Validation of thermal indices for water status identification in grapevine

The use of thermal imaging represents a substantial progress in monitoring plant water status and therefore drought stress in field conditions. However, the effective use of thermal imaging requires consistent methods for data acquisition and image analysis. We determined the temperature variation of grapevine canopies by the use of thermal imaging in a proximal manner, and calculated stomatal conductance index (IG) and crop water stress index (CWSI), aiming to assess the plant water status that was measured as variations in stomatal conductance. The study was conducted in a hillside commercial vineyard with Graciano (Vitis vinifera L.) vines grown under two different water statuses. Leaf stomatal conductance was measured to determine plant water status and indices derived from individual grapevine leaves, clusters and canopies were assessed by thermal imaging. Measurements were carried out under different light conditions (sunlit and shaded part of the canopy) and at different times of the day (morning, midday and afternoon) to analyze the robustness and sensitivity of thermal imaging for detecting changes in a range of plant water status and experimental conditions.