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Anti-oomycete activity of polyphenols from bay laurel leaves extracts

Oomycetes from the genus Phytophthora are plant pathogens that cause enormous economic and environmental damage. Extracts of various plants are considered promising and environmentally – friendly alternative to synthetic fungicides and are increasingly tested as anti-oomycete agents. Thus, we have tested the anti-Phytophthora activity of Bay Laurel (Laurus nobilis L.) leaves extracts, using two Phytophthora species with wide host range as models - P. plurivora and P. cactorum. Bay Laurel (Laurus nobilis L.) is a valuable medicinal plant from Lauraceae family, which has been widely used as spice and flavouring agent. Furthermore, due to the numerous bioactive compounds, essential oils and plant extracts show a wide range of biological activities such as antimicrobial, preservative, antioxidant and antifungal properties. The aim of this research was to determine the yields of total phenols extracted from the Bay Laurel leafs using different solvents and to test the anti—oomycete potential of phenolic compounds. In order to investigate the effect of different solvents on the extraction efficiency of polyphenols, ethanol (ethanol-water), acetone (acetone-water), methanol (methanol-water), ethanol-acetone-methanol (ethanol-acetone-methanol-water) and water were used. Mass fraction of total phenols of Bay Laurel leaves varied considerably as function of solvent nature and ranged from 18.4 to 59.9 mg GAE/g dry leaves, for pure acetone and methanol-water extracts, respectively. The highest mass fraction of polyphenols was obtained by using methanol-water. These results clearly demonstrate the influence of the solvent on the extractability of phenolic compounds, and water addition to the solvent improved the total phenols extraction for ethanol, methanol and acetone. Thus, binary solvent system containing hydro-organic solvents was superior to mono-component solvent systems regarding the extraction of total phenols. Next, the prepared plant extracts were tested for anti-Phytophthora activity using the modified well diffusion method. Results, expressed as inhibition of oomycete radial growth, have showed that both organic and hydro-organic solvent extracts of Bay Laurel leaves exhibited high contents of polyphenols and good anti–Phytophtora activity. In conclusion, L. nobilis extracts contain bioactive natural substances and may be considered as promising anti-oomycete agents in the future.

Bay Laurel, Laurus nobilis L., polyphenols, Oomycetes, Phytophtora

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