Qualitative and quantitative composition of the phyllosphere of 3 local and introduced broad bean varieties was studied in relation to pathogenesis of Stemphylium botryosum the cause of Stemphylium leaf spot. The three varieties dif¬fered in their disease reaction to the pathogen. Higher counts of epiphytic microflora were enhanced by the introduced variety «N.A. 29», than the local Romy and Giza 2 varieties. An apparent positive relation was found between absolute numbers of actinomycetes and disease resistance. However, a negative correlation was shown between the relative density of fungal population in the phyllosphere and resistance. Popul¬ation pattern of microorganisms in the phyllosphere was also studied. Some bacterial groups (i.e. Bacillus spp., micrococci and non pigmented rods) were common to all varieties, but certain other groups were associated with a particular variety. Alternaria spp. and Penicillium spp. were also common fungi in the phyllosphere of all varieties, but other genera of fungi were associated with one variety. Considerable numbers of antagonists to the Stemphylium leaf spot pathogen were dete¬cted in the phyllosphere of all varieties. Antibiotic values of different groups of microorganisms varied with the variety. Maximum antibiotic value was recorded by the epiphytic bacteria of N.A. 29 variety. Two isolated fungi arising from the phyllosphere of the resistant Giza 2 variety were active antagonists to the pathogen. From this study, it could be concluded that the phyllosphere microflora play an important role in the pathogenesis of leaf parasites. |
