Genetic Diversity And Molecular Diagnose Of Rhizoctonia Solani Isolated From Solanaceae Vegetable Crops

Sixty-five samples were collected from rhizosphere soil, hot pepper and tomato plants showing damping-off, root rot and stem rot in Taian, Shouguang of Shandong Province and Zhouzhi, Taibai of Shaanxi Province from 2005 to 2006. Thirty-nine Rhizoctonia solani isolates were obtained from these samples.The results of anastomosis group (AG) identification and sequence analysis of 5.8S rDNA-ITS of the isolates showed that thirty-six isolates (92.3%) belonged to AG-4, while only three (7.7%) belonged to AG-5. The isolates of AG-4 could further be divided into two subgroups of AG-4-HG-I and AG-4-HG-III. The 5.8S rDNA-ITS sequences of the selected isolates of the two subgroups had the 99%~100% identity with standard isolates of AG-4-HG-I and AG-4-HG-III (from GenBank). Among the analyzed isolates, AG-4-HG-I subgroup was the dominant with the frequency of 79.5%. Subgroup AG-4-HG-III with the frequency of 12.8% was the second. This is the first report that subgroup AG4-HG-III of Rhizoctonia solani isolated from Solanaceae vegetable crops in China.Ten random RAPD primers were used to assess the genetic variation of 21 isolates of Rhizoctonia solani isolates. A total of 179 polymorphic bands were amplified. The results showed that the rate of polymorphism of the isolates was 100%. The dendrogram constructed by Unweighted Pair Group Method using Arithmetic Average (UPGMA) suggested that 21 isolates could be divided into 2 RAPD groups with a genetic distance of 0.43. The isolates of AG-4 could further be divided into 2 RAPD groups with a genetic distance of 0.34. It proves that the isolates have an abundant genetic diversity.The pathogenicity of 39 isolates were evaluated in tomato with artificial inoculation method. The results showed that virulence of all these isolates were significantly different. The virulence of 36 isolates belonged to AG-4 group were significantly different. While the virulence of isolates belonged to AG-4-HG-III subgroup were lower in tomato. No significant correlation was found between the RAPD groups (RG) and their virulence groups (VG). Therefore, although the RAPD analysis is a good method to proved that the isolates of Rhizoctonia solani have an abundant genetic diversity, it's not a good method to prove that all the isolates correlation was found between the RAPD groups and their virulence. According to rDNA-ITS sequence analysis result of the different isolates of Rhizoctonia solani, a pair of specific primers for AG-4 group were designed. The molecular diagnose results showed that a sequence about 500bp only be amplified by PCR from Rhizoctonia solani isolates which belonged to AG-4. This pair of specific primers could be used to develop a fast molecular diagnose to test the disease of Solanaceae vegetable crops infected with Rhizoctonia solani AG-4 at early stage.