Berry composition and wine quality of Pinot noir as affected by leaf area to crop load ratio

Abstract

The effect of vine leaf area (LA) relative to crop load (CL) was investigated in the cool climate growing region of Canterbury, New Zealand, using Pinot noir (clone 10/5) Vertical Shoot Positioning (VSP) trained vines. Three weeks after fruit-set, vine leaf numbers were standardized with two of the four basal leaves retained in all cases. LA treatments were 12 leaves (1L), 6 leaves (0.5L) or 3 leaves (0.25L) per shoot. CL treatments were full crop (1C), half crop (0.5C) or quarter crop (0.25C) by removing equal numbers of primary and secondary clusters, producing five different treatment ratios (TMR), “0.25”, “0.5”, “1”, “2” and “4”. Treatments were applied in a 4-replicate split plot design. Grapes were harvested on April 4, 2014 and replicates 1 & 4 and 2 & 3 were combined to make two wines from each treatment. LA/CL (cm²/g) was estimated from a subsample of shoot leaf areas divided by total yield per vine after harvest. Starch dry weight in roots was not affected by crop load, but was decreased with leaf removal, while pruning weight was increased with increasing TMR, indicating that the fruiting capacity for next season could be reduced by limited leaf numbers. Juice °Brix was negatively, while juice pH was positively, related with increasing levels of leaf removal. Total red pigments, tannin concentration and total phenolics in skin extracts were decreased by greater leaf removal (p < 0.05, p < 0.01 and p < 0.05, respectively). Results suggest shading appeared not to be a limiting factor for the synthesis of phenolic compounds, or to have an impact on fruit composition in general (i.e. potassium, malic or tartaric acids). The concentration of total red pigments, tannin and total phenolics in wine were not significantly different between treatments, though some visual differences were observed using the CIELab method on native wine samples. HPLC analysis of wine showed that two procyanidins dimers, rutin, caffeic acid and caftaric acid were affected by crop removal only, while quercetin, quercetin-glucuronoide 1 and protocatechuic acid were affected by leaf removal only. Kaempferol-glucoside, p-hydroxybenzoic acid and p-coumaric acid were affected by both leaf removal and crop removal treatments. GCMS analysis showed the concentrations of fatty acids and some esters were higher when more leaves and more crop were retained, and that the concentrations of C6 alcohols were positively related with TMR. Some wine parameters showed the same patterns as that found for grapes, including pH, colour hue, degree of red pigment colouration, and kaempferol-glucoside concentration, along with the CIELab visual colour pattern. Thus, the fruit characteristics can be transferred into wine. It appears that the most appropriate LA/CL or TMR to produce quality wines were not the extreme values (e.g. the highest or lowest LA/CL, or TMR =“0.25” or “4”) based on the chemical analysis in this study. In fact, lower to medium levels of leaf and crop removal were desired, based on the concentrations of phenolics, volatile aroma compounds, carbohydrate in grapevine roots, along with other parameters measured in this project.