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 investigate the antifungal activity of fresh and stored OMW, as well as its ethyl acetate extract, against several phytopathogenic 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