EVALUATION OF N-2-FIXATION AND YIELD OF BAMBARA GROUNDNUT [VIGNA-SUBTERRANEA (L.) VERDC.]

Five Bradyrhizobium strains (280A, 221A, 100M, and CB756) isolated fro m three leguminous species (Arachis hypogaea, Siratro sp., and Macroty loma africanum) were evaluated on five bambara groundnut [Vigna subter ranea (L.) Verdc., syn. Voandzeia subterranea (L.) Thou.] genotypes (1 B, 3C, 49A, 75A, and 89C) grown in Malawi. Each of the cultivars forme d nodules with all Bradyrhizobium strains tested, but differences in s ymbiotic effectiveness were observed among the strains. Strains M100, 280A, and 2209A were more effective overall than 2212A and CB756. Ther e were significant Bradyrhizobium strain differences (P = 0.01) in nod ule number, nodule mass, yield of dry matter (DM), and total nitrogen. The differences in shoot DM and total N between cultivars were also s ignificant, being highest for genotypes 89C and 49A and lowest for gen otype 3C. Nodule numbers, nodule mass, shoot dry weight, and the amoun t of N in plant tops were influenced independently by the Bradyrhizobi um or host genotype as no significant host x microsymbiont interaction was observed for any of the traits measured. The contribution from N- 2-fixation to the total N accumulated in the plant shoots was 81-90%. This study showed that testing for symbiotic effectiveness in the bamb ara groundnut Bradyrhizobium symbiosis should include assessment of se ed yields.