Chloroplast and nuclear genome analysis of the parentage of lemons

Chloroplast DNA (cpDNA) restriction fragment length polymorphisms were used to study the parentage of lemons [Citrus limon (L.) Burm. f.] and several other putative hybrids. The 30 citrus accessions studied included nine lemo ns, three pummelos [C. maxima (Burm.) Merrill], three citrons (C. medica L. ), three mandarins (C. reticulata Blanco, C. clementina Hort. Ex. Y. Tan., and C. sunki Hort. ex. Tan.), and single representatives of 13 other taxa. Pour different fragments of citrus cpDNA were amplified by polymerase chain reaction using four universal chloroplast primers and amplification produc ts were digested with four endonucleases, Rsa I, Dra I, Hae III, and Mbo I. A total of 104 different restriction fragments were scored and used for ph ylogenetic analysis by parsimony. The three taxa which have been proposed a s ancestral Citrus L. sp., C medica, C. maxima, and C. reticulata, had dist inct cpDNA patterns. Pommelo contributed the chloroplast genome to lemons, sweet orange [C. sinensis (L.) Osbeck], and Bergamot orange(C. bergamia Ris so and Bolt.), and mandarin contributed the chloroplast genome to rough lem ons (C. jambhiri Lush.), Rangpur lime (C. limonia Osbeck), and 'Mexican' li me [C. aurantifolia (Christm.) Swing.]. Data suggest that the particular ac cessions of these ancestral species that were studied were not directly inv olved in the hybridization events that created these hybrids, since they ha ve similar but not identical cpDNA restriction fragments. Using inter-simpl e sequence repeat markers that amplified from nuclear genomic DNA, a set of samples including pummelos, citrons, mandarins, sour oranges (C. aurantium L.), and 'Samuyao' papeda (C,micrantha Wester) were tested as possible par ents of lemons. Sour orange and citron together had an nuclear and chloropl ast fragments found in lemon and are therefore proposed to be the maternal and paternal parents, respectively, of many commercial lemon cultivars, inc luding 'Lisbon', 'Eureka', 'Villafranca', and 'Monachello'.