Harnessing Cooperative Bacterial Consortia to Enhance Agronomic Performance, Yield, and Grain Quality of Lupinus luteus Under Field-Based Drought Conditions

The use of microbial consortia has emerged as a promising strategy to improve crop performance under abiotic stress, although their effectiveness under field conditions remains variable. Here, we evaluated whether plant growth-promoting (PGP) bacterial consortia assembled based on synergistic PGP traits can improve physiological performance, yield, and grain quality of yellow lupine (Lupinus luteus L.) under field-based drought conditions. A semi-controlled, field-based pot experiment was conducted under contrasting water regimes (irrigated and drought) to evaluate four rhizobacterial strains (Microbacterium sp. S13.2, Variovorax sp. S14.7, Bacillus sp. S31, and Lysinibacillus sp. S34), assembled into four consortia: two characterized by high (C1 and C2) and two by low (C3 and C4) auxin production and ACC deaminase activity, along with an uninoculated control. Physiological responses were monitored across phenological stages through stomatal conductance and photosynthetic pigments, while agronomic traits, yield components, and grain quality were assessed at harvest. Inoculation effects were stage-dependent and became more evident under drought conditions. Consortia C1(Microbacterium sp. S13.2 + Variovorax sp. S14.7) and C2 (Bacillus sp. S31 + Lysinibacillus sp. S34) consistently improved biomass accumulation, seed number, and grain yield compared to the uninoculated control, whereas C3 (Lysinibacillus sp. S34 + Variovorax sp. S14.7) and C4 (Bacillus sp. S31 + Variovorax sp. S14.7) showed limited or neutral effects. Multivariate analysis indicated distinct performance strategies, with C1 associated with higher productivity and C2 with improved yield stability under drought. Grain quality parameters remained stable across treatments. These results show that cooperative microbial consortia can improve lupine performance under water-limited conditions, and their effectiveness depends on the functional interactions among consortium members.