Indices of light microclimate and canopy structure of grapevines determined by 3D digitising and image analysis, and their relationship to grape quality

A new method combining 3D digitising of plants in the field, creation of virtual pictures of the foliage canopy and spectral analysis of the resulting images was applied in a vineyard near Montpellier, France, to the canopies of grapevines (cv. Merlot, Vitis vinifera L.) trained on four trellis systems and separated into two vigour classes. Virtual images of the canopy were suitable for calculating viticultural indices which describe canopy structure as well as some attributes of the light microclimate. Values of the computed variables were in good agreement with the same variables obtained by traditional means and reported in the literature. Structure indices were correlated among themselves and with indices related to radiation variables. The data confirm that division of the canopy is the major distinguishing factor for canopy structure and light microclimate while shoot orientation is the main determinant for bunch exposure. Grape composition was related to both structure indices and indices related to radiation variables. Thus, sugar content was related to the amount of functional leaf area supplying the fruit and to the light environment of leaves. In contrast, titratable acidity and pH were not related to any of these variables. The concentration of anthocyanins and phenolics appeared to be related directly to leaf exposure to light and to interactions between light and temperature effects on bunches. The usefulness of using digitising and imaging is discussed.