الفهرس 
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Abstract
-STUDIES ON SOME CUCUMBER DISEASES IN EGWT
The present work is dealing with the most important
cucumber diseases in Egypt i.e. downy and powdery mi !dews
which incited by Pseudoperonospora cubensis (Berk. & Curt.)
Rostow., and Sphaerotheca fu~i8inae (Schlect. ex. Fr.) Poll.,
respectively.
The importance of the concerned diseases is restricted
in their destructive effect on the cucumber growing areas in
the world and Egypt.
The present study included the identification of the
two diseases in the northern gavernorates of Egypt and the
identification of the causal agents via microscopic
examination and the application of Koch’s postulates
The study revealed that injection proved to b~ the best
inoculation technique for cotyledons, while spraying procedure
was releable for the inoculation of the true leaves.
Evaluation of 14 local and introduced cucumber cvs.
against both downy and powdery mildews indicated that
RS83136 CV. was relatively resistant against downy mildew
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and immune against powdery mildew. While Wisconsin 2843 was
the most resistant CV. to downy mil~ew.
On the other hand, the obtained results indicated that
the cucumber CV. Rawa (RS83908) F• was the most susceptible
one to powdery mildew.
The study also included the effect of certain factors
on photosynthesis(Light-darkness-photosynthetic inhibitors),
the end product of the process i.e. glucose and some respiratory
inhibitors on downy mildew disease development.
This study resulted in the following items :
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1- Factors affecting or retarding photosynthesis i.e. (darkness
photosynthetic inhibitor) led to the failure of
disease development and in another words induction of
resistance in plant against the fungus.
2- Delay of photosynthesis plus addition of essential end
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product of the process (i.e. glucose} led to the
appearance of symptoms ( i . e .·downy mi 1 dew) .
3- Addition of photosynthetic end product without blocking
photosynthesis resulted in the increase of disease
severity.
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Generally, it could be concluded that the pathogen to
be developed and to induce disease symptoms, must obtain
the pro9ucts of photosynthesis to use it for its growth and
multiplication. On the other hand, delay of photosynthesis
via darkness or perhaps by minimizing light intensity, or by
shadowing led to the induction of resistance in cucumber
plants against the infection of downy mildew.
The results also indicated that the respiratory
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inhibitor viz. Iodoacetate exhibited similar effect to that
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induced by the photosynthetic inhibitor.
The study focussed a spot light on the possibility of
control! ing that diseases by the appl icati”on of certain
chemicals i .e.Ridomil MZ72, Ridomil plus 45, Afugan, Robigan,
sodium carbonate,sodium chloride,food salt,commercial sugar,
Urea and Aspirin.
The obtained results clarified that :
1- Application of the chemicals before inoculation decreased
downy mildew disease severity with the exception of
commercial, analard salt and Urea. However, applications
after inoculation were effective except the acetyl
salcilate treatment which significantly increased disease
severity.
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2- Similar behaviour was obtained with the percentage of
infected leaves due to the application of the same
treatments.
3- The sodium carbonate. Urea + Sugar. Ridomi 1 p 1 us and
Aspirin treatments increased the sporulation of downy
mildew when applied before inoculation, while most of the
t~eatments decreased sporulation when applied after
inoculation.
4- The applications of sodium carbonate, Afugan, Robigan.
Aspirin and Urea significantly decreased the percentage
of infected leaves and disease severity of powdery mildew
comparing with the rest treatments.
5- Chlorophyll content in the tested plants was increased
significantly by the Urea application treatment.
6- Nitrogen content significantly increased by the application
of Ridomil plus.
7- Most of the treatments did not affect phosphorous content
in the tested plants with the exception of Aspirin
treatment which increased this ratio.
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8- Sodium carbonate. Urea, (Urea + Sugar). and Ridomil MZ
significantly increased potassium content in the
treated plants.
9- Total sugars were significantly increased by sodium
chloride treatment and were decreased by the applications
of either commercial salt or Ridomil MZ.
10-C/N ratios were increased by sodium chloride. However,
Sugar and Aspirin treatments led to a decrease of
such ratios.
11-Plant length and leaf area did not show any significant
response toward the application treatments except the
commercial sugar treatment which significantly increased
the dry ma~ter content.
12-Application before inoculation resulted in the increment
of female flowers ratio in case of commercial •salt and
sugar treatments. However,application of Aspirin, Ridomil
MZ and sugar after inoculation increased those ratios.
13- The number of fruit/plant were significantly increased
by the application of Ridomil MZ.
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