Genetic Diversity And Population Differentiation Of Rhizobia Isolated From Robinia In Northwest China

In order to investigate the genetic diversity and phylogeny of169rhizobial strainsisolated from root nodules of Robinia in Tarim of Xingjiang province, Zhangye of Gansuprovince and Zhongwei of Ningxia Province of China,16S rDNA PCR-RFLP, rep-PCR,16SrDNA sequences analyses and intro-species genetic structure analysis were used in thisstudy.Based on the combined result of the PCR-RFLP and phologenetic analysis of16S rDNA,169rhizobial strains were classified into three genuses, including Mesorhizobium, Rhizobiumand Sinorhizobium. Seventy-four isolates were assigned into Mesorhizobium genus, sixty-nineRhizobium genus and twenty-six Sinorhizobium genus.The rep-PCR fingerprint analyses of169strains indicated that the genetic distance of allpairs of strains fell into the range of0to0.4and all stains were clustered into three branchesat the level of70%similarity, corresponding to Mesorhizobium, Rhizobium andSinorhizobium, respectively.We chose33strains that clustered with M. amorphae at the test of16S rDNA toinvestigate the degree of population differentiation. They distributed in six populations andhad a different number of samples. We sequenced the nifH, recA and atpD and combinedthem into one single dataset. In total, we recovered26haplotypes based on the combineddataset. Five haplotypes from Clade A occurred more than two populations, i.e. H1-H5, whilethe remnant21haplotypes were private for only special population, which showed the greatdifferentiation between pairs of population. AMOVA analyses revealed the most geneticvariations (85.61%) were distributed in the within populations.Phylogenetic analyses of the recovered26haplotypes identified three tentative clades(A,B and C), all of which had distinct geographic range. The Clades A and B containing25haplotypes with a star-like phylogeny are distributed across most of the sampled populationswhile Clade C with only one haplotype was fixed only in Population ZW1.Although thesamples in the present study were only collected from six regions and the available samplesare limited, our finding suggested that there was great differentiation in different populations. Our studies have exhibited abundantly genetic diversity on rhizobia retrieved fromRobinia across diverse sampled region. In addition, for the complement of the richness ofdiversity in rhizobial resources, the determination of rhizobial phylogenetic status, thisresearch has profoundly provided a valuable reference and has substantially established asolid basis.