Microbial Allies in Agriculture: Harnessing Plant Growth-Promoting Microorganisms as Guardians against Biotic and Abiotic Stresses

Plants face many biological and non-biological challenges throughout their life cycle, from seed to harvest. These challenges have recently increased due to climate changes. Strategies for confronting different types of stresses depend on the type of stress, the cultivated plant, climatic conditions, soil characteristics, water variables, cost, and management system. Chemical methods (fertilizers and pesticides) have been widely used to manage abiotic and biotic stresses, but they raise concerns about environmental contamination, toxic residues, and the development of resistant pathogens. Eco-friendly strategies have recently become one of the most important approaches to obtaining high-quality and quantitative plant-based products. Microbial inoculants, such as plant growth-promoting microorganisms (PGPM), offer a sustainable alternative to chemical methods. PGPM can augment plant growth and nutrition, improve plant tolerance to abiotic stresses, and reduce the growth of certain pathogens. They employ a variety of mechanisms to alleviate stressors and boost plant resilience, including nutrient assimilation, production of metabolites, and activation of systemic resistance. This review aims to elucidate the impact of PGPM, with a particular focus on plant growth-promoting bacteria (PGPB), and their mechanisms of action on plants under varying stressors, while also identifying areas for further research in both PGPB and other non-bacterial organisms.