Thirty-one nodulating rhizobium strains were collected from root nodules of spring and winter type faba bean cultivars grown in micro ecoarea, i.e. the same field in Chengdu plain, China. The symbiotic efficiency and phylogeny of these strains were studied. Effectively nitrogen fixing strains were isolated from both winter type and spring type cultivars. Based on phylogenetic analysis of 16S rRNA gene and concatenated sequence of atpD, glnII and recA genes, the isolates were assigned as Rhizobium anhuiense and a potential new Rhizobium species. The isolates were diverse on symbiosis related gene level, carrying five, four and three variants of nifH, nodC and nodD, respectively. Strains carrying similar gene combinations were trapped by both winter and spring cultivars, disagreeing with the specificity of symbiotic genotypes to reported earlier faba bean ecotypes.
To find wide host range compatible potential inoculant strains with high efficiency in N fixation, we isolated rhizobia from soybean root nodules in Sichuan. Most of the isolated rhizobia were no-or low-effective strains. Eight out of 75 isolates promoted significantly the growth of soybean cultivar Gongxuan No. 1. When tested with three more soybean cultivars, the isolates assigned as Bradyrhizobium japonicum SCAUs36, Bradyrhizobium diazoefficiens SCAUs46, and Ensifer fredii SCAUs65 promoted significantly (P<0.05) the growth of each cultivar. The nodC and nifH genes of bradyrhizobial SCAUs36 and SCAUd46 and E. fredii SCAUs65 grouped together with those of broad host range strains. In field experiments with two more soybean cultivars, B. diazoefficiens SCAUs46 and E. fredii SCAUs65 performed well both in mild and hot-dry climates, implying that the isolates were potential inoculants to be applied in diverse soil and climate conditions.
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