Variations in the Levels of Individual Phenolic Compounds in Grapevine Latent Buds during Eco-Dormancy, Following Chemically-Induced Stress Conditions

Abstract

The goal of viticulture in Greece, where it is one of the country’s briskest economic activities, is satisfying grape yields. Nevertheless, owing to the ongoing climate change, that goal is impeded by a major obstacle in the form of an insufficient period of chilling temperatures which are becoming briefer. Consequently, the shorter period of cold leads to poor budbreak which, in turn, results in reduced yields. In order to meet the chilling requirements that several plants (including the grapevine) require for bud dormancy release, agronomists have resorted to treatments with chemical regulators. This study aimed at identifying and quantifying during eco-dormancy the individual phenolic compounds, together with their possible variations, in the latent buds of the ‘Prime©’ and ‘Ralli’ table grape cultivars. The study induced chemical stress by means of four different solutions, at three discrete dates per year, for three consecutive years. Phenolics were analyzed via HPLC. Their quantitative analysis showed variations both between the varieties and between the samples of those varieties. The analysis indicated that the phenolic content continued progressing during the annual growth cycle. Higher rates of increase in the phenolic content were observed in the first three days following each application, which implies an immediate stress response mechanism. Strong positive correlations were detected between several polyphenols. Luteolin, despite registering a positive correlation with quercetin, resveratrol, o-coumaric, did not do so with the remaining polyphenols. The results confirmed that chemically-induced stress conditions affect the phenolics content. Moreover, depending on the date of application, significant changes appear in the variations of those phenolics.