Antifungal activity of traversianal, a diterpenoid aldehyde from Cercospora sp. ME202, against rice blast fungus Pyricularia oryzae

Abstract Natural products from microorganisms are a rich resource for the identification of effective antifungal agents against plant pathogenic fungi. Traversianal, a diterpenoid produced by Cercospora spp., exhibits antifungal activity against Colletotrichum orbiculare, a pathogen that causes cucumber anthracnose. However, its effects on other fungi have not been investigated. Therefore, this study evaluated the antifungal activity of traversianal, derived from Cercospora sp. ME202, on Pyricularia oryzae, a rice blast pathogen. Traversianal exhibited a concentration-dependent inhibitory effect on conidial germination, with complete inhibition at 30 ppm. In the thin-layer chromatography bioassay, traversianal was detected as an antifungal zone at Rf 0.91, indicating mycelial growth inhibition. In addition, the time course of the fungicidal activity against P. oryzae, evaluated using double-fluorescent staining with fluorescein diacetate and propidium iodide, showed that most of the conidia were killed after 48 h of treatment with 40 ppm traversianal. In experiments with rice plants, blast lesion formation on rice leaves was significantly suppressed by pretreatment with traversianal. These results suggest the potential of traversianal as an inhibitory compound for the control of rice blast disease.