Winter hardiness, root physiology, and gene expression in successive fall dormancy selections from 'Mesilla' and 'CUF 101' alfalfa

Fall dormancy is positively associated with alfalfa (Medicago sativa L.) winter survival, but the physiological bases for this association are not understood. Our objective was to determine how incremental changes in fall dormancy due to genetic selection influenced autumn height and winter survival, root physiology, and expression of a cold acclimation responsive gene family. Seed from each of three cycles of selection for contrasting (greater or less) fall dormancy using 'Mesilla' and 'CUF 101' as parents were planted in rows in the field (Starks-Fincastle, fine-silty, mixed, mesic, Aerie Ochraqualf) in West Lafayette, IN, in May 1997 and 1998. Plant height was measured in October and roots were sampled in December. Plant survival was determined in March of the year following seeding. Fall dormancy (reduction in shoot height in October) increased in a linear manner over the three cycles of selection for both Mesilla and CUF 101. A positive linear relationship was observed between fall height and winter injury in both years. Root sugar and protein concentrations increased as fall dormancy increased in populations derived from both Mesilla and CUF 101. Expression of the cold acclimation-responsive gene, RootCAR1, was positively associated with winter survival, and may be useful as a molecular marker for identifying winter hardy plants among semi-dormant or nondormant alfalfa germplasm in December of the seeding year.