RAPD genetic diversity of Albanian olive germplasm and its relationships with other Mediterranean countries

RAPD markers were used for the study of 19Albanian olive cultivars and two wild olives (oleasters). A total of 76polymorphic bands (4.8 polymorphic markers per primer) out of 107 reproducible were obtained using 16 primers. The number of bands per primer ranged from 4 to 10,whereas the number of polymorphic bands ranged from 1 to 9, corresponding to 71%of the total amplification products. All the accessions could be identified by the combination of four primers: OPA-19;OPA-02; OPK-16 and OPP-19. The dendrogram,based on Jaccard's index, included three major groups according to their origin: 1)most of the cultivars from the area of Berat (South of Albania) 2) cultivars from the Centre and Centre-North of Albania and3) cultivars from the Centre and North-West of Albania along with the oleaster from Elbasan. In order to evaluate the origin of Albanian cultivars they were compared to those diffused in other countries like Greece, Italy and Turkey, due to geographical and historical affinity among these countries, by using a one way AMOVA. Although most of the genetic diversity was attributable to differences among cultivars within each country (91.47%) significantφ-values among countries(φ_st = 0.085; p < 0.001)suggested the existence of RAPD phenotypic differentiation. Significant φ-values in all pairs formed by Albania with the other countries were observed. These results are consistent with the autochthonous origin of Albanian cultivars. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genetic diversity and relationships between wild and cultivated olives (<Emphasis Type="Italic">Olea europaea</Emphasis> L.) in Sardinia as assessed by SSR markers

The genetic relationships within and between wild and cultivated olives were examined and clarified in an isolated and restricted area, such as the Mediterranean island of Sardinia. Wild (21 individuals) and cultivated olive trees (22 local cultivars from a germplasm collection and 35 ancient trees) were genotyped by means of 13 SSR loci. Five cases of synonymy were observed and nine distinct genotypes were identified in the collection. Five novel genotypes were also detected among the ancient trees. Differences on the allelic composition and heterozygosity levels were found between wild and cultivated trees. Model-based clustering method classified the olive trees into two major gene pools: (a) wild genotypes and (b) local cultivars from the collection and from heritage olives. Regarding the cultivated plant material, we observed that: (a) most of the Sardinian cultivars shared the same allelic profiles with the ancient cultivated trees and (b) the majority of these cultivars and all the novel genotypes were not related to any other cultivars included in this study. These findings as well as the detection of unique alleles and a certain wild genetic background at some cultivars revealed by the Bayesian analysis may indicate their autochthonous origin. The synonymy cases found between local cultivars and Italian mainland cultivars indicate interchange of genetic material among these growing areas, suggesting thus a possible allochthonous origin. The information obtained can assist in the management of an olive collection and sheds some light on the survival of true oleasters and the origin of Sardinian cultivars.     

SSR markers reveal the uniqueness of olive cultivars from the Italian region of Liguria

Twenty-three important Ligurian olive accessions corresponding to 16 cultivars were studied using 12 SSR markers and 40 Mediterranean cultivars were included in the study in order to investigate the relationships between Ligurian and Mediterranean germplasm. All SSRs produced polymorphic amplifications. One hundred and forty-nine alleles were found in the 63 accessions analysed. Twenty-two alleles were specific to germplasm from Liguria and of these 12 were unique to single cultivars. Heterozygosity and discriminating power calculated in this regional germplasm were high on average (0.70 and 0.74) and not so much lower than the values in the total sample that includes cultivars from different Mediterranean countries (0.77 and 0.88 respectively). No cases of genetic identities were found between Ligurian and Mediterranean accessions. Several cases of homonyms and synonyms within the Ligurian germplasm were explained. Cluster analysis generally revealed a clear discrimination of the profiles from Liguria and Italy with respect to the cultivars from other Mediterranean countries. Only one Ligurian cultivar, “Negrea”, appeared to have a different origin, grouping with the Mediterranean cultivars.     

Microsatellite marker-based identification of mother plants for the reliable propagation of olive (Olea europaea L.) cultivars in Australia

Summary

Olive production in Australia has continued to increase in recent years, however there remains a high degree of confusion on the genetic identities of the cultivars being grown. In the present study, seven microsatellite (simple sequence repeat; SSR) loci were used to identify a set of 53 olive tree samples from different sources. The microsatellite DNA profiles of all 53 tree samples, including seven unknown trees, were compared with the SSR profiles of 14 reference olive cultivars. A total of 60 fragments (alleles), averaging 8.57 alleles per microsatellite locus, were amplified. High average values were found for the observed heterozygosity, the expected heterozygosity, and the polymorphic information content (0.73, 0.74, and 0.72, respectively). While all seven microsatellite markers proved useful for characterisation and identification purposes, a combination of three SSR primer pairs (DCA9, DCA18, and EM030) was sufficient to distinguish all 53 olive samples. The microsatellite allelic profiles allowed the 53 tree samples to be grouped into 23 genotypes. The allelic profiles of 14 of these genotypes matched with their reference cultivars, while the genetic identities of the remaining nine genotypes could not be confirmed. Some of these unknown genotypes may have been derived from feral olive trees, or were due to mislabelling and/or planting errors among Australian olive cultivars. Our results confirm the usefulness of microsatellite markers as a tool for cultivar differentiation and identification, and indicate the need for reliable identification of mother plants for commercial propagation.     

Agronomic evaluation of seedlings from crosses between the main Spanish olive cultivar ‘Picual’ and two wild olive trees

Summary

Until recently, olive breeding programmes have been based exclusively on cultivated olive germplasm (Olea europaea subsp. europaea var. europaea), in contrast to breeding in other fruit crops where the use of wild relatives has been widely reported. In this study, ten agronomic traits were evaluated in two progenies derived from controlled crosses between the Spanish olive cultivar ‘Picual’ (female) and two wild (O. europaea subsp. europaea var. sylvestris) genotypes (males). The results of this evaluation were compared with the progenies of crosses between ‘Picual’ (female) and the three cultivars, ‘Sikitita’, ‘Meski’, and ‘Zaity’ (male). The two ‘Picual’ × wild genotype progenies had the highest mean values for vigour traits (i.e., tree height and trunk diameter). Progenies from both ‘Picual’ × wild genotype crossess also showed the highest percentages of trees (53.8% and 37.5%) with a short juvenile period, compared to the progenies from crosses between ‘Picual’ and each of the three cultivars ‘Sikitita’, ‘Meski’, and ‘Zaity’ (0%, 5%, and 3.6%, respectively). Significant differences were also observed between progenies in fruit traits as well as in oil contents and fruit weights. Progenies from both crosses with wild olive showed lower values for the fruit traits evaluated than the cultivated olive progenies. However, significant improvements were achieved compared to fruit traits in the wild parents. The implications of these results for the future use of wild germplasm in olive breeding programmes are discussed.     

Genetic characterization and identification of new accessions from Syria in an olive germplasm bank by means of RAPD markers

Thirty-two olive cultivar accessions from Syria, most of them obtained from collecting expeditions, were characterized by means of RAPD markers before being introduced in the World Germplasm Bank of Cordoba. A total of 79 polymorphic bands(6.1 polymorphisms per primer) out of 93(7.1 bands per primer) were scored for the13 primers used, corresponding to 84.9% of the amplification products. Thirty-one different genotypes were clearly discriminated. Differences were not found among the amplification profiles from different individuals of the same cultivar. Only two cases of mislabeling or errors of planting were found. Fourteen accessions corresponding to 6 homonyms were discriminated by RAPDs as different genotypes. The dendrogram obtained by RAPD analysis included three major groups. Some evidence of relationships of the Syrian accessions studied according to their geographic origin and/or diffusion was found. For instance, cultivars from the Central Syria (Tadmur/Palmyra)such as Toffahi', ‘Abbadi Abo Gabra’-1033,‘Abo Kanani’, ‘Shami’-1041, ‘Abbadi Shalal’ ‘Adgam’-844 and ‘Majhol’-1013 clustered in Group 1 and 2. Six cultivars from Northern Syria clustered in Group 2. But it was not found a geographic structure for the cultivars from South and West of Syria. These results agree with the hypothesis of autochthonous origin of most of the olive cultivars. Some associations between cultivars from Central Syria and their fruit size were observed. This suggests that fruit size was a criterion of local selection in olive cultivars of this area. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic diversity and relationships of wild and cultivated olives at regional level in Spain

Genetic diversity and relationships between local cultivars and wild olive trees from three important Spanish olive-growing regions, Andalusia (South), Catalonia and Valencia (from Eastern Mediterranean Coastal area), were studied by means of eight SSR loci. Distinct allelic composition and heterozygosity levels were found in wild olive populations and cultivars. The observed patterns of genetic variation revealed: a) the independent clustering of Andalusian wild olives in a separate gene pool, b) the belonging of wild populations and most cultivars from Catalonia to another gene pool, c) the joined clustering of Andalusian and a set of Valencian cultivars in a third gene pool, and d) clustering of wild individuals from Valencia to the three different gene pools. These results suggest that wild populations of Andalusia may represent true oleasters, the ones from Catalonia may be feral forms derived from cultivar seed spreading, while the population of Valencia seems to be the most admixed one. The significant differentiation between Andalusian and most Catalonian cultivars is indicating an independent selection of olive cultivars in the two regions. The detection of a certain wild genetic background in some Catalonian and Valencian cultivars and the similarity found between wild and cultivated forms may suggest the use of local wild trees in olive domestication. The proposed scenario for the development of olive cultivars in Andalusia includes an empirical selection of outstanding local wild genotypes followed by various generations of crosses and various replanting campaigns, as well as possible introductions of ancestral cultivars. Therefore, our findings would lead us to support the hypothesis that the current diversity found in Spanish olive cultivars may be regionally differentiated and due to both, autochthonous and allochthonous origin. The information obtained in this work gives insights into the genetic resources of the main olive producing country, demonstrating that wild olive populations and local cultivars both represent potential sources of useful variability for olive breeding programs.