Alleviation of Drought Stress and Plant Growth Promotion in Mungbean through Rhizospheric Actinobacteria

Drought is a major cause for decreasing in crop yield and agricultural productivity around the Globe. The application of drought tolerance Actinobacteria to agroecosystem improves the growth and protect from water scarcity and they can be better alternative for natural farming and sustainable agriculture for aride and semi-aride regions. Herein, we isolated ten morphologically different actinobacteria from the rhizospheric soil of Datura and Khejri plants which are surviving in the nature without any special treatment provided. All the isolated bacteria were screened in-vitro for their drought tolerance capability for different time intervals against polyethylene glycol 8000 (PEG8000) with 5%, 10% and 10% concentration to media which produce moisture stress in which medium bacteria were growing. Among them best five bacterial isolates were selected and named RADM1 to RADM5 for further experimentation. Physiological characterizations were done through their ability to grow in different temperature, pH ranges and NaCl concentration supplemented with the 5% PEG8000. Morphology of the bacteria was Grams positive and mycelium producing same as typical Actinobacterial species and for biochemical diversity stains were able to IMVIC test and carbohydrate utilization through IMVIC test. Enzymatic observations of isolates were resulted positive for nitrate reduction, catalase production and negative for starch hydrolysis. PCR amplification and 16S rRNA gene sequencing in BlastN found maximum similarity of three species with Streptomyces clavuligerus and two species with Rhodococcus erythropolis and submitted to NCBI gene bank database with accession number PQ114139 (RADM1), PQ120343 (RADM2), PQ114109 (RADM3), PQ120390 (RADM4), PQ039766 (RADM5). In pot trial of mungbean, all the isolates showed better performance in bacterial treatments with an average increase in physiological parameters like, seedlings shoot length (52.70% and 9.62%), root length (35.63% and 17.25%), fresh weight (42.8% and 13.76%) dry weight (45.25% and 21.24%) in compared to uninoculated induced drought and watered treatments. Stress features of seedlings revealed significant increase in proline and chlorophyll contents whereas decrease in MDA contents than the untreated plants which indicates actinobacteria reduced water scarcity and damage of plant membrane. IMPORTANCERhizosphere of plant contains diversity of microbes with different abilities to support the plant growth. The role of plant growth promoting bacteria in soil presented and their association with plant can be the one reason for survive of the plant against the abiotic stress conditions like drought, salinity, temperature or pH. The actinobacteria found in the rhizosphere have evolved multiple strategies to assist plants in managing the adverse effects of drought. These strategies may include alterations in phytohormones, which play a vital role in enabling plants to withstand environmental stresses, modifications to root structures, accumulation of osmolytes, enhancements in the plants antioxidant defense mechanisms, synthesis of exopolysaccharides, and the identification of particular genes that support plant growth and improve drought resilience. These actinobacteria as bioinoculant can be the better alternative for the chemical fertilizers use and protect from the water scarcity.