Ash dieback is an often-fatal disease caused by the fungus Hymenoscyphus fraxineus (T. Kowalski) Baral, Queloz & Hosoya. It emerged in Europe during the 1990s and poses a substantial threat to ash populations. In Hungary, symptoms were first detected on common ash (Fraxinus excelsior L.) in 2008. The disease also severely impacts another native species, the narrow-leaved ash (Fraxinus angustifolia Vahl). An effective strategy for counteracting ash decline is to identify and utilize sources of tolerance. We are monitoring the health status of the selected trees that demonstrate low susceptibility (plus trees) and conducting molecular genetic studies to enable their genetic characterization and individual identification using 16 nuclear microsatellite (nSSR) markers. The PCoA (Principal Coordinates Analysis) separated the eight assessed groups into two distinct clusters based on the taxonomic traits. Based on the Structure analysis results, K = 2 was the most probable cluster number. Hybridization was also indicated in the case of several individuals across various groups. We intend to incorporate the results in the establishment of seed orchards using the selected plus trees, considering the taxonomical, geographical, and genetic distinctiveness of the different groups.
Molnár et al. (Wed,) studied this question.