Effect of agronomic programmes with different susceptibility to deoxynivalenol risk on emerging contamination in winter wheat

Deoxynivalenol (DON) is the most prevalent mycotoxin in small cereal crops throughout the world, and its occurrence is closely linked to the presence of Fusarium Head Blight (FHB) disease. In order to minimize the sanitary risk, wheat cropping systems are commonly designed to control DON contamination, as this represents the main target contaminant. However, several other mycotoxins and secondary metabolites produced by Fusarium and other fungal species have been detected in wheat. The objective of this study was to evaluate whether the application of agronomic programmes with different susceptibility to DON contamination could also affect the occurrence of emerging mycotoxins in wheat kernels. Field experiments have been conducted in North Italy, under naturally-infected conditions, over a period of 3 growing seasons, by comparing 4 field programmes, which were constituted by the combination of wheat cultivars (a durum wheat variety that is susceptible to DON contamination and a common moderately resistant one) and 2 fungicide applications at heading (untreated control compared to an azole application at heading). Grain samples have been analyzed by means of a dilute-and-shoot multi-mycotoxin LC-MS/MS method, and 43 fungal metabolites were detected. In addition to DON, the most abundant compounds were aurofusarin, culmorin and deoxynivalenol-3-glucoside, which were detected in all the growing seasons and agronomic strategies. Other trichothecenes and zearalenone derivatives were also found, but in clearly lower concentrations. Contamination by enniatins and moniliformin, produced by other Fusarium species e.g. Fusarium avenaceum, alternariol, alternariol methyl ether and tentoxin, produced by Alternaria species, has been observed for all the compared growing seasons. The presence of other mycotoxins and secondary metabolites was clearly affected by the climatic conditions: fumonisin, beauvaricin, bikaverin, fusaric acid and butenolid were detected in the warmer growing seasons, while chrysogine, infectopyrone, secalonic acid and ergot alkaloids (sum of 13 toxins) were only found in the more rainy and cool seasons. Equisetin, decalonectrin, toxin T-2 and HT-2 were only found in traces. The application of the field programmes clearly affected DON contamination in each growing season: a significant increase in this toxin has been observed moving from the lowest risk agronomic strategy to the highest one. The application of the most favourable DON control field programme (a moderately resistant variety combined with fungicide application at heading) reduced the content of this mycotoxin by 89%, compared to the worst programme (untreated susceptible variety). The application of the less risky agronomic strategy for DON contamination led to a significant reduction (>84%) of all the other mycotoxins produced by the DON producing fungal species. Moreover, although the considered agronomic factors (variety susceptibility and fungicide application) resulted in a control efficacy that varied in function of the environmental conditions and the type of mycotoxin, the results show a clear reduction trend, after the application of agronomic strategies that are able to minimize the DON content, for almost all the other Fusarium, Alternaria, Claviceps and Penicillium metabolites. The results summarized in this work, which have been obtained under different environmental and agronomical conditions, allow a first assessment to be made of the agronomic strategies that could be applied to control emerging mycotoxins in wheat.