The relationship between field winter injury and fall growth score for 251 alfalfa cultivars

The winter hardiness of alfalfa cultivars (Medicago sativa L.) affects stand persistence in northern climates. Fall growth, a measure of fall dormancy, has been associated with alfalfa winter hardiness in some areas of North America, including Minnesota. This study evaluated 251 North American alfalfa cultivars for fall growth and winter injury and determined the relationship between fall growth and winter injury scores under Minnesota winter conditions. All cultivars were established by transplanting 9-wk-old plants into space-planted field plots in June 1991, 1992, and 1993. Plants were clipped in mid July and early September each yr and overwintered in the field. Fall growth was measured as individual plant height in mid-October 1992 and 1993. Winter injury was evaluated in May each year. Entries differed for fall growth and winter injury score in all years. The 2-yr-mean fall growth score was related to the 3-yr-mean winter injury score (r² = 0.85). Only seven of 251 entries fell outside the 95% confidence interval of the linear regression of winter injury score on fall growth score. Fall growth scores from 1992 and 1993 were correlated (r² = 0.88). Winter injury scores from 1992, 1993, and 1994 were also correlated (r² = 0.69-0.96). Although concerns exist about the use of fall growth score to predict winter hardiness in less severe climates, it remains a useful predictor of alfalfa winter hardiness in Minnesota when winter injury data are not available.