Breeding for cold tolerance in common annual legume cover crops

Abstract There has been a significant increase in cover crop adoption, with land use nearly doubling over the last decade. Winter legume cover crops provide several ecosystem services, such as weed suppression and reducing soil erosion, while serving as an excellent nitrogen source for subsequent cash crops. Hairy vetch ( Vicia villosa R.), crimson clover ( Trifolium incarnatum ), and winter pea ( Pisum sativum L.) are three major winter annual legume cover crops in the United States. However, varying winter survival rates have reduced their reliability compared with winter hardy grasses like cereal rye ( Secale cereale ). Winter hardy cultivars have been selected and bred in winter pea, which are also used as food and forage crops, but fewer breeding efforts toward cold tolerance have been made in hairy vetch or crimson clover. Despite the current breeding efforts, all three species can suffer from winter damage in the winter hardiness zone 6 and below. Developing winter hardy annual legume cover crops requires a multifaceted approach, including cultivar selection and hybridization, quantitative trait locus isolation, management practice improvement, and identification of new sources of winter hardiness. Cold acclimation, deacclimation resistance, and reacclimation potential are possible mechanisms to explore in the cold tolerance of these winter cover crops. Cold tolerance can be evaluated in field and controlled environments using visual scoring, chlorophyll fluorescence, and ion leakage assays.