Johann Martínez-Lüscher,* Marshall Alexander Pierce, Luca Brillante, and Sahap Kaan Kurtural
*University of California, Davis, Oakville Experimental Vineyard, 1380 Oakville Grade, Oakville, CA 94562 (jdmar@ucdavis.edu)

Canopy management and fruit load control seek to maintain a balance between a vine’s sources and sinks. In fact, balanced vines may produce more consistent yields and ripen more evenly. This study aims to study the relationship between source–sink ratios and important parameters for production logistics and grape quality, such as progress of ripening and grape composition at harvest. After homogenizing all vines (Vitis vinifera cv. Cabernet Sauvignon) by removing laterals and adjusting the number of shoots to 20, we tested three levels of canopy density and fruit load combined in a factorial design (3 by 3). Three canopy levels with 100, 66, or 33% of the leaves were combined with three fruit loads, 100, 66, or 33% of the fruit, corresponding to 30, 20, or 10 clusters per vine, respectively. Carbon fixation rates were transiently higher in plants with 33% of the canopy mediated by higher chlorophyll content, although this did not compensate for their smaller leaf area. The onset of ripening was sequentially delayed in 66% and 33% canopy treatments. The progress of ripening, accumulation of soluble solids, and loss of acidity (increase in pH and decrease in total acidity), was also slower in 66% and 33% canopy treatments than in vines with 100% of the canopy. The time to reach commercial maturity (>25 Brix) was delayed six weeks for the 33% canopy level. Surprisingly, fruit load did not have a significant effect on the progress of ripening. When comparing all treatments at commercial maturity, the treatment maintaining 100% of the canopy had the highest total acidity and lowest pH. The anthocyanin content was slightly lower in this treatment. These results provide a basis to control the speed of ripening, aiming to coalesce variability within a vineyard or optimize the tank capacity through sequential ripening.

Funding Support: Oakville Experimental Vineyard