Breeding of dwarf sour cherries suitable for commercial production in the harsh conditions of the Canadian prairies began in the 1940s. Long-term breeding efforts have combined high frost resistance, dwarf growth and good fruit quality into the final product. The result of breeding at the University of Saskatchewan is sour cherries with excellent taste and high sugar content. They also have very good potential for mechanical harvesting, which is essential for commercial fruit production.
Dr. Les Kerr, head of the Forestry Farm Shelterbelt Centre spent 40 years privately breeding sour cherries with the the goal of developing a hardy sour cherry variety for the Prairies.. During his intensive work, he crossed European sour cherry varieties Prunus cerasus and Mongolian sour cherry Prunus fruticosa. He sought to combine the extreme frost resistance and dwarf growth of the Mongolian sour cherry with the fruit quality of the European sour cherry.
His work was not forgotten. It was continued by Dr. Nelson, Rick Sawatzky and later Dr. Robert Bors, working in the Sour Cherry Research and Breeding Program at the University of Saskatchewan. In the 1980s, Dr. Kerr donated the entire sour cherry gene pool to the University. A few years later, another phase of breeding began, when crosses were made between frost-resistant selections of large-fruited Mongolian sour cherries and the best European sour cherry cultivars. The result was hybrids with a 75% Prunus cerasus genome and a 25% Prunus fruticosa genome.
These hybrids had balanced characteristics of both their parents. They acquired extreme frost resistance, good fruit quality, only the size of the fruit was half that of the best sour cherry varieties. A common feature of these hybrids was that they had a genetically innate low growth. Mature trees reached a height of only 2-2.5 m. This was an advantage, there was no need for grafting onto rootstocks, they could be grown on their own roots.
This was a promise for the future, as dwarf sour cherries could be easily propagated vegetatively by woody cuttings or in vitro. And in large series and at low cost. Dwarf sour cherries have been bred in Saskatchewan from the beginning for commercial production and processing in the food industry. The shrub shape predisposes such plants to planting in a line, similar to saskatoon berries, black chokeberries or raspberries, with the width between the rows sufficient to allow the passage of a combine harvester.
In 1999, the first dwarf sour cherry cultivar from Saskatchewan, CARMINE JEWEL, was created. Currently, the Carmine Jewel variety is supplemented by other new dwarf sour cherry varieties, which are closer in size to European sour cherries. The growth characteristics make them suitable for growing in small gardens, although this was not the purpose of the breeders at first. The fruits have a dark red color, with a pleasant sweet juice when ripe, which is not expected in sour cherries.
In 2004, the ROMANCE dwarf sour cherry series was introduced. This series includes the Juliet, Romeo, Cupid, Valentine and Crimson Passion varieties. In subsequent years, the BIG RED, SWEET THING and CUTIE PIE varieties were bred.
The MUSKETEER series was bred in 2021-2022 in honor of the 100th anniversary of horticulture at the University of Saskatchewan. It includes the varieties d'Artagnon, Athos, Porthos and Aramis.
Commercial Potential
The dominant product supplied to the market by cherry growers in the state of Michigan is the filling for traditional cherry pie. However, the problem with modern cherries is the lack of coloring in the pulp. During processing, rapid oxidation occurs and the color turns brown. To prevent this, agents must be used during processing that prevent rapid oxidation, or at least slow it down. Finally, it is necessary to add artificial coloring so that the cherry pie filling has an attractive fresh color that sells well. The dark purple color of the flesh of dwarf sour cherries is unique. Saskatchewan sour cherries are used not only as an excellent raw material for the production of cherry pie filling. Likewise, health-promoting products such as sour cherry juice, sour cherry wine, dried sour cherries or sour cherry muffins are an interesting addition to the market.
