Abstract
BackgroundBasal leaf removal is widely practiced to increase grape cluster sunlight exposure that controls berry rot and improves quality. Studies on its influence on volatile compounds in grape berries have been performed mostly in Mediterranean or marine climate regions. It is uncertain whether similar efficiency can be achieved when grape berries are grown under continental climate. This study aimed to dissect the variation in volatile compound production and transcriptome in sunlight-exposed grape berries in a dry-hot climate region and to propose the key genes related to the variation.ResultsFour cluster sunlight exposure strategies, including basal leaf removal at pepper-corn size stage, leaf removal at véraison (LR-V), leaf moving at véraison (LM-V), and half-leaf removal at véraison, were implemented at the north foot of the Mt. Tianshan region of northwestern China. Various cluster exposure treatments resulted in a decline in the concentrations of norisoprenoids and monoterpenes in ripening grape berries. Both β-carotene and lutein, the substrates of norisoprenoid biosynthesis, were reduced by cluster sunlight exposure. K-means cluster analysis showed that some genes involved in biosynthesis such as VviTPS55, VviTPS60, VviTPS66, VviCCD4a and VviCCD4b exhibited lower expression levels in exposed berries at least at one of the tested stages. Two C6-derived esters with fruity attributes, ethyl hexanoate and hexyl acetate, were reduced markedly. In contrast, main C6 alcohol compound levels were elevated in the LR-V- and LM-V-treated grape berries, which corresponded to the up-regulated expression of VviLOXA, VviLOXO and VviADH1 in the oxylipin pathway. Most of the differentially expressed genes in the exposed and control berries were enriched to the “stress response” processes, and this transcriptome difference was accumulated as the berries matured. Besides, LR-V treatment stimulated a significant up-regulation in photosynthesis-related genes in the grape berries, which did not happen with LM-V treatment.ConclusionsCluster sunlight exposure in dry-hot climate viticulture resulted in different volatile-targeted transcriptomic and metabolic responses from those obtained in the temperate Mediterranean or marine climate region. Therefore, a modified canopy management should be adopted to improve the aroma of grape berries.
Highlights
Basal leaf removal is widely practiced to increase grape cluster sunlight exposure that controls berry rot and improves quality
Our previous study has shown that leaf removal or leaf moving at véraison, which exposes grape clusters to sunlight until harvest, can markedly improve the accumulation of flavon-3-ols and reduce the concentrations of anthocyanins in grape berries grown on the north foot of the Mt
Four cluster sunlight exposure strategies including leaf removal at the pepper-corn size stage (LR-PS), leaf removal at véraison (LR-V), half-leaf removal at véraison (HLR-V), and leaf moving at véraison (LM-V)
Summary
Basal leaf removal is widely practiced to increase grape cluster sunlight exposure that controls berry rot and improves quality. Some canopy management practices such as leaf removal, cluster thinning, grapevine training, and leaf moving are widely used to optimize the canopy microclimate, allow varying sunlight exposure, control berry yield, and improve grape berry and wine quality [2]. Among these viticulture practices, leaf removal in a cluster zone ( called basal leaf removal) has been most commonly conducted, primarily because of its ability to promote sunlight exposure and airflow as well as to reduce foliage cover and disease incidence [3, 4]. The aim of the present study was to dissect the variation in volatile compound metabolome and transcriptome in these exposed grape berries in this dry-hot climate region
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