Preventing multiple resistance above all: New insights for managing fungal adaptation

Sustainable crop protection is vital for food security, yet it is under threat due to the adaptation of a diverse and evolving pathogen population. Resistance can be managed by maximising the diversity of selection pressure through dose variation and the spatial and temporal combination of active ingredients. This study explores the interplay between operational drivers for maximising the sustainability of management strategies in relation to the resistance status of fungal populations. We applied an experimental evolution approach to three artificial populations of Zymoseptoria tritici, an economically significant wheat pathogen, each differing in initial resistance status. Our findings reveal that diversified selection pressure curtails the selection of resistance in naïve populations and those with low frequencies of single resistance. Increasing the number of modes of action most effectively delays resistance development, surpassing the increase in the number of fungicides, fungicide choice based on resistance risk, and temporal variation in fungicide exposure. However, this approach favours generalism in the evolved populations. The prior presence of multiple resistant isolates and their subsequent selection in populations override the effects of diversity in management strategies, thereby invalidating any universal ranking. Therefore, the initial resistance composition must be specifically considered in sustainable resistance management to address real‐world field situations. Experimental evolution serves as a significant tool in investigating the factors influencing antifungal adaptation in fungi. In this study, we utilised the model wheat pathogen species, Zymoseptoria tritici, and two contrasting fungicidal modes of action associated with varying resistance risks. Our findings illustrate that the initial population composition, especially the presence of multiple resistance, is the primary determinant of adaptive trajectories.