Why warmer winters could prove less fruitful for growing blackcurrants
THEY are luscious soft fruits, popular for their tart flavour, versatility and until now, for being recognised as easy to grow. But Scots experts are warning that warmer winters may impact the future of the humble blackcurrant.
The bunches of dark purple berries that grow in spring are valued for being abundant in vitamin C and having a rich dietary value, offering “therapeutic potential” in a myriad of diseases.
For most of us, though, they are simply a go-to fruit whose flavour is ideal for pies, jams and cordials.
But speaking at the British Ecological Society’s annual meeting in
Birmingham today, a research group based at the James Hutton Institute in Dundee will highlight that rising temperatures during winters ahead may not provide sufficient chilling for blackcurrants in the UK, delaying the start of the growing season and resulting in reduced yields and lower fruit quality.
Like many fruit crops and woody plants, blackcurrants – which were first cultivated in Europe in the 17th century – require a period of chilling before they start to grow, reducing the risk of frost damage to new buds and ensuring buds burst rapidly in the spring and flower together, when pollinators are abundant.
A research group based at the institute, however, has found that milder winter conditions may cause blackcurrant crops to flower later in the year, produce fewer fruit and, over repeated years, have a reduced plant lifespan.
“Blackcurrants have particularly high chill requirements and so are already seeing the effects of milder winters,” said Dr Katharine Preedy, of Biomathematics and Statistics Scotland.
A key crop worth about £10 million a year to the UK economy, blackcurrants are primarily processed as an ingredient and juice for major brands, such as Ribena.
Understanding how different blackcurrant varieties may respond to climate change is critical to farmers, the researchers say.
About 35 per cent of the crop currently grown is known to require 1,800 hours of chilling below 7°C.
Some varieties, however, need far lower temperatures and others can tolerate warmer temperatures as long as the chilling lasts longer.
Many farmers co-ordinate processing with apple producers in shared facilities, so a delayed blackcurrant season may force them to harvest unripe fruit of poorer quality – or they might miss the chance to process the fruit at all.
Dr Preedy added: “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, such as blueberries, cherries, apples and plums.”
To explore the relationship between chilling period and bud opening, the ecologists carried out controlled temperature experiments, at temperatures ranging from -4°C to +8°C for up to 150 days, on 20 different blackcurrant varieties.
The findings were then compared with blackcurrant cuttings sent in from farmers across the UK and temperature data obtained from the Met Office.
They found that each blackcurrant variety preferred different levels of chilling. In addition, some were able to compensate for warmer winter temperatures if they were chilled for long enough, while for other more sensitive varieties, longer chilling periods did not compensate for being less cold, causing erratic bud break.
The differences lie in the genetics, as some varieties have evolved in different climatic regions or are the result of selective breeding over the years.
“If we can understand this, farmers can carefully select varieties based on the climate and conditions in which they are going to be planted, and breeders can develop varieties that are more resilient to both warmer winters or periods of extreme cold”, said study collaborator, Professor Hamlyn Jones, of Dundee University.
Currently, 12 varieties are widely grown in the UK and Ribena invests in the British Blackcurrant Breeding Programme, co-ordinated by the James Hutton Institute.
While previous varieties were produced with tougher skins to increase shelf life, this research demonstrates the potential to develop varieties that can cope better with a changing climate.
“In the future, we hope to identify genetic markers associated with the ability to withstand variable winters, so we can rapidly breed new varieties of blackcurrants”, concluded Dr Preedy.
In a 2012 article published by the Royal Society of Chemistry, the authors noted: “Blackcurrants have demonstrated significant therapeutic potential in a myriad of disease states.
“In addition, blackcurrant possesses a high content of vitamin C, contributing to the high antioxidant activity of berries. Some of the properties of blackcurrants include anthocyanins.”
Anthocyanins are the pigments that give red, purple and blue plants their colouring that can have antioxidant effects and offer anti-inflammatory and anti-viral benefits.
Dr Preedy will present the research today to 1,200 ecologists from more than 40 countries.
They have particularly high chill requirements