The pathogenicity of two strains of the fungus Rhizoctonia solani Kuhn, and a strain of a related fungus,Corticinm praticola Kotila, to throe hosts, was studied, to determine which factors affect the specificity of parasitism. One R.solani strain parasitized lettuce, the other, cabbage, and the third fungus C.praticola parasitized both these hosts. Wheat was not severely parasitized by any of these fungi. Pathogenicity was unrelated to the stimulation of fungus growth by host exudates, which also had little effect on the formation of infection cushions, by which these fungi normally penetrate their hosts. The surface configuration of the host, and the contact stimulus were important in penetration, and attachment of the fungi. Adhesive structures were formed on non-living surfaces by each fungus, but not on damaged host surfaces. Each fungus penetrated only some tissues of each host. Pathogenicity was found to be unrelated to the inhibitory effect of host tissue on fungus growth, but was correlated to the speed of invasion and direction of advance of the hyphae inside the host tissues. A hypersensitive reaction took place, but this could not account for the specificity of parasitism. Pectolytic and cellulolytic enzymes were produced in culture by each fungus when grown on synthetic substrates. Enzyme activity was unrelated ti the growth of the fungi, and to pathogenicity. Extracts of diseased plants contained pectolytic and cellulolytic enzymes, but their activity was unrelated to that of culture filtrates from synthetic media, and also unrelated to pathogenicity. These extracts were toxic to young seedlings, but toxicity too, was unrelated to the specificity of parasitism. The toxic principle was thermolabile and may have been enzymic, and was able to macerate young seedling tissues.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:602177 |
| Date | January 1963 |
| Creators | De Silva, Robert Lucian |
| Publisher | Imperial College London |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/10044/1/13206 |
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