In this project, researchers wanted to understand how different grapevine cultivars respond to a changing climate, in different areas. This study specifically considered maturity, vintage and temperature indices.
- Day of year maturity (DOYM) was used in this study – this is the date at which grapes reach a certain designated sugar level. The purpose was to exclude factors such as picking date being affected by changing wine styles over the years or harvesting due to logistical reasons.
- Four regions in Victoria, Australia, across a range of climatic zones were selected for the study.
- 23 different cultivars, all in commercial vineyards were considered.
- Trends in the DOYM between 1999 and 2018 (covering at least seven years) were analysed against vintage and two temperature indices namely seasonal growing degree day (GDDSep–Mar) and Spring Index.
- The role of yield on the timing of DOYM was investigated to further advance previous studies.
- In all cultivars, in all vineyards DOYM advanced as temperature indices increased. In most cases, the advancement was significant.
- There was more variation with temporal advancement of DOYM. One cultivar showed a significant advancement at two of three sites and another showed a significant delay. Six of the ten delayed DOYM trends were seen at the warmest vineyard.
- Generally, as yield increased, the DOYM was later. Despite this, the effect of the primary covariates of interest (Vintage Year, GDDSep–Mar or Spring Index) was maintained when controlling for yield.
- Later ripening cultivars advanced their DOYM more rapidly than earlier ripening cultivars.
- Different cultivars advanced DOYM at significantly different rates in the same vineyard.
- For a cultivar grown at several sites, the DOYM advancement was more rapid at cooler sites. This could be because at warmer sites, temperatures probably reach a point where optimal photosynthesis cannot occur.
Significance of the study
With a warming climate, harvests have become more compressed. This often means that grapes have to be harvested for logistical reasons, rather than at optimum ripeness. Knowledge gained from this study highlighted that different cultivars respond to a changing climate in different ways. As temperatures increase, maturity is expected to slow again. This information can help to support decision making with regards to suitability of certain cultivars for specific areas.
Cameron,P.R. Petrie,E.W.R. Barlow, C.J. Patrick, K. Howell, S. Fuentes. Advancement of grape maturity: Comparison between contrasting cultivars and regions. Australian Journal of Grape and Wine Research, January 2020, Vol.26 (1), pp.53-67 https://doi.org/10.1111/ajgw.12414