The extract of Hypoxylon spp. Sj18 kills the pinewood nematode through nematode-associated bacteria

Abstract

Pine wilt disease, caused by the pinewood nematode (PWN), is a highly contagious and serious coniferous tree disease worldwide, resulting in considerable economic and environmental losses. Chemical insecticides are effective, but they lead to drug resistance and environmental pollution, which makes them inadvisable for widespread use by spraying. The extract of Hypoxylon spp. Sj18 (a fungus genus) demonstrated strong nematicidal effects on PWN in the laboratory, resulting in more than 96% nematode mortality within eight hours. Effective nematicidal compounds A and B were separated from the water extract of the Sj18 dry powder by resin, activated carbon and Sephadex. A+B had no significant nematicidal effect in the presence of antibiotic or when used for aseptic PWN, suggesting that it works through PWN-associated bacteria. The nematicidal effect of A+B on different PWN-associated strains revealed that Serratia marcescens, was an important vector strain for killing PWN. Liquid chromatography–mass spectrometry and subsequent experiments revealed that the molecular formula of A was C₁₉H₄₄N₁₉O₁₂S₂ and contained peptide bond. In addition, B proved to be maltose.