Finding a way to fight fungus without fungicides is a long game, but CSIRO researchers in Adelaide are making significant progress.
Dr Ian Dry and colleagues have moved onto the third stage of a complex, multi-layered initiative to breed new wine grape varieties with a built-in resistance to powdery and downy mildew and, they hope, a structure that helps limit the risk of botrytis.
All three stages have been funded by Wine Australia, and the drivers are both economic and environmental; fungicides are costly and vineyards need a lot of them. In Europe, wine grapes account for only 8 per cent of agricultural production by area but 70 per cent of fungicide use, and the picture in Australia is similar.
In Australia, environmental and marketing considerations also mean that proven technologies involving genetic modification cannot be countenanced, certainly in the immediate future.
The best solution is to try to build in resistance. It does not occur naturally in our commonly used wine grape varieties because they all were bred in Europe well before powdery and downy mildew first crossed the Atlantic from the Americas. You can’t have natural resistance to something you’ve never encountered.
The CSIRO team created a first generation of such varieties in 2009 and these are being evaluated in field trials. The aim is to find the 20 best white and red varieties, based on consistent performance over a number of growing seasons in terms of good yields, good acid and pH at harvest and consistently high sensory scores.
For that project, the team was able to build on the work of French researcher Alain Bouquet, who spent 20+ years ‘backcrossing’ a wild North American grapevine with proven resistance to premium European varieties. Backcrossing involves multiple rounds of breeding, each time ensuring you
have captured the resistance gene you want without also bringing across negative traits that could impact on vine and fruit quality.
In the recently completed second CSIRO project, the team started the process of developing a second generation of new wine grape varieties.
‘It was a great advance to develop premium winegrape varieties with mildew resistance, but we knew there was a danger that over time a disease isolate may evolve to break down the resistance and then you’re back to square one’.
- Dr Ian Dry
‘But if you combine resistance genes from two different genetic sources into the same plant – a process known as stacking or pyramiding – you reduce the risk considerably.’
The aim is to create varieties that incorporate resistance from both the North American species and newly identified species from China, where natural resistance is also found.
Chinese researchers had previously identified wild Vitis species with resistance to powdery and downy mildew, but no-one had done the necessary backcrossing to create a wine grape variety incorporating these genes. To achieve that in five years rather than 20, Dr Dry’s team called on two innovations.
Grafted vines ready to be planted out
The first was to use DNA markers to identify plants that had inherited the right gene at the seedling stage rather than having to go through full field trials – a process called ‘marker assisted selection’.
The second was to use a unique rapid grapevine breeding system, known as the microvine, developed by CSIRO. The microvine allows the full range of trials and selection processes to be carried out quickly and efficiently on rapid-flowering dwarf plants in a greenhouse rather than having to plant breeding lines in the field and wait two to three years for them to fruit
That project also was a success (you can read the full report here) and in June the team began the third stage, which will try to create new wine grape varieties in which the mildew resistance genes from the North American and Chinese species are combined.
‘We’ll then take the best of those into field for testing and then through small-scale winemaking to look for those elite second-generation varieties,’ Dr Dry said.
The work has its limitations, notably that any new varieties will be just that – new varieties with new and unfamiliar names. The amount of modification to the base vinifera species will be too much for it to be known by its original name.
However, Dr Dry says there is immediate potential to use the new varieties in blending, as well as the chance that something new and exciting will emerge.
‘Hundreds of years ago a breeder crossed Sauvignon Blanc with Cabernet Franc to produce Cabernet Sauvignon and that could happen again. Something we produce could be the next unique variety.’
CSIRO technician Angelica Jermako pollinating a microvine