BREEDING COMMON BEAN FOR IMPROVED BIOLOGICAL NITROGEN-FIXATION

Common bean (Phaseolus vulgaris L.), which is an important food crop i n the Americas, Africa and Asia, usually is thought to fix only small amounts of atmospheric nitrogen. However, field data indicate consider able genetic variability for total N2 fixation and traits associated w ith fixation. Studies have shown that selection to increase N2 fixatio n 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 sele ction facilitate quantification of selection criteria, and (5) a breed ing procedure that allows maximum genetic gain for N2 fixation and rec ombination with essential agronomic traits is chosen. Breeding lines c apable of fixing enough atmospheric N2 to support seed yields of 1000- 2000 kg ha-1 have been identified and new cultivars with high N2 fixat ion potential are being released.