Evaluation of Multi-functional Rhizobium sp. Isolates of Urdbean (Vigna mungo L.) as Bio-inoculant for Enhancing Productivity and Soil Health

Eighteen Rhizobium sp. isolates from diverse soils of Uttarakhand were characterized for plant growth promoting (PGP) traits and evaluated for nodulation, growth and yield of urdbean (Vigna mungo L.) and soil properties in a field trial. The isolates differed in sole carbon (C) source utilization profile and grew well at 28±2 oC. Among these, 11 isolates grew at 35±2 °C and 6 isolates at 40±2 °C. Isolates P-2, P-5, P-7, A-3, A-6, A-7, A-11, K-6 and C-1 solubilized P, isolates P-7, P-8, A-3, A-6, A-7, A-15 and K-6 secreted indole acetic acid (IAA) while P-2, P-7, P-8, A-3, A-6, A-7, A-9, A-18, K-12, C-1 and D-1 produced siderophores in in vitro conditions. Seed inoculation of rhizobial isolates significantly increased the nodule number from 18.1 to 45.2 per cent and nodule dry weight from 12.2 to 45.5 per cent over the uninoculated control at 45 days after sowing (DAS). The plant dry weight due to different isolates was significantly higher by 25.0 to 70.8 per cent at 30 DAS and 24.8 to 71.4 per cent at 45 DAS over the uninoculated control, respectively. Different isolates did not enhance the grain and straw yields significantly; nevertheless A-7 (isolated from VPKAS, Almora) produced 28.2 and 15.2 per cent more grain and straw yields over the uninoculated control, respectively. Inoculation of the isolates also significantly increased the grain N uptake by 23.9 to 86.9 per cent, straw N uptake by 21.9 to 108.7 per cent, grain P uptake by 20.2 to 72.4 per cent and straw P uptake, by 15.0 to 87.2 per cent over the uninoculated control. Different Rhizobium sp. isolates significantly improved the microbial biomass C from 32.5 to 255.3 per cent, organic C from 5.1 to 96.6 per cent, available N from 16.4 to 71.8 per cent and available P from 20.5 to 88.6 per cent over uninoculated control in the post-harvest soil. Isolate A-7 was found superior to others followed by C-1, P-7, and A-3 in beneficial effects on urdbean yield and soil properties.