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

Bouffartigue C, Debille S, Fabreguettes O, Cabrer AR, Pereira-Lorenzo S, Flutre T, Harvengt L (2020)

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 significant structure and identified two clusters at 18 SSRs. One cluster gathers trees from south-east France and Corsica (RPP1), and another cluster gathers trees from all other sampled regions (RPP2). A substructure was detected at 10 SSRs suggesting differentiation within both RPP1 and RPP2. RPP1 was split between south-east France and Corsica. RPP2 was split between northwest France, Aveyron, Pyrenees, and a last cluster gathering individuals from several other regions.