Correspondence between the Compositional and Aromatic Diversity of Leaf and Fruit Essential Oils and the Pomological Diversity of 43 Sweet Oranges (Citrus x aurantium var sinensis L.)

Abstract

Orange (Citrus x aurantium var sinensis) is the most widely consumed citrus fruit, and its essential oil, which is made from the peel, is the most widely used in the food, perfume, and cosmetics industries. This citrus fruit is an interspecific hybrid that would have appeared long before our era and would result from two natural crosses between mandarin and pummelo hybrids. This single initial genotype was multiplied by apomictic reproduction and diversified by mutations to produce hundreds of cultivars selected by men essentially based on phenotypic characteristics of appearance, spread of maturity, and taste. Our study aimed to assess the diversity of essential oil composition and variability in the aroma profile of 43 orange cultivars representing all morphotypes. In agreement with the mutation-based evolution of orange trees, the genetic variability tested with 10 SSR genetic markers was null. The oils from peels and leaves extracted by hydrodistillation were analyzed for composition by GC (FID) and GC/MS and for aroma profile by the CATA (Check All That Apply) method by panelists. Oil yield varied between varieties by a factor of 3 for PEO and a factor of 14 for LEO between maximum and minimum. The composition of the oils was very similar between cultivars and was mainly dominated by limonene (>90%). However, small variations were observed as well as in the aromatic profile, with some varieties clearly distinguishing themselves from the others. This low chemical diversity contrasts with the pomological diversity, suggesting that aromatic variability has never been a selection criterion in orange trees.

Keywords: CATA; CCI; GC (FID); GC/MS; SSR; TSS; fruit shape; pulp acidity; yield of essential oil.

Figure 1

Boxplots representing the distribution of different phenotypic traits among 43 orange cultivars. (A) fruit weight, (B) fruit shape, (C) external fruit peel color, (D) number of fruit segments, (E) peel thickness, (F) total soluble solids, (G) titrated acidity, (H) yield of PEO, and (I) yield of LEO. PD: polar diameter, ED: equatorial diameter.

Figure 2

A heatmap representing the phenotypic diversity of the 43 orange cultivars based on the 8 pomological descriptors. The color range from yellow to dark red indicates the degree of value of the observed trait in the orange population, respectively, from weak to strong. Bloody cultivars are represented in red, navels in green, non-acidic in purple, and classic (blond) cultivars in black. PD: polar diameter, ED: equatorial diameter, CCI: citrus color index, NS: number of fruit segment, TSS: total soluble solids.

Figure 3

A heatmap representing the diversity of the 43 orange cultivars based on their composition of the 26 major leaf oil compounds. The color range from yellow to dark red indicates the degree of the observed trait value in the orange population. Bloody cultivars are represented in red, navels in green, acid-free in purple, and classic (blond) cultivars in black.

Figure 4

A heatmap representing the diversity of the 43 orange cultivars according to the 20 major peel oil compounds. The color range from yellow to dark red indicates the degree of value of the observed trait in the orange population, respectively, from weak to strong. Bloody cultivars are represented in red, navels in green, acid-free in purple, and classic (blond) cultivars in black.

Figure 5

Results of triangle tests conducted on essential oils from the peels of four orange cultivars. The stars above the arrows between two cultivars indicate that a significant difference was observed based on the triangle test (p ≤ 0.05).

Figure 6

Correspondence Factor Analysis (CFA) representing the diversity of the 43 orange cultivars according to the 15 descriptors (represented in blue) of the aroma profiles of the essential oils is significantly different between cultivars according to the Cochran test (p ≤ 0.05). ‘Blood’ cultivars are represented in red, ‘navel’ in green, ‘acidless’ in purple, and ‘blond’ cultivars in black.