Propagation of novel hybrid sweetgum phenotypes for ornamental use via somatic embryogenesis. (Special Issue: New methods of in vitro plant propagation.)

摘要

Somatic embryogenesis may have greater potential for propagation of forest trees for ornamental purposes than for production forestry. Somatic embryogenesis-derived hybrid sweetgum (Liquidambar styraciflua x Liquidambar formosana) clones, originally developed for pulp and paper and biomass energy, have displayed a range of growth rates and other phenotypic variation. While some of the fast-growing clones show promise for fiber production, others offer potential as ornamental trees. We investigated variables to try to improve somatic seedling quality of the most interesting hybrid sweetgum clones. A pre-germination cold treatment of at least eight weeks improved both germination frequency and conversion frequency of the somatic embryos to close to 100%, and produced more vigorous plantlets than embryos given a four-week cold treatment or no cold treatment. Germinating embryos vertically in test tubes rather than on plates of gelled medium helped eliminate a problem with crooked root collars in the resulting somatic seedlings, which had previously been found to lead to a higher chance of stem breakage. The potential for a group of eight-year-old hybrid clones that had displayed outstanding growth rates in a test planting to be propagated via somatic embryogenesis using mature tree tissues was studied using staminate inflorescence explants collected from dormant buds. Embryogenesis induction for the three clones ranged in the study from 1.6% to 12.8%, depending on clone and plant growth regulator treatment, with NAA providing a higher induction frequency than TDZ. A demonstration planting of somatic seedlings representing seven hybrid sweetgum clones revealed a number of potentially useful ornamental phenotypes after one season of growth, with some clones growing over 1.1 m in 4 months and others with dwarf or shrub phenotypes. Some clones also displayed striking fall leaf color. The manipulation of embryogenic suspension cultures of the hybrid clones will enable the synchronous production of thousands of propagules of the most desirable clones for horticultural and other applications.