A Trailing, Low-temperature Tolerant, Double-flowered Interspecific Torenia

Torenia fournieri Linden is a popular summer bedding plant but cannot overwinter due to low-temperature intolerance. Few trailing and double-flowered Torenia cultivars are available on the markets. The objective of the study was to breed a trailing, low-temperature tolerant, and double-flowered Torenia. Crosses were made using T. fournieri ‘Clown Rose’ and T. benthamiana Hance, a trailing, Taiwan-native perennial species. On day 16 after pollination, self-pollinated ‘Clown Rose’ had fully developed embryo and endosperm whereas ‘Clown Rose’ × T. benthamiana had arrested at the heart/torpedo stage embryo and degenerating endosperm. The hybrid ovules were then rescued on 1/2 MS medium with 6% sucrose and thus the hybrid seedlings were obtained. After 15/13 ^oC treatment for two months, the hybrid progenies grew well and flowered whilst ‘Clown Rose’ died. We treated the nodes of the hybrid with 1% colchicine in vitro and obtained a tetraploid line with larger flowers. Floral buds of the tetraploid line were treated with 1 mM sodium azide and then cultured in vitro to induce adventitious buds.  Following ex vitro rooting and culture, a double-flowered mutant was selected with trailing and low-temperature tolerant characteristics.