A preharvest treatment of ethephon and methyl jasmonate affects mechanical harvesting performance and composition of 'Verdejo' grapes and wines

Abstract

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 preharvest 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 oxidative 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 different shaking frequencies, 400 and 425 shakes min^-1). The preharvest treatment did not significantly affect product losses during mechanical harvesting at 400 shakes min^-1but, 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.