Effect of sunlight exposure on berry composition and aromatic profile of Vitis vinifera L. cv. “Yellow Muscat”

Abstract

Muscat grape cultivars are known for the strong aromatic properties they confer to wines. However, the strength of the aroma depends on multiple variables including variety, environmental conditions during the growth season and cultural practices. The spatial distribution of leaves as well as bunch position may impact on the radiation load received by the berries. Since optimizing aromatic composition of Muscat varieties is of major importance in Northern Italy, the purpose of this investigation was to ascertain whether different training systems, affecting direct grape exposure to sunlight, may influence the varietal aromatic composition of the grapes. During two years with contrasting conditions, an investigation was carried out from veraison to harvest on the variety ‘yellow Muscat’ trained to ‘pergola veronese’ and ‘guyot’. Measurements aiming at defining bunch microclimate, pulp and bunch temperatures were conducted using weather stations as well as thermocouples inserted into the pulp of random berries. While average bunch temperatures in ‘guyot’ were only ~ 1 °C higher than in ‘pergola’ in both seasons, significant differences were observed in terms of bunch daily temperature range between the two training systems. In ‘guyot’, bunches experienced maximum temperatures 5-7 °C higher than in ‘pergola’, reaching a maximum of 46°C, i.e. 12°C above air temperature, in 2014 season. Significant differences in the aromatic profile of ‘yellow Muscat’ grapes were observed between the two training systems both in terms of total terpene compounds and their free- or bound-form levels. In particular, at grape maturity, the total concentration of aroma component was prevalent in ‘pergola’ in all categories. It is possible to state that cooler conditions benefitted the development of monoterpenes in the ,local study and their levels seemed to be affected by the training system but also highly influenced by seasonal meteorological conditions.