Background: Domestication generally implies a loss of diversity in crop species relative to their wild ancestors because of genetic drift through bottleneck effects. Compared to native Mediterranean fruit species like olive and grape, the loss of genetic diversity is expected to be more substantial for fruit species introduced into Mediterranean areas such as apricot (Prunus armeniacaL.), which was probably primarily domesticated in China. By comparing genetic diversity among regional apricot gene pools in several Mediterranean areas, we investigated the loss of genetic diversity associated with apricot selection and diffusion into the Mediterranean Basin.Results: According to the geographic origin of apricots and using Bayesian clustering of genotypes, Mediterranean apricot (207 genotypes) was structured into three main gene pools: ‘Irano-Caucasian’, ‘North Mediterranean Basin’ and ‘South Mediterranean Basin’. Among the 25 microsatellite markers used, only one displayed deviations from the frequencies expected under neutrality. Similar genetic diversity parameters were obtained within each of the three main clusters using both all SSR loci and only 24 SSR loci based on the assumption of neutrality. A significant loss of genetic diversity, as assessed by the allelic richness and private allelic richness, was revealed from the ‘Irano-Caucasian’ gene pool, considered as a secondary centre of diversification, to the northern and southwestern Mediterranean Basin. A substantial proportion of shared alleles was specifically detected when comparing gene pools from the ‘North Mediterranean Basin’ and ‘South Mediterranean Basin’ to the secondary centre of diversification.Conclusions: A marked domestication bottleneck was detected with microsatellite markers in the Mediterranean apricot material, depicting a global image of two diffusion routes from the ‘Irano-Caucasian’ gene pool: North Mediterranean and Southwest Mediterranean. This study generated genetic insight that will be useful for management of Mediterranean apricot germplasm as well as genetic selection programs related to adaptive traits.

In order to optimize the management of genetic resources, in most cases a representative sample of the germplasm collections needs to be developed. The establishment of a core collection is thus of major importance either to minimize the cost associated with the management of the associated germplasm or to apply analysis onto representative bases. In order to select a representative core collection among the Tunisian apricot germplasm of 110 accessions large, the Maximization strategy algorithm was used. This algorithm was shown to be the most convenient when using both morphological traits and molecular markers. Three core collections based on morphological characters, molecular markers or the combined data were compared. Our data indicate that both the molecular and the morphological markers have to be considered to obtain a core collection that represents the global diversity of the 110 accessions. Using this method, a subset of 34 selected accessions was found to represent accurately the 110 accessions present in the whole collection (75 to 100% for the morphological characters and 97% of the molecular markers). These results show that the combination of molecular and morphological markers is an efficient way to characterize the apricot core collection and provides an exhaustive coverage for the analyzed diversity on morphological and genetic bases.

Graft and seed propagated apricots in North Africa (Algeria, Morocco and Tunisia) are identified as being from the southwestern Mediterranean gene pool. However, recently introduced varieties from northern Mediterranean areas are also encountered in this region. Do gene exchanges occur between local apricot and introduced varieties? We addressed this question by analyzing the genetic structure of 183 accessions using 24 nuclear microsatellite markers and a model-based Bayesian clustering method. We classified these accessions into 4 genetic clusters: cluster 1 from Morocco, cluster 2 from northern, central and southern Tunisia which were all propagated by grafting, cluster 3 from the oasis region in Tunisia and the Messaad region in Algeria, and finally, cluster 4 (green) included accessions belonging to the northern Mediterranean gene pool. These accessions were more diversified and genetically differentiated with respect to local North African apricot. The results revealed the presence of admixed accessions between the local gene pool and introduced varieties, mainly in seed propagated populations, thus highlighting the presence of gene exchanges between northern and southern Mediterranean countries. Our findings should be useful for improving the management and conservation of Maghrebian apricot genetic resources.