The fungal community changes over time in developing wheat heads.

Under normal conditions, wheat is colonized by a multitude of fungi that can have beneficial or adverse effects on plant growth and yield. To study the effect of spraying wheat heads with fungicides on the fungal community from emergence to harvest we applied an amplicon sequencing approach on single wheat heads. The climatic data showed that the spring of 2014 was very dry and without precipitation in the two weeks around flowering. An initial quantitative PCR showed that the total amount of fungal DNA increased during the entire period, without significant difference between sprayed and control wheat heads. Amplicon sequencing of the internal transcribed spacer 2 (ITS2) region showed that operational taxonomic units (OTUs) identified as Sporobolomyces roseus dominated in the first weeks, whereas Alternaria infectoria OTUs dominated in the last weeks before harvest. The only observed significant difference was that the control wheat heads contained more of the powdery mildew causing Blumeria graminis f. sp. tritici OTUs compared with the sprayed wheat heads. The dry conditions around flowering most likely also had an effect on Fusarium head blight infection as Fusarium OTUs were only sporadically encountered. Analyses of secondary metabolites produced by Fusarium and Alternaria in the wheat heads confirmed the observations from the amplicon sequencing. Enniatin B was the most frequent contaminant present in four sprayed (49-538 ng/g) and three control (56-355 ng/g) wheat heads. The A. infectoria secondary metabolites infectopyrone and 4Z-infectopyrone were however consistently observed in all samples collected the last five weeks before harvest.