Christopher Chen, Johann Martinez-Luscher, and Kaan Kurtural* 
*University of California Davis, 595 Hilgard Lane, Davis, CA 95616 (skkurtural@ucdavis.edu)

Interactive effects of selective cluster shading and water deficits on proanthocyanidin content and composition of Cabernet Sauvignon grapes grown in Oakville, CA, were investigated, aiming to mitigate the deleterious effects of solar overexposure. The experiment used three colors of shade nets with an untreated control and two applied water amounts arranged factorially in a split-plot design with four five-vine replicates. The three colors of shade nets (black, aluminet, and pearl) were placed onto the canopy on both sides (1000 mm) adjacent to the fruiting zone at fruit set. Two water deficits were applied starting at fruit set: a sustained deficit irrigation treatment (SDI) received 65% of estimated crop evapotranspiration (ETc) and regulated deficit irrigation (RDI) received 25, 65, and 65% ETc at fruit-set to veraison, veraison to harvest, and harvest to leaf fall, respectively. Primary metabolism (net carbon exchange, transpiration, stomatal conductance, intrinsic water use efficiency, mid-day leaf water potential, components of yield) was assessed every 21 days and secondary metabolism (berry skin and seed proanthcyoanidins) were assessed six times starting at 4 Brix. Proanthocyanidins were characterized by acid-catalysis in the presence of excess phloroglu-cinol, followed by reversed-phase HPLC. Water deficits resulted in transient stress on the grapevines that received RDI between fruit set and veraison. Net carbon exchange, stomatal conductance, and intrinsic water use efficiency were not affected consistently. Although berry mass showed a significant increase with shade nets, water deficits did not affect it. Aluminet had the least yield than the other treatments. Mean degree of polymerization (mDP) of skin proanthocyanidins was not affected, but seed tissue mDP of black and red nets under SDI and blue nets under RDI decreased significantly. The results indicate that colored shade nets may negatively impact yield and, in combination with SDI or RDI, tactile sensation through decreased mDP in seeds.

Funding Support: HP Olmo Research Funds