Characteristics of the Fruit Quality and Volatile Compounds of 'Cheongsoo' Grape by Treatment with Different Plant Growth Regulators

Wine grape is characterized by small berry-type fruits, which contain seeds and juicy pulp enclosed in thick skin. 'Cheongsoo', a Korean grape cultivar selected in 1995, is rich in flavor and used as both a wine and a table grape. The effects of growth regulator treatments including GA3 alone or in combination with thidiazuron (TDZ) or forchlorfenuron (FCF) have been studied in different Korean grape cultivars to select for traits such as seedless and firm fruits and to prevent berry shatter. However, growth regulators such as cytokines have been shown to delay the growth of grapes. Here, we assessed the effect of three growth regulators on 'Cheongsoo' grape through investigation of grape quality characteristics and the development of volatile flavor components. Three treatments of growth regulators, specifically 100ppm GA3 + 5ppm 1% TDZ, 100ppm GA3 + 5ppm 0.1% FCF and 100ppm GA3 alone, were applied at 14 days after full bloom while untreated grapes were used as control. Five quality characteristics of 'Cheongsoo' grape were investigated including the sugar, fatty acid and n-alkane contents, acidity and the degree of volatile compound production. Treatment with growth regulators resulted in greater average fruit weight of 6.30 - 6.48 g compared to the 4.49 g of untreated grapes. However, the sugar content of untreated grapes was 1°Brix higher (16.6 ± 0.55) than that of grapes treated with growth regulators. Similarly, the volatile compound and acid content of untreated grapes were elevated, with the latter being 0.67 ± 0.04% (w/v), which was 0.1% higher than grapes treated with growth regulators. The content of hexanal, (E)-2-hexenal, 4-hexen-1-ol, and (E)-2-hexen-1-ol derived from the C6 compounds and fatty acids were higher in grapes treated with growth regulators, also these compounds appeared abundant in immature fruits. The n-alkane content was more predominant in untreated grapes, mostly in the wax layers of grape skin, and it was degraded to fatty acids through various pathways. Collectively, treatment of Cheongsoo grape with growth regulators resulted in reduction of fruity volatile compounds that are essential for the production of good quality wine grapes.