Collective term for antimicrobial chemical compounds, some of which have an oxidation-inhibiting effect, which are formed in plants as a defence reaction. The name is derived from phyto (plant) and alexin (defence). Host-specific phytoalexins can be present in principle, but are only produced in significant quantities by plants when they are attacked by harmful microorganisms such as bacteria and fungi, but also under stress conditions such as UV light or insect in festation. They then rapidly accumulate at the site of infection within a few hours. So far, more than 12,000 different species have been discovered. Phytoalexins that become active in the vine belong to a group of phenols called stilbenes. They are formed in the leaves and berry skins when they are attacked by various diseases such as downy or powdery mildew and botrytis. This slows down or inhibits the spread of the diseases.
Three common phytoalexins also found in grapes are catechin, resveratrol and viniferin. The concentration of these substances in wine depends on the grape variety, climate, cultivation method and vinification. In cool and humid regions, the risk of disease is greater and thus the need for defensive substances increases. As a rule, red wines contain ten times the amount of white wines, because the usual maceration process extracts many more of these substances from the skins and they end up in the wine. The phytoalexins contained in wine also have a positive, health effect. They are therefore used in chemotherapy against cancer and as a preventive against heart disease. In the context of plant protection, the targeted transfer of "foreign phytoalexins" to vines can increase resistance to various diseases. See also under tannins and vine enemies.
