Phylogenetic origin of limes and lemons revealed by cytoplasmic and nuclear markers.
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AutorCurk,Franck; Ollitrault,Frederique; Garcia-Lor,Andres; Luro,Francois; Navarro,Luis; Ollitrault,Patrick
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 cultivatedCitrusspecies result from interspecific hybridization between four basic taxa (C. reticulata,C. maxima,C. medicaandC. 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 133Citrusaccessions. 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 theCitrusgenus. 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 medicacontributed to all limes and lemons and was the direct male parent for the main sub-groups in combination withC. micranthaor close papeda species (forC. aurata,C. excelsa,C. macrophyllaandC. aurantifolia- 'Mexican' lime types of Tanaka's taxa),C. reticulata(forC. limonia,C. karnaandC. jambhirivarieties of Tanaka's taxa, including popular citrus rootstocks such as 'Rangpur' lime, 'Volkamer' and 'Rough' lemons),C. aurantium(forC. limettaandC. limon- yellow lemon types - varieties of Tanaka's taxa) or theC. maxima*C. reticulatahybrid (forC. limettioides- 'Palestine sweet' lime types-andC. meyeri). Among triploid limes,C. latifoliaaccessions ('Tahiti' and 'Persian' lime types) result from the fertilization of a haploid ovule ofC. limonby a diploid gamete ofC. aurantifolia, whileC. aurantifoliatriploid accessions ('Tanepao' lime types and 'Madagascar' lemon) probably result from an interspecific backcross (a diploid ovule ofC. aurantifoliafertilized byC. medica). As limes and lemons were vegetatively propagated (apomixis, horticultural practices) the intra-sub-group phenotypic diversity results from asexual variations.