Nutritional status of vines affected with esca proper

Abstract

A vineyard of the cv. Trebbiano d’Abruzzo located in Abruzzo, Italy,  was monitored for more than ten years to distinguish healthy vines not only from vines with the visual leaf symptoms of esca, but also from those vines that were esca-infected but did not produce any visual symptoms for one or more growing seasons. In the period 2004–2006, leaves and berries were collected at four phenological growth stages from three groups of vines: healthy vines, infected vines showing esca symptoms, and infected vines that did not show symptoms. The macro and micro-elements of the leaves and berries, and the quality parameters of the must were determined. Esca did not seem to affect nutrient uptake in the vines. Nevertheless there were some differences in the nutrient levels of the leaves between healthy and diseased vines consistent with the degradation of the leaf blade caused by esca. Berries from symptomatic vines were less ripe at the time of harvesting and therefore had higher levels of mineral elements. These berries also had higher levels of nitrogen, which are thought to be associated with the defence response of diseased vines to esca, as are higher levels of iron in the leaves of diseased vines. The study confirmed earlier findings that fruit composition did not differ greatly between healthy and diseased-but-asymptomatic vines. In the three-year study period there were differences in the incidence of leaf symptoms and differences in nutrient levels attributable to fertiliser applications and rainfall. These differences suggested that the amount of mineral nutrients affected the onset of esca symptoms: a higher availability of nutrients in a growing season increased the proportion of diseased vines with symptoms and lowered the proportion of diseased vines without symptoms, whereas in a growing season with the lower levels of  water and potassium, the yield was reduced, but this was accompanied by an increase in the proportion of diseased vines without symptoms. It is suggested that a higher availability of nutrients for diseased vines lowers the resistance of these vines and, by improving the nutrition not only of the vines themselves but also of the esca fungi, increase fungal virulence, as a result of which there is a greater incidence of diseased vines showing leaf symptoms.