Inoculation With Azospirillum brasilense and Bacillus amyloliquefaciens Enhances Tomato Resilience to Severe Water Deficit: A Comprehensive Morpho-Physiological and Biochemical Analysis.

Water scarcity, intensified by climate change, threatens tomato (Solanum lycopersicum) productivity, impacting growth, metabolism and secondary metabolite production. This study evaluated the effects of Azospirillum brasilense and Bacillus amyloliquefaciens inoculation in mitigating water stress in the Ibiza cultivar under 100%, 50% and 25% water replenishment. Severe water deficits significantly reduced morphological parameters, such as height, leaf number and dry mass. However, inoculation with B. amyloliquefaciens, particularly in combination with A. brasilense, enhanced dry mass accumulation, stem diameter and root development. Physiological analyses revealed higher electrolyte leakage and compromised membrane integrity due to water stress. Biochemical responses included increased antioxidant enzyme activity (SOD, CAT and APX) and proline accumulation, both modulated by bacterial inoculation. Interestingly, chlorophyll content increased at 25% water availability, suggesting an adaptive mechanism, while DNA content decreased. Secondary metabolites (flavonoids and phenolics) also responded to the interaction between irrigation levels and bacterial inoculation. The findings demonstrate that inoculation with A. brasilense and B. amyloliquefaciens is an effective approach to enhance tomato tolerance to water deficits by improving agronomic performance, strengthening antioxidant defences and regulating secondary metabolite production. This strategy supports the development of sustainable and adaptive agricultural practices in the face of increasing water scarcity.