Baseline sensitivity and control efficacy of a new QiI fungicide, florylpicoxamid, against Botrytis cinerea

Gray mold caused by Botrytis cinerea is an airborne plant pathogen with a necrotrophic lifestyle that infects more than 200 crops worldwide. Florylpicoxamid is a second-generation picolinamide fungicide inspired by a natural product. Florylpicoxamid targets the Qi site of the mitochondrial cytochrome bc1 complex and is currently being registered in China for the control of gray mold in a variety of crops. Although a broad spectrum of activity and attributes have been reported for florylpicoxamid, little is known about its effectiveness against gray mold or its protective and curative properties.Florylpicoxamid exhibited substantial inhibitory activity against 12 tested species of plant-pathogenic fungi, with effective concentration for 50% growth inhibition (EC50 ) values ranging from 0.017 to 2.096 μg ml-1 . A total of 129 isolates of B. cinerea from ten regions were tested for their sensitivity to florylpicoxamid, and the mean EC50 value was 0.04 ± 0.017 μg ml-1 . Furthermore, florylpicoxamid was observed to substantially inhibit all developmental stages of B. cinerea, with mycelial development, sclerotium germination, germ tube elongation and conidial germination being restrained with an EC50 value of 0.051 ± 0.0072, 0.012 ± 0.0069, 0.019 ± 0.0041 and 0.0062 ± 0.0007 μg ml-1 , respectively. No cross-resistance was observed between florylpicoxamid and quinone outside inhibitor (QoI), methyl benzimidazole carbamates or succinate dehydrogenase inhibitor. Florylpicoxamid also exhibited protective and curative activity against the development of B. cinerea infection in tests on tomato fruits. At application rates of 90, 112.5 and 135 g a.i. ha-1 , florylpicoxamid was also observed to provide more-effective control than boscalid (300 g a.i. ha-1 ).This study demonstrated that the novel fungicide florylpicoxamid exhibits strong inhibitory activity against B. cinerea, regardless of the resistance profiles of those isolates to tested fungicides with different modes of action. This makes florylpicoxamid a powerful new solution to optimize gray mold control and manage fungicide resistance. © 2022 Society of Chemical Industry.