Evaluation and Assessment of Diversity of Rhizobia for the Establishment of Annual Medics in Soils at Different pH Levels.

Annual medics are used as high quality forage. These are especially grown at high pH soils of the southern Great Plains and can produce up to 112 Kg of nitrogen per hectare with effective inoculants. Selection of better adapted medics in association with appropriate symbiotic bacterial partner is agronomically important. This study is aimed at developing inoculants for the introduction of medics in herbage system in USA. Four soil types with different pH (Vashti, TX, Bonti sandy loam pH 4.6; Burneyville, OK, Eufaula loamy sand pH 8.0; Burneyville, OK, Norwood clay loam pH 8.0; Gene Autry, OK, Dale silt loam pH 5.2) were used for the isolation of indigenous rhizobia. Two methods were used for the isolation. First method was the isolation of rhizobia by soil dilution and second method was by trapping. Eight different species of medics (M. orbicularis, M. polymorpha, M. minima, M. rigidula, M. rigiduloides, M. arabica, M. lupulina and M. truncatula) were used as trapping mediator for rhizobia in different soil types. By direct isolation method 36 isolates (7 from Bonti, 5 from Dale, 11 from Eufaula and 13 from Norwood soils) were isolated. By trapping method, nodules were recovered only from Norwood clay loam soil at pH 8.0. Only M. truncatula was able to form nodules in Eufaula loamy sand. The 16S rDNA Sequencing was used for characterization of all the isolates. On the basis of sequence similarity, it’s been found that the all rhizobia recovered from the root nodules belong to Sinorhizobium group. The 10% isolates from Bonti soil, 10% isolates from Dale soil, 60% isolates from Eufaula soil and 65% isolates from Norwood soil showed similarity with Sinorhizobium group. The Diversity among the Sinorhizobium group was studied on the basis of BOX profile. A significant diversity was observed among soil isolates. These isolates exhibited 3 patterns (pattern A, B and C), while the nodules isolates exhibited only one pattern .These results imply that only one type of Sinorhizobium population is able to nodulate all 8 Medics sp. When a neighbor joining phylogenetic tree was constructed on the basis of 16S rDNA sequences of isolates with the reference strains of Sinorhizobium sp., all the nodules isolates grouped with Sinorhizobium meliloti with strong bootstrap support. The competitiveness of the indigenous rhizobia vs. commercial inoculants will be studied in green house experiments in order to select a potent candidate for the production of biofertilizer for fodder legumes.