Abstract

Citrus plants are able to produce defense compounds such as coumarins and furanocoumarins to cope with herbivorous insects and pathogens. In humans, these chemical compounds are strong photosensitizers and can interact with medications, leading to the “grapefruit juice effect”. Removing coumarins and furanocoumarins from food and cosmetics imply additional costs and might alter product quality. Thus, the selection of Citrus cultivars displaying low coumarin and furanocoumarin contents constitutes a valuable alternative. In this study, we performed ultra-performance liquid chromatography coupled with mass spectrometry analyses to determine the contents of these compounds within the peel and the pulp of 61 Citrus species representative of the genetic diversity all Citrus. Generally, Citrus peel contains larger diversity and higher concentrations of coumarin/furanocoumarin than the pulp of the same fruits. According to the chemotypes found in the peel, Citrus species can be separated into 4 groups that correspond to the 4 ancestral taxa (pummelos, mandarins, citrons and papedas) and extended with their respective secondary species descendants. Three of the 4 ancestral taxa (pummelos, citrons and papedas) synthesize high amounts of these compounds, whereas mandarins appear practically devoid of them. Additionally, all ancestral taxa and their hybrids are logically organized according to the coumarin and furanocoumarin pathways described in the literature. This organization allows hypotheses to be drawn regarding the biosynthetic origin of compounds for which the biogenesis remains unresolved. Determining coumarin and furanocoumarin contents is also helpful for hypothesizing the origin of Citrus species for which the phylogeny is presently not firmly established. Finally, this work also notes favorable hybridization schemes that will lead to low coumarin and furanocoumarin contents, and we propose to select mandarins and Ichang papeda as Citrus varieties for use in creating species devoid of these toxic compounds in future breeding programs.

Highlights

  • Citrus originate from the tropical and subtropical regions of Southeast Asia and their culture was initiated in India and China during the first millenary BC [1]

  • Exceptions to this latter rule, when the pulp appears more concentrated than the peel, were observed in the cases of Deep Red and Pink pummelo and Bouquettier de Nice and Chinotto sour oranges for which the pulp is exceptionally rich in furanocoumarins from the bergapten group (Tables A and G in S1 File)

  • Peel prominence regarding coumarin and furanocoumarin contents must be related to the presence of lysogenic cavities in the flavedo, where large quantities of essential oils and polyphenolics are stored

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Summary

Introduction

Citrus originate from the tropical and subtropical regions of Southeast Asia and their culture was initiated in India and China during the first millenary BC [1]. Swingle and Reece (1967) [5] and Tanaka (1977) [6], which recognize 16 and 162 species, respectively, remain the two major classification systems currently used This last decade, molecular analyses have provided decisive information regarding Citrus domestication and the relations between various cultivated species of Citrus [7,8,9,10,11,12,13,14]. C. sinensis, C. aurantium, C. paradisi, and tangors had a 2 ancestral taxa admixture structure (C. reticulata and C. maxima) with variable contributions. The origins of C. limon and C. aurantifolia (Swingle and Reece taxonomy) are more complex and come from 2 or 3 taxa hybridization. Citrus amblycarpa secondary species displayed approximately 50% contributions from C. reticulata and C. micrantha [14]

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