Study On The Pathogenic Factors And Genetic Diversity Of Ustilaginoidea Virens

On the virulence of six different strains of Ustilaginoidea virens biological characteristics at different temperatures, pH, carbon, nitrogen conditions were determined and analyzed in this study. The results showed that the optimum temperature for hyphae growth was 28℃, and the colony of isolates with weak pathogenicity grow faster than the isolates of strong pathogenicity in 7d post inoculation, the optimum pH for hyphae growth was 6.0-7.0. The peptone is the best nitrogen source for the isolates with weak pathogenicity and the beef extract is the best nitrogen source for the isolates with strong pathogenicity, KNO3 and Mannitoi can’t provide nitrogen source for the U. virens and the carbamide can restrain the growth of the U.virens. The U.virens can use most carbon source, but lactose can not be used, the sucrose is the best carbon source of the weak pathogenicity strains and the glucose is the best carbon source of the strong pathogenicity strains.Inoculation conditions for false smut of rice(caused by Ustilaginoidea virens (Cooke) Tak)was studied under field condition. Among three inoculation stages of rice the case inoculated 7 d before emergence of panicle resulted in optimum diseased effect., the best Infection period of U. virens was 7 d before emergence of panicle. In these inoculation experiments of 14 d before emergence of panicle and the day before emergence of panicle, we found that high concentrations were better than low concentrations, however, at 7d before emergence of panicle, high concentrations were no better than low concentrations, speculated that only when the concentration of U. virens spores in the rice reaches the threshold value to disease.The factors influencing incidence rates of rice false smut were studied with orthogonal design by means of artificial inoculation on field. The results showed that the varieties were the greatest factor of influence. The sowing time is the later the better. The level of nitrogen fertilizer takes less influence.Sporulation, growth rate and pathogenicity of these strains were evaluated by biological methods and data were analyzed by using the software SPSS20.0. The correlation coefficient of sporulation and pathogenicity is 0.765 and the significance probability is 0.001, the correlation coefficient of growth rate and pathogenicity is 0.035 and the significance probability is 0.685. These strains of Ustilaginoidea virens were revealed and compared on the basis of 9 biological indices using ward cluster analysis. The results of clustering dendrogram indicated, all strains were grouped into 2 major clusters when the squared Euclidean distance is 25. The result revealed that the strains from seven provinces along the Yangtze River basin were similar, and the other strains from other origins (Heilongjiang, Liaoning and Guangxi) were similar. When the squared Euclidean distance is 5, the similarity between biological characteristics of the strains from neighboring provinces is high, and those strains were in the same group.Their genetic diversities were further investigated by using Rep-PCR. The genomic fingerprint profiles of 111 strains were generated by BOX-PCR, REP-PCR and ERIC-PCR respectively. The genetic diversities of the U. virens population were 0.73 (in BOX),0.62 (in ERIC) and 0.60 (in REP), respectively. The number of polymorphic bands was between 7 and 13 of each examined isolate were detected through BOX-PCR analysis. According to cluster analysis of UPGMA,6 clusters were grouped based on the boundary level of 0.70 average distances; the predominant group was group one which included 57 strains (51.4%). The strains of U. virens from Anhui, Sichuan, Guangxi, Hubei and Yunnan were grouped into group land group 4. The strains from Jiangsu, Zhejiang, Heilongjiang and Liaoning were grouped into group 2,3,5,6, accordingly. There was some correlation between BOX groups and geographic regions, No relationships were observed between BOX groups and their biological characteristics. There was significant relationship between BOX groups and the geographical regions, these results suggested that, naturally, U. virens in China might not be spread over long distances. No significant relationships were observed between BOX groups and their biological characteristics.