Evaluation, Propagation, and Improvement of Gordonieae Trees and an Interspecific Hypericum Hybrid

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Experiments were conducted to evaluate disease tolerance of Franklinia Bart. ex Marshall, Gordonia Ellis, Schima Reinw. ex Blume and their hyrids to Phytopthora cinnamomi Rands., develop an effective vegetative propagation protocol of the three parental genera, and induce shoot regeneration and polyploidy in leaves of Hypericum hybrid H2003-004-016 cultured in vitro. Some trees in the Theaceae tribe Gordonieae are highly susceptible to root rot caused by P. cinnamomi. A collection of Gordonieae taxa were evaluated for tolerance to this pathogen. Abies fraseri (Pursh) Poir was included in the study as a positive control. Container-grown trees were inoculated with 3 isolates of P. cinnamomi, and symptoms were rated twice a week over an 84 day period during the summer of 2008. None of the Schima khasiana Dyer or Schima wallichii Choisy exhibited any root rot symptoms or mortality, while the rest of the taxa showed symptoms at varying levels over time. Symptoms in F. alatamaha and A. fraseri were apparent before other taxa, and mortality for both species reached 100% by the end of the experiment. Comparison of area under the disease progress curve (AUDPC) values indicated that F. alatamaha was the most susceptible, followed by A. fraseri. There was no significant difference in AUDPC among the more tolerant taxa including G. lasianthus, both Schima species, and the intergeneric hybrids. Hybrid taxa were similar to their more tolerant parental genus, indicating that tolerance to P. cinnamomi is a partially dominant trait in these plants. To develop an effective vegetative propagation protocol for 5 taxa of Gordonieae trees, hardwood, semihardwood, and softwood terminal stem cuttings were taken and treated with 0, 2500, 5000, 7500, or 10000 ppm potassium salt of indolebutyric acid (K-IBA) solution. The concentration of K-IBA affected rooting percentage in hardwood cuttings of F. alatamaha, G. lasianthus, and S. remotiserrata and had varying effects on root number and length of longest root amongst the different taxa and growth stages. Franklinia alatamaha and G. lasianthus were rooted at high percentages (>50%) at all growth stages, and S. khasiana rooted at high percentages (72%) from softwood cuttings. Schima remotiserrata Hung T. Chang and S. wallichii cuttings exhibited poor rooting (<25%) at all growth stages, with the highest rooting percentages for both species occurring at the hardwood stage. Hypericum H2003-004-016 is a complex hybrid between Hypericum frondosum Michx., Hypericum galioides Lam., and Hypericum kalmianum L. In vitro shoot regeneration and application of dinitroaniline herbicide oryzalin (3,5-dinitro-N4,N4-dipropylsufanilamide) were investigated as a means of inducing allopolyploidy. Regeneration was optimized for callus and shoot production through culture of leaf segments on MS medium supplemented with benzylamino purine (BA) or meta-topolin (mT) (5, 10, 15 μM) in combination with indoleacetic acid (IAA) (0, 1.25, 2.5, 5 μM). Both BA and mT treatments produced regenerative callus and shoots. Maximum regenerative callus (94%) and shoot production (18 shoots per callus) were optimized at 5 μM BA + 3.75 μM IAA. The exposure of regenerative callus to oryzalin at 0, 7.5, 15, 30, 60, and 90 μM concentrations for 3, 6, and 9 days was investigated for polyploid induction. There was no survival for any of the 60 and 90 μM oryzalin treatments, but all other treatments exhibited some survival and polyploidy induction. Both oryzalin concentration and exposure duration significantly influenced callus survival. Only concentration was a significant factor in polyploidy induction. The greatest percent (44.4%) of polyploids was produced at 30 μM oryzalin. Spontaneous chromosome doubling occurred in 8.3% of control explants receiving no oryzalin treatment.



Gordonieae Franklinia Gordonia Schima Hypericum ph





Horticultural Science