The infection process and growth of Verticillium fungicola in mushroom sporophore tissue was studied by light and scanning and transmission electron microscopy. The lesions produced on infection of mature sporophores result from the collapse of host cells brought about by cell wall degrading enzymes produced by the pathogen. The presence of enzymes capable of degrading a mushroom cell wall preparation was demonstrated in vitro. The mechanisms involved in the development of sporophore deformities were studied using expanding stipe tissue as a convenient model of whole sporophore expansion. Deformities occurred only when rapidly expanding tissue was inoculated and were associated with stimulation of host cell expansion by the pathogen. V.fungicola showed limited ability to parasitise a number of artificially inoculated Basidiomycete fruit bodies although rust and powdery mildew fungi were readily colonised by the pathogen. The ecology of V.fungicola was studied to establish likely sources of inoculum as an aid to disease control. Using a specifically developed medium, Verticillium species were isolated from soil, leaf litter, horticultural peat, chalk and insects. Verticillium species were not isolated from a range of wild Basidiomycete fruit bodies and plant pathogenic microfungi. Major problems were encountered in identifying isolates, due to their morphological variability and to the inadequate and often conflicting taxonomic information available. The majority of the 300 isolates obtained were tested in an in vitro pathogenicity assay but only 3 gave scores equivalent to V.fungicola. Mushroom beds were inoculated with 50 isolates but none reproduced the entire range of symptoms characteristic of the disease. Benomyl insensitivity in wild populations of Verticillium species was also investigated. In some species (eg. Verticillium psalliotae and Verticillium bulbillosum) the majority of isolates tested were insensitive although sensitive isolates did occur. In others (eg. Verticillium lecanii) all isolates tested were sensitive but selection experiments suggested that insensitive individuals were present in the population.
|Date of Award||1983|