Impact of some agronomic practices on grape skins anthocyanin content

Abstract

Wine colour is the first quality characteristic to be assessed, especially regarding red wines. Anthocyanins are very well known to be the main responsible compounds for red wine colour. Red cultivars can synthesize and accumulate anthocyanins in berry skin to express their colour. However, anthocyanin accumulation is often influenced by a series of factors, such as genetic regulation, phytohormones, environmental conditions and viticultural management. Therefore, it is mandatory to improve grape anthocyanic content, namely by viticulture practices preferably those that can contribute to maintain or increase the sustainability of the ecosystem. The aim of this work was to study how different agronomic practices (cover crops, irrigation and crop level), in a Mediterranean Portuguese vineyard with cv. Trincadeira, one of the most important cultivar in this region, influence the amount of anthocyanins in grapes and therefore affect the wine quality. The research was carried out in 2010 on a vineyard located at Évora, south of Portugal, in a 9 year-old grapevines. The trained system was a vertical shoot positioning with a pair of movable wires, being the vines spur-pruned on a bilateral Royat cordon system. The experimental design was a split-split-plot with 4 replications and three factors per replicate: two types of soil management between rows, three different irrigation management and two crop levels, in a total of 48 elemental plots. Each elemental plot had 4 adjacent rows with 12 vines each, and all the measurements were made in the two central rows. The two types of soil management studied between rows, already existing in the vineyard, were: Traditional Tillage (TT) (soil cultivation to a height of 15 cm, 3 times during spring) and Natural Cover Crops (NCC) with resident species. In both treatments a 0.8 m-wide herbicide strip was achieved beneath the vines allowing a width of the planter of about 1.7 m. The three different irrigation managements studied were: Standard – rainfed, Early Irrigation (EI) – weekly irrigation of 15.6 mm since three weeks before veraison until one week before harvesting, and Late Irrigation (LI) – 12 mm application per week since one week after veraison until two weeks before picking. At harvest, berries were randomly hand-picked and analyzed. Anthocyanins were determined by HPLC-DAD. In the edapho-climatic conditions of Alentejo, the irrigation affected berry weight, pH and titratable acidity and also induced significative differences in individual anthocyanins. Concerning soil management, natural cover crop seems to be a promising practice when comparing to traditional tillage, since grapes from NCC presented higher values of soluble solids and anthocyanins, besides being an advantageous technique for soil conservation, a real problem in our conditions. Diminishing crop level originated grapes with higher soluble solids, lower acidity, higher pH and higher content of individual anthocyanins.