Maternal inheritance of chloroplast DNA in intergeneric sexual hybrids of "true citrus fruit trees" revealed by PCR-RFLP analysis

PCR-RFLP analysis was employed to clarify the inheritance pattern of chloroplast DNA (cpDNA) in six kinds of intergeneric sexual hybrids among five genera, i.e. Fortunella, Eremocitrus, Poncirus, Microcitrus and Citrus within the "true citrus fruit trees" group of the subtribe Citrinae (Rutaceae). Two cpDNA gene regions were amplified from each material via PCR as following: one region of tRNA (trnD-trnT) and a variable region bounded by the conserved sequences in ribulose-1,5-bisphosphate carboxylase large subunit (rbcL) and open reading frame 106 (ORF106). Twelve restriction endonucleases (MspI, XbaI, RsaI, AluI, HinfI, ScrFI, StyI, HaeIII, Sau3AI, NdeII, HhaI and TaqI) were used for RFLP analysis of the amplified regions of cpDNA. Polymorphisms were detected with five (HinfI, RsaI, NdeII, ScrFI and XbaI) and four (HinfI, RsaI, HaeIII and Sau3AI) enzymes for rbcL-ORF106 and trnD-trnT regions, respectively. All progeny examined in each kind of the intergeneric sexual hybrid exhibited maternal inheritance of cpDNA. Also, cpDNA analysis for determining the maternal parent of a natural hybrid, Microcitrus virgata (Sydney hybrid) indicated that M. australis (Planch.) Swing. was the female parent of M. virgata.