Genetic diversity loss
Modern rose hybrids have lost more than a quarter of their genetic diversity since the early 19th century.
The domestication of roses can be traced back about 5000 years and were cultivated independently in China and Mediterranean regions. The diversification during the 19th century is associated with crosses between the two previously isolated genetic backgrounds. The number of hybrids grew from about 100 in the early 1800’s to approximately 5,000 varieties today.
Thibault Leroy, from the University of Angers, France, and his colleagues, reconstructed the history of roses in Europe using genetic data for more than 200 varieties, plus the whole genome of 32 varieties. They found a progressive shift from a European to a more Asian-like genetic background, with Hybrid tea roses exhibiting a three-quarter Asian genetic background. The Asian varieties exhibited lower resident diversity compared to ancient European varieties, partly due to a more ancient and intense history of selection in Asia, as well as to some specific genomic footprints of artificial selection.
In their report titled “Dark side of the honeymoon: reconstructing the Asian x European rose breeding history through the lens of genomics”, Leroy et al describe roses as representing a common heritage of mankind, and serve as a significant commercial cornerstone in the ornamental sector in addition to being used as a source of food and medicine in some societies. Diversity is needed to face different threats, including diseases, pests, changes in climate, as well as more intrinsic factors associated with evolution under low effective population sizes, and therefore reduce mid- and long-term extinction risks.
Grafting however, makes the long-term maintenance of ancient varieties possible, allowing the backcrossing of modern varieties, improved regarding some specific traits, with more ancient and genetically diverse varieties. This restoration of this genetic diversity is however only possible if the ancient garden roses are maintained over the long term.
The genome mapping of rose hybrids also identified genetic traits that could guide breeders developing hardier plants less reliant on chemicals to avoid disease such as black spot.
https://www.biorxiv.org/content/10.1101/2023.06.22.546162v3.full.pdf