Effect of foliar applications on the qualitative and quantitative characters of cv. Assyrtiko and cv. Mavrotragano in the island of Santorini, under vineyard conditions

Abstract

The Mediterranean basin is regarded as one of the world’s most affected regions by climate changes. Traditionally, viticulture in this region has been coping with high temperatures, heat waves and drought. Such particularly extreme conditions, which induce severe abiotic stress on plants, are expected to intensify due to the predicted climate changes in the future. Santorini Island seems not to be an exception. The increase of temperature and solar radiation, in combination with the low availability of water, made necessary the development and the application of methods in order to cope with the abiotic stresses of the grapevine. This study examined the foliar applications and their effect on the qualitative and quantitative characteristics of the grapes by spraying application of the two indigenous varieties of the vineyard of Santorini (Greece), Assyrtiko, and Mavrotragano. The experiment took place in the cultivation season 2019-2020. Specifically, treatments with kaolin and calcium carbonate, two inert materials capable of reflecting radiation were evaluated. In the case of Assyrtiko, the effect of kaolin and calcium carbonate was examined on two different training systems, on the traditional training system of Santorini ‘kouloura’, and on a single Guyot training system. In the case of Mavrotragano, the effect of kaolin and calcium carbonate was examined on the vines which are trained in double Guyot training system. Mechanical analyses of the grapes and berries were performed, as well as measurements of the characters of the must during the stage of technological maturity. The content of the phenolic compounds was determined in the skins and seeds and the antioxidant capacity of the samples was measured by using different methods, FRAP and DPPH, by the use of spectrophotometry. At the same time, the analysis of High-Pressure Liquid Chromatography (HPLC) indicated the concentrations of the main individual sugars and acids in the must as well as the measurements of the skin individual anthocyanins for cv Mavrotragano. The results of the treatments showed that the analyses related to weight, length, and width of the grapes and berries and the measurements of pH and total titratable acidity for both training systems and both varieties did not seem to be affected. Also, compared to grapes from control treatments, the levels of most phenolic compounds and anthocyanins of the sprayed samples mostly increased, and as a result, this leads to grapes of better quality, thus better wine quality, since most measurements conducted in the current experiment are also directly correlated with the organoleptic properties of the wine. Therefore, the use of kaolin and calcium carbonate through foliar applications constitutes an important means of adaptation of the vines which are grown under conditions of drought, in terms of economic and environmental sustainability reasons, while improving the quality of grapes.