Wine changes with age and it appears that rootstocks may as well. Research in South Australia’s Riverland, Langhorne Creek and Limestone Coast regions has revealed differences over time in the yield rankings and the salt exclusion performance of a variety of mature grafted vines when compared with their younger selves.
Yield assessment during one of the historic rootstock comparison trials
Research leader Tim Pitt, from PIRSA’s South Australian Research and Development Institute (SARDI), says the findings 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 are available.
SARDI’s long history with rootstock investigations has been made possible through both government and wine sector funding. During the 1970s and ’80s, and into the early ’90s, the then South Australian Department of Agriculture (now PIRSA) made a significant commitment 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.
The work had not been revisited until Mr Pitt and SARDI colleagues revisited one of the historic trial sites on the Limestone Coast and ‘got a sense that things are changing’.
‘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 an obvious place to do the work, given that 75 per cent of new vineyards in the region incorporate rootstocks into their plantings, and funding for the project – which included both wine grapes and citrus – was provided under the South Australian River Murray Sustainability program (SARMS).
Mr Pitt did worry that he might not be able to find enough of the old trial sites still intact, given that all had been handed over to host irrigators to manage as commercial plantings, but his fears proved unfounded and the owners were receptive. In their recent SARMS project, he and colleague Mark Skewes visited nine sites in the Riverland and three in Langhorne Creek.
They did so with an open mind and a simple question: 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’, Mr Pitt said.
‘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.’
The latest report provides 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, there are implications for other regions and vineyards where rootstocks are – or may become – an important part of producing quality fruit for the Australian wine sector.
You can access the report here. SARDI also has prepared a useful factsheet here. The Rootstock selector tool will soon be updated with this new information.