The frequency of occurrence of four <I>Fusarium</I> spp. on wheat in the Moravia region, Czech Republic, was determined by polymerase chain reaction (PCR). Grain samples were collected during 2003–2006 at grain purchase centres. The dominant species was <I>F. graminearum</I>, which was recorded in all samples of the first 3 years of the study and in 88% of them in 2006. The previously more frequent <I>F. culmorum</I> was detected in 100 % of the samples only in 2005; in the preceding two years

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... he frequency of its detection was lower, 84% and 60%, and in 2006 it was detected in 55% of the samples. <I>Fusarium avenaceum</I> had a very low occurrence in the years 2003–2004, but in 2005 it was recorded in 100% of the samples. In 2006 it was the opposite – total absence of this species. A quite different situation was found in the occurrence of the fourth species – <I>F. poae</I>. In the years 2005 and 2006 it was only detected in 10%, resp. 2% of the samples, compared to markedly higher occurrences in the previous years. A comparison of the current weather development with the long-term mean at the Troubsko locality suggests that years with a relatively long, wet and cold start of the growing season and warmer end of vegetation (late May–July) will favour <I>F. graminearum</I>.