Inheritance of N2 fixation efficiency in cowpea

Summary Host plant genetics of N₂ fixation in the cowpea (Vigna unguiculata (L.) Walp.) — Rhizobium symbiosis was investigated in the field with a mixed strain inoculum and in the greenhouse with a single strain inoculum. Five cowpea genotypes, including H-Brown Crowder and L-Bush Purple Hull, were used to generate populations for genetic studies. Diallel analysis for general combining ability (GCA), specific combining ability (SCA) and reciprocal effects was carried out for the N₂ fixation variables nitrogenase activity, nodule number, nodule weight, and top dry weight, in the field study. Generation mean analysis and heritability estimates were performed on the greenhouse population which included P₁ (H-Brown Crowder), P₂ (L-Bush Purple Hull), F₁, F₁. F₂, BC₁, and BC₂. Positive and significant correlations were observed between nitrogenase activity and both nodule weight and nodule number. Correlation coefficients between top dry weight and the other 3 variables were not significant. Estimates of SCA were highly significant for all variables except top dry weight, while those of GCA were significant only for nodule weight. Generation mean analysis revealed that additive gene action was more prominent than dominance and interallelic gene action for nodule number and nitrogenase activity, while the opposite was true for nodule weight and top dry weight. Narrow sense heritability estimates were moderately high for nodule number (0.55) and nitrogenase activity (0.62), and low for nodule weight (0.39) and top dry weight (0.17).Texas Agricultural Experiment Station Technical Article 20385. Research supported in part by a grant under USAID PASA AG/TAB 610-9-76 (USDA-CSRS-701-15-59).