Selective Modification of Alfalfa toward Acclimatization in a Subarctic Area of Severe Winter Stress 1

A‐syn.B, a strain of variegated alfalfa ( Medicago media Persoon) possessing exceptional adaptation to subarctic conditions, has been developed during the past two decades at the College Research Center in subarctic, interior Alaska (63.8° N. lat.). This strain was synthesized from persistent plants remaining after winters had eliminated the less hardy bulk of populations from numerous alfalfa cultivars in experimental field plantings. A‐syn.B displayed significantly better winter survival in the field than 33 other strains from Canada, northern Europe, and the conterminous USA. Etiolated growth in autumn, an estimate of stored reserves, was expressed in greater amount and over a longer period by A‐syn.B than by ‘Rhizoma,’ ‘Rambler,’ or ‘Vernal,’ varieties that are considered extremely winter‐hardy elsewhere. A‐syn.B sustained less injury to artificial freeze stress than Vernal. This new strain is considered to represent selection for genotypes better adapted for reserve storage and coldhardiness development than midtemperate alfalfa varieties under the brief term of short photoperiods in the Subarctic prior to onset of winter. Another Alaskan synthetic, A‐syn.A, derived from artificial crosses of M. media X M. falcata backcrossed to M. falcata , was superior to A‐syn.B in two of five tests and inferior to pure M. falcata in winter survival only in one test that was exposed to greatest winter stress. A‐syn.B was superior in winter survival to varieties of alsike, red, and strawberry clovers ( Trifolium spp.), birdsfoot trefoil ( Lotus corniculatus L.), crownvetch ( Coronilla varia L.), and sainfoin ( Onobrychis viciaefolia Scop.), and less hardy than two native Alaskan legumes.