Using R. mucronulatum, R. schlippenbachii, R. japonicum, R. yedoense and R. indicum, which are widespread in the vicinity of Suweon, Korea, this study was carried out to determine the optimum germinating temperature of each species and to investigate the light effect to develope the method of seed propagation of these Rhododendron spp.
The results are concluded as follows:
1. The seeds of 5 rhododendron species did not germinate at constant temperature under darkness, but they tended to germinate under dark when alternating temperature range was increased.
2. The seeds of 5 species could germinate easily at constant temperature under light. In R. mucronulatum, R. schlippenbachii and R. japonicum, which are deciduous, the seed germination was best at 20℃ and 25℃ but not good ai high temperature 35℃. However in R. yedoense and R. indicum seeds, which are evergreen, germinated well at high temperature 30℃ and 35℃.
3. Three deciduous rhododendron seeds germinated well at alternating temperature 20-30℃, 15-20℃ and 15-30℃ respectively, while two evergreen seeds germinated at high alternating temperature 20-35℃ and 20-30℃ under light respectively. The alternating temperature under light showed additive effect of seed termination of rhododendrons than that constant temperature under light.
4. In R. schlippenbachii the best germination (64%) was obtained by prechilling the seed at 5℃ for 4 weeks. R. japonicum seeds germinated best at 5℃ of prechilling treatment for 4 weeks. But R. mucronulatum, R. yedoense and R. indicum seeds did not germinate well prechilling treatment.
5. R. mucronulatum seeds showed the highest germination with 83% on 4th day after seeding under 72hr long light treatment. The germination of these seeds increased with increase of light duration. The highest germination of these seeds was 72% at 5000 lux in long light duration of 24hrs. The germination percent of seeds increased with increase of light duration at each of ligh intensities.
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