Evaluation of N2-fixation and yield of Bambara groundnut [Vigna subterranean (L.) Verde.]
Keywords:Bambara groundnut, Vigna subterranea, Bradyrhizobium, Nitrogen fixation, Effectiveness of rhizobia
AbstractFive Bradyrhizobium strains (280A, 2209A, 2212A, 100M, and CB756) isolated from three leguminous species (Arachis hypogaea, Siratro sp., and Macrotyloma africanum) were evaluated on five bambara groundnut [Vigna subterranea (L.) Verdc., syn. Voandzeia subterranea (L.) Thou.] genotypes (1B, 3C, 49A, 75A, and 89C) grown in Malawi. Each of the cultivars formed nodules with all Bradyrhizobium strains tested, but differences in symbiotic effectiveness were observed among the strains. Strains M100, 280A, and 2209A were more effective overall than 2212A and CB756. There were significant Bradyrhizobium strain differences (P = 0.01) in nodule number, nodule mass, yield of dry matter (DM), and total nitrogen. The differences in shoot DM and total N between cultivars were also significant, being highest for genotypes 89C and 49A and lowest for genotype 3C. Nodule numbers, nodule mass, shoot dry weight, and the amount of N in plant tops were influenced independently by the Bradyrhizobium or host genotype as no significant host × microsymbiont interaction was observed for any of the traits measured. The contribution from N2-fixation to the total N accumulated in the plant shoots was 81-90%. This study showed that testing for symbiotic effectiveness in the bambara groundnut - Bradyrhizobium symbiosis should include assessment of seed yields.