Identification of Rhizospheric Actinomycete Streptomyces lavendulae SPS-33 and the Inhibitory Effect of its Volatile Organic Compounds against Ceratocystis fimbriata in Postharvest Sweet Potato (Ipomoea batatas (L.) Lam.)

Black spot disease, which is caused by the pathogenic fungal <i>Ceratocystis fimbriata</i>, seriously affects the production of sweet potato and its quality during postharvest storage. In this study, the preliminary identification of the rhizosphere actinomycete strain SPS-33, and its antifungal activity of volatiles <i>in vitro</i> and <i>in</i> <i>vivo</i> was investigated. Based on morphological identification and phylogenetic analysis of the 16S rRNA gene sequence, strain SPS-33 was identified as <i>Streptomyces lavendulae.</i> Volatile organic compounds (VOCs) emitted by SPS-33 inhibited mycelial growth and sporulation of <i>C. fimbriata</i> <i>in vitro</i> and also induced a series of observable hyphae morphological changes. In an <i>in vivo</i> pathogenicity assay, exposure to SPS-33 significantly decreased the lesion diameter and water loss rate in sweet potato tuberous roots (TRs) inoculated with <i>C. fimbriata</i>. It increased the antioxidant enzymes' activities of peroxidase, catalase, and superoxide dismutase as well as decreased malondialdehyde and increased total soluble sugar. In the VOC profile of SPS-33 detected by a headspace solid-phase micro extraction (HS-SPME) and gas chromatography-mass spectrometry (GC-MS), heptadecane, tetradecane, and 3-methyl-1-butanol were the most abundant compounds. 2-Methyl-1-butanol, 3-methyl-1-butanol, pyridine, and phenylethyl alcohol showed strong antifungal effects against <i>C. fimbriata</i>. These findings suggest that VOCs from <i>S. lavendulae</i> SPS-33 have the potential for pathogen <i>C. fimbriata</i> control in sweet potato postharvest storage by fumigant action.