Biological nitrogen fixation potential of pea lines derived from crosses with nodulation mutants

The process of biological nitrogen fixation (BNF) through nodules of legumes benefits soil fertility, increases crop productivity and reduces the requirement for chemical fertilizers. Pea is an important pulse crop in temperate regions of the world. The N fixation capacity of pea in Canadian environments ranges from 50% to 55% of crop N requirement. Nodulation mutants in pea have been developed but not evaluated in a breeding program. To determine the potential of 20 pea lines derived from crosses between two nodulation mutants (Rondo nod3 and Frisson P88 Sym29) and Saskatchewan adapted pea cultivars CDC Meadow and CDC Dakota, for BNF and agronomic performance. Pea lines were evaluated in replicated multi-location field trials. In four of the trials, a 15N isotope treatment was applied two weeks after planting to estimate the percentage of N derived from air (%Ndfa) using the 15N isotope dilution protocol. Additionally, standard agronomic assessments for pea were collected from each plot, as well as grain yield and seed protein concentration. Biological N fixation capacity of the pea lines ranged from 50% to 80%. Several of the pea lines performed significantly better than the check cultivars CDC Meadow and CDC Dakota for yield, percentage protein and BNF capacity. Pea lines, especially those arising from crosses with CDC Dakota, had on average 10% more seed yield, 2–3% more seed protein, and fixed 5% more N than CDC Meadow and CDC Dakota. The %Ndfa showed moderately high and significantly positive correlation with days to flowering (r = 0.47, p