Studies On Biological Characters Of Venturia Inaequalis And Resistant Mechanism Of Apple

Apple scab, caused by Venturia inaequalis, is one of the most serious diseases of apple in China. It has been becoming more and more serious in Shaanxi province since 1997. Its continual prevalence seriously threatens the sustainable development of apple production. However, less work has been reached on biological characters and pathogenical variation of pathogen as well as resistance of hosts which would make much sense to make clear about the epidemic regulation of apple scab. Therefore, we carried on the researches on pathogen biological characters and resistant mechanism of apple to apple scab, the main results were obtained as follows.1. Eighteen isolates were isolated from the fresh infecting leaves of apple in orchards of 12 generant regions. The isolates were all pathogens of apple scab according to the shape and sporulation type of their conidia. There have cultural polymorphism among different isolates. The difference exhibited in: conidial size, colony colour and fringe flatness, growth rate on PSA medium and ability of sporulation.2. Five apple cultivars were inoculated with 18 single spore isolates of Venturia inaequalis collected from main apple grown areas in Shaanxi province. Results showed that there was obvious difference in pathogenicity among those testing isolates that could produce different types of disease spots in their size, shape and color on the same inoculated host. Based on the host reaction and cluster analysis of disease severity, isolates could be divided into three categories: strong ( pathotypeâ… ),intermediate( pathotypeâ…¡) and weak pathogenicity (pathotypeâ…¢) respectively. Resistance of 15 tested hosts to apple scab was identified by means of inoculation with 3 isolates whose pathogenicity were different. Different cultivars could be divided into 4 categories:HR(2 cultivars),MR(1 cultivars),MS(6 cultivars) and HS(6 cultivars), according to their reactions.3. Changes of enzyme activity of POD, SOD, PPO and PAL of 3 different resistant cultivars that were inoculated with pathogens and water were determined in different time. Results showed that the enzymes took part in the defense of hosts against the infection of pathogens were in different levels. By means of measuring the enzymes activity of different cultivars which were inoculated with water, we found in 12h to 48h after inoculation, examination of enzyme activity of POD and PAL could be used as an assistant method for resistant identification.