Field assessment of symbiotic efficiency, growth-promoting ability and phylogeny of soybean rhizobial strain SCAUs8

Abstract:

[Objective] Soybean is the important legume crops in China. We can reduce chemical nitrogen fertilizer effectively by soybean-rhizobia symbiosis. The former screened soybean rhizobial strain SCAUs8 was used in field inoculation to two important soybean planting regions, in Sichuan. In addition, we identified the taxonomic position of this strain. [Methods] Field experiments were conducted to investigate the effect on soybean production by inoculating soybean rhizobia strain SCAUs8 in Sichuan hilly area and Panxi area. We studied the stress-tolerance of SCAUs8 with the point inoculation method. Growth-promoting ability was determined through Salkowski colorimetric method. Multilocus sequence analyses (16S rRNA, atpD, recA, glnⅡ, nodC, nifH) were amplied to identify the phylogenetic position of SCAUs8. [Results] Field experiments showed that plant fresh weight and dry weight inoculated with SCAUs8 were significantly higher than that of no inoculation control (CK). The yield increased significantly by 21.4%?29.7% compared with CK. The strain SCAUs8 could grow at pH 5.0?10.0. It could be resistant to 0.5% NaCl, and the growth temperature range was 10?40 °C. Growth-promoting capability of secreting heteroauxinc (IAA), was also be detected. By analyses of 16S rRNA, atpD, recA, glnⅡ, nodC and nifH sequences, we found that SCAUs8 clustered closely to Bradyrhizobium diazoefficiens USDA110T with 100% similarities. [Conclusion] SCAUs8 was a good candidate matching with main planting cultivars of Sichuan soybean. This strain had alkaline and acid tolerance, wide growth temperature range and could secrete growth-promoting IAA, although the salt tolerance of it was weak. Phylogenic study proved that strain SCAUs8 was assigned as B. diazoeffciens.

Key words:Rhizobia, Housekeeping genes, IAA, Symbiotic nitrogen-fixing