First evaluations on the relationship between esca symptoms and trans-resveratrol in the leaf.

Abstract: The formation of foliar symptoms of esca in grapevine has not been clarified yet; probably, symptoms are associated with toxins released by vascular pathogens involved in the disease, and translocated to the leaf by the transpiration stream. Long term investigations recently conducted in Central Italy on two vineyards cv. "Trebbiano d'Abruzzo" infected with esca proper, showed significantly highest levels of trans-resveratrol in symptomatic leaves at the pre-bunch closure. Further investigations carried out on symptomatic leaves with different symptom severity revealed increasing levels of trans-resveratrol with the severity of symptoms on leaf. These results seem to show that trans-resveratrol is not able to stop the development of foliar symptoms. Moreover, cut leaves immersed with their petioles in Phaeomoniella chlamydospora cultural filtrates combined with progressive doses of trans-resveratrol did not reveal any visible effect of the stilbene. After pre-bunch physiological changes leading to berry maturation and carbohydrate accumulation occurred. In this period the leaf showed a drastic decrease of trans-resveratrol levels in symptomatic leaves, and low levels of the stilbene were noticed until veraison. Probably the strong decline of trans-resveratrol can be interpreted as a proof of a different response of the plant to the disease, in the time in which foliar symptoms spread up to harvest. Further studies are undergoing. [...]