Identification of antifungal compound isolated from Cercospora sp. ME202 and evaluation of its inhibitory activity against Colletotrichum orbiculare

Cucumber anthracnose, caused by Colletotrichum orbiculare, is controlled using fungicides, but the fungus can develop resistance. We previously showed that an ethyl acetate extract of the culture filtrate of Cercospora sp. ME202 (ME202-ECF) has fungicidal activity and inhibits the formation of anthracnose lesions caused by C. orbiculare, but we did not identity the antimicrobial compound(s) or analyze the potential to suppress disease progression. Here, we isolated and identified antifungal compounds produced by Cercospora sp. ME202 and evaluated their antifungal activity against C. orbiculare. We purified he active compound using column chromatography and high-performance liquid chromatography, identified it as traversianal, a tricyclic diterpenoid aldehyde with a molecular weight of 316.4 from ME202-ECF, then determined its structure using liquid chromatography-mass spectrometry with electrospray ionization and nuclear magnetic resonance spectroscopy. In a thin layer chromatography bioassay at Rf 0.92, the isolated traversianal inhibited mycelial growth. Traversianal also inhibited conidial germination of C. orbiculare at 2-10 ppm and had fungicidal activity against conidia at 5-10 ppm after 24 h treatment. Pretreatment of cucumber leaves with 10, 20, or 30 ppm traversianal significantly suppressed lesion formation by C. orbiculare without phytotoxicity. Thus, traversianal produced by Cercospora sp. ME202 has potential as a new fungicide against C. orbiculare.