Berry temperature as affected by canopy structure/trellis system/pruning method in grapevine cv. Syrah

Abstract

The aim of the work was to evaluate the effect of different canopy structures, deriving from two trellis structures and three pruning methods, on berry internal temperature, juice composition and main skin phenol traits of cv Syrah grape. The work was done at the ARC Experiment Farm in Robertson, South Africa. The following treatments were compared: VSP (hand spur pruned cordon), mechanical pruning, and minimal pruning. For each treatment, on both row sides, four measurement clusters were installed, each consisting of 12 temperature sensors. Continuous berry temperatures were measured for three days during the maturation period, in the 2012 and 2013 vintage years. Temperature was recorded on either sun-exposed or shaded bunches. At harvest, berry weight, juice soluble solids and skin color intensity, tone and total phenolics were analyzed.

Pruning methods and canopy structures affected berry temperature, especially in exposed clusters. During the sunniest day hours, berries showed higher temperature than the ambient air, reaching the highest temperatures (+9 °C at 11:00) in the berries of mechanically pruned vines. Increasing berry temperatures enhanced juice total soluble solid concentration in grapes of VSP/spur pruned and of mechanically pruned vines, with a greater effect on the former. Increasing berry temperature enhanced total skin phenol concentration in grapes of VSP/spur pruned and of mechanically pruned vines until 29-30 °C; higher temperatures showed a negative effect. Berry temperature did not affect total soluble solid and total skin phenol concentration in grapes of minimally pruned vines.