Genetic and chemical diversity of citron (Citrus medica L.) based on nuclear and cytoplasmic markers and leaf essential oil composition

Citrus medica L. essential oil improves anxiety-like behaviors accompanied by fatigue through α7-nAChR receptor-mediated neuroprotection effects

ETHNOPHARMACOLOGICAL RELEVANCE

Citrus medica L. has been cultivated in China for over two thousand years, with the effects of soothing the liver, regulating qi. Studies have shown that it can relieve anxiety. Its combination with other traditional Chinese medicines has been widely used in clinical practice assist in the treatment of anxiety and depression. The essential oil rich in peel is important active substance of Citrus medica L. A large number of studies have confirmed that essential oils are commonly used to relieve pain, psychological stress and induce relaxation. However, there are currently no studies on the effects of Citrus medica L. essential oil (CEO) on anxiety.

AIM OF THE STUDY

Anxiety has become the most common mental illness worldwide, so effective and diverse prevention and control methods are urgently needed. The main objective of this study is to evaluate the therapeutic effect and optimal administration route of CEO on anxiety caused by different susceptibility factors, and to further explore its potential mechanism for improving anxiety, providing scientific guidance for the application of CEO.

MATERIALS AND METHODS

Induce anxiety models caused by fatigue or stress, and use animal behavior as an indicator to evaluate the CEO. To illustrate the underlying mechanisms of anti-anxiety effect of CEO, histological examination, immunofluorescence staining and Western Blot were carried out.

RESULTS

The results showed that the safer inhalation administration was more effective. Compared with the stress-induced anxiety model, CEO has a more obvious effect on fatigue-induced anxiety. After CEO administration, the frequency, time, and movement distance of fatigue-type anxious mice in Open Field Test (OFT) increased significantly. During Elevated Plus Maze Test (EPM), the mice spent more time and have more entry in the open arm. Further research found that CEO can significantly increase cerebral blood flow, recover damaged neurons in the hippocampus. RNA-seq analysis investigated that CEO can significantly improve gene expression in the hippocampus of fatigue accompanied anxiety mice. The underlying mechanism is significantly related to cholinergic system pathways. Further research found that the alpha-7 nicotinic acetylcholine receptor (α7-nAChR) in anxious mice was down-regulated, accompanied by decreased activation of its downstream ERK/CREB. Inhaling essential oil improved fatigue-induced anxiety by reversing this phenomenon.

CONCLUSIONS

The results demonstrated that CEO have a significant anti-anxiety effect, especially fatigue induced anxiety. Our research results verify the accuracy and effectiveness of symptomatic treatment strategies for anxiety caused by different susceptibility factors, and provide scientific guidance for the rational use of CEO.

Chemical and Biological Study of the Essential Oil Isolated from Fruits of Citrus x limonia

Citrus x limonia is an aromatic species, known locally in Ecuador as limón mandarina or limón chino. In the present study, the chemical composition and biological activity of the essential oil isolated from this species were determined. The essential oil was extracted through hydrodistillation. The chemical composition and enantiomeric distribution of the essential oil were determined by gas chromatography. Antimicrobial activity was determined using the broth microdilution method against tree Gram-positive cocci, a Gram-positive bacillus, four Gram-negative bacilli, a fungus, and a yeast. The antioxidant activity was determined through ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) and DPPH (2,2-diphenyl-1-picrylhydrazyl) methods. The spectrophotometric method was used to determine anticholinesterase activity. In the essential oil, thirty-nine compounds were identified, which represented 99.35% of the total composition. Monoterpene hydrocarbons were the most representative group in terms of number of compounds (thirteen) and in terms of relative abundance (91.39%). The main constituents were found to be limonene (57.38 ± 1.09%), γ-terpinene (13.01 ± 0.37%), and β-pinene (12.04 ± 0.63%). Five pairs of enantiomers were identified in the essential oil from fruits of Citrus x limonia. The essential oil presented a minimum inhibitory concentration of 4000 μg/mL against Aspergillus niger. The antioxidant activity of essential oil was weak per the ABTS method, with a SC50 of 1.26 mg/mL. Additionally, the essential oil exhibited moderate anticholinesterase activity, with an IC50 of 203.9 ± 1.03 µg/mL. This study provides the first comprehensive analysis of the chemical composition and biological activities of the essential oil from fruits of Citrus x limonia.

Chemical Composition, Enantiomeric Distribution and Antimicrobial, Antioxidant and Antienzymatic Activities of Essential Oil from Leaves of Citrus x limonia

Citrus x limonia is an aromatic species belonging to the Rutaceae family. In the present study, the chemical composition, enantiomeric distribution, and biological activity of the essential oil isolated from leaves of Citrus x limonia were determined. The essential oil was extracted through hydrodistillation. The chemical composition of the essential oil was determined by gas chromatography (GC) coupled to a flame ionization detector (GC-FID), and a mass spectrometer detector (GC-MS) using a nonpolar column. The enantiomeric distribution was performed using two enantioselective chromatographic columns. Antimicrobial activity was determined using the broth microdilution method. The antimicrobial activity was tested against eight bacteria and two fungi. The antioxidant activity was determined through ABTS and DPPH methods. The spectrophotometric method was used to determine anticholinesterase activity. In the essential oil, forty-three compounds were identified. These compounds represent 99.13% of the total composition. Monoterpene hydrocarbons were the most representative group in number of compounds (fourteen) and in terms of relative abundance (65.67%). The main constituent is found to be limonene (25.37 ± 0.80%), β-pinene (23.29 ± 0.15%) and sabinene (8.35 ± 0.10%). Six pairs of enantiomers were identified in the essential oil from fruits of Citrus x limonia. The essential oil showed moderate antibacterial activity against Gram-positive cocci Enterococcus faecalis, and Gram-positive bacillus Lysteria monocytogenes with a MIC of 1000 μg/mL. The oil exhibited strong antifungal activity against fungi Aspergillus niger, and yeasts Candida albicans with a MIC of 250 and 500 μg/mL, respectively. The antioxidant activity of essential oil was weak in ABTS method with a SC50 of 9.12 mg/mL. Additionally, the essential oil presented moderate anticholinesterase activity with an IC50 of 71.02 ± 1.02 µg/mL.

Comparative genetic mapping and a consensus interspecific genetic map reveal strong synteny and collinearity within the Citrus genus

Introduction

Useful germplasm for citrus breeding includes all sexually compatible species of the former genera Citrus, Clymenia, Eremocitrus, Fortunella, Microcitrus, Oxanthera, and Poncirus, now merged in the single Citrus genus. An improved knowledge on the synteny/collinearity between the genome of these different species, and on their recombination landscapes, is essential to optimize interspecific breeding schemes.

Method

We have performed a large comparative genetic mapping study including several main clades of the Citrus genus. It concerns five species (C. maxima, C. medica, C. reticulata, C. trifoliata and C. glauca), two horticultural groups resulting from interspecific admixture (clementine and lemon) and two recent interspecific hybrids (C. australis x C. australasica and C. maxima x C. reticulata). The nine individual genetic maps were established from GBS data of 1,216 hybrids.

Results and discussion

The number of SNPs mapped for each parent varies from 760 for C. medica to 4,436 for the C. maxima x C. reticulata hybrid, with an average of 2,162.3 markers by map. Their comparison with C. clementina v1.0 assembly and inter-map comparisons revealed a high synteny and collinearity between the nine genetic maps. Non-Mendelian segregation was frequent and specific for each parental combination. The recombination landscape was similar for the nine mapped parents, and large genomic regions with very low recombination were identified. A consensus genetic map was successfully established. It encompasses 10,756 loci, including 7,915 gene-based markers and 2,841 non-genic SNPs. The anchoring of the consensus map on 15 published citrus chromosome-scale genome assemblies revealed a high synteny and collinearity for the most recent assemblies, whereas discrepancies were observed for some older ones. Large structural variations do not seem to have played a major role in the differentiation of the main species of the Citrus genus. The consensus genetic map is a useful tool to check the accuracy of genome assemblies, identify large structural variation and focus on analyzing potential relationships with phenotypic variations. It should also be a reference framework to integrate the positions of QTLs and useful genes identified in different analyses.

Health-Promoting Properties and Potential Application in the Food Industry of Citrus medica L. and Citrus × clementina Hort. Ex Tan. Essential Oils and Their Main Constituents

Citrus is an important genus in the Rutaceae family, with high medicinal and economic value, and includes important crops such as lemons, orange, grapefruits, limes, etc. The Citrus species is rich sources of carbohydrates, vitamins, dietary fibre, and phytochemicals, mainly including limonoids, flavonoids, terpenes, and carotenoids. Citrus essential oils (EOs) consist of several biologically active compounds mainly belonging to the monoterpenes and sesquiterpenes classes. These compounds have demonstrated several health-promoting properties such as antimicrobial, antioxidant, anti-inflammatory, and anti-cancer properties. Citrus EOs are obtained mainly from peels, but also from leaves and flowers, and are widely used as flavouring ingredients in food, cosmetics, and pharmaceutical products. This review focused on the composition and biological properties of the EOs of Citrus medica L. and Citrus clementina Hort. Ex Tan and their main constituents, limonene, γ-terpinene, myrcene, linalool, and sabinene. The potential applications in the food industry have been also described. All the articles available in English or with an abstract in English were extracted from different databases such as PubMed, SciFinder, Google Scholar, Web of Science, Scopus, and Science Direct.

Chemical Variability of Peel and Leaf Essential Oils in the Citrus Subgenus Papeda (Swingle) and Few Relatives

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.

Genetic, morphological and chemical investigations reveal the genetic origin of Pompia (C. medica tuberosa Risso & Poiteau) - An old endemic Sardinian citrus fruit

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.

Genotyping by sequencing can reveal the complex mosaic genomes in gene pools resulting from reticulate evolution: a case study in diploid and polyploid citrus

BACKGROUND AND AIMS

Reticulate evolution, coupled with reproductive features limiting further interspecific recombinations, results in admixed mosaics of large genomic fragments from the ancestral taxa. Whole-genome sequencing (WGS) data are powerful tools to decipher such complex genomes but still too costly to be used for large populations. The aim of this work was to develop an approach to infer phylogenomic structures in diploid, triploid and tetraploid individuals from sequencing data in reduced genome complexity libraries. The approach was applied to the cultivated Citrus gene pool resulting from reticulate evolution involving four ancestral taxa, C. maxima, C. medica, C. micrantha and C. reticulata.

METHODS

A genotyping by sequencing library was established with the restriction enzyme ApeKI applying one base (A) selection. Diagnostic single nucleotide polymorphisms (DSNPs) for the four ancestral taxa were mined in 29 representative varieties. A generic pipeline based on a maximum likelihood analysis of the number of read data was established to infer ancestral contributions along the genome of diploid, triploid and tetraploid individuals. The pipeline was applied to 48 diploid, four triploid and one tetraploid citrus accessions.

KEY RESULTS

Among 43 598 mined SNPs, we identified a set of 15 946 DSNPs covering the whole genome with a distribution similar to that of gene sequences. The set efficiently inferred the phylogenomic karyotype of the 53 analysed accessions, providing patterns for common accessions very close to that previously established using WGS data. The complex phylogenomic karyotypes of 21 cultivated citrus, including bergamot, triploid and tetraploid limes, were revealed for the first time.

CONCLUSIONS

The pipeline, available online, efficiently inferred the phylogenomic structures of diploid, triploid and tetraploid citrus. It will be useful for any species whose reproductive behaviour resulted in an interspecific mosaic of large genomic fragments. It can also be used for the first generations of interspecific breeding schemes.

Finding Noemi: The Transcription Factor Mutations Underlying Trait Differentiation Amongst Citrus

A recent study by Butelli et al. (Curr. Biol. 2019;29:158-164) has demonstrated that the linked traits of exceptionally low fruit acidity and the absence of anthocyanins in leaves and flowers and proanthocyanidins in seeds of the citrus are the result of mutations in the Noemi gene encoding a bHLH transcription factor.

Noemi Controls Production of Flavonoid Pigments and Fruit Acidity and Illustrates the Domestication Routes of Modern Citrus Varieties

In citrus, the production of anthocyanin pigments requires the activity of the transcriptional activator Ruby. Consequently, loss-of-function mutations in Ruby result in an anthocyaninless phenotype [1]. Several citrus accessions, however, have lost the ability to produce these pigments despite the presence of wild-type Ruby alleles. These specific mutants have captivated the interest of botanists and breeders for centuries because the lack of anthocyanins in young leaves and flowers is also associated with a lack of proanthocyanidins in seeds and, most notably, with an extreme reduction in fruit acidity (involving about a three-unit change in pH). These mutants have been defined collectively as "acidless" [2-4]. We have identified Noemi, which encodes a basic helix-loop-helix (bHLH) transcription factor and which controls these apparently unrelated processes. In accessions of Citron, limetta, sweet lime, lemon, and sweet orange, acidless phenotypes are associated with large deletions or insertions of retrotransposons in the Noemi gene. In two accessions of limetta, a change in the core promoter region of Noemi is associated with reduced expression and increased pH of juice, indicating that Noemi is a major determinant of fruit acidity. The characterization of the Noemi locus in a number of varieties of Citron indicates that one specific mutation is ancient. The presence of this allele in Chinese fingered Citrons and in those used in the Sukkot Jewish ritual [5] illuminates the path of domestication of Citron, the first citrus species to be cultivated in the Mediterranean. This allele has been inherited in Citron-derived hybrids with long histories of cultivation.

Genetic structure and diversity of natural and domesticated populations of Citrus medica L. in the Eastern Himalayan region of Northeast India

Citron (Citrus medica L.) is a medicinally important species of citrus native to India and occurs in natural forests and home gardens in the foothills of the eastern Himalayan region of northeast India. The wild populations of citron in the region have undergone rapid decline due to natural and anthropogenic disturbances and most of the remaining individuals of citron are found in fragmented natural forests and home gardens in the region. In order to assess the genetic structure and diversity of citron in wild and domesticated populations, we analyzed 219 individuals of C. medica collected from four wild and eight domesticated populations using microsatellite markers. The genetic analysis based on five polymorphic microsatellite loci revealed an average of 13.40 allele per locus. The mean observed and expected heterozygosity values ranged between 0.220–0.540 and 0.438–0.733 respectively among the wild and domesticated populations. Domesticated populations showed close genetic relationships as compared to wild populations and pairwise Nei's genetic distance ranged from 0.062 to 2.091 among wild and domesticated populations. Analysis of molecular variance (AMOVA) showed higher genetic diversity among‐ than within populations. The analysis of population structure revealed five groups. Mixed ancestry of few individuals of different populations revealed exchange of genetic materials among farmers in the region. Citron populations in the region show high genetic variation. The knowledge gained through this study is invaluable for devising genetically sound strategies for conservation of citron genetic resources in the region.

Phylogenetic origin of limes and lemons revealed by cytoplasmic and nuclear markers

BACKGROUND AND AIMS

The origin of limes and lemons has been a source of conflicting taxonomic opinions. Biochemical studies, numerical taxonomy and recent molecular studies suggested that cultivated Citrus species result from interspecific hybridization between four basic taxa (C. reticulata,C. maxima,C. medica and C. micrantha). However, the origin of most lemons and limes remains controversial or unknown. The aim of this study was to perform extended analyses of the diversity, genetic structure and origin of limes and lemons.

METHODS

The study was based on 133 Citrus accessions. It combined maternal phylogeny studies based on mitochondrial and chloroplastic markers, and nuclear structure analysis based on the evaluation of ploidy level and the use of 123 markers, including 73 basic taxa diagnostic single nucleotide polymorphism (SNP) and indel markers.

KEY RESULTS

The lime and lemon horticultural group appears to be highly polymorphic, with diploid, triploid and tetraploid varieties, and to result from many independent reticulation events which defined the sub-groups. Maternal phylogeny involves four cytoplasmic types out of the six encountered in the Citrus genus. All lime and lemon accessions were highly heterozygous, with interspecific admixture of two, three and even the four ancestral taxa genomes. Molecular polymorphism between varieties of the same sub-group was very low.

CONCLUSIONS

Citrus medica contributed to all limes and lemons and was the direct male parent for the main sub-groups in combination with C. micrantha or close papeda species (for C. aurata, C. excelsa, C. macrophylla and C. aurantifolia--'Mexican' lime types of Tanaka's taxa), C. reticulata(for C. limonia, C. karna and C. jambhiri varieties of Tanaka's taxa, including popular citrus rootstocks such as 'Rangpur' lime, 'Volkamer' and 'Rough' lemons), C. aurantium (for C. limetta and C. limon--yellow lemon types--varieties of Tanaka's taxa) or the C. maxima × C. reticulate hybrid (for C. limettioides--'Palestine sweet' lime types--and C. meyeri). Among triploid limes, C. latifolia accessions ('Tahiti' and 'Persian' lime types) result from the fertilization of a haploid ovule of C. limon by a diploid gamete of C. aurantifolia, while C. aurantifolia triploid accessions ('Tanepao' lime types and 'Madagascar' lemon) probably result from an interspecific backcross (a diploid ovule of C. aurantifolia fertilized by C. medica). As limes and lemons were vegetatively propagated (apomixis, horticultural practices) the intra-sub-group phenotypic diversity results from asexual variations.

Advanced development in phytochemicals analysis of medicine and food dual purposes plants used in China (2011-2014)

In 2011, we wrote a review for summarizing the phytochemical analysis (2006-2010) of medicine and food dual purposes plants used in China (Zhao et al., J. Chromatogr. A 1218 (2011) 7453-7475). Since then, more than 750 articles related to their phytochemical analysis have been published. Therefore, an updated review for the advanced development (2011-2014) in this topic is necessary for well understanding the quality control and health beneficial phytochemicals in these materials, as well as their research trends.

Volatile and Flavonoid Composition of the Peel of Citrus medica L. var. Corsican Fruit for Quality Assessment of Its Liqueur

The volatile and flavonoid compositions of the peel of Citrus medica L. var. Corsican fruits cultivated in Corsica were studied according to the maturity of the citron fruits measured using growing degree-days. Quantitative variation with the stage of development of the fruit was observed using gas chromatography, gas chromatography-mass spectrometry, and liquid chromatography-mass spectrometry/mass spectrometry. Thirty volatile compounds were identified in the peel essential oil. Limonene and γ-terpinene were the major compounds. The volatile compositions of commercial citron liqueurs were also characterized by high amounts of monoterpene hydrocarbons with the same two major components. The main flavonoid components of citron fruits and derived liqueurs were rutin and neohesperidin. This chemical characterization can be used for quality assessment of food products from C. medica var. Corsican.

Citrus leaf volatiles as affected by developmental stage and genetic type

Major volatiles from young and mature leaves of different citrus types were analyzed by headspace-solid phase microextraction (HS-SPME)-GC-MS. A total of 123 components were identified form nine citrus cultivars, including nine aldehydes, 19 monoterpene hydrocarbons, 27 oxygenated monoterpenes, 43 sesquiterpene hydrocarbons, eight oxygenated sesquiterpenes, two ketones, six esters and nine miscellaneous. Young leaves produced higher amounts of volatiles than mature leaves in most cultivars. The percentage of aldehyde and monoterpene hydrocarbons increased, whilst oxygenated monoterpenes and sesquiterpenes compounds decreased during leaf development. Linalool was the most abundant compound in young leaves, whereas limonene was the chief component in mature ones. Notably, linalool content decreased, while limonene increased, during leaf development in most cultivars. Leaf volatiles were also affected by genetic types. A most abundant volatile in one or several genotypes can be absent in another one(s), such as limonene in young leaves of lemon vs. Satsuma mandarin and β-terpinene in mature leaves of three genotypes vs. the other four. Compositional data was subjected to multivariate statistical analysis, and variations in leaf volatiles were identified and clustered into six groups. This research determining the relationship between production of major volatiles from different citrus varieties and leaf stages could be of use for industrial and culinary purposes.

Chemotaxonomic study of Citrus, Poncirus and Fortunella genotypes based on peel oil volatile compounds--deciphering the genetic origin of Mangshanyegan (Citrus nobilis Lauriro)

Volatile profiles yielded from gas chromatography-mass spectrometry (GC-MS) analysis provide abundant information not only for metabolism-related research, but also for chemotaxonomy. To study the chemotaxonomy of Mangshanyegan, its volatile profiles of fruit and leaf and those of 29 other genotypes of Citrus, Poncirus, and Fortunella were subjected to phylogenetic analyses. Results showed that 145 identified (including 64 tentatively identified) and 15 unidentified volatile compounds were detected from their peel oils. The phylogenetic analysis of peel oils based on hierarchical cluster analysis (HCA) demonstrated a good agreement with the Swingle taxonomy system, in which the three genera of Citrus, Poncirus, and Fortunella were almost completely separated. As to Citrus, HCA indicated that Citrophorum, Cephalocitrus, and Sinocitrus fell into three subgroups, respectively. Also, it revealed that Mangshanyegan contain volatile compounds similar to those from pummelo, though it is genetically believed to be a mandarin. These results were further supported by the principal component analysis of the peel oils and the HCA results of volatile profiles of leaves in the study.

Bioactive constituents in Prunus africana: geographical variation throughout Africa and associations with environmental and genetic parameters

Prunus africana--an evergreen tree found in Afromontane forests--is used in traditional medicine to cure benign prostate hyperplasia. Different bioactive constituents derived from bark extracts from 20 tree populations sampled throughout the species' natural range in Africa were studied by means of GC-MSD. The average concentration [mg/kgw/w] in increasing order was: lauric acid (18), myristic acid (22), n-docosanol (25), ferulic acid (49), β-sitostenone (198), β-sitosterol (490), and ursolic acid (743). The concentrations of many bark constituents were significantly correlated and concentration of n-docosanol was highly significantly correlated with all other analytes. Estimates of variance components revealed the highest variation among populations for ursolic acid (66%) and the lowest for β-sitosterol (20%). In general, environmental parameters recorded (temperature, precipitation, altitude) for the samples sites were not correlated with the concentration of most constituents; however, concentration of ferulic acid was significantly correlated with annual precipitation. Because the concentration of compounds in bark extracts may be affected by tree size, the diameter of sampled plants at 1.3m tree height (as proxy of age) was recorded. The only relationship with tree diameter was a negative correlation with ursolic acid. Under the assumption that genetically less variable populations have less variable concentrations of bark compounds, correlations between variation parameters of the concentration and the respective genetic composition based on chloroplast and nuclear DNA markers were assessed. Only variation of β-sitosterol concentration was significantly correlated with haplotypic diversity. The fixation index (F(IS)) was positively correlated with the variation in concentration of ferulic acid. Principal Components Analysis (PCA) indicated a weak geographic pattern. Mantel tests, however, revealed associations between the geographic patterns of bioactive constituents and the phylogenetic relationship among the populations sampled. This suggests an independent evolution of bark metabolism within different phylogeographical lineages, and the molecular phylogeographic pattern is partly reflected in the variation in concentration of bark constituents. The results have important implications for the design of strategies for the sustainable use and conservation of this important African tree species.