الفهرس 
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Abstract
Isolation trials carried out from onion bulbs showing the symptom of neck rots collected from Giza, EI-Minia and Sohag governorate Isolation process revealed five Botrytis sp isolates recognized as B1 to B5.
During isolation, the associated fungi were recorded. Eighty four percent of isolated fungi from diseased onion bulbs from Giza belonged to B. aI/ii, while other fungi ranged from 2.2 to 4.9%. In case of diseased onion bulbs from Minia B. al/i represented 82.3% while other fungi ranged from 2.4 to 8.1%. Isolation process from diseased onion bulbs from Sohag reveled 75.4 of isolated fungi belonged to B aI/ii, while other fungi ranged from 1.3 to 13.1%.
Pathogenicity tests were carried out on onion seedling and bulbs cv Giza 6. Data showed that B 1 caused the highest disease severity followed by B 5 among the tested ones. These isolates caused 49.4% and 40.1 bulbs rot tissues respectively. Inoculation onion seedling with isolate B1 induced 58.3% diseased plants with 3.71 disease severity. The disease incidence was 37.1 and severity was 1.28 as a result of inoculation with B4
Among the tested cultivars, Giza 6 shows the lowest infection rate. The percent of infection with B1 was 58.3% and the disease severity was 2.5. White cultivar showed the highest infection rate. Concerning isolate N, B4, onion varieties of Race 504, White and Shandaweel 1 showed the highest infection rate. Percentages of infected plants were 85.2, 69.8 and 62 with disease severity 2.6,2.9 and 3.1 respectively.
The obtained data shows that the infection by B. allii decreased onion bulbs storagability. The weight of healthy onion of the tested cultivars decreased during storage from 16.6 to 32 % fter 5 months in storage and the infected onion lost about 27.1 to 67.9 of the weight during the same period. The highest decrease in weight was recorded in White cv and Race 5.4 .
Effect of pH values on growth of B. allii was studied by growing the fungus using Czapek’s liquid and solid media with different pH values. The best growth parameters i.e. the linear growth, number of spores/ ml and dry weight were obtained at pH 6.0 and 7. Maximum mycelial dry weight and sporulation for Fusarium sp were occurred at pH 7
Obtained data showed that the highest growth parameter for B. allii was obtained between 15-20°C.