ABSTRACT
The main problem hampering the crop growth and productivity in today’s world is drought, which is the result of global climate change events and is estimated to have reduced cereal productivity by 9%–10% (Lesk et al., 2016). More than 50% of the cultivable lands by 2050 are going to face devastating drought consequences on plant growth (Vinocur & Altman, 2005). Plant and water relationships were affected by drought stress at both cellular and whole plant levels, resulting in various physiological complex processes and phenotypical responses in plants. Oxidative stress is generated within the sub-cellular compartments due to alleviated levels of reactive oxygen species (ROS). ROS consist of superoxide radical (O2), hydrogen peroxide (H2O2), and the hydroxyl radical (OH), all of these affect the building components of the cell (lipids, proteins, carbohydrates, nucleic acids, etc.) and cause cell demise (Mittler, 2002). Therefore, there is an increased interest among the scientists in finding solutions to water-associated problems such as drought and its impacts on food security. Particularly, there is an utmost need to redress different solutions, which will improve the drought tolerance in crop plants, so as to satisfy the food requirement with the limited water resources in today’s world (Mancosu et al., 2015). Crop productivity can be increased by inoculating the plants facing drought stress with plant growth promoting rhizobacteria (PGPR) (Ngumbi and Kloepper, 2016). The thin layer of soil immediately surrounding the plant roots is an extremely important and active area for root activity and metabolism and is known as rhizosphere. A large number of microorganisms such as bacteria, fungi, protozoa, and algae coexist in the rhizosphere. The microorganisms that colonize the rhizosphere can be classified according to their effects on plants and the way they interact with roots, some being pathogens whereas others trigger beneficial effects. The microorganisms inhabiting the rhizosphere and beneficial to plants are termed PGPR. Various species of bacteria like Pseudomonas, Azospirillum, Azotobacter, Klebsiella, Enterobacter, Alcaligenes, Arthrobacter, Burkholderia, Bacillus, and Serratia have been reported to enhance the plant growth. There are several PGPR inoculants currently commercialized that seem to promote growth through at least one mechanism; suppression of plant disease (Bioprotectants), improved nutrient acquisition (Biofertilizers), or phytohormone production (Biostimulants).
