Abiotic stress tolerance and root nodule-associated bacteria in Lablab purpureus

Climate change effects pose significant challenges to 21st-century society. Abiotic stresses such as salinity and drought represent a major risk to biodiversity and threaten crops, leading to economic losses and food security concerns. Promoting sustainable agriculture is both a solution and a necessity to address these challenges, requiring the assessment of stress-tolerant crops and the identification of beneficial microorganisms to enhance resilience, soil health, and productivity while reducing agrochemical reliance. In this study, we assessed the tolerance of Lablab purpureus, an underutilised non-European legume with high nutraceutical potential, to saline and water stress. Nodule-associated bacteria were isolated from two Mediterranean ecosystems, and three salt-tolerant strains (CJND1, LN1RA and LN3BA) were selected to evaluate their interaction with the alien crop, L. purpureus, and their effects on plant abiotic stress tolerance and traits. We analysed phenological, biomass, and root traits, photosynthetic pigments, osmolytes, ion contents (Na+, Cl−, K+, Ca2+), oxidative stress markers, antioxidant compounds, and antioxidant enzyme activities. The bacteria produced heterogeneous effects. CJND1 and LN3BA promoted root length, whereas LN3BA also increased root surface area. LN1RA increased the Cha/Chb ratio and enhanced nodulation under water stress. Overall, nodule-associated bacteria positively influenced root traits. Salinity reduced biomass, increased proline levels, and led to Na+ and Ca2+ accumulation in roots while blocking Na+ translocation to aerial parts, whereas water stress activated glutathione reductase. Our results suggest that L. purpureus is a promising crop for mild salt stress in the Mediterranean and reveal the heterogeneity of the plant and root nodule bacteria interactions, highlighting their agronomic potential.