EXPLORING STRESS TOLERANT PGPR FOR DROUGHT RESILIENCE IN GREEN GRAM AND CLUSTER BEAN

Abstract

Rhizosphere soil samples of mungbean and clusterbean were collected from Jodhpur, Pali, Jalore, Nagaur, Ajmer, Barmer and Jaisalmer districts of Rajasthan and bacterial isolations were done. Isolates were screened for plant growth promoting attributes like phosphate and potassium solubilization, siderophore, ammonia, hydrogen cyanide, indole acetic acid production, phytase and catalase activities. Isolates which possessed three or more PGP attributes and which showed growth at 20% PEG 6000 were used to treat mungbean and clusterbean seeds. Bacterial treatment increased seedling shoot length by 2-32 % in mungbean and 2-8% in clusterbean, and root length by 6-18 % in mungbean and 1-21% in clusterbean. The treatments also increased root and shoot dry weights, with significant increase observed in treated mungbean seeds. The bacterial isolates which showed better results in the lab were used for studies in pots and in field. In pots under drought stress, the isolates G8-7, G10-1 and MPSB2 enhanced mungbean seed weight, significantly. In clusterbean, the isolates G8-7, G10-1, G12-3, G21-9 and MPSB2 significantly enhanced the plant dry weight and seed weight under drought stress. Study on effect of PGPR treatment on the antioxidant status of plants showed that catalase and peroxidase were produced by the plants in less amounts under stress following bacterial treatment. In clusterbean, all the treatments significantly reduced the enzyme levels to 40-80% compared to control under drought stress. The cultures, G8-7, G12-3 and G21-9 also improved the crop physiological parameters, mainly the leaf area, nitrate reductase activity, chlorophyll fluorescence and the relative water content, under drought stress conditions. Under field conditions, the isolates G10-1 and G12-3, followed by G21-9, G8-7 and MPSB2 increased the yield and yield attributes significantly as compared to control. These promising isolates have been identified by 16SrRNA gene sequencing as Rhizobium pusense, Bacillus pseudomycoides, Bacillus subtilis and Acinetobacter baumannii.