Cover crop potential of pea lines derived from crosses with nodulation mutants

Over the past century, numerous studies have addressed the physiology and genetics of biological nitrogen fixation (BNF) in legumes—targeting improvements through screening of existing germplasm, hybridization, and mutagenesis. Although these efforts have not been successful in commercializing grain pea (Pisum sativum) varieties with enhanced BNF, they offer promising avenues for improving pea BNF for forage and cover crop (CC) cultivation. To examine this approach, we tested the performance of a panel of 20 pea lines derived from crosses between high-yielding pea cultivars and two supernodulated pea mutants, Frisson-Sym29 and Rondo-nod3. The pea lines, parents, and mutant checks were trialed during the 2020 and 2021 growing seasons in Chico, CA, under rainfed conditions. Nodulation, the percent of nitrogen derived from the atmosphere (%Ndfa), biomass and nitrogen accumulation, and days to flowering of progenies were compared to their parent varieties and mutant donors. Overall, tested materials performed similarly in both study years. The pea produced an average dry biomass of 1694 kg in 2020 and 1964 kg in 2021 while accumulating 53.3 kg N ha⁻¹ in 2020 and 57.1 kg N ha⁻¹ in 2021. The materials produced up to 120 and 126 nodules plant⁻¹, weighing 126 and 217 mg plant⁻¹, in 2020 and 2021, respectively. Genotypic variations for agronomic and N-fixation traits were mainly associated with variations of parent cultivars and mutants. This study suggests that screening nodulation and aboveground and belowground biomass at pre-commercial breeding stages might yield effective CC varieties compared to screening solely for %Ndfa and grain yield.