Small and with the ability to draw the jaws together from just one tiny taste, crab apples are often overlooked in favour of their far sweeter cousins.
And unless they’ve been smothered in sugar and used in jellies and preservatives, the tart and tiny fruits would seem to be fairly useless.
However, a major DNA project is now looking into whether the much-maligned Scottish native crab apple might have genetic ‘super-powers’ which could help boost the fortunes of other, tastier, varieties in the face of climate change.
A native crab apple from the Royal Botanic Garden Edinburgh is among 25 apple varieties – around half of them Scottish heritage apples with names like Bloody Ploughman and Stirling Castle – to have had their genetic ‘blueprint’ successfully sequenced as part of the Darwin Tree of Life project which eventually aims to sequence the genome of all 60,000 species of complex life in Britain and Ireland.
Unravelling the DNA of apple varieties means scientists can now study the relatedness and origins of the apples and analyse whether useful genes may be found to help boost resilience to weather conditions, disease or improve taste.
The native crab apple is of particular interest to scientists as, unlike domestic cultivated varieties which made their way from East Asia along the Silk Road route as a result of passing traders and animals, its roots lie in the aftermath of the last ice age, when the European crab apple colonised the British Isles.
The hope is that Scotland’s surviving native crab apple trees undiluted as a result of hybridisation with domestic apples, might harbour specific genetic features which could be used to improve the fortunes of their tastier neighbours.
Of course, the suggestion that crab apples may have super genes will bring little comfort to gardeners currently faced with picking countless tiny apples from their lawn.
However, Dr Max Coleman of RBGE said: “Even though crab apple fruits are small and sour, there might be genetic qualities that could be beneficial to our domestic apple crops.
“It might be that there are some disease resistance or adaptation to local conditions; maybe where the apple comes from the climate might be different – the west coast for example – which makes them more resilient to certain weather conditions.
“There could be something really genetically useful in the wild apple.”
The £9.4m Wellcome-funded Darwin Tree of Life project has been described as having the potential to transform biodiversity for the next century and beyond. It aims to sequence the entire genome of 2000 species during its first phase.
The genomes will then provide unprecedented insight into how species evolved and uncover new genes, proteins and metabolic pathways which could help develop new treatments for disease or solutions to the issue of food security.
While RBGE’s focus has been on providing the project with ferns, bryophytes, lichens and Scottish flowering plants, its collection of heritage apples – which includes names long since overtaken by supermarket varieties – have already been analysed.
Dr Coleman said genetic work has already established that domestic apples originated in Asia. “It is easy to imagine the apple trees in the RBGE garden have always been here and that the apple is a native Scottish tree. But in fact the domestic apple is a product of travel and trade, of accidents in hedges and painstaking hard graft.
“In the forests of the Heavenly Mountain (Tian Shan) the Central Asian wild apple can look much like our familiar fruit. Thousands of years ago people and animals on Heavenly Mountain picked the largest, sweetest fruit and this was the first step on the road to domestication.
“People and animals spread apples as they travelled.”
These crossed naturally with wild apple species in Siberia, the Caucasus and Europe, enabling apples to adapt and adding genetic variability, he added.
From there, gardeners used cultivation techniques to adapt apples into sweeter, larger or more robust varieties.
While there are now over 2,500 varieties of apples in the UK – and 7,000 worldwide – shoppers often find themselves restricted to a handful of familiar supermarket varieties such as Golden Delicious, Pink Lady and Granny Smiths.
While traditional Scottish apples such as James Grieve, Coul Blush Hawthornden and Bloody Ploughman which were once grown in vast quantities, now tend to be restricted to individual gardens and small orchards.
The ‘pure’ native crab apple may be eventually become even rarer – a study carried out in 2017 claimed hybridisation with domestic apples and crab apples could lead to their disappearance in the same way the wild cats are affected by hybridisation with domestic cats.
The research, led by forestry consultant Rick Worrell, studied around 200 native crab trees in Scotland, with around 60 to 70% in the uplands found to be true ‘Malus sylvestris’ rather than hybrids or other species, while in the lowlands, domestic apples and hybrids appear to be in the majority.
The research also revealed how most of the native crab apples studied appeared to be “incredibly resilient” adding: “They blow over and resprout freely as ‘phoenix trees’. They frequently grow hollow then collapse, but then get a second wind and start growing again.
“Broken limbs will live on and recover provided they are connected to the main stem by the thinnest strip of bark. So far, we have only found one tree apparently affected by disease.”
Leaves from the RBGE garden’s apples were sent to the Wellcome Sanger Institute in Cambridgeshire where sugars, proteins and other chemicals were removed and the long strands of DNA were carefully extracted. High powered machines are then used to read the millions of letters of the apples DNA.
While the project is currently sampling just one native crab apple, it’s likely that there will be slight differences in the genetic make up of crab apples found in different parts of the country, where trees have adapted to specific conditions.
Dr Coleman added: “Generating the genome gives us a starting point for this specific crab apple, but I would predict there would be variations across Scotland.
“By unpicking the secrets of our apple’s history, as recorded in its DNA, we can understand and protect the incredible diversity of these fruits for generations to come.”
Tie piece Once thriving in orchards across the country – in particular in the Clyde Valley were commercial fruit growers produced homegrown varieties – once common Scottish varieties of apples with evocative names and distinctive tastes have been overtaken by supermarket varieties.
Bloody Ploughman was cultivated in the mid-19th century and said to have been named after a ploughman who was caught stealing the blood red apples, and consequently shot.
Stirling Castle, a flat cooking apple said to be good for making apple foam, was developed by a Stirling nurseryman in 1831. Bright yellow Hawthornden was first recorded in 1780s and named after 16th century poet, William Drummond of Hawthornden.
One of the better-known Scottish dessert apples, James Grieve, was named after its Edinburgh breeder who developed the variety in the 1890s.
Golden coloured Coul Blush was raised by Sir George Mackenzie at Coul House in Contin, Ross-shire, in 1827, and is Britain’s most northerly apple.