Advancement of grape maturity – comparison between contrasting varieties and regions

Abstract

Context and purpose of the study – Grapevine phenology has advanced across many regions, nationally and internationally, in recent decades under the influence of increasing temperatures, resulting in earlier vintages (Jones and Davis, 2000, Petrie and Sadras, 2008, Tomasi et al., 2011, Webb et al., 2011. Earlier vintages have several ramifications for the wine industry. There are direct implications on quality, due to the fruit ripening during the hotter conditions of summer and early autumn, which then impacts grape composition and wine style (Sadras et al., 2013, Buttrose et al., 1971, Mira de Ordũna, 2010). There are also indirect implications where the fruit is perceived to ripen at a faster rate and the crop reach optimum maturity over a shorter period (Coulter et al., 2016). This can result in the grapes being harvested according to the winery processing schedule rather than when they are optimally ripe. This study aims to advance our understanding of the response of different varieties and regions to warming temperatures.

Materials and Methods – This research utilized an historical data set, covering 18 years, multiple varieties and four separate vineyard sites located in different climatic zones in Victoria, Australia. The data were analysed using mixed models to understand differences in the day of year maturity changes between varieties and vineyard sites.

Results – The data analysis suggested that the rate of advancement of day of maturity as a function of seasonal Growing Degree Days (September to March) varies significantly between varieties with some varieties being quite resistant to the temperature increases being experienced. There is some evidence that later ripening varieties are advancing their day of year maturity at a more rapid rate than earlier ripening varieties which helps to explain the vintage compression being observed in Australia. While yield had a significant association with the day of year maturity for some varieties, this was found to be an additional effect and not at the expense of the response to temperature indices. An understanding of how different varieties are responding to changing climates will assist in future planting decisions and determine how to best adapt to climate change. It will also demonstrate the degree of genetic variation available in modern grape varieties in response to changing vineyard climates, which varieties are the most resilient and how they may best be managed.