Restoring Fertility for Novel Interspecific Hybrids between Kalanchoe garambiensis and K. nyikae Using Colchicine Treatment

Interspecific hybridization is an effective strategy in Kalanchoe breeding programs for the introduction of new traits. Wild species within the Kalanchoe genus are valuable genetic resources for providing new horticulture traits and to improve environmental adaptations. However, reproductive barriers associated with fertilization and hybrid sterility must be overcome to produce fertile hybrid progenies. To approach the breeding objectives for Kalanchoe cut flower cultivars with long stem traits and adaptation to tropical/subtropical regions, a tropical species endemic to Taiwan, Kalanchoe garambiensis Kudo, was used as a parent to cross with other long stem Kalanchoe species. Reciprocal crossing was effective in overcoming interspecific unilateral incompatibility in our crossed pairs. One superior hybrid, ‘103-1’, produced capsules without seeds by selfing and backcrossing with pollens from either parent. Other than the seedless trait, failure of pollen releasing from anther, pollen aggregation and no pollen germination in ‘103-1’ suggested its F(1) sterility. Colchicine treatments on apical buds of ‘103-1’ successfully overcame potential meiotic abnormalities by doubling ploidy. For the first time, fertile interspecific hybrids of K. garambiensis and K. nyikae Engler were generated. The fertile hybrid has further produced progeny populations by crossing with K. nyikae or K. blossfeldiana von Poelln, ‘Ida’.