The application of phosphate-solubilizing microbes (PSMs) as biofertilizers in agricultural systems has not satisfactorily solved the problem of reducing our reliance on chemical phosphorus (P) fertilizers. Ongoing efforts are continually trying to translate promising laboratory results to successful deployment under field conditions, which are typically met with failure. In this review, we summarize the state-of-the-art research on PSMs and their role in the terrestrial P cycle, including previously overlooked molecular and cellular mechanisms underpinning phosphate solubilization. PSMs capable of transforming either organic or complexed inorganic P compounds are discussed. By providing environmentally secure and environmentally friendly ways to increase the accessibility of phosphate, these bacteria effectively transform insoluble phosphate molecules into forms that plants can utilize, encouraging crop growth and increasing nutrient usage effectiveness. The use of PSMs in agriculture sustainably improves crop productivity and has enormous potential for tackling issues with global food security, reducing environmental damage, and promoting sustainable and resilient agricultural systems. Furthermore, due to resource shortages, the changing global climate and need to reduce environmental risks associated with the overuse of chemical phosphate fertilizer, PSMs have the potential to be sustainable biofertilizer alternatives in the agricultural sector. Phosphate-solubilizing microorganisms constitute a cutting-edge field in agriculture and environmental science. In addition, this paper elaborates on the groups and diversity of microbes hitherto identified in phosphate solubilization. Also, factors that had hitherto hindered the reproducibility of lab results in field settings are succinctly highlighted. Furthermore, this paper outlines some biofertilizer formulations and current techniques of inoculation according to the test crop/strain. Finally, laboratory, greenhouse, and field results are presented to acquaint us with the current status of the use of PSM-based biofertilizers.

We explored the activation of defense genes and the changes in volatile profiles in olive (Olea europaea var. Picual) plants subjected to mechanical wounding and prior soil inoculation with the fungus Trichoderma afroharzianum T22. Our findings indicate a sustained effect of the inoculant in olive plants, which shifted the constitutive volatile emission more significantly towards an aldehyde-dominated blend than the mechanical damage alone. Furthermore, we found that wounding alone did not alter the expression of hydroperoxide lyase genes associated with aldehyde biosynthesis. However, this expression was significantly enhanced when combined with prior T22 inoculation. Mechanical wounding amplified the plant's immediate defensive response by enhancing the upregulation of the direct defense enzyme acetone cyanohydrin lyase. Trichoderma afroharzianum T22 also modulated direct defense, although to a lesser extent, and its effect persisted 9 months after inoculation. Metagenomic analyses revealed that aerial mechanical damage did influence specific root bacterial functions. Specifically, an upregulation of predicted bacterial functions related to various metabolic processes, including responses to biotic and abiotic stresses, was observed. On the contrary, T22's impact on bacterial functional traits was minor and/or transient.

Plant growth promoting rhizobacteria are classified as microorganisms residing in the rhizosphere, possessing diverse capabilities linked to plant development and well-being. PGPRs through various direct and indirect mechanisms, exert their influence on plant development. The advantages offered by these bacteria encompass heightened accessibility to nutrients, synthesis of phytohormones, facilitation of shoot and root growth, defense against numerous plant pathogens, and diminished disease susceptibility. Furthermore, PGPR contributes to plant resilience against environmental stresses like salinity and drought, alongside the synthesis of enzymes that mitigate the damaging effects of heavy metals. In the realm of sustainable agriculture, PGPR has emerged as a pivotal strategy, showcasing the potential to curtail the reliance on synthetic fertilisers and pesticides. This is achieved by fostering plant vigour and health, as well as augmenting soil quality. While a multitude of investigations regarding PGPR can be found in the literature, this review places emphasis on studies that have practically applied PGPR to sustainable production. These applications enable a reduction in the consumption of fertilisers like phosphorus and nitrogen, as well as fungicides, while concurrently enhancing nutrient absorption. With the overarching aim of advancing sustainable agricultural practices, diverse aspects are covered in this review, including various government schemes and initiatives, innovative fertilisation methods, the role of seed microbiomes in rhizosphere colonisation, the diversity of rhizospheric microorganisms, nitrogen fixation as a means to minimise chemical fertiliser use, phosphorus solubilisation and mineralisation, and the synthesis of siderophores and phytohormones to decrease reliance on fungicides and pesticides.