Potential of combined ethephon and methyl jasmonate treatments for improving mechanical harvesting of wine grapes.

Abstract

Abscission agents could reduce the damage to grapes and the volume of juice released during mechanical harvesting, avoiding undesirable oxidation and fermentation processes before the winemaking begins. Plant growth regulators such as ethephon or methyl jasmonate have been shown to be effective separately to reduce fruit detachment force (FDF) in different grapevine cultivars, however, additive and interaction effects of both products in combined treatments have not been evaluated yet. The objective of this study was to evaluate the potential use of ethephon and methyl jasmonate, separately or in combination, as abscission agents to improve the quality of machine-harvested 'Verdejo' wine grapes. The experiments were conductedin 2009, 2010 and 2011, using a fully crossed factorial design where mature clusters of 'Verdejo' grapevineswere sprayed with different solutions containing methyljasmonate (0, 10, 20 or 40 mmol L-1) and ethephon (0 or 1000 mg L-1). FDF and stem end condition of the berries were monitored for a maximum of 8 days after the applications. Ethephon reduced FDF 4 days after treatment in all growing seasons, maintaining valuesbelow those of controls until harvest. Methyl jasmonatehad less effect than ethephon and declined FDF from 6-8 days after the sprayings. An additive effect was detected in the analysis of variance, which makes the combination of ethephon and methyl jasmonate moreeffective than either agent alone. The lowest FDFvalues just before harvest corresponded to cotreated plants, with reductions up to 45% relative to untreated controls. Moreover, combined treatments significantly increased the percentage of detached berries presenting dry stem scars up to 8 days after the application, reaching accumulated values up to 60% in 2011. Both abscission agents little affected must composition parameters, and did not produce adverse effects as preharvest fruit drop or defoliation. These results demonstrate that combined treatments with ethephon and methyl jasmonate are potentially useful to improve quality of mechanically harvested 'Verdejo' grapes. Additional research is needed to provide the exact concentrations of abscission agents required for consistent fruit loosening in practical applications, and to establish the optimal harvester settings in treated vineyards at different growing sites.