Enhanced yield and fruit quality of redglobe grapevines by abscisic acid (ABA) and ethanol applications

Aims: Redglobe has become a popular table grape cultivar in Egypt. However, in warm climates the berries often fail to develop a full red color in addition to having lower total soluble solids (TSS) at harvest time. Here we evaluate the potential for enhancing the quality of Redglobe grapes with applications of abscisic acid (ABA) and ethanol under field conditions. Methods and results: Abscisic acid (300 mg/L) and/or ethanol (10% v/v) treatments were applied twice (10% and 75% of colored berries) for two seasons (2006 and 2007), and their effect on yield and fruit quality (TSS/acidity, anthocyanin content, firmness, and attachment force) was investigated. The application of ABA did not significantly affect yield when compared to the untreated control, whereas the ethanol treatment, alone or in combination with ABA, resulted in a significant yield increase. Total soluble solids and the ratio between TSS and acidity were increased by all treatments. The highest TSS/acidity ratio resulted from the ABA treatment due primarily to an 18% decrease in total acidity. In this regard, ABA was the most effective treatment. The total anthocyanin content in berry skins increased by approximately 48 and 38% with the ABA and ethanol treatments, respectively. Still, the highest anthocyanin content was obtained with the application of both ethanol and ABA (54% higher than in the untreated control). Berries that were treated with ethanol were markedly firmer and had higher attachment force than those of the other treatments. Conclusion: The results indicate that the combination of ABA and ethanol is more effective in improving the color of Redglobe grapes but may also increase production efficiency. However, the ethanol treatment alone was more effective in increasing yield and berry firmness and appears to be an alternative to ABA in improving fruit quality in general. Significance and impact of the study: The results obtained in this study will be useful to improve the fruit quality of Redglobe grapes in the field under warm conditions.