Novel approach to link the physiological response of maize to drought and the occurrence of mycotoxins

Increased frequency of heatwaves and droughts are some of the aspects by which climate change threatens maize cultivation (Zea mays L.), thus playing a crucial role in global food security. The impact of drought on maize production is multifaceted. Firstly, drought stress during the critical stages of germination, flowering and pollination can lead to decreased plant growth, pollen production, nutrient uptake and ultimately to lower grain yields (1). In addition, prolonged periods of drought increase the spread of pests and diseases, which further exacerbate the vulnerability of maize crop and may compromise yield quality (2). However, the introduction of irrigation could only partially limit the damaging effects of severe water stress on maize performance. Therefore, improving the knowledge of the physiological response to water scarcity of this crop may be crucial for agronomic choices in the field. In this context, we monitored 20 maize fields, characterized by the simultaneous presence of irrigated and non-irrigated areas, along a soil grain size gradient in the Friuli Venezia Giulia region throughout the growing season, at four phenological stages (i.e., beginning of stem elongation, flowering, milk maturation, dent maturation). In particular, we considered the plant individual functional response (i.e., plant height, SLA, leaf DMC, leaf chlorophyll, carotenoid and flavonoid content, kernel DW, kernel C:N, kernel δ13C), and the aflatoxin and fumonisin content of the kernel in relation to irrigation conditions and climate data (i.e., total precipitation, mean temperature). We found that the soil structure effect is overruled by the effect of climate and/or irrigation. As we expected the absence of irrigation and low total precipitation led to a reduction of plant biomass and kernel production whereas interaction between irrigation and phenological stage had significant effect on leaf pigments (i.e., chlorophyll) and secondary metabolites (i.e., flavonoid). Moreover, irrigation enhanced the kernel C:N ratio and δ13C, whereas reduced the amount of aflatoxins. Our further investigations aim at evaluating the interplay between the climatic variables, the soil structure and the individual traits on the ultimate content of mycotoxins in the kernel, with two distinct irrigation regimes and at the given different phenological stages adopting a structural equation modelling approach.