A multivariate analysis of phenotypic traits of strains of Fusarium graminearum and F. meridionale supports structure by species

Fusarium head blight (FHB) of wheat and Gibberella ear and stalk rot (GER and GSR) of maize are diseases of worldwide importance. Several phylogenetic species belonging to the Fusarium graminearum species complex (FGSC) cause FHB and GER/GSR in Brazil, but the dominant species varies depending on host. Fusarium graminearum is the most frequent cause of FHB, while F. meridionale is more often associated with GER/GSR. These two species are distinguished based on fixed sequence variations at a few genetic loci; however, relevance of these differences to reproduction, pathogenicity and toxigenicity has not been fully explored. A range of phenotypic traits were evaluated for a group of strains of F. graminearum and F. meridionale from wheat and maize. These included radial growth on agar plates, sexual and asexual reproduction, fungicide sensitivity, toxigenicity and pathogenicity on wheat and maize. Although intraspecies variation was observed for most traits, a multivariate analysis showed the strains were strongly structured by species, regardless of host origin. Increased sexual or asexual reproduction, deoxynivalenol production and aggressiveness on wheat heads were most important for distinguishing strains of F. graminearum, while faster mycelial growth in culture, nivalenol production and reduced colonization on detached maize silks were most important for distinguishing strains of F. meridionale. Thus, the phylogenetic distinction between F. graminearum and F. meridionale is supported by phenotypic differences that are relevant for pathogenicity (aggressiveness and mycotoxin production on wheat heads and maize silks, mycelial growth and sexual and asexual reproduction) and disease management (tebuconazole sensitivity).