Environmental stress, plant traits, and their phenological legacies determine mycotoxin content in maize

Maize ( Zea mays L.), one of the most important staple crops, is highly vulnerable to fungal infection by Aspergillus and Fusarium species, which produce aflatoxins and fumonisins respectively. Temperature and precipitation interplay in affecting both plant performance and mycotoxin dynamics, but their effects might also depend on plant phenology. Timely identification of risk conditions is therefore essential to address preventive strategies. In 2022 we monitored 20 rainfed maize fields across a pedo-climatic gradient in NE Italy at four phenological stages, namely beginning of stem elongation, end of tassel emergence, milk maturation, dent maturation. At each stage we measured plant functional traits representing maize growth and morpho-physiology; moreover, at harvest, kernel production and mycotoxins accumulation were quantified. All variables were then related to environmental conditions (precipitation, mean temperature, soil texture). Our results showed that both aflatoxins and fumonisins were strongly related to environmental drivers already at stem elongation. The explained variance decreased afterwards, but increased again at harvest. Fumonisins increased when seasonal rainfall was higher, while aflatoxins content was mediated by plant response (plant height and kernel δ 13 C). These findings suggest a strong interplay between crop phenology, stress responses, and the occurrence of mycotoxins, shedding new light on the stress-induced vulnerability of plants to mycotoxin production. Stress timing is crucial, as it also affects final harvest conditions and points out possible underlying plant response legacies. We hence stress the importance of early-season monitoring of crops and tailored predictive models to anticipate mycotoxin risk in maize under variable climate scenarios. • Aflatoxin risk in maize is set early in the season, already before stem elongation • Fumonisins increase with temperature during growth stages and seasonal rainfall • Seasonal rainfall boosts both fumonisin and aflatoxin contamination • Aflatoxins depend on plant response to environment, fumonisins only on environment • Models’ predictive power is higher early in the season and shortly before harvest