Studies On The Flora And Distribution Of Powdery Mildews In Gansu Province(Ⅱ)

The results of the preliminary studies showed: the powdery mildews fungi were widespread and common in all parts of Gansu province, more than 180 collections have been studied in which teleomorphic taxa have been described, 39 species belonging to 5 genera parasited on 133 host plants are known. All the collections were studied very critically with the help of upto date literature and the genera and species were confirmed according to the key provided by Zheng Ruyong et. al.(1987) and Braun U.. In the listed species two Species first reported in Gansu province were listed as follows: Erysiphe galeopsidis and Erysiphe ademophorae .The powdery mildews' ecological distribution of different areas showed: this kind pathogens were common at Gansu Province. Diversity of the host plants affected Erysiphales diversity directly, it also has a close relations with relative humidity (RH) of the environmentMost infected host plants had a well-distribution or distributed as patches.The population diffusion index and other indices of aggregations were determined in the study of spatial pattern of Engelhardtia roxburghiana Wall, powdery mildew . T he results showed that all indices were of an aggregation pattern when disease incidence were below 60%.On the bases of the results a method of sampling-double cross lineis suggested and the sample number may be between 1700-2000.