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Leaf removal treatments were applied to Riesling during 1990 and 1991, and to Cabernet Franc and Optima in 1991. Clusters were sampled to examine the effect of berry exposure, berry contact, time of sampling, and cultivar on cuticular membrane formation and the occurrence of bunch rot (Botrytis cinerea Pers.:Fr.). Non-contact and contact cuticle proper and epicuticular wax berry samples were examined qualitatively using cryogenic scanning electron microscopy and quantitatively using enzymatic separation and chloroform extraction.

Exposed Riesling samples had 18.6% and 35.0% more epicuticular wax and cuticle proper respectively than shaded samples. Non-contact Riesling samples had 15.7% and 35% more epicuticular wax and cuticle proper than contact samples, and although significant, epicuticular wax and cuticle proper weights of Riesling increased by only 5.7% and 4.5% respectively, between veraison and harvest. Although exposed cuticular membrane samples from all 3 cultivars had more epicuticular wax and cuticle proper than shaded samples, large differences between cultivars were present. Clusters from the hand leaf removal (i.e. exposed) treatment of all 3 cultivars examined had significantly less bunch rot than clusters from the control (i.e. shaded). Cabernet Franc was the most tolerant end Optima the most susceptible of the 3 cultivars to bunch rot. Time of sampling and differences between years also influenced the occurrence of bunch rot for Riesling with less rot present at veraison compared to harvest and less rot present at the 1990 compared to the 1991 harvest. Exposure, cultivar and level of contact within the cluster are all important factors in the cuticular membrane formation process and contribute greatly to the overall susceptibility of a grape cultivar to bunch rot when grown in a temperate climate.

In order to gain an understanding of the capacity of severely shaded leaves to be productive in dense canopies, the effects of increased shading on morphology, dry-matter partitioning, and whole-plant net carbon exchange rate (NCER) were investigated on greenhouse-grown Vitis vinifera L. `Chardonnay' grapevines. Vines were subjected to whole-plant shading levels of 0%, 54%, 90%, and 99% of direct sun 3 weeks after potting. Data were collected 8 to 10 weeks after potting. Nonlinear regression was used to investigate the relationship of leaf morphological traits and organ dry weights to increased shading. Leaf size was maintained with increased shading to approximately the 90% shading level, while leaf fresh weight, volume, density, and thickness were immediately reduced with increased shading. Root dry weight was most affected by increased shading, and root to shoot ratio was reduced. When nonlinear regressions were produced for light response curves, light compensation point was reduced by approximately 49% by moderate shading, and 61% by severe shading. Shaded leaves approached the asymptote of the light response curve more quickly, and had reduced dark respiration rates, indicating that the morphological compensation responses by the vine allow shaded leaves to use available light more efficiently. However, the long-term ramifications of reduced root growth in the current year on vines with shaded leaves may be significant.