| Rice sheath blight is considered to be the most destructive disease among the three serious rice diseases in China. Rice sheath blight is caused by Rhizoctonia solani AG-1 IA with a very wide host range and a very complex genetic structure. So far, very little was known about the genetic structure of this pathogen, which has made the disease control especially the sheath blight resistance breeding a difficult task. Hence, more and more pathologists and rice breeders have paid great attention to it. In this research, dozens of isolates of Rhizoctonia solani AG-1 IA from rice in Nanning were analyzed for virulence and electrophoretic profiles of esterase isozymes and soluble proteins, as well as the DNA fingerprinting by RAPD analysis, in order to characterize the genetic variation and genetic relationship in isolates of this pathogenic fungi. The main results were summarized as the following:1. Developed a reliable inoculation technique allowing to differentiate the variability in virulence of R. solani AG-1 IA isolates. Rich diversities on virulence of R. solani AG-1 IA were revealed by pathogenicity tests, and the differences in the isolates and their interaction were significant. There was no correlation between the isolates' pathogenicity and their cultural characters, but high correlation between the maturity of the isolates and their virulence.2. Twenty five isolates of R. solani AG-1 IA were characterized by esterase isozyme and soluble protein electrophoretic patterns, which revealed considerablediversity among these isolates at physiological and biochemical levels. In the EST electrophoretic patterns, a total of 11 phenotypes were detected within 25 isolates of R. solani AG-1 IA, and two characteristic bands specific to R. solani AG-1 IA with Rf values of 0.58 and 0.81 were obtained. However, the patterns of soluble protein showed remarkably different, 23 polymorphic bands were obtained among the total bands of 26, and the isolates with high virulence showed some specific bands and had 3 to 5 more protein bands than the weaker ones. Cluster analyses based on protein patterns also indicated that there was certain correlation between the virulence and protein polymorphism of R. solani AG-1 IA, but not statistically significant.3. Among the 25 R. solani AG-1 IA isolates analyzed by RAPD, 161 electrophoretic phenotypes were obtained by amplifying with 15 arbitrary primers and 5 two-primer, including 143 polymorphic bands, and the rate of the polymorphisms was 88.82%. All the isolates were different at DNA level with the highest genetic similarity of 99% and the lowest of 47%, which indicated that there were many heteroplasmic heredity locus in the pathogen, suggesting a high genetic variation potential among them.4. Both of the dendrograms which based on the protein patterns and RAPD data, showed that there were significant correlations between DNA and protein of/?. solani AG-1 IA. Both of the cluster analyses resulted in one major cluster comprising the majority of isolates tested, which sharing 80% similarity. In addition, both of them shared a uniform cluster that comparing the isolate No.24. All isolates that with high similarity at protein level shared higher similarity at DNA level as well. The results suggested that the variability of protein in the pathogen was due to the variation in DNA. RAPD analyses showed more genetic diversity among the isolates ofR. solani AG-1 IA than the protein patterns did. |
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