Petioles from infected trees spread Verticillium dahliae

摘要

As long as the host plant remains alive, Verticillium dahliae usually only colonizes the host xylem vessels. After the host dies, the fungus may colonize the moribund tissues and form large numbers of microsclerotia. Following incorporation into thesoil and decomposition of the infected plant material, these microsclerotia become available as inoculum to infect new plants. It is well-known that as a result of this mechanism, V. dahliae can be spread to orchard trees on residues from field crops, such as potato, cotton and tomato, when these crops are grown between the trees (intercropping-systems) or on neighbouring fields (6). However, infected trees themselves are also an often neglected source of inoculum. It has been shown for several tree species [Acer spp. (7), Liriodendron tulipifera (2), Olea europaea (4) and Fraxinus excelsior (3)] that petioles from diseased trees can carry V. dahliae. In olive and ash infection percentages of 10 and 25 percent, respectively, have been reported. Moreover, in olive (4) as well as in ash (3) the presence of microsclerotia in leaf petioles has been demonstrated. Thus, after incorporation into the soil and decomposition, infected petioles may contribute to the spread of Verticillium wilt in tree nurseries