The genetic factor controlling the mode of plastid DNA (ptDNA) inheritance in Rhododendron was investigated using polymerase chain reaction-single-stranded conformation polymorphism (PCR-SSCP) analysis at the trnL– trnF intergeneric region. In the cross of R kaempferi var. macrogemma × R. simsii, a low frequency of paternal ptDNA inheritance was observed in the progeny. In the cross of R transiens × R. simsii, a high frequency of paternal ptDNA was observed in the progeny. When the F1 plants from R kaempferi var. macrogemma × R transiens were used as seed parents and were crossed with R simsii, the pattern of ptDNA inheritance was segregated into 2 types among cross combinations at a ratio of 1:1, namely, low (2.0-11.1%) and high (32.6-66.6%) frequencies of paternal ptDNA inheritance, although the F1 plants had identical ptDNA from R kaempferi var. macrogemma. From these results, we conclude that the mode of ptDNA inheritance is controlled by at least one major gene in the maternal nucleus.
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