Intrapopulation Recombination for 15N-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 ¹⁵N-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 ¹⁵N-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 ¹⁵N-determined N₂ fixation.