Towards elite mildew resistant selections suitable for industry use

Abstract

This project evaluated 1200 field-planted downy and powdery mildew resistant vines to identify elite selections with superior agronomic performance and desirable wine attributes. Vines were assessed for a number of agronomic traits including yield, berry maturity date and mildew resistance over multiple seasons. Elite selections with a range of flavour styles were identified. The potential for robust flavours at low sugar levels for low alcohol wine production was also investigated. As part of the selection process, methods for field evaluation were developed and small-scale winemaking methods developed for assessment of wine made from single vines. No mildew infection was observed on the unsprayed vines during the term of the project and sensory evaluation of the white wines identified aromatic wines and diverse flavour profiles for highly coloured red wines. Twenty red and 20 white berry vines were selected for further evaluation in regional trials. Unique wines with robust flavour styles, produced with low input costs from mildew resistant vines, may assist the Australian industry to reduce future risks.

Summary

The breeding of new disease resistant wine grape selections has become a priority in a number of countries (Dry et al. 2010). These new varieties, with resistance to downy and powdery mildew, offer the opportunity to substantially reduce the use of fungicide sprays and lower the cost of production. A previous Wine Australia project (Thomas and Dry, CSP 0904) described the use of DNA markers in a marker-assisted selection (MAS) process to identify 1200 new mildew selections that were planted in the field for evaluation. This project report describes the screening process used to identify the 20 best red and 20 best white berry individuals from those 1200 selections.

Strategies to evaluate new selections require both field evaluation and wine evaluation over a number of years to account for the different response of plants to seasonal variation. This is especially important for the screening of selections of diverse genetic background. The 1200 vines were assessed in the field for a large number of traits from budburst until harvest and it was found that there was large variation between individuals for all traits measured. A large diversity in berry chemistry was also found. Of all the traits measured in the field, the most important for selection was final yield and harvest (berry maturity) date. Selections were discarded if they had low yield and/or had a late harvest date because the berries did not reach maturity until late in the season.

Wine chemistry and sensory was an important part of the screening process and small-scale winemaking methods were developed for single vines of both red and white berry selections. Wine sensory panels included industry winemakers to ensure that wines of commercial interest were identified. The results showed that small-scale wine made from single vines was an effective screen to identify superior selections. Red wines favoured by the panel had high colour and a diversity of flavours that ranged from like Cabernet Sauvignon to Shiraz as well as some unique styles. The highly coloured wines had red flesh parentage and these were found to also have high antioxidant potential. The white wines most favoured by the sensory panel were aromatic and floral. An examination of the parentage of these selections showed that they had a Muscat or Riesling parent. The 20 superior selections for both reds and whites captured a range of wine styles and flavour and aroma profiles.

Low alcohol wines were also made from selected red and white berry vines by harvesting early at low sugar levels. The objective was to see if it was possible to make attractive low alcohol styles without the need for additional manipulations in the winery. The sensory results indicated that the reds showed the most promise, producing a Beaujolais style, but further research was required.

The diversity of aromatic and floral flavours and aromas observed from wine of selections with Muscat parentage indicated that it would be a good parent for future breeding. To improve future selection processes, this study developed a SNP DNA marker so that progeny at the seedling stage could be screened for muscat flavour. This SNP marker has been incorporated into a SNP panel that can be used to rapidly screen seedlings for the following traits, before field planting; powdery and downy mildew resistance, berry colour, flower sex (fruitfulness), stature and muscat flavour.

Another important outcome of this research is the finding that, for future screening efforts, it is not necessary to collect data on all of the traits measured in this study, and that only a subset of traits needs to be measured for an effective selection process that includes yield data, harvest date, wine chemistry, pH of must and wine sensory.

Unique wines with robust flavour styles produced with low input costs from mildew resistant vines may assist the Australian industry reduce future risk. Larger scale regional field trials will assist in determining the suitability of the 20 best red and white berry vines to produce acceptable yields under different management treatments and different climates. It is also expected that regional trials will assist with industry adoption by providing the opportunity for regional industry to assist in the evaluation of the wines.