Biostimulants offer a sustainable strategy to improve plant growth and stress resilience, particularly under limited water availability. We evaluated seven biostimulant treatments, including beneficial bacteria, mycorrhizal fungi, seaweed extract with humic acid, and their combinations, on early growth and physiological responses of tomato (Solanum lycopersicum L.) under well–watered and drought-stressed conditions. Plants were assessed before and after a seven-day controlled drought period using a range of morphological and physiological traits, including height, effective quantum yield of PSII (ΦPSII), stomatal conductance (gs), and leaf pigment profile. Results showed that microbial treatments that included Bacteria + Mycorrhizae (B + M) maintained ΦPSII above 0.60 and preserved height gain relative to the control, while seaweed-based formulations with humic acid (S + H) exhibited significant reductions in height of up to 35% compared with full irrigation. In addition, the bacterial treatment (B) significantly increased the root/shoot ratio under drought, indicating enhanced carbon allocation to roots. These findings demonstrate that specific microbial-based biostimulant combinations can better maintain physiological performance and growth under water limitation, supporting their potential use in sustainable tomato production systems.
Garrido-Ruiz et al. (Thu,) studied this question.