Background and Aims: Pre-veraison auxin treatments can delay grape berry ripening, but there is little information about their effects on berry development and wine composition. The aim of this study was to further investigate these effects and explore the practical implications of delaying ripening. Methods and Results: Treatment of pre-veraison Vitis vinifera L. cv. Shiraz berries with 1-naphthaleneacetic acid (NAA) significantly delayed ripening as measured by the accumulation of total soluble solids (TSS) and anthocyanins. The onset of the post-veraison phase of berry size increase was delayed in NAA-treated fruit, but these fruit were significantly larger than Control fruit at harvest. NAA-treatments significantly increased the synchronicity of berry sugar accumulation. GC-MS analysis of wine headspace volatiles showed significant, but largely small, differences in the concentration of 19 compounds. No significant difference in sensory properties was found between replicate small-scale wine lots made from Control and NAA-treated fruit. Conclusions: Auxin treatment delayed berry ripening, increased the synchronicity of sugar accumulation between berries, increased berry size and changed the levels of some volatile compounds, but did not affect wine sensory properties. Significance of the Study:We propose that NAA sprays might be used to delay grape berry ripening and increase the synchronicity of sugar accumulation, and therefore ripening, without deleterious effects on wine quality. This may be useful in controlling winery intake and fruit composition. AbbreviationsABA abscisic acid; BR brassinosteroid; BTOA benzothiazole-2-oxyacetic acid; dpis days post initial spray;GC-MS gas chromatography-mass spectrometry; IAA indole-3-acetic acid; NAA 1-naphthaleneacetic acid; RI retention index; SPME-GC-MS solid phase microextraction gas chromatography-mass spectrometry; TSS total soluble solids

Preveraison treatment of Shiraz berries with either 1-naphthaleneacetic acid (NAA) or Ethrel delayed the onset of ripening and harvest. NAA was more effective than Ethrel, delaying harvest by 23 days, compared to 6 days for Ethrel. Sensory analysis of wines from NAA-treated fruit showed significant differences in 10 attributes, including higher "pepper" flavor and aroma compared to those of the control wines. A nontargeted analysis of headspace volatiles revealed modest differences between wines made from control and NAA- or Ethrel-treated berries. However, the concentration of rotundone, the metabolite responsible for the pepper character, was below the level of detection by solid phase microextraction-gas chromatography-mass spectrometry in control wines, low in Ethrel wines (2 ng/L), and much higher in NAA wines (29 ng/L). Thus, NAA, and to a lesser extent Ethrel, treatment of grapes during the preveraison period can delay ripening and enhance rotundone concentrations in Shiraz fruit, thereby enhancing wine "peppery" attributes.

Abstract. Grape (Vitis vinifera L.) berries are considered to be nonclimacteric fruit as they do not exhibit a large rise in ethylene production or respiration rate at the onset of ripening (veraison). However, ethylene may still play a role in berry development and in ripening in particular. (2-Chloroethyl)phosphonic acid (CEPA), an ethylene-releasing reagent, delayed ripening when applied early in berry development. In agreement with a role for ethylene in controlling the timing of ripening, the application of an inhibitor of ethylene biosynthesis, aminoethoxyvinylglycine (AVG), advanced ripening, as did abscisic acid, when applied during the preveraison period. Applications of CEPA nearer to the time of veraison enhanced berry colouration. Changes in the expression of ethylene biosynthesis and receptor genes were observed throughout berry development. Transcript levels of some of these genes were increased by CEPA and decreased by AVG, suggesting changes in ethylene synthesis and perception during the preveraison period that might contribute to the biphasic response to CEPA (ethylene). The significant delay of ripening in field-grown grapes through the application of CEPA also indicates that this may be useful in controlling the timing of veraison, and therefore harvest date, in warmer climates.