Studies on pathogenicity differentiation and cultured properties of Alternaria alternata in Chongqing

The pathogenicity for 13 strains of Alternaria alternata were studied,which were collected and isolated from different regions in Chongqing,were used to inoculate the detached leaves with suspension liquid and cultured properties were studied on PDA.The pathogenicity differentiation was shown by severity of the brown spots.Of the strains studied,3 appeared to be relatively powerful virulence,with a disease index of 686,632 and 618,respectively;2 were moderately virulence,with a disease index of 570 and 556,respectively,one showed relatively weak virulence,with a disease index of 229,5 were weak virulence,with disease indexes of 49,56,97,146 and 48,respectively,the other 2 were nonvirulent,and the most virulent strain was not found.The results indicated the ability of penetrating detached leaves and growth and their pathogenicity had a certainly common trend.The strains differing in pathogenicity existed in different tobaccogrowing area,and even strains with different virulence were found to be present in the same plot.The cultured properties of 13 strains were the same as that of the other reported strains,and the pathogenicity of strains was found to be related to their performance under cultured conditions. 