| The fungus genus Rhizoctonia DC belongs to Agonomycetales Hyphomycetes, Deteromycotn, i. e. anamophic Ceratobasidium, Thanatephorus etc., widespread. In a wide sense also used for mycelial pathogens bolong to Epidorhiza (Tulasnella), opadorhiza (Cebacina),Thanatophyton (Helicobasidium), and even to ascomycetes (Ascorhizoctonia). Its species consists of a wide array of genetical variation and diversities. Beacause of the economic and ecological importance, eyes of many scientists have focused on it. It is difficult for us to identify this kind of fungi because of the absence of distinctive taxonomic features.The method of anastomosis grouping had become the most useful tool toward understanding genetic diversity in Rhizoctonia and applied successfully in classifying Rhizoctonia into different groups in the early 70's of 20 century. However, anastomosis group(AG) can't give us enough information of genetic and phylogenetic diversities between AG or intraspecific group(ISG) , and within AG or ISG. Molecular technology is the most popular and powerful tool in the study of genetic variation of fungi.The objectives of this study were (1) to understand the genetic variation of Rhizoctonia from main winter wheat growing areas in China, (2) to study genetic diversity of Rhizoctonia, classified into different AG, from different regions of Yunnan Province, (3) to clarify the genetic diversity of isolates belonging to AG1-IA from different host (rice and corn). All the studies are based on the RAPD and rDNA-ITS sequence analysis methods. The main results gained are summarized as follows: 1. Pathogenicity of 37 isolates of Rhizoctonia, screened from 55 isolates from the different regions in Shandong province, were determined on three winter wheat varieties by inoculation test. The 37 isolates were divided into 4 groups of pathogenicity based on average disease index: highest (4), higher (7), moderate (18), and weak (8). 2. Genetic variation of the 36 isolates of binucleate Rhizoctonia from Shandong province was analyzed by RAPD assay. Fifteen oligonucleotide primers were selected from 140 RAPD primers. A total of 171 RAPD bands were amplified, and 161 were polymorphic bands. The rate of polymorphism of the isolates was 94.15%. The dendrogram derived from RAPD data by UPGMA suggested that the 36 isolates could be divided into 4 RAPD groups with a genetic distance of 0.33. Three isolates, wk-6, wk-37, and wk-13, each of them made a separate group. The other 33 isolates, the members of AG-D, made the 4th group, and could be further divided into 7 subgroups with a genetic distance of 0.25. It proves that the isolates of wheat eyespot disease have an abundant genetic diversity. No significant correlation was found between the RAPD groups and their pathogenicity. 3. Genetic variation of 37 isolates of binucleate Rhizoctonia from Hebei, Anhui, Henan, Shanxi, Jiangsu and Shandong Provience was analyzed by RAPD assay with 15 RAPD primers. The dendrogram derived from RAPD data by UPGMA suggested that the 37 isolates could be divided into 3 RAPD groups with a genetic distance of 0.30. The largest group consisted of 34 isolates, and all of them were AG-D members. The other two groups contained 2 and 1 isolates, respectively, which have relatively long distance with AG-D standard isolates. Further analysis indicated that the RAPD groups of isolates belonging to AG-D have significant correlation with their locations. It proves that the genetic variations of Rhizoctonia cerealis have significant relations to the environment they lived.4. The 5.8S rDNA-ITS regions from 21 isolates selected intentionally from 72 isolates of Rhizoctonia based on RAPD were cloned and sequenced, and from anastomosis tester strains of AG-D and CAG1, were download from Genbank. The results derived from alignment of the sequence and phylogenetic analysis indicated that there was a sequence similarity of 52.1%-99.8% on the ITS-5.8S rDNA region of all the isolates. The isolates tested can be divided into three groups. The largest g...
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