A new study published in the Proceedings of the National Academy of Sciences details the ancient origins and hybridization processes that led to the modern strawberry’s complex genetic makeup. Leading the research, former University of Florida post-doctoral researcher Zhen Fan, now at Zhejiang Agriculture and Forestry University in China, traced the evolutionary history of strawberry chromosomes over centuries.

The research shows that modern strawberries are octoploids, possessing eight sets of chromosomes, unlike most species that are diploid with two sets. 

“The modern strawberry has about four times as much DNA as the most ancient wild strawberries," said Vance Whitaker, UF/IFAS professor of horticultural sciences, a co-author of the study, and Fan’s former supervisor. “This happened through hybridization (crossing) of up to four distinct wild species over a long time,” Whitaker added.

According to Whitaker, reconstructing the history of early strawberry species has been challenging because some of these ancient species went extinct long ago, making direct study impossible. Fan’s research indicates that various ancient species crossed with each other before the modern strawberry emerged, suggesting a more complex genetic background than previously understood.

The findings aim to assist future breeding efforts by providing a clearer understanding of the plant’s hybridization history. “One day, we would like to reconstruct the modern strawberry from simpler species by making the crosses ourselves,” Whitaker explained. “Better understanding how the strawberry formed will help us do that and could lead to breeding better varieties that are more genetically diverse and resistant to pests and diseases.”

Strawberry’s complex ancestry also highlights the challenges faced by breeders. “With multiple species in its background, the strawberry is fun and challenging to work with for a breeder like me,” Whitaker noted.

The study’s significance extends beyond strawberries. Doug and Pam Soltis, professors at the Florida Museum of Natural History and co-authors, contextualized the findings: “Strawberry might be the opposite of a purebred, but it is typical of the complexities we see in natural populations of plants, complicated evolutionary histories of repeated hybridization, introgression, and genome doubling.”

“The methods developed for reconstructing the evolutionary history of strawberries may be useful in other crops where the ancestry is also uncertain,” Pam Soltis said. “Polyploidy (more than two sets of chromosomes) is very common in wild plants, and occurs in other organisms as well. I look forward to applying these methods to the study of wild polyploid species for which we know almost nothing about their evolutionary history.”

Featured photo: Vance Whitaker, UF/IFAS strawberry breeder. Courtesy, UF/IFAS photography.

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