Cytological and genetic clarification of paternal inheritance of chloroplast genome in Rhododendron.

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The genetic factor controlling the mode of plastid DNA (ptDNA) inheritance in Rhododendron was investigated using polymerase chain reaction?single-stranded conformation polymorphism analysis at the trnL?trnF intergeneric region. When the reciprocal cross between R. kaempferi var. macrogemma (MCR) (F type) and R. transiens (TRA) (S type) was conducted, a high frequency of paternal ptDNA inheritance was observed in S × F and a low frequency of paternal ptDNA was observed in the reverse cross, as reported previously. When F1 plants from the cross between MCR and TRA were used as seed parents and crossed with R. simsii (SIM) (another F-type species), the pattern of ptDNA inheritance was segregated into 3 types : maternal》 paternal〓biparental, maternal〓paternal》 biparental, and maternal 《paternal》 biparental. This segregation occurred among the cross combinations even though the seed parents and MCR had identical ptDNA. From these results, we conclude that the mode of ptDNA inheritance is controlled mainly by the maternal nuclear gene(s).