In vitro and field response of Alternaria alternata to fungicides applied in soft wheat cropping systems for Fusarium Head Blight control

Introduction: The co-occurrence of Alternaria and Fusarium species on wheat represents a food safety concern due to the accumulation of their mycotoxins in grains. While fungicides are widely applied to control Fusarium Head Blight (FHB), their effects on Alternaria alternata growth and mycotoxin production remain poorly investigated. This study aimed to evaluate the activity of different fungicides, largely used to control FHB, against A. alternata both in vitro condition and in soft wheat fields under two different crop systems, minimum or conventional tillage.Materials and methods: The sensitivity of A. alternata to fungicides was evaluated by mycelial growth assay. The impact of sub-lethal doses of each fungicide on conidial germination and mycotoxin production was also evaluated. Field trials were performed over two growing seasons (2023-2025), to assess the effects of prothioconazole and difenoconazole, alone or in mixture, applied at flowering stage, on Fusarium and Alternaria.Results and discussion: In vitro, difenoconazole and the mixture difenoconazole prothioconazole showed a strong activity against A. alternata growth, while they had little to no effect on the related mycotoxin production. On the contrary, prothioconazole and folpet were effective to inhibit fungal growth, but, at sub-lethal doses, stimulated the production of altertoxin I, alternariol, alternariol monomethyl ether, altenuene and tenuazonic acid. In the field, prothioconazole showed the highest efficacy, reducing both FHB incidence and severity, and the accumulation of Fusarium mycotoxins deoxynivalenol and zearalenone in the kernels. Despite the detection of A. alternata in all plots, no significant differences were observed, since Alternaria contamination in wheat kernels never exceeded 20% and Alternaria toxins were not detected. Compared to minimum tillage, conventional tillage in combination with fungicide treatment improved grain yield and reduced Fusarium colonization and mycotoxin accumulation. This study allow us to hypothesize that flowering is not the most susceptible stage for Alternaria infection, and that Black Point disease is influenced by both environmental conditions and the interactions among fungal species co-occurring on wheat. This study provides the basis for further research aimed at identifying the wheat phenological stages most susceptible to A. alternata infection and determining the optimal timing for fungicide application to effectively control Black Point disease.