Genetic diversity and symbiotic efficiency difference of endophytic rhizobia of Medicago sativa.

Research on rhizobium diversity has paved the way for diversification of rhizobial germplasm resources. Seventy-three endophytic bacterial isolates were collected from seven tissues of five alfalfa varieties in three geographic locations in Gansu, China, and restriction fragment length polymorphism (RFLP) fingerprinting of 16S rRNA and analysis of concatenated sequence of three housekeeping genes atpD, glnII and recA, and symbiotic genes nodC and nifH were used for strain identification. Results showed that the endophytic strains were genetically diverse at different taxonomic levels, and Ensifer meliloti (31) and Agrobacterium radiobacter (12) are common Medicago sativa endophytic bacteria in Gansu, China. The nifH genes (97%-98% sequence identity) of E. meliloti strains were more diverse than their nodC genes (99%-100% sequence identity), although they evolved from a common ancestor. The dispersion degree of symbiotic phenotypes of E. meliloti strains on M. sativa cvs. Gannong No. 3, Gannong No. 9, and Qingshui was much less than that on M. sativa cvs. Longzhong and WL168HQ. This suggested that the symbiotic efficiency of E. meliloti strains on the former three alfalfa varieties was similar, and that on the later two was discrepant. Their symbiotic efficiency differed primarily according to alfalfa varieties, to a lesser extent, tested strains, indicating the difference of sensitivity of different alfalfa varieties to rhizobial strains.