Genetic Structure Of Populations Of Rhizoctonia Solani Anastomosis Group-1IA From Maize And Rice Based On SSR

Rhizoctonia solani J.G. Kuhn are geographically distributed worldwide and showed a host range of more than250plant species. Currently, R. solani can be divided into14anastomosis groups and several AGs have been subdivided further into subgroups that differ for one or more biochemical, genetic, or pathogenic characteristics. R. solani AG1-IA belonged to anastomosis groups1(AG1) subgroup IA and caused severe disease in corn, rice and soybean, named banded leaf and sheath blight of corn or sheath blight of rice. Analysis of the distribution of genetic diversity within and among populations can be used to identify patterns of gene migration. And knowledge of the genetic structure of pathogen populations is hypothesized to offer insight into their future evolutionary potential, which could be useful to optimize the management of resistance genes in agriculture. The objectives of this study were (1) to analyse and describe the genetic structure within and among R. solani AG1-IA infecting maize from8different provinces of China by SSR analysis and (2) to measure gene and genotype diversity in R. solani AG-1IA populations infecting rice in Shandong and to determine whether they differ markedly from those of isolates from Guangdong regions.1. Collection and identifacation of Rhizoctonia solani AG1-IASamples showed symptome of banded leaf and sheath blight of corn from Anhui, Jiangsu, Shanxi, Henan, Shandong, Hebei, Liaoning and Jilin provinces were collected and isolates of R. solani were obtained from diseased maize sheath. Total of104isolates from maize were identified as AG1-IA according to hyphal anastomosis and5.8SrDNA-ITS sequence. Samples of rice sheath blight were collected from Linyi, Dongying and Jiyang of Shandong province and total of51isolates from rice were identified as AG1-IA according to hyphal anastomosis and5.8SrDNA-ITS sequence. The other10AG1-IA isolates were obtained from Guangdong province.2. Pathogenicity differentiation of R. solani AG1-IA from maizeThe pathogenicity of104AG1-IA isolates from maize were tested on detached corn leaves under controlled conditions. All the isolates could be divided into3types according to the DPS system UPGMA cluster analyzing data. Twenty nine isolates such as LY1-3-1, YWK-195and SZ002-19had high pathogenicity that showed longer lesion in maize than others. Eleven isolates showed lower pathogenicity and64isolates formed middle lesion on maize leaves. The pathogenicity of different AG1-IA isolates showed no relationship with the geography sites that means the virulente strains of AG1-IA existed in different areas and distributed randomly. 3. DNA fingerprinting of R. solani AG1-IA from maizeGenetic diversity was detected among104isolates by using SSR markers. On the basis of amplification, total of36bands were identified based on10SSR markers in104AG1-IA isolates. A range of2-5bands in each pair of primers could be detected. The result of cluster analysis using UPGMA showed that all the104strains were divided into different groups according to genetic similarity coefficient from0.57to1.00. These data suggested that R. solani AG1-IA on maize existed rich genetic diversity and there was no obvious correlation between SSR grouping of AGl-IA from maize and geographic origins.Nei’s genetic diversity index was highest at Jiangsu and Anhui province, respectively were0.4544and0.4630. Shannon’s index also was highest at Jiangsu and Anhui province, respectively were0.8402and0.8001. It showed that Genetic structure of R. solani populations from Jiangsu and Anhui province was more complex than other regions. Genetic distance was largest between Anhui and Hebei province, and smallest between Jilin and Henan province.For analysis of the genetic differentiation of populations, there was a certain degree of genetic differentiation among populations and within populations. The variation among populations accounted for24.6%, while within populations was75.4%. Therefore, the variation mainly occurred within populations.4. DNA fingerprinting of R. solani AG1-IA from riceA total of10pairs of SSR primers were selected for amplification of highly polymorphic bands. A total of32bands were identified based on10SSR markers in61R. solani isolates from4areas. A range of2-5bands in each pair of primers could be detected. The result of cluster analysis from UPGMA showed that the tested strains were divided into different groups as different genetic similarity coefficient from0.50to1.00. It showed that strains isolated from different regions, mostly were clustered as geographical origins, indicating that there was a certain of correlation between SSR grouping and geographical origins.Nei’s genetic diversity index was highest at Guangdong, and was0.4228; Shannon’s index was highest at Guangdong, and was0.7309. It showed that strains isolated from Guangdong had complex genetic structure. Genetic distance was largest between Guangdong and Jiyang, and smallest between Linyi and Jiyang.For analysis of the genetic differentiation of populations, there was a certain degree of genetic differentiation among populations and within populations. The variation among populations accounted for17.4%, while within populations was82.6%. Therefore, the variation mainly occurred within populations.