Demethylation Inhibitor Fungicides Have a Significantly Detrimental Impact on Population Growth and Composition of Nectar Microbial Communities

Demethylation inhibitor (DMI) fungicides are a mainstay of modern agriculture due to their widespread use for crop protection against plant-pathogenic fungi. However, DMI residues can disperse and persist in the environment, potentially affecting non-target fungi. Previous research has demonstrated that DMIs and other fungicides inhibit yeast growth in floral nectar microbial communities and decrease fungal richness and diversity of exposed flowers with no apparent effect on bacteria. Nevertheless, the effect of DMIs on the population growth of different species of nectar inhabitants and the dynamics of these microbial communities remains understudied. To address these issues, in this study we created synthetic microbial communities including yeasts (Metschnikowia reukaufii and Metschnikowia pulcherrima) and bacteria (Rosenbergiella epipactidis and Comamonas sp.) and propagated them in culture media containing different DMIs (imazalil, propiconazole, and prothioconazole) at different doses or no fungicide. Our results showed that DMIs have a significant impact on some of the most common microbial inhabitants of floral nectar by favoring the growth of bacteria over yeasts. Furthermore, habitat generalists such as M. pulcherrima and Comamonas sp. were more impacted by the presence of fungicides than the nectar specialists M. reukaufii and R. epipactidis, especially upon dispersal across habitat patches. Future research should determine if the patterns observed in the present study hold true for other species of nectar microbes and explore the interaction between growth limitation due to fungicide presence, dispersal limitation, and other mechanisms involved in community assembly in floral nectar.