HortScience (Jul 2023)
‘Rebecca’s Appalachian Angel’: A Cultivar of Flowering Dogwood (Cornus florida) with Large Leaves and Floppy White Bracts
Abstract
Flowering dogwoods (Cornus florida L.) are relatively small deciduous trees that are popular as landscape ornamentals and native to the eastern United States and Canada. Cornus florida is classified in the red-fruited, big-bracted dogwood clade, which also includes C. nuttallii Audubon ex Torr. and A. Gray) (Pacific dogwood) and C. kousa F. Buerger ex Hance (Kousa dogwood; Asian dogwood) (Call et al. 2016; Eyde 1988; Mantooth et al. 2017). Flowering dogwood cultivars have showy bracts in spring, brilliant red foliage in fall, distinct red berries into winter, and graceful year-round architecture that has earned them a reputation for four-season appeal (Cappiello and Shadow 2005). Cornus florida has achieved the status of state flower or tree in North Carolina, Virginia, and Missouri (Missouri Botanical Garden 2023; NC State Extension 2023). In 2019, cultivars of flowering dogwood ranked third in value for deciduous flowering trees in the U.S. and generated more than $31 million in wholesale and retail sales from 1.2 million trees. Tennessee leads the United States in the number of dogwood plants sold, selling almost twice the number of trees as Oregon, the state ranked second in the country (US Department of Agriculture National Agriculture Statistics Service 2020). Although flowering dogwoods are well known for their year-round appeal, they are best recognized for their spring display of inflorescences where the large white to pink to red “floral” bracts subtend a collection of 20 to 30 small, less conspicuous flowers. The bracts are commonly referred to as petals but are modified leaves (Cappiello and Shadow 2005). The ornamental interest of C. florida also extends to the developing leaves, which vary in color by cultivar. Some leaves are various shades of green, whereas others have either red-pigmented, some degree of red pigment, or variegated leaves. The pink and red colors in the vegetative tissues of dogwoods are a result of anthocyanin biosynthesis (Wadl et al. 2011). Cornus florida is native to eastern North America and ranges from Massachusetts to Florida and northwest into Ontario, Canada, and south to Texas (Little 1979). In addition to being a significant ornamental species, this understory tree also plays a large ecological role, especially with calcium in the soils of forest habitats. Cornus florida leaves and fruits are high in calcium, making the leaves especially important for the calcium cycle in forests (Thomas 1969) and landscapes. Flowering dogwood fruits are small, single-seeded (occasionally dual-seeded) drupes that develop in clusters of up to 12 on the inflorescence disc and range in color from orange to red. In addition to a high concentration of calcium, the fruits also contain abundant fats and proteins, which makes them an important source of nutrients for wildlife (Halls 1977). Various mammals and birds feed on the berries of C. florida and use the trees as habitat (Eyde 1988; Stiles 1980). Pollination is affected by a variety of insects, but the main groups are andrenid and halictid bees as well as cerambycid beetles (Rhoades et al. 2011). Cornus florida blooms in late March/early April in the southern United States with its leaves emerging either shortly before or after or concurrently with flowering depending on the location and cultivar. Flowering is affected by physical location of the tree and is considerably delayed in the northern United States and Canada compared with the southern United States. The bracts vary from round to narrowly ovate to cordate and cover the true flowers throughout the winter. The timing of flowering depends on air temperature (De La Pascua et al. 2020; Reader 1975), making the early emerging bracts of C. florida susceptible to frost damage and subsequent infection by Elsinoe cornii Jenkins and Bitanc. (spot anthracnose). This malady causes the bract tissues to produce red-purple lesions, which cause only cosmetic damage and presents no future consequences for the tree. Pests and diseases have plagued C. florida in the past few decades. The main pest of C. florida is the common dogwood borer (Syanthedon scitula) but can largely be mitigated with cultural techniques (Fulcher et al. 2012). The emergence of dogwood anthracnose (caused by Discula destructiva Redlin) in the mid-1970s devastated natural populations of C. florida, especially in the cooler climates and mountains of the eastern United States (Hadziabdic et al. 2010; Pais et al. 2020; Redlin 1991). However, dogwood anthracnose has not been a major concern for nursery production in recent years (Fulcher et al. 2012) because of prophylactic chemical control measures, lack of conducive environments (cool, wet, and shady) for disease development in the nurseries, and the introduction of the only anthracnose resistant cultivar, ‘Appalachian Spring’ (Windham et al. 1998). Furthermore, many locations with a favorable environment for disease development now lack dogwoods. The primary disease problem with C. florida for the nursery industry as well as homeowners and the landscape industry is the annual epidemic of powdery mildew caused by Erysiphe pulchra (Cooke and Peck) U. Braun and S. Takam (Klein et al. 1998; Li et al. 2009; Windham et al. 2005). This disease emerged in the United States in approximately 1994 and, although not fatal to trees, caused the destruction (unsalable) of tens of millions of dogwoods in production at the time. The presence of powdery mildew has caused the management costs of dogwoods to skyrocket from only $120/ha/year to $1975/ha/year (Li et al. 2009). The Appalachian Series of C. florida including ‘Appalachian Joy’ (PP 18,238 P2) (Trigiano et al. 2016), ‘Jean’s Appalachian Snow’ (13,099 P2), ‘Karen’s Appalachian Blush’ (13,165 P2) and ‘Kay’s Appalachian Mist’ (13,098 P2) (Windham et al. 2003) and ‘Erica’s Appalachian Sunrise’ (unpublished, 2020; PP32468) are resistant to powdery mildew and have somewhat mitigated the higher cost of production.
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