Abstract

Cowpea (Vigna unguiculata L. Walp) has a major role in daily diet of the rural community and poor urban population, serving as a source of energy, protein and minerals, in developing countries. Its straw used for animal feed, and the crop also improves soil fertility by fixing the atmospheric nitrogen. However, its productivity is constrained by lack of improved varieties and poor agronomic practices. A field experiment was conducted at Ziway, central rift valley of Ethiopia, to evaluate the response of cowpea varieties to Bradyrhizobia inoculation. The treatment consisted of four Bradyrhizobia strains (control, GN-100, GN-102 and MB-140) and five cowpea varieties (Bole, Black eye-bean, TVU1977.0D1, Assebot and White Wonder). The experiment was carried out using a randomized complete block design with three replications. The results revealed marked varietal differences in plant growth, nodulation, yield and yield components. Of the five cowpea varieties studied, Black eye-bean generally showed superior performance in most measured parameters. Bradyrhizobium inoculation significantly (p≤0.05) increased plant growth, nodulation, yield and yield components. The interaction effect of variety and Bradyrhizobium caused significant variations in the number of nodules, number of seeds, hundred seed weight and seed yield. The highest grain yield was recorded from Black eye-bean variety (3.08 t/ha) and Bradyrhizobium strain GN-102 (3.11 t/ha) inoculation. It could, thus, be deduced that the use of strain GN-102 and variety Black-eye bean markedly increases the productivity of the crop in the region.

Key words: Bradyrhizobia, cowpea, nodulation, growth, yield components.