Location: Floral and Nursery Plants Research2012 Annual Report
1a. Objectives (from AD-416):
The primary objective of this work is to develop seedless cultivars of invasive or potentially invasive nursery crops. Secondary objectives are to develop new technologies and methods to facilitate theses efforts and to further enhance pest resistance, adaptability, and commercial potential of these crops.
1b. Approach (from AD-416):
These efforts will focus on traditional breeding methods to develop seedless cultivars. Tetraploid clones will be identified or developed and then hybridized with diploids to create triploids. Additional approaches will include mutation breeding, wide hybridization and breeding for double flowers lacking pistils. Resulting progeny will be assessed for fertility and commercial merit. Target crops will include: amur maple (Acer ginnala), barberry (Berberis spp.), catalpa (Catalpa spp.), elaeagnus (Elaeagnus spp.), flowering crabapple (Malus spp.), flowering pear (Pyrus spp.), lace-bark elm (Ulmus parvifolia), miscanthus (Miscanthus spp.), mimosa (Albizia julibrissin), Norway maple (Acer platanoides), privet (Ligustrum spp.), spirea (Spiraea spp.), St. Johnswort (Hypericum spp.), and winged euonymus (Euonymus alatus).
3. Progress Report:
The objective of this agreement is to develop methodologies, approaches, and ultimately seedless cultivars of invasive, but commercially important, nursery crops. Ongoing efforts have been successful in building germplasm collections, methods development, and initiating tetraploid clones of the principal taxa of interest. As these tetraploids reach maturity, interploid crosses have been initiated resulting in triploid hybrids which are then evaluated for fertility and commercial characteristics. Additional efforts are focused on developing methods for inducing sterility through mutation treatments. Non-invasive cultivars of these species provide environmentally friendly and commercially desirable alternatives to older, invasive forms of these plants. Additional benefits from these seedless plants include elimination of nuisance fruits, reduced pollen-induced allergies, and improved flowering and re-blooming characteristics. These new technologies and products will be made available to the nursery industry and will ultimately benefit the environment and the general public. Ongoing progress has been made in the development of tetraploid and triploid plants in diverse genera of woody taxa. We have been successful in developing tetraploids of Acer tartaricum subsp. ginnala (amur maple), Acer platanoidies (Norway maple), Albizia julibrissin (mimosa), Cytisus spp. (Scotch broom), Exochorda (pearlbush), and Ulmus parvifolia (lacebark elm). As these plants reach reproductive age, we will complete interploid crosses to develop triploids. In some cases induced tetraploids can be sterile. In 2011 we released a new seedless, tetraploid form of Exochorda named ‘Blizzard’. In addition to tetraploids, we have successfully developed triploid forms of Campsis sp. (trumpet vine), Elaeagnus spp., Euonymus alatus (winged euonymus), Hypericum androsaemum (tutsan St. Johnswort), Koelreuteria paniculata (goldenraintree), Ligustrum spp. (privet), Miscanthus spp. (maiden grass), Pyrus spp. (flowering pear), and Spiraea japonica (Japanese spiraea). These plants are currently being evaluated for commercial merit and fertility. Studies were completed in 2011 to evaluate fertility of triploid trumpet vines and a new highly infertile triploid was documented and will be released under the name of ‘Chastity’. Fertility and reproductive pathways of triploid miscanthus were evaluated in an extensive study and published. Triploid plants were evaluated for male and female fertility using pollen viability staining and seed set and germination, respectively. Pollen viability staining, seed set, and seed germination from triploid plants were reduced compared with diploids but varied considerably within each cytotype. Overall, relative female fertility of individual triploids clones [(%seed set x %germination for triploid)/(%seed set x %germination for diploid control)] was reduced substantially and ranged from 49% to 0.7%. Additionally, the reproductive pathways of triploid plants were examined by evaluating the 2C genome sizes of progeny derived from open pollination. The limited progeny arising from open-pollinated triploids were predominantly aneuploids. The considerable reduction in female fertility in some triploid clones combined with the limited production of primarily aneuploid progeny provides highly infertile alternatives to existing diploid cultivars. Procedures have been developed for inducing sterility through mutation treatments for Berberis thunbergii (Japanese barberry) and Miscanthus spp. Tissue culture and chromosome doubling procedures have been successfully developed for Acer platanoides (Norway maple). Studies to evaluate the fertility of new seedless barberries have been initiated.