Identifying Winter Hardy Alfalfa (Medicago sativa) for Northwestern Canada

Abstract

Winter kill is one of the most serious problems affecting alfalfa production in northwestern Canada. A rapid and accurate means of assessing winter hardiness is invaluable in developing new cultivars for this region. This program was designed to define some plant and environmental factors responsible for winter injury and to develop tests to identify plants with high yield potential and resistance to severe winter stress in northwestern Canada. The program has determined that the cold hardiness of alfalfa can change from year to year depending upon the plant and/or environmental conditions during the growing season. Three factors have been identified to be responsible for increasing the potential for winterkill: (1) low food reserves in the roots and crowns, (2) water saturated soil during the fall hardening period and (3) a late flush of growth in the fall from developing crown buds. A method was developed for separating the differences in winter hardiness between cultivars under field conditions. The method consisted of defoliating test plants at frequent intervals prior to winter then removing snow cover in early winter to induce a temperature stress. Germplasm sources from Ft. Smith and Ft. Providence in Canada\u27s Northwest Territories (N. W. T.), two cultivars from the USSR (Taezhnaya and Krasnouphimskaya-6), and one synthetic from Beaverlodge (BL 78-5) demonstrated considerable potential for increased yield and persistence over adapted cultivars to reduce the effects of a stressfull winter environment on alfalfa production in northwestern Canada