African violet (Saintpaulia ionantha H. Wendl., syn. Streptocarpus ionanthus (H. Wendl.) Christenh.), of the family Gesneriaceae, is an economically important ornamental species. We have utilized leaf explants, Murashige and Skoog (MS) medium, and combinations of thiamine (vitamin B-1) and indole-3-butyric acid (IBA) for the development of an efficient method for rapid and high-quality shoot multiplication and root induction in S. ionantha. In the establishment step, primary explants (complete leaf; blade together with petiole) were cultured on the medium containing 100 mg L-1 phloroglucinol (PG), 0.5 mg L-1 gibberellic acid (GA(3)), 0.1 mg L-1 IBA, 2 mg L-1 6-benzylaminopurine (BAP), 0.1 mg L-1 thiamine and 250 mg L-1 antibiotic (Cefotaxime). Secondary explants (complete leaf with 5 mm of a stem), obtained from the establishment step, were transferred to the proliferation media enriched with different concentrations of thiamine (0, 0.05, 0.1, 0.15, 0.2 and 0.25 mg L-1) and IBA (0, 1, 2, 3, 4 and 5 mg L-1). A total of 36 combinations of these compounds were investigated as a factorial test on the basis of a completely randomized design. Results showed that the shortest time until axillary bud emergence (6.03 days), the highest number of green leaves (13.01), lowest number of yellow leaves (2.09), longest shoot length (7.20 cm), highest shoot fresh (6 g) and dry (1.2 g) weights and maximum multiplication coefficient (6) were obtained in the explants grown on the medium augmented with 2 mg L-1 IBA together with 0.1 mg L-1 thiamine. The highest number of microshoots (20.38 per explant) was produced on the medium enriched with 2 mg L-1 IBA and 0.2 mg L-1 thiamine. The shortest time until root emergence (11.15 days) and longest root length (1.94 cm) were achieved in a medium enriched with 4 mg L-1 IBA with 0.2 mg L-1 thiamine. The largest number of roots (79.7 per explant) was formed on the medium supplemented with 4 mg L-1 IBA and 0.2 mg L-1 thiamine. The treatment of 4 mg L-1 IBA and 0.25 mg L-1 thiamine was the best for root fresh and dry weights. In most measured traits, the lowest values were observed in the control medium. Rooted plantlets were transferred to pots filled with perlite and peat moss in 2:1 proportion and acclimatized to ambient greenhouse conditions with an even 98.6% survival rate. Therefore, the beneficial effect of thiamine in combination with IBA was confirmed and this protocol can be implemented for the mass production of African violet.
