Chromosome doubling of Torenia hybrids by using efficient adventitious shoot regeneration in vitro

Torenia is a popular summer bedding plant, with an increasing number of commercial Torenia cultivars derived from interspecific crosses. Interspecific hybrids are often sterile, which limits their further use in breeding programs, but chromosome doubling is a way to restore pollen fertility. Efficient regeneration is required to obtain chromosome-doubled plants through colchicine treatment in tissue culture. Scarification of leaf explants enhanced adventitious shoot regeneration when cultured on MS medium with 2 mg L^‑1 BA. Leaf explants with scarification were cultured on the MS medium with BA for 15 days, then transplanted to MS medium without BA and supplemented with colchicine. The number of regenerated shoots per explant decreased from 12 to 0.26 with an increase in colchicine concentration. Treatment with 1500 mg L^‑1 colchicine for 20 days was found to be optimal for tetraploid induction. All the tetraploid Torenia produced fertile pollen, with the pollen germination percentage varying from 8.7 to 65.4 depending on hybrids. The tetraploid Torenia had bigger flowers and leaves compared with the diploid plants.