Soybean Rhizobia in Indian Soils: Populations, Host Specificity and Competitiveness

Abstract

Soybean is the most important of crop legumes with the highest share of production and source of biologically fixed nitrogen. Indigenous soybean rhizobia in Vertisols of Central India and other soils were assessed for cross nodulation, bacteriocin production and competitiveness. Survey of rhizobial populations in the rhizosphere of post-summer rainy season soybean revealed low number; the most probable number by plant infection test ranged from 0.5 to 3.3 × 103 cells g−1 soil but improved in the rhizosphere of cool season chickpea as 3.6–9.6 × 103 cells g−1. Soybean was nodulated by its native slow and fast growing rhizobia as well as by chickpea rhizobia. However soybean rhizobia did not nodulate crops belonging to four other cross inoculation groups-alfalfa (Trigonella), clover, pea, chickpea but nodulated Vigna (cowpea). Nodule occupancy by three indigenous nod+ nif+Bradyrhizobium sp. R33 and R35 and Rhizobium R51 varied from 52 to 68 % of which only one-R33 was a strong bacteriocin producer while the other two were not. The results are important for rhizobial strain selection for biofertilizers.