Regional evaluation of new germplasm – pathway to adoption

Abstract

Fungicide applications for the control of the two most important diseases of winegrapes in Australia, powdery mildew and downy mildew, could be significantly reduced by the breeding of new mildew- resistant winegrape varieties. Twenty new 1st generation white and red mildew-resistant winegrape varieties containing the Run1/Rpv1 resistance locus from Muscadinia rotundifolia were selected for evaluation in three unsprayed replicated trials in both warm/hot and cool climate grape growing regions in Australia. Vines were evaluated for viticultural and wine sensory characteristics over a number of seasons and a subset of white and red 1st generation varieties identified which show potential for further large-scale evaluation by industry.

Summary

The Wine Australia Strategic Plan 2015-2020 identified “Increasing Competitiveness” as a major priority to increase the prosperity of the Australian Wine Industry. One of the strategies identified to improve the performance of Australian vineyards was through the availability of new grapevine varieties that tolerate biotic stressors, generated through plant breeding programs. As part of a previous co-investment project with Wine Australia (CSP0904), CSIRO successfully bred new 1^st generation (gen.) white and red varieties that are resistant to powdery and downy mildew. These 1^st gen. mildew-resistant varieties contain a single gene conferring powdery mildew resistance (Run1) and a single gene conferring downy mildew resistance (Rpv1), introgressed as a single locus (Run1/Rpv1), from the wild North American grape species Muscadinia rotundifolia.

The 1^st gen. breeding program described in WA project CSP0904 was based on crosses between a Run1/Rpv1 breeding line (VRH3294) with a selection of 8 premium white (Chardonnay, Frontignac, Muscadelle, Muscat Gordo Blanco, Riesling, Sauvignon Blanc, Verdelho & Viognier) and 9 premium red (Dunkelfelder, Durif, Grenache, Petit Verdot, Sangiovese, Shiraz, Sumoll, Tannat & Tempranillo) winegrape varieties. Cabernet Sauvignon was not used as a breeding parent because of the possibility of in-breeding depression when crossed with the VRH3294 breeding line which was itself derived from a cross with Cabernet Sauvignon. From these crosses over 1200 progeny plants were selected by marker-assisted selection to contain the Run1/Rpv1 locus and these were evaluated, as single vines, in an unsprayed block in the Barossa Valley over a number of seasons for viticultural performance and wine sensory attributes as described in Wine Australia Project CSP1303.

This analysis led to the selection of the 20 best performing 1^st gen. white and red mildew-resistant selections based on disease resistance, yield, high acid at harvest and consistently high sensory scores of single vine micro-ferments which were derived from crosses with 4 white (Frontignac, Muscat Gordo Blanco, Riesling, Verdelho) and 3 red (Dunkelfelder, Shiraz, Tannat) premium winegrape parents.

The next phase of the evaluation process was to undertake larger scale replicated trials in regional sites to (a) determine the performance of the different selections in different environments and management systems and (b) provide more fruit for evaluation of the sensory characteristics of wine produced from small-scale ferments of fruit harvested from multiple vines. This project undertook a comprehensive evaluation of the viticultural performance and sensory characteristics of the 20 best 1^st gen. white and red selections from regional trials in both the warm/hot regions of Irymple (Victoria) and Wagga Wagga (NSW), as well as the cooler viticultural region of Orange (NSW). In Irymple this involved 3 vines per selection (1 replicate of 3 vines), in Wagga Wagga 24 vines per selection (6 replicates of 4 vines) and in Orange 48 vines per selection (6 replicates of 8 vines).

In the warm/hot regions, all 1^st gen. white and red selections were found to be highly resistant to powdery mildew and downy mildew infection, even in the absence of fungicide applications. However, it was observed in Wagga Wagga, that the reduced application of sulphur for powdery mildew control led to a higher incidence of mite damage, requiring sulphur sprays to be applied at the beginning of the season to control mite infestation. Plantings of 1^st gen. varieties in Orange were also found to be free of powdery mildew and downy mildew except for season 2021/21, when the high rainfall conditions in Orange were highly conducive for downy mildew infection resulting in the appearance of some limited infection on the leaves of some 1^st gen. selections. However, the level of downy mildew infection observed on unsprayed 1^st gen. selections was still much lower than that observed on premium (susceptible) varieties planted elsewhere in the district which had undergone full spray programs.

Small-scale ferments (40 - 80 kg) of grapes harvested from Irymple, Wagga Wagga and Orange were carried out at the Charles Sturt Winery using the same small-scale protocol to minimize variation in chemical and sensory attributes due to the winemaking process. Wine was produced from all 1^st gen. varieties planted in Irymple, Wagga Wagga and Orange over at least two vintages. Sensory analysis of wines made from 1^st gen. varieties grown in Irymple and Wagga Wagga were carried out 4 - 6 times by a range of different tasting panels comprising winemakers, growers and wine industry representatives.

Small-scale winemaking presents various challenges in terms of consistency and reproducibility such that, in any one vintage, the quality of individual wines may be less than optimal and not be a true reflection of the potential quality of the variety under investigation. Furthermore, given the large number of varieties to be evaluated at each vintage, it was also not feasible to make replicate wines from each variety. As a result, a compromised vintage, in any one year, may have a major impact on the overall ranking of that wine at the end of the evaluation period, if the ranking was based on average scores across all tastings. To minimize the impact of a potentially compromised vintage, wines (varieties) were ranked according to the number of times the average score of the tasting panel was ranked in the top 5 wines tasted. This number was then divided by the total number of times that wine had been scored, to give a percent of top 5 rankings. This also enabled comparison of wines that had been tasted a different number of times.

While there was significant divergence between ranking of individual wines by different tasting panels, there were also some clear trends across different vintages and different tasting panels as to which of the twenty 1^st gen. varieties produce the highest ranked wines. Comparison of these selected highly ranked white and red 1^st gen. wines, with reference wines made from premium white (Chardonnay & Riesling) or red (Cabernet Sauvignon & Shiraz) varieties grown at the same location, in blind tastings, indicated that several 1^st gen. varieties were ranked equal to or higher than the reference wines.

Sensory analysis of wines made from 1^st gen. varieties planted in Orange was somewhat compromised by cool and wet weather in both seasons such that most varieties did not reach the target ripeness, resulting in wines low in alcohol. In addition, due to the later planting of the Orange vines, vintages only became available at the end of the project thereby limiting opportunities for tastings of the Orange wines. Despite these limitations, comparison of the highest ranked 1^st gen. white and red varieties from the hot/warm regions with the Orange wines indicated some overlap suggesting that these 1^st gen. white and red varieties may be suited to wine production across both warm/hot and cool regions.

It is well established that increasing average temperatures associated with climate change will make it increasingly challenging to produce red wines with acceptable colour in Australia’s warm/hot grape growing regions because of the negative impact of high temperature on anthocyanin production. The introduction of the red flesh trait from the teinturier variety Dunkelfelder, into selected 1^st gen. red varieties, in addition to the Run1/Rpv1 mildew resistance locus, resulted in wines with 2.0 - 5.5 times higher levels of anthocyanins than those derived from premium red skin varieties grown under the same conditions in either Irymple or Wagga Wagga and fermented using the same small-scale protocol. Furthermore, anthocyanin levels of the wines made from selected red flesh varieties grown in Irymple and Wagga Wagga (i.e. varieties that were found to be highly ranked based on sensory analysis) were 1.6 - 4.4 and 1.8 - 5.4 times higher, respectively, than those measured in commercially available reference premium red wines.

On the basis of data collected in this project, 7 white and 7 red 1^st gen. varieties have been identified which show sufficient potential for further large scale-evaluation by the Australian wine industry in the warm/hot grape growing regions. Average yields for these seven 1^st gen. white selections ranged from 23.6 - 50 t/ha in Irymple and 10.8 - 20.7 t/ha in Wagga Wagga. Average yields for the seven 1^st gen. red selections ranged from 20.5 - 34.8 t/ha in Irymple and 10.4 - 15.4 t/ha in Wagga Wagga. Harvest dates for the seven 1^st gen. white selections fall in the range observed for Chardonnay and Riesling in these warm/hot regions. Harvest dates for six of the seven 1^st gen. red selections fall into the range observed for Cabernet Sauvignon and Shiraz at the same location, while one selection was found to ripen up to 2-3 weeks before Cabernet Sauvignon and Shiraz providing an opportunity for growers/wineries to expand the harvest window for red grapes in warm/hot regions. Of the 7 red 1^st gen. varieties chosen, 6 have red flesh making them highly attractive for the production of high colour red wines from hot regions. In addition, 4 of the selected 1^st gen. varieties (3 white & 1 red) show a more open bunch architecture than premium varieties commonly in use, making them highly attractive to growers in regions with a high risk/incidence of botrytis bunch rot.

Another important outcome of this project has been the engagement with the Australian wine sector through tasting sessions, workshops and seminars to highlight the potential benefits of these new 1^st gen. mildew-resistant varieties in terms of reduced production costs, reduced environmental footprint and the opportunity for product differentiation. As a result, 9 growers/wineries have already elected to undertake larger scale evaluation of 1^st gen. mildew-resistant varieties on their properties in SA, Vic and NSW under Plant Evaluation agreements using propagation material sourced from the regional trial plantings.

The breeding of 1^st gen. mildew-resistant varieties and their evaluation in regional trials has provided an opportunity for Australian growers and winemakers to gain an understanding and appreciation of the potential economic and environmental benefits that new winegrape varieties offer, over existing varieties, in dealing with challenges such as disease control and climate change. It has also demonstrated to Australian wine producers that the new generation of winegrape hybrids, developed through backcrossing and marker-assisted selection, have the potential to not only produce wines of equal quality to the traditional French varieties but also provide new opportunities for product differentiation.