Classical and molecular characterization of the new species of Verticillium longisporum (V. dahliae var. longisporum Stark 1961; comb. nov. Karapapa et al., 1997) pathogenic to oilseed rape

摘要

Verticillium wilt in winter-sown oilseed rape (Brassica napus L. ssp. oleifera) is caused by the host-specific, near-diploid species Verticillium longisporum (11). It is a serious problem, widespread in Europe that has not yet been reported from theUK, even though oilseed rape is widely grown. Therefore, a potential threat exists in view of the very large area of the crop now cultivated in the UK, and the susceptibility of oilseed rape and Brassica-related species (1, 8, 27, 28). The only known report of an outbreak of Verticillium wilt in any Brassica crop caused by V. dahliae in the UK, was an isolated event reported for Brussels sprouts in the Evesham area during 1957 (9), but evidence presented here suggests that V. longisporum was actually responsible for this infection. Verticillium wilt of oilseed rape has caused economic losses in Sweden since 1960 (23). In Germany, it occurs in the whole country but mainly in the North (15, 26). There are also indications of isolated outbreaks in Franceover the last ten years (Dr. Hortense Brun, INRA, Le Rheu, personal communication), in Poland (20), southern Russia and The Ukraine (Dr. L. Portenko, personal communication), as well as Denmark (Dr. K. Zeise, personal communication). Krikun and Bernier(14) reported symptoms caused by V. dahliae in Canadian oilseed rape and mustard after experimental inoculation with two isolates of the fungus from potato and pea respectively, but there have been no reports of any disease outbreaks in rape/canola in Canada at that time or since. A similar Verticillium disease problem occurs in other Brassica-related crops, such as Chinese cabbage (B. campestris var. pekinensis), Japanese radish (Raphanus sativus) in Japan (8, 25), and in various Brassica crops in China (Yen-Yun, personal communication). Ciccarese et al. (5) reported severe outbreaks of Verticillium wilt on Cichorium intybus (chicory) and B. rapa ssp. tara (broccoli raab) in Southern Italy. Bush et al., (2) also previously reported Capsella bursa-pastoris to be infected by v. dahliae after artificial inoculation. In 1990, commercial cauliflower (B. oleraceae L. var. botrytis) fields in coastal California in the United States were reported to be affected by V. dahliae; by 1992 the disease had become asignificant threat to cauliflower production (12). Verticillium wilt of cauliflower has also occurred in the Netherlands, Germany and Japan (12). All commercially available cauliflower cultivars, and also other Brassicas: Chinese cabbage, cabbage (B. o.capitata L.) and bok choi (B. chinensis L.) were susceptible to isolates from infected cauliflower plants whereas broccoli (B. o. italica), a close relative of cauliflower, although exhibiting occasional blackening of the vascular system, did not show any leaf chlorosis, defoliation, wilting or stunting and the fungus was never isolated from this host (12, 22). In France, the pathogen has also been re-isolated from cauliflowers grown intensively in plastic tunnels for seed production in Finnistaire, during 1990 (Dr. Jeremy Sweet, personal communication).