Diazotrophs for Enhancement of Productivity of Major Cereal Crops Under Abiotic Stresses

Population explosion has created tremendous pressure on agricultural productivity of major cereal crops. Due to anthropogenic activities and improper management of natural resources, instances of abiotic stresses have increased many folds. Abiotic stresses include salinity, drought, waterlogging, extreme temperatures, and heavy metal stresses that hamper plant growth at its various growth and developmental stages by producing stress ethylene, reactive oxygen species (ROS), osmotic stresses, water stresses, cell toxicity, reducing nutrient mineralization and phytohormonal activities that enhance growth. Nitrogen is abundantly required by plants especially in stressed conditions, but usage of chemical fertilizers results in problems like eutrophication and long-term excessive use can lower soil quality. Diazotrophic bacteria are plant growth promoting bacteria (PGPB) that provide one of the most ecofriendly and sustainable ways to combat abiotic stresses along with fixing atmospheric nitrogen. There are many mechanisms applied by diazotrophic PGPB to protect plants from stresses such as by production of osmolytes, exopolysaccharides (EPS), ROS scavenging enzymes, 1-aminocyclopropane-1-carboxylate (ACC) deaminase, regulate transcription of plant innate genes for stress tolerance, regulate phytohormones, solubilize minerals like phosphorus, zinc, and potassium, and produce siderophores. Here in this chapter emphasis is given on the role of diazotrophs in abiotic stress management in major cereal crops including wheat, rice, and maize.