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Increasing the source/sink ratio in Vitis vinifera (cv Sangiovese) induces extensive transcriptome reprogramming and modifies berry ripening

BackgroundCluster thinning is an agronomic practice in which a proportion of berry clusters are removed from the vine to increase the source/sink ratio and improve the quality of the remaining berries. Until now no transcriptomic data have been reported describing the mechanisms that underlie the agronomic and biochemical effects of thinning.ResultsWe profiled the transcriptome of Vitis vinifera cv. Sangiovese berries before and after thinning at veraison using a genome-wide microarray representing all grapevine genes listed in the latest V1 gene prediction. Thinning increased the source/sink ratio from 0.6 to 1.2 m2 leaf area per kg of berries and boosted the sugar and anthocyanin content at harvest. Extensive transcriptome remodeling was observed in thinned vines 2 weeks after thinning and at ripening. This included the enhanced modulation of genes that are normally regulated during berry development and the induction of a large set of genes that are not usually expressed.ConclusionCluster thinning has a profound effect on several important cellular processes and metabolic pathways including carbohydrate metabolism and the synthesis and transport of secondary products. The integrated agronomic, biochemical and transcriptomic data revealed that the positive impact of cluster thinning on final berry composition reflects a much more complex outcome than simply enhancing the normal ripening process.

The Semi-Minimal-Pruned Hedge: A Novel Mechanized Grapevine Training System

A novel grapevine training system, semi-minimal-pruned hedge (SMPH), designed for mechanized pruning and harvesting was established on Sangiovese. The system was derived from adult spur-pruned cordon (SPC) vines that were modified to form a mechanically pruned hedge. SMPH heights of 80 cm and 120 cm were compared to SPC from 2005 to 2008, with an average of 332 and 479 buds per meter of row on SMPH 80 and 120, respectively, compared to 18 count nodes per meter of row on the hand-pruned SPC. The hedged vines had a larger leaf area, greater leaf area/crop ratio, and 35 to 40% yield increase compared to SPC, but there were no differences in juice soluble solids, pH, and acidity across the treatments. Berry skin anthocyanins were higher in hedged vines, notably the SMPH 120. The SMPH had more numerous but less compact and smaller clusters free of botrytis compared to SPC. While SMPH 120 showed a tendency to alternate bearing, this effect was minimal in SMPH 80. Single-shoot growth measured in 2006 was lower in SMPH vines, and total seasonal canopy light interception was higher compared to SPC vines. SMPH single-leaf assimilation was similar to SPC vines. Mechanical harvesting of both SMPH treatments was successful. These findings suggest that the two SMPH systems warrant further commercial evaluation because of their positive response to mechanization, grape yield, and quality and low susceptibility to bunch rot.

The Effectiveness of Basal Shoot Mechanical Leaf Removal at the Onset of Bloom to Control Crop on cv. Sangiovese (V. vinifera L.): Report on a Three-year Trial

Vine basal shoot leaves are known to be the primary nutritional source for fruit set at the onset of bloom. The effectiveness of mechanical removal of this foliage at that date was tested from 2012 to 2014 to control the cropping of high-yielding cv. Sangiovese in a “Toscana rosso” TGI (Typical Geographic Indication) district in Tuscany, where the yield threshold is 16 t/ha. A tractor-mounted leaf remover featuring sideby- side rotary suction and feed rollers was employed along a 50 cm basal area of cropping shoots at the beginning of bloom; control was the usual manual thinning of clusters carried out at veraison in the same vineyard. Mechanical leaf removal eliminated about 30% of leaf area and some shoots and inflorescences, thus reducing cropping potential and even resulting in a physiological effect, as the resulting clusters were composed of lower numbers of berries and were less compact and less susceptible to mould than the control. By harvest, the defoliated vines showed higher leaf area, most likely because leaf removal at the onset of bloom may have triggered compensatory new growth, and their grapes had a higher content of soluble solids than the thinned control. While both treatments kept the yield below the 16 t/ha threshold – leaf removal at an estimated 15.1 t/ha and manual cluster thinning at 15.6 t/ha – mechanical defoliation notably reduced yearly labour input: an estimated 4 h/ha against the 38 h/ha from thinning.

DIFFERENTIAL EXPRESSION OF GENES IN BERRIES OF CV. 'SANGIOVESE' (VITIS VINIFERA L.) DURING RIPENING FOLLOWING CLUSTER THINNING AT VÉRAISON

Cluster thinning is considered a technique, which, through an increase in the source-sink ratio, could lead to improvements in grape berry sugar and anthocyanin concentration. In this research, agronomical, biochemical and molecular approaches were combined to understand the ripening mechanisms leading to a final berry composition in ?Sangiovese? vines submitted to thinning (CT, 50% of total clusters removed at veraison). The yield reduction in CT vines implied a significant increase in leaf area/crop weight ratio, which caused acceleration in berry ripening rate immediately after the treatment and higher values of soluble sugars at harvest compared to control vines (C). Anthocyanin accumulation was strongly and positively affected by the thinning and it increased in parallel with soluble sugar content, reaching higher values than C at harvest. Microarray analyses, carried out with a NimbleGen array assembled on the basis of the 12X Vitis vinifera genome sequence, allowed for discrimination between CT and C at the end of veraison (13.8% of 29,550 genes analyzed were differentially expressed between CT and C at this stage). Genes involved in carbohydrate metabolism and flavonoid accumulation were analyzed in more detail. As a result, the CT transcriptional profile was characterized by an increase in expression of putative sugar storage genes, which usually follow carbohydrate utilization as an energy source. The increase of source/sink ratio positively influenced anthocyanin structural and transcriptional regulatory genes and especially those involved in anthocyanin transport, which were strongly up-regulated in CT compared to C. The results of this research confirm the key role of the source/sink ratio in conditioning sugar metabolism and reveals that carbohydrate availability is a crucial issue in triggering the expression of genes involved in anthocyanin biosynthesis during ripening under field conditions.