Harnessing rhizosphere microbes: the synergistic roles of PGPR and AMF in sustainable tomato production under stress

L.) is among the most economically important vegetable crops worldwide, yet its production is severely constrained by multiple biotic and abiotic stresses, including pathogens, pests, drought, salinity, and heavy metal toxicity. Amid intensifying climate change and increasing demands for sustainable agriculture, plant growth-promoting rhizobacteria (PGPR) and arbuscular mycorrhizal fungi (AMF) have emerged as key beneficial rhizospheric microorganisms with significant potential for enhancing plant stress tolerance and promoting growth. PGPR directly promote the growth of tomato plants through biological nitrogen fixation, solubilization of phosphate and potassium, siderophore-mediated iron uptake, and the production of phytohormones. Indirectly, PGPR suppress pathogens, activate induced systemic resistance (ISR), reinforce cell walls, enhance the activities of antioxidant enzymes, and regulate the accumulation of osmolytes. AMF form symbiotic associations with the roots of tomato plants, enhancing nutrient and water absorption via extraradical mycelial networks, improving phosphorus and nitrogen uptake, modulating abscisic acid (ABA), jasmonic acid (JA), and strigolactone signaling pathways, activating mycorrhiza-induced resistance (MIR), and enhancing photosynthetic efficiency and water-use efficiency under stress. The co-inoculation of PGPR and AMF yields synergistic effects by facilitating mutual colonization, optimizing nutrient bioavailability, coordinately strengthening antioxidant and osmotic regulation systems, and reinforcing systemic defense responses, thereby conferring more robust and efficient stress tolerance than single inoculations. Despite significant advances, key challenges persist in elucidating tripartite molecular crosstalk, maintaining stability during field applications, and developing tailored microbial consortia. This review synthesizes the individual and synergistic mechanisms through which PGPR and AMF enhance the resilience of tomato plants to biotic and abiotic stresses, offering valuable insights for engineering microbial communities to enhance stress resistance in crops.