Effect of Leaf to Fruit Ratio on Fruit Quality and Shoot Development in `Carignane' and `Zinfandel' Wine Grapes

¹ Department of Viticulture and Enology, University of California, Davis.

I. `Carignane' shoots were girdled and defoliated to varying degrees. The most rapid coloration of fruit occurred on shoots with 16 or more leaves. The lowest amount of color at harvest occurred with shoots with 2 leaves. The lowest shoot weight was in girdled shoots with 4 leaves. The weight per cluster increased up to shoots with 12 leaves. Degrees Balling was sharply reduced by fewer number of leaves per shoot. Sixteen or more leaves per shoot produced high percentages of starch and total available carbohydrates in the shoots.

2. The experiment was repeated with `Zinfandel' with similar results. Shoot weight reached a maximum when there were 8 leaves, but weight per cluster reached a maximum when all leaves except those on lateral shoots were retained. Eight leaves produced a maximum size berry; but all leaves, including those on laterals, were needed to produce the highest degrees Bailing reading. The leaf area produced by lateral shoots was greater than that produced by the primary shoot.

3. An experiment with `Carignane' showed there is no significant difference in shoot weight, cluster weight, degrees Balling or percentage of acid whether leaves are located on the apical or basal part of the shoot. When shoot tips and lateral shoots were allowed to grow, the Balling reading was higher than where they were absent.

4. An experiment in which `Carignane' fruit was harvested at weekly intervals showed that, in general, color rose with degrees Balling.