Trans-resveratrol and leaf symptom expression in Esca of grapevine

Esca of grapevine is a serious disease which in some aspects is still lacking full understanding, including the nature of foliar symptoms. Leaves collected at different phenological growth stage from esca symptomatic grapevines cv. Trebbiano d'Abruzzo showed the presence of higher concentrations of trans-resveratrol, the major stilbene produced in grapevine, compared to leaves from healthy plants. The increased levels of trans-resveratrol were supposed to be associated with the host-plant defence response, thought it also raises new questions on a possible role of the stilbene in the foliar symptom development. In 2009, symptomatic leaves were collected from the above mentioned grapevines and were divided into 4 classes calculating symptom severity as the percentage of chlorosis and necrosis on the total leaf area. For each class, leaves were collected at pre-bunch closure, post-veraison and harvest, and the level of trans-resveratrol was determined. The results showed higher concentrations of trans-resveratrol in symptomatic leaves collected at pre-bunch closure compared to what observed at the other growth stages. These results are in agreement with our previous findings and the stronger response of leaves might be correlated with the leaf functioning at the different phenological growth stages; moreover, the increasing of concentrations of trans-resveratrol with the increasing of the severity of leaf symptoms seems to exclude an involvement of the stilbene in the formation of symptoms. Further investigations on cut leaves inoculated with pathogen culture filtrates and/or trans-resveratrol may lead to a better understanding of the relationship between the stilbene and the foliar symptom expression.[...]