Enhanced varieties and clones to meet the challenges of climate change and deliver lower alcohol wines

Abstract

Wine grape varieties originating from a diverse range of countries and regions, and advanced CSIRO breeding lines, have been assessed. The results demonstrate that there are significant opportunities to broaden the genetic base of varieties available to the Australian industry to enhance its capability to meet the challenges associated with climate change, limited water supply and drought and high alcohol content. Specifically, varieties have been identified with short seasonality to improve water use efficiency; small canopies to minimise transpiration and improve water use efficiency; long seasonality to ripen in cooler conditions; optimal pH and titratable acidity and unique aroma and flavour profiles

Summary

The capability of the Australian wine industry to meet challenges associated with predicted climate change scenarios may be limited by the restricted number of winegrape varieties currently grown. These challenges include the consistent supply of quality product in a variable and changing environment; the effects of temperature on fruit composition and wine attributes; a compression of the seasonal cycle, leading to an inability to process fruit at optimum maturity and, adapting to limited water supply and drought. Furthermore, there is a need to address the issue of high alcohol content in many Australian wines. The potential to exploit genetic variability to meet these challenges through adoption of alternative varieties has been assessed. A systematic approach has been used to phenotype more than 500 varieties and specific clones (i.e. a total of 880 genotypes) in the CSIRO germplasm collection for traits, considered to be important to the Australian wine industry, for climate change adaptability. In addition, 10 advanced CSIRO breeding lines and 100 CSIRO ‘Best selections’ identified in previous small-scale winemaking studies were included. The varieties, originating from a diverse range of countries and regions were assessed over four seasons in the Sunraysia region of North West Victoria, a major hot irrigated region. The study included close monitoring of vine phenology (i.e. budburst, flowering, veraison and harvest date); measurement of key growth characteristics (shoot fruitfulness, leaf area index, berry weight and estimates of yield); measurement of berry composition (total soluble solids, pH, titratable acidity, malic and tartaric acids, yeast assimilable nitrogen, mineral ion concentrations and in red varieties, total anthocyanins and phenolics) and, the production and evaluation of small- scale wines of selected varieties and CSIRO breeding lines. The information has been stored in a searchable form in FileMaker Pro13 database. The project has demonstrated that there are significant opportunities to further broaden the genetic base and range of varieties with traits that will enable the Australian industry to adapt to future climate change scenarios and address the issue of high levels of alcohol. Adoption of enhanced varieties will enable the industry to maintain its production base in existing regions, despite the impacts of climate change, and minimise the significant economic, social and environmental costs of re-positioning and developing wine grape production and processing in new regions. The study has identified varieties, grown under hot conditions with: • short seasonality to improve water use efficiency in hot irrigated regions. Such varieties may also be useful to diversify the production base in cooler regions
• smaller canopies to minimise transpiration, improve water use efficiency and improve production efficiencies, if used in high density plantings
• long seasonality to ripen in cooler conditions and extend the season
• optimal pH and titratable acidity levels which may enable crops to be harvested at lower maturity to produce lower alcohol wines
• improved composition (pH, organic acids, colour) and wine flavour and aroma which may provide opportunities for marketing at higher price points. The study has described significant, but stable variation in key traits across the varieties driven by the genotype, despite varying environmental conditions (i.e. climate, site, vine age and management practices). These included a difference of six weeks in budburst, a two-fold difference in seasonality (i.e. budburst to harvest) with harvest spread over a four month period, five-fold differences in fruitfulness and LAI, 15-fold differences in berry weight, 10-fold differences in berry mineral ion concentrations and large differences in key measurements of fruit composition (pH, titratable acidity, organic acid composition, yeast assimilable nitrogen and, in red varieties, total anthocyanins and phenolics). Very few of the imported varieties had low pH levels which would enable minimal acid addition for pH adjustment. In contrast, a number of the CSIRO breeding lines had excellent fruit composition with optimal pH and acid levels. Those selections showing good wine quality attributes warrant further development for release to industry. Interrogation of the data has shown that varieties with the most optimal fruit composition for winemaking were those that ripened early in the season and had small berries. Late ripening varieties and those with large berries could be expected to have high pH with low levels of total soluble solids, titratable acidity and yeast assimilable nitrogen. The study also showed that the ability of a variety to achieve acceptable levels of maturity also had a strong genetic component. Ripening of some varieties appeared to cease at low maturities whereas in other varieties it increased rapidly, possibly due to wilting in hot conditions. Varieties with high TSS, would be expected to have higher tartrate and YAN levels and in some seasons, higher pH. The study has provided strong evidence, across the varieties, linking key measurements of berry composition used by industry (i.e. pH, titratable acidity, organic acid composition and yeast assimilable nitrogen) with berry mineral concentration, particularly K, S and Mg, canopy size (LAI) and berry weight. Further research is required to understand the genetic control of these processes and enhance the understanding of the relationships described. Of particular interest would be studies into uptake and transport of minerals into the berry and their role in pH buffering and ion balance. The potential to manipulate fruit composition of individual varieties through control of vine vigour by irrigation, pruning or canopy management and nutrition management warrants further research. Small-scale winemaking has been used to identify a range of interesting varieties and CSIRO breeding lines that have potential for industry use. For red wine production, the strong relationship between berry anthocyanins and wine spectral properties is of particular interest as it shows that varieties with high levels of berry anthocyanins, a trait that was very stable across seasons, can be selected to produce wines with high colour for use as alternative varieties or for blending where existing varieties may be impacted by climate change. Furthermore, a small component of the project involving measurement of wine aroma and flavour compounds using GCMS has shown that wine of 11 varieties tested, displayed unique flavour and aroma profiles. Further research to assess the potential of the technology to identify wines from across a broader range of varieties; develop links with sensory profiling by trained panels; and describe relationships with flavour and aroma precursors in berries would have high scientific merit and value to the industry, particularly in developing objective measures of fruit quality for existing and alternative varieties.