Noninvasive evaluation of the degree of ripeness in grape berries (Vitis vinifera L. cv. Bacchus and Silvaner) by chlorophyll fluorescence

The use of chlorophyll fluorescence measurements to noninvasively evaluate degrees of ripeness was investigated in berries at various stages of ripening from two white grapevine cultivars (Vitis vinifera L. Cv. Bacchus and Silvaner). Berries were characterized by diameter, weight, and density and by concentrations of fructose, glucose, sucrose, and total sugars, as well as fructose/glucose ratios, and also by chlorophyll fluorescence at F-O and F-M levels and the fluorescence ratio FV/FM. Pearson product moment correlation analysis on data from both cultivars revealed clear negative associations between F-O and concentrations of fructose, glucose, and total sugars, and fructose/glucose ratios (correlation coefficient < -0.89). Curvilinear trend-lines were established for plots of F-O versus concentrations of fructose, glucose, and total sugars, but a linear relationship between F-O and fructose/glucose ratios was found: the corresponding coefficients of determination were always > 0.82. Therefore, chlorophyll fluorescence measurements are well-suited to determine noninvasively sugar accumulation in grape berries during ripening.