The Origin of Cultivated Citrus as Inferred from Internal Transcribed Spacer and Chloroplast DNA Sequence and Amplified Fragment Length Polymorphism Fingerprints

Abstract

Citrus species are among the most important fruit trees in the world and have a long cultivation history. However, until now, the exact genetic origins of cultivated Citrus such as sweet orange (Citrus sinensis), lemon (C. limon), and grapefruit (C. paradisi) have remained unidentified. In the present study, amplified fragment length polymorphism (AFLP) fingerprints, nuclear internal transcribed spacer (ITS), and three plastid DNA regions (psbH – petB, trnL – trnF, and trnS - trnG) of 30 accessions of the cultivated citrus and their putative wild ancestors were analyzed in an attempt to identify their paternal and maternal origins. Molecular phylogenetic trees were constructed based on the AFLP data, and chloroplast DNA and ITS sequences using the genus Poncirus as the outgroup. Our results indicated that bergamot (C. aurantifolia) and lemon were derived from citron (C. medica) and sour orange (C. aurantium), and grapefruit was a hybrid that originated from a cross between pummelo (C. grandis) and sweet orange. Rough lemon (C. limon) was probable as a parent of rangpur lime (C. limonia) and guangxi local lemon (C. limonia). Our data also demonstrated that sweet orange and sour orange were hybrids of mandarin (C. reticulata) and pummelo, while rough lemon was a cross between citron and mandarin. For mexican lime (C. aurantifolia), our molecular data confirmed a species of Papeda to be the female parent and C. medica as the male. These findings provide new information for future study on the taxonomy, evolution, and genetic breeding of Citrus.