Drought-Tolerant Plant Growth-Promoting Rhizobacteria Associated with Millets

Millets are drought-resistant, low-maintenance crops, and are a perfect fit for multiple cropping systems under irrigated and dryland farming. Drought resilience in millets is partially attributed to the plant's ability to selectively encourage the growth of drought-adaptive, multifarious plant growth-promoting rhizobacteria (PGPR). Beneficial PGPR plays a key role in aiding millet's growth under water-limited stress conditions as well as protects the plants from various drought-associated biotic and other abiotic stresses. As a component of the plant-soil feedback mechanism, millets actively restructure the rhizosphere microbial assemblages, and their functions through modulations in the composition, and concentration of the root exudates. Therefore, microbiome engineering poses an interesting avenue for formulating a productive abiotic stress management system for crops cultivated under drought-related stress environments. Our current understanding of the complex crosstalk between root-associated microbes and crops are grown under drought is largely drawn from non-millet plants. Limited resources and studies have revealed that effective PGPR employs fundamental mechanisms of drought stress alleviation that include the regulation of phytohormones (auxin and cytokinin), solubilization of phosphate, production of ACC deaminase to lower ethylene level, accumulation of compatible solutes, etc. In this chapter, we discussed how millets exposed to water-limited conditions influence the rhizosphere microbial colonization as a component of the cry-for-help strategy. Additionally, we highlighted the role of beneficial PGPR and their core strategies of drought amelioration in various millet crops. We propose that future research efforts should attempt to elucidate the interactions of PGPR strains with the host plant in field conditions and to gain insights into PGPR-induced molecular and metabolic switches in millet crops.