Synergistic Effects of Arbuscular Mycorrhizal Fungi and Bradyrhizobium Improve Drought Resilience and Productivity of Mung Bean

Drought stress is a major abiotic constraint limiting mung bean (Vigna radiata L.) productivity in arid and semi-arid agroecosystems. This study investigated the individual and synergistic effects of Bradyrhizobium sp. and arbuscular mycorrhizal fungi (AMF) on plant growth, nutrient acquisition, mycorrhizal colonization, and yield of mung bean under contrasting soil moisture regimes. A greenhouse pot experiment was conducted using a factorial completely randomized design with six microbial treatments (uninoculated control, Acaulospora scrobiculata, Claroideoglomus etunicatum, Bradyrhizobium sp., and their respective co-inoculations) and three field capacity levels (50, 75, and 100%). Drought stress was imposed gravimetrically 20 days after sowing. Water limitation significantly reduced growth, biomass accumulation, nutrient uptake, mycorrhizal colonization, and yield in uninoculated plants. In contrast, microbial inoculation markedly mitigated drought-induced adverse effects, with co-inoculation showing the strongest response. Plants receiving combined AMF and Bradyrhizobium inoculation exhibited significantly higher plant height, shoot and root biomass, total dry matter, nitrogen and phosphorus uptake, and yield attributes across all moisture regimes, particularly under severe drought (50% field capacity). Mycorrhizal dependency increased with increasing drought severity, highlighting a greater functional reliance on AM symbiosis under water-limited conditions. Enhanced drought tolerance was closely associated with increased root colonization and improved nutrient acquisition driven by synergistic AMF–Bradyrhizobium interactions. These findings demonstrate that tripartite symbiosis represents a sustainable bio-inoculant strategy to enhance drought resilience and productivity of mung bean under climate change-induced water stress.