Differential influence of timing and duration of bunch bagging on volatile organic compounds in Cabernet Sauvignon berries (Vitis vinifera L.)

Background and Aims Bunch bagging is a grapevine canopy management strategy to protect bunches from light, heat stress and disease pressure. The aim of this study was to unveil the effects of timing and duration of bunch bagging on grape volatile organic compounds (VOCs) at the transcriptomic and metabolic levels. Methods and Results Seven bunch bagging treatments of varying timing and duration were implemented with Cabernet Sauvignon grapes. Regardless of timing and duration, bagging significantly reduced nerol, benzaldehyde, benzeneacetaldehyde and p-cymene, and increased the concentration of phenol and 3,5-dimethylbenzaldehyde. The decrease of nerol by bagging was associated with the down-regulation of the gene encoding glycosyltransferase14 at veraison. Bagging and re-exposing bunches at the preharvest stage inhibited and benefited the accumulation of C6 alcohols. Furthermore, we infer that the higher concentration of total benzenoids in all bagged berries was due to the down-regulated expression of phenylpropanoid biosynthesis genes. The concentration of the dominant norisoprenoid, beta-damascenone, was not impacted by bunch bagging from veraison to harvest and was increased by bagging from veraison to post-veraison. All other treatments, however, reduced this compound, which was due to a lower concentration of beta-carotene and lutein, and the down-regulation of VviCCD4a and VviCCD4b. Conclusions Both timing and duration of bunch bagging can affect biosynthesis and accumulation of VOCs. Significance of the Study Insights from this study provide new knowledge on bunch bagging, as well as information regarding the sensitivity of VOCs to light and the timing of light exposure during grape ripening.