Chapter 1 - Plant growth-promoting microbiomes: History and their role in agricultural crop improvement

Abstract

The exponential growth of the human population creates a burden on existing natural resources, including raw materials, food, fodder, and fuel. The ever-increasing demand is met through chemical-intensive agricultural practices such as chemical fertilizers and pesticides, which leads to environmental damage through loss of soil fertility and microbiota, biomagnification, and loss of biodiversity. Therefore, to meet the ever-growing demand, agricultural productivity needs to increase through a more sustainable and environmentally friendly approach within the next few decades. One of the most promising strategies for increasing productivity with an environmentally friendly approach is incorporating plant growth-promoting microbiomes as a part of mainstream agricultural practice. Microbes are an integral component of the soil ecosystem; they transform unavailable, insoluble soil nutrients to available forms, protect plants, and have multifaceted influences on soil health. Over thousands of years, microorganisms have been used for various agricultural practices through technological advancements, including nutrient enrichment, biocontrol activity, plant growth promotion, and enhancing yield production. With the rapid advancement of biotechnological techniques over the past few decades that helped identify new biomolecules, microbes, and genetic improvement of plant species, the current pace of new food production has accelerated by many folds. With these advancements, humankind is witnessing an extensive scale application of microorganisms in the agriculture sector that are environmentally sustainable measures. However, target-specific microorganisms such as plant growth promoters and phytopathogen controllers are required by different crops as per their requirements. Specific microbes help the plant grow well in their presence through multiple direct and indirect mechanisms. The direct mechanisms include atmospheric nitrogen (N2) fixation, various enzymes, phytohormones synthesis, and mineral solubilization in the soil. In contrast, the indirect mechanism includes inhibiting phytopathogens through systemic acquired resistance (SAR) and induced systemic resistance (ISR). Microbes that associate with plants can also serve as a key to overcoming abiotic stresses like soil salinity, reclamation of degraded land, and restoring lost habitats. The microbes also reduce greenhouse gas (GHGs) emissions and the carbon footprint along with increasing the net nutrient use efficiency (NUE). Finally, microbiome engineering and its field application are sustainable, eco-friendly strategies to solve multifaceted agriculture-associated problems. This review provides an overview of utilization promoting microbiomes for plant growth, new emerging technologies, and their importance in agricultural crop improvement.