The verticillium threat to Canada's major oilseed crop: canola

Verticillium wilt of winter oilseed rape (Brassica napus subsp. oleifera), reported previously as being caused by Verticillium dahliae Klebahn, or V. dahliae var. longisporum Stark, 1961, has caused serious economic losses in Sweden since 1960 and is now widespread in Europe. We have recently fully characterized and reclassified this host-adapted, near-diploid pathogen at the species level: Verticillium longisporum comb, nov. (Karapapa, Bainbridg e, and Heale. 1997. Mycol. Res. 101: 1281-1294, and Karapapa, Bainbridge, a nd Heale. 7th International Verticillium Symposium, Cape Sounion, Athens, G reece, Oct. 1997. Abstr, p. 12). This pathogen causes yield losses, both in oilseed rape and related Brassica, in Europe, Asia, and Japan, but has not yet been reported on the U.K. oilseed rape crop or on the Canadian canola crop. Verticillium wilt in cauliflower in California, reported in 1994-1995 as involving a relatively large-spored V. dahliae with high nuclear DNA co ntent, may be the first evidence of the presence of V. longisporum in North America. The threat this organism poses to the Canadian canola crop is mai nly considered here in relation to the following: field disease symptoms, a seedling screening test for virulence/resistance, potential resistance sou rces within the genus, host resistance and glucosinolate content, and cross infection. We conclude with possible suggestions for disease control.