Genetic Diversity Among Historical Olive (Olea europaea L.) Genotypes from Southern Anatolia Based on SSR Markers

Genetic variation and relationships between Azerbaijani and Turkish olive genetic resources

Olive (Olea europaea L.) is one of the most economically important crop from east to the west around the world. The aim of this research was to investigate the genetic relationship among 41 olive genotypes, including 11 well-known Turkish cultivars and 30 Azerbaijani olive genotypes using simple sequence repeat (SSR) markers. In this study, 19 SSR markers were amplified 115 polymorphic SSR alleles. The number of polymorphic alleles ranged from 3 to 10 with an average of 6.05. The observed heterozygosity (Ho) varied from 0.05 to 0.93 with an average of 0.63 and expected heterozygosity (He) differed from 0.26 to 0.86 with an average of 0.72. The polymorphism information content (PIC) ranged from 0.23 to 0.85 with a mean of 0.68. A UPGMA cluster analysis grouped olive genotypes into two distinct clusters and both clusters were divided into two subgroups. Similarly, STRUCTURE analysis assigned olive genotypes into two different gene pools (K = 2) and four gene pools were identified representing the two subgroups by STRUCTURE analysis for K = 4. The genetic similarity of olive genotypes ranged from 0.36 to 0.95. These results revealed that there was a high genetic variation among 30 Azerbaijani olive genotypes. 'Ayvalık 1'and 'Ayvalık 2' from Azerbaijani olive genotypes were different from Turkish local olive cultivar, "Ayvalık" indicating homonymy. This research also highlighted that Azerbaijani olive genotypes were totally distinct from Turkish olive cultivars demonstrating that these olive genotypes might have been imported to Azerbaijan from different countries other than Turkey. The outcomes of this study indicated that these diverse olive genotypes could be useful for development of new olive varieties in Azerbaijan and future breeding programs between two countries could be enhanced by means of these results.

Plasticity of fruit and oil traits in olive among different environments

Olive is a long-living perennial species with a wide geographical distribution, showing a large genetic and phenotypic variation in its growing area. There is an urgent need to uncover how olive phenotypic traits and plasticity can change regardless of the genetic background. A two-year study was conducted, based on the analysis of fruit and oil traits of 113 cultivars from five germplasm collections established in Mediterranean Basin countries and Argentina. Fruit and oil traits plasticity, broad-sense heritability and genotype by environment interaction were estimated. From variance and heritability analyses, it was shown that fruit fresh weight was mainly under genetic control, whereas oleic/(palmitic + linoleic) acids ratio was regulated by the environment and genotype by environment interaction had the major effect on oil content. Among the studied cultivars, different level of stability was observed, which allowed ranking the cultivars based on their plasticity for oil traits. High thermal amplitude, the difference of low and high year values of temperature, negatively affected the oil content and the oleic acid percentage. Information derived from this work will help to direct the selection of cultivars with the highest global fitness averaged over the environments rather than the highest fitness in each environment separately.

GBS-derived SNP catalogue unveiled wide genetic variability and geographical relationships of Italian olive cultivars

Information on the distribution of genetic variation is essential to preserve olive germplasm from erosion and to recover alleles lost through selective breeding. In addition, knowledge on population structure and genotype-phenotype associations is crucial to support modern olive breeding programs that must respond to new environmental conditions imposed by climate change and novel biotic/abiotic stressors. To further our understanding of genetic variation in the olive, we performed genotype-by-sequencing on a panel of 94 Italian olive cultivars. A reference-based and a reference-independent SNP calling pipeline generated 22,088 and 8,088 high-quality SNPs, respectively. Both datasets were used to model population structure via parametric and non parametric clustering. Although the two pipelines yielded a 3-fold difference in the number of SNPs, both described wide genetic variability among our study panel and allowed individuals to be grouped based on fruit weight and the geographical area of cultivation. Multidimensional scaling analysis on identity-by-state allele-sharing values as well as inference of population mixtures from genome-wide allele frequency data corroborated the clustering pattern we observed. These findings allowed us to formulate hypotheses about geographical relationships of Italian olive cultivars and to confirm known and uncover novel cases of synonymy.

Genetic flow among olive populations within the Mediterranean basin

Background

The olive tree is a typical crop of the Mediterranean basin where it shows a wide diversity, accounting for more than 2,600 cultivars. The ability to discriminate olive cultivars and determine their genetic variability is pivotal for an optimal exploitation of olive genetic resources.

Methods

We investigated the genetic diversity within 128 olive accessions belonging to four countries in the Mediterranean Basin (Italy, Algeria, Syria, and Malta), with the purpose of better understanding the origin and spread of the olive genotypes across Mediterranean Basin countries. Eleven highly polymorphic simple sequence repeat (SSR) markers were used and proved to be very informative, producing a total of 179 alleles.

Results

Cluster analysis distinguished three main groups according to their geographical origin, with the current sample of Maltese accessions included in the Italian group. Phylogenetic analysis further differentiated Italian and Maltese olive accessions, clarifying the intermediate position of Maltese accessions along the x/y-axes of principal coordinate analysis (PCoA). Model-based and neighbor clustering, PCoA, and migration analysis suggested the existence of two different gene pools (Algerian and Syrian) and that the genetic exchange occurred between the Syrian, Italian and Maltese populations.

Discussion

The close relationship between Syrian and Italian and Maltese olives was consistent with the historical domestication and migration of olive tree from the North Levant to eastern Mediterranean basin. This study lays the foundations for a better understanding of olive genetic diversity in the Mediterranean basin and represents a step toward an optimal conservation and exploitation of olive genetic resources.

Recent developments in olive (Olea europaea L.) genetics and genomics: applications in taxonomy, varietal identification, traceability and breeding

The latest results in DNA markers application and genomic studies in olive. Olive (Olea europaea L.) is among the most ancient tree crops worldwide and the source of oil beneficial for human health. Despite this, few data on olive genetics are available in comparison with other cultivated plant species. Molecular information is mainly linked to molecular markers and their application to the study of DNA variation in the Olea europaea complex. In terms of genomic research, efforts have been made in sequencing, heralding the era of olive genomic. The present paper represents an update of a previous review work published in this journal in 2011. The review is again mainly focused on DNA markers, whose application still constitutes a relevant percentage of the most recently published researches. Since the olive genomic era has recently started, the latest results in this field are also being discussed.