Submitted to: Mycologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/14/2000
Publication Date: N/A
Interpretive Summary: Species of the filamentous fungus Fusarium cause many devastating plant and animal diseases, including fatal human infections. Furthermore, these molds produce a wide range of toxins that contaminate feed and food intended for animal and human consumption. As such, these fungi pose a serious threat to plant and animal health and food safety. The purpose of this study was to use molecular genetic techniques to characterize a cosmopolitan complex known as Fusarium solani. Molecular tools developed in this investigation have made it possible to accurately characterize the host range and geographic distribution of these mycotoxigenic pathogens for the first time. Evolutionary relationships inferred from the molecular data strongly indicate that F. solani comprises at least 50 genetically distinct species that exhibit a strong biogeographic structure world-wide. At present, the only reliable way to accurately detect and identify these pathogens is through use of the molecular tools developed in this study. Results of this study strongly indicate that a molecular evolutionary approach is essential to monitor the global distribution of these mycotoxigenic fungi and the toxins they produce.
Technical Abstract: Phylogenetic relationships and biogeography of the phytopathogenic Nectria haematococca-Fusarium solani species complex, section Martiella of Fusarium, were inferred from sequence data from the nuclear large subunit 28S rDNA, the nuclear ribosomal internal transcribed spacer (ITS) region and translation elongation factor (EF-la) gene introns and exons. Although a partition homogeneity test detected significant incongruence between the 28S rDNA and ITS datasets, results of the nonparametric Wilcoxon signed-ranks Templeton test indicated that the data could be combined. Maximum parsimony analysis of the combined dataset identified 15 heterothallic, 7 homothallic, and 4 putative strictly mitosporic, phylogenetically distinct ingroup species. Included among these were 10 formae speciales described for F. solani which were all resolved as phylogenetically distinct species by the molecular phylogeny. Of these, F. solani f. sp. cucurbitae races 1 and 2 appear to represent reproductively isolated biological species with independent evolutionary origins. Results of the molecular phylogeny also provide strong support for clades within New Zealand, South America, Africa and India-Sri Lanka, suggesting that this complex may be gondwanic in origin. The complex historical biogeography of this complex appears to reflect vicariant events associated with the fragmentation of Gondwanaland, possible gondwanic range expansions together with relatively recent distributional changes in these fungi associated with movement of economically important plants.