Grape phenol accumulation as related to cultural practices involving changes of light microclimate

Abstract

Light is known as an important factor influencing grape quality, especially its phenolic content that is essential for the organoleptic properties and the nutraceutical effect of this fruit. The present study focuses on some influences of the manipulation of canopy light quantity and quality on grape final attributes. Three experiments were carried out. The 1st experiment investigated the effects of the light environment, at cluster level, changed by the applying of the technique of leaf-removal on a renowned black-berry wine grape variety typical of Southern Italy (Negroamaro). The 2nd experiment investigated the influence of Yellow and Pink photoselective plastic films, compared to a Neutral one, on a black-berry table grape variety (Black Magic) grown under protected conditions to advance the grape ripening. In both these experiments, the changing of the grape skin anthocyanin profile was particularly analysed. The 3rd experiment aimed to assess the effects Yellow and Red photoselective hail-nets, compared to a Neutral one, on the chemical and physical characteristics of the grape produced by the principal Italian white-berry table grape variety (Italia). The 1st experiment compared four treatments (ND, MD, D50% and DA having respectively 0%, 32%, 50% and 63% defoliation intensities). The phenol concentration of Negroamaro grapes were adequately improved by a high illumination regime induced by the defoliation. The D50% grapes reached the highest sugar accumulation. This treatment, differently from the others, had leaf removal not concentrated in the bunch zone but distributed along the entire canopy, thus likely benefited from a better leaf illumination and higher leaf CO2 uptake per leaf area unit. The DA grapes, that were the most lighted, were the richest in skin anthocyanins, especially the methylated ones, and produced the wine richest in color, although its anthocyanin content did not differ from that of D50% wine. The color tonality of D50% wine was intermediate between that of DA and ND wine. The color tonality of MD wine was the worst, likely due to the lowest percentage of Delphinidin 3-O-glucoside and Malvidin 3-O-glucoside. The wine obtained by DA treatment, compared to the other ones, had the highest percentage of Delphinidin 3-O-glucoside that is known to give a blue nuance to the wine colour, improving its visual appreciation. In the 2nd experiment, Black Magic grape grown under neutral plastic film gave the best results. This behaviour favours the nutraceutical proprieties of the grape production. In photoselective thesis the main effects on grape quality seemed exerted by the PAR reduction, more than by the specific modification of light quality; the canopy trained to overhead “tendone” system filters and attenuates at a great extent the light available at bunch level. Between the photoselective films, the Pink one tended to induce a lower concentration of polyphenols; in the second year this gap increased and became statistically significant, likely due to the rapid opacification of this type of film. The anthocyanin profile showed a lower methylation in the grapes of the Yellow treatment. This is likely correlated to a higher reddish nuance and to a lower blue nuance found in the berry skin colour. On the other hand, the higher methylation level showed by the anthocyanins produced by the grape of the Pink treatment was likely correlated to a high green nuance of its skin colour respect to that of the grape of the yellow treatment, and to a high blue nuance compared to the grapes of both Yellow and Neutral treatments. Delphinidin, the precursor of blue/purple Petunidin and Malvidin derivatives was higher in the Neutral treatment and similar between Yellow and Pink thesis. In the present study, the difference in Delphinidin concentration seemed not reflected by the berry skin colour. The 3rd experiment showed that the photoselective nets did not improve the polyphenol content in the skins of Italia grapes. The coloured net treatments, especially the red one, gave grape with less total polyphenols, flavonoids and proanthocyanidins, although the differences of these latter did not rich the level of statistical significance. Light quality modifications