Heat leaving blackcurrant growers blue
ITS plump juicy berries may be the essence of warm summers but now the humble blackcurrant bush is under threat from our increasingly warm winters.
Like many fruit plants, blackcurrants need a heavy frost to ensure that their buds break properly in the spring when there are plenty of pollinators around to produce fruit.
Milder conditions driven by climate change are causing the bushes to flower later in the year, which has led to a steep decline in harvests and fruit quality.
Researchers at the James Hutton Institute in Dundee fear the lifespan of plants will be cut short if the problem persists – presenting a bleak outlook for Britain’s blackcurrant growers.
Presenting preliminary findings at the British Ecological Society’s annual meeting in Birmingham, the researchers said it was vital to understand how different varieties of the fruit responded to different temperatures.
Blackcurrants are worth about £10million a year to the UK economy and the soft drink company Ribena buys 95 per cent of the British crop. Around 35 per cent of the crop is known to require 1,800 hours of chilling below 7C (45F), while some varieties need far lower temperatures.
Controlled experiments were done at temperatures ranging from minus 4C (25F) to 8C (46F) for up to 150 days on 20 different varieties of blackcurrant. The results were then compared to blackcurrant cuttings sent in from farmers across the UK and temperature data obtained from local meteorological stations.
Researchers found that each variety preferred different levels of chilling, and that some were able to compensate for warmer winter temperatures if the period of cooling they experienced was longer, while some were not. The difference lies in genetics, with varieties evolving in different climatic regions or due to selective breeding, the study found.
Dr Katharine Preedy, from Biomathematics and Statistics Scotland, said: ‘Blackcurrants have particularly high chill requirements and so are already seeing the effects of milder winters. Blackcurrants are like the canary in the mine. If we can understand what they need in a changing climate, we can apply our knowledge to similar crops like blueberries, cherries, apples and plums.
‘We hope to identify genetic markers associated with the ability to withstand variable winters, so we can rapidly breed new varieties of blackcurrants.’
Professor Hamlyn Jones, from the University of Dundee, said understanding the genetics would help farmers select varieties based on the climate and conditions blackcurrants were grown in.
In 2017, a bumper blackcurrant crop of around 12,000 tons followed an exceptionally dry winter coupled with a period of warm weather with temperatures topping 30C (86F).
The ideal weather conditions also led to higher than normal Brix levels – the concentration of fruit sugars.
Most commercial blackcurrant crops are grown from varieties named after Scottish mountains and developed by the James Hutton Institute. They include Ben Avon, Ben Dorain, Ben Sarek and Ben Connan.