Starch and Sugar in Canes of Summer-PrunedVitis viniferaPlants

Abstract

Plants of Vitis vinifera, var. Chasselas Dore were summer-pruned at various times after harvest in order to secure a second, winter crop. Dry weight, starch content, reducing sugar and non-reducing sugar-content in canes of such treated plants were determined from July 1953 until February 1954. As controls, normally winter-pruned plants were used. Highest fertility was found in the latest-pruned plants, which also gave the largest yields. The earliest-pruned plants had the lowest fertility and gave the smallest crop. Dry weight in the controls was highest during September, and dropped some what during January and February. In the summer-pruned vines dry weight decreased immediately after pruning and rose again at the time of the termination of the induced growth-period. Starch-content in the controls increased strongly from the time of beginning of the experiments until November, decreased afterwards and rose again in January. Starch-content of all the treated vines, independently of time of summer pruning, followed mostly the trend of the starch-content of the controls, but differed from it by being at a minimum in November and by not rising in January. The trend in the reducing and non-reducing sugar-content is similar in the treated and non-treated plants. However, there is always a temporary decrease in sugar immediately after the pruning. In all the plants there was an increase in the reducing sugars in February and at the same time a decrease in the non-reducing sugar. No starch-sugar conversion could be found during the winter period.