# Chemical variability of peel and leaf essential oils in the Citrus subgenus Papeda (Swingle) and relatives

Clémentine Baccati, Marc Gibernau, Mathieu Paoli, Patrick Ollitrault, Félix Tomi, Luro François

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## To cite this version:

Clémentine Baccati, Marc Gibernau, Mathieu Paoli, Patrick Ollitrault, Félix Tomi, et al.. Chemical variability of peel and leaf essential oils in the Citrus subgenus Papeda (Swingle) and relatives. Plants, 2021, 10 (6), pp.1117. 10.3390/plants10061117. [https://hal.science/hal-03262123](https://hal.science/hal-03262123)

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# Chemical variability of peel and leaf essential oils in the *Citrus* subgenus *Papeda* (Swingle) and relatives

Clémentine Baccati <fnref n="1" />, Marc Gibernau <fnref n="1" />, Mathieu Paoli <fnref n="1" />, Patrick Ollitrault <fnref n="2" />,<fnref n="3" />, Félix Tomi <fnref n="1" />, * and François Luro <fnref n="2" />

**Abstract:** Citrus fruits of the subgenus Papeda include little-exploited wild forms with a potentially large and original aromatic diversity. The essential oils obtained from peels and leaves of the folowing seven species of the Citrus subgenus Papeda,namely: C. hystrix, C. micrantha, C. macroptera, C. ichangensis (3 accessions), C. latipes (2 accessions), C. junos & C. macrophylla, were investigated by GC, GC-MS and 13C NMR spectrometry in order to describe the chemical variability. A total of 60 compounds were identified in peel oils, accounting for 91.6 to 100% of the total peel oil compo-sition. Limonene was the major component in almost all samples, excepted for C. micrantha & C. hystrix oils where β-pinene dominated. Concerning the leaf oils, 76 compounds were identified, accounting for 93.6% to 99.3% of the total composition. Among them, the major components were: citronellal for C. hystrix & C. micrantha; sabinene, linalool and β-pinene for C. macroptera; (E) and (Z) ocimene for two accessions of C. ichangensis, and sabinene for the third accession; limonene, linalool and citronellal for one accession of C. latipes, and γ-terpinene, geranial, neral and β-pinene for the other one; γ-terpinene, β-phellandrene and p-cymene for C. junos and finally geranial, neral and limonene for C. macrophylla. We highlighted here a strong chemical diversity not only among the sections of the subgenus Papeda, but also between the species of these sections, and even at an intraspecific level.

**Keywords:** Papeda; Citrus; essential oil; chemical composition; diversity

## 1. Introduction

Citrus trees are native to Southeast Asia and their exceptional diversity is the result of both migration and geographical isolation during its evolution time [1] (Wu et al. 2018, Nature). The current cultivated forms are the result of crosses between species that evolved in Southeast Asia [2–5] (Ollitrault et al. 2003; Nicolosi, 2007; Garcia-Lor et al. 2012; Wu et al. 2014). There are also Oceanic species such as the taxa Eremocitrus and Microcitrus. The main characteristic of citrus is the presence of highly aro-matic essential oils in tissue storage cells of the fruit, leaf and flower (petals). These es-sential oils are complex mixtures that can contain hundreds of compounds with a very wide chemical variability particularly prized by the aromatic and cosmetic industry [6] (Demarcq et al. 2021 JAFC). The composition of essential oils of the large majority of citrus fruits grown for consumption is very well documented [7] ("Citrus oils" book Dugo & Mondello 2011). A large part of the aromatic diversity found in citrus fruits is however under-exploited. For example, citrus fruits of the Papeda subgenus are largely unknown.

<footnote n="1">¹ Université de Corse-CNRS, UMR 6134 SPE, Route des Sanguinaires, 20000 Ajaccio, France;
clementine.baccati@gmail.com (C.B.); gibernau_m@univ-corse.fr (M.G.); paoli_m@univ-corse.fr (M.P.);
tomi_f@univ-corse.fr (F.T.)</footnote>

<footnote n="2">² UMR AGAP Institut, Univ Montpellier, CIRAD, INRAE, Institut Agro - 20230, San Giuliano, France</footnote>

<footnote n="3">³ CIRAD, UMR AGAP, F-20230 San Giuliano, France</footnote>

<footnote>* Correspondence: tomi_f@univ-corse.fr; tel.:+33-495-52-4122.</footnote>
Swingle (1943) considered that there were 2 subgenera in Citrus: Papeda and Citrus [8]. In the subgenus Papeda, he defined 2 sections (Papeda and Papedocitrus) with respectively 4 species (hystrix, macroptera, micrantha and celebica) listed in the first one and 2 species (C. ichangensis (Ichang papeda) and C. latipes (Khasi papeda)) in the second one. The section Papedocitrus is considered as intermediate between the two sub-genera Papeda and Citrus (Swingle 1943). In the chapter entitled "Botany of citrus and its wild relatives" Swingle & Reece (1967) described the subgenus Papeda as follows: "pulp-vesicles containing numerous droplets of acrid oil; petioles long and very broadly winged, but not cordate, often nearly as broad as the leaf blades; stamen usually free....flowers larger and petioles very long, 1.75-3 longer than broad" [9]. Recently, exploitation of the Citrus genome by molecular markers and sequencing has demonstrated that Papeda is a non-homogeneous group actually consisting of two very distinct (polyphyletic) genetic groups, one with C. hystrix (or C. micrantha) as a reference and the other with C. cavaleriei (or C. ichangensis) [1,10] (Wu et al. 2018; Talon et al. 2020). These two genetic groups are considered to be two ancestral species that have generated through outcrossing with other ancestral species (C. maxima, C. reticulata, C. medi-ca) some cultivated varieties such as Yuzu (C. reticulata × C. ichangensis) or Alemow (C. micrantha × C. medica) [1,11,12] (Ollitrault et al. 2012; Curk et al. 2016; Wu et al. 2018). Ollitrault et al. (2020) [13] proposed a new classification taking into account phyloge-netic relationships and sexual compatibility and give the correspondence with the former classifications built by Tanaka [14], Swingle and Reece [9], Zhang and Mabber-ley [15]. In the Papeda group, there are two true species, the first one is C. cavaleriei H. Lév. ex Cavalerie from West-central and Southwestern China, which includes C. ichangensis Swingle and C. latipes (Swingle) Tanaka. The second one is C. micrantha Wester from Southern Philippines, which includes two varieties micrantha (Biasong) and microcarpa (Samuyao) and Combava (C. hystrix DC) but named by Zhang & Mabberley, C. hystrix DC (2008) [15]. This new classification confirms in some ways that of Swingle and Reece who had divided the Papeda group into two sections. It should be noted that the classification of Melanesian papeda (including Eremocitrus and Microcitrus) has not been considered in this phylogenomic taxonomy. In terms of genetic diversity, there are very few studies concerning the Papeda group of Citrus. Those concerning C. macroptera [16] (Malik et al. 2013) and C. cavaleriei (or C. ichangen-sis) [17] (Yang et al. 2017) show nevertheless a great intraspecific genetic diversity.

Data concerning the chemical composition of peel and leaf oils from Citrus classi-fied as Papeda are scarce. The literature is mainly focused on cultivated hybrids, as C. junos known as Yuzu [18,19] (Uehara et al., 2000; Huang and Pu). Leaf oil composition was also reported in C. ichangensis [20–22] (Zhang et al food chem 2017; Liu plos one 2013, Zhang 2020). C. hystrix is also well described in the literature [21–24] (Dugo & DiGiacomo 2002, Waikedre, Zhang 2017, Zhang 2020), while C. macroptera leaf oil was only described by Huang et al. [19] and Waikedre et al. [24]. C. latipes and C. macro-phylla were described only once in the same publication [25] (Hijaz et al., 2016). For C. macrophylla it could be due to its only used as a rootstock for citrus cultivation [26] (Ollitrault and Luro 2001). To our knowledge, there is no chemical data concerning C. micrantha in the literature.

The chemical composition of peel and leaf essential oils determined by (i) Gas Chromatography associated by retention indices (RI) calculated for polar and apolar columns (GC-FID) with (ii) Gas Chromatography-mass spectrometry (GC-MS) provide abundant information, not only for metabolism-related research, but also for chemo-taxonomy. Thus, several papers developed this approach [27,28]
(Xi 2015; Jing 2015). The chemotaxonomy of Mangshanyegan (C. nobilis), was determined by comparison of volatile profiles of fruits and leaves and those of 29 other genotypes of Citrus, Poncirus, and Fortunella [20] (Liu Plos one 2013). The chemical components identified in the peels of 66 citrus germplasms from four Citrus species (mandarin, orange, pomelo and lemon) were used for biomarker mining, thirty potential biomarkers were identified and four compounds (β-elemene, valencene, nootkatone, and limettin) were validated as biomarkers after a study involving 30 Citrus germplasms [29] (Zhang et al., 2019). However, Luro et al. [30] found that the diversity based on leaf oil compositions from Citrus medica L. did not agree with the molecular diversity and was unsuitable for in-traspecific phylogenetic studies (phytochem 2012).

In this context, the aim of this study was to investigate the diversity of chemical composition of peel and leaf oils from Citrus belonging to the subgenus Papeda present in the INRAE-CIRAD CRB citrus germplasm bank (Corsica, France). All accessions are fully indexed in a plot with identical climatic and agronomic conditions of growing [31] (Luro et al. 2017 AGRUMED). These conditions are suitable to study the relation-ship between chemistry and taxonomy and to produce a reference data of Papeda peel and leaf oils composition. We analyzed ten samples from seven species: firstly 3 Papeda species (C. hystrix, C. micrantha and C. macroptera) and 2 Papedocitrus species (three ac-cessions of C. ichangensis and two accessions of C. latipes) to characterize the two sec-tions of the subgenus Papeda; and secondly 2 relatives species (C. junos and C. macro-phylla), in order to discuss the inheritance of chemical characters.

## 2. Results and Discussion

In total, 60 compounds were identified in peel oils, accounting for 91.6% to 100% of the total oil composition (Table 1), whereas 76 compounds were identified in leaf oils, accounting for 93.6% to 99.3% (Table 2).

### 2.1. Peel oils

Among the ten studied accessions, only nine peel oil samples were obtained by hydro-distillation of peels because one accession of C. ichangensis didn't produce a suf-ficient amount of fruits.

All the peel oil samples were widely dominated by monoterpene hydrocarbons, mostly because of the abundance of limonene (20.7 – 81.4%), as described in the litera-ture [23] (Dugo & Di Giacomo, 2002). Despite this common characteristic, several chemical profiles were observed.

#### 2.1.1. Section Papeda

C. hystrix & C. micrantha, showed low contents of limonene (respectively 25.2 and 20.7%) associated with higher contents in β-pinene, which was the major component (35.0 and 33.4%). While C. hystrix oil showed a large amount of sabinene (22.7%), C. micrantha oil contained a noticeable quantity of oxygenated monoterpenes with cit-ronellol (6.8%), α-terpineol (6.6%), terpinen-4-ol (3.8%), citronellyl acetate (3.1%) and other smaller components. According to the literature, this low content of limonene is usual in C. hystrix, the review of Lawrence [32] give the following main components : β-pinene (20.4
– 42.2%), sabinene (13.0 – 25.9%), citronellal (3.4 – 16.8%), limonene (2.8 – 14.2%), terpinen-4-ol (3.8 – 8.9%) and α-terpineol (1.7 – 7.4%) (Dugo & Di Giacomo, 2002, chapter 14).

C. macroptera oil exhibited limonene (53.8%), sabinene (12.4%) and beta-pinene (3.9%) associated with monoterpene alcohols such as linalool (11.8%) and ter-pinen-4-ol (4.3%). As observed for C. hystrix and C. micrantha, the percentage of oxy-genated monoterpenes was elevated (18.6%). This composition of C. macroptera peel oil is different than the one described by Rana & Blazquez [33] with 55.3% limonene, 4.7% of (E)-β-caryophyllene and 3.5% geraniol and the other one described by Miah et al. [34] with 73.5% limonene, 3.4% δ-cadinene and 3.0% α-terpineol.

### 2.1.2. Section Papedocitrus

C. ichangensis and C. latipes oils were characterized by high percentages of limo-nene varying between 42.3 and 66.9%. However, a strong chemical variability was observed for the Papedocitrus section. The accession ich-3 of C. ichangensis exhibit-ed a usual composition dominated by monoterpene hydrocarbons: limonene (58.2%), sabinene (9.6%), β-phellandrene (8.8%) and p-cymene (4.4%) and mostly terpinen-4-ol (7.3%) for the oxygenated compounds. Conversely, the accession ich-2 showed an atypical composition characterized by a ratio 1/1 of monoterpenes (42.8% of hydro-carbons and 1.9% of oxygenated monoterpenes) and sesquiterpenes (33.4% of hydro-carbons and 7.3% of oxygenated sesquiterpenes) and a noticeable quantity of acyclic compounds (6.0%). Moreover, the percentages of β-bisabolene (18.4%) and intermedeol (4.7%) were remarkable, likewise other sesquiterpenes identified in smaller propor-tions such as trans-α-bergamotene (3.2%), γ-muurolene (3.1%), valencene (2.7%) and (E)-nerolidol (1.6%). Although, a recent study revealed that among several C. ichangen-sis peel oils, one of them contained higher amounts of sesquiterpenes than monoter-penes [21] (Zhang et al., 2017). In this study, α-cadinene, β-bourbonene and the acyclic esters butyl butanoate and ethyl hexanoate were reported in C. ichangensis peel oil. Another study described the composition of C. ichangensis peel oil, with higher per-centage of limonene (61.0 – 70.4%) but similar amounts of β-bisabolene (9.3 – 13.0%) and (E)-nerolidol (3.1 – 3.9%) [20] (Liu et al, 2013). Our results agreed with published results about the presence of both acyclic compounds and a large range of sesquit-erperne hydrocarbons in C. ichangensis.

The two accessions of C. latipes peel oil lat-1 and lat-2 exhibited a slightly differ-ence in the percentage of limonene (66.9 vs. 50.4%) and also differed by the presence of myrcene in noticeable amount (18.8% and 1.6% respectively). No chemical data were found about peel oil of C. latipes in the literature.

### 2.1.3. Relatives

Peel oils of C. junos and C macrophylla were characterized by high contents of limonene, respectively 79.9 and 81.4%, and γ-terpinene, respectively 8.8 and 5.0%. The chemical composition we observed for C. junos is similar than those described by Dugo & Di Giacomo [23] with a percentage of limonene varying between 60.4 and 82.4%, mainly associated with γ-terpinene (7.6 – 10.7%) and linalool (0.9 – 5.6%). No data were found about peel oil composition of C. macrophylla.

These compositions widely dominated by limonene are frequently observed in many Citrus species such as C reticulata Blanco [35] (around 70%) and C. sinensis, C. aurantium, C. paradisi, C. aurantifolia [23] (around 90%) (Lota et al., 2000 and Dugo et Di Giacomo 2002). Citron (C. medica) peel oils are known to contain variable amounts of limonene (39.5 – 94.3%), either as the only major component or associated with ge-ranial/neral or γ-terpinene [36] (Venturini et al., 2010). In the same way, lemon
(C. limon) peel oils can contain uneven quantities of limonene (38.1 – 95.8%), in associa-tion or not with other major components like γ-terpinene, linalool, β-pinene [37] (Lota et al, 2002). Nevertheless, the proportion of limonene in peel essential oil of citrons (C. medica) and lemons (C. limon) is lower (between 40 and 50%) [23,30] (Luro et al. 2012; Dugo et Di Giacomo 2002 ). The two Citrus x Papeda hybrids, Alemow and Yuzu, have a higher proportion of limonene in the leaf essential oil than their two respective Citrus parents. These are 2 cases of transgressive inheritance already ob-served in a clementine x mandarin population [38] (Tomi et al. 2008).

In our sampling, Papedocitrus (C. ichangensis and C. latipes) peel oils constituted an intermediate between low amounts of limonene observed in Papeda section (around 25%) and high percentages (around 80%) in the relative species, C. junos & C. macro-phylla.

2.2. Leaf oils

The ten leaf oil samples exhibited a chemical composition dominated by mono-terpenes, as usually found in Citrus leaf essential oils [23] (Dugo & Di Giacomo. 2002). However, we observed a tremendous quantitative variability among the major com-ponents: sabinene (0 – 44.6%), β-pinene (0 – 15.7%), (Z)- β-ocimene (tr – 18.2%), (E)-β-ocimene (0.2 – 62.7%), γ-terpinene (0 – 28.2%), linalool (0.2 – 24.6%), citronellal (0 – 78.1%), neral (0 – 18.9%), geranial (0 – 24.7%).

C. hystrix, C. micrantha and C. macrophylla were dominated by oxygenated mono-terpenes, whereas C. junos, C. ichangensis (3 accessions) and C. macroptera were domi-nated by monoterpene hydrocarbons. The last species, C. latipes, exhibited a ratio be-tween hydrocarbon/oxygenated terpenes close to 1.

The yields of the ten leaf oil samples varied drastically between 0.015 to 0.18 % (Table 2). For example, the three samples of C. ichangensis exhibited very different yields and obviously, a strong intraspecific variability.

2.2.1. Section Papeda

Combava (C. hystrix DC.) & Biasong (C. micrantha Wester)

C. hystrix and C. micrantha leaf oils exhibited a close chemical composition strong-ly dominated by citronellal (respectively 78.1 and 76.1%) and its derivatives, citronel-lol (3.4 and 4.4%) and citronellyl acetate (0.7 and 5.1%).

Similar compositions were previously reported for C. hystrix oils: citronellal be-tween 58.9 and 81.5%, citronellol between 6.0 and 8.2% and citronellyl acetate between 0.9 and 5.1% [23] (Dugo & Di Giacomo. 2002). The recent review about C. hystrix re-vealed that some authors described leaf oils with 1.4 to 72.5% citronellal, while others described leaf oil dominated by limonene (40.7 – 83.9%) [39] (Agouillal et al, 2017). A New-Caledonian study showed a drastically different chemical composition of C. hys-trix leaf oil dominated by terpinen-4-ol (13.0%), β-pinene (10.9%), α-terpineol (7.6%) and citronellol (6.0%) with a very low content in citronellal (2.7%) [24] (Waikedre et al.. 2010). Finally, the study of Zhang et al. [22] show four accessions of C. hystrix, with different major components: one of them with citronellal and geranyl acetate, another one with geranial and geranyl acetate, and two with
geranyl acetate associated with either citronellal or geranial (Zhang et al. 2020). To our knowledge, there is no existing description of C. micrantha oil in the literature.

It's interesting to note that in many phylogeny studies, C. micrantha and C. hystrix are grouped together [40] (Froelicher 2011) or even formed a separate cluster [41,42] (Nicolosi et al., 2000; Penjor et al., 2013). In other studies without C. hystrix, C. micran-tha is still grouped with another lime, the Mexican lime [1,43] (Wu et al., 2018; Car-bonell-Cabalero et al., 2015). These phylogenetic studies seem indicate that in this case, genetics and chemistry agreed to consider C. micrantha and C. hystrix as related spe-cies. The recent publication of Ollitrault et al. (2020) [13] even consider them as syno-nyms.

### Melanesian papeda (C. macroptera Montr.)

The leaf oil of C. macroptera is characterized by large amounts of sabinene (32.4%), β-pinene (15.7%) and linalool (18.2%), as well as significant percentages of (E)-β-ocimene (8.6%) and terpinen-4-ol (3.8%).

Two articles reported the chemical composition of this essential oil. The first one reported was characterized by the pre-eminence of sabinene (20.9%) associated with geranyl acetate (15.5%), β-phellandrene (9.1%), geranial (8.7%), (E)-β-ocimene (8.0%) and neral (6.8%) [19] (Huang & Pu. 2000), whereas hydrocarbons were the main com-ponents in the second one: β-pinene (33.3%), α-pinene (25.3%), p-cymene (17.6%) and (E)-β-ocimene (6.7%), this time with very few sabinene (4.8%) and no geranyl acetate [24] (Waikedre et al).

So, the composition described herein produced a new chemical composition, sug-gesting a significant variability in this species, as previously observed with DNA mo-lecular markers [16] (Malik et al, 2013).

### 2.2.2. Section Papedocitrus

#### Ichang papeda (C. ichangensis Swingle)

The essential oils of C. ichangensis showed a significant intraspecific diversity. Two accessions, "ich-1" and "ich-2", were characterized by a dominance of the two (E) / (Z)- β-ocimenes, in variable amounts 18.2% / 62.7% and 13.0% / 32.4% respectively. The first accession ich-1 also showed appreciable amounts of linalool (9.3%) and linalyl ac-etate (10.8%). Moreover, these ocimene-type oils contained an appreciable amount of alismol (1.7 and 1.6%), an unusual sesquiterpene in Citrus genus. Indeed, occurrences of alismol in Citrus oils have already been found in kumquats (Fortunella genus) [44] (Sutour et al., 2015) and in C. x jambhiri [45] (Kasali et al., 2009). The third accession ich-3 is completely different and is dominated by sabinene (44.6%), associated with β-phellandrene (11.7%) and terpinen-4-ol (8.4%).

In a recent study, Zhang et al. [22] reported the chemical composition of ten ac-cessions of C. ichangensis (Zhang et al., 2020). Five over ten oil samples exhibited (E)-β-ocimene as major component, associated with linalyl acetate in four accessions and α-pinene in another one, whereas two over ten oil samples were dominated by sabinene, associated with γ-terpinene and limonene. In our sampling a similar ratio: 2/1 between these two compositions was observed. The three other accessions of C. ichangensis of this study are mostly composed of γ-terpinene for two of them, and li-nalyl acetate for the last one. Moreover, the authors indicated that percentages of ses-quiterpenes hydrocarbons such as (E)-β-caryophyllene, (E)-β-farnesene, β-elemene or germacrene D were punctually high, in the same way as in our sampling.
Another Citrus oil known to contain appreciable amount of ocimene is a lemon named "Poire du Commandeur" or "Peer lemon" (C. lumia), a supposed pumme-lo/mandarin hybrid [12] (Curk et al. 2016) characterized by high contents in β-pinene (41.4%) and (E)-β-ocimene (15.8%), associated with linalool (11.2%), limonene (8.6%) and sabinene (4.8%) [37] (Lota et al. 2002).

The strong intraspecific diversity observed at the level of aromatic compounds is in agreement with
the high genetic diversity of this taxa observed at the DNA level [17] (Yang et al. 2017).

Khasi papeda (C. latipes (Swingle) Tanaka)

The two accessions were characterized by a ratio hydrocarbon/oxygenated ter-penes close to 1 but
with drastically different chemical compositions. The first oil sam-ple lat-1 was dominated by limonene
(41.0%), associated with linalool (24.6%) and cit-ronellal (14.1%), while the second one lat-2 was
characterized by an association γ-terpinene (19.5%), geranial (15.6%) neral (11.6%) and β-pinene
(9,7%). We observed that citronellal (14.1%), citronellol (1.8%) and citronellyl acetate (1.0%), the main
components of C. hystrix and C. micrantha, presented a noticeable amount in lat-1 ac-cession.

The only description found in the literature gave neral as major component (24.6%), followed by an unusual high amount of undecanal (19.6%), β-phellandrene (11.4%), limonene (10.5%) and linalool (7.6%) [25] (Hijaz et al, 2016).

2.2.3. Relatives

Yuzu (C. junos Sieb. Ex Tan)

Fresh leaves of C. junos produced an essential oil composed of γ-terpinene (28.2%), p-cymene (11.4%), β-phellandrene (11.2%) and linalool (10.4%). This oil also showed appreciable amounts of p-cymenene (6.2%), (E)-β-ocimene (5.0%), α-pinene (4.8%), limonene (4.7%) and β-pinene (4.1%). It could be pointed out that this oil also exhibited 2,5-dimethoxy-p-cymene (1.4%), a compound not identified in others Papeda acces-sions.

The chemical composition of C. junos leaf oil is known to present a great chemical variability [23] (Dugo & Di Giacomo. 2002. chapter 14). A complete study concerning chemical composition of 110 Citrus species shows the intraspecific variability of C. ju-nos oils [19] (Huang & Pu. 2000). Ten cultivars of C. junos were investigated, showing very different profiles dominated by (i) methyl-N-methyl anthranilate (a compound rather known to be found in high contents in Citrus reticulata Blanco mandarins), or (ii) γ-terpinene, in proportions varying from 22.6 to 53.2%. Three accessions of this study exhibited a composition very similar to ours, with γ-terpinene (25.7 – 26.6%), p-cymene (11.5 – 12.8%), β-phellandrene (8.2 – 12.0%) and linalool (5.8 – 8.1%). An-other study gives a near chemical composition with the same major components but in a different ranking with 25.4% linalool, 15.6% γ-terpinene, 11.2% β-phellandrene and 9.5% p-cymene [46] (Kamiyama, 1970).

This chemical composition dominated by the association γ-terpinene/p-cymene/linalool is frequently
reported for mandarin leaf essential oils such as wase (C. unshiu), fuzhu (C. unshiu), owari (C unshiu),
kunembo (C. nobilis), szibat (C. suhuiensis) and sunki (C. sunki) [47] (Lota et al., 2001). This
characteristic of the chemical profile of Junos could be inherited from its male relative, the mandarin.
### Alemow (C. macrophylla Wester)

The leaf oil of C. macrophylla was characterized by large amounts of geranial (24.7%), neral (18.9%), limonene (17.7%) and in smaller proportions γ-terpinene (6.2%), p-cymene (4.3%), linalool (4.3%) and citronellal (3.5%).

A chemical composition reported in literature showed the same major components but in a different ranking: limonene (31.4%), geranial (22.8%), neral (16.1%) and citronellal (13.9%), followed by δ-3-carene (3.5%) and α-terpinene (3.4%) [25] (Hijaz et al., 2016).

This type of composition dominated by the association geranial/neral limonene is also found in leaf essential oils of citrons and some limes [37] (Lota et al., 2002). This characteristic of the chemical profile of Alemow might be inherited from its citron male relative.

## 3. Materials and Methods

### 3.1. Plant Material

According to the Swingle and Reece systematics (1967), ten accessions were selected to represent the diversity of the subgenus Papeda: three Ichang papeda (C. ichangensis Swing.) and two Khasi papeda (C. latipes (Swing.) Tan.) for section Papedocitrus, Biasong (C. micrantha Wester), Combava (C. hystrix D.C.) and Melanesian papeda (C. macroptera Montr.) for section Papeda. Two other Citrus species related to Papeda have been added: Alemow (C. macrophylla Wester; C. micrantha x C. medica) and Yuzu (C. junos Sieb. ex Tan.; C. ichangensis x C. reticulata) (Table 1). All the trees are maintained in the INRAE-CIRAD citrus collection (certified as Biological Resource Center (BRC) citrus NF96-600) localized in San Ghjulianu (France. Corsica): latitude 42°17′N; longitude 9°32′E; Mediterranean climate; average: rainfall and temperature: 840 mm and 15.2°C per annum, respectively; soil derived from alluvial deposits and classified as fersiallitic; pH range 6.0–6.6 [31] (Luro et al. 2017).

About 100 g of fruit peels and 200 g of leaves were randomly picked all around the tree. The fresh materials were submitted to water distillation for 3 hours using a Clevenger type apparatus. Peel oil yields being influenced by the presence of variable amounts of albedo during the peeling of the epicarp, they were not calculated. Distillation yields of leaf oils were calculated using the weight of essential oil/weight of fresh leaves ratio. Each sample was analyzed by gas chromatography with two columns and gas chromatography coupled with mass spectrometry (GC-MS) in order to determine the chemical composition. To avoid any misidentification, some samples, selected on the basis of the chromatogram profile, were analyzed with carbon-13 nuclear magnetic resonance (13C NMR) following a methodology developed in our laboratory [48] (Tomi et al., 1995).

### 3.2. Gas Chromatography (GC) Analysis

GC analyses were performed on a Clarus 500 FID gas chromatograph (Perki-nElmer, Courtaboeuf, France) equipped with two fused silica gel capillary columns (50 m x 0.22 mm, film thickness 0.25 µm), BP-1 (polydimethylsiloxane) and BP-20 (polyethylene glycol). The oven temperature was programmed from 60 to 220 °C at 2°C/min and then held isothermal at 220°C for 20 min, injector temperature: 250°C; detector temperature: 250°C; carrier gas: hydrogen (1.0 mL/min); split: 1/60. The relative pro-
portions of the oil constituents were expressed as percentages obtained by peak area normalization, without using correcting factors. Retention indices (RIs) were deter-mined relative to the retention times of a series of n-alkanes with linear interpolation ('Target Compounds' software of PerkinElmer). The EOs samples (50 mg) were diluted in 1mL deuterated chloroform (CDCl3).

### 3.3. Mass Spectrometry

The EOs were analyzed with a PerkinElmer TurboMass detector (quadrupole, Perkin Elmer, Courtaboeuf, France), directly coupled to a PerkinElmer Autosystem XL (PerkinElmer), equipped with a fused silica gel capillary column (50 m x 0.22 mm i.d.. film thickness 0.25 µm), BP-1 (polydimethylsiloxane). Carrier gas: helium at 0.8 mL/min; split: 1/75; injection volume: 0.5 µL; injector temperature: 250°C; oven tem-perature programmed from 60 to 220°C at 2°C/min and then held isothermal (20 min); ion source temperature: 250°C; energy ionization: 70 eV; electron ionization mass spectra were acquired over the mass range 40–400 Da. Oil samples were diluted in deuterated chloroform with 50 mg of essential oil in 1 mL of CDCl3.

### 3.4. NMR Analysis

13C NMR analyses were performed on an AVANCE 400 Fourier Transform spec-trometer (Bruker, Wissembourg, France) operating at 100.623 MHz for 13C, equipped with a 5 mm probe, in CDCl3, with all shifts referred to internal tetramethylsilane (TMS). 13C NMR spectra were recorded with the following parameters: pulse width (PW): 4 µs (flip angle 45°); acquisition time: 2.73 s for 128 K data table with a spectral width (SW) of 220.000 Hz (220 ppm); CPD mode decoupling; digital resolution 0.183 Hz/pt. The number of accumulated scans ranged from 2000–3000 for each sample (around 40 mg of oil in 0.5 mL of CDCl3). Exponential line broadening multiplication (1.0 Hz) of the free induction decay was applied before Fourier Transformation.

### 3.5. Identification of Individual Components

Identification of the components was based on: (i) comparison of their GC reten-tion indices (RIs) on polar and apolar columns. determined relative to the retention times of a series of n-alkanes with linear interpolation ('Target Compounds' software of PerkinElmer). with those of authentic compounds [49] (McLafferty & Stauffer. 1988); (ii) computer matching against commercial mass spectral libraries [50,51] (McLafferty & Stauffer. 1994; König et al., 2001) and by comparison of spectra with literature data [52,53] (Joulain & König. 1998; Adams. 2007) and (iii) comparison of the signals in the 13C NMR spectra of EOs with those of reference spectra compiled in the laboratory spectral library. with the help of a laboratory-made software [48,54,55] (Tomi et al.. 1995; Tomi & Casanova. 2006; Bighelli & Casanova. 2009). In the investi-gated samples. individual components were identified by NMR at contents as low as 0.5%.

## 4. Conclusions

The two sections of Papeda are clearly distinguishable in the compositions of both the leaf and the fruit peel essential oils. This supports the classification of Swingle who proposed two sections in Papeda. Furthermore, as stated in this classification, the sec-tion Papedocitrus is an intermediate
between the two subgenera Papeda and Citrus, and certain aromatic compounds, such as limonene content, seem to confirm this status.

A great chemical diversity was observed in leaf oils and peel oils of representa-tives of Papeda and Papedocitrus sections. However, for some of them (Biasong and Combava) the chemical profiles are very close, reflecting a close genetic relationship. On the other hand, the 3 representatives of C. ichangensis present very different pro-files as between the 2 of C. latipes. The two Citrus x Papeda hybrids demonstrate that crosses between these two taxa can create a high variability in the aromatic composi-tion of essential oils. Prospects for exploiting this aromatic diversity are offered by the combination of these little-known citrus fruits with field crop species.

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<table><caption>Table 1. Chemical composition of peel essential oils of nine *Papeda* oil samples</caption><thead><tr><th>N°</th><th>RI<sub>A</sub></th><th>RI<sub>P</sub></th><th>Name</th><th>hys</th><th>mic</th><th>mapt</th><th>lat-2</th><th>ich-3</th><th>lat-1</th><th>ich-2</th><th>jun</th><th>maph</th></tr></thead><tbody><tr><td>1</td><td>923</td><td>1022</td><td>α-thujene</td><td>0.2</td><td>0.1</td><td>0.1</td><td>0.4</td><td>0.1</td><td>1.0</td><td>-</td><td>0.4</td><td>0.3</td></tr><tr><td>2</td><td>931</td><td>1020</td><td>α-pinene</td><td>3.0</td><td>2.4</td><td>1.3</td><td>2.2</td><td>2.1</td><td>2.4</td><td>-</td><td>1.6</td><td>1.0</td></tr><tr><td>3</td><td>945</td><td>1070</td><td>camphene</td><td>0.2</td><td>0.3</td><td>-</td><td>tr</td><td>-</td><td>tr</td><td>-</td><td>-</td><td>-</td></tr><tr><td>4</td><td>966</td><td>1127</td><td>sabinene</td><td>22.7</td><td>1.0</td><td>12.4</td><td>0.1</td><td>9.6</td><td>0.3</td><td>0.1</td><td>0.1</td><td>0.1</td></tr><tr><td>5</td><td>972</td><td>1116</td><td>β-pinene</td><td>35.0</td><td>33.4</td><td>3.9</td><td>3.5</td><td>0.7</td><td>1.9</td><td>-</td><td>0.8</td><td>0.6</td></tr><tr><td>6</td><td>977</td><td>1221</td><td>butyl butyrate</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>2.4</td><td>-</td><td>-</td></tr><tr><td>7</td><td>981</td><td>1166</td><td>myrcene</td><td>0.9</td><td>1.0</td><td>2.1</td><td>1.6</td><td>2.1</td><td>18.8</td><td>0.2</td><td>1.9</td><td>1.6</td></tr><tr><td>8</td><td>996</td><td>UD</td><td>hexyl acetate</td><td>-</td><td>-</td><td>-</td><td>0.3</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>9</td><td>998</td><td>1170</td><td>α-phellandrene</td><td>-</td><td>0.1</td><td>-</td><td>0.2</td><td>0.3</td><td>-</td><td>-</td><td>0.4</td><td>-</td></tr><tr><td>10</td><td>1010</td><td>1185</td><td>α-terpinene</td><td>-</td><td>0.4</td><td>0.3</td><td>0.1</td><td>0.1</td><td>0.2</td><td>-</td><td>0.2</td><td>tr</td></tr><tr><td>11</td><td>1013</td><td>1276</td><td>p-cymene</td><td>0.7</td><td>0.8</td><td>1.1</td><td>7.0</td><td>4.4</td><td>6.5</td><td>0.3</td><td>1.3</td><td>2.6</td></tr><tr><td>12</td><td>1022</td><td>1215</td><td>β-phellandrene *</td><td>0.3</td><td>1.0</td><td>0.5</td><td>3.9</td><td>8.8</td><td>0.2</td><td>-</td><td>2.7</td><td>0.1</td></tr><tr><td>13</td><td>1022</td><td>1205</td><td>limonene *</td><td>25.2</td><td>20.7</td><td>53.8</td><td>66.9</td><td>58.2</td><td>50.4</td><td>42.3</td><td>79.9</td><td>81.4</td></tr><tr><td>14</td><td>1026</td><td>1237</td><td>(Z)-β-ocimene</td><td>-</td><td>-</td><td>-</td><td>-</td><td>tr</td><td>-</td><td>-</td><td>-</td><td>0.5</td></tr><tr><td>15</td><td>1037</td><td>1255</td><td>(E)-β-ocimene</td><td>-</td><td>0.4</td><td>0.2</td><td>0.2</td><td>0.1</td><td>0.1</td><td>-</td><td>0.4</td><td>0.8</td></tr><tr><td>16</td><td>1049</td><td>1251</td><td>γ-terpinene</td><td>-</td><td>1.3</td><td>1.0</td><td>10.1</td><td>1.0</td><td>16.2</td><td>-</td><td>8.8</td><td>5.0</td></tr><tr><td>17</td><td>1062</td><td>1446</td><td>cis-linalool oxide THF form</td><td>0.5</td><td>0.3</td><td>1.2</td><td>tr</td><td>tr</td><td>-</td><td>-</td><td>-</td><td>0.1</td></tr><tr><td>18</td><td>1075</td><td>1474</td><td>trans-linalool oxide THF form</td><td>0.3</td><td>0.2</td><td>0.6</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>0.1</td></tr><tr><td>19</td><td>1079</td><td>1288</td><td>terpinolene</td><td>-</td><td>1.1</td><td>0.3</td><td>0.5</td><td>0.3</td><td>0.7</td><td>-</td><td>0.4</td><td>0.2</td></tr><tr><td>20</td><td>1086</td><td>1551</td><td>linalool</td><td>0.9</td><td>2.2</td><td>11.8</td><td>0.3</td><td>0.7</td><td>0.1</td><td>0.4</td><td>1.0</td><td>0.3</td></tr><tr><td>21</td><td>1111</td><td>1565</td><td>cis-p-menth-2-en-1-ol</td><td>tr</td><td>-</td><td>0.2</td><td>-</td><td>0.3</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>22</td><td>1133</td><td>1574</td><td>isopulegol</td><td>-</td><td>1.5</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>23</td><td>1133</td><td>1483</td><td>citronellal</td><td>3.4</td><td>1.5</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>tr</td></tr><tr><td>24</td><td>1144</td><td>1567</td><td>isoneopulegol</td><td>-</td><td>1.0</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>25</td><td>1160</td><td>1672</td><td>cryptone</td><td>-</td><td>-</td><td>-</td><td>0.1</td><td>0.4</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>26</td><td>1163</td><td>1604</td><td>terpinen-4-ol</td><td>1.2</td><td>3.8</td><td>4.3</td><td>0.5</td><td>7.3</td><td>0.1</td><td>tr</td><td>0.1</td><td>0.1</td></tr><tr><td>27</td><td>1175</td><td>1699</td><td>α-terpineol</td><td>0.8</td><td>6.6</td><td>0.4</td><td>0.7</td><td>0.5</td><td>0.2</td><td>0.3</td><td>0.1</td><td>0.2</td></tr><tr><td>28</td><td>1173</td><td>1415</td><td>butyl hexanoate</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>1.5</td><td>-</td><td>-</td></tr><tr><td>29</td><td>1175</td><td>1417</td><td>hexyl butyrate</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>0.8</td><td>-</td><td>-</td></tr><tr><td>30</td><td>1199</td><td>1837</td><td>trans-carveol</td><td>0.2</td><td>-</td><td>-</td><td>tr</td><td>-</td><td>-</td><td>0.6</td><td>-</td><td>tr</td></tr><tr><td>31</td><td>1212</td><td>1769</td><td>citronellol</td><td>0.1</td><td>6.8</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>32</td><td>1217</td><td>1683</td><td>neral</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>0.5</td></tr><tr><td>33</td><td>1237</td><td>1851</td><td>geraniol</td><td>tr</td><td>1.0</td><td>0.1</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>34</td><td>1245</td><td>1753</td><td>geranial</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>0.6</td></tr><tr><td>35</td><td>1309</td><td>2275</td><td>limonene-1,2-diol</td><td>-</td><td>-</td><td>-</td><td>0.1</td><td>tr</td><td>-</td><td>0.6</td><td>-</td><td>-</td></tr><tr><td>36</td><td>1333</td><td>1697</td><td>α-terpinyl acetate</td><td>-</td><td>-</td><td>-</td><td>0.3</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>37</td><td>1334</td><td>1664</td><td>citronellyl acetate</td><td>-</td><td>3.1</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>38</td><td>1361</td><td>1759</td><td>geranyl acetate</td><td>1.1</td><td>2.1</td><td>-</td><td>tr</td><td>0.2</td><td>tr</td><td>-</td><td>-</td><td>0.1</td></tr><tr><td>39</td><td>1369</td><td>1611</td><td>hexyl hexanoate</td><td>0.1</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>0.5</td><td>-</td><td>-</td></tr><tr><td>40</td><td>1370</td><td>1614</td><td>butyl octanoate</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>0.8</td><td>-</td><td>-</td></tr><tr><td>41</td><td>1375</td><td>1492</td><td>α-copaene</td><td>0.3</td><td>0.2</td><td>0.4</td><td>-</td><td>-</td><td>-</td><td>0.1</td><td>-</td><td>tr</td></tr><tr><td>42</td><td>1387</td><td>1591</td><td>β-elemene</td><td>0.2</td><td>0.2</td><td>0.4</td><td>-</td><td>tr</td><td>-</td><td>-</td><td>-</td><td>0.1</td></tr><tr><td>43</td><td>1410</td><td>1569</td><td>cis-α-bergamotene</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>0.3</td><td>-</td><td>tr</td></tr><tr><td>44</td><td>1417</td><td>1597</td><td>(E)-β-caryophyllene</td><td>0.1</td><td>0.1</td><td>1.7</td><td>-</td><td>-</td><td>0.1</td><td>-</td><td>-</td><td>0.3</td></tr><tr><td>45</td><td>1417</td><td>1572</td><td>α-santalene</td><td>-</td><td>-</td><td>-</td><td>-</td><td>0.5</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>46</td><td>1432</td><td>1586</td><td>trans-α-bergamotene</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>3.2</td><td>-</td><td>0.6</td></tr><tr><td>47</td><td>1447</td><td>1667</td><td>(E)-β-farnesene</td><td>-</td><td>-</td><td>-</td><td>0.2</td><td>-</td><td>-</td><td>1.8</td><td>0.1</td><td>tr</td></tr></tbody></table>
<table><tbody><tr><td>48</td><td>1469</td><td>1688</td><td>γ-muurolene</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>3.1</td><td>-</td><td>-</td></tr><tr><td>49</td><td>1475</td><td>1708</td><td>germacrene D</td><td>-</td><td>0.2</td><td>0.3</td><td>-</td><td>0.1</td><td>0.7</td><td>-</td><td>0.6</td></tr><tr><td>50</td><td>1481</td><td>1718</td><td>β-selinene</td><td>-</td><td>tr</td><td>-</td><td>-</td><td>-</td><td>2.0</td><td>-</td><td>-</td></tr><tr><td>51</td><td>1488</td><td>1718</td><td>valencene</td><td>-</td><td>-</td><td>-</td><td>0.1</td><td>-</td><td>2.7</td><td>-</td><td>-</td></tr><tr><td>52</td><td>1490</td><td>1723</td><td>α-selinene</td><td>tr</td><td>tr</td><td>0.1</td><td>-</td><td>-</td><td>0.7</td><td>-</td><td>-</td></tr><tr><td>53</td><td>1495</td><td>1750</td><td>(E,E)-α-farnesene</td><td>-</td><td>1.7</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>0.1</td></tr><tr><td>54</td><td>1500</td><td>1727</td><td>β-bisabolene</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>18.4</td><td>-</td><td>0.9</td></tr><tr><td>55</td><td>1505</td><td>1758</td><td>γ-cadinene</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>1.1</td><td>-</td><td>-</td></tr><tr><td>56</td><td>1513</td><td>1757</td><td>δ-cadinene</td><td>0.1</td><td>0.3</td><td>0.5</td><td>tr</td><td>-</td><td>-</td><td>-</td><td>0.1</td></tr><tr><td>57</td><td>1548</td><td>2043</td><td>(E)-nerolidol</td><td>-</td><td>tr</td><td>0.2</td><td>-</td><td>0.9</td><td>1.6</td><td>-</td><td>-</td></tr><tr><td>58</td><td>1550</td><td>1826</td><td>germacrene B</td><td>-</td><td>0.3</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>tr</td></tr><tr><td>59</td><td>1611</td><td>2254</td><td>alismol</td><td>-</td><td>0.3</td><td>0.1</td><td>-</td><td>-</td><td>1.0</td><td>-</td><td>0.1</td></tr><tr><td>60</td><td>1641</td><td>2229</td><td>intermedeol</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>4.7</td><td>-</td><td>-</td></tr><tr><td colspan="4">Monoterpene hydrocarbon</td><td>88.2</td><td>63.7</td><td>76.9</td><td>96.7</td><td>87.7</td><td>98.7</td><td>42.8</td><td>98.7</td><td>94.3</td></tr><tr><td colspan="4">Oxygenated monoterpene</td><td>8.5</td><td>30.1</td><td>18.6</td><td>2.0</td><td>9.4</td><td>0.4</td><td>1.9</td><td>1.2</td><td>2.0</td></tr><tr><td colspan="4">Sesquiterpene hydrocarbon</td><td>0.7</td><td>3.2</td><td>3.4</td><td>0.3</td><td>0.6</td><td>0.7</td><td>33.4</td><td>0.1</td><td>2.6</td></tr><tr><td colspan="4">Oxygenated sesquiterpene</td><td>0.0</td><td>0.3</td><td>0.3</td><td>0.0</td><td>0.9</td><td>0.0</td><td>7.3</td><td>0.0</td><td>0.1</td></tr><tr><td colspan="4">Acyclic compound</td><td>0.1</td><td>0.0</td><td>0.0</td><td>0.3</td><td>0.0</td><td>0.0</td><td>6.0</td><td>0.0</td><td>0.0</td></tr><tr><td colspan="4">TOTAL</td><td>97.5</td><td>97.3</td><td>99.3</td><td>99.3</td><td>98.6</td><td>99.9</td><td>91.5</td><td>100.0</td><td>98.9</td></tr></tbody></table>

Order of elution and relative percentages of individual components are given on an apolar column (BP-1) excepted those with an asterisk (*) for which percentages were taken on polar column (BP-20); RI<sub>A</sub>. RI<sub>P</sub>: retention indices measured on apolar and polar capillary columns respectively; tr: trace level (<0.05%); hys: C. hystrix, mic: C. micrantha, mapt: C. macroptera, lat: C. latipes, ich: C. ichangensis, jun: C. junos, maph: C. macrophylla.
<table><caption>Table 2. Chemical composition of leaf essential oil of ten *Papeda* oil samples.</caption><thead><tr><th>N°</th><th>RI<sub>A</sub></th><th>RI<sub>P</sub></th><th>Name</th><th>hys</th><th>mic</th><th>mapt</th><th>ich-1</th><th>ich-2</th><th>ich-3</th><th>lat-1</th><th>lat-2</th><th>jun</th><th>maph</th></tr></thead><tbody><tr><td>1</td><td>923</td><td>1022</td><td>α-thujene</td><td>tr</td><td>-</td><td>0.3</td><td>-</td><td>tr</td><td>0.5</td><td>-</td><td>0.8</td><td>2.0</td><td>0.2</td></tr><tr><td>2</td><td>931</td><td>1020</td><td>α-pinene</td><td>0.1</td><td>-</td><td>2.0</td><td>tr</td><td>tr</td><td>2.2</td><td>0.1</td><td>2.0</td><td>4.8</td><td>0.5</td></tr><tr><td>3</td><td>965</td><td>1342</td><td>6-methyl-5-hepten-2-one</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>0.3</td><td>-</td><td>0.5</td></tr><tr><td>4</td><td>966</td><td>1127</td><td>sabinene</td><td>3.0</td><td>tr</td><td>32.4</td><td>-</td><td>tr</td><td>44.6</td><td>0.2</td><td>1.4</td><td>0.7</td><td>0.1</td></tr><tr><td>5</td><td>972</td><td>1116</td><td>β-pinene</td><td>0.5</td><td>0.1</td><td>15.7</td><td>-</td><td>tr</td><td>1.6</td><td>0.3</td><td>9.7</td><td>4.1</td><td>0.5</td></tr><tr><td>6</td><td>981</td><td>1166</td><td>myrcene</td><td>0.5</td><td>0.4</td><td>1.8</td><td>1.7</td><td>1.1</td><td>2.3</td><td>0.7</td><td>0.8</td><td>1.4</td><td>0.6</td></tr><tr><td>7</td><td>998</td><td>1170</td><td>α-phellandrene</td><td>-</td><td>-</td><td>0.2</td><td>0.1</td><td>0.1</td><td>1.3</td><td>-</td><td>0.3</td><td>1.7</td><td>-</td></tr><tr><td>8</td><td>1006</td><td>1153</td><td>δ 3 carene</td><td>tr</td><td>-</td><td>1.9</td><td>0.4</td><td>0.7</td><td>-</td><td>-</td><td>-</td><td>-</td><td>tr</td></tr><tr><td>9</td><td>1010</td><td>1185</td><td>α-terpinene</td><td>0.1</td><td>-</td><td>1.0</td><td>-</td><td>-</td><td>2.2</td><td>-</td><td>0.3</td><td>0.8</td><td>tr</td></tr><tr><td>10</td><td>1013</td><td>1276</td><td>p-cymene</td><td>tr</td><td>-</td><td>0.1</td><td>-</td><td>tr</td><td>0.2</td><td>0.2</td><td>5.1</td><td>11.4</td><td>4.3</td></tr><tr><td>11</td><td>1022</td><td>1215</td><td>β-phellandrene *</td><td>0.1</td><td>-</td><td>0.7</td><td>0.1</td><td>0.1</td><td>11.7</td><td>tr</td><td>3.4</td><td>11.2</td><td>-</td></tr><tr><td>12</td><td>1022</td><td>1205</td><td>limonene *</td><td>2.4</td><td>0.1</td><td>2.7</td><td>0.4</td><td>0.1</td><td>3.1</td><td>41.0</td><td>4.0</td><td>4.7</td><td>17.7</td></tr><tr><td>13</td><td>1026</td><td>1237</td><td>(Z)-β-ocimene</td><td>tr</td><td>0.1</td><td>1.8</td><td>13.0</td><td>18.2</td><td>0.7</td><td>0.1</td><td>0.1</td><td>0.2</td><td>0.3</td></tr><tr><td>14</td><td>1037</td><td>1255</td><td>(E)-β-ocimene</td><td>0.2</td><td>0.6</td><td>8.6</td><td>32.4</td><td>62.7</td><td>3.7</td><td>2.2</td><td>3.0</td><td>5.1</td><td>0.6</td></tr><tr><td>15</td><td>1049</td><td>1251</td><td>γ-terpinene</td><td>0.5</td><td>-</td><td>1.6</td><td>tr</td><td>-</td><td>3.5</td><td>0.1</td><td>19.5</td><td>28.2</td><td>6.2</td></tr><tr><td>16</td><td>1057</td><td>1467</td><td>trans-sabinene hydrate</td><td>tr</td><td>tr</td><td>0.2</td><td>-</td><td>-</td><td>0.6</td><td>-</td><td>-</td><td>tr</td><td>tr</td></tr><tr><td>17</td><td>1062</td><td>1446</td><td>cis-linalool oxide THF form</td><td>tr</td><td>tr</td><td>1.1</td><td>-</td><td>tr</td><td>0.2</td><td>0.1</td><td>tr</td><td>-</td><td>0.2</td></tr><tr><td>18</td><td>1073</td><td>1442</td><td>p-cymenene</td><td>-</td><td>-</td><td>-</td><td>-</td><td>tr</td><td>-</td><td>tr</td><td>-</td><td>6.2</td><td>-</td></tr><tr><td>19</td><td>1075</td><td>1474</td><td>trans-linalool oxide THF form</td><td>tr</td><td>-</td><td>0.6</td><td>-</td><td>tr</td><td>0.1</td><td>tr</td><td>-</td><td>-</td><td>0.1</td></tr><tr><td>20</td><td>1079</td><td>1288</td><td>terpinolene</td><td>0.1</td><td>tr</td><td>0.7</td><td>0.3</td><td>tr</td><td>0.8</td><td>tr</td><td>0.9</td><td>2.0</td><td>0.2</td></tr><tr><td>21</td><td>1086</td><td>1551</td><td>linalool</td><td>3.4</td><td>1.2</td><td>18.2</td><td>9.3</td><td>0.2</td><td>1.0</td><td>24.6</td><td>6.1</td><td>10.4</td><td>4.3</td></tr><tr><td>22</td><td>1087</td><td>1550</td><td>cis-sabinene hydrate</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>0.5</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>23</td><td>1111</td><td>1565</td><td>cis-p-menth-2-en-1-ol</td><td>-</td><td>-</td><td>0.2</td><td>-</td><td>-</td><td>0.5</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>24</td><td>1117</td><td>1375</td><td>allo-ocimene</td><td>-</td><td>-</td><td>-</td><td>0.4</td><td>0.4</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>25</td><td>1126</td><td>1630</td><td>trans-p-menth-2-en-1-ol</td><td>-</td><td>-</td><td>0.1</td><td>-</td><td>-</td><td>0.3</td><td>-</td><td>-</td><td>0.6</td><td>-</td></tr><tr><td>26</td><td>1133</td><td>1574</td><td>isopulegol</td><td>0.8</td><td>0.9</td><td>-</td><td>-</td><td>-</td><td>-</td><td>0.2</td><td>-</td><td>-</td><td>0.1</td></tr><tr><td>27</td><td>1133</td><td>1483</td><td>citronellal</td><td>78.1</td><td>76.1</td><td>-</td><td>-</td><td>-</td><td>0.3</td><td>14.1</td><td>1.0</td><td>-</td><td>3.5</td></tr><tr><td>28</td><td>1145</td><td>1567</td><td>isoneopulegol</td><td>0.3</td><td>0.3</td><td>-</td><td>-</td><td>-</td><td>-</td><td>tr</td><td>-</td><td>-</td><td>-</td></tr><tr><td>29</td><td>1159</td><td>UD</td><td>isogeranial</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>0.2</td><td>tr</td><td>0.4</td></tr><tr><td>30</td><td>1163</td><td>1604</td><td>terpinen-4-ol</td><td>0.3</td><td>-</td><td>3.8</td><td>tr</td><td>tr</td><td>8.4</td><td>-</td><td>0.4</td><td>0.2</td><td>0.2</td></tr><tr><td>31</td><td>1175</td><td>1699</td><td>α-terpineol</td><td>0.1</td><td>-</td><td>0.2</td><td>3.1</td><td>tr</td><td>0.3</td><td>0.1</td><td>0.3</td><td>0.1</td><td>0.6</td></tr><tr><td>32</td><td>1212</td><td>1769</td><td>citronellol</td><td>3.4</td><td>4.4</td><td>-</td><td>-</td><td>-</td><td>0.1</td><td>1.8</td><td>0.2</td><td>-</td><td>0.1</td></tr><tr><td>33</td><td>1212</td><td>1804</td><td>nerol</td><td>0.1</td><td>-</td><td>-</td><td>0.8</td><td>-</td><td>0.1</td><td>0.1</td><td>2.3</td><td>-</td><td>0.2</td></tr><tr><td>34</td><td>1215</td><td>1597</td><td>thymyl methyl oxide</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>0.3</td><td>-</td></tr><tr><td>35</td><td>1217</td><td>1683</td><td>neral</td><td>tr</td><td>-</td><td>-</td><td>-</td><td>-</td><td>0.1</td><td>0.8</td><td>11.6</td><td>-</td><td>18.9</td></tr><tr><td>36</td><td>1237</td><td>1851</td><td>geraniol</td><td>0.6</td><td>1.2</td><td>-</td><td>2.3</td><td>tr</td><td>0.3</td><td>0.1</td><td>0.4</td><td>-</td><td>0.6</td></tr><tr><td>37</td><td>1241</td><td>1560</td><td>linalyl acetate</td><td>-</td><td>-</td><td>-</td><td>10.8</td><td>-</td><td>-</td><td>0.1</td><td>-</td><td>-</td><td>0.2</td></tr><tr><td>38</td><td>1245</td><td>1753</td><td>geranial</td><td>0.1</td><td>-</td><td>-</td><td>-</td><td>tr</td><td>0.2</td><td>1.0</td><td>15.2</td><td>-</td><td>24.7</td></tr><tr><td>39</td><td>1268</td><td>2192</td><td>thymol</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>1.1</td><td>-</td></tr><tr><td>40</td><td>1303</td><td>1697</td><td>methyl geranate</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>0.7</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>41</td><td>1334</td><td>1664</td><td>citronellyl acetate</td><td>0.7</td><td>5.1</td><td>-</td><td>-</td><td>-</td><td>0.3</td><td>1.0</td><td>-</td><td>-</td><td>0.4</td></tr><tr><td>42</td><td>1335</td><td>1472</td><td>δ-elemene</td><td>-</td><td>0.3</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>0.3</td><td>0.1</td><td>0.1</td></tr><tr><td>43</td><td>1343</td><td>1728</td><td>neryl acetate</td><td>0.1</td><td>tr</td><td>-</td><td>1.2</td><td>-</td><td>0.2</td><td>0.1</td><td>1.1</td><td>-</td><td>0.5</td></tr><tr><td>44</td><td>1361</td><td>1759</td><td>geranyl acetate</td><td>1.2</td><td>2.9</td><td>-</td><td>2.4</td><td>-</td><td>5.0</td><td>0.1</td><td>0.1</td><td>-</td><td>2.1</td></tr><tr><td>45</td><td>1375</td><td>1492</td><td>α-copaene</td><td>0.2</td><td>0.3</td><td>-</td><td>0.1</td><td>tr</td><td>-</td><td>tr</td><td>-</td><td>-</td><td>0.1</td></tr><tr><td>46</td><td>1387</td><td>1591</td><td>β-elemene</td><td>tr</td><td>0.5</td><td>-</td><td>-</td><td>tr</td><td>-</td><td>tr</td><td>0.3</td><td>tr</td><td>0.3</td></tr></tbody></table>
<table><tbody><tr><td>47</td><td>1399</td><td>1872</td><td>2,5-dimethoxy-para-cymene</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>1.4</td><td>-</td></tr><tr><td>48</td><td>1417</td><td>1597</td><td>(E)-β-caryophyllene</td><td>1.1</td><td>0.8</td><td>0.5</td><td>1.4</td><td>-</td><td>-</td><td>2.9</td><td>0.1</td><td>0.1</td><td>2.7</td></tr><tr><td>49</td><td>1427</td><td>1638</td><td>γ-elemene</td><td>tr</td><td>-</td><td>-</td><td>-</td><td>0.3</td><td>-</td><td>-</td><td>-</td><td>tr</td><td>-</td></tr><tr><td>50</td><td>1432</td><td>1586</td><td>trans-α-bergamotene</td><td>0.1</td><td>-</td><td>-</td><td>0.1</td><td>0.1</td><td>-</td><td>1.1</td><td>-</td><td>-</td><td>0.6</td></tr><tr><td>51</td><td>1447</td><td>1667</td><td>(E)-β-farnesene</td><td>-</td><td>0.1</td><td>-</td><td>0.1</td><td>0.3</td><td>-</td><td>-</td><td>tr</td><td>tr</td><td>tr</td></tr><tr><td>52</td><td>1449</td><td>1667</td><td>α-humulene</td><td>0.1</td><td>0.1</td><td>0.1</td><td>0.2</td><td>0.2</td><td>-</td><td>0.2</td><td>0.1</td><td>tr</td><td>0.3</td></tr><tr><td>53</td><td>1469</td><td>1688</td><td>γ-muurolene</td><td>-</td><td>0.1</td><td>-</td><td>0.2</td><td>0.3</td><td>-</td><td>-</td><td>-</td><td>-</td><td>tr</td></tr><tr><td>54</td><td>1471</td><td>1668</td><td>guaia-6,10(14)-diene</td><td>-</td><td>-</td><td>-</td><td>0.3</td><td>0.4</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>55</td><td>1475</td><td>1708</td><td>germacrene D</td><td>0.1</td><td>0.2</td><td>-</td><td>-</td><td>-</td><td>0.1</td><td>0.6</td><td>1.2</td><td>tr</td><td>0.9</td></tr><tr><td>56</td><td>1481</td><td>1718</td><td>β-selinene</td><td>-</td><td>-</td><td>-</td><td>0.4</td><td>0.5</td><td>-</td><td>tr</td><td>-</td><td>-</td><td>tr</td></tr><tr><td>57</td><td>1490</td><td>1723</td><td>α-selinene</td><td>-</td><td>-</td><td>-</td><td>tr</td><td>0.3</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>58</td><td>1490</td><td>1732</td><td>bicyclogermacrene</td><td>0.3</td><td>0.2</td><td>0.4</td><td>-</td><td>-</td><td>0.1</td><td>0.3</td><td>0.1</td><td>0.1</td><td>0.4</td></tr><tr><td>59</td><td>1495</td><td>1750</td><td>(E,E)-α-farnesene</td><td>0.2</td><td>0.8</td><td>0.3</td><td>-</td><td>0.4</td><td>0.1</td><td>-</td><td>-</td><td>-</td><td>0.2</td></tr><tr><td>60</td><td>1500</td><td>1727</td><td>β-bisabolene</td><td>0.1</td><td>-</td><td>-</td><td>0.7</td><td>1.2</td><td>-</td><td>1.5</td><td>0.1</td><td>-</td><td>0.9</td></tr><tr><td>61</td><td>1513</td><td>1757</td><td>δ-cadinene</td><td>0.3</td><td>0.3</td><td>0.1</td><td>0.5</td><td>0.3</td><td>-</td><td>tr</td><td>-</td><td>tr</td><td>0.2</td></tr><tr><td>62</td><td>1534</td><td>2079</td><td>β-elemol</td><td>tr</td><td>0.1</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>1.1</td><td>-</td><td>-</td></tr><tr><td>63</td><td>1548</td><td>2043</td><td>(E)-nerolidol</td><td>0.2</td><td>tr</td><td>0.3</td><td>0.5</td><td>0.6</td><td>1.3</td><td>tr</td><td>0.3</td><td>tr</td><td>tr</td></tr><tr><td>64</td><td>1549</td><td>1825</td><td>germacrene B</td><td>-</td><td>0.5</td><td>-</td><td>0.4</td><td>0.6</td><td>tr</td><td>-</td><td>0.4</td><td>tr</td><td>0.2</td></tr><tr><td>65</td><td>1563</td><td>2121</td><td>spathulenol</td><td>-</td><td>-</td><td>0.1</td><td>0.1</td><td>tr</td><td>0.1</td><td>0.1</td><td>0.1</td><td>-</td><td>0.7</td></tr><tr><td>66</td><td>1570</td><td>1978</td><td>caryophyllene oxide</td><td>tr</td><td>-</td><td>-</td><td>1.8</td><td>-</td><td>-</td><td>0.2</td><td>-</td><td>-</td><td>0.4</td></tr><tr><td>67</td><td>1592</td><td>2033</td><td>humulene oxide II</td><td>-</td><td>-</td><td>-</td><td>0.3</td><td>0.2</td><td>-</td><td>-</td><td>-</td><td>-</td><td>tr</td></tr><tr><td>68</td><td>1611</td><td>2254</td><td>alismol</td><td>-</td><td>0.1</td><td>-</td><td>1.7</td><td>1.6</td><td>0.1</td><td>-</td><td>0.4</td><td>-</td><td>0.3</td></tr><tr><td>69</td><td>1616</td><td>2197</td><td>eremoligenol</td><td>-</td><td>-</td><td>-</td><td>0.4</td><td>-</td><td>-</td><td>0.1</td><td>0.3</td><td>-</td><td>-</td></tr><tr><td>70</td><td>1618</td><td>2176</td><td>γ-eudesmol</td><td>-</td><td>tr</td><td>-</td><td>0.1</td><td>-</td><td>-</td><td>tr</td><td>0.6</td><td>-</td><td>-</td></tr><tr><td>71</td><td>1625</td><td>2169</td><td>τ-cadinol</td><td>-</td><td>-</td><td>0.1</td><td>0.3</td><td>0.1</td><td>-</td><td>-</td><td>0.2</td><td>tr</td><td>0.1</td></tr><tr><td>72</td><td>1634</td><td>2225</td><td>β-eudesmol</td><td>-</td><td>-</td><td>-</td><td>0.7</td><td>0.8</td><td>-</td><td>0.2</td><td>0.6</td><td>tr</td><td>-</td></tr><tr><td>73</td><td>1639</td><td>2216</td><td>α-eudesmol</td><td>-</td><td>-</td><td>-</td><td>1.1</td><td>0.1</td><td>-</td><td>tr</td><td>0.5</td><td>-</td><td>-</td></tr><tr><td>74</td><td>1651</td><td>2145</td><td>β-bisabolol</td><td>-</td><td>-</td><td>-</td><td>0.4</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>75</td><td>1668</td><td>2215</td><td>α-bisabolol</td><td>-</td><td>-</td><td>-</td><td>0.4</td><td>0.5</td><td>-</td><td>0.1</td><td>-</td><td>-</td><td>0.1</td></tr><tr><td>76</td><td>2098</td><td>2610</td><td>(E)-phytol</td><td>-</td><td>0.3</td><td>0.7</td><td>3.0</td><td>1.4</td><td>tr</td><td>1.1</td><td>0.2</td><td>0.1</td><td>0.5</td></tr><tr><td colspan="12">Monoterpene hydrocarbon</td><td>7.4</td><td>1.3</td><td>71.5</td><td>48.6</td><td>83.4</td><td>78.3</td><td>44.9</td><td>51.2</td><td>84.4</td><td>31.1</td></tr><tr><td colspan="12">Oxygenated monoterpene</td><td>88.9</td><td>92.2</td><td>24.4</td><td>30.0</td><td>0.2</td><td>19.1</td><td>44.1</td><td>39.1</td><td>14.1</td><td>57.2</td></tr><tr><td colspan="12">Sesquiterpene hydrocarbon</td><td>2.5</td><td>4.2</td><td>1.3</td><td>4.3</td><td>4.8</td><td>0.3</td><td>6.6</td><td>2.4</td><td>0.3</td><td>7.0</td></tr><tr><td colspan="12">Oxygenated sesquiterpene</td><td>0.2</td><td>0.2</td><td>0.6</td><td>7.7</td><td>3.9</td><td>1.5</td><td>0.6</td><td>4.1</td><td>0.0</td><td>1.5</td></tr><tr><td colspan="12">Oxygenated diterpene</td><td>0.0</td><td>0.3</td><td>0.7</td><td>3.0</td><td>1.4</td><td>0.0</td><td>1.1</td><td>0.2</td><td>0.1</td><td>0.5</td></tr><tr><td colspan="12">TOTAL</td><td>99.0</td><td>98.3</td><td>98.5</td><td>93.6</td><td>93.8</td><td>99.3</td><td>97.2</td><td>97.1</td><td>98.9</td><td>97.3</td></tr><tr><td colspan="12">Yields (%; w/w)</td><td>0.05</td><td>0.02</td><td>0.02</td><td>0.18</td><td>0.17</td><td>0.08</td><td>0.08</td><td>0.03</td><td>0.04</td><td>0.10</td></tr></tbody></table>

Order of elution and relative percentages of individual components are given on an apolar column (BP-1) excepted those with an asterisk (*) for which percentages were taken on polar column (BP-20); RI<sub>A</sub>. RI<sub>P</sub>: retention indices measured on apolar and polar capillary columns respectively; tr: trace level (<0.05%); hys: C. hystrix, mic: C. micrantha, mapt: C. macroptera, lat: C. latipes, ich: C. ichangensis, jun: C. junos, maph: C. macrophylla.
<table><caption>**Table 3.** List of studied species and accessions.</caption><thead><tr><th>Scientific name</th><th>Common name</th><th>Sample</th><th>ICVN</th></tr></thead><tbody><tr><td>C. hystrix DC.</td><td>Combava</td><td>hys</td><td>0100630</td></tr><tr><td>C. macroptera Montr.</td><td>Melanesian</td><td>mapt</td><td>0100686</td></tr><tr><td>C. micrantha Wester</td><td>Biasong</td><td>mic</td><td>0101140</td></tr><tr><td rowspan="3">C. ichangensis Swingle</td><td rowspan="3">Ichang papeda</td><td>ich-1</td><td>0100687</td></tr><tr><td>ich-2</td><td>0110241</td></tr><tr><td>ich-3</td><td>0110240</td></tr><tr><td rowspan="2">C. latipes (Swingle)</td><td rowspan="2">Khasi papeda</td><td>lat-1</td><td>0110243</td></tr><tr><td>lat-2</td><td>0100844</td></tr><tr><td>C. junos Siebold ex</td><td>Yuzu</td><td>jun</td><td>0100988</td></tr><tr><td>C. macrophylla Wester</td><td>Alemow, Kolo</td><td>maph</td><td>0110058</td></tr></tbody></table>

ICVN: International Citrus Varietal Numbering
<figure><img src="image_3.png" /><figcaption>**Figure 2.** Three-dimensional Principal Component Analysis of leaf oil samples (components higher than 2%). Green: *hys*: *C. hystrix*, *mic*: *C. micrantha*, *mapt*: *C. macroptera*; Red: *lat*: *C. latipes*, *ich*: *C. ichangensis*; Blue: *wil*: *C. wilsonii*, *jun*: *C. junos*, *maph*: *C. macrophylla*.</figcaption></figure>

<figure><img src="image_4.png" /></figure>