Intrapopulation Recombination for ¹⁵N‐Determined Dinitrogen Fixation Ability in Common Bean

The quantity of N 2 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 15 N‐determined N 2 fixation ability. The objective was to determine whether intrapopulation recombination and selection could be used to improve N 2 fixation. Four agronomically acceptable lines were selected, based on their acetylene reduction‐determined N 2 fixation ability, from an inbred backcross (IB) line population created from a cross between the high N 2 ‐fixing donor parent ‘Puebla 152’ and a commercial, low N 2 ‐fixing recurrent parent ‘Sanilac’. These four IB lines were intercrossed, advanced to the F 3 , and the six resulting F 3 populations with 25 F 3 families per population were evaluated for N 2 fixation in a low‐N field using 15 N‐depleted (NH 4 ) 2 SO 4 . The six F 3 population means differed significantly and were superior to ‘Sanilac’ for N 2 fixation ability and yield, indicating significant improvement over ‘Sanilac’. Four F 3 population means were similar to ‘Puebla 152’, indicating selection advance towards high N 2 fixation while retaining favorable agronomic characteristics. Fifty percent of the F 3 families were superior to ‘Sanilac’ for N 2 fixation and one family exceeded ‘Puebla 152’, indicating that intrapopulation recombination produced improvement of 15 N‐determined N 2 fixation.