Original£ºCotton Science£¬2006£¬18(4)£º228-232
A New Detection Method of Wilting Virulence Induced by Phytotoxin from Abstract:A new method to measure the virulence of phytotoxin wilting caused by Verticillium dahliae through pricking on leaf surface and spreading phytotoxin on pricked area has been developed. First, phytotoxin of V. dahliae £¨V.d.-toxin£©of V991 strain£¬a severe defoliating virulence strain of V. dahliae to cotton£¬was partially purified with Sephacryl S-200 HR; next, 20~50 pits were pricked with a small needle in 0.5 cm2 on the surface of cotyledon or euphylla of cotton seedling; then, certain volume of V.d.-toxin solution was spread on the 0.5 cm2 of the leaves; and in 24 h after the treatment, wilting spots were appeared and recorded it. The water and BSA treatments were employed as controls. The virulence of wilting could be divided into five classes from 0 to ¢ô . Apart from the purified V.d.-toxin, the filtrate (liquid culture medium filtered after culturing V.d. over 7 days) can be also used for this method. To identify its general use of this method, eight V.d .strains were inoculated on leaves of 3 cotton cultivars. These V.d.strains included: severe wilting virulence (V991, T9, V56 and V146), weak wilting virulence (V110, V246, V250) and medium wilting virulence (V3-10-1). By pricking small pits on cotton leaf surface and spreading V.d. -toxin onto the pricked area, it was easily to observe the wilting symptom and to evaluate their wilting virulence. With this method, the 8 tested strains were classified into corresponded groups, for instance, V120, V991 and T9 were divided into the severe type of wilting virulence. This grouping result was as same as that formerly conducted through traditional methods (such as soaking seedling method). To determine the optimum cotton growing stage and part of the leaf on cotton plant, both cotyledon and euphylla in seedling and euphylla in adult plant were tested. As the result, this method could be utilized as early as in seedling stage, and cotyledon was better than euphylla since it was easy to prick but not easy to get through. However the extent of wilting varied with the temperature of environment, cotyledon or euphylla, and the concentration of V.d. -toxin used. To determine the differential reaction of cotton cultivars to V.d.-toxin with this method, four upland cotton cultivars (Ejing-3, B99261, CCRI 12 and Xingluzao-7) were used, and the coherence between V.d. -toxin soaking method and our new method was compared. The result proved that both methods got very similar by multiply tests.
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