Mycotoxin Production and Molecular Variability of European and American Isolates of Fusarium Culmorum
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The main causative agents of Fusarium head blight are Fusarium graminearum and Fusarium culmorum. We examined the mycotoxin-producing abilities and molecular variability of 37 Fusarium culmorum isolates collected from the Pan-Northern Hemisphere, together with isolates representing related species. Mycotoxin-producing abilities of the isolates were tested by thin layer chromatography and by PCR using primer pairs specific for the Tri7 and Tri13 genes. Thirty isolates belonged to chemotype I (producing deoxynivalenol and 3-acetyl-deoxynivalenol), while seven represented chemotype II (producing nivalenol and/or fusarenone X). The presence of a functional Tri7 gene correlated well with nivalenol production. Isolates belonging to chemotype I were in general more pathogenic in in vitro tests than those belonging to chemotype II. Phylogenetic analysis of the random amplified polymorphic DNA profiles (RAPD) of the isolates enabled the isolates to be clustered into different groups. Most isolates from Hungary exhibited identical RAPD profiles. A similar clustering was found on the tree based on restriction analysis of the intergenic spacer region data. Sequence analysis of a putative reductase gene fragment of the isolates was also carried out. A correlation was detected between the geographic origin of the isolates and their position on the cladogram produced based on sequence data. The presence of mating type gene homologues was also tested with primer pairs specific for MAT1-1 and MAT1-2. The isolates carried either MAT1-1 or MAT1-2 homologues. No correlation was observed between clustering of the isolates based on RAPD, restriction analysis of the intergenic spacer region or sequence data and the distribution of MAT idiomorphs. Similarly, no correlation was detected between mycotoxin-producing abilities or aggressiveness and molecular characteristics of the isolates. Statistical analysis of RAPD data and lack of strict correlation between trees based on different data sets supported the view that Fusarium culmorum has a recombining population structure. The presence of mating type gene homologues in the isolates indicates that the recombining population structure is caused by ongoing or past meiotic exchanges.
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