Alfalfa plant death during the summer versus the winter in interior British Columbia

Single plants of 12 alfalfa (Mediccigo sativa L.) cultivars, chosen to represent a range of winter hardiness and resistance to verticillium wilt (Verticillium albo-atrum), were space planted to determine the time of plant death during the year. Plant mortality was assessed in spring and fall for three consecutive years. The relationship between plant survival during summer or winter and the cultivars’ resistance to verticillium wilt or fall growth was examined. During the first 2 yr of this field study, natural mortality during both summer and winter ranged from 1.0 to 2.1%. But by the third year an average of 9% of the plants died during the summer. Survival during the third summer was correlated (r = 0.76, P = 0.004) with the veritcillium wilt resistance measured using a greenhouse screening test, but was not correlated with fall growth of the cultivars. During the third winter, plant death for all cultivars averaged 67%. Survival of a cultivar during the winter was negatively correlated (r = −0.84, P = 0.001) with its fall growth, but not with its verticillium wilt resistance. These results indicate that programs to develop alfalfa cultivars with long-term persistence in the interior region of British Columbia should include both fall growth and verticillium wilt resistance in their selection criteria.Key words: Verticillium wilt, winter injury, fall dormancy, winter hardiness, stand persistence