Genetic variability of relict Rhododendron ferrugineum L. populations in the Northern Apennines with some inferences for a conservation strategy.

Rhododendron ferrugineum L. (Ericaceae) is a subalpine shrub that can be found throughout the Pyrenees and the Alps. The Northern Apennines are one of the southernmost limits of its geographical range. Local populations are very few, small and scattered over three mountain groups of the chain. In this study, the genetic diversity of such three Apennine populations (AP1, AP2 and AP3) was analysed and compared to the one of three populations from the near Maritime Alps and of six populations from the Central-Eastern Alps. Genetic variations across microsatellite markers revealed that the Apennine populations show some clonal individuals and the lowest genetic diversity values (AP1 and AP3 A[18] values are 2.46 and 2.31, respectively), as well as heterozygosity deficiency with respect to the Alpine populations. Genetic relationships among populations (Nei’s genetic distance) showed that, according to their geographical distribution, populations from the Central-Eastern Alps and from the Maritime Alps clustered in two separate groups, while the three Apennine populations were associated to either of the two main clusters. PCA analysis showed a clear separation of the three Apennine populations according to the high Fst values detected (AP1-AP2 = 0.427; AP1-AP3 = 0.446; AP2-AP3 = 0.325). Mantel test revealed a significant correlation between genetic and geographical distance matrices (r = 0.314, P = 0.001, 999 permutations). Considering the geographical and ecological peripheral condition of these populations and the high impact of the climatic changes on their habitat, we suggest an ex situ conservation strategy by a germplasm bank to preserve the most of their genetic variability.