Modeling sugar accumulation dynamics of a wide variety of grape cultivars (Vitis vinifera L.)

Abstract

Context and purpose of the study – Climate change is a major challenge in wine production. The IPCC (2014) projected that by the end of the 21st century average temperatures will increase by 1-3.7°C. Consequently, harvest dates could advance by approximately 30 days. A general observed trend is the increase in berry sugar content and decrease in organic acids, posing challenges for winegrowers. Variability among cultivars is a precious resource to adapt viticulture to a changing environment.The aim of this study is to model and compare the sugar accumulation dynamics for a wide variety of Vitis Vinifera (L.) grape cultivars. Determining ripening dynamics with the help of a single mathematical function will allow for cultivar classification and provide a means of determining suitability of grape cultivars under conditions of climate change, or in potentially new wine producing regions.

Material and methods – Berry samples were collected from 50 different Vitis Vinifera (L.) cultivars at four replicate locations within a common-garden randomized complete block design at the ISVV from 2012-2018. Samples were collected weekly between mid-veraison and maturity, from which berry fresh weight, reducing sugar, and other parameters were measured. The integrative indicator of water status (∂13C) was measured at maturity for every cultivar. A 3-parameter logistic function was fitted for sugar accumulation expressed in both concentration (g/L) and content (mg/berry).

Results – A logistic model was parameterized to the sugar accumulation data from 50 grape cultivars and ripening traits were extracted. Analysis of variance revealed there was a strong cultivar effect on the rate of sugar accumulation, while there was a strong year effect on the total sugar concentration accumulated. The length of the ripening period showed to be dependent on both year and cultivar. This research aids in determining the suitability of grape cultivars under changing climate conditions or in newly projected viticultural areas. The coefficients extracted from the model allow for the testing of other hypotheses and research questions. One of the questions under investigation, is whether the rate of sugar accumulation is influenced by water deficit (∂13C) and climatic variables (temperature, PAR, etc.).