Genetic analysis and PCR-based identification of major Fusarium species causing head blight on wheat in Japan

Identifying the Fusarium species cause Fusarium head blight (FHB) and produces mycotoxins in wheat and other cereal is difficult and time consuming because of confusing phenotypic classification systems. In Japan, the F. graminearum complex, F. culmorum, F. avenaceum, and Microdochium nivale predominantly cause FHB. The internal transcribed spacer (ITS) and 5.8S of rDNA, a partial sequence of beta-tubulin and mitochondrial cytochrome b (cytb) genes of the four species were PCR-amplified and analyzed. On the basis of the ITS, beta-tubulin and cytb sequences, F. avenaceum and M. nivale are distinct from the F. graminearum complex and F. culmorum, whereas the F. graminearum complex is closely related to F. culmorum. Moreover, thiophanate-methyl-resistant isolates of the F. graminearum complex and F. culmorum did not have an amino acid substitution at amino acid codon 198 or 200 of beta-tubulin. In contrast, very highly or highly thiophanate-methyl-resistant isolates of M. nivale had Glu (GAG) substituted with Ala (GCG) or Lys (AAG) at codon 198, respectively. The allele-specific PCR assay was used to identify the F. graminearum complex and F. culmorum, and these Fusarium species could be distinguished rapidly.