Levels of trans-resveratrol in leaves of vines affected with "esca"

A survey was carried out on esca symptomatic vines, diseased asymptomatic vines and healthy vines in vineyards previously inspected for more than 15 years. The levels of trans-resveratrol were determined on leaves with different symptoms severity and on leaves of asymptomatic vines, and compared with what assessed on leaves from healthy plants, at three different phenological growth stages. Moreover, in the laboratory, leaves collected from healthy vines were immersed in cultural filtrates of Phaeomoniella chlamydospora (Pch) or in sterile liquid growth medium and then in a suspension of trans-resveratrol or distilled water to assess the possible effects. The levels of transresveratrol in symptomatic leaves were particularly high at pre-bunch closure but also at harvest, increasing with the severity of foliar symptoms. At veraison, a dramatic decrease in trans-resveratrol content was observed and no differences were noticed among the different leaf groups or subgroups. In the laboratory test trans-resveratrol did not show any kind of effect on cut leaves previously immersed in Pch filtrates compared to what was observed for distilled water. The response of the plant to foliar symptoms as trans-resveratrol production varied in different phenological stages probably in relation to specific physiological conditions occurring at these stages. The correlation between transresveratrol levels and severity of symptoms on the leaf surface noticed at pre-bunch closure and at harvest but not at veraison as well as the lack of effects on cut leaves allowed us to hypothesize that trans-resveratrol is not involved in the control of foliar symptoms. However, taking into account the current hypothesis on the origin of foliar symptoms, trans-resveratrol may be considered as an important factor to better understand the plant response to symptoms expression.