Legumes–Microbes Interactions Under Stressed Environments

Abstract

Legumes and their associated microbes are common and exist in different environments. Microbes have evolved many mechanisms, which enable them to cope with changing environment. Resilience to these changes is essential to their survival and depends on rapid and efficient control of genetic expression and metabolic responses. Legumes establish several mutual, antagonistic, and beneficial interactions with microbes, which are occasionally subject to unfavorable (stressed) environmental conditions. Stressed terrestrial environments include, deserts with arid climate (warm and dry), salt-affected soils, alkaline and acidic soils, soils contaminated with toxic metals, and nutrient deficiency. During the course of development, microbes inherit traits that enable them to survive under undesirable conditions. Legumes, however, are stress-sensitive plants, and only few of them can withstand stressed environments. Legume rhizospheres colonized by a consortium of microbes are influenced by nutrient-rich root exudates. Legumes and microbes exhibit mutual relationships such as, association, symbiosis, and parasitism and live together in one habitat for long periods. The associated microorganisms include plant-growth-promoting rhizobacteria (PGPR), which are either nitrogen-fixing or not, and many fungi. Symbiotic organisms include mycorrhiza and the root-nodule bacteria (rhizobia). Recent molecular and genetic tools have assisted in discovering new effective stress-tolerant microbes. This chapter broadens the scope of microbes interfering with growth of legumes a relationship that has been misunderstood to be restricted to rhizobia. Therefore, future investigations have to consider a consortium of microbes in order to improve productivity of legume crops.