EVALUATION OF ALFALFA LINES FOR REACTION TO WINTER CROWN ROT IN FIELD TRIALS IN SASKATCHEWAN

The effect of winter crown rot [Coprinus psychromorbidus] on stand density and forage dry-matter yield of alfalfa (Medicago sativa) was examined during 1986-90 in field trials in Saskatchewan. Eight alfalfa cultivars and one synthetic line were examined at each of five sites. Epidemics occurred at three sites during the study. At Loon Lake, stand injury in inoculated plots in the spring after the epidemic averaged 98% and first-cut yield losses were 79%. At Melfort, stand losses were 24% and first-cut losses were 20%. At Swift Current, stand losses were 21% and first-cut losses were 10%. At each site, some stand recovery occurred over the growing season. As a result, losses in total yield over the year were lower than losses in first-cut yield. Damage caused by disease and low-temperature injury in the winter after the initial epidemic resulted in losses in stand and yield as great as those incurred initially. Line S-7312, selected for resistance to winter crown rot, exhibited the lowest losses in the study. Percentage losses in stand density after an epidemic were correlated with percentage losses in yield, but were not correlated with yield after subsequent low-temperature injury. Regression analysis was used to develop equations to estimate yield loss based on loss in stand caused by winter crown rot.