The goals of this research are to improve a system of cloning oaks (Quercus) using a containerized stoolbed and cutting technique. We investigated the effect of propagule position on rooting in two oak species, Quercus bicolor and Quercus macrocarpa, using cuttings and determined the effect of light, stem banding treatments and phenological aging (over a nine-week period) on rooting in cuttings. Anatomical investigations into the effects of etiolation, auxin efficacy and stock plant root restriction on productivity in this system were investigated. We hope to develop practical guidelines detailing the implementation of these methods so that growers may readily adopt these new methods.

The genus Quercus is one of the most important genera of woody plants in the northern hemisphere, with probably between 400-500 species. The high degree of environmental adaptability and genetic variation that exists in oaks makes vegetative propagation highly desirable. However, most oaks used in the landscape are propagated by seed because of the difficulty of propagating them asexually, either by cuttings, tissue culture or budding. The resulting seedlings vary in traits and superior plants are rarely introduced into the trade. Recently, however, the propagation of oaks has been improved by using the practice of etiolation in conjunction with a modified stoolbed technique. Research work here at the Urban Horticulture Institute is looking into ways of improving propagation using this technique. Moreover, oak hybrids have only rarely been able to be propagated and introduced into the nursery industry because of the difficulty in asexual propagation. Now, with successful asexual propagation techniques, it is possible to produce clones of oaks and to screen them for improved characteristics such as tolerance to alkaline soils, drought and poor drainage.

Greenhouse-grown hybrid oak seedlings were asexually propagated using the etiolated stoolbed method developed by Amissah and Bassuk. After chilling for three months, seedlings were cut back to 4 cm and grown under 98 percent light exclusion using black cloth in a 25 degree C greenhouse. When basal shoots were 8-10 cm long, the basal 2 cm of these etiolated shoots were treated with 8,000-indole butyric acid and covered with a bottomless pot filled with a moist peat/perlite mix. The apices of the shoots were uncovered and allowed to acclimate to light over a oneweek period by gradually raising the black cloth. After four-to-six weeks, the pots of peat/perlite mix were removed and rooted shoots removed from the stock plant and individually planted into containers to encourage strong root growth for the remainder of the growing season.
Clones of the oak hybrids were planted into sandy loam soil adjusted to 6.2 and 8.0 pH with lime. Chlorophyll will be measured and shoot growth measured at monthly intervals. As clones of the hybrids become more numerous, screening for hardiness in USDA Zone 5 will occur by allowing some clones to remain in the field for several years and their viability measured. Additionally, some clones will be exposed to flooding and drought intervals and their growth rates and carbon assimilation measured. Observations of plant growth habit, fall color and ease of transplanting will complete the screening process.

If our research leads to an effective and commercially viable technique for vegetative propagation of oaks and other woody plants, then superior trees and plants with desirable traits such as pest resistance, environmental stress tolerance, modified form and superior fall color could be selected for and cloned. There are many woody plants that could benefit from such a technique.
Moreover, this would allow growers to produce a new crop of highly desirable plants for the shade-tree market.

• Horticultural Research Institute
• Schmidt Foundation

• Naalamle Amissah (Horticulture)
• D. Paolillo (Plant Biology)