Genetic diversity of on-farm selected olive trees in Moroccan traditional olive orchards
Selecting desired agronomic traits may lead to a loss of genetic diversity in crop species. A molecular investigation was conducted to determine how well a set of olive (Olea europaea L.) accessions sampled in Moroccan traditional orchards represented the entire Moroccan olive diversity range. We therefore collected, in traditional agroecosystems from northern and central Morocco, a total of 88 olive trees chosen for their agronomic traits based on local farmers' knowledge. Using 12 SSR loci, 45 trees (51.1%) had a genotype identical to the ‘Picholine Marocaine’ variety, while the remaining samples were classified into 27 different SSR profiles. Two categories of genotypes were identified: (i) genotypes closely related to the ‘Picholine Marocaine’ variety and probably resulting from intensive vegetative propagation from a limited number of clones, and (ii) genotypes displaying a high number of dissimilar alleles which may have originated from selected spontaneous seedlings. A significant difference in allelic richness was revealed between the 28 on-farm selected genotypes and the overall olive diversity, represented by 57 local genotypes, indicating that the on-farm selected trees represented a subsample of Moroccan genetic diversity. This could be explained by the prevalence of ‘Picholine Marocaine’ in traditional orchards, while some original genotypes with favourable agronomic traits resulting from local farmers' selection were also identified. Applying an ethnobotany approach combined with criteria to fulfil farmers' household needs could be particularly relevant and better explain the obtained results.