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Differences in morphology, ITS, IGS, mtSSU and β-tubulin sequences and UP–PCR hybridization were compared between morphologically identified F. avenaceum, F. arthrosporioides, F. anguioides, F. tricinctum, F. graminum and F. acuminatum strains. According to the combined β-tubulin, IGS and ITS tree, the strains of the Fusarium avenaceum/F. arthrosporioides/F. tricinctum species complex species can be divided into seven clusters supported by bootstrap values higher than 50%. The two main groups of European F. avenaceum, which cannot be distinguished by morphology, were separated in the tree based on β-tubulin sequences and less clearly in trees based on IGS and ITS sequences. MtSSU sequences were identical in all F. avenaceum and F. tricinctum strains studied. The European F. avenaceum strains of main group II had identical β-tubulin sequences with one American F. avenaceum strain and four European F. arthrosporioides strains, while F. avenaceum strains of main group I were closely related to two European F. arthrosporioides strains and to one Japanese F. anguioides strain. According to the combined β-tubulin/IGS/ITS sequence tree, European F. arthrosporioides strains were divided into four groups; F. tricinctum strains formed a well-supported cluster, in which two European clusters were separated from one African isolate. In the IGS sequence tree two European F. acuminatum strains together with one American F. acuminatum strain formed a cluster, which was separate from another American F. acuminatum strain. The F. acuminatum cluster was nested within the large F. tricinctum cluster together with one F. reticulatum strain in the combined IGS/β-tubulin tree. Several strains may be intermediates between the F. avenaceum/F. arthrosporioides/F. anguioides and F. tricinctum clusters and represent their own species. These results are partially supported by the results of UP–PCR hybridization analysis. Thus the molecular results may be helpful in future revision in the taxonomy of these species.

We studied the occurrence of genotypes of Gnomonia setacea by RAPD-PCR analysis at two natural sites in SW Finland to study site-, tree- and leaf-level genetic diversity. The analysis was performed with two primers by using 40 isolates from a total of 250 colonies isolated from two trees from each of two sites. Genetic diversity of G. setacea was found to be very high: every isolate studied was a unique genotype, even within the same leaf. This is probably due to sexual reproduction and the horizontal transmission system of airborne spores. Genotype distribution exhibited site-level similarity, indicating limited spore deposition and the ability to form local populations.