Dear Editor,Verticillium wilt,caused by the soil-boe fungus Verticillium dahliae,poses a major threat to a broad host range of more than 400 plant species,including economically important cotton (Bell,1992).V.dahliae is especially difficult to control because it persists in soil as resting structures,called microsclerotia,for several years in the absence of a host plant.The dormant microsclerotia are the primary infectious propagules and germinate when they are stimulated by root exudates.Infection of cotton roots by V.dahliae in soil naturally leads to the colonization of vascular tissues,from the parasitic to saprophytic phase,when mycelia and melanized dormancy microsclerotia are produced in the infected cotton,resulting in vessel blockage and cotton wilt disease (Gerik and Huisman,1988).