Spaeth and team win ASHS award for plum research

Scientists in the UC Davis Department of Plant Sciences have used modern genetic tools to reconstruct the family tree of plums bred by the legendary 19^th-century horticulturalist Luther Burbank. 

Their model will be useful for plant breeders and people who manage seed banks for all kinds of crops, because it reveals how to look for useful genetic combinations that can be used to breed better varieties. 

The paper describing their work was published in HortScience and has won a 2025 Outstanding Cross-Commodity Publication Award from the American Society for Horticultural Science. 

In the process of tracing Burbank's steps, the team produced “the most comprehensive genetic survey of Burbank’s work to date,” wrote Rachel Spaeth, who authored the paper while a doctoral student with the graduate group in horticulture and agronomy. She worked in the lab of Dan Potter, a professor and the department chair.

To reconstruct the family tree, Spaeth and team used high-throughput genome sequencing to map the location of genetic traits in cultivars kept at the National Clonal Germplasm Repository for Mediterranean Tree Fruit, Nut Crops and Grapes, housed at UC Davis. The team also looked at the genes of trees still growing at Burbank’s original properties and grafts collected from trees through the California Rare Fruit Growers, the world’s largest organization of amateur fruit growers.

Then, they used different analysis tools to figure out where specific traits came from, how different plum ancestors are related to each other and where they mixed in the past. That information, in turn, can reveal which varieties passed on useful traits.

Among the fascinating results, Spaeth teased out four major varieties of Prunus within Burbank’s breeding lines. Among those, P. simonii was prevalent in the vast majority of the fresh-market plums he developed, something little-known before. Furthermore, the genetic lines she uncovered point to Burbank likely using crosses between P. simonii and P. salicina early in his career as parents for later breeding lines.

Teamwork and local connection: Burbank and Wickson

Additional team members in the department included Dominique Pincot, a postdoc soon to be named an assistant project scientist who works with the UC Davis Strawberry Research and Breeding program. Team members also included Spaeth’s dissertation committee: Professors Dan Potter (department chair), Patrick J. Brown and Tom Gradziel.

John Preece also contributed. He is the retired research leader at the National Clonal Germplasm Repository for Mediterranean Tree Fruit, Nut Crops and Grapes, operated by the United States Department of Agriculture on the UC Davis campus. Spaeth, who has since graduated, is now a research horticulturalist at the repository.

The AHSH award recognizes the most outstanding papers in each of six categories that were published in the previous year.

Fun fact: Luther Burbank also developed the Wickson plum, a cross between Japanese and Chinese varieties. In 1894, Burbank named the plum in honor of supporter and pomologist Edward J. Wickson, who was a University of California professor and administrator instrumental in establishing the University Farm -- the start of UC Davis. Wickson Hall on campus is named after him, and UC Davis pomologists have their offices there.

Related links

Read the paper here: “Relatedness of Luther Burbank’s Plum (Prunus sp.) Introductions Based on Genotyping by Sequencing.”

National Clonal Germplasm Repository for Mediterranean Tree Fruit, Nut Crops and Grapes

California Rare Fruit Growers