| Genetic diversity and phylogeny of 55 slow-growing rhizobia isolated from peanut (Arachis hypogaea) in China were determined by analysis of host-plant range, phynotype, 16S rRNA RFLP, 16S rRNA sequence, 16S-23S IGS RFLP, RAPD, REP-PCR, DNA-DNA hybridization homology. At the same time, the competitive nodulation capacity of rhizobia, effect of host plants and soil pH on the rhizobia were determined for screening and improvement of high effective rhizobium inoculant.Results of host-plant range test shown that all slow-growing isolates could effectively form nodules on Arachis hypogaea and Phaseolns vulgaris. They could not nodulate on Visia sativa, and part of them could nodulate Glycin soja and Glycin max.Results of phenotype test shown that all peanut isolates and reference strains of B. japonicum and B. elkanii were clustered into a group and differed from the other genus of fast-growing rhizobia in low similarity. At the similarity of 65%, all slow-growing strains could be divided into I and II groups which were further divided into LA, IB, Ha, lib and lie subgroups in the similarity of 78%.Results of 16S rRNA PCR-RFLP and its sequence analysis shown that strains tested were closed to B. japonicum and B. liaoningense, but they were relatively far from B. elkanii phylogenetically and their sequence divergences were from less than 1% up to 3-4% respectively. Although belonging to the same genotype, representative strain JZ1 was closed to USDA110, and HA1 was clustered into the same branch with USDA110, USDA122 and USDA127, but WC7 and SD4 were clustered independently.Strains tested were divided into three IGS types according to size of 16S-23S rRNA IGS PCR. At the similarity of 69%, strains tested were separated from B. japonicum and could be further divided into A, B, C, D and E subgroup at the similarity of 84%. Subgroup A composed of strains HNS1, SDT3 and SDT4 was belonged to IGS-II. Subgroup B mainly composed of strains from Shandong to IGS-III. Subgroup C was composed of strains from Henan, Shandong, Wuchang and Anhui. Subgroup D was composed of strains from Hongan, and Subgroup E was composed of strains from Henan and Wuchang. Subgroup C, D and E were all belonged to IGS-I.Results of RAPD analysis shown that peanut isolates and reference strain Bj were divided into A, B, C, D, E F and G subgroups at the similarity of 75%. The reference strain of Bj were clustered into subgroup G independently. At relatively higher similarities, strainstested from different area were further clustered which reflected the effect of geographical factor on rhizobia genetic diversity.Results of REP-PCR tests shown that at the similarity of 60% peanut isolates were separated from Bj which indicated that there existed phylogenetic difference between peanut isolates and Bj. At similarity of 65%, peanut isolates were divided into Groupl and II, and subdivided into IA, IB, IIC, IID, HE and IIP 5 subgroups at high similarities.Results of G+C mol% test shown that all slow-growing isolates were belong to the same species. More than 70% DNA-DNA homologies were determined among 4 representative strains USDA6, and USDA110 (type strains of B. japonicum). Low DNA homologies were detected with USDA76 (type strain of B. elkanii). The results show that peanut isolates tested all be identified into 2 biovars of the B. japonicum.From the above results, it can be concluded that peanut isolates have various genetic diversities. At relatively low similarity, strains tested were divided into Groupl and II. Group I was further divided into IA and IB, and Group II was divided into Ha, lib and He. IA was mainly composed of the strains from Sandong province. IB was composed of strains from Anhiu, Henan and Wuchang. IIa were composed of HNS 1, SDT3 and SDT4; lib were mainly composed of strains from Jinzhou; Ilc were solely composed of strains from Hongan. Strains of Ha and lie can nodulate on Glycin so/a and Glycin max. All the results suggested that peanut isolates are all belong to biovars of B. japonicum. They are designed...
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