Genetic and morphological diversity of chestnut tree (Castanea sativa Mill.) in Lombardy sub mountain areas

Castanea sativa Mill. is a multi-functional species with a high ecological and cultural relevance. Thanks to its features, chestnut has become an essential element of subsistence for many societies in mountain and sub-mountainous areas.In this context, the principal aim of this study was to characterize the chestnut germplasm grown in pilot areas of the Lombardy Region (Municipality of Serle, province of Brescia, and the Varese Prealps, province of Varese) by integrating genetic and morphometric data analysis, in order to evaluate the regional chestnut genetic resources and promote their conservation. Twelve polymorphic microsatellite (SSRs) markers were used for genotyping 467 trees sampled between 2021 and 2022 in eight fruit tree orchards and three natural populations. Leaves and embryos were sampled for each individual to evaluate inter and intra-population gene flow. In parallel, a subset of fifty individuals from different collection sites were selected for replicated fruit morphological and nutritional analyses (specific carbohydrates, moisture, fat, protein, ash and fibers). The genetic data showed a number of clones identified as "Marrone" in Serle area. The analysis of the genetic structure, conducted with a Bayesian method and Principal Coordinates Analysis, showed different gene pools representing the two geographical areas. The combined data of mother plants and embryos from Varese showed high genetic similarity among individuals of the same area, whereas we found high genetic divergence between mother plants and embryos in Serle area. In addition, we found large inter-individual variation of several morphological traits, with the dimensional characteristics principally affected by local environmental drivers. Our results suggest that the genetic diversity and structure of the cultivated chestnut populations was shaped by different historical management systems in the two areas.