Within-Vineyard, Within-Vine, and Within-Bunch Variability of the Rotundone Concentration in Berries of Vitis vinifera L. cv. Shiraz.

This study characterizes the environmental factors driving rotundone concentrations in grape berries by quantifying rotundone variability and correlating it with viticultural parameters. Dissection of the vineyard into distinct zones (on the basis of vigor, electrical soil conductivity, and slope), vine into orientations to sun (shaded/unshaded), and grape bunches into sectors (upper and lower and front and back) shows the influence of vine vigor, sunlight, and temperature. Occurrence of the highest rotundone concentration was observed in shaded bunch sectors and vines and from higher vigor vines in the southern-facing areas of the vineyard. The highest concentration of rotundone is consistently found at the top and in shaded sectors of bunches, and this correlates to lower grape surface temperatures. Modeling showed that berry temperature exceeding 25 °C negatively affects the rotundone concentration in Shiraz. Both natural and artificial shading modulated the grape surface and air temperature at the bunch zone and increased the rotundone concentration, without affecting other grape berry quality parameters. Thus, temperature and possibly sunlight interception are the main determinants of rotundone in grape berries. Vineyard topography, vine vigor, vine row, and grape bunch orientation influence the level of berry shading and can, therefore, adjust bunch surface and zone temperatures and influence the berry rotundone concentration.