Study On Regularity Of Occurrence And Epidemic Of Plasmopara Viticola Causing Grape Downy Mildew In Xinjiang

Grape downy mildew, caused by Plasmopara viticola. The grape production regions are divided into epidemic, generally epidemic and barely epidemic region by investigating the occurring, historical occurrence and climatic conditions during May to August from 2012 to 2014 in Xinjiang. Yili river valley represents epidemic region; generally epidemic region is mainly areas along Tianshan mountains in northern Xinjiang, Kuerle, Akesu Atushen, etc; barely epidemic region incorporate Turpan, Hami and dry regions in southern Xinjiang. Its distribution related to the local climate conditions, especially rainfall. In the years with more rainfall, infection occurred seriously in epidemic and generally epidemic region.The primary source of P. viticola was determined through not a matter of observating overwintering of diseased branches, morphology of oospores(pre-overwintering oospores and overwintered oospores), plant residues as the primary infection source and grape downy mildew in greenhouse. The results showed that the fungus overwinters as oospores on plant residues in wine-growing region of Shihezi, and oospores are the source of the primary infection, however the diseased seedlings could be the primary source in greenhouse. Few oospores were sought with conventional methods, which was easy to find oospores in the process of grinding–sieving–centrifugating–microscopic examination.The primary infection characteristics were identified by surveying administration, primary infection sites, positions and topography, and analyzing relation between primary infection and climatic factors, the primary infection mainly takes place in the environment with low-lying, luxuriant growth, branches untrimmed, weed infestation, near the ground and high air humidity. Accoding to these reasons, many proposes and measures of the prevention and control must be taken before it become more serious.The germination optimal conditions and survival time in different artificial environment for the sporangia were determined through setting different conditions in incubator. It is shows that the germination can only occur in the free water within a range of 10℃ to 25℃ with an optimum of 15℃ to 20℃. The survival time shorten with the increase of temperature and humidity. UVC is also important factor to the survival timer which can surviver only 3 hours under 0.64×102 μW/cm2 UVC in Shihezi. In September, the sporangia will be dead under point-blank light of sunlight after 4 hours in Shihezi.The result from SPSS software showed that the rainfall in the middle of May and the beginning of June were the main factors which influence the occurred time of primary infection, and then established the discriminant model, the accuracy of the data for back-test 75.0%. The rainfall and greater than 5 mm rainfall frequency in August and rainfall and greater than 2 mm rainfall frequency in June to August were the main factors which influence the disease severity, and then established the discriminant model, the accuracy of the data for back-test 100.0%.