Inheritance and Quantitative Trait Loci Mapping of Aromatic Compounds from Clementine (Citrus × clementina Hort. ex Tan.) and Sweet Orange (C. × sinensis (L.) Osb.) Fruit Essential Oils

Abstract

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.

Keywords: blood sweet orange; essential oil yield; genetic linkage map; genotyping by sequencing; quantitative trait loci; single-nucleotide polymorphism markers.

Figure 1

Histogram depicting the distribution of essential oil yield expressed in g for 100 g of dry mass of peel of the population of 77 hybrids and the 2 parents.

Figure 2

Distribution of the representation of 31 aromatic compounds (expressed in %(w/w)) in the population of clementine × orange hybrids; the clementine and orange values are represented by orange and red dots, respectively.

Figure 3

Correlations between the 31 major compounds. The colored disc indicates the strength of the correlation (coefficient).

Figure 4

Heatmap representing the diversity of the 77 hybrids and their parents based on the amounts of the 31 major compounds. For each compound, the darker the box, the higher its value.

Figure 5

Histogram representing the distribution of the intensity of the sensory aroma notes (A) ‘orange’ and (B) ‘clementine’ among the progeny of 73 hybrids, from no aroma note (0) to very intense (4).

Figure 6

Marey diagram of the relationships between marker positions in the clementine pseudochromosome assembly Chr1 to Chr9 (ordinate) and positions on the genetic maps of LG1 to LG9 (abscissa). Red dots are SNP markers with congruent positions between the physical map and linkage groups. The green circle shows the zone with markers in the inverted position between the physical map and linkage group.

Figure 7

Manhattan plot representing SNP markers linked to decanal expression. Each point represents the genetic map position (in cM) of an SNP marker on an LG (abscissa) and its LOD score (on the ordinate) of linkage disequilibrium with decanal variation. The genetic distances on the x-axis are the sum of the lengths (in cM) of the nine linkage groups. The significance level (in red) of the LOD score was calculated via permutation test (p ≤ 0.05).

Figure 8

Graphical representation of the positions of QTLs on the 9 linkage groups with their marker density (horizontal black lines). The confidence intervals of the QTLs are represented to the right of each linkage group by colored rectangles: green corresponds to the aliphatic aldehydes, blue corresponds to the monoterpenes, red corresponds to the sesquiterpenes and black corresponds to PEO yield.