Improving Winter Hardiness in Nondormant Alfalfa Germplasm

Abstract

Alfalfa (Medicago sativa L.) adapted to the midwestern USA typically becomes dormant in autumn to survive winter stress. Nondormant alfalfa germplasm produces higher biomass yield during autumn but usually dies during the winter. The objective of this study was to test the hypothesis that recurrent selection could decrease winter injury in nondormant alfalfa populations. Between 1997 and 2000, three cycles of selection were conducted at Ames, IA, in four nondormant cultivars (5939, GT13R+, CUF101, and Magna 8) by recurrently selecting the most vigorous plants in the spring following establishment. In May 2001, the original cultivars and the three cycles of selection (C0, C1, C2, and C3) of each cultivar were transplanted with six check cultivars in the field at Ames, IA, and West Lafayette, IN. Biomass yield was measured in September and November 2001 at both locations. In November 2001, half of the plants in each plot were removed and roots were analyzed for total sugar, starch, and protein concentrations. The remaining plants were scored for winter injury in April 2002. Strong negative linear trends were observed across cycles for both winter injury and autumn plant height. In contrast, forage biomass yields showed little change. Root total sugar concentration in November increased with cycle of selection, but root starch, protein, and amino acid concentrations remained constant. Little change was noted among cycles for forage nutritive value. Selection based solely on winter injury can improve winter hardiness of nondormant populations. A concomitant decrease in autumn plant height may not affect autumn yield.