Application of bioactive plant substances from olive tissues and grapes pomace in non-chemical disease control

Grape pomace as by-product is approximately 20% of the harvested grapes and it is a very rich source of bioactive polyphenolic compounds, especially stilbenoids, phenolic acids and flavonoids. These polyphenols have been shown to exert beneficial effects for human health, and also linked to several functions in plants, such as defense against invading phytopathogens. In a similar manner, phenolic compounds in Olea europaea tissues possess pharmacological properties and are considered natural antioxidants, thus inhibiting the Gram-positive microorganisms involved in olive fruit fermentation. Oleuropein, the main phenolic compound present in O. europaea fruits and leaves (up to 14% of the dry weight in unripe olives), and its aglycon, obtained from oleuropein by hydrolysis, are well-known pharmacologically active molecules with potential applications as antimicrobial agents in some fairly common olive tree diseases. Moreover, oleuropein (derived from olive tissues) and its derivatives (derived from olive mills waste waters) have a variety of biochemical roles, including anti-inflammatory and antithrombotic activities. Our aim is to exploit these natural antioxidants by using them as phytoprotective agents against various known economically important pathogens in Greece. Our current findings show high antimicrobial activity of oleuropein against phytopathogenic bacteria. We have determined the minimum inhibitory concentration (MIC) of those compounds against various economically important pathogens such as Gram-positive or Gram-negative bacteria. They have also been shown to inhibit or delay the rate of radial growth of some plant-pathogenic fungi. The antimicrobial activity of these substances of variable purity extracts has been tested in vivo against various commercial varieties of vegetables, fruits and flowers. The results have been compared with those obtained from commercially approved phytoprotectants of organic agriculture.

Acknowledgements: This work is funded by a research grant PEP-Crete (KR-19, co-financed by the E.U.-European Regional Development Fund, the Regional Authority of Crete and the Greek Ministry of Development-General Secretariat Research & Technology).