Kaan Kurtural,* Nazareth Torres, Runze Yu, and Johann Martinez
*University of California Davis, 1 Shields Avenue, Davis, CA, 95616 (skkurtural@ucdavis.edu)

In commercial winegrape production, canopy management practices are used to control the source-sink balance, and improve the cluster microclimate to enhance berry composition. The aim of this study was to identify the optimal ranges of berry solar radiation exposure (exposure) for upregulation of flavonoid biosynthesis and thresholds for their degradation, to evaluate how canopy management practices such as leaf removal, shoot thinning, and a combination of both affect the grapevine yield components, berry composition, and flavonoid profile. Three experiments were conducted in Oakville, CA. The first assessed changes in grape flavonoid content driven by four degrees of exposure. In the second, individual grape berries subjected to different exposures were collected from two cultivars (Cabernet Sauvignon and Petit Verdot). The third experiment examined three canopy management treatments i) LR (removal of five to six basal leaves), ii) ST (thinned to 24 shoots per vine) and iii) LRST (a combination of LR and ST) and an untreated control (UNT). Berry composi­tion, flavonoid content and profiles, and 3-isobutyl 2-methoxypyrazine were moni­tored during berry ripening. Although increasing canopy porosity through canopy management practices can be helpful for other purposes, this may not be the case of flavonoid compounds after a certain proportion of kaempferol is achieved. Results revealed different sensitivities to degradation within the flavonoid groups; flavo­nols were the only monitored group that was upregulated by solar radiation. Within different canopy management practices, the main effects were due to ST. Under environmental conditions in this trial, ST and LRST hastened fruit maturity; however, a clear improvement in flavonoid compounds (more anthocyanin) was not observed at harvest. Methoxypyrazine content decreased with canopy management practices studied. Although some berry traits were improved (2.5 Brix increase in berry total soluble solids) due to canopy management practices (ST), this resulted in a four-fold increase in labor operations cost, a two-fold decrease in yield, with a 10-fold increase in anthocyanin production cost per hectare that should be assessed together.

Funding Support: UC ANR