Yield components and leaf/fruit ratio effects on quality in ‘Solaris’

Since 2000, Denmark has emerged as a commercial wine-producing country and with ongoing climate changes and especially the introduction of new early ripening cultivars like ‘Solaris’, the potential for a growing wine industry is on the rise. However, viticulture in the cool Scandinavian climate is still relatively nascent, leaving many questions surrounding optimal cultural practices unanswered. A particularly debated aspect is the optimal fruit/leaf ratio, crucial for striking the right balance between grape quality and the economic potential yield. To address this, manipulations of the leaf/fruit ratio and cropping levels were implemented through early and late cluster thinning, and/or shoot thinning in the ‘Solaris’ cultivar across four vineyards. The effects on yield components were investigated based on fruiting shoots collected prior to the regular harvest, encompassing measurements of shoot length, weight, leaf number, and leaf area. Additionally, the clusters on the collected shoots underwent examination for weight, number of berries, and berry size, followed by juice extraction. Utilizing Fourier-transform infrared spectroscopy (FTIR), juice analysis provided data on sugars, acids, pH, and yeast available nitrogen. Results indicated that early cluster thinning and shoot thinning did not significantly impact yield components, with outcomes varying across locations. Late cluster thinning, however, exhibited an increase in sugar concentration and a decrease in acid levels in the juice across most locations. The treatments, coupled with location differences, resulted in a substantial variation in the leaf/fruit ratio, ranging from a few cm² g^-1 to over 70 cm² g^-1. This variation unveiled a clear leaf/fruit response affecting fruit quality, as expressed by glucose and fructose content. The findings underscored ‘Solaris’ as capable of producing high-quality berries in the cool Danish climate, with an optimal yield/quality balance, at a leaf/fruit ratio of 15-20 cm² g^-1,.