Evaluating winter-hardiness and developing a screening method for freezing tolerance in the leguminous cover crop Hairy Vetch (Vicia villosa R.)

Abstract

Hairy vetch (Vicia villosa R.) is a winter-annual legume that is grown as a cover crop and forage. In addition to reducing soil erosion and suppressing weeds, the species can facilitate enough biological N fixation to supplement or replace the N requirements of maize. Although more winter tolerant than most leguminous winter-annuals, it does not reliably overwinter in temperate environments such as the upper Midwestern United States. Our objectives were to screen a collection of accessions for winter-hardiness and develop a screening method for freezing tolerance in a laboratory setting. To identify winter-hardy germplasm, we evaluated the winter survival of 30 accessions in nine Minnesota environments. Mean percent survival among accessions ranged from 15 to 82% and resembled a bimodal distribution. Due to large variation among and within environments, a method of controlled freezing was developed to supplement field evaluations and advance breeding efforts. No differences in freezing tolerance were found among accessions without prior exposure to cold acclimation. However, large differences were apparent when plants were first grown for two weeks in greenhouse conditions and then cold acclimated for four weeks (3°C; short-day photoperiod). Lethal temperatures were determined from six 24-hr programmed freezing treatments. Programmed cycles began at -3°C and gradually decreased to target temperatures ranging from -13 to -21°C. This method of controlled freezing correlated highly with winter survival in field evaluations (rs = 0.77). This study highlights the value of priori testing of experimental parameters in controlled freezing studies and the importance of validating such methods with field evaluations.