Whole genome scanning of a Mediterranean basin hotspot collection provides new insights into olive tree biodiversity and biology.

Olive tree (Olea europaea L. subsp. europaea var. europaea) is one of the most important species of the Mediterranean region and one of the most ancient species domesticated. The availability of whole genome assemblies and annotations of olive tree cultivars and oleaster (O. europaea subsp. europaea var. sylvestris) has contributed to a better understanding of genetic and genomic differences between olive tree cultivars. However, compared to other plant species there is still a lack of genomic resources for olive tree populations that span the entire Mediterranean region. In the present study we developed the most complete genomic variation map and the most comprehensive catalog/resource of molecular variation to date for 89 olive tree genotypes originating from the entire Mediterranean basin, revealing the genetic diversity of this commercially significant crop tree and explaining the divergence/similarity among different variants. Additionally, the monumental ancient tree 'Throuba Naxos' was studied to characterize the potential origin or routes of olive tree domestication. Several candidate genes known to be associated with key agronomic traits, including olive oil quality and fruit yield, were uncovered by a selective sweep scan to be under selection pressure on all olive tree chromosomes. To further exploit the genomic and phenotypic resources obtained from the current work, genome-wide association analyses were performed for 23 morphological and two agronomic traits. Significant associations were detected for eight traits that provide valuable candidates for fruit tree breeding and for deeper understanding of olive tree biology.

Protein and mineral nutrient contents in kernels from 72 sweet almond cultivars and accessions grown in France, Greece and Italy.

Almond protein and potassium (K), phosphorus (P), calcium (Ca) and magnesium (Mg) contents were determined in 72 cultivars and accessions grown in France, Greece and Italy, as part of the networking of European SAFENUT AGRI GEN RES project, which aimed to explore and valorize the almond genetic resources in Europe. Great variation was found in the nutrient content and the amount of nutrient supplied when consuming the recommended daily amount of one serving of almond, among the different genotypes assayed. The variation among the different genotypes was greatest for Ca, followed by the protein content; the latter also exhibited the lowest variation considering the harvest year. Results from a principal component analysis showed that P and Mg were the most discriminant elements for categorizing samples. Cluster analysis showed groups of samples with interesting characteristics for breeding. There was no clear distinction among the different origins of samples. Correlation analyses between weather conditions and the nutrients assayed showed that the mean temperature recorded in the period between March and September was positively correlated with Ca and P only in France, a place where the greatest climatic difference between years was observed.

AFLP reveals structural details of genetic diversity within cultivated olive germplasm from the Eastern Mediterranean.

Amplified fragment length polymorphism (AFLP) analysis was used to assess genetic inter-relationships among olive varieties cultivated in the Eastern Mediterranean Basin. The genotypes sampled included most of the important cultivars from Turkey, Greece and the Middle East and selected genotypes from the Western Mediterranean area. A total of 119 polymorphic markers were generated from five selective primer-pair combinations. The combined data sets generated by just two primer-pairs were adequate to discriminate between all 65 genotypes, while each primer-pair could individually identify up to 64 genotypes. A factorial correspondence analysis (FCA) plot indicated that the cultivars clustered into two relatively modestly defined groups. The first broad group was dominated by cultivars from Turkey but also included genotypes originating from the Middle East (Syria and Lebanon) that collectively formed a tight subcluster. The second group comprised Greek cultivars and those originating from the Western Mediterranean. A significant genetic distance value between Greek and Turkish cultivars was provided by an analysis of molecular variance (AMOVA). There was also evidence of substructure here, with an apparent separation of most Spanish and Italian clones. These findings are in general accordance to previous suggestions of an East-West divergence of olive cultivars, although the dichotomy is less extensive than reported previously and complicated by regional variation within each group.