L. Uzquiza¹, R. González¹, M.R. González¹, M.W. Fidelibus² and P. Martín^1
1 Departamento de Producción Vegetal y Recursos Forestales, Universidad de Valladolid, Palencia, Spain
² Department of Viticulture and Enology, University of California, Davis, USA

SUMMARY Previously we showed that the combined application of ethephon and methyl jasmonate to grapes (Vitis vinifera L.) may decrease fruit detachment force and promote the formation of an abscission layer between the pedicels and berries, without causing pre-harvest yield losses or defoliation (Uzquiza et al., 2013). Theoretically, such effects could help minimize the physical damage to berries and the volume of must released during mechanical harvesting which could, in turn, reduce the opportunity for undesirable oxida-tive processes to occur before the product comes into the winery. The aim of this work was to study the effects of this treatment on mechanical harvesting performance, and on must and wine quality. The experiments were conducted in 2011 and 2013, in a ‘Verdejo’ vineyard located in ‘Rueda’ Appellation d’Origine area (North-Central Spain). In a completely randomized factorial design different treatments were compared, combining the application of abscission agents (ethephon 1,000 mg∙L-1 plus methyl jasmonate 8,960 mg∙L-1 sprayed on the clusters 10 days before harvesting, versus untreated controls), and type of harvest (manual picking and mechanical at differ-ent shaking frequencies, 400 and 425 shakes·min-1). The preharvest treat-ment did not significantly affect product losses during mechanical harvesting at 400 shakes·min-1 but, at 425 shakes·min-1, total losses in treated vines were 4.2% higher than in untreated. The percentage of free must in the harvested mass was lower in treated vines (20.6%) than in controls (23.2%) when shaking frequency was higher. The abscission agents tended to reduce potassium content in the must and increased hydroxycinnamic acid and total polyphenol contents, but they did not affect colour intensity or oxidative stability of wines. Keywords abscission, oxidation, plant growth regulators, polyphenol, Vitis vinifera L.

Significance of this study What is already known on this subject? The combined application of ethephon and methyl jasmonate to grapes some days before harvest may decrease fruit detachment force and promote the formation of dry stem scars in the abscission zone, without causing significant preharvest yield losses or defoliation. What are the new findings? For the first time, the effects of abscission agents on mechanical harvesting of grapes have been evaluated. Treatment of ethephon plus methyl jasmonate reduced the release of must, reduced potassium content in the product and increased total polyphenol content. What is the expected impact on horticulture? Preharvest treatments of ethephon plus methyl jasmonate could help to minimize the physical damage to mechanically harvested wine grapes and contribute to enhance the quality of musts and wines.

E-mail: pmartinp@pvs.uva.es  

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Received: 12 November 2014 | Revised: 4 February 2015 | Accepted: 7 February 2015 | Published: 17 June 2015 | Available online: 17 June 2015