Fumigant activity of volatiles of Streptomyces globisporus JK-1 against Penicillium italicum on Citrus microcarpa

Antifungal activity against Penicillium italicum of volatile substances from Streptomyces globisporus JK-1 grown on autoclaved wheat seed was studied in vitro and in planta. Fungal spore germination and mycelial growth of P. italicum cultures as well as sporulation and disease incidence on fungal-inoculated fruit were suppressed in the presence of the volatiles. For naturally infected fruit, disease incidence was reduced from 25% to 7.5%. Suppression of the infection process of P. italicum on Shatang Mandarin fruit (Citrus microcarpa) was observed via scanning electronic microscopy, showing inhibited spore germination on the Shatang Mandarin, and abnormal morphology for conidiophores and hyphae exposed to the volatiles. Based on gas chromatography/mass spectrophotometric analyses, 41 volatile organic compounds were identified from the volatiles of S. globisporus JK-1, and the most abundant compound was trans-1,10-dimethyl-trans-9-decalol (geosmin), an earthy smelling substance. Among these, technical grade formulations of eight were chosen for further study: phenylethyl alcohol, caryophyllene, dimethyl disulfide, dimethyl trisulfide, acetophenone, d-limonene, isoledene, and aromadendrene. d-Limonene, isoledene and aromadendrene showed no observable antifungal activity in vitro and in planta at tested concentrations. Both phenylethyl alcohol and caryophyllene showed weak inhibitory activity in vitro but no significant efficacy against P. italicum on Shatang Mandarin. Dimethyl disulfide or dimethyl trisulfide showed antifungal activity in vitro and efficacious control on Shatang Mandarin at a concentration of 100 μL L−1 of airspace in treatment containers. Acetophenone showed antifungal activity in vitro at a concentration of 100 μL L−1and efficacious control on Shatang Mandarin at the highest concentration of 1000 μL L−1. Volatiles from S. globisporus JK-1 have potential for control of blue mold of citrus species through fumigant action.