BackgroundDespite its primary economic importance, genomic information on olive tree is still lacking. 454 pyrosequencing was used to enrich the very few sequence data currently available for the Olea europaea species and to identify genes involved in expression of fruit quality traits.ResultsFruits of Coratina, a widely cultivated variety characterized by a very high phenolic content, and Tendellone, an oleuropein-lacking natural variant, were used as starting material for monitoring the transcriptome. Four different cDNA libraries were sequenced, respectively at the beginning and at the end of drupe development. A total of 261,485 reads were obtained, for an output of about 58 Mb. Raw sequence data were processed using a four step pipeline procedure and data were stored in a relational database with a web interface.ConclusionMassively parallel sequencing of different fruit cDNA collections has provided large scale information about the structure and putative function of gene transcripts accumulated during fruit development. Comparative transcript profiling allowed the identification of differentially expressed genes with potential relevance in regulating the fruit metabolism and phenolic content during ripening.

Cultivar identification is a primary concern for olive growers, breeders, and scientists. This study was aimed at examining the SSR markers retrieved from the literature and currently used in olive study, in order to select those most effective in characterizing the olive accessions and to make possible the comparison of data obtained by different laboratories. Olive microsatellite profiles were assessed by four independent laboratories, which analyzed 37 pre-selected SSR loci on a set of 21 cultivars. These SSR markers were initially tested for their reproducibility, power of discrimination and number of amplified loci/alleles. Independent segregation was tested for each pair of SSRs in a controlled cross and the allelic error rate was quantified. Some of them were finally selected as the most informative and reliable. Most of the alleles were sequenced and their sizes were determined. Profiles of the reference cultivars and a list of alleles with their sizes obtained by sequencing are reported. Several genetic parameters have been analysed on a larger set of cultivars allowing for a deeper characterization of the selected loci. Results of this study provide a list of recommended markers and protocols for olive genotyping as well as the allelic profile of a set of reference cultivars that would be useful for the establishment of a universal database of olive accessions

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RAPDs, AFLPs and SSRs were compared in terms of their informativeness and efficiency in a study of genetic diversity and relationships among 32 olive cultivars cultivated in Italy and Spain. SSRs presented a higher level of polymorphism and a greater information content, as assessed by the expected heterozygosity, than AFLPs and RAPDs. The lowest values of expected heterozygosity were obtained for AFLPs, which, nevertheless were the most efficient marker system due to their capacity to reveal the highest number of bands per reaction and because of the high values achieved for a considerable number of indexes. All three techniques discriminated the genotypes very effectively, but only SSRs were able to discriminate the cultivars Frantoio and Cellina. The correlation coefficients of similarity were statistically significant for all three marker systems used but were lower for the SSR data than for RAPDs and AFLPs. For all markers a high similarity in dendrogram topologies was obtained although some differences were observed. All the dendrograms, including that obtained by the combined use of all the marker data, reflect some relationships for most of the cultivars according to their geographic diffusion. AMOVA analysis detected greater genetic differentiation among cultivars within each country than it did between the two countries.

The olive (Olea europaea L.) is a typical important perennial crop species for which the genetic determination and even functionality of self‐incompatibility (SI) are still largely unresolved. It is still not known whether SI is under gametophytic or sporophytic genetic control, yet fruit production in orchards depends critically on successful ovule fertilization. We studied the genetic determination of SI in olive in light of recent discoveries in other genera of the Oleaceae family. Using intra‐ and interspecific stigma tests on 89 genotypes representative of species‐wide olive diversity and the compatibility/incompatibility reactions of progeny plants from controlled crosses, we confirmed that O. europaea shares the same homomorphic diallelic self‐incompatibility (DSI) system as the one recently identified in Phillyrea angustifolia and Fraxinus ornus. SI is sporophytic in olive. The incompatibility response differs between the two SI groups in terms of how far pollen tubes grow before growth is arrested within stigma tissues. As a consequence of this DSI system, the chance of cross‐incompatibility between pairs of varieties in an orchard is high (50%) and fruit production may be limited by the availability of compatible pollen. The discovery of the DSI system in O. europaea will undoubtedly offer opportunities to optimize fruit production.