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EVIDENCE FOR INTROGRESSIVE HYBRIDIZATION BASED ON CHLOROPLAST DNA POLYMORPHISMS AND MORPHOLOGICAL VARIATION IN WILD EVERGREEN AZALEA POPULATIONS OF THE KIRISHIMA MOUNTAINS, JAPAN

Published online by Cambridge University Press:  04 December 2000

N. KOBAYASHI
Affiliation:
Institute of Agriculture & Forestry, University of Tsukuba, Tsukuba, Ibaraki 305–8572, Japan. Present address: Tatebayashi Azalea Research Station, Tatebayashi, Gunma 374–0005, Japan
T. HANDA
Affiliation:
Institute of Agriculture & Forestry, University of Tsukuba, Tsukuba, Ibaraki 305–8572, Japan. Present address: Tatebayashi Azalea Research Station, Tatebayashi, Gunma 374–0005, Japan
K. YOSHIMURA
Affiliation:
Forestry & Forest Products Research Institute, Kukizaki, Ibaraki 305–8687, Japan
Y. TSUMURA
Affiliation:
Forestry & Forest Products Research Institute, Kukizaki, Ibaraki 305–8687, Japan
K. ARISUMI
Affiliation:
Faculty of Agriculture, Kagoshima University, Kagoshima 890–0065, Japan
K. TAKAYANAGI
Affiliation:
Faculty of Agriculture, Kagoshima University, Kagoshima 890–0065, Japan
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Abstract

For the purpose of determining the origin of horticultural evergreen azalea cultivars, this study was focused on the natural populations of azalea in Kyushu (south main island of Japan). The Kirishima mountains, the volcanic mountain mass in Kyushu, are an important centre of diversity for the Japanese evergreen azaleas. Rhododendron kiusianum Makino grows above 1000m alt., whereas R. kaempferi Planch. is distributed below 600m alt. Putative natural hybrid populations of these two species are found in the intermediate region (1000–600m alt.). These two species have been clearly distinguished by their respective morphological features. Rhododendron kiusianum has small pink-purple flowers and small elliptical leaves, whereas R. kaempferi has larger red-orange flowers with dark blotches and large oblong leaves. Interspecific hybrids show phenotypes within the range of the two species, especially with regard to flower colour and leaf shape. A morphological cline of these characteristics corresponding to altitude has been observed between these two species. PCR-RFLP analysis of chloroplast DNA detected specific bands for the two species in the 16S rDNA region when digested with HhaI restriction enzyme. Populations of interspecific hybrids were composed of individuals that had a banding pattern of either R. kiusianum or R. kaempferi. This indicates that R. kiusianum and R. kaempferi are clearly distinct species. Furthermore, natural hybrid populations consist of individuals that have one of two cpDNA. Some individuals in the populations of R. kiusianum (T-1430 and T-1030) possess the cpDNA pattern of R. kaempferi, which suggests that cytoplasmic introgression has occurred in the populations of R. kiusianum from R. kaempferi.

Type
Research Article
Copyright
© 2000 Trustees of the Royal Botanic Garden, Edinburgh

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