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We report here an efficient and high-frequency protocol for direct shoot bud differentiation from mature leaves and petioles of greenhouse-grown Begonia tuberhybrida plants. Shoot buds were induced directly on the adaxial surface of leaf tissues from not only at the cut ends, but also across the entire surface of both leaf and petiole segments. The highest frequency of shoot bud formation was 90%, and the maximum number of shoots (132) per leaf explant was achieved with modified Murashige and Skoog (MS) (Murashige and Skoog, 1962) media supplemented with 1.0 mg·L−1 α-naphthalene acetic acid (NAA) and 2.0 mg·L−1 thidiazuron (TDZ). In petioles, the highest frequency of shoot buds was 82%. A maximum number of 33 shoots per explant was achieved with 0.5 mg·L−1 NAA and 2.0 mg·L−1 TDZ. The number of shoots produced in both explants was drastically reduced in the treatment with benzyl-aminopurine (BAP) alone or in combination with NAA and/or TDZ. The regenerated shoots were rooted on MS medium supplemented with 0.5 mg·L−1 NAA. All the elongated shoots developed into complete, rooted plantlets within 3 months. All the plantlets were successfully transferred to soil in pots in the greenhouse and they produced morphologically normal flowers. Chemical names used: α-naphthalene acetic acid (NAA), N-phenyl-N′-1,2,3-thiadiazol-5ylurea (TDZ; thidiazuron), 6-benzyl aminopurine (BAP)

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Protocols for in vitro propagation are reported for interspecific hybrids of Exacum L., derived from Sri Lankan taxa. Four genotypes were used to evaluate the effects of MS (Murashige and Skoog) and WP (Woody Plant) media supplemented with 2-iP, BA, or KIN during establishment and multiplication phases. In addition, rhizogenesis and associated root characteristics were evaluated using MS medium supplemented with NAA or IBA. Overall, either 2-iP or BA was significantly more effective than kinetin in establishment and shoot proliferation with significant genotype × treatment interactions present. Maximum multiplication rates were achieved in the following genotype-hormone combinations: E-6, 2 mg·L-1 BA (4.5 per explant); E-23, E-32, and E-37, 2 mg·L-1 2-iP (3.5, 2.5, and 3.6 per explant, respectively). In vitro rhizogenesis was greatest in liquid MS medium supplemented with 1 mg·L-1 NAA while significantly reduced rooting was observed with IBA supplements. Our results demonstrate that micropropagation of Sri Lankan Exacum hybrids is possible and that adequate multiplication and rooting percentages can be achieved. However, the high level of genetic variation identified requires genotype-specific media modifications. Chemical names used: benzyladenine (BA); 2-isopentenyladenine (2-iP); indole-3-butyric acid (IBA); α-naphthaleneacetic acid (NAA); kinetin (KIN).