BREEDING COMMON BEAN FOR IMPROVED BIOLOGICAL NITROGEN-FIXATION

Common bean (Phaseolus vulgaris L.), which is an important food crop in the Americas, Africa and Asia, usually is thought to fix only small amounts of atmospheric nitrogen. However, field data indicate considerable genetic variability for total N2 fixation and traits associated with fixation. Studies have shown that selection to increase N2 fixation will be successful if: (1) discriminating traits (selection criteria) are measured precisely, (2) variability in germplasm is heritable, (3) selected parents are also agronomically suitable, (4) units of selection facilitate quantification of selection criteria, and (5) a breeding procedure that allows maximum genetic gain for N2 fixation and recombination with essential agronomic traits is chosen. Breeding lines capable of fixing enough atmospheric N2 to support seed yields of 1000-2000 kg ha-1 have been identified and new cultivars with high N2 fixation potential are being released.