[Optimising the shoot load of grapevine: trials on the Chasselas cultivar]
1996
Murisier, F. | Zufferey, V. (Station federale de recherches en production vegetale de Changins, Pully (Switzerland). Centre viticole du Caudoz)
A field trial on the shoot load of grapevine was performed from 1987 to 1995 with the cv. Chasselas trellised with the Guyot system (200 x 85 cm) at the experimental estate of the Swiss Federal Agricultural Research Station of Changins at Pully. Four levels of shoot load were compared (6, 8, 10, and 12 shoots per vine). Diminishing the number of shoots per vine resulted in a lowering of yield that is not proportional to the number of shoots left. A compensation phenomenon was observed at the level of bud fertility and bunch weight. Both increased when the number of shoots was lowered. The increase in fertility may be explained by the higher weight of individual shoots that were left when pruning. Reducing the number of shoots resulted in an increase of the mean weight of shoots. A better illumination of buds of vines with a low shoot load may also result in a better flower induction. The increase in sugar content of must resulting from a lowering of yield was less important than that observed in our trials of yield limitation by cutting grape bunches. A part of the sugars was probably used for shoot growth, which was stronger in plots with low shoot load. The total leaf surface was lower when the shoot load was low, but the foliar surface exposed to light remained practically unchanged. Under the conditions of this trial, it was not advantageous to leave more than 6 to 8 shoots per vine. With this load level, the vine foliage was already crowded. The relationship between the foliar surface exposed to light or the external surface of the canopy of leaves and the total weight of grapes provides an explanation for the variation of the sugar content of must
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