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Despite their importance in food processing, perfumery and cosmetics, the inheritance of sweet orange aromatic compounds, as well as their yield in the fruit peel, has been little analyzed. In the present study, the segregation of aromatic compounds was studied in an F1 population of 77 hybrids resulting from crosses between clementine and blood sweet orange. Fruit-peel essential oils (PEOs) extracted by hydrodistillation were analyzed by gas chromatography coupled with flame ionization detection. Genotyping by sequencing was performed on the parents and the hybrids. The resulting “clementine × sweet blood orange” genetic map consists of 710 SNP markers distributed in nine linkage groups (LGs), representing the nine citrus chromosomes, and spanning 1054 centimorgans. Twenty quantitative trait loci (QTLs) were identified, explaining between 20.5 and 55.0% of the variance of the major aromatic compounds and PEO yield. The QTLs for monoterpenes and aliphatic aldehydes predominantly colocalized on LGs 5 and 8, as did the two QTLs for PEO yield. The sesquiterpene QTLs were located on LGs 1, 3, 6 and 8. The detection of major QTLs associated with the synthesis of aliphatic aldehydes, known for their strong aromatic properties, open the way for marker-assisted selection.

Rootstock is widely used for the cultivation of citrus fruits because it brings resistance or tolerance to diseases or environmental constrains and modulates the fruit quality. Polyploidization is a widespread improvement strategy in citrus. The objective was to evaluate the effect of rootstock and ploidy level on the composition of essential oils. Two trials were conducted, one displaying a 'Navelina' orange grafted on three rootstocks and a second combining two ploidy levels (di and tetraploid) of scion ('Pineapple' orange) and rootstock ('Carrizo' citrange). The composition of peel essential oil (PEO) was analyzed by gas chromatography coupled with mass spectrometry, and a panel of experts analyzed its flavor variation with a triangle test approach. The rootstock influenced the yield and composition of the orange PEO, with a low impact on flavor. Neither the rootstock nor the scion ploidy level affected the PEO yield. Only the tetraploid level of the scion significantly modified the PEO composition, reducing the oxygenated compound fraction. Sensitive significant differences were detected between the reference sample (diploid scion–diploid rootstock) and the three other combinations. These results suggest that for the profiling of an aromatic flavor, the rootstock is a key element as is the ploidy level of the scion.

The Papeda Citrus subgenus includes several species belonging to two genetically distinct groups, containing mostly little-exploited wild forms of citrus. However, little is known about the potentially large and novel aromatic diversity contained in these wild citruses. In this study, we characterized and compared the essential oils obtained from peels and leaves from representatives of both Papeda groups, and three related hybrids. Using a combination of GC, GC-MS, and 13C-NMR spectrometry, we identified a total of 60 compounds in peel oils (PO), and 76 compounds in leaf oils (LO). Limonene was the major component in almost all citrus PO, except for C. micrantha and C. hystrix, where β-pinene dominated (around 35%). LO composition was more variable, with different major compounds among almost all samples, except for two citrus pairs: C. micrantha/C. hystrix and two accessions of C. ichangensis. In hybrid relatives, the profiles were largely consistent with their Citrus/Papeda parental lineage. This high chemical diversity, not only among the sections of the subgenus Papeda, but also between species and even at the intraspecific level, suggests that Papeda may be an important source of aroma diversity for future experimental crosses with field crop species.

Sour oranges (Citrus aurantium L.) are well known in the processing and cosmetics industries for the aromatic properties of their essential oils. Intercultivar genetic and aromatic diversity is not well documented. The objective of this study was to evaluate the impact of morphological selection and genetic mechanisms of varietal diversification (mutation or hybridization) on the aromatic and odor variability of sour orange essential oils. Forty-five sour orange accessions from INRAE-CIRAD citrus Biological Resources Center (France) were assessed for ten simple sequence repeat (SSR) and 54 single nucleotide polymorphism (SNP) markers, nine morphochemical fruit traits and with the aromatic components of leaf and peel essential oils. Thirty-nine sour oranges displayed no intercultivar molecular polymorphism and six genotypes originated from interspecific hybridizations involving sour orange, citron, pummelo or mandarin. The peel essential oil (PEO) diversity was low, in accordance with the genetic diversity. The predominance of limonene (>90%) prevents any possible correlation to be made between the composition and the variation in sensory profiles detected by panelists. Few compounds in the leaf essential oil (LEO), such as linalool, linalyl acetate, α-terpineol and geraniol were significantly different across sour oranges varieties. The morphological fruit attributes mainly used in varietal selection differed highly across the main genetically identical group of sour orange accessions. These results confirm that mutation can generate variability in aromatic compounds and aromas and that their exploitation requires an improvement in characterization processes.

Orange fruit abscission usually occurs at the final stage of fruit maturation but in some areas of citrus production, in advance of the usual harvest period, and sometimes suddenly and intensely. The reasons for this precocious citrus fruit abscission remains unclear. Therefore, the aim of this study was to try to clarify what the determinants of this phenomenon are. A multi-site experimentation was carried out on six orange cultivars, in Corsica, Spain and Tunisia where the phenomenon of early massive fruit drop varies. Climatic parameters, fruit maturity parameters and fruit detachment force (FDF) were recorded along the fruit maturation period. Respectively to the fruit drop, the FDF decreased in Tunisia and in Spain until the fruit falls, whereas in Corsica, it remained relatively constant throughout fruit maturation. Although data on fruit maturity parameters (rind color, acidity and total soluble solids) differed at the three sites, their evolution was similar during the period of maturation. FDF was not related to changes in any fruit maturity parameters, and more likely depended on changes in temperatures on days when the mean temperature was above 13 °C. Massive fruit abscission could be linked to the earlier more rapid restart of vegetative growth in Tunisia and Spain than in Corsica.