Comparison of respiration rate of eight onion varieties
after 8 months storage at 0oC.
Respiration rate
root sprout
mg CO /kg/hr
(0-5)
leave (cm)
XP-H667
26.46
3.05
2.73
3.20
XP-H742
28.18
2.15
3.76
2.75
Yellow Globe
33.06
2.17
4.11
3.21
Autumn Beauty
27.68
1.79
4.19
3.33
XP-W207
20.26
1.41
2.85
3.15
XP-H348
22.05
2.01
2.39
3.24
Danvers
18.41
0.88
3.04
4.95
XP-H195
25.39
0.70
1.46
3.33
Varieties
length of 1st
no. of
outer s>
Sapparo
Yellow Globe
74
Appendix 4.
ABA concentration and respiration rate of eight
onion varieties after 1 month storage at 0oC.
74a
Appendix 4.
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OZ
r^-
OJ
i
I
CO
LJ
I
ro
(UJ6/6U)
CD
i
a
V8V
I
75
Appendix 5.
IR spectrum of unknown phenolic with Rf = 0.86 in BAW
and RF = 0.74 in 2% acetic acid.
A.
Unknown
B.
Protocatechuic acid
C.
Catechol
D.
Catechol (Sample)
^fc
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76
Appendix 6.
1.
Chemical structures of major phenolics constituents of
Yellow Globe Danvers onion.
Catechin
HO
2.
Catechol
OH
3.
H
Chlorogenic acid
COOH
OK
^ ./\
OH
OH
HO \
4.
Caffeic acid
HO
CH.'CHCO.H
-OH
5.
Quercetin
77
6.
7.
Arbutin
H H OHH
HOCHC-C-C-rf-CHOK'
Protocatechuic acid
CO OH
OH
OH
N
)-0H
78
Appendix 7.
Comparison of respiration rate of eight onion varieties
after 8 month storage at 0oC.
Respiration rate
(mg of C02/kg/hr)
with dry outer scale
without dry outer scale
XP-H667
29.48
28.81
XP-H742
37.56
35.69
Sapparo Yellow Globe
26.35
40.27
Autumn Beauty
32.55
36.58
XP-W207
21.11
30.20
XP-H348
27.50
35.97
Yellow Globe Danvers
21.42
34.16
XP-H195
24.08
49.45
Varieties