INTRAPOPULATION RECOMBINATION FOR N-15-DETERMINED DINITROGEN FIXATION ABILITY IN COMMON BEAN

The quantity of N2 fixed in common bean (Phaseolus vulgaris L.) is a quantitatively inherited trait that shows sufficient genetic variability for improvement through breeding, but there is little information on gain from selection for N-15-determined N2 fixation ability. The objective was to determine whether intrapopulation recombination and selection could be used to improve N2 fixation. Four agronomically acceptable lines were selected, based on their acetylene reduction-determined N2 fixation ability, from an inbred backcross (IB) line population created from a cross between the high N2-fixing donor parent 'Puebla 152' and a commercial, low N2-fixing recurrent parent 'Sanilac'. These four IB lines were intercrossed, advanced to the F3, and the six resulting F3 populations with 25 F3 families per population were evaluated for N2 fixation in a low-N field using N-15-depleted (NH4)2SO4. The six F3 population means differed significantly and were superior to 'Sanilac' for N2 fixation ability and yield, indicating significant improvement over 'Sanilac'. Four F3 population means were similar to 'Puebla 152', indicating selection advance towards high N2 fixation while retaining favorable agronomic characteristics. Fifty percent of the F3 families were superior to 'Sanilac' for N2 fixation and one family exceeded 'Puebla 152', indicating that intrapopulation recombination produced improvement of N-15-determined N2 fixation.