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  • Author or Editor: Andrew Riseman x
  • Journal of the American Society for Horticultural Science x
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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).

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Interspecific hybrids of exacum (Exacum L.) display variable responses to zinc nutrition. Our research compared two genotypes with contrasting zinc efficiency phenotypes in terms of root cation exchange capacity (CEC), whole plant 65Zn uptake, and the effects of Cu+2 and Mg+2 on 65Zn uptake and partitioning to shoot tissues. Results show that the zinc efficient and inefficient genotypes had significantly different root CEC [27.2 and 16.9 cmol(+)·kg-1 root dry weight (DW), respectively] and whole plant 65Zn uptake rates (0.048 and 0.026 μmol·h-1·g-1 DW, respectively). In equimolar concentrations to Zn+2, Cu+2 reduced Zn+2 uptake by approximately 50% in both genotypes while supplemental Mg+2 enhanced Zn+2 uptake. In addition, Mg+2 facilitated a larger proportion of absorbed 65Zn to the upper shoot of the efficient genotype. We conclude zinc is absorbed through a specific Zn+2/Cu+2 transporter and that zinc efficiency in exacum is based on a combination of apoplastic and symplastic traits. In addition, a secondary Mg+2 × Zn+2 interaction may contribute to the zinc efficiency phenotype.

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