الفهرس 
Material and methodsOnly 14 pages are availabe for public view
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Abstract
Potato 1s considered one of the most important
export vegetable crop in Egypt. Unfortupate1~ this
crop is affected many diseases in the field, storage
and during transport. Potato tuber rot caused by
different species of Fusarium causes great economie
losses during storage, transportation and during the
growing season. This study was carried out to :
a) determine the causal agents of potato tuber rots,
b) to study factors affecting the disease incidence
and spread, c) to study parasitic behaviour and chemical
changes occurring during this period, and d)
disease control methods under laboratory, storage
and field conditions.
The most important results obtained in this
study are summarized as follows :
1. Seven different species of the genus Fusarium,
causing potato tuber rots, were isolated and identified.
The most prevalent were F. oxysporum and
F. sambucinum. The latter is considered as the first
record of this species on potatoes in Egypt. Also,
l. 1ateritium and l. reticulatum were first recorded
on potatoes.
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2. The most virulent species, causing tuber rots
and seed piece decay were F. sambucinum,!. solani
and F. avenaceum, while F. reticulatum and F. later.-tium
were the least virulent.
3. Potato tuber stem-end was the most sensitive
site for Fusarium spp. entrance and infection. While,
rose-end and tuber sides were less susceptible.
4. ~. eambucinum was the most virulent causing
sprout rot on all varieties Arr~n Banner and
Claudia variety were z-ea Lstan t to F. solani,
F. avenaceum, F. oxysporum, F. reticulatum and
F. latertium, while Arr”an and Grata was resistant to
l. semitectwn. On the other hand, Spollnta was the
most susceptible variety to all Fusarium spp.
5. During storage infection with F. sambucinum
increased gradually at 10-25°C. then decreased at 30°0.
o
and 35 C. Infection of Alpha and King Edward varieties
with F. avenaceum increased at 10-20°0., while,
l. solani was more virulent at 30 and 35°0.
6. Potato tuber rots increased consequently till
80 % R.H. and there was no significant differences
between 90, 95 and 100 % relative humidity.
7. Slice rot, caused by!. sambucinum, decreased
by elongate curing period for all potato varieties.
It was found that placing tuber wounded slices in
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good ventilated areas for 1-4 days gained best results
against the infection by F. sambucinum. Potato
varieties differed in their sensitivity to infection
depending on their ability for wound suberization.
Arran Banner and Alpha were resistant, while King
Edward and Spounta were susceptible.
8. Degree of maturity has significant effect on
potato tuber rots during storage period. Tuber rot
increased by increasing tuber maturity.
9. Increasing inspection intervals during storage
period increased tuber rots in Nawalla compared
with examination one time at the end of storage period.
10. Alpha, Arran Banner and Rosalai varieties were
resistant, Claustar, Claudia and Dimont were less
resistant, while Grata, Spounta and King Edward were
susceptible. On the other hand, Baraka, Clada and
Cara were highly susceptible to Fusarium potato
tuber rot in Nawalla.
11. Change in growth period affected chemical constituents
in tubers tissues Fusarium rotsl
a) Increasing growth period caused reduction of
total and non-reducing sugars in King Edward variety.
Reducing and non-reducing sugars increased susceptibility
to tuber rot. Reducing sugars decreased in
Alpha tubers by prolonging growth period. It was
·also found that total, reducing and non-reducing sugars
increased in tubers inoculated with l·sambucinum
except in Alpha tubers 110, 120 and 130 days old
when reducing sugars decreased after inoculation.
b) Total and free phenols decreased by increasing
plant age. Rate of reduction in King Edward was more
than in Alpha cultivar. Total and free phenols increased
after inoculation with the causal agent.
c) Amino acid content was higher in 80 days old tubers
than in 90, 100, 110, 120 and 130 days old. Inoculating
Alpha tubers increased all amin~acids compared
with non-inoculated ones except Alanine, Leucine, and
Iso-leucine which were higher in non-inoculated tubers.
In King Edward tubers, non-inoculated tubers contained
higher amounts of amino acid than in inoculated ones,
except Arginine and Aspartic at 80 and 90 days old,
Tyrosine at 80 days old and Proline and Valine at all
ages.
12. Storage period also affected reaction potato
tuber rots :
a) Increasing storage period increased sugar contents
especially at the end of the storage period.
b) Orthodihydroxyphenol contents increased after all
storag~ periods after inoculation in both Alpha and
King Edward varieties. Rate of accumulation of
theiJe phenols was higher in tubers inoculated immediately
after harvesting than in tubers inoculated
one, two or three months after harvesting. It was
also found that Alpha tubers contained higher quantities
of orthdihydroxyphenols than King Edward.
These phenols decreased by prolonging storage period
for both varieties.
c) Total, free and conjugated phenols decreased gradually
by prolonging storage period.
13. Sugar content decreased by increasing storage
temperature and inoculation with the causal agent in
both Alpha and King Edward. On the other hand, orthodihydroxyphenols
decreased by increasing storage
temperature and rate of infection increased in both
cultivars. OrLhodihydroxyphenol content was higher
in Alpha tubers than in King Edward.
14. Orthodihydroxyphenol contents increased by prolonging
curing period in all varieties. It reached
maximum in Alpha and Arran Banner varieties, while
Clada and Spounta contained the least amounts of the
phenols.
15. Inoculated tubers of Alpha variety exhibited
higher auxin activities than in King Edward variety
at all Rf (a ) values except at Rf (a) 0.7 and 1.0.
Inculation decreased auxins activity in Alpha var.
at all Rf (8) except Rf 0.6, 0.7 and 0.9. On the
other hand, King Edward showed less activities except
at 0.1, 0.1 and 1.0.
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Concerning gibberellins, inoc.King Edward gained more
activity than Alpha var.except at Rf 0.6.
lated tubers, King Edward tubers
In inocuwith
F. ~bucinum showed higher activity at all Rf values
except at Rf (s) 0.6 and, while Alpha was less
active after inoculation at 0.1, 0.3 and o. 5 Rf
value.
16. Pectinase and cellulase enzymes increased gradually
by increasing incubation temperature of
cultures till 20°0. then it decreased at 30 and 35°0.
for all Fusarium species except F. solani was which
polygalacturonase enzymes activity increased at 20.
25 and 30 °c. then decreased at 35 0c. However.
o
activity of theseenzymes increased at 35 c. when
l. oxysporum was used. Concerning!. semi tectum
enzymes activity increased by increasing incubation
o 0 temperature till 20 c. then decreased at 25 C •• incr-
° eased again at 30 c. then decreased at 35 0C.
17. l. sambucinum showed higher activity in producing
pectinase and cellulase enzymes when inoculated tubers
were incubated at different temperatures. Activity
enzyme increased in inoculated tubers by increasing
incubation temperature till 20°C. then decreased at
25, )0 and 35 °C. In non-inoculated tubers. pectinmethylesterase
increased till 20°C. then decreased at while polygalacturonase and cellulase increased till
o 0 25 c. then decreased at 30 and 35 C. The same results
were obtained in Alpha and King ~dward varieties. In
general, activity of these enzymes was somewhat higher
in King Edward variety than in Alpha inoculated and
non-inoculated tubers.
18. Effect of different relative humidities on cellulase
and pectinase enzymes in the host inoculated
with three Fusarium species it was found that pectinmethylesterase
increased by increasing relative
humidity till 90 %. This occurred when ~. sambucinum
and F. avenaceum were used in inoculation. This
enzymes increased till 80 % R.H. when F. solani was
used. It was also found that polygalacturonase
increased till 95 % R.H. when ”inoculating with
F. sambucinum. In case of F. solani and E.avenaceum
this enzyme increased till 90 % R.H. But cellulase
enzyme increased gradually till 100 % R.H. in the
three Fusarium tested. Similar results were obtained
in both Alpha and King ~dward varieties but the enzymes
activity were higher in King Edward than in Alpha
tubers.
19. Phenoloxidase enzyme activity increased in
cultural filtrate of l. sambucinum than the other two
species, F. solani and !.. avenaceum. While, enzyme
activity was nearly similar in the mycelium of the
three species.
20. Peroxidase enz~]e activity in culture filterate
of F. sambucinum was higher than in F. solani and
l. avenaceum. Concerning the mycelium, the enzyme
activity was similar in the cultural filtrate of the
three species.
21. Rate of increase of phenoloxidase activity was
higher in Alpha tubers than in other tested varieties.
Spounta and Clada were the least ones. Peroxidase
activity reached its maximum in Claudia variety after
2 minutes, While it reached its highest activity in
Arran Banner after 3-4 minutes and after 5 minutes
in Alpha variety.
22. It was found that Tecto (thiabendazole), as a
systemic fungicide, reduced rots of potato tubers
artificially inoculated with F. sambucinum, using
least concentration of active ingredients. Using high
concentrations of this product did not cause phytotoxicity
on tuber germination. On the other hand,
high concentrations of chlorotha1onil or Vitavax/
Captan caused toxicity on tuber germination.
23. Thiabendazole (Tecto) can pentrate the tuber
periderm at distance of 16 and 20 Mm. inside the
tuber tissues. However, this fungicide prevented
spore germination of l. sambucinum upto 98 % at s110es ~ .
to 5 depth after 6 days of tuber treatment with 100 ppm.
24. Pectolytic and cellulolytic activities were
inhibited by using Tecto, Benlate, Vitavax/Captan
and Chlorothalonil at 1, 25, 50 and 100 ppm was the
most effective in reducing enz~nes activity. Enzymes
activity reducing reached the maximum at the time of
adding fungicides to the medium. F. sambucinum cultures
were used in this experiment.
25. Using a mixture of Tecto or VitavaxlCaptan
(fungicide) and 10 % Sevin (insecticide) dusting at
1 : 1 (1~25 kg/ton tubers) reduced potato tuber rots.
26. Using VitavaxfThiram, Orthocide-8J, Terrazol,
Terrachlor and Agrimycin 500, increased average percent
of tuber storage rots when adding thoroughly
after digging more than when using after two weeks
of harvesting.
Vitavax/Captan and Benlate fungicides decreased
tuber rots in the field under artificial and natural
conditions.