The remote hybridization and polyploid breeding in genus Rhododendron, so called azaleas and rhododendrons

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Genus Rhododendron consists of five subgenera. Various intersubgeneric hybridizations were conducted among four subgenera ; Hymenanthes, Rhododendron, Pentanthera and Tsutsutsi along with interspecific or remote hybridizations between species and/or cultivars belonging to section Rhododendron of subgenus Rhododendron.Of these various hybridizations following cross combinations were succeeded and many capsules were obtained, that is, Hymenanthes Rhododendron(or reverse), Hymenanthes Pentanthera, Tsutsutsi Pentanthera and Rhododendron Pentanthera. However, seeds of Rhododendron Hymenanthes and those of Rhododendron Pentanthera failed to germinate and cross combinations, Pentanthera Hymenanthes, Pentanthera Rhododendron and Tsutsutsi Rhododendron even failed to produce capsules. As being expected, hybridizations between species and/or cultivars belonging to Rhododendron were more successful than those between subgenera, although the degree of success was inferior as compared with interspe … More cific hybridizations within Hymenanthes, Pentanthera or Tsutsutsi because of genetic divergence attained in the process of evolution in Rhododendron. The offsprings obtained from Hymenanthes Rhododendron or Hymenanthes Pentanthera were expected to produce excellent yellow cultivars, whereas almost all of those from Tsutsutsi Pentanthera failed to form chlorophyll and thus more extensive hybridizations would be needed. The offsprings obtained from crosses within Rhododendron were also expected to produce forms with excellent yellow or blue flowers. In the latter case introduction of cytoplasm of pink forms was revealed to afford more vigorous growth.An attempt to produce polyploid was done using ordinary colchicine treatment, but it failed because summer of Kagoshima was too hot for survival of treated plants. Therefore, tissue culture was examined in which multiple shoot regeneration could induce. With the addition of cytokinins into media multiple soot production was revealed to be feasible. In the preliminary experiment, plantlets which seemed to be polyploid were obtained through 0.05% colcemid treatment for 3 to 5days. Less