GENOTYPIC VARIATION IN BIOLOGICAL NITROGEN-FIXATION BY COMMON BEAN

Field experiments were performed in Austria, Brazil, Chile, Colombia, Guatemala, Mexico and Peru as part of an FAO/IAEA Co-ordinated Researc h Programme to investigate the nitrogen fixing potential of cultivars and breeding lines of common bean (Phaseolus vulgaris L.). Each experi ment included approximately 20 bean genotypes which were compared usin g the N-15 isotope dilution method. Great differences in nitrogen fixa tion were observed between and within experiments, with average values of 35% N derived from atmosphere (% Ndfa) and highest values of 70% N dfa being observed. These values which were larger than had been repor ted previously for common bean, were observed only when environmental factors were favorable. Therefore, common bean lines are available, wh ich can support high biological nitrogen fixation. These can be used e ither directly as cultivars for production or in breeding programmes t o enhance nitrogen fixation in other cultivars.