Bacterial-mediated drought tolerance: Current and future prospects

With ongoing climate change, the severity, frequency and duration of drought in cotton (Gossypium hirsutum L.), soybean (Glycine max L.), and corn (Zea mays L.) producing areas around the world are predicted to increase. Plants' tolerance to drought stress needs to be improved in order to allow growth of crops that satisfy food demands under limited water resource availability. Plant-associated microbial communities, such as mycorrhizal fungi, nitrogen-fixing bacteria, and plant growth-promoting rhizobacteria (PGPR), enhance crop productivity and provide stress resistance. PGPR represent a wide range of root-colonizing bacteria with excellent root colonizing ability and capacity to produce a wide range of enzymes and metabolites that help plants tolerate both biotic and abiotic stresses. Their roles in the management of abiotic stresses such as drought are only beginning to gain attention. In this review, we synthesize research concerning bacterial-mediated drought tolerance in agricultural crop plants. We summarize in a table and provide details of most relevant and recent studies about the crop system studied, experimental system, means of applying drought stress, and physiological traits measured (such as relative water content, photosynthesis). Furthermore, we highlight the research needed to understand mechanisms behind observed bacterial-mediated drought tolerance and the need to homogenize and develop screening protocols.