Influence of Crop Load and Cluster Microclimate on Yield and Fruit Quality in `Seyval Blanc'

Abstract

A 2-year field study was initiated in 1994 to examine the interactions between crop load and cluster exposure and their influences on the yield and fruit quality of mature, own-rooted `Seyval blanc' grapevines. Light, moderate, and heavy crop loads were established near bloom by cluster-thinning vines planted at 2.6 × 3.0-m spacing to around 20, 40, and 80 clusters per vine, respectively. At veraison, three clusters per vine were given one of three natural shaded treatments: fully exposed, partially shaded, and densely shaded. Vines with the heavy crop load produced higher yields per vine and lower cluster and berry weights. Heavy vine clusters tended to be more green in 1994 and possessed lower pH and soluble solid concentrations in both years compared to other crop loads. Compared to densely shaded clusters, fully exposed clusters had smaller average cluster and berry weights, lower titratable acidity, higher pH and soluble solid concentrations, and more yellow coloration. In 1994, no significant interactions were found for any fruit quality or yield characteristics. In 1995, significant interactions were found for soluble solids and hue angle, but not for yield, pH, or titratable acidity. These results suggest that the crop load of the vine and microclimate around the cluster, in addition to their individual effects, sometimes interact to affect fruit quality in `Seyval blanc' wine grapes.