Screening Of Highly Efficient Stylosanthes Rhizobia

Stylosanthes is an important leguminous forage. Planting stylosanthes vigorously is a significant method to solve the problem of deficiency of leguminous forage in the south of China. Inoculating efficient rhizobia is a major way to increase the yield of legume. This study investigates the distribution areas of stylosanthes in our country, and assays the physical and chemical properties of the soil and the abundance of indigenous rhizobia there.55 strains rhizobia are screened out by the means of isolation, purification and microscopic examination. The taxonomic status and phylogeny of stylosanthes in China are determinated preliminary through the sequence of partial 16SrDNA.20 strains rhizobia which are selected by rhizobia-back test and phylogenetic tree inoculate Stylosanthes guianensis cv. Reyan No.2 and 5 under the condition of steriled soil culture, from which efficient nitrogen fixation rhizobia that are adaptable to recommended variety can be screened out.The results showed that:(1) The distribution areas where the soil characteristics vary widely are located to south of the 25 degrees north latitude and have big difference in nutrient condition. The growing acreage is reduced, but the cultivation sites are increasing.(2) The contents of the rhizobia in different cultivation sites are significantly different, which range from 0.7×102 rhizobia/g to 7.5×106rhizobia/g. Most of them are low and suitable for inoculation by which the yield of stylosanthes can be increased.(3) 55 strains rhizobia belong to Bradyrhizobium via 16SrDNA sequencing and BLAST, and are divided into 8 groups with the most similar to the known rhizobia in phylogenetic tree.(4) According to the result of soil cultivation, we screen out 3 strains YM11-1, BS1-1 and LZ3-2 which can match with Reyan No.2,and No 5,2 strains LY2-1 and PS5-1 which only match with Reyan No.2, and 1 strain SM5-1 which only matches with Reyan No.5.