Utility of leaf removal timing and irrigation amounts on grape berry flavonoids under climate change

Abstract

Context and purpose of the study – The dormant and growing season temperatures in California USA have been increasing with more clear sky days. A consequence increasing temperatures and clear sky days is water deficit conditions. Viticulturists must determine appropriate balances of canopy management and irrigation budgeting to produce suitable yields without compromising berry chemistry. In response, a study designed to test the interactive effects of leaf removal timing and applied water amounts on Cabernet Sauvignon/110R in Napa Valley, CA.

Material and methods – We performed a field experiment with 7‐year‐old Cabernet Sauvignon grafted on 110R (Vitis berlandieri × Vitis rupestris) rootstock. A factorial design with leaf removal timing (pre‐ bloom and post‐fruit set, compared to an untreated control) and applied water amounts (1.0, 0.5 and 0.25 of crop evapotranspiration replacement (ETc)) was used. We measured plant water status, leaf gas exchange, primary and secondary metabolites in response to treatments.

Results – Stem water potential was lower in the 0.25 ETc regardless of leaf removal treatments. A 40% reduction in net carbon assimilation was evident in the 0.25 ETc treatments, as well. Likewise stomatal conductance was lower with 0.25 ETc. Leaf removal timing did not affect leaf gas exchanges. There was no effect of leaf removal on components of yield, including the number of berries set. The 0.25 ETc treatment reduced berry mass and yield, but 0.5 and 1.0 ETc treatments were not different from each other. Stem water potential integrals were well related to speed of total soluble solids accumulation. There was a significant interaction of leaf removal and irrigation on pruning weight and Ravaz Index. Reducing the irrigation resulted in a significant increase of anthocyanin concentration; however, there was no increase in its biosynthesis. The ratio of 3’4’5‐OH to 3’4’‐OH anthocyanins was greater with 0.25 and 0.50 ETc compared to 1.0 ETc. Leaf removal affected flavonol content, specifically kaempferol‐3‐o‐ glucoside concentration well as its content a per berry basis which was greater with leaf removal regardless of its timing. Berry skin proanthocyanidins in either concentration or content, or mean degree of polymerization were not affected by treatments applied. Clear skies and longer periods with minimal precipitation paired with reduction in irrigation had a stronger influence on berry chemistry than leaf removal application. Our results indicated that cluster microclimate without leaf removal was already optimized within the confines of this study. Although not as impactful, there still appears to be potential for understanding leaf removal influence on berry physiology and its effect on vine balance in premium regions.