Potential and applications of plant growth promoting rhizobacteria (PGPR)

Global agriculture currently suffers from pollution caused by the widespread use of chemical fertilizers and pesticides. These agrochemicals, when consumed in food, can harm human health (e.g. increasing risks of cancer and thyroid disorders) and damage the environment by reducing soil fertility, among other effects. Thus, there is a high demand for biological agents, such as microorganisms, that could partially or fully replace these agrochemicals.Plant growth-promoting rhizobacteria (PGPR) are promising in this regard, as they can enhance plant growth and productivity sustainably. These bacteria promote plant growth and development through both direct and indirect mechanisms. Directly, PGPR increase plant growth by making phosphorus, nitrogen, and other essential minerals more available to plants, as well as by regulating plant hormone levels. Indirectly, PGPR inhibit pathogenic microbes that otherwise hinder plant growth and development, for instance, through the production of siderophores. In addition, PGPR show synergistic and antagonistic interactions with microorganisms within the rhizosphere and beyond in bulk soil, which indirectly boosts plant growth rate. Studies indicate that PGPR can improve plant health and yield across a variety of plant species, under both favourable and challenging conditions. As a result, PGPR have the potential to reduce the global reliance on harmful agricultural chemicals that disrupt environmental health. Additionally, the demand for PGPR as biofertilizers and biopesticides is growing globally, further highlighting their potential as powerful alternatives in sustainable agriculture. Numerous bacteria act as PGPRs, which have been described in the literature as effective in enhancing plant growth. In order to improve the efficacy of PGPRs, it is important to study their characteristics and mode of application since there is a gap between their mode of action (mechanism) for plant growth and their role as biofertilizers.