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Background and Aims: As grapegrowers move to adapt to climate change, they need more detailed information on what cultivars to plant and where to plant them. The aims of this study were to understand how different cultivars in different regions are responding to changes in climate, in order to inform future cultivar selections. Methods and Results: Trends in the day of year maturity (DOYM) between 1999 and 2018 were analysed for 23 grape cultivars (covering at least 7 years) and four Victorian vineyard regions against vintage year, seasonal growing degree day (GDD Sep-Mar ) and Spring Index. In most cases there were significant trends in DOYM advancement as a function of GDD Sep-Mar and spring index. Temporal advancement of DOYM was more variable. One cultivar showed a significant advancement at two of three sites and another showed a significant delay. Different cultivars advanced DOYM at significantly different rates at a given site, later ripening cultivars advanced DOYM faster than earlier ripening cultivars and for a cultivar grown across several sites, the DOYM advancement was faster at cooler sites. Conclusions: Grapevine cultivars respond to warming temperature differently and the advancement of grape maturity is predicted to slow as temperature further increases. Significance of the Study: The study showed diversity in the phenological response of cultivars to temperature, which may be utilised to better adapt to climate change.

Background and Aims The major phenological events, such as harvest, are critical periods in the wine business calendar requiring much planning and organisation of resources, yet anticipation of the timing of these events is still imprecise. The aims of this study were to better understand why grape maturity (defined here as the day of the year the grapes reached 11.5 Bé) is advancing, and how different cultivars and regions are responding to the seasonal temperature conditions. Methods and Results Trends in rate of ripening (Bé/day or Bé/°C day) and the day of year veraison (DOYV) were analysed at four Victorian vineyard regions and included 24 cultivars covering 20 years. There was a significant difference between cultivars in their rate of ripening with later ripening cultivars ripening more slowly (Bé/day). Higher yield slowed the rate of ripening (Bé/day), significantly at two vineyards. No significant temporal trends were observed for the rate of ripening nor for the interval between DOYV and day of year maturity (DOYM), as related to Vintage Year or Springtime Temperature (max), although these may become apparent with a longer series of data and resulting smaller confidence intervals. Different cultivars, however, had a significantly different rate of change for this interval over time, and higher yield was associated with a longer interval length. Day of year veraison advanced significantly as related to Springtime Temperature (max) at all vineyards, and at a significantly different rate for different cultivars at three of the four vineyards. There was a positive association between yield and DOYV. Conclusions These results suggest that the observed advancement of grape maturity can be explained by the advancement of veraison, rather than an increase in the rate of ripening, for these cultivars in these regions. Significance of the Study The study showed that there is existing cultivar diversity which, if better understood, could help better anticipate phenological timing, improve vineyard management and assist in adapting to climate change.

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The variability of grapevine phenological stages under climate change has been studied in many winegrowing regions, with many reporting an advancement of the major phenological stages, particularly flowering, veraison and harvest. This study aimed to compare these regional patterns to integrate our understanding of grapevine responses. Average daily January–March (JFM) mean temperatures were correlated with day of year budburst (DBUD) and average daily springtime March–May (MAM) maximum temperatures were correlated with day of year flowering (DFLO), day of year veraison (DVER) and day of year harvest (DHAR) for 17 vineyards and showed an advancement of the associated phenological stage with increased temperature for each index. There were significant differences between vineyard groups for the rate of advancement of DBUD, DVER and DHAR which suggests that the response of phenological stage to temperature is not linear and varies between cultivars. Only the interval between DBUD and DFLO showed a significant shortening as related to MAMMax, suggesting that the advancement of grape maturity as related to increasing springtime maximum temperature is largely due to the shortening of the DBUD to DFLO interval.