Drought-tolerant endophytic actinobacteria promote growth of wheat (Triticum aestivum) under water stress conditions

Drought tolerant endophytic actinobacteria Streptomyces coelicolor DE07, S. olivaceus DE10 and Streptomyces geysiriensis DE27 were isolated from cultivated plants of arid and drought affected regions of Rajasthan, India. These isolates exhibited plant growth promotion traits and intrinsic water stress tolerance from -0.05 to -0.73 MPa. Maximum auxin production was observed in majority of actinobacterial cultures in the logarithmic to stationary phase of growth. Significant enhancement of wheat seedling vigour was recorded by the inoculation of these endophytic actinobacteria. S. olivaceus DE10 recorded maximum accumulation of indole 3-acetic acid (84.34 mu g mg(-1) protein). Culture and cell-free extract of the endophytes was applied on to wheat seeds to assess the effect on growth in water-stressed soil. Maximum yield was recorded with the inoculation of S. olivaceus DE10 culture (492.77 kg ha(-1)) and cell-free extract (262.31 kg ha(-1)). Co-inoculation of S. olivaceus DE10 + S. geysiriensis DE27 recorded highest yield of 550.09 kg ha(-1) while their cell-free extract yielded 524.92 kg ha(-1). Overall, wheat seeds treated with cultures showed better plant growth and yield in comparison to control. Direct coating of cultures on seeds yielded better performance than cell-free extract coated on seeds and co-inoculation of cultures or cell-free extract proved better than single culture inoculations. Production of phytohormones, plant growth promotion traits combined with water stress tolerance potential in these endophytic actinobacteria played a cumulative synergistic role that supported enhanced plant growth promotion of wheat in the stressed soil.