Antifungal Activities of Volatile Secondary Metabolites of Four Diaporthe Strains Isolated from Catharanthus roseus

Abstract

Four endophytic fungi were isolated from the medicinal plant, <i>Catharanthus roseus</i>, and were identified as <i>Diaporthe</i> spp. with partial translation elongation factor 1-alpha (<i>TEF1</i>), beta-tubulin (<i>TUB</i>), histone H3 (<i>HIS</i>), calmodulin (<i>CAL</i>) genes, and rDNA internal transcribed spacer (ITS) region (<i>TEF1</i>-<i>TUB</i>-<i>HIS</i>--<i>CAL</i>-ITS) multigene phylogeny suggested for species delimitation in the <i>Diaporthe</i> genus. Each fungus produces a unique mixture of volatile organic compounds (VOCs) with an abundant mixture of terpenoids analyzed by headspace solid-phase microextraction (SPME) fiber-GC/MS. These tentatively-detected terpenes included α-muurolene, β-phellandrene, γ-terpinene, and α-thujene, as well as other minor terpenoids, including caryophyllene, patchoulene, cedrene, 2-carene, and thujone. The volatile metabolites of each isolate showed antifungal properties against a wide range of plant pathogenic test fungi and oomycetes, including <i>Alternaria alternata</i>, <i>Botrytis cinerea</i>, <i>Colletotrichum gloeosporioides</i>, <i>Fusarium graminearum</i>, and <i>Phytophthora cinnamomi.</i> The growth inhibition of the pathogens varied between 10% and 60% within 72 h of exposure. To our knowledge, the endophytic <i>Diaporthe</i>-like strains are first reported from <i>Catharanthus roseus</i>. VOCs produced by each strain of the endophytic <i>Diaporthe</i> fungi were unique components with dominant monoterpenes comparing to known <i>Diaporthe</i> fungal VOCs. A discussion is presented on the inhibitive bioactivities of secondary metabolites among endophytic <i>Diaporthe</i> fungi and this medicinal plant.