Relationship between Nuclear Genome Construction and the Plastome-genome Incompatibility of Progenies from Intra- and Inter-ploid Cross of Evergreen Azaleas × Rhododendron japonicum f. flavum

Abstract

In intersubgeneric crosses of diploid evergreen azaleas (EV) × diploid Rhododendron japonicum f. flavum (JP), many progenies become albino as a result of plastome-genome incompatibility between a plastid genome from EV and a nuclear genome from JP. To clarify the mechanism of the incompatibility, inter- and intra-ploid crosses of diploid (2x) EV × diploid (2x) JP, tetraploid (4x) EV × tetraploid (4x) JP, 2x EV × 4x JP, and 4x EV × 2x JP were conducted. Seeds were obtained in all crosses, although the number of progenies per capsule was relatively low in crosses with 4x JP as a pollen parent. Plastome-genome incompatibility between a plastid genome from EV and a nuclear genome from JP was observed in progenies from 2x EV × 2x JP, 4x EV × 4x JP, and 2x EV × 4x JP, but not in 4x EV × 2x JP. This result indicates that plastome-genome incompatibility was broken by relative increase of the genome from EV in the nuclear genome of progenies.