Abstract Aims This study aimed to assess the effects that long-term exposure to sub-lethal concentrations of demethylation inhibitor (DMI) fungicides have on the population growth dynamics of the floral nectar yeast specialist Metschnikowia reukaufii. Methods and results Synthetic populations of M. reukaufii were propagated for 112 days in presence of sublethal concentrations of imazalil (0.031, 0.125, and 0.5 μg mL−1) or no fungicide. ANOVA of aligned rank transformed colony forming unit (CFU) data showed that log10CFU values significantly depended on the treatment, the propagation step, and the interaction between these factors. However, hierarchical clustering of the series of log10CFU data did not reveal a clear differentiation of the control vs. imazalil treatments. Moreover, significant differences in median log10CFU were only observed in the first propagation step between the treatments containing 0.125 and 0.5 μg mL−1 of imazalil, and between some earlier vs. later propagation steps in the artificial nectars containing 0.031 and 0.5 μg mL−1 of imazalil (#2 vs. 24, and #1 vs. 4 and #1 vs. 24, respectively). Finally, continuous exposure to imazalil did not clearly select for increased resistance (i.e. higher minimum inhibitory concentration (MIC)) of M. reukaufii populations to DMI and non-DMI fungicides. Conclusions The results of this study suggest that exposure to sublethal concentrations of imazalil might not have a significant long-term effect on the growth dynamics of M. reukaufii. However, given the ephemeral and highly dynamic nature of nectar microbial communities, even a short-term growth effect such as the one detected in the present study might be ecologically relevant.
Quevedo-Caraballo et al. (Tue,) studied this question.