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To obtain basic informations for use in Korean native Rhododendron breeding program, we performed intra- and interspecific crosses among three Korean species, one Japanese species, and one group of unidentified species. Generally intraspecific crosses were very compatible, but most interspecific crosses except several cross combinations showed incompatibilities. R. mucronulatum for. albiflorum crossed well with R. mucronulatum. Four accessions of unidentified species showed no genetic barriers with R. yedoense var. poukhanense and high compatibility each other within group. Crosses between R. japonicum and unidentified species u3 showed unilateral cross compatibility, i.e., there was compatibility only when R. japonicum was used as pollen parent. Therefore u3 presented the possibility of a bridge role in crosses between Korean native rhododendron and Japanese ones. R. schlippenbachii was incompatible in crosses both as seed parent and as pollen parent with the other species. Pollinations using a stored pollen of R. mucronulatum with the other species produced no capsules, but R. mucronulatum produced a little seeds from crosses with flowering forced unidentified species u4. Pollen germination and pollen tube growth in the female parent were good in all cross combinations which was compatible or incompatible. Therefore the cross incompatibility among Korean native rhododendron species may be due to interspecific genetic barriers after arrival of pollen tube at ovary. We discussed several subjects related to results of this experiment.
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