Response of Trichoderma green mould disease agents in oyster mushroom to the essential oils from four medicinal plants

Abstract: Production of oyster mushrooms (Pleurotus ostreatus) is severely impacted by
various Trichoderma species, which cause green mould disease. Biopesticides based on
essential oils offer a potential alternative to synthetic pesticides for disease prevention in crop
protection. Four essential oils extracted from medicinal plants grown in Serbia, namely thyme (Thymus serpyllum), basil (Ocimum basilicum), yarrow (Achillea millefolium), and St. John’s wort (Hypericum perforatum), were assayed for their in vitro fungicidal properties against two Trichoderma species isolated from oyster mushroom substrate (Trichoderma pleuroti, strain KM11, and T. pleuroticola, strain KM12, 2018, North Macedonia). The oils were tested using the contact microdilution and the fumigant macrodilution method with either pathogen mycelial inoculum or spore suspension. The minimum fungicidal concentration (MFC), minimum inhibitory concentration (MIC), and percentage of mycelial growth inhibition (PGI) were determined. The thyme essential oil was lethal for both species when the contact microdilution method was used at 12.5 µl/ml (MFC), while no fungicidal effect of the remaining three oils was found at the selected concentrations (MFC > 25 µl/ml). Furthermore, no fungicidal effect of either oil was recorded on any tested pathogen using the fumigant method (MFC > 0.32 µl/ml of air phase). Three oils (thyme, basil, and yarrow) showed fungistatic contact activity against both Trichoderma species, while two oils (thyme and basil) showed fungistatic fumigant activity at various MIC values. The strongest contact activity on both species was shown by the thyme oil (МIC = 1.56 µl/ml), while the oils of basil and yarrow exhibited a slightly lower antifungal activity. The basil oil was found to demonstrate the strongest fumigant activity against both pathogens at various MIC values with PGI in a range from 50.73 to 100 %. The St. John’s wort oil stimulated mycelial growth of both species. These essential oils could be recommended for further in vitro and in vivo testing.