Development Of Simulative Model For Apple Scab Epidemic In Spring In Shanxi Province

Apple scab (Venturia inaequalis) is a serious disease of apples in temperate regions throughout the world, because the causal fungus can infect the leaves and fruits. Infected leaves may drop early resulting in weaken trees, Infected fruits may be blemished and deformed. Though apple scab is the internal quarantine disease, the disease was expanding to large areas and threatening to apple sustainable production in China.The epidemic process of apple scab in spring was divided into the six following parts: vegetative growth of apple leaves,maturity of ascospores, ascospores discharge and landing on apple leaves; germination of ascospores; infection of ascospores and expanding of lesions. The relation between environmental factors and the primary components of the epidemic process of apple scab in spring was described and sub-models were developed.Dates of Accumulative temperature (degree day) from 10th April to 10th July in 1997-2003 were used for developing degree-day accumulative model that provided other sub-models with data of degree-day accumulation. Areas and ages of leaves and probit of mature ascospores were calculated by Sub-model for vegetative growth of apple leaves and ascospores maturity. Numbers of ascospores landed on leaves were predicted by sub-model for discharge and landing of ascospores which were presumedly taken them as a 'Black-box'. The probit of ascospores producing appresora was predicted by sub-model of ascospores germination with accumulative temperature (degree hour),average temperature and duration of wetness. The efficiency of ascospores infection to leaves was calculated by sub-model for average ages of leaves. The daily increased area and the number of lesions were predicted by lesion expanding sub-model based on driving variant of accumulative temperature. According to the frame of collectivity design, SMEASS model was composed of sub-models that were coupled with visual structure programming language-Delphi 7.0 in operating system-windows XP. In order to confirm the best prevent and control period, the model was used to forecast incidence of apple scab throughout one incubation period with the aid of over 0.25 mm rainfall after 10th April and start point of accumulative temperature on 10th April. Incubation period and number of primary inoculum were a constant put into the model. Through the sensitivity determination of the model, it found that date of rainfall had the most sensitivity to influence on apple scab severity, but it had the less influence on numbers of apple scab lesions on the individual apple branch. According to the result of simulated test by changing rainfall and numbers of primary inoculum, it found that the incidence of apple scab which primary inoculum caused was relatively high in duration of the first rainfall from 30th April to 20th May. Compared the result from investigation of numbers of lesions on the single branch with the result of SMEASS model by Chi-square test, it indicated that the value of X2 was 0.2309, the corresponding probability value was 0.9725. The value of X2 showed that simulative result was consistent with one of field investigation.The structure of model that reflected the epidemic of apple scab in spring in Shanxi Province was basically reasonable and result of forecasting was desirable, and supplied a solid foundation of theory for integrated apple scab management.