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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. Conclusion: The genetic structure within and between our sampling regions is likely the result of natural events (recolonization after the last glaciation) and human activities (migration and exchanges). These advances on our knowledge of chestnut genetic diversity and structure will benefit conservation and help our local partners' valorization efforts. [ABSTRACT FROM AUTHOR]

Launched in 1987, the French National Programme for the Conservation of Native Elm Genetic Resources focused on the ex situ conservation of clones of adult field elms (Ulmus minor Mill.) survivors of the Dutch elm disease (DED) pandemic. It was later expanded to include the in situ dynamic conservation of populations of European white elm (U. laevis Pall.) and wych elm (U. glabra Huds.). The national collection contains 441 clones, partly characterized and evaluated in a European project. The pathological tests and experimental plantations did not reveal clones truly resistant to DED but provided material for the restoration of hedgerows. Two conservation units of white elm and one of wych elm were selected, enriching the pan-European EUFORGEN network for dynamic conservation of forest genetic resources. This programme provides feedback on genetic conservation strategies for forest trees in a health crisis. New partners are invited to make use of the scientific potential of the clone bank and experimental plots. [ABSTRACT FROM AUTHOR]