Physiological, biochemical, and yield responses of bean plants to water deficit: contrasts between species and bacterial modulation

Abstract

Water deficit constrains legume productivity, yet the physiological strategies underlying interspecific variation in drought tolerance and the extent to which beneficial bacteria can enhance crop resilience remain poorly integrate. Here, a comparative physiological approach across species was used to identify mechanisms of drought tolerance in beans and determine whether the extremophilic bacterium Pseudomonas alcaligenes Med1 improves drought resilience in common bean. In a first experiment, Phaseolus vulgaris and Vigna unguiculata were subjected to progressive water deficit followed by rehydration. In a second experiment, non- inoculated and Med1-inoculated P. vulgaris cv. Palo plants were evaluated throughout vegetative and reproductive development under well-watered and water- deficit conditions. V. unguiculata displayed earlier stomatal regulation and better preserved plant water status, photosynthetic pigments, cytokinins, and carbon balance during drought. Together with enhanced antioxidant capacity, these responses supported rapid post-drought recovery and maintained yield. By contrast, P. vulgaris experienced greater dehydration, depletion of carbon reserves, and loss of pigments and cytokinins, with persistent physiological impairment after rehydration and consequent reductions in biomass and yield. Inoculation with Med1 improved water status and intrinsic water-use efficiency in P. vulgaris and induced antioxidant and osmoprotective adjustments, particularly during reproductive development. However, these responses were insufficient to prevent drought-induced photosynthetic and yield limitations. Notably, Med1 increased sugar, protein, and amino acid contents in developing seeds and enhanced P, Ca, Fe, and Zn concentrations in mature seeds, irrespective of water availability. These findings reveal that drought tolerance in V. unguiculata relies on coordinated stomatal regulation, water conservation, maintenance of carbon resources, and post-stress recovery, whereas Med1 provides targeted physiological and nutritional benefits rather than complete protection against water deficit in P. vulgaris cv. Palo. These results highlight the importance of integrating intrinsic plant drought-adaptation strategies with microbial approaches to improve legume resilience. Keywords: Phaseolus vulgaris; Vigna unguiculata; Pseudomonas alcaligenes Med1; water deficit.