Study On Group Diversity Of Ustilaginoidea Virens In Sichuan Province

Rice false smut is a worldwide fungal disease in rice caused by Ustilaginoidea virens (cooke) Tak, which harmed the panicles of rice and produced rice fade balls. It was all along ignored before 1980s' because of its occasionally happening on the middle- and latex-riped rice. Since 1980s', however, with the change of rice c+++++ultivars and increasing of fertilization in the paddyfield, rice false smut in China has being more and more serious, which not only influences greatly on the yield and quality of rice, but ustiloxins also cause poisoning to human and animals. Up-to-now, the disease has become one of the major rice diseases in all the major rice production areas in China.It was limited to research on the incidence of natural field observation and investigation in the past, but there were less deep-research reports on the process of pathogen infection, differentiation of pathogenicity, the host's resistance mechanism and disease-resistance breeding. Because of the low incidence rate of inoculation, there was no study on the differentiation of pathogenicity of U. virens. In order to provide the theoretical basis of prevention and the cultivation of resistant varieties, we studied the pathogenicity of U. virens,culture characters and AFLP analysis of genetic diversity, the main results gained were as follows:1 The strains of U. virens had obvious differentiation of pathogenicity. 59 strains of U. virens isolated from different region and rice varieties in Sichuan were tested for pathogenicity on two rice varieties of Gangyou182 and Gangyou94-11 at 7～9 days before heading, the results showed that there was great difference of Diseased Panicle Rate and Disease Index.Theses differences suggested that the strains of U. virens had obvious differentiation of pathogenicity and the pathogenicity of U. virens may had relate to the geographic distribution to a certain extent but no changes in law, but it had no relate to the rice variety.2 The culture characters of U. virens were very rich. 59 strains of U. virens were showed eight colonial morphologies in terms of colony color, shape, surface uplift or depression in XBZ solid medium, every morphology included different numbers of strains, and the rate of the strains of the first and the eighth morphologies were 25.42% and 23.73%; all strains showed four mycelia characteristics in PS liquid medium after shaking-culture of 7days, the most rate of the strains is the first mycelia characteristic which was 33.90%. At the same time, different strains had different abilities of sporulation. The differentiation of culture characters and the ability of sporulation of U. virens had no relate to the differentiation of pathogenicity.3 The genetic of U. virens was stable in a small range, and the coefficient was up to 0.62. It was protuced 129 clear strips by AFLP analysis, which included 88 polymorphism strips and was up to 68.22%. Cluster analysis result suggested that the cluster group had relate to the geographic distribution and the pathogenicity to a certain extent, but no relate to rice variety.