Date of Award

Fall 2025

Project Type

Thesis

Program or Major

Agricultural Sciences

Degree Name

Master of Science

First Advisor

Rebecca G Sideman

Second Advisor

Iago Hale

Third Advisor

Marta Lima

Abstract

Seedless table grape production in cool-climate regions like the Northeastern U.S. is limited by cold temperatures, short growing season, and relatively few adapted cultivars. American species (Vitis labrusca) or interspecific hybrids offer more disease and cold resistance as compared to European species (V. vinifera), however, small berry size, lower yields, and low fruit quality have been some of the limitations for these cultivars. This study evaluated the effects of gibberellic acid (GA3) and cluster thinning under different training systems to improve cluster and berry quality in seedless table grape cultivars. The first experiment focused on ‘Concord Seedless’, examining the effects of GA3 application timing and concentration on cluster quality and shot berry incidence in vines grown in two training systems: Vertical Shoot Positioning (VSP) and Munson (M). The second experiment evaluated cluster thinning intensity in ‘Mars’ and ‘Canadice’ under these two training systems. Trials were conducted across multiple seasons at the Woodman Horticultural Research Farm in Durham, NH. Our study showed that post-bloom GA3 application improved cluster weight and reduced shot berry frequency. In contrast, pre-bloom GA3 did not increase cluster weight but did increase frequency of thinned berries and percentage of clusters with stem curling. Pre-bloom GA3 treatments followed by a single post-bloom GA3 treatment also showed symptoms of berry thinning and stem curling. Vines grown using the Munson training system had higher cluster weight and lower frequency of shot berries as compared to VSP training system. In 2022, heavy cluster thinning reduced both total and marketable yield compared to light thinning and the control (no thinning) but resulted in higher total soluble solids (TSS). In 2024, heavy thinning only increased berry weight and TSS in ‘Mars’ when trained to a vertical shoot positioning (VSP) system. Overall, the Munson training system outperformed VSP in terms of total yield and marketable cluster weight in the same year. Based on these results, our study does not support heavy thinning for ‘Mars’ and ‘Canadice’, as the loss in marketable yield was not adequately offset by gains in berry or cluster quality. These findings highlight the importance of tailoring GA3 use and cluster thinning strategies to specific cultivars and training systems to improve fruit quality and productivity in cool-climate table grape production.

Download

Share

COinS