Warmer winters 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, researchers have found.
Like many fruit crops and woody plants, blackcurrants are said to require a period of chilling before they start to grow in spring. This is said to reduce the risk of frost damage to new buds and ensures that buds burst rapidly in the spring and flower together, when pollinators are abundant.
A research group based at the James Hutton Institute in Scotland says that milder winters may cause blackcurrant crops to flower later in the year, produce fewer fruit, and over repeated years, have a reduced plant lifespan.
Dr Katharine Preedy from Biomathematics and Statistics Scotland says: “Blackcurrants have particularly high chill requirements and so are already experiencing the effects of milder winters.”
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 like Ribena.
About 35 per cent of the UK crop is known to require 1,800 hours of chilling below 7degC. Some varieties, however, need far lower temperatures and others can tolerate warmer temperatures as long as the chilling lasts longer, according to the researchers.
Dr Preedy says: “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.”
To explore the relationship between chilling period and bud opening, the ecologists carried out controlled temperature experiments at temperatures ranging from -4 to +8degC 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 local Met Office stations.
They found that each blackcurrant variety responded differently to different levels of chilling. Some varieties were able to compensate for warmer winter temperatures if they were chilled for long enough, whilst for other more sensitive varieties, longer chilling periods did not compensate for being less cold, causing erratic bud break, according to the researchers.
The differences lie in genetics, as some varieties have evolved in different climatic regions or are the result of selective breeding over the years, says Prof Hamlyn Jones from the University of Dundee.
“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.”