Viticulture experts have been given another tool for cultivar selection and adapting to a warmer climate thanks to a study into cell death in grapes undertaken by the University of Adelaide in South Australia .
A team from the university has determined the condition is is triggered by a lack of oxygen, usually brought on by increased temperatures.
In a release, Professor Steve Tyerman, Chair of Viticulture at the University of Adelaide’s Waite campus, said the discovery had industry-wide implications because cell death changed the flavor profile of the grapes.
“In 2008 we discovered the phenomenon of cell death in grapes, which can be implicated where there are problems with ripening. We’ve since been trying to establish what causes cell death,” Professor Tyerman said.
“Although there were hints that oxygen was involved, until now we’ve not known of the role of oxygen and how it enters the berry.”
The research by Professor Tyerman and PhD student Zeyu Xiao from the University’s Australian Research Council (ARC) Training Centre for Innovative Wine Production identified that grapes suffered oxygen shortages during ripening that in turn led to cell death.
The team used a miniature oxygen measuring probe – the first time this has been done in grapes – to compare oxygen profiles across the flesh inside Chardonnay, Shiraz and Ruby Seedless table grapes.
They found the level of oxygen shortage closely correlated with cell death within the grapes and that respiration measurements indicated that this would be made worse by high temperatures during ripening.
“By manipulating oxygen supply we discovered that small pores on the surface of the berry stem were vital for oxygen supply, and if they were blocked this caused increased cell death within the berry of Chardonnay, essentially suffocating the berry,” said Xiao.
“We also used micro x-ray computed tomography (CT) to show that air canals connect the inside of the berry with the small pores on the berry stem.”
“Shiraz has a much smaller area of these oxygen pores on the berry stem which probably accounts for its greater sensitivity to temperature and higher degree of cell death within the berry.”
Professor Tyerman said that for every 10C increase in temperature the demand for oxygen in plants doubled.
“If a heatwave hits and the temperature rises from 30C to 40C the respiration rate doubles and the grapes need to get oxygen in at twice the rate,” he said.
Professor Tyerman said cell death occurred naturally about 100 days after flowering and previous research showed that sugar accumulation stopped when this cell death begins.
He said that heat waves could start the process of cell death any time before this 100-day window and that would change the flavour profile of the berry.
The only solution available to the problem was to keep the grapes cool, he said.
The University of Adelaide is also researching different ways to cool vineyards, including using microsprays and night irrigation, although Professor Tyerman said even watering was slightly problematic because the water blocked the tiny pores and inhibited oxygen uptake.
“The cause of cell death was something we didn’t know before and something we now have to take into account in the management of vineyards,” Professor Tyerman said.
The research was conducted in collaboration with Dr Victor Sadras, South Australian Research and Development Institute (SARDI), and Dr Suzy Rogiers, NSW Department of Primary Industries, Wagga Wagga. It was published in the Journal of Experimental Botany,
The study was supported by the Australian Government’s Industrial Transformation Research Program, Wine Australia and industry partners.