Enhancing fruit quality of cold-hardy interspecific table grapes through gibberellic acid applications

Abstract

The University of Minnesota has been breeding interspecific grapes for cold-climate production over the past 125 years. Recent efforts in table grape breeding have resulted in three new cold-hardy table grape cultivars that exhibit excellent fruit quality characteristics, such as seedlessness, flavor, and texture. However, their berry size is relatively small compared to commercial table grapes. Gibberellic acid (GA) is a plant growth regulator that can enhance fruit quality, such as increasing berry size and berry firmness. GAis typically applied pre- and/or post-bloom, and its efficacy varies based on dosage, timing, and cultivar. While extensively tested on Vitis vinifera cultivars, GAhas never been evaluated on interspecific grapes. Our aim was to evaluate the effects of GAtreatment in the vineyard on fruit quality of three new cultivars and three commercial cultivars. Clusters were treated at flowering and berry set (5mm) with 0, 25, or 50 ppm GA in two growing seasons. Results showed that all six cultivars exhibited significantly larger berry diameter and weight at 50 ppm. Asimilar trend was observed at 25 ppm, but statistical significance varied by cultivar and season. GAtreatment generally reduced berry count per cluster, but cluster weight remained unchanged. These results demonstrate that GA application is an effective strategy to enhance berry size in cold-hardy interspecific table grapes.