Uncovering the effectiveness of vineyard techniques used to delay ripening through meta-analysis

Abstract

Context and purpose of the study – One of the most concerning trends associated with increasing heat and water stress is advanced ripening of grapes, which leads to harvesting fruit at higher sugar concentrations but lacking optimal phenolic (i.e. color and mouthfeel) and aromatic maturity. Mitigation techniques for this phenomenon have been studied for many years and practices to delay sugar accumulation have been identified, including antitranspirants, delayed pruning and late-source-limitation techniques. Evaluation of the efficacy of these vineyard practices has occurred across a wide range of environments, vintages, varieties and growing conditions. To assess the broader efficacy of these three vineyard practices, which are easy-to-implement and cost-effective, a meta-analytic approach was adopted using data retrieved from 43 original studies.

Material and methods – A systematic review of published studies on techniques to delay ripening was conducted searching several databases (Web of Science, Pub Med and Google Scholar). This initial database was further screened, and inclusion/exclusion criteria were applied, keeping only studies that met the prerequisites for meta-analysis. Effect size values were calculated as the difference between total soluble solids (TSS) in the control and treated groups to numerically express advanced ripening (negative effect size), delayed ripening (positive effect size) as well as the intensity of the delay. Standard errors were calculated for effect size values and used as a proxy for study accuracy. Forest plots were employed to calculate the average effect of each treatment and associated confidence intervals. Meta-regression models were built to identify relationships between effect size values and important viticultural parameters, including environmental and growing conditions.

Results – Data curation returned 242 effect size values for three practices proposed to delay ripening: antitranspirants (n = 102), delayed pruning (n = 45) and late source limitation (n = 56). Average effects for all treatments were significant, confirming the stability of treatment effects for the vineyard practices investigated. Factors impacting the effectiveness of the treatments were identified through meta-regression. For antitranspirants, the intensity of the delay was dependent on the active compound utilized as well as the timing of spraying. Late pruning was more effective when applied at later stages of apical bud development, and the ability to delay ripening adopting this approach was dependent on vine yield. Similarly, yield was an important parameter impacting the efficacy of late source limitation practices, which also resulted in larger delays when grapes were harvested at higher sugar concentrations. This study shows the usefulness of meta-analysis to demonstrate broader applicability of specific studies through a comprehensive, quantitative and fully data-driven analysis.