Phylogeny and Molecular Diagnosis of Mycotoxigenic Fungi

Phylogenetic studies of the fungi that produce the five major groups of mycotoxins are reviewed, with a focus on studies employing ribosomal and/or β-tubulin (BenA) gene sequences. The toxins aflatoxin and ochratoxin A are produced by several Aspergillus and Penicillium species classified in the Trichocomaceae, Eurotiales. The toxins fumonisin, deoxynivalenol and zearalenone are produced by several Fusarium species classified in the Nectriaceae, Hypocreales. Studies of ribosomal genes have revealed that the present generic concepts for Aspergillus, Penicillium and Fusarium will require some adjustment in order to conform to phylogenetic principles. Phylogenetic studies have resulted in generally narrower species concepts in all three genera but there is good correlation between these species and mycotoxin production. The development of molecular diagnostics for the critical mycotoxigenic species is considered, with particular emphasis on the development of DNA hybridization probes that can be used to detect and identify multiple species using species and/or clade specific oligonucleotides designed from one or more genes. As an illustration, a virtual array for identifying Aspergillus species and groups of species producing aflatoxin is presented, based on oligonucleotides selected and optimized from a database of internal transcribed spacer and partial β-tubulin sequences assembled from GenBank. It was possible to design acceptable oligos for all species and groups in the complex using the β-tubulin gene, but only for one species and the larger group using the less variable internal transcribed spacer of the ribosomal DNA.