Aroma is an important quality trait of grapes and often the focus of consumers, viticulturists and grapevine breeders.  Kyoho is a hybrid between Vitis vinifera and Vitis labrusca with a strawberry-like scent, while 87-1 is an early-ripening mutant of Muscat hamburg, belonging to Vitis vinifera, with a rose scent.  In this study, we compared their aroma compositions and concentrations during berry development by headspace-SPME combined with gas chromatography-mass spectrometry (GC-MS), and analyzed the expression differences of enzyme-encoding genes in the LOX-HPL, MEP and MVA metabolic pathways by qRT-PCR.  Twelve esters were detected in Kyoho during the whole berry development and they were abundant after veraison, but no esters were detected in 87-1 berries.  Linalool was the dominant terpene among the 14 terpenes detected in 87-1 berries, while limited amounts of terpenes were detected in Kyoho berries.  qRT-PCR analysis indicated that the low expression of VvAAT might explain the low content of ester volatiles in 87-1 berries, and the low expression of coding genes in the MEP pathway, especially VvPNLinNer1, might be the reason for the low content of volatile terpenes in Kyoho berries.  The results from this work will promote our understanding of aroma metabolic mechanisms of grapes, and offer some suggestions for grape aromatic quality improvement.

This study investigated the influence of red, green, blue, and white paper bags on the free volatile compound development of Kyoho grape berries from green to harvest.  Seven functional groups of volatiles were identified during the development of Kyoho grape berries including esters, aldehydes, alcohols, terpenes, ketones, acids, and hydrocarbons.  Esters and aldehydes were abundant in Kyoho grape berries, mainly represented by ethyl acetate, ethyl butyrate, and (E)-2-hexenal.  They accumulated quickly after veraison and slightly decreased toward maturation.  Red, green, blue, and white paper bags promoted the accumulation of esters and inhibited the accumulation of aldehydes, also inhibited the accumulation of alcohols, tepenes, ketones, and acids.  Their effect from strong to weak was green, blue, red, and white paper bags.  The expression profiles of genes in the lipoxygenase-hydroperoxide lyase (LOX-HPL) pathway were also analyzed and the results indicated that the regulation of red, green, blue, and white paper bags on aldehydes, alcohols, and esters volatile aromas was at transcriptional level.  The results expanded our comprehension in grape aroma biosynthesis and berry bagging technique in table grape cultivation.