The Sensitivity and Resistance Risk of Pathogens to Phenamacril in Fusarium Crown Rot of Wheat

Fusarium crown rot is a global soil-borne disease that poses a serious threat to wheat production. Phenamacril, as a myosin-5 inhibitor, exhibits highly effective antifungal activity against Fusarium species. This study monitored the sensitivity of FCR pathogens to phenamacril and assessed their resistance risk under laboratory .The results showed that the mean EC50 values of phenamacril against F. pseudograminearum and F. graminearum were 0.474 ± 0.180 μg/mL and 0.396 ± 0.089 μg/mL, respectively. Under fungicide selection pressure, F. pseudograminearum was more prone to developing resistance, particularly generating a higher number of mutants at low concentrations, which preliminarily suggests that it possesses a relatively high intrinsic risk of resistance development.. Additionally, it exhibited more point mutation sites with a dispersed distribution; 21 different mutation types were detected in just 35 mutants. Fitness assessment indicated that most resistant strains showed no significant differences in mycelial growth and pathogenicity compared to their parents, but sporulation capacity exhibited interspecific differences: sporulation in F. pseudogramin earum mutants was comparable to or even higher than that of their parents, whereas it was significantly reduced in most F. graminearum mutants. This characteristic of "high resistance with low fitness cost" suggests a higher resistance risk of F. pseudograminearum to phenamacril under laboratory conditions. Therefore, when using phenamacril in production, measures such as continuous field sensitivity monitoring and rotation or mixture with other fungicides possessing different mechanisms of action should be implemented to effectively delay the emergence of resistance.