Dynamics of Fusarium graminearum inoculum on residues of naturally infected winter and summer crops

Fusarium graminearum is considered the main cause of Fusarium head blight (FHB) in Argentina. The development of this pathogen is dependent on weather conditions, and its occurrence results in economic losses associated with yield reduction, lower quality of grains, and frequent contamination with mycotoxins. The main inoculum source for FHB is F. graminearum perithecia in crop debris where the pathogen survives saprophytically. The adoption of conservationist tillage practices, which leave crop residues on the soil surface, impacts on the volume of inocula available which, in combination with the lack of FHB resistant wheat cultivars, increases the risk of disease development. Our objective was to analyze the long-term dynamics of F. graminearum inocula on different winter and summer crop residues. To do so, five winter cereal species (soft and durum wheat, barley, rye and tritordeum) were cultivated and harvested, and soybean was sown under no-till on the crop debris. The presence and viability of Fusarium graminearum propagules were later evaluated on the residues of the six crops in the 14 months following the harvest of soybean. A qPCR fungal quantification method was developed using previously available primers. The results obtained confirmed the presence and viability of the inoculum in all substrates throughout the time considered. Furthermore, a direct relationship was found between the amount of inoculum in the residues of the soybean sown under a zero-tillage system and the inoculum in the residues of the winter cereals previously sown. This research provides information that could help reduce the sources of F. graminearum inoculum and establish pre-harvest management strategies aimed at preventing mycotoxin contamination in the food chain.