Anastomosis Group Determination And Genetic Diversity Of Rhizoctonia Solani In Sichuan

At present, Maize banded leaf and sheath blight (BLSB) (Rhizoctonia solani) is one of the destructive disease in the world. With the continuous expansion of the corn planting area, wide application of hybrid varieties, fertilization amount increasing and the increase of planting density, has lead to the occurrence, development and spread of BLSB becomes more and more serious. We had do fusion group identification, pathogenicity and analysis of genetic diversity for those isolates collected from different regions in Sichuan province. The obtained main results were as follows:1. One hundred and twenty-eight isolates were obtained from the three hundred and eighty-one BLSB samples of maize collected from 92 townships (town) in Sichuan Province. To identify the fusion group, the obtained isolates were tested by pairing growth with standard strains AG1-IA. The results showed that there are 125 strains of mycelia hyphae fused with standard strains and only three strains of mycelia hyphae do not fused with the standard strains, each with a percentage of 97.66% and 2.34%. The strains were not fused with AGl-IA are No.104, No.109 and No.119.2. Three maize varieties that medium resistance to BLSB, were used to do pathogenicity test for 129 strains, using SPSS 20.0 to do multiple comparison for strain’s disease grade. The results showed that there are significant differences between all strains, maize varieties, and strains and maize varieties. It suggested that the pathogenic ability of the strain depends on the strain, the variety and the interaction between them,Strains were tested for Duncan’s multiple range analysis of significant difference, the results show that the different strains exist different degree of divergence in pathogenicity. According to the 0.05 level of significance,the isolates were classified into strong, medium and weak three types, respectively, accounting for the percentage is 26.36%、27.13% and 46.51%. With the exception of a few areas, the all rest areas have all virulence strains, therefore, there are no obvious relationship between pathogenicity and its acquisition3. We analyzed the genetic diversity of 128 strains, which were collected from different regions in Sichuan Province, and AG1-IA by ISSR markers. We obtained 9 primers from 35 selected primers, which can give a clear stripe and good polymorphism. After PCR,99 bands were obtained, including 79 polymorphism bands, and the polymorphism proportion is 79.8%.According to the dendrogram constructed by UPGAM method:in the similarity coefficient of 0.69, strains can be divided into 3 categories:strain account for the largest number are the class Ⅰ;strain No.119 is class Ⅱ; strain No.109 is classified as a class III. When the similarity coefficient was 0.72 and the class I can be divided into 4 groups. Through the study found that the similarity coefficient of the isolates between 0.52-0.95, indicating that the 126 AGl-IA fusion strains collected from different regions and 2 non AGl-IA fusion exists abundant genetic diversity.The AGl-IA fusion from different regions have a phenomenon of population genetic differentiation, there are also similarities. Strains collected from Guang’an and Ya’an, most of them were distributed in first sub group of first groups, and strains collected from Neijiang were distributed in first sub group and second group of first groups, while strains collected from Zigong were distributed in the first sub group and second group of first groups. The rest taken from the same area were distributed in each group, so there is no better clustering together. At the same time, strains collected from different areas were cluster together, indicating no significant correlation between genetic differentiation of AGl-IA fusion strains and the difference of geographical position.Strains with different pathogenicity had no obvious distinction, different pathogenicity strains distrubuted in every sub group and group. Therefore, experiments show that the ISSR analysis can not distinguish different pathogenic strains effectivly.