The Effect of Annual and Bi-annual Pruning on the Seasonal Changes in Xylem Formation in the Grapevine

Growth-ring development and seasonal changes in starch content were examined in annually as well as bi-annually pruned grapevines. Cambium was generally found to be active (in its normal season) from the middle of April to the end of July, with the main period of activity being May to June. As a result of an additional pruning in August a second period of cambial activity began in the middle of September and lasted until the middle of November, with the main activity occurring in October. In the 'normal' early summer season cambial activity was found to expand from the canes in a basipetal direction, whereas in the late summer season it recommenced simultaneously in the trunks and canes. In vines that had been pruned twice in the preceding year the early summer xylem increment was smaller than in those which had been pruned only once and the total increment of two growth-rings per year was similar to that of the one growth-ring in the latter, once pruned, plants.