2018 ASHS Annual Conference

The increase in day time temperatures, particularly the intermittent heat spikes during engustment, is negatively affecting the biosynthesis, retention, and degradation of flavonoids content and organic acids in grapevine berry. There is lack of information on how to mitigate radiative damages and degradation that may occur under these conditions. A field experiment was conducted with Cabernet Sauvignon/110R in Oakville, CA using one meter, black, polyethylene shade nets of 40% light transmissivity, to determine the effects of partial solar radiation exclusion and applied water amounts on productivity, primary and secondary metabolites of grapevine berry flavonoid profiles. One netting treatment, of 40% Black net (Black-40), and one untreated control, with no nets, were applied shortly after fruit-set at Eichhorn-Lorenz stage 29 and retained until harvest. Two applied water amounts of 0.65 crop evapotranspiration (0.65 ET_c, Control) and 1.3 ET_c, were applied. At harvest, there was no effect of treatments applied on juice pH or titratable acidity. However, individual berry mass was greater in controls than shade net treatments. Diurnal cluster temperature shifts were recorded on both sides of the canopy. During peak daytime temperatures, cluster temperatures were 3.9°C greater in plants without the Black-40 applied to the canopy; although no effect was attributed to applied water amounts. Cluster damage attributed to solar radiation exposure was quantified. Although yield was unchanged, damaged cluster count and mass were significantly greater in treatments without shade netting applied. Anthocyanins and flavonols of berry skins were measured using C18 revered-phase HPLC. At harvest, treatments without shade nets had greater flavonol content, but a lower tri/dihydroxylation ratio than Black-40 treatments. However, anthocyanin content was greatest in Black-40 berries. Our results provide evidence that, regardless of applied water amounts in a vineyard, shade netting may alleviate the stresses that excessive solar radiation exposure puts on grape berry. It may do so without greatly affecting yield at harvest, and instead mitigates the amount of visible radiation damage on the fruit itself.