Characterisation of nuclear microsatellite markers for Fraxinus excelsior L. and their transferability to six related species

Common ash (Fraxinus excelsior L.) is an economically and ecologically important tree species in Europe acutely threatened by ash dieback. Here, we present a new set of Simple Sequence Repeat markers for F. excelsior and six related ash species based on published in silico designed primers. Forty SSR markers, mainly from genic regions, were tested for amplification and polymorphism and characterized in two ash populations in Germany. Transferability of polymorphic markers to six related Fraxinus species (F. angustifolia, F. ornus, F. quadrangulata, F. pennsylvanica, F. americana and F. biltmoreana) was also assessed. Eighteen markers, predominantly from genic regions including three markers closely linked to candidate genes for ash dieback, were successfully amplified and polymorphic in F. excelsior, of which between 10 to 17 were transferable to one of the six related species. High genetic diversity was found in the two ash populations (N_a = 7.8 and 6.9, H_e = 0.71 and 0.68), while low genetic differentiation between populations (F_ST = 0.025) was observed. The newly characterised SSR markers extend the set of genetic markers available for F. excelsior and six other ash species for future studies on the genetic diversity and structure of ash populations.