Genetic Diversity And Phylogeny Of Soybean Rhizobia In Sichuan, China

In order to investigate the diversity and phylogeny of 171 soybean rhizobium strains isolated from Sichuan province of China,16S rDNA PCR-RFLP, ERIC-PCR, 16S rDNA, recA, atpD, glnⅡ, nodC and nifH sequences analyses were used in this study.The results of 16S rDNA PCR-RFLP indicated that all the tested strains had 39 16S rDNA PCR-RFLP types, and there were 27 types for fast-growing rhizobium while the others were slow-growing rhizobium. The type 19(58 strains) had the most strains which were all slow-growing rhizobium, then it was the type3(34 strains) for fast-growing rhizobium.All of the fast-growing rhizobium had 60 heredity types in ERIC-PCR analysis, and it were clustered into 18 groups(Al-A18) at the similarity of 80%. The predominant group A1 had 20 strains of type3, while A10 had 9. The slow-growing rhizobium also had 60 heredity types, and it were clustered into 8 groups(B1-B8) at the similarity of 78%. The 8 groups all had the strains of type 19, and B2 had the most, while the strains of B1, B5 and B6 all were type 19.Picked out 74 representative strains to analyse the housekeeping genes(recA, atpD, glnll) and symbiotic genes(nodC and nifH) based on 16S rDNA PCR-RFLP and ERIC-PCR. The results of 16S rDNA indicated that the tested strains were Sinorhizobium(21 strains), Rhizobium(9 strains), Agrobacterium(8 strains), Aurantimona(4 strains), Ochrobactrum(1 strains), Klebsiella(1 strains), Bradyrhizobium(30 strains).Housekeeping genes(recA, atpD, glnll) analysis had good consistency with 16S rDNA, but also some differences. s96, s152 and s163 were got together with R. tibeticum CCBAU85039 in the 16S rDNA phylogenetic tree, but they were separated in the phylogenetic trees of recA, atpD and glnll. So s96,s152 and s163 could be new species. The results of MLSA(recA-atpD-g1nⅡ) indicated that MLSA phylogenetic tree was more stabilization than single gene phylogenetic tree, and also could separate strains clearer.The phylogenetic trees of symbiotic genes(nodC and nifH) had obvious differences with the other genes. Some strains gathered at 100% similarity in nodC and nifH phylogenetic trees, but had more genetic relationship in other genes phylogenetic trees. It may be lateral transfer occured in symbiotic gene of different rhizobias, so even though some rhizobias had the same or similar symbiotic genes, but their genetic background were different.Took above-mentioned into consideration, this study showed that abundantly genetic diversity exhibited on rhizobia retreived from soybean in Sichuan province of China, Bradyrhizobium (82 strains) was the predominant genus, then it was the Sinorhizobium (53 strains). Some of the representative strains of B.japonicum and B. diazoefficiens had the same 16S rDNA PCR-RFLP types, such as s10 and s8 were both type19. So, would separate all of the strains in Bradyrhizobium, should do analysis about diversity and phylogeny of all the strains.