Exogenous Sugar Effects on Fruit Quality in 'Petit Verdot' Grape Berry in Vitro

The test material in this experiment was the wine grape variety 'Petit Verdot' (Vitis vinifera L.cv. Petit Verdot). Sucrose, glucose, fructose, and rhamnose were selected for sugars, with mass fractions of 2%, 5% and 8%, respectively. The grape was sprayed with exogenous sugars and cultured in vitro for 12 days in a plant growth incubator. The rate of fruit color change was monitored and analyzed, and the primary quality indicators such as titratable acids, reducing sugars, anthocyanins and non-anthocyanin phenolics were examined extensively using principal component analysis. According to the results, under in vitro culture conditions, fructose, sucrose and rhamnose improved grape fruit quality significantly, while glucose had no obvious effect on grape fruit quality. In terms of improving the comprehensive quality of fruit, the best treatment effect was fructose, with 8% Fru ranking the first, 5%Fru ranking the second and 2% Fru ranking the ninth. The optimum concentration of 2% Suc ranked third overall, 8% Suc ranked fifth overall, and 5% Suc ranked eighth. Rhamnose optimal concentration of 5%, ranked in the fourth, 2% Rha ranked sixth, 8% Rha ranking behind in the control group, as the 12th. Glucose function was not obvious to improve the quality of the grapes, 2% Glu ranking in the seventh, higher than that of control group two, while both 5% and 8% Glu ranked lower than the control, at 13 and 11, respectively. According to the scores of principal component 1 and principal component 2, fructose significantly promoted the accumulation of anthocyanins and phenols (principal component 1), in which 5% Fru scored the highest, 8% Fru the second and 2% Fru the third. Sucrose significantly increased the content of soluble solids, reducing sugars and titratable acids (principal component 2), with 2% Suc scoring highest, 5% Suc second, and 8% Suc sixth. To sum up, different kinds of sugar into the skin cells may have different metabolic pathways and metabolites, the mechanisms of metabolism of different types of sugars in grape skin cells need to be further explored.