Wine changes with age and it appears that the rootstocks the vines grow on may as well.
Research in South Australia's Riverland, Langhorne Creek and Limestone Coast regions has revealed differences over time in yield and performance in a variety of mature grafted vines when compared with their younger selves.
Research leader Tim Pitt, from PIRSA's South Australian Research and Development Institute (SARDI), went back to original rootstock trial sites originally planted during the 1970s and '80s, and into the early '90s.
Mr Pitt said the trial sites were part of a significant commitment decades ago by the South Australian Department of Agriculture (now PIRSA) to investigate the potential for rootstocks to enhance the performance of both grape and citrus crops.
In the case of viticulture, more than 50 replicated rootstock trials were established across the state's main wine regions. The performance of multiple varieties grafted to more than 30 rootstock genotypes was measured over the next 5–10 years and the results have formed the basis of rootstock selection decisions ever since.
These original trials had not been revisited until now.
The findings, Mr Pitt said, present some interesting questions and may lead growers and nurseries to rethink some of their rootstock selections and recommendations now that long-term performance data is available
Inspired by results from a Limestone Coast project, Mr Pitt said he and fellow SARDI colleagues ‘got a sense that things were changing' when they started working at one of the original trial sites.
"We were getting a different yield trend than had been reported in the first six years of life of the vines and we saw in other work, suggestions that the salt exclusion properties for some rootstocks were also changing as the vines aged," he said.
"We knew we had rootstock trials in their third or fourth decade of productive life, managed under commercial situations, so we thought it would be worth going back and comparing current performance with the data collected in those early years."
The Riverland was chosen as the main site for the project as 75 per cent of new vineyards in the region incorporate rootstocks into their plantings.
Funding for the project – which looked at both wine grapes and citrus – was provided under the South Australian River Murray Sustainability program (SARMS) Industry-led Research Sub-Program (IRSP).
The IRSP supported nine research projects and other targeted research initiatives, all of them designed to improve regional productivity and innovation and address specific industry research priorities.
As part of the SARMS-funded project, he and colleague Mark Skewes visited nine viticulture sites in the Riverland and three in Langhorne Creek.
They did so with an open mind and a simple question, he said.
"The advice going out to growers is based on data and trends measured decades ago, but are those data and trends the same?"
"The answer is that some change is happening. Yield performance is not as stable as we would previously have thought; some rootstocks are showing altered salt exclusion properties; others are suggesting greater tolerance to dieback than expected.
"The long-term performance of grafted vines is certainly worth looking at in more detail."
A report based on the research provides more detailed findings about the performance of specific rootstock by scion combinations in the Riverland and Langhorne Creek.
While results are specific to the regions studied, Mr Pitt said there were implications for other regions and vineyards where rootstocks are – or may become – an important part of producing quality fruit for the Australian wine sector.
SARMS is contributing to the South Australian Government's commitment and implementation of the Murray-Darling Basin Plan. SARMS is funded by the Australian Government and is being delivered by Primary Industries and Regions SA (PIRSA) over six years to mid-2019.