Social network analysis of the genealogy of strawberry: retracing the wild roots of heirloom and modern cultivars

Abstract

The widely recounted story of the origin of cultivated strawberry (Fragaria × ananassa) oversimplifies the complex interspecific hybrid ancestry of the highly admixed populations from which heirloom and modern cultivars have emerged. To develop deeper insights into the three century long domestication history of strawberry, we reconstructed the genealogy as deeply as possible—pedigree records were assembled for 8,851 individuals, including 2,656 cultivars developed since 1775. The parents of individuals with unverified or missing pedigree records were accurately identified by applying exclusion analysis to array-genotyped single nucleotide polymorphisms. We identified 187 wild octoploid and 1,171 F. × ananassa founders in the genealogy, from the earliest hybrids to modern cultivars. The pedigree networks for cultivated strawberry are exceedingly complex labyrinths of ancestral interconnections formed by diverse hybrid ancestry, directional selection, migration, admixture, bottlenecks, overlapping generations, and recurrent hybridization with common ancestors that have unequally contributed allelic diversity to heirloom and modern cultivars. Fifteen to 333 ancestors were predicted to have transmitted 90% of the alleles found in country-, region-, and continent-specific populations. Using parent-offspring edges in the global pedigree network, we found that selection cycle lengths over the last 200 years of breeding have been extraordinarily long (16.0-16.9 years/generation) but decreased to a present-day range of 6.0-10.0 years/generation. Our analyses uncovered conspicuous differences in the ancestry and structure of North American and European populations and shed light on forces that have shaped phenotypic diversity in F. × ananassa.

Diversification, spread, and admixture of octoploid strawberry in the Western Hemisphere

“…The cultivated garden strawberry Fragaria × ananassa Duchesne is unusual for a domesticated crop. It is a homoploid hybrid of two wild octoploids, has a very recent domestication history (<300 years) that is well‐ documented, and the progenitor species and populations are well‐known (Darrow, 1966; Hardigan et al, 2021; Pincot et al, 2021).…”

“…It was these two species, Fragaria virginiana from North America and Fragaria chiloensis from South America, that would result in the spontaneous hybrid formation of the cultivated strawberry F . × ananassa throughout Europe in the 18th century after being transported from the western hemisphere (Darrow, 1966; Pincot et al, 2021). Their wide range, including sympatry in North America where natural hybrids have been previously observed (Dillenberger et al, 2018), and role as progenitors to an important agricultural crop has produced great interest from evolutionary biologists and ecologists as well as plant breeders.…”

Novel Fusarium wilt resistance genes uncovered in natural and cultivated strawberry populations are found on three non-homoeologous chromosomes

“… 2020 , 2021a ; Pincot et al. 2021 ). The host differential panel was assembled to maximize the probability of differentiating races and identifying sources of resistance to different Fof isolates (Online Resource 1).…”

“…We extracted the pedigree records for Wiltguard (an outlier in the CA population) and the 141 non-CA individuals from the database described by Pincot et al. ( 2021 ) to show that the genetic relationships among most of these individuals and their ascendants were complex and intertwined (Fig. 2 ; Online Resource 5).…”

“…They concluded that the resistant allele ( FW1 ) had fortuitously survived early breeding bottlenecks and originated in the earliest known ancestors of the California population (Pincot et al. 2018 , 2021 ; Hardigan et al. 2021a ).…”