R. W. G. Dennis

Bio: R. W. G. Dennis is an academic researcher. The author has an hindex of 1, co-authored 1 publications receiving 2145 citations.

Multiple evolutionary origins of the fungus causing Panama disease of banana: Concordant evidence from nuclear and mitochondrial gene genealogies

Abstract: Panama disease of banana, caused by the fungus Fusarium oxysporum f. sp. cubense, is a serious constraint both to the commercial production of banana and cultivation for subsistence agriculture. Previous work has indicated that F. oxysporum f. sp. cubense consists of several clonal lineages that may be genetically distant. In this study we tested whether lineages of the Panama disease pathogen have a monophyletic origin by comparing DNA sequences of nuclear and mitochondrial genes. DNA sequences were obtained for translation elongation factor 1α and the mitochondrial small subunit ribosomal RNA genes for F. oxysporum strains from banana, pathogenic strains from other hosts and putatively nonpathogenic isolates of F. oxysporum. Cladograms for the two genes were highly concordant and a partition-homogeneity test indicated the two datasets could be combined. The tree inferred from the combined dataset resolved five lineages corresponding to “F. oxysporum f. sp. cubense” with a large dichotomy between two taxa represented by strains most commonly isolated from bananas with Panama disease. The results also demonstrate that the latter two taxa have significantly different chromosome numbers. F. oxysporum isolates collected as nonpathogenic or pathogenic to other hosts that have very similar or identical elongation factor 1α and mitochondrial small subunit genotypes as banana pathogens were shown to cause little or no disease on banana. Taken together, these results indicate Panama disease of banana is caused by fungi with independent evolutionary origins.

Fungal Endophytes of Tree Leaves

Abstract: The term epiphyte is used in general to characterize organisms that subsist only on plant surfaces. De Bar’s (1866) definition of endophytes—all the organisms that colonize internal plant tissues—was also used by Petrini (1986). In the same volume, Carroll (1986) restricted the use of the term endophyte to organisms that cause asymptomatic infections within plant tissues, excluding pathogenic fungi and mutualists such as mycorrhizal fungi. In view of the additional findings discussed in this chapter, however, I feel that this definition is no longer tenable. I propose, therefore, that Carroll’s definition be expanded to include all organisms inhabiting plant organs that at some time in their life, can colonize internal plant tissues without causing apparent harm to their host. This would account for those endophytic organisms that have a more or less lengthy epiphytic phase and also for latent pathogens that may live symptomless in their hosts for some time in their life.

Molecular systematics and phylogeography of the Gibberella fujikuroi species complex.

Abstract: Phylogenetic relationships of the phyto-pathogenic Gibberella fujikuroi species complex were investigated by maximum parsimony analysis of DNA sequences from multiple loci. Gene trees inferred from...

Epidemiology of wheat head blight and maize ear rot caused by Fusarium graminearum

Abstract: (1982). Epidemiology of wheat head blight and maize ear rot caused by Fusarium graminearum. Canadian Journal of Plant Pathology: Vol. 4, No. 2, pp. 195-209.