The effect of cluster thinning on phenolic maturity of Vitis vinifera cv. Xinomavro grapes

Abstract

Aims: The purpose of this study is to determine the effect of cluster thinning at veraison stage on berry phenolic maturity of the red Hellenic Vitis vinifera grape variety «Xinomavro » and more precisely on the anthocyanin content. It is noted that this variety is relatively poor in anthocyanins, but it has a high level of astringency.

Methods and results: This study was conducted in four experimental vine-plots within a vineyard located in the VQPRD area of Naoussa and more specifically at Giannakoxori Imathia (Northern Greece). Cluster removal was done manually on three vine-plots (the 4th one being the control) leaving one cluster per sprout (shoot). The sampling was started almost a month before grape-harvest and was repeated 2, 3 or 4 times during the ripening, depending on the vine-plot, with an interval of 3 to 7 days between each sampling. A total of 17 berry samples, coming from the vineyard mentioned above, were studied. The total phenols were assessed by UV spectrophotometry and the concentration of phenolic acids and catechin of seeds was determined by UV-HPLC.

Conclusions and significance of the study: The concentration of total anthocyanins during grape ripening in vine-plots that had been thinned out was increased compared to the control vine-plot. This increase varied from 52 to 89% for the study plots and 10% for the control plot. The skin tannin content was increased by 56.2 to 114% for plots that had been thinned out and only by 17.7% for the control plot. In contrary, the seed tannin content decreased during ripening by 27.2 to 50.6% compared to 23.5% for the control plot. As for phenolic acids and catechin in seeds, we conclude that catechin was the most abundant compound. Consequently, cluster thinning appeared to have contributed to the increase of the total phenolic content of the specific « Xinomavro » Greek variety and more precisely of the anthocyanins.