Genetic Diversity Of Venturia Inaequalis Of Shaanxi(China) With AFLP Analysis

Apple scab, caused by Venturia inaequalis (Cooke) Wint., is one of the most serious apple fungal diseases of orchards all over the world. Apple scab also known as black spot, scab or mildew. It would cause weakness of trees, early drops of leaves, dehisce and abnormality of fruits, which made apple fruits lose their values. Since 1997, sustainable development of apple industry in Shaanxi Province was threatened by the continued occurance of the disease. Researchs on the pathogen were mainly about biology, morphology, pathogenicity but little about its genetic diversity. It would provide evidence for forecasting the disease and breeding resistant varieties if we confirmed the genetic diversity and its relationship with inaequalis shape, species virulence, disease transmission of inaequalis in Shaanxi Province.In this study, 46 strains of Venturia inaequalis from different regions of Shaanxi Province were purified for AFLP analysis to export their genetic diversity and relationships . The main results are shown as follows.1. Three kinds of methods were compared for DNA extraction of apple scab pathogen and SDS method was considered as the most suitable method, with which high-purity, high-quality mycelium genomic DNAs were abtained for AFLP analysis of Venturia inaequalis.2. Factors affecting AFLP analysis were discussed. A suitable AFLP reaction system for Venturia inaequalis was established by means of optimizing the major reaction conditions such as the amount of restriction enzymes, restriction enzyme digestion time, pre-amplification, selective amplification of dNTP, MgCl2 and Taq DNA polymerase.3. 25 primer pairs were adopted for AFLP analysis of 46 Venturia inaequalis strains. Using these primer pairs 421 bands were generated of which 326 bands were polymorphic ratio for 77.4%. The genetic similarity coefficients of genetic diversity were among 0.8151 ~ 0.9487 which revealed the great divergence of Venturia inaequalis strains in Shaanxi Province.The strains which isolated from Xunyi Gala and Xingping Gala showed highest similarity coefficient while the strains isolated from Xunyi Gala and Xingping Red Star was lowest. Gst coefficient among different groups from Venturia inaequalis of Shaanxi Province was 0.37, which signified that 37% of the total variation from different groups, 63% of the total variation within groups.4.Based on AFLP analysis from 46 strains, UPGMA phylogenetic tree was constructed using NTSYS software adopted 0.71 as the threshold value. The Venturia inaequalis strains were classified into two categories. The strains isolated from Xunyi Gala, Xingping Gala and Xunyi Fuji clustered one branch, while the strains from Xunyi Red Star, Xingping Red Star, Xunyi Qinguan and Xingping Qinguan came together. The results showed that the genetic diversity of apple scab pathogen strains had no significant relationship with geographical origin. but close related to varieties of host cultivars.