Scientists are working to unravel the mystery of why some grapevines suffer a slow death.
While researchers around the world are constantly fine-tuning strategies for managing grapevine trunk diseases, until now little sustained work has been done on finding ways to make vines less susceptible in the first place.
The clue may lie in the stark difference in the impact of disease on different grape varieties, according to Scientists at the South Australian Research & Development Institute (SARDI).
When Dr Mark Sosnowski assessed trunk disease symptoms in 178 different wine grape varieties in SARDI’s comprehensive germplasm collection in the Barossa Valley, he found that the severity of trunk disease ranged from zero to nearly 100%.
“All of these vines were planted just metres apart in the same soil and had been there for the same time, around 35 years, yet some were virtually dead while others were largely untouched,” he said. “That’s when we decided something had to be going on.”
While the results are preliminary, the SARDI team has expanded the scope of the project to test differences between clones of the same grape variety, study the impact of different rootstocks and compare biochemical makeup of the vine tissue in different varieties.
“We’re talking about the health and longevity of the oldest vines that usually produce the premium wines with the highest returns.”
Funding has been provided by the Australian Wine and Grape Authority and the study is in collaboration with the University of Adelaide.
Dr Sosnowski will highlight the work in a paper at the International Workshop on Grapevine Trunk Diseases being hosted by SARDI in Adelaide from 18 November (the first time the meeting has been held in Australia).
Delegates will visit SARDI’s research centre in the Barossa Valley to see the proof first hand.
Trunk disease is a generic term for a range of diseases that slowly kill vines. The most common in Australia are Eutypa and Botryosphaeria dieback, which affect all wine regions of Australia.
Both are found worldwide and are caused by fungal spores entering the vine through the fresh cuts made during pruning or reworking. Their progress is slow (5-10 cm per year) but relentless, and the only possible response is to cut out the dead wood.
Affected vines can have strong healthy shoots in some areas, and sparse stunted growth in others. Yield losses of up to 1500 kilograms a hectare have been reported in severely infected Cabernet Sauvignon and Shiraz vines. Eventually the vines die.
While trunk disease is not the biggest short-term risk (or priority) in a vineyard – Downy Mildew, Powdery Mildew and Botrytis can wipe out an entire vintage if not managed properly – Dr Sosnowski has no doubt it has become of highest importance in all Australian regions and most winemaking countries.
“We’re talking about the health and longevity of the oldest vines that usually produce the premium wines with the highest returns,” he said.
That’s something South Australia can certainly relate to. While Australia is very much a New World wine producer, South Australia has the world’s oldest vines because, through a combination of good luck and even better biosecurity management, it has never been affected by Phylloxera, the pest that has ravaged vineyards in Europe and elsewhere.
Some vines in South Australia are more than 120 years old.
Dr Sosnowski said it was unlikely vines could be made resistant to disease. The aim was to identify more tolerant material and, by better understanding how different varieties are affected, to screen for risk when new varieties and clones are developed.
“If we are growing vines that aren’t susceptible to infection in future then less emphasis will need to be placed on protecting the wounds and remediating vines, which takes time and money,” he said.
The SARDI team has been asked to expand its research in New Zealand and already has surveyed 700 vineyard blocks in key wine growing regions.
The sobering news for vineyard managers across the Tasman is that the vines suffering most severely from trunk diseases in the SARDI collection were Sauvignon Blanc, New Zealand’s predominant variety.