Attributes of Cyazofamid-Resistant Phytophthora litchii Mutants and Its Impact on Quality of Litchi Fruits

In this study, we determined the sensitivity of 148 Phytophthora litchii isolates to cyazofamid, yielding a mean EC50 value of 0.0091 +/- 0.0028 mu g/mL. Through fungicide adaptation, resistant mutants (RMs) carrying the F220L substitution in PlCyt b were derived from wild-type isolates. Notably, these RMs exhibited a lower fitness compared with the parental isolates. Molecular docking analysis further revealed that the F220L change contributed to a decrease in the binding energy between cyazofamid and PlCyt b. The total phenol and flavonoid contents in the litchi pericarp treated with cyazofamid on day 5 were significantly higher than in other treatments. Overall, the laboratory assessment indicated a moderate risk of cyazofamid resistance in P. litchii, but the emergence of the F220L change could lead to a high level of resistance. Thus, cyazofamid represents a promising agrochemical for controlling postharvest litchi downy blight and extending the shelf life of litchi fruits.