Molecular aspects of virulence in the causal agent of Dutch elm disease, Ophiostoma novo-ulmi

Dutch elm disease has been one of the most economically destructive plant diseases of the last 100 years. The American elm (Ulmus americana ) has great value in the urban landscape but has been decimated by Ophiostoma ulmi (sensu lato) across North America since the early 1920's with mortality in some areas as high as 95%. The highly aggressive elm pathogen Ophiostoma novo-ulmi Brasier has potential as a model system for other destructive Ophiostoma species and other fungal plant pathogens. Thus, deciphering the genetic basis for virulence in this fungus is an important step in determining the best methods of controlling Dutch elm disease and other destructive plant diseases. This work describes the cloning and characterization of the gene encoding the cell wall-degrading enzyme, polygalacturonase, and characterization of glycosylation mutants of O. novo-ulmi. The genetic variation, vegetative compatibility and dsRNA virus infection in the O. novo-ulmi population in Winnipeg, Manitoba, Canada is also detailed.; Cell wall-degrading enzymes (CWDEs), and polygalacturonase in particular, have important roles in fungal virulence and host/pathogen recognition and initiation of host defense responses. Precisely how polygalacturonases act in the Dutch elm disease system is unknown. The work presented in this thesis showed that disruption of the polygalacturonase gene in O. novo-ulmi reduced the expression of wilt symptoms in host trees and likely had a role in contributing to the overall aggressiveness and parasitic fitness of the fungus.; Glycosylation enzymes are likely to affect virulence and host/pathogen interactions in the pathology of Dutch elm disease. Callus tissue of clonal Ulmus americana was used to determine if O. novo-ulmi, treated by random insertional mutagenesis followed by enrichment for glycosylation mutants, would show variation in interaction with callus tissue relative to the wild type. The activity of the secreted pectinolytic enzyme polygalacturonase was assayed in the mutants to determine whether interference with glycosylation machinery would have a deleterious effect on the secretion or activity of glycoproteins produced by this pathogen. Several of the putative glycosylation mutants demonstrated a lack of pectinolytic activity without a corresponding decrease in mRNA expression of polygalacturonse. (Abstract shortened by UMI.)...