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Introduction
Plant Growth-Promoting Rhizobacteria (PGPR) are rhizosphere-dwelling plant-beneficial bacteria that have been reported to convey a favourable influence on plant growth and development by a variety of mechanisms and confers defence against pathogens or diseases (Mashabela et al. 2022a; Mhlongo et al. 2020). PGPR promotes plant growth by either direct or indirect mechanisms (Goswami et al. 2016). Direct modes of PGPR actions include supplying phytonutrients such as fixed nitrogen or solubilised minerals from the soil to improve plant nutrition and regulate phytohormone levels to promote plant growth and development (Kalam et al. 2020). Indirect mechanisms involve the production of specialised secondary metabolites, which can combat plant pathogens through induced systemic resistance (ISR) in the plant (Mashabela et al. 2022a; Meena et al. 2020). This mechanism enhances the plant's resistance to diseases and other harmful pathogens. Highly sophisticated communication networks that are triggered at various levels of interaction, such as inter-species, intra-species, and inter-kingdom interactions, are used to regulate these direct or indirect mechanisms of action (Menezes et al. 2021; Phour et al. 2020). PGPR can establish a beneficial relationship with their host through these interactions by secreting different compounds, such as phytohormones, siderophores, enzymes, and antibiotics. Additionally, PGPR can encourage the production of secondary metabolites in plants that may have significant ramifications for sustainable agriculture and the creation of innovative plant-based products, which can enhance plant growth, improve crop yield, and increase plant resilience to environmental stress (Kousar et al. 2020; Sunita et al. 2020).
For PGPR to be utilized in agriculture in efficient and long-lasting ways, it is crucial to understand the basis of their interactions. PGPR-PGPR interactions can affect the variety and composition of the microbial population in the rhizosphere, which can affect plant development and health and even the microbial community in the area. These interactions may take place through either mutualistic or competitive mechanisms (Hassani et al. 2018). For instance, in the mutualistic mechanism, certain PGPR strains may recruit other PGPR strains in the rhizosphere through a phenomenon termed chemotaxis. The recruited PGPR may have complementary functions, such as nitrogen fixation, establishment of biofilms, or production of antimicrobial compounds, that can enhance the overall growth-promoting and pathogen-fighting abilities of the community resulting in increased plant growth and health (Garbeva et al....