The hazelnut breeding and genetics program at Oregon State University (OSU) has named and released two disease-resistant, red-leafed ornamental cultivars of European hazelnut, Corylus avellana L. The cultivars bring to the nursery industry new combinations of interesting growth habit, leaf form and color, and resistance to the fungal disease eastern filbert blight (EFB).
‘Red Dragon’, released in 2008, exhibits contorted growth in the shoots and leaves, and has beautiful dark purple and red color in the young foliage (Fig. 1). The red pigmentation is also seen in the young stems, bud scales, the nut husks, immature nut shells and the catkins, the male inflorescences.
‘Red Dragon’ is named for the image of a mythical Chinese dragon that the twisting shoots evoke. It is slightly more vigorous and its branches are less pendulous than those of ‘Contorta’ (also known as ‘Harry Lauder’s Walking Stick’), the well-known green-leafed contorted hazelnut of the nursery trade. Its leaves are moderately contorted and rolled, which partially exposes the contorted shoots to view during the growing season. The red coloration in the leaves fades as the leaves age, becoming an attractive mixture of red new growth and green older leaves.
Like most European hazelnuts, the natural growth habit of ‘Red Dragon’ is a multi-stemmed shrub and if a single-stemmed tree form is desired, the sucker shoots arising at the base of the plant must be cut off several times during the spring and summer. With sucker removal, ‘Red Dragon’ grows into a round-headed, upright-spreading tree form, reaching 10 feet in height in 15 years (Fig. 2). In either growth form, pruning to open up the canopy and highlight the snaking, twisted shoots will maximize the enjoyment of this ornamental trait (Fig. 3).
‘Red Dragon’ will produce small nuts in red husks, but only if there is another compatible hazelnut nearby to provide pollen, as hazelnuts will not set seeds through self-pollination. In the Willamette Valley, this could occur commonly, but nuts and husks may not be seen when it is planted elsewhere. Fall leaf color is an unassuming but pleasant yellow.
The catkins on ‘Red Dragon’ add attractiveness in the winter, especially when they elongate during bloom in late winter or early spring. The female flowers are inconspicuous tiny red filaments, much smaller than those of witch hazel or winter hazel. ‘Red Dragon’ can be a stand-alone focus plant in a landscape that provides year-round interest.
The second ornamental hazelnut from our breeding program is ‘Burgundy Lace’, a cutleaf type with purple-red leaf color. A controlled cross was made in 1998 between two selections carrying the recessive allele for dissected leaf margins, derived from their common parent, C. avellana f. laciniata. One of these parents had red leaves, a dominant trait in hazelnut.
‘Burgundy Lace’ was chosen as the superior selection from among 38 seedlings in 2005, and after testing in a replicated trial for seven years, was named and released in 2015.
The leaf margins of ‘Burgundy Lace’ are deeply incised or dissected (Fig. 4), giving the tree canopy a lighter, airier appearance than standard European hazelnut. New leaf growth is a striking purple red, with the top surface of the leaves being darker than the undersides. As with all other red leaf forms of hazelnut, the red color is overtaken by green as the leaves age, and the canopy is a mixture of dark green older leaves and the purple-red young leaves.
With sucker removal, ‘Burgundy Lace’ grows as an upright-spreading, moderately vigorous tree that can reach 15 to 20 feet in height at 15 years (Fig. 5). Bud scales, immature husks and nuts, young shoots and catkins are also pigmented red.
Both ‘Burgundy Lace’ and ‘Red Dragon’ have the single dominant gene from the cultivar ‘Gasaway’ that confers resistance to the strain of EFB that occurs in the Pacific Northwest.
EFB is a tree-killing fungal disease that is endemic to the central and eastern United States. Wherever the disease exists, it has severely limited the long-term survivability of European hazelnut. EFB is now widespread throughout western Oregon, Washington and coastal British Columbia. Both of the new ornamental cultivars have remained free of EFB after many years of field exposure under high disease pressure at our research farm and in controlled inoculations.
Disease resistance in other areas of the U.S. may be similar or less than in Oregon, based on our experience with commercial nut varieties, but will be significantly better than a selection that does not have the ‘Gasaway’ gene. They have also survived unscathed through a -10 F freeze in December 2014 and mid-winter cold hardiness of buds and wood is expected to be similar to that of ‘Contorta’. ‘Red Dragon’ is intended as a replacement for ‘Contorta’, which is extremely susceptible to EFB.
Based in Corvallis, Oregon, the breeding program has been focused on genetic improvement of hazelnut for Oregon’s commercial hazelnut industry since 1969. The program has been led by Dr. Shawn Mehlenbacher for the past 33 years. In that time, we have selected and released more than 20 new main crop cultivars and pollinizers, plus these two ornamental types. The ornamental cultivars came about through investigation of the inheritance of naturally occurring growth habit, leaf color and leaf form mutants. We are always striving to learn more about the inheritance and interaction of the numerous growth and color variants in hazelnut.
We have identified several mutants in addition to contorted growth and red leaf color, including two chlorophyll deficiency (yellow leaf) mutants, pendulous growth, yellow female style color, and cream-colored pollen. Most of these mutants are recessive traits, meaning that they are expressed in an individual only if it inherits a recessive allele from both parents. If it were simply a matter of crossing two siblings that each have a recessive allele, the breeding effort would be easy. But because of the self-incompatibility issue, many individuals cannot be crossed in such a direct fashion.
In the case of ‘Red Dragon’, it required finding two seedlings, both descended from ‘Contorta’, that could be intercrossed and both carrying the recessive allele for contorted growth. Hopefully, we will one day produce more interesting combinations, such as a cutleaf contorted or a cutleaf pendulous, or combinations of the yellow, green and red leaf colors. The search goes on, to add to our knowledge about the genetics of hazelnut and to also bring beautiful, unusual ornamentals to the nursery trade.
‘Red Dragon’ and ‘Burgundy Lace’ are protected by U.S. plant patents and propagation for sale is restricted to nurseries that have licensed the rights to do so. If you are interested in becoming a licensee, contact Denis Sather in the OSU Office for Commercialization and Corporate Development at Oregon State University at [email protected].
David Smith has worked as an assistant to the hazelnut breeder in the Horticulture Department at Oregon State University since 1982. He can be reached at [email protected].
