Genetic Diversity, Screening And Application Of High Efficient Symbiotic Soybean Rhizobia Isolated From The Regions Of Loess Plateau In China

The nodules from soybean were collected from 15 different regions of 4 provinces including Shanxi, Shanxi, Gansu and Ningxia, in Loess Plateau of China, and 262 strains were isolated and purified. This paper reported that genetic diversity and phylogeny of soybean rhizobia isolated from the regions, screening of high efficient symbiotic soybean rhizobia and application of different inoculation methods and nitrogen fertilizer.The soybean rhizobia were analysed through BOX-PCR, 16S rDNA PCR-RFLP, 16S-23S IGS PCR-RFLP and 16S rRNA gene sequencing. The three methods of BOX-PCR, 16S rDNA PCR-RFLP and 16S-23S IGS PCR-RFLP were in good agreement with the results which showed that all strains tested ascribed to two groups: the genus of Sinorhizobium and Bradyrhizobium phylogenetically. The analysis of 16S rRNA gene of five representative strains indicated that they were related to type strains S. fredi(i180 isoltes), B. japonicum(18 isoltes) and B. liaoningense(2 isoltes), homology coefficient with type strains was 100% respectively. Soybean rhizobia isolated from the regions of Loess Plateau in China showed rich genetic diversity. S. fredii was the dominant species. Bradyrhizobium accounted for 10% of the strains tested only.Representative strains were chosen according to the results of genetic diversity, soybean cultivars and origins. They were used to select highly competitive and effective rhizobial strains which were compatible with soybean cultivars jindou 25 and jindou 23 by using pot experiment in sterile vermiculite and soil. 2 strains required were more effective compatibled with jindou 25 and jindou 23 respectively.These strains were used for further study for influence of nitrogen levels on their nodulation and nitrogen fixation efficiency. The results showed that small amounts of nitrogen application had positive effect on pomoting root nodule number and nitrogen fixation, on the contrary, excessive N cannot promote and even inhibit nodule number and dry matter accumulation amount.The influence of nitrogen levels on rhizobia inoculation soybean was studied by field experiment in Yanan, Shanxi. The results indicated that the less N, the more nodule number and nodules dry weight; the plant dry weight on the ground and yield demonstrated N-50% is the best of all, followed by N-25%, and N(0), N (100%) and CK was the worst.Inoculation methods were done by field experiment in Fenyang, Shanxi. Three methods of inoculation were liquid inoculant spraying in the seed or seed dressing or rhizobia treated with a peat-based powder inoculation in the furrow for nodulation in soybean. The results indicated that liquid inoculant spraying for strain 4345 is the best, nodule number and dry weight increased more than two times compared with the other two; plant dry matter and total nitrogen accumulation amount increased more than 20%; the yield of soybean increased more than 2%. The result of seed dressing was better for strain 4338, both plant dry matter and total nitrogen increasing obviously. Inoculation in the furrow was the worst for the two strains.