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United States Department of Agriculture

Agricultural Research Service

Research Project: DEVELOPMENT AND APPLICATION OF MOLECULAR PHYLOGENETICS OF FUNGI TO ENHANCE FOOD SAFETY AND FOOD SECURITY

Location: Bacterial Foodborne Pathogens & Mycology Research Unit

Title: A Multilocus Genealogical Concordance Approach to Species Delimitation within the Fusarium graminearum Species Complex of Cereal Head Blight Pathogens

Authors
item O`donnell, Kerry
item Ward, Todd
item Rooney, Alejandro
item Kistler, H
item Gale, Liane
item Aoki, Takayuki -
item Geiser, David -
item Nicholson, Paul -
item Sarver, Brice -

Submitted to: International Congress of Mycology Proceedings and Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: August 6, 2010
Publication Date: August 6, 2010
Citation: O Donnell, K., Ward, T.J., Rooney, A.P., Kistler, H.C., Gale, L.R., Aoki, T., Geiser, D.M., Nicholson, P., Sarver, B.A. 2010. A Multilocus Genealogical Concordance Approach to Species Delimitation within the Fusarium graminearum Species Complex of Cereal Head Blight Pathogens. International Congress of Mycology Proceedings and Abstracts.

Technical Abstract: Fusarium head blight (FHB) of wheat and barley currently ranks as one of the most destructive and economically devastating plant diseases worldwide. Outbreaks and epidemics of FHB pose a double threat to cereal production: (i) the disease is frequently responsible for poor seed quality and reductions in yields, which can result in significant price discounts to producers, and (ii) infected cereals are often contaminated with trichothecene and estrogenic mycotoxins. Cereals heavily contaminated with these mycotoxins are unsuitable for food or feed. Over the past decade, we have been employing genealogical concordance phylogenetic species recognition (GCPSR; Taylor et al. 2000. Fungal Genet. Biol.) to investigate species limits based on global collections of B-trichothecene toxin producing fusaria, the primary etiological agents of FHB. In our initial study (O’Donnell et al. 2000. PNAS), GCPSR-based phylogenetic analyses, employing DNA sequence data from six nuclear genes totaling 7.1 kb, revealed that F. graminearum comprised at least seven phylogenetically distinct and geographically distinct species lineages (designated the Fg clade), among which gene flow appeared to be greatly restricted over a time scale spanning multiple speciation events. In a series of subsequent publications, that further characterized the genetic diversity within the Fg clade, we extended these analyses to include portions of 12 nuclear genes totaling 15.9 kb of aligned nucleotide sequence data. Our global surveys of FHB genetic diversity and mycotoxin potential were greatly advanced by the development of a multilocus genotyping (MLGT) assay, which enabled the high throughput determination of FHB species identity and trichothecene chemotype (Ward et al. 2008. Fungal Genet. Biol.). The MLGT assay has proven to be highly robust in screening for novel FHB genetic diversity within Fg clade. To date, every strain identified as belonging to the B-trichothecene clade, but not matching any of the species probes, has proven to be a novel Fg clade species when subjected to GCPSR-based analyses. Our current data indicates the Fg clade (F. graminearum sensu lato) comprises at least 16 phylogenetically distinct and biogeographically structured species, suggesting several lineages evolved via allopatric speciation. Results of these studies indicate that species radiations have taken place in North and South America, Asia and possibly Australia. Phylogenetic species recognition greatly outperforms morphological and biological species recognition within the Fg clade and generally within most other lineages within Fusarium. In addition, recent developments in phylogenetic analyses allow for estimation of species-level relationships when there is discordance among gene trees. Maximum likelihood (Kubatko et al. 2009. Bioinformatics) and Bayesian (Liu 2008. Bioinformatics) methods are employed to attempt to resolve topological discrepancies and resolve relationships among lineages. These approaches take into account information contained in each gene region to arrive at a species-level estimation of relationships. Lastly, results of these studies have practical implications for the control of FHB and mycotoxin contamination of cereals worldwide, and they highlight the need for an integrated international disease control program to prevent the further spread of these economically devastating pathogens via global commerce.

Last Modified: 8/27/2014
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