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 fungalCeratocystis fimbriata, 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 volatilesin vitroandin vivowas investigated. Based on morphological identification and phylogenetic analysis of the 16S rRNA gene sequence, strain SPS-33 was identified asStreptomyces lavendulae.Volatile organic compounds (VOCs) emitted by SPS-33 inhibited mycelial growth and sporulation ofC. fimbriatain vitroand also induced a series of observable hyphae morphological changes. In anin vivopathogenicity assay, exposure to SPS-33 significantly decreased the lesion diameter and water loss rate in sweet potato tuberous roots (TRs) inoculated withC. fimbriata. 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 againstC. fimbriata. These findings suggest that VOCs fromS. lavendulaeSPS-33 have the potential for pathogenC. fimbriatacontrol in sweet potato postharvest storage by fumigant action.Keywords:Ipomoea batatas(L.) Lam.;Streptomyces lavendulae;volatile organic compound;fumigant;antimicrobial