| Apple scab, caused by Venturia inaequalis (Cooke) Wint., is one of the most serious diseases of apple and ornamental crabapple. Both leaves and fruits can be infected and particularly infected leaves may drop resulting in unsightly trees, with poor fruit production. Infected fruits are blemished and often severely deformed. In China, apple scab that only occurred in a few of local sites was determined as quarantine significance. Study on apple scab is very few in China. It was a new disease found firstly in 1997 in Xinping, Liquan, Yangling, and Xunyi in Shaanxi province. The qualitative and quantitative analysis for epidemioloyg of apple scab were studied, and the main results were obtained as follows. 1. The biological characteristics of V. inaequalis had been preliminarily studied. Standard biological parameters were acquired. The total of 228 isolates were isolated from the infecting fruits and leaves of apple in orchards of Xunyi, Xinping, Qianxian, Yangling, and Meixian county, Shaanxi province. The isolates were all pathogens of apple scab according to the shape and sporulation type of conidia, and determined results of Koch's postulates. Favourable media for the growth and sporulation of V. inaequalis include apple leaf juice agar medium, V8 medium and PSA. 2. Epidemiology of apple scab in semi arid plateau in Shaanxi province was studied with field-investigating, general survy, and spore-trapping during 2001-2003. Results showed that ascospores were validated as the inoculum of primary infection of V. inaequalis and conidia could not overwinter on arid plateau of Weibei. Mycelia overwintered in twigs in open was impossible.3. Seasonal epidemic curve and function for apple scab were conducted according to the systematic data of the disease in orchard. Two peaks of apple scab appeared in the first 10 days of July and in the beginning of September respectively during apple growing seasons in Xunyi county, Shaanxi province.4. Factors affecting epidemics of apple scab were studied on the basis of temperature, relative humidity, rainfall and epidemic levels of the disease during 1997-2003 with stepwise regression. Results showed that the key factors affecting epidemics of apple scab were rainfall in April and August, average daily relative humidity of last December and average daily temperature in January and July. Prediction model was set up through collecting meteorologic and disease epidemic data in 1997-2003. Back prediction of apple scab occurrence in 1997-2003 was carried out respectively and less than 0.5 of absolute residue value was determined as the statistical standard. Results indicated that predictive model had highly accurate ratio.5. The simulation model of apple scab in spring (SMASS) was developed to simulate dynamics of apple scab in spring based on 12 models, such as leaf area, twig leaf area, pseudothecium number, probability of ascus, number of released ascospore, concentration of ascospore in air, number of landed ascospore, duriation of leaf wetness, probability of germinated ascospore, probability of effieciency infection, area of lesion, and number of lesion. SMASS was written in Borland Delphi 5.0 which was Oriented Object Programming (OOP). The executing file was standard 32 bit windows program. The verification and validation of SMASS were analyzed. Temporal dynamic of apple scab in orchard was logically explained by SMASS. The main parameters of the model were all sensitive. Results showed that SMASS might be a powerful tool for simulating and optimizing management program of apple scab. But further work is needed to improve its precision and accuracy.6. Quantity of DNA of V. inaequalis extracted by CTAB method, SDS method, Parker's method and modified SDS method was detected by ultraviolet spectrometer. Results showed that DNA quantity determined by modified SDS method was much more than that of other three methods. It was twice DNA quantity extracted by Parker's method. A260 nm / A280 nm value of DNA obtained from modified SDS method was between 1.700 and 1.900...
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