Genetic Diversity, Screening And Application Of High Efficient Symbiotic Rhizobia Isolated From Sesbania Cannabina In The Yellow River Delta

Sesbania cannabina is an excellent leguminous crop for saline-alkaline soil amelioration. Inculation with high-efficient rhzibia will promote the plant growth and is promising to improve the saline-alkaline soil amelioration. The nodules of Sesbania cannabina were collected from 5 sampling sites in Yellow River delta and 2 sampling sites in the tidal flat of Rudong County,which is one of the introduction area of Sesbania cannabina to North China. 198 strains were isolated and purified. We analysed the genetic diversity, species composition and correlation with soil factors of the Sesbania cannabina rhizobia.18 representative isolates were classified according to sequence analysis of rec A gene and used for further genetic diversity and phylogenetic analyses based on 16 S r RNA gene, housekeeping genes(rec A, atp D and gln II) and symbiotic genes(nod A and nif H). In the Yellow River, all the isolates were cataloged into 9 genospecies: E. meliloti, R. pusense, N. huautlense and undefined Ensifer sp. I, Ensifer sp. II, Ensifer sp. III, Rhizobium sp. I, Rhizobium sp. II, “Sesbanrhizobium” sp.. Ensifer sp. I was the dominant group, occupying 71%. In the tidal of Rudong County, all the isolates were classified into E. meliloti, E. sesbania, N. huautlense, Ensifer sp. I, Rhizobium sp. I. E. meliloti and N. huautlense were the dominant groups, occupying 45%, 42%, respectively. The species composition of Sesbania cannabina rhizobia in the Yellow River has changed dramatically compared with that of Rudong County, which indicated the distribution of Sesbania cannabina rhizobia showed biogeographic characteristics. p H showed significantly positive correlation with the genetic diversity(P<0.05). And within a certain range, the genetic diversity tended to be higher as the p H of soil increased.The salt content and available P of soil were determined as the significant factors for distribution of Sesbania cannabina rhizobia.The phylogenies of nod A and nif H demonstrated the possible lateral of symbiltic genes. And in this way, some rhizobia adapted to local soil types or ecoregions developed their nodulation ability on Sesbania cannabina.In plant inoculation assay of greenhouse, all the representive isolate could form nodules with Sesbania cannabina. Ensifer sp. I YIC4027 showed the best growth-promoting efficiency, excellent nodulation and nitrogen fixation ability and aline-alkaline tolerance,which was chosed as rhizobia inoculator to Sesbania cannabina in the further plot experiments in the Yellow River delta. The plot experiments indicated that compared to the Sesbania cannabina without Ensifer sp. I YIC4027 inoculant, the fresh shoot and root weights increased significantly by 46.2% and 26.1%, respectively. And the soil salt content decreased by 20%~25%. Compared to the blank field, the soil salt content decreased with a 64%~79% drop from 0.46% to 0.12% and the content of available N, available K, available P in the soil increased by 29.12%, 32.47%, 29.91%, respectively. In conclusion, Sesbania cannabina inoculated with high efficient symbiotic rhizobia Ensifer sp. I YIC4027 performed well in saline-alkaline soil amelioration in the Yellow River Delta, which is promising for widespread applications.