الفهرس 
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Abstract
Pink root rot disease of onion caused by Py~enochae~a
te~~e~~~~~(Hansen); Gorenz; Walker and Larson is considered an
important disease which seriously attacks onion plant roots in
both nurseries and permanent plantations, causing serious damage
for roots; great losses of bulbs weight and in turns of seed prcduction.
The results of this research could be summarized as follows:
1. Survey study indicated that the disease was widly prevalent
in sandy soils of Ismailia and Fayoum governorates in the
seasons 1986 and 1987 as the average percent of infection ranged
from 17.66-26.28% whereas the infection was limited in the heavy
clay soils of Upper Egypt governorates (Giza; Beni-Suef and Assiut)
as the infection ranged from 3.47-8.94% only.
2. There was no obvious correlation between the onion pink
root rot incidence and the meterological elements i.e. the average
of maximum; minimum and mean of temperature degrees; relative
humidity and rain fall occurred during the surveyed times.
3. Two distinguished groups of fungi were obtained from
onion transplants showing typical pink root rot symptoms from
different fifteen localities belonging to the five mentioned
governorates. The first group included 15 isolates were identified.
as Fu~aA~um oXy4poAum Schl. f. s. cepae (Hanz.); Snyder
and Hansen, and the second group included seven isolates were
identified as PYAenOdha~a ~eAAe~~Ai4(Hans.); Gorenz; Walker
and Larson.
4.a} Frequency study indicated that F. OXY6po~um f. sp.
~epae was isolated only (100% frequency) from all samples collected
from all localities belonging to Giza and Beni-Suef governorates
and one locality from each of EI-Fayoum and Ismailia
governorates.
b) Both F. oXY-6po~um f. sp , c.epae and Pyltenochae:ta
teltlte6t~i6 were isolated from one locality of Assiut governorate;
three localities from each of EI-Fayoum and Ismailia
governorates, as the percent frequency of the former ranged from
73.1-90.5% whilest that of the later ranged from 9.4-24.1%.
c) The percentage of the colonies comprising the both
pathogens-isolated simultaneously from the same root segments
ranged from 1.1 to 7.1%.
5.a) Pathogenici ty test of all P. te~~e6:t~i6 isolates on
the natural susceptible onion Cv. Giza-20 indicated that isolate
No.3-collected from Ismailia governorate_was the most
pathogenic isolate causing pink root rot infection to 61.94 %
of the tested plants with percent severity 41.9% and 33.79 %
according to infected and tested plants, respectively. Whereas
the least pathogenic isolate No.1, infected not more than 26.40%
of tested plants with a severity 19.1% and 3.49% concerning to
the infected and tested plants respectively.
b) All F. oxyltpO~um f. sp. c.e.pae isolates were pathogenic
inducing typical symptoms of basal rot disease, imparting
the roots with reddish colour in earlier stages and causing dry
rot of the stem plates of the infected plants in the later ones.
6. The conventional onion Cvs. namely. Shandaweel-l; Giza-6
and Giza-20 showed clearly significant differences in the susceptibility
against the artificial inoculation with the causal agent.
Shandaweel-l proved to be resistant; Giza-6 was moderately resistant
and Giza-20 was highly susceptible.
7. The morphological; cultural and physiological characteristics
of the all isolates of P . .te.JtJte.6tJt..(.6 were studied and
could be summarized as follows
a) The isolates varied in the linear growth; dry weight
of mycelium; the colour and the nature of growth; and the production
of pycnidia; pycnidio and conidio-spores. All isolates
produced such structures with great similar morphology, when
grown on solid or liqued PDA and C’zapek1s media at 27oC. However
the isolates were greatly differed in their measurements of
the length and/or the width of pycnidia; bristles; pycnidio and
conidio-spores.
b) The complicated carbon sources greatly affected the
rate of growth; dry weight of mycelium and the production of
pycnidia; pycnidio and conidio-spores of all Pylte.noc.haeta .teJtltu.tJU.6
isolates, as the starch or cellulose containing media were better
for the growth and sporulation than pectin containing one. Also,
the high stimulation effect of either starch or cellulose decreased
once pectin was added with starch and cellulose singly or
together.
c) Natural media i.e. onion dextrose agar CODA); potato
dextrose agar (PDA); corn meal agar CCMA) and synthetic one
medium, sucrose ammonium nitrate were the best for giving the
highest linear growth and production of pycnidia; pycnidio and
conidio-spores of isolate No.3. Natural media produced more
vigorous growth with huge number of pycnidia compared with those
obtained on synthetic media.
d) Reduced monosaccharides (glycerol; mannitol; mannose;
glucose and dextrose) and glucose plus sucrose, encouraged the
fungal growth more than the non-reduced disaccharides (maltose
and lactose). Whereas the reverse effect was concluded on
pycnidia production. Glucose; dextrose; sucrose and glucose
plus sucrose were better for pycnidiospores production. All
carbon sources were suitable for the production of conidiospores
with the exception for glycerol; mannitol and lactose.
e) Glycerol or mannitol containing media gave very weak
colonies with irrigular margins. Mannose containing one produced
yellowish lemone growth particularly arround the main inocula.
Glucose or dextrose containing media induced normal white greyish
colonies surrounded by yellow zones. Non-reduced disaccharide
sugars containing media greatly varied in their effect, as maltose
containing medium gave white yellowish colonies while sucrose containing
one produced vigorous colonies with some yellow pigment
arround the main inocula, meanwhile lactose containing medium
gave very weak colonies which looked alike that occurred on the
plane agar medium.
f} Concerning the effect of nitrogen sources, the nitrogenous
salts NaN03; KN03 and NH4N03 and amino acid arginine
increased the linear growth rather than other nitrogen sources.
Only NH4N03 containing medium was the best for increasing pycnidia;
pycnidio and conidio_spores. As for cultural morphology,
the media containing NaN03; KN03 or NH4N03 gave very strong
growth; grey yellowish in colour with regular margins and contained
great number of pycnidia. Arginine containing medium produced
vigorous growth with yellowish pigment far from the main
inoculum. Treptophan containing one gave relatively vigorous;
aerial and greyish growth, whereas the growth was very poor and
looking alike the growth on plane agar on the media containing
either Glycine or methionine. Ammonium tartarate gave limited
growth which was flattened; completely connected with the medial
surface and had an irregular margin. Urea was completely considered
a non suitable nitrogen source for nitrogen nutrition.
g) The C/N ratios 30/3 (the normal); 40/3 and 50/3 were
the most suitable for giving the highest linear growth and producing
the maximum number of pycnidia; pycnidio and conidio~
spores. The ratios (30/5); (30/10) and (30/15) also gave considerable
mycelial growth but greatly varied in their effects on
sporulation. However omitting either carbon or nitrogen gave
hyaline colonies lacking from any of pycnidia; pycnidio and
conidia-spores.
h) Optimum temperature for the maximum growth and production
of different spores was 2SoC. and the increasing or decreasing
the temperature above or down the optimum temperature
resulted a sharp reduction in the growth and formation of such
structures. However. a complete inhibition of both mycelial
growth and spore production occurred at 10 and 40oC.
i) The suitable range of pH for the growth and sporulation
of PyJr.enoc.haeta teJtJtutJU6 was 6.9-7. 7 . However the fungal growth
did not affect when the pH decreased to very acidic condition
(till 3.2), whereas the growth was greatly decreased as pH values
increased to very alkaloide conditions (till 10.0).
8. The role of hydrolytic enzymes, Pectin-Methyl-Estrase
(PME); Poly-Galacturonase (PG) and Cellulase (CX) as well as the
role of oxidative enzymes, Polyphenoloxidase and Peroxidase were
studied -in v-ivo and -in v-itJr.o in relation to the virulence of
isolates on both the susceptible Giza-20 onion Cv.
and modified C’zapek’s medium, respectively.
a) The activities of PME; PG and CX were higher in diseased
than healthy onion transplants.
b) There was a clear correlation between the isolates virulence
and the production of such pectinolytic and cellulolytic
enzymes through the root and bulb tissues, as the most virulent
isolate (No.3) produced the highest activities. Moderate virulent
isolate (No. 1;4 and 6) showed moderate activities, whilest
the least virulent ones (No. 2;5 and 7) produced the least quantities
of such enzymes.
c) The activities of pectinolytic enzymes produced by all
isolates were rather high in diseased roots than those determined
in the bulb tissues of the diseased transplants. Meanwhile all
-
isolates approximately produced Cellulase enzyme at. equal high
levels in the root tissues and relatively low ones in the bulbs.
261
b) Polyphenoloxidase and Peroxidase activities were obviously
increased in diseased rather than those determined in healthy
tissues of both roots and bulbs. Also, there was a possitive
correlationbetween the virulence of the causal organism isolates
and the increasing of Polyphenoloxidase activity after inoculation,
whereas no correlation was observed according to Peroxidase
activity and the virulence of the tested isolates.
e) Polyphenoloxidase activity was higher in the bulb tissues
of transplants infected with any of the tested isolates than
those determined in the root tissues. Whereas the Peroxidase
activity was highr in the root tissues of diseased transplants
with isolates No. 1;2;6 and 7 than those of its bulbs, whereas
the reverse was true concerning to isolates No. 3;4 and 5.
f) The seven isolates of P.te~he6t4~6 greatly differed
in their PG enzyme activity in vit40 . Isolate No. 3 secreted
the highest quantity; isolates No. 1;2;4;6 and 7 showed moderate
ones whilest isolates No. 5 secreted the least quantity of PG.
The secretion of PME was also greatly differed by such isolates,
as isolates No. 1 and 2 showed higher PME activity than that of
isolates No. 3;4;5;6 and 7 which relatively produced the same
quantity of such enzyme. As for Cx activity, all isolates approximately
showed the same activity level in degrading CMC containing
medium. As regard to oxidative enzymes, Peroxidase and
Polyphenoloxidase activities in filterates of all tested isolates
were very limited.
9.a} Hydrolytic enzymes, PG; PME and CX were clearly increased
in root and bulb tissues of diseased onion transplants of all
tested Cvs. than those of healthy ones but in different levels
concerning to their resistance and/or susceptibility.
b) Gradual increasing of such activities were correlated
with the pink root rot disease development, reaching the maximum
after 90 days from inoculation, meanwhile such increase was very
limited in healthy tissues.
c) PME activity was higher in the root tissues of diseased
and healthy transplants of all Cvs. than in its bUlbs.
d) PG activity increased in the root tissues rather than
in the bulbs of diseased transplants in both susceptible (Giza-20)
and moderately resistant (Giza-6)Cvs. whereas the reverse was
true in the resistant Cv. Shandaweel-l. On the other hand the
activity of such enzyme in the healthy bUlbs of susceptible and
moderately resistant Cvs. was relatively higher than those recorded
in its roots.
e) CX activity was higher in the root tissues than those
occurred in the bulb ones of diseased transplants of all tested
evs. Meanwhile the reverse was enough in the case of healthy
tissues.
IO.a} Pink root rot infection increased Polyphenoloxidase
activity in the infected roots of resistant Cv. Shandaweel-l
particularly after 90 days from inoculation.
b) The bulbs of healthy and diseased transplants of all
eva. showed higher ac~ivity of such enzyme than those of their
roots either after 30; 60 or 90 days from inoculation.
c) The activity of this enzyme decreased after 60 days
in the root tissues of both diseased and healthy transplants for
all tested evs. then a remarkable increase was assayed after 90
days, whilest a continual increase of such enzyme was generally
recorded in the their bulbs.
11. a) The infection also clearly increased Peroxidase
activity in the root and bulb tissues of diseased transplants
than healthy ones, but the rate of increasing was higher in the
root than in the bulb tissues of all tested Cvs. either after
30; 60 or 90 days from inoculation.
b) The activity of Peroxidase was generally increased in
both the root and bulb tissues of diseased and healthy transplants
after 60 days rather than after 30 days, then dropped after
90 days.
l2.a) The activities of hydrolytic enzymes, PG; PME and Cx
were decreased in the root tissues of transplants treated with
any of the tested fungicides rather than in untreated ones transplanted
to infested soil.
b) There was a positive correlation between the fungicidal
effectiveness and the inhibition of such hydrolytic enzymes.
c) The activities of such enzymes were rather high in
the roots than those of the bulbs of transplants treated with
the least effective fungicides, whereas the reverse was true,
particularly in the case of PG and ex, when transplants treated
with the most eff@c~ive fungicides.
13. a) On the other hand the infection increased oxidative
enzymes, po1ypheno10xidase and Peroxidase particularly in root
than bulb tissues in the transplants treated with any of the
tested fungicides.
b) Oxidative enzyme activities were generally higher in
the root tissues than those assayed in the bulb ones.
14. There was a positive correlation between the isolates
agressiveness of P. tekke~tki~ and the mycotoxin production.
15. In vitkO I Bavistin (50%); Benlate (50%) and Folicure
(25%) EC prevented the fungal growth and sporulation at 3;5 and
10 ppm respectively. Topsin-M (70%); Vitavax (75%) and Vitavax/
capt an (75%) at 50 ppm gave the same effect. Vitavax/thiram
(75%) gave complete inhibition for the fungal growth at 100 ppm,
whereas both Ronilan (50%) W.P. and Ronilan (5%) dust lead to
the same results at 300 ppm. The fungicides KZ (50%) l20-W.P.;
Sumisc1ex (50%) W.P. and Sumisclex (50%) D.Fl. were the least
effective and failed to inhibit the fungal growth and spores
production even at 500 ppm.
16. The fungicides applied in greenhouse as dip treatments,
Folicure (25%) EC.; Sumisclex (50%) W.P.; Sumisc1ex (50%) D.Fl.
and Ronilan (50%) W.P. minimized the disease infection as well
as the severity of pink rotted roots of the susceptible onion
Cv. Giza-20 followed by Ronilan (5%) dust (as soil treatment)
and KZ (50%) 120 W.P. (as dip treatment).
17. Under fie1d conditions, Folicure (25%) E.C.; Sumisclex
(50%) D.Fl. and sumisclex (50%) W.P. were significantly the
most effective fungicides which reduced the infection of the
pink root rot disease incidence to minimum possible level and
gave the highest yield followed by Ronilan (50%) w.P.; Ronilan
(5%) dust and KZ (50%) 120 W.P.
18. In NPK nutrition trial under greenhouse conditions,
exceeding nitrogen to a level equal the double of recommended
rate, increased the percentage of pink root infection whilest
the severity of infection was decreased when either the nitrogen
decreased or the phosphorus increased. However, no differences
in disease severity were recorded when the level of
potassium either increased or decreased above or down its recommended
rate.
19. Under field conditions, increasing nitrogen over the
recommended rate increased the infection of pink root rot
disease and obvious reduction in onion yield. Increasing or
decreasing either phosphorus or potassium- in combinations with
nitrogen recommended rate- resulted opposite and satisfactory
results as the disease incidence was clearly decreased and the
yield either increased or at least remained constant. In unfertilized
treatment (N.P.K.), highest infection and lowest
onion yield could be occurred.
20. a) The tenth of January was the best for minimizing
the pink root rot disease incidence and giving the highest
onion yield. The infection was increased and the yield was
decreased with the earliness of planting time.
b) Under open field conditions and natural infection,
Shandaweel-l showed relatively resistance ev. and gave the
highest yield. Giza-20 Cv. showed high susceptibility and yielded
the low~crop yield meanwhile, Giza-6 showed intermediate
reaction.
21. a) After 30 days from inoculation, the total individual
free amino acids was decreased in the whole diseased transplants
of the susceptible Cv. Giza-20 and the resistant Cv.
Shandaweel-l but to a limited level in the later, whilest the
inoculation increased the total amino acids~in the whole transplants
of the moderately resistant Cv. Giza-6.
b) Total free amino acids was sharply decreased in the
roots of the susceptible Cv. and slightly decreased in both
resistant and moderately resistant Cvs.
c) Such totals remained constant in the bulb tissues of
inoculated resistant transplants and increased in both susceptible
and moderately resistant ones.
d) All amino acid groups were decreased in the roots of
inocUlated resistant transplants except for sulphoric group
(especially L-Cystine) which sharply increased. This group was
decreased as well as all amino acid groups in the susceptible
roots. However sulphoric; amino; and aromatic groups were
clearly decreased and hydroxylic; alephatic; emino and basic
groups were obviously increased in the moderately resistant ev.
e) sulphorie; hydroxylie and emino groupS were increased
in the bulb tissues of inoculated resistant ev., whereas amino;
basic and alephatic groups were decreased, meanwhile only aromatic
group remained constant. Concerning to both susceptible
and moderately resistant Cvs., most amino acid groups were increased.
22.a) After 60 days from inoculation, the total free amino
acids of the whole transplants were increased in the resistant
Cv. whereas, reverse reaction was observed in both moderately
resistant and susceptible Cvs.
b) Only sulphoric group was increased in the roots of
resistant and susceptible Cvs. and the rest groups were decreased.
Whilest slight increase in the amino group was observed
only in moderately resistant Cv. and all the rest groups were
also decreased.
c) In the infected bulb tissues of the susceptible Cv.,
sulphoric; alephatic; amino and basic groups were decreased,
meanwhile hydroxylic; aromatic and amino groups were increased.
However, sulphoric; alephatic; amino; emino and basic groups
were decreased rather than those detected after 30 days from
inoculation. The bulbs of infected transplants of the resistant
Cv. contained higher cons. of amino and emino groups and less
cons. of the rest groups rather than those detected in the
healthy bulbs. Hydroxylic; aromatic; amino; basic and alephatic
groups were sharply decrease, meanwhile sUlphoric and emino
groups were remained constant in the bulbs of inoculated moderate
resistant cv.
23. a) After 90 days from inoculation, the total free amino
acids in the whole susceptible transplants was sharply increased
compared with those detected in the control transplants or those
determined after 60 days. Slight increase in such total was
observed in the resistant transplants, meanwhile the total free
amino acids was decreased in the transplants of moderate resistant
cv ,
b) Only sulphoric group (particularly L-Cystine) and
emino group (especially L-Hydroxy proline) were decreased in the
root tissues of the resistant Cv. meanwhile its infected bulb
tissues contained higher concentrations of sulphoric; hydroxylic;
aromatic and emino groups in particular with L-Cystine; DLThrionine
and DL-Tyrosin; Treptophan and L-Proline respectively.
c) In the infected roots of the susceptible Cv., only
the sulphoric group (particularly L-Cystine) was found with
higher concentration, whilest all amino acid groups were concentrated
in its bulb tissues, except for emino group.
d) with regard to the moderate resistant Cv., non-polar
alephatic group; amino and sulphoric groups especially DL- oc
alanine; Glutamic acid and L-Cystine respectively were concentrated
in the inoculated roots whilest non-polar alephatic group
(particularly Glycine) was accumulated in its bulbs.
24. a) After 30 days from transplantation, the total phenols
were higher in the healthy roots of resistant Cv. Shandaweel-l
thas=tbose of mode~ate resistant Cv. Giza-6 and the susceptible
Cv. Giza-20 •
b) Inoculation increased the total phenols in both the
roots and the bulbs of the moderate resistant and susceptible
Cvs. rather than those of the resistant one.
c) Also, free phenols were clearly increased in the root
tissues of the moderate resistant and susceptible Cvs. after
inoculation whereas the reverse was true according to resistant
Cv.
d) Conjugated phenols were icnreased in the root tissues
of all tested Cvs. as the result of infection.
e) Free phenols were obviously decreased in the bulb
tissues of the resistant and the moderate resistant Cvs.
whereas such phenols were clearly increased in the bulbs of susceptible
one.
25. a) After 60 or 90 days from inoculation, the diseased
roots of both the resistant and moderate resistant evs. contained
total phenolic compounds less than in healthy ones, whilest.
these compounds were accumulated in the diseased roots of the
susceptible Cv., however such compounds were increased in the
bulb tissues of all diseased Cvs. but to high; moderate and
slight levels in susceptible; resistant and moderate resistant
Cvs., respectively.
b) Free phenols were greatly decreased, moderately increased
and greatly increased in the diseased roots of the resistant,
moderate resistant and susceptible Cvs. respectively.
Reverse reactions were recorded concerning free phenols in the
bulb tissues of the tested Cvs. respectively too.
c) Conjugated phenols were increased in the diseased
roots of resistant Cv. and were decreased in the moderate resistant
and susceptible ones, whilest the reverse was true in the
bulb tissues of these Cv s,
26. a) Reducing sugars were slightly increased in the roots
and bulbs of diseased transplants of all Cvs. after 30 days from
inoculation.
b) Non-reducing sugars were decreased in the root and
bulb tissues of inoculated transplants of the resistant Cv.
Shandaweel-l. Such sugars were slightly increased in the inoculated
roots of the moderate resistant Cv. Giza-6 and decreased
in its bulb tissues. Whereas these compounds were increased
in both root and bulb tissues of the susceptible Cv.
Giza-20.
c) Total soluble sugars were increased in the diseased
roots of either susceptible or moderate resistant Cvs. and was
being constant in the inoculated resistant Cv. However, the
reverse reaction was found in the bulb tissues of the tested Cvs.
27. After 60 or 90 days from inoculation, reducing; nonreducing
and total soluble sugars were decreased in the root
and bulb tissues of inoculated transplants of resistant and
moderate resistant Cvs. Such sugars were generally increased in
the root and bulb tissues of the susceptible Cv. particularly
after 90 days from inoculation.