Systematics, Phylogeny and Trichothecene Mycotoxin Potential of Fusarium Head Blight Cereal Pathogens

Summary Economically devastating outbreaks and epidemics of Fusarium head blight (FHB) or scab of wheat and barley have occurred worldwide over the past two decades. Although the primary etiological agent of FHB was thought to comprise a single panmictic species, Fusarium graminearum, a series of studies we conducted over the past decade, employing genealogical concordance/discordance phylogenetic species recognition (GCPSR) 1) , revealed that this morphospecies comprises at least 16 phylogenetically distinct species (referred to hereafter as the F. graminearum species complex ＝FGSC). Results of a multilocus molecular phylogeny, based on maximum parsimony and maximum likelihood analyses of 12 combined genes comprising 16.3 kb of aligned DNA sequence data, suggest that the different species groups within the FGSC radiated in Asia, North America, South America, Australia and/or Africa. The significant biogeographic structure of these lineages, together with evidence of disjunct species in Asia and North America, are consistent with widespread allopatric speciation within the FGSC. In contrast to the results obtained using GCPSR, morphological species recognition using conidial characters and colony morphology was only able to distinguish 6 species and 3 species groups among the 16 species within the FGSC, highlighting the need for sensitive molecular diagnostic tools to facilitate species identifi cation. A validated multilocus genotyping assay was developed to address the need for species determination and trichothecene toxin chemotype prediction, and this assay has been extraordinarily useful in the discovery of novel FGSC species represented in our global FHB surveys. Ongoing molecular and phenotypic analyses are being conducted to elucidate the full spectrum of FHB pathogen diversity, their trichothecene toxin potential and biogeographic distribution. Increased understanding of the distribution and agricultural signifi cance of variation within the FGSC is needed for the development of novel disease and mycotoxin control strategies, including improvements in agricultural biosecurity designed to limit the introduction and spread of non-indigenous FHB pathogens.