Induction of Fertile Amphidiploids by Artificial Chromosome-doubling in Interspecific Hybrid between Dianthus caryophyllus L. and D. japonicus Thunb

Abstract

Amphidiploid induction by chromosome-doubling is the most efficient method of utilizing a sterile interspecific hybrid for breeding. Previously, although we successfully obtained an interspecific hybrid between carnation (Dianthus caryophyllus L.) and Dianthus japonicus Thunb., the hybrid was sterile. In the present study, therefore, attempts were mode to induce amphidiploids to restore the fertility by artificial chromosome-doubling, i.e., by applying drops of a colchicine solution on to the shoot tips of greenhouse-grown plants or by treating nodal segments excised from in vitro-grown plants by incubation in a colchicine or amiprophos-methyl (APM) solution. Among 156 hybrid plants regenerated after these treatments, nine were revealed to be tetraploids, in addition to one octoploid and 88 mixoploids. Colchicine dropping treatment at a concentration of 2,000 mg·l−1 for one day led to the highest rate (14%) of tetraploid formation, whereas 10% tetraploid formation was obtained by in vitro shaking culture with 5 and 10 mg·l−1 APM for 24 hrs. The amphidiploids exhibited a larger flower size and later flowering time than the original diploid hybrid, and the fertility of both pollen and seed was restored. These amphidiploids are expected to be used for the breeding of carnation cultivars, which are suitable for growing under the Japanese climatic conditions.