Constraining Evolution of Alternaria alternata Resistance to a Demethylation Inhibitor (DMI) Fungicide Difenoconazole

Abstract

Evolution of fungicide resistance in plant pathogens is one of major concerns in sustainable plant disease management. In this study, the genetics and potential of developing resistance to a demethylation inhibitor (DMI) fungicide, difenoconazole, in the fungal pathogen Alternaria alternata was investigated using a comparative analysis of genetic variation in molecular (Single Sequence Repeats, SSR) and phenotypic (fungicide tolerance) markers. No difenoconazole resistance was found in the 215 A. alternata isolates sampled from seven different ecological zones in China despite the widespread use of the fungicide for more than 20 years. This result suggests that the risk of developing resistance to difenoconazole in A. alternata is low and we hypothesize that the low risk is likely caused by fitness penalties incurred by resistant mutants and the multiple mechanisms involving in developing resistance. Heritability and plasticity account for ∼24 and 3% of phenotypic variation, respectively, indicating that genetic adaptation by sequence variation plays a more important role in the evolution of difenoconazole resistance than physiological adaptation by altering gene expression. Constraining selection in the evolution of A. alternata resistance to difenoconazole was documented by different patterns of population differentiation and isolate-by-distance between SSR markers and difenoconazole tolerance. Though the risk of developing resistance is low, the findings of significant differences in difenoconazole tolerance among isolates and populations, and a skewing distribution toward higher tolerance suggests that a stepwise accumulation of tolerance to the fungicide might be occurring in the pathogen populations. As a consequence, dynamic management programs guided by evolutionary principles such as spatiotemporal rotations of fungicides with different modes of action are critical to prevent the continued accumulation of tolerance or the evolution of resistance to difenoconazole and other DMI fungicides.

Induced expression of CYP51 associated with difenoconazole resistance in the pathogenic Alternaria sect. on potato in China

“…The mean EC 50 values of the 16 resistant isolates was 7.29 μg mL −1 , which was 52‐fold higher than the sensitive isolates. These results suggest that DMI resistance occurs in the natural populations of Alternaria from potato in China but they differ slightly from previous publications in which no DMI resistance was reported . Two factors may contribute to the difference.…”

“…These results suggest that DMI resistance occurs in the natural populations of Alternaria from potato in China but they differ slightly from previous publications in which no DMI resistance was reported. 10,11 Two factors may contribute to the difference. First, unlike previous studies, we included all early blight pathogens of Alternaria sect.…”

“…Although DMIs have been used for many years in potato fields, no field resistance has been reported. 10,11 The resistance status of DMI fungicide in Alternaria sect. isolates from potato remains unknown.…”

“…DMIs are thought to be a class of fungicides with inherent medium resistance risk (FRAC). Although DMIs have been used for many years in potato fields, no field resistance has been reported . The resistance status of DMI fungicide in Alternaria sect.…”

The Antifungal Activity of Gallic Acid and Its Derivatives against Alternaria solani, the Causal Agent of Tomato Early Blight

“…The inoculated plants were covered with polythene bags for 24 h to increase the humidity and after that, the plants were kept under greenhouse conditions. Disease incidence (DI%) was evaluated and data were collected three times regularly (7,14, and 21 days post-inoculation (dpi)) to observe the progress of early blight disease. The experiment was repeated twice with the same experimental design as described above.…”