Submitted to: Phytopathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/17/2007
Publication Date: 2/1/2008
Citation: Suga, H., Karugia, G.W., Ward, T.J., Gale, L.R., Tomimura, K., Nakajima, T., Miyasaka, A., Koizumi, S., Kageyama, K., Hyakumachi, M. 2008. Molecular Characterization of the Fusarium graminearum Species Complex in Japan. Phytopathology. 98(2):159-166. Interpretive Summary: Fungal pathogens within the Fusarium graminearum species complex cause a variety of diseases on cereal crops worldwide, including Fusarium head blight (FHB) of wheat and barley, and ear and stem rots of maize. Taken together, these diseases result in billion dollar losses to agriculture each year. In addition, these fungi contaminate cereal grains with trichothecene mycotoxins that pose a serious threat to animal health and food safety. Recently, unprecedented species and toxin variation has been identified among these pathogens. Detailed information on the distribution and significance of this variation is required to inform effective plant quarantine and disease control efforts. To that end, we report the development of molecular tools for rapid identification of two of the most important FHB pathogen species and prediction of their toxin types. These tools were validated via a survey of FHB isolates from Japan, where we documented significant geographical differences in the distribution of these species and toxin types that may be associated with average daily temperature. We also found no evidence of natural hybridization between these species, which could lead to the rapid transfer of pathogen adaptations.
Technical Abstract: Members of the Fusarium graminearum species complex (teleomorph: Gibberella zeae) are important cereal pathogens worldwide and belong to one of at least nine phylogenetically distinct species. We collected 298 isolates of the F. graminearum species complex from wheat or barley from 2001 to 2004 in Japan and investigated species and trichothecene chemotype compositions. Phylogenetic analyses and species-diagnostic PCR-RFLP revealed the presence and differential distribution of F. graminearum s. str. and F. asiaticum in Japan. F. graminearum s. str. is predominant in the north, especially in the Hokkaido area, while F. asiaticum is predominant in southern regions. In the Tohoku area, distinct co-occurrence of these species was observed. Trichothecene chemotyping of all strains by multiplex PCR revealed significantly different chemotype compositions of these species. All 50 isolates of F. graminearum s. str. were of a 15- or 3-acetyl deoxynivalenol type, while 173 (71 %) out of 246 strains of F. asiaticum were of a nivalenol type. The possibility of gene flow between the two species was investigated by use of 15 PCR-RFLP markers developed in this study, as interspecies hybridization of F. graminearum s. str. and F. asiaticum was previously achieved in vitro, and was also achieved in this study using Japanese strains. However, no obvious hybrids were detected from 98 isolates examined, including isolates collected from regions where both species co-occur.