Background and Aims Grapevine bunch compactness is an important trait with impact on fruit quality, mainly affecting the susceptibility to bunch rot. Many and different variables have been reported to have a significant influence on the variation of bunch compactness in particular cultivars, but little is known about the role of such variables in a wider framework. The aim of this work was to identify and weight the features responsible for the natural variation in bunch compactness in a large and diverse grapevine collection. Methods and Results Different statistical tests were sequentially applied to select the determining variables most influencing bunch compactness. Significant and low correlation was obtained for most of the variables studied for three consecutive seasons, confirming the multifactorial nature of this trait. Multivariate analyses indicated that there are three groups of variables with a significant influence on bunch compactness. Two groups, represented by the total number of berries per bunch and by the length of the first ramification of the bunch, are major factors responsible for the trait variation, whereas berry dimensions have a secondary role. Conclusions Bunch compactness is defined by the difference between its morphological (apparent) volume and its actual (solid) volume. The results showed that the actual volume is mainly determined by the total number of berries, whereas the morphological volume also depends on its spatial arrangement, determined by the architecture of the rachis. Significance of the Study This is the first multiyear study of bunch compactness at a multicultivar level, and it has allowed the selection and weighting of the main variables affecting the trait. These variables are suitable targets to study the underlying genetics of the trait.

BackgroundTemperature and solar radiation influence Vitis vinifera L. berry ripening. Both environmental conditions fluctuate cyclically on a daily period basis and the strength of this fluctuation affects grape ripening too. Additionally, a molecular circadian clock regulates daily cyclic expression in a large proportion of the plant transcriptome modulating multiple developmental processes in diverse plant organs and developmental phases. Circadian cycling of fruit transcriptomes has not been characterized in detail despite their putative relevance in the final composition of the fruit. Thus, in this study, gene expression throughout 24 h periods in pre-ripe berries of Tempranillo and Verdejo grapevine cultivars was followed to determine whether different ripening transcriptional programs are activated during certain times of day in different grape tissues and genotypes.ResultsMicroarray analyses identified oscillatory transcriptional profiles following circadian variations in the photocycle and the thermocycle. A higher number of expression oscillating transcripts were detected in samples carrying exocarp tissue including biotic stress-responsive transcripts activated around dawn. Thermotolerance-like responses and regulation of circadian clock-related genes were observed in all studied samples. Indeed, homologs of core clock genes were identified in the grapevine genome and, among them, VvREVEILLE1 (VvRVE1), showed a consistent circadian expression rhythm in every grape berry tissue analysed. Light signalling components and terpenoid biosynthetic transcripts were specifically induced during the daytime in Verdejo, a cultivar bearing white-skinned and aromatic berries, whereas transcripts involved in phenylpropanoid biosynthesis were more prominently regulated in Tempranillo, a cultivar bearing black-skinned berries.ConclusionsThe transcriptome of ripening fruits varies in response to daily environmental changes, which might partially be under the control of circadian clock components. Certain cultivar and berry tissue features could rely on specific circadian oscillatory expression profiles. These findings may help to a better understanding of the progress of berry ripening in short term time scales.