In Vitro and Ex Vivo Antifungal Activities of Metconazole against the Rice Blast Fungus Pyricularia oryzae

Rice blast, caused by the filamentous fungusPyricularia oryzae, has long been one of the major threats to almost all rice-growing areas worldwide. Metconazole, 5-(4-chlorobenzyl)-2, 2-dimethyl-1-(1H-1, 2, 4-triazol-1-ylmethyl) cyclopentanol, is a lipophilic, highly active triazole fungicide that has been applied in the control of various fungal pathogens of crops (cereals, barley, wheat), such as theFusariumandAlternariaspecies. However, the antifungal activity of metconazole againstP. oryzaeis unknown. In this study, metconazole exhibited broad spectrum antifungal activities against sevenP. oryzaestrains collected from rice paddy fields and the wild type strain P131. Scanning electron microscopic analysis and fluorescein diacetate staining assays revealed that metconazole treatment damaged the cell wall integrity, cell membrane permeability and even cell viability ofP. oryzae, resulting in deformed and shrunken hyphae. The supplementation of metconazole in vitro increased fungal sensitivity to different stresses, such as sodium dodecyl sulfate, congo red, sodium chloride, sorbitol and oxidative stress (H2O2). Metconazole could inhibit key virulence processes ofP. oryzae, including conidial germination, germ tube elongation and appressorium formation. Furthermore, this chemical preventedP. oryzaefrom infecting barley epidermal cells by disturbing appressorium penetration and subsequent invasive hyphae development. Pathogenicity assays indicated a reduction of over 75% in the length of blast lesions in both barley and rice leaves when 10 μg/mL of metconazole was applied. This study provides evidence to understand the antifungal effects of metconazole againstP. oryzaeand demonstrates its potential in rice blast management.