Inhibitory effects of five fungicides on the growth and development of Peronophythora litchii

Objective  This study aims to analyze the effects of commonly used fungicides against oomycete pathogens on various developmental stages of Peronophythora litchii, in order to provide a theoretical basis for the precise management of litchi downy blight.

Method The effects of pyraclostrobin, mancozeb, dimethomorph, metalaxyl, and propamocarb hydrochloride on the mycelial growth, sporangiophore morphology, sporangium production, zoospore release, cyst germination, and oospore production of six strains of P. litchii were investigated using the growth rate method and microscopic observation techniques.

Result Pyraclostrobin exhibited strong inhibitory effects on multiple developmental stages of P. litchii, with EC₅₀ values of 0.003–0.270 μg/mL for mycelial growth, sporangium formation, zoospore release, cyst germination, and oospore production. Dimethomorph inhibited mycelial growth, sporangium production, cyst germination, and oospore formation, with EC₅₀ values of 0.017–1.834 μg/mL; however, its effect on inhibiting cyst germination was relatively weak. Metalaxyl was effective against mycelial growth, sporangium formation, and oospore production, with EC₅₀ values of 0.005–0.037 μg/mL; similarly, this fungicide was less effective in inhibiting cyst germination. Mancozeb affected mycelial growth, zoospore release from sporangia, and cyst germination, with EC₅₀ values of 0.993–42.151 μg/mL. Propamocarb hydrochloride inhibited mycelial growth and sporangium production, with EC₅₀ values of 26.988–519.308 μg/mL; it was ineffective in inhibiting zoospore release and cyst germination. However, at concentrations above 50 μg/mL, it caused sporangiophore malformation and reduced branching.

Conclusion This study reveals the differences in the inhibitory characteristics of pyraclostrobin, dimethomorph, metalaxyl, mancozeb, and propamocarb hydrochloride on the key developmental stages of P. litchii, providing experimental evidence to elucidate the mechanism of action of different fungicides against oomycete diseases, as well as a theoretical basis and practical guidance for the precise and scientific control of litchi downy blight.