Harnessing plant growth promoting microorganisms for sustainable agriculture

Environmental protection, economic viability, and social equity are the key components of sustainable agriculture. Environmental protection involves improving soil health with reduced chemical use, promoting biodiversity, and mitigating climate change-induced stresses. Soil is home to a diverse range of microbes, many of which have a beneficial effect on associated plants, promoting their growth, development, and yield. They are broadly termed as plant growth-promoting microorganisms (PGPMs) and are natural inhabitants of diverse soils. Soil health is intimately linked to plant–microbe interactions. PGPMs utilize attributes such as biological nitrogen fixation, phosphate solubilization, phytohormone synthesis, siderophore production, and biofilm formation at the root surfaces to promote plants’ growth, development, and yield. Besides, other phytohormones, abscisic acid is a key signaling molecule that mediates a range of adaptive responses to drought, salinity, and cold stress. PGPMs also act as biocontrol agents against various plant pathogens via synthesizing antibiotics and triggering the plant's immune system (i.e., induced systemic resistance, ISR). Abiotic stress is a major constraint to agricultural productivity. They confer abiotic stress tolerance through biosynthesis of antioxidants, volatile organic compounds, osmolytes, stress-tolerant and defense phytohormones (e.g., Ethylene, Jasmonic acid, and Salicylic acid), and 1-aminocyclopropane-1-carboxylate deaminase. More importantly, they often provide cross-protection against multiple abiotic stresses. Recent genomic and molecular advances have detailed valuable insights into this complex mechanism. Reducing input costs is economically vital for farmers. PGPMs are a cost-effective tool. In this article, we review the available knowledge on PGPMs, their implications in enhancing plant growth, development, and yield, as well as their role in alleviating abiotic stresses. We have also discussed the potential constraints and way forward in their use as a biofertilizer, as well as the effect of climatic conditions on this use. PGPMs is an umbrella term for a taxonomically diverse group of microbes, showing many agronomically important traits. They promote plant growth and development, enhance yield, and are an eco-friendly alternative to synthetic herbicides and pesticides (i.e., biocontrol agents). They also confer cross-protection to plants against multiple abiotic stresses. Approaches such as rhizopspheric engineering and their use as biofertilizer are vital to sustainable agriculture.