Effect of Verticillium Wilt on Forage Yield of Alfalfa in Southern Alberta. H. C. HUANG, Research Centre, Agriculture and Agri-Food Canada, P.O. Box 3000, Main, Lethbridge, Alberta, Canada T1J 4B1. S. N. ACHARYA, M. R. HANNA, G. C. KOZUB, and E. G. SMITH, Research Centre, Agriculture and Agri-Food Canada, P.O. Box 3000, Main, Lethbridge, Alberta, Canada T1J 4B1. Plant Dis. 78:1181-1184. Accepted for publication 20 September 1994. Copyright 1994 Agriculture and Agri-Food, Canada. DOI: 10.1094/PD-78-1181.

The incidence of Verticillium wilt and the forage yield of 12 cultivars of alfalfa (Medicago saliva) were compared in an irrigated field naturally infested with Verticillium albo-atrum near Lethbridge, Alberta. The alfalfa cultivars were seeded in 1986 and examined annually for Verticillium wilt and forage dry matter yield during 1987-1993. The incidence of wilt varied from year to year, and averaged over the years, the resistant cultivars Barrier, AC Blue J, Pioneer 5444, and Vertus had a significantly (P < 0.01) lower incidence than the moderately resistant cultivars Maris Kabul, Admiral, and Trumpetor and the susceptible cultivars Excalibur, WL3I6, Apollo II, Beaver, and Pacer. Differences in yield were not significant (P > 0.05) until the third year. During the 7-yr trial, the total forage yields of resistant cultivars Pioneer 5444, Barrier, and AC Blue J (87,143, 86,850, and 85,398 kg/ ha, respectively) were significantly (P < 0.01) higher than those of the susceptible cultivars Beaver and Pacer (75,420 and 73,519 kg/ha, respectively). The moderately resistant cultivars Maris Kabul, Admiral, and Trumpetor had intermediate yields. Although the cultivar Vertus was resistant to the disease, its total forage yield was significantly (P < 0.01) lower than that of resistant cultivars Pioneer 5444, Barrier, and AC Blue J. These results illustrate the impact of Verticillium wilt on alfalfa production in southern Alberta.