Two main genetic clusters with high admixture between forest and cultivated chestnut (Castanea sativa Mill.) in France

Abstract

& Key message A moderate genetic diversity, the absence of a significant genetic differentiation between wild and cultivated stands and a highly admixed genetic structure of sweet chestnut with two main clusters were observed in France using two different data sets with 10 and 18 microsatellites. & Context Renewed interest in European chestnut in France is focused on finding locally adapted populations partially resistant to ink disease and identifying local landraces. & Aims We genotyped trees to assess (i) the genetic diversity of wild and cultivated chestnut across most of its range in France, (ii) their genetic structure, notably in relation with the sampled regions, and (iii) to a lesser extent the relations between French chestnuts with 10 cultivated chestnuts from the Northwest of Spain that were previously classified in the Iberian or Italian groups. & Methods A total of 693 trees in 16 sampling regions in France were genotyped at 24 SSRs and 1401 trees in 17 sampling regions at 13 SSRs. & Results Genetic diversity was moderate in most sampling regions, with redundancy between them. No significant differentiation was found between wild and cultivated chestnut. A genetic structure analysis with no a priori information found a low yet Timothée Flutre and Luc Harvengt contributed equally to this work.

Gene flow between wild trees and cultivated varieties shapes the genetic structure of sweet chestnut (Castanea sativa Mill.) populations

“…The long history of broadening the natural distribution of sweet chestnut and the domestication within the range of local population had influenced the germplasm diversity of Switzerland 25 , whereas intermixing of the cultivated genes with the surrounding wild populations influenced the populations of Spain 51 and Italy 29 . In addition, in France 41 , Italy and Spain 38 , the interaction between the orchards and the wild populations can particularly be observed in the “instant domestication” cases, i.e., grafting of the spontaneously grown chestnuts, which diminishes the genetic differences between the orchard and the wild population.…”

“…Human influence on the species is also evident in the high number of marron varieties, with over 300 known in Italy alone 31 . The diversity of European marron varieties has been analyzed using gSSRs in Switzerland 32 , Italy 12 , 33 – 35 and the Iberian Peninsula 36 – 41 , as well as using the EST-SSRs markers in Italy and Spain 42 . In addition, researchers looked into introgression and hybridization between cultivated and wild populations 3 , 22 , 35 , 43 – 45 .…”

The demographic history of Castanea sativa Mill. in southwest Europe: A natural population structure modified by translocations

“…Finally, the germplasm WM3 present in stands 16, 18 and 24 (Figure 6a,b) probably comes from the naturalization of the traditional variety “Luguesa”, which could be an introduced variety in northwestern Iberia (Fernández‐López & Fernández‐Cruz, 2015), probably from southeast France (Bouffartigue et al, 2020). “Luguesa” is one of the earliest flushing and producing varieties in northwestern Iberia (Fernández‐López, 2014), a characteristic consistent with the hypothesized origin.…”

“…Finally, the germplasm WM3 present in stands 16, 18 and 24 (Figure 6a,b) probably comes from the naturalization of the traditional variety "Luguesa", which could be an introduced variety in northwestern Iberia (Fernández-López & Fernández-Cruz, 2015), probably from southeast France (Bouffartigue et al, 2020).…”

Development of Highly Validated SNP Markers for Genetics Analyses of Chestnut Species.

“…A number of molecular markers have been previously developed in chestnuts, especially SSRs (e.g. Buck et al 2003;Marinoni et al 2003;Durand et al 2010;Fernández-Cruz and Fernández-López 2012;Pereira-Lorenzo et al 2017;Bouffartigue et al 2020;Laurent et al 2020;Nishio et al 2021). However, SNPs have some important advantages over SSRs (Guichoux et al 2011).…”