The genetic diversity of selections and wild populations of myrtle revealed by molecular geographic contexts.

Myrtus communis L. is an aromatic shrub widely diffused in the Mediterranean area. A growing interest for this species is due to its pharmacological and aromatic properties. This study explored the genetic diversity and population structure of 460 myrtle plants including 46 selections genotypes and 414 wild accessions from Sardinia using 14 SSR markers. Genetic diversity parameters showed that 10 markers were sufficiently polymorphic to move forward in the further analysis. The observed heterozygosity ranged from 0.21 (Porto Ferro) to 0.44 (Olia Speciosa), with an average value of 0.32. This parameter significantly varied considering the genetic origin of the plant (selections and natural), and the localization of the myrtle sampling sites (North, Center and South area) (P < 0.0001). The selections showed an observed heterozygosity's lower (0.40) compared to the wild group (0.45). Based on the geographic division of Sardinia, North region grouped myrtle accessions with the highest level of genetic diversity (0.45), followed by the Central area (0.43) and the South, that collect the lowest value (0.42). Bayesian clustering analysis divided the myrtle accessions in two principal groups, which are in accordance with the division in selections and natural populations. Significant different distribution of the two clusters was found: one cluster was mainly distributed in the South-Center of Sardinia, while the other cluster was predominant the North area (Pearson, P = 0.003). The results presented in this paper, and in particular the characterization of the in situ conserved germplasm, represent an important step for planning future ex situ collections to reinforce the genetic base of breeding programs, allowing to diversify the industrial potential of products derivatives from myrtle.