Plant survival and root and bud composition of alfalfa populations selected for contrasting fall dormancy

Fall dormancy is correlated with improved winter survival in alfalfa (Medicago sativa L.), but the physiological basis for this association is not understood. Our objectives were to determine how selection for contrasting fall dormancy influenced (i) fall height and winter survival, (ii) crown bud development, and (iii) sugar, starch, and protein concentration and composition of roots and crown buds. Three cycles of selection for contrasting fall dormancy were conducted in Davis, CA using 'Norseman', 'Lahontan', 'CUF 101', and 'Wadi Qurayat' as parental sources. Seed of parental cultivars and seed of progeny from the third cycle of selection were planted in rows in the field (Starks-Fincastle, fine-silty, mixed, mesic Aeric Ochraqualf) in West Lafayette, IN, in May 1993 and 1994, and roots and crown buds were sampled at approximately monthly intervals between September and December. Plant survival was determined in March of the year following seeding. Parental cultivar differences in fall dormancy and winter survival were associated with changes in crown bud development, elevated total nonstructural carbohydrate and sugar concentrations in buds, and sugar and protein accumulation in roots. Cultivar differences in fall dormancy also influenced polypeptide composition of green buds and roots. Selection for greater fall dormancy reduced the height of CUF 101 and markedly improved its winter survival. Concentrations of sugars and proteins in buds and roots of the dormant selection of CUF 101 increased to values similar to those observed for the fall-dormant, winter-hardy Norseman. Selection solely for contrasting fall dormancy can alter cold acclimation in buds and roots and winter survival of alfalfa.