Citrus fruits have been introduced to the Mediterranean area from Asia for centuries and spontaneous crosses have generated several hybrid forms, some of which have had agricultural or industrial success while others have remained niche food or ornamental products, or have disappeared. Pompia (C. medica tuberosa Risso & Poiteau) is an old endemic citrus fruit from Sardinia of unknown genetic origin. Initial phenotypic and molecular characterizations revealed a high degree of similarity with lemon (C. limon (L.) Burm.) and citron (C. medica L.). To identify the ancestors of Pompia, 70 citrus species of the Citrus genus were genotyped with 36 codominant molecular markers (SSR and InDel) of nuclear and cytoplasmic genomes. Diversity analysis and allelic comparisons between each citrus species at each locus indicated that Pompia resembles lemon and limonette of Marrakech, i.e. the result of a cross between sour orange (C. aurantium L.) and citron, where citron was the pollinator. Two Italian citron varieties were identified as potential male parents, i.e. Diamante and Common Poncire. However, we were unable to differentiate varieties of sour oranges because varietal diversification in this horticultural group resulted from DNA sequence variations that SSR or InDel markers could not reveal. Rhob el Arsa and Poncire de Collioure were found to be two synonyms of Pompia. Pompia appeared to be equally distinct from citron, lemon and sour orange based on the overall analysis of the fruit, leaf and seed phenotype, and juice chemical composition. At the leaf level, the Pompia essential oil (EO) composition is close to that of citron whereas the zest is much closer to that of sour orange.

Simple sequence repeats (SSR) markers and secondary metabolite composition were used in combination to study seven varieties of citrus for the first time. With reference to established accessions of citrus, two of the varieties (Chanh Giay and Ma Nao Pan) were predicted to be Mexican key limes, while three were mandarin hybrids (Nagpur, Pontianak and Dalandan) and the remaining two (Qicheng and Mosambi) were related to the sweet orange. Notably, Dalandan was genetically more like a mandarin despite often referred to as an orange locally, whereas Mosambi was more likely to be a sweet orange hybrid although it has also been called a sweet lime due to its green peel and small size. Several key secondary metabolites such as polymethoxyflavones (sinensetin, tangeretin etc.), furanocoumarins (bergapten, citropten etc.) and volatiles (citronellol, α-sinensal etc.) were identified to be potential biomarkers for separation of citrus species. However, despite having similar genetic profiles, variations in the volatile profile of the two limes were observed; similarly, there were differences in the secondary metabolite profiles of the three mandarin hybrids despite having a common ancestral parent, highlighting the usefulness of genetic and compositional analyses in combination for revealing both origins and flavour profiles especially in citrus hybrids. This knowledge would be crucial for variety screening and selection for use in flavour or fragrance creation and application.

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The great genetic and phenotypic diversities characterize the mandarin species (Citrus reticulata). The present study aimed to evaluate a part of this diversity with molecular markers and through the composition of leaf (LEO) and fruit peel (PEO) essential oils. Seventy-two cultivars were chosen for this study to represent some wild and cultivated mandarins growing in the same orchards. The essential oils were analyzed via gas chromatography (retention indices) and via gas chromatography coupled with mass spectrometry. The low similarity of ‘Tachibana’ and ‘Korail tachibana’ with mandarins and other species suggested that they were pure mandarins but were not involved in the genesis of the cultivated forms. This distinction was also evident at the aromatic level with specific compounds or unusual proportions, such as δ-3-carene in PEO or β-phellandrene at 24.9% in ‘Korail tachibana’ LEO. ‘Kunembo’ and ‘Ben di gang ju’ were genetically and chemically identical, with a high proportion of myrcene (>20%) in their LEO. In general, the genetic diversity of SSR markers was higher than the chemical diversity. From the 72 accessions, 54 genotypes were identified, with only 8 aromatic profiles in PEO and 9 in LEO. This diversity of essential oils of mandarins offers new perspectives for the research and validation of new aromatic properties for food and cosmetic purposes.