Enumeration of Native Rhizobial Population Nodulating Phaseolus vulgaris of North-western Himalaya

Optimal native rhizobial population required for efficient nodulation of Phaseolus vulgaris, leading to maximum dry matter production and nitrogen accumulation in legume crops. Notably, there has been limited investigation into, especially in the NWH region of Uttarakhand. To address this, the study employed the Most Probable Number technique across 12 sites in 5 districts of Uttarakhand. The results revealed a wide range of rhizobia populations, ranging from less than 1 x 102/g of soil to 3.1 x 104/g of soil. These varying number of rhizobia were found in perfect corelation with the organic carbon content, microbial biomass carbon and dehydrogenase activity of soils. Two locations, "Seli sama" (100/g of soil) and "Sui" (1000/g of soil), displayed MPN values below the threshold population required for optimal nodulation. Furthermore, locations with a high number of native rhizobia but relatively low biological nitrogen fixation, specifically "Daranti" (MPN: 31000/g of soil, BNF: 4.92 mg plant /g) and "Gwaldam" (MPN: 31000/g of soil, BNF: 4.88 mg plant /g), have shown the potential to enhance biological nitrogen fixation through the introduction of efficient rhizobial inoculants or by maintaining a high number of effective native rhizobia in the soil.