Identification of the causal organism of bacterial wilt of mulberry and its biovars

The causal organism of mulberry wilt and its characteristics were studied for effective management of the disease which severely occurred recently in Hangzhou Region of Zhejiang Province, China. Fifteen bacterial strains were isolated from the samples of bacterial wilt infected mulberry plants in Tonglu and Lin’an counties of the province. They were identified as Ralstonia solanacearum after 25 items of bacteriological tests, colony morphology, pathogenicity test, Biolog and FAME analysis, RAPD-PCR test and compared with the 4 standard reference strains. It was confirmed that R.solanacearum is the causal organism of the mulberry wilt and demonstrated that except Biovar Ⅴ certain amount of Biovar Ⅳ also exists in mulberry, which was 73.3% and 26.7% of the 15 isolates, respectively. A new simple and reliable method for mulberry pathogenicity test of the bacterium was established in this study.