Impact of Cluster-Thinning Timing and Severity on Winegrape Yield and Quality: A Meta-Analysis of 50 Years of Research
Josh VanderWeide,* Paolo Sabbatini, and Simone
D. Castellarin
*The University of British Columbia, 2205 East Mall,
Vancouver/British Columbia/V6T 1Z4, Canada (j.vanderweide@ubc.ca)
To attain high-quality fruit, winegrape producers utilize management practices to achieve a balance between vegetative and reproductive growth (leaf area-to-yield ratio [LAY]). A commonly used strategy to obtain a balanced ratio is cluster thinning (CT). This practice has been researched extensively over the past 50 years; however, no consensus has been established regarding the influence of CT timing and severity on fruit quality. The main objectives of this work were to understand whether CT timing (bloom [B], pea-size [PS], lag phase [LP], or veraison [V]) or severity (low [15 to 35%], moderate [36 to 55%] or high [56 to 75%]) influences vine performance and fruit quality. We surveyed 160 publications on CT in vinifera winegrapes and subsequently reduced this pool to 78 studies via 10 data curation steps. We reported the influence of CT timing and severity on production (vine yield, LAY, berry weight) and quality (total soluble solids [TSS], pH, titratable acidity, total anthocyanins, total phenolics) parameters. We also specifically evaluated whether CT timing or severity altered the tradeoff between the decrease in yield and the subsequent increase in TSS. Regardless of timing or severity, CT significantly enhanced the LAY, TSS, and pH, while reducing yield. CT timing showed little influence on quality parameters, although the tradeoff between yield reduction and the increase in TSS was slightly more efficient when applied later in the season (LP and V) than early (B and PS). Moreover, CT severity affected TSS; only the moderate range (36 to 55%) increased this parameter. Interestingly, cultivar greatly influenced the capacity of CT to increase fruit quality, while climate (growing degree days, precipitation) during the experimental season did not. Winegrape quality was more influenced by CT severity than timing. This work has important implications for grape producers and their approach to improving grape quality.
Funding Support: This work was financially supported by the NSERC Discovery program (AWD-000128 NSERC 2020).
