Preliminary Study On Rhizobium From Caragana In Ordos Region

Caragana rhizobia is a kind of symbiotic nitrogen fixing bacteria which can infect Caragana plants and can form a nodule in the root, its wide distribution, infection and strongth, to promote plant growth, improve soil fertility and improve the micro ecological environment plays an important role. At present, the domestic research on genetic diversity of Caragana rhizobia are very few, therefore, in this paper,43 strains of Erdos and Hangjinqi Balagong sites were conducted phylogenetic analysis based on16S rDNA, physiological and biochemical characteristics of Caragana rhizobia, inoculation experiment. The growth of Caragana plant affected by Caragana rhizobia will be performed in the further study. The main results are as follows:1. Rhizobia isolated from Erdos samples have a degree of diversity, and they are distributed in the 3 phylogenetic branches, belong to Rhizbobium and Mesorhizobium. Rhizobia isolated from Hangjinqi Balagong sample points show some diversity, and they are distributed in the 4 phylogenetic branches, belong to Agrobacterium and Mesorhizobium. Mesorhizobium was the dominant genus among them. Phylogenetic analyses showed that originate from the same sample were basically all together.2. Determination of two representative strains of physiological and biochemical characteristics, results showed that (1) Strain Ⅰ grow faster than Strain Ⅱ in 1-7 days YMA culture and obtained greater biomass; (2) both strain Ⅰ and Ⅱ do not absorb Congred dye; (3) both strain Ⅰ and Ⅱ can grow in 1%[Na+] YMA medium; (4) the pH range which strain Ⅰ and Ⅱ can grow is from 6.0 to 9.0, the pH value that strain Ⅰ obtained maximum biomass is PH=8.0, and the pH value that strain Ⅰ obtained maximum biomass is PH=7.0; (5) Strain Ⅰ and Ⅱ both can use mannitol and sucrose better, can not make good use of lactose, maltose and soluble starch, but they have big difference in make use of glucose; (6) Strain Ⅰ and Ⅱ can utilize organic nitrogen better than inorganic nitrogen, among all tested nitrogen source yeast extract powder is the significant best for them growth.3. In the inoculation experiment, the results show that the plants inoculated strains Ⅰ, Ⅱ are both significantly better than the control plants. (1) shoot height and root length ofthe plants inoculated strain Ⅱ is higher and longer than those of the plants inoculated strain Ⅰ; (2) the dry weight and fresh weight of plants inoculated strain Ⅱ is higher and longer than those of plants inoculated strain Ⅰ; (3) on the nodules, plants inoculated strain Ⅰ produce bigger nodules than plants inoculated strain Ⅱ, but on the contrary, plants inoculated strain Ⅱ produce more nodules than plants inoculated strain Ⅰ.