Analysis of genetic relationship among Arbutus unedo L. genotypes using RAPD and SSR markers

The strawberry tree (Arbutus unedo L.) is an underutilized, drought tolerant, fire resistant species with a south western distribution in Europe, and with ecological and putative socio-economical impact in Portugal and Mediterranean countries. Our aim was to develop an appropriate set of molecular markers to enable genetic diversity to be assessed and to fingerprint Arbutus unedo genotypes for breeding and conservation purposes in Portugal. Twenty-seven trees from a broad geographic range were screened with 20 random amplified polymorphic DNA (RAPD primers) and 11 microsatellite markers (SSR). The RAPDs generated 124 bands, 57.3% of which were polymorphic, with an expected heterozygosity of 27%. We cross-amplified 11 SSR primers developed for Vaccinium spp., and 5 were found to be polymorphic in A. unedo, with 75% of expected heterozygosity, a number of alleles of 11.6, a null allele frequency of 7.6% and a polymorphic information content of 71%. Although the SSRs were more polymorphic and informative than the RAPDs, both markers displayed high genetic variability with the gathered data. No geographic pattern was observed in the genetic variation distribution based on both marker systems, and the lack of correlation between genetic and geographical matrices was confirmed by Mantel tests. Likely, no correlation was found between pairwise SSR and RAPD band-sharing matrices. These results and their implications on A. unedo breeding and conservation programs are discussed.