Antifungal effect of fresh and stored olive mill wastewater and its ethyl acetate extract against plant pathogenic fungi

Olive mill wastewater (OMW) has serious environmental implications due to its high organic matter content, particularly its phenolic compounds. Using OMW in crop protection has been suggested as an environmentally friendly alternative to reduce the impact of chemical pesticides on human health and the environment. This study aimed to in- vestigate the antifungal activity of fresh and stored OMW, as well as its ethyl acetate extract, against several phytopatho- genic fungi: Syncephalastrum racemosum, Paramyrothecium roridum, Fusarium oxysporum, and Verticillium dahliae. OMW was stored at 25 °C and 45 °C for three months, and both fresh and stored OMW were used in non-sterile, sterile, and centrifuged conditions. Phenolic and flavonoid compounds were extracted and identified by high-performance liquid chromatography (HPLC) analysis. Results showed that fresh OMW and its derivative compounds significantly inhibited the studied fungi. In contrast, OMW storage, sterilization, and centrifugation increased the mycelium growth of the fungi, particularly S. racemosum, which demonstrated relative resistance to stored OMW and its ethyl acetate extract. During storage, some phenolic and flavonoid compounds disappeared (resorcinol and vanillic acid), while the concentration of others increased (gallic acid, chlorogenic acid, and quercetin). This work highlights the potential use of fresh OMW as a bio-agent to protect plants from fungal diseases.