Effect of Rhizobium spp. Inoculation on Growth and Grain Yield of Cowpea (Vigna unguiculata) Under Greenhouse and Ex Vitro Conditions

Abstract

Cowpea (Vigna unguiculata (L.) Walp.) is an agriculturally important legume capable of establishing symbiotic associations with nitrogen-fixing bacteria. Biological nitrogen fixation through Rhizobium spp. represents a potential agroecological strategy for improving crop productivity while reducing dependence on inorganic nitrogen fertilizers. The objective of this study was to evaluate the effects of Rhizobium spp. inoculation and inorganic fertilization on nodulation, plant biomass, pod production, grain yield, and 100-seed weight of cowpea under greenhouse and ex vitro conditions. Four treatments were evaluated: (1) uninoculated and unfertilized control, (2) inorganic fertilization, (3) inorganic fertilization combined with Rhizobium spp. inoculation, and (4) Rhizobium spp. inoculation without inorganic fertilizer. A total of 400 plants were evaluated throughout the experimental study. Under ex vitro conditions, plants inoculated exclusively with Rhizobium spp. produced 371 ± 104 pods, grain yield of 0.47 ± 0.14 kg m⁻², and a 100-seed weight of 25.07 ± 0.17 g. Inoculation alone also increased fresh and dry biomass by 123% and 75%, respectively, relative to the control. In contrast, combining inorganic fertilizer and Rhizobium spp. markedly reduced active nodulation relative to inoculation alone. These findings indicate that Rhizobium spp. inoculation can improve important agronomic characteristics of cowpea and represents a potential strategy for sustainable legume production and biological nitrogen management.