Arbuscular mycorrhizal fungi and Bradyrhizobium co-inoculation enhances nitrogen fixation and growth of green grams (Vigna radiata L.) under water stress

Green gram (Vigna radiata L. Wildzek) is a neglected crop with great potential to boost food security among small scale farmers. Inoculation of this crop with beneficial soil microbiota can sustainably improve its production especially under water stress conditions. Here, we aimed at determining the effect of bradyrhizobia and arbuscular mycorrhizal fungi (AMF) co-inoculation on growth and nitrogen fixation of green grams under water stress conditions. Potted green grams variety KS20 were planted in sterilized soil and inoculated with Bradyrhizobium, Funneliformis mosseae, Rhizophagus irregularis, a commercial consortium of four AMF isolates (Rhizophagus irregularis, Funneliformis mosseae, Glomus etunicatum and Glomus aggregatum) and a consortium of the four aforementioned AMF isolates and Bradyrhizobium. The plants were subjected to three water stress levels, irrigation after interval of 4 days, 8 days and 12 days and maintained for 50 days. After harvesting, the plants were measured for nodulation, percentage root mycorrhizal colonization, growth parameters and shoot nitrogen (N), phosphorous (P) and potassium (K). Remarkably, all AMF inoculations significantly P <= 0.05 increased shoot dry weight (SDW), root dry weight (RDW) and P compared to Bradyrhizobium and control plants under all the watering regimes. Inoculation with Rhizophagus irregularis resulted to highest shoot dry weight, root dry weight and P under water regime 3, which provided the most intense water stress condition. Moreover, strong positive correlation (R-2 = 0.8765, P = 0.006) was observed between shoot dry weight, P and AMF root colonization under all watering regimes.