Diversity of citron (Citrus medica) and phylogenetic analysis of related citron hybrids using molecular markers and essential oil composition

Citrus diversity is known to be essentially supported by three essential basic species, mandarin, pummelo and citron, which are at the origin of quite all the cultivated citrus. Based on studies of phenotype, the citron group (Citrus medica) is supposedly low in genetic diversity compared to mandarins and pummelos. To assess the diversity of the citron group we analyzed the molecular polymorphism of nuclear and cytoplasmic genetic markers and the variation in composition of essential oils from leaves and peels of 24 varieties of citron or apparent hybrids of citron. Our results demonstrate that the citron group has a relatively high allelic diversity, probably due to multiple introductions of different varieties. Self-fertilization was the mode of reproduction which most frequently led to the development of commercial varieties with specific aromas and flavors, such as the cultivar ‘Corsican’, a putative ‘Common Poncire’ self-crossed hybrid. However, some varieties appeared to be interspecific hybrids related to citron but only by the male parent. This varietal diversity was probably favored by spreading seeds to extend the cultivation of citron in Mediterranean countries. The chemical diversity does not always correspond to genetic diversity but nevertheless reveals specific profiles associated with some genotypes. (Resume d'auteur)