Microbe-Mediated Plant Growth Promotion: A Mechanistic Overview on Cultivable Plant Growth-Promoting Members

Abstract

The global demand for increasing agricultural productivity and declining farming land resource has posed a severe threat to crop production and agroecosystems. The use of chemical and mineral fertilizers has boosted up the agricultural productivity but considerably diminished the soil fertility, soil health, and sustainability. Improvement in agricultural sustainability requires the combined holistic approach integrating optimal use of soil fertilization, soil physical properties, soil biological processes, and soil microbial diversity, combining integrated plant nutrient management. Since past few decades, plant growth-promoting bacteria (PGPB) and plant growth-promoting rhizobacteria (PGPR) have replaced the conventional use of chemical fertilizers and pesticides in horticulture, silviculture, agriculture, environmental remediation, and cleanup strategies, and utilization of such microbial candidates for improving soil health and nutrient availability for plants is a vital practice since antiquity. Apart from the phytostimulatory effects on plants, PGPBs are potent colonizers of plant root or rhizosphere that improve both crop and soil health through various direct and indirect approaches such as nitrogen fixation, phosphate solubilization, quorum sensing, siderophore production, antimicrobials, volatile organically, mineral solubilization, induced systemic resistance, nutrient acquisition, modification of soil texture, soil porosity, etc. Increase in biomass, yield, seedling emergence, root proliferation, and timely flowering are the direct benefits that make these microbes most preferred in the agricultural crop production, with a high market demand. Researchers are now moving way forward to decipher their molecular mechanisms of plant beneficiation through genomic comparisons, real-time protein expressions revealing the ecophysiology, and niche adaptation that might facilitate functioning of these beneficial microbes. In this chapter, we have highlighted the status and recent trends of some important plant-beneficial bacterial members, their growth-promoting abilities, and genomic perspectives for sustainable use in crop productivity.