Activity of the Novel Fungicide SYP-34773 against Plant Pathogens and Its Mode of Action on <i>Phytophthora infestans</i>

Abstract

SYP-34773 is a pyrimidinamine derivative and a novel fungicide modified from diflumetorim. This study determined the antimicrobial spectrum of SYP-34773, which showed it could strongly inhibit the growth of some important plant pathogens including fungi and oomycetes. In particular, <i>Phytophthora infestans</i> is an oomycete sensitive to SYP-34773, and the mycelium growth stage was found to be the most sensitive stage, with an EC₅₀ value of 0.2030 μg/mL. At a concentration of 200 μg/mL, SYP-34773 displayed an excellent control efficacy of 69.55% and 81.48% against potato and tomato blight disease caused by <i>P. infestans</i> under field conditions, respectively. Mode of action investigations showed that this fungicide could cause severe ultrastructure damage to the mycelia of <i>P. infestans</i>, inhibit its respiration, and increase the cell membrane permeability of this pathogen. The results of this study could provide useful information for the fungicide registration and application of SYP-34773 as a novel fungicide.