The genus Cornus contains 58 species of trees, shrubs, and herbs with C. florida L. and C. kousa F. Buerger ex Hance considered the most economically important to the ornamental tree industry (Wadl et al. 2014). These trees display various sized colorful bracts of white, pink, or red in the spring; vibrant green, red, or variegated foliage in the summer; and brilliant-red foliage in the fall. The showy foliage and colorful bracts make Cornus species prized ornamentals. Cornus florida is native to North America and grows wild as an important understory tree in many native forests. Cornus kousa, the Asian or Chinese dogwood, is native to east Asia and has the ability to hybridize with C. florida (Cappiello and Shadow 2005; Mattera 2016; Mattera et al. 2015; Molnar et al. 2017; Orton 1993; Shearer and Ranney 2013a, 2013b). Asian dogwood was introduced to North America primarily for ornamental purposes due to its showy bracts and tolerance to many pathogens, including powdery mildew [Erysiphe pulchra (Cooke & Peck) U. Braun & S. Takamatsu] and dogwood anthracnose (Discula destructiva Redlin) that plague C. florida (Holmes and Hibben 1989; Ranney et al. 1995; Wadl et al. 2014). As of 2020, there have been more than 70 cultivars of Asian dogwood developed, and some interspecific hybrids between C. florida and C. kousa have been released for use in home and commercial landscapes (Cappiello and Shadow 2005; Nowicki et al. 2018, 2020). The first interspecific hybrid was released in the early 1990s and is known as the C. × rutgersensis cultivar (Mattera 2016; Mattera et al. 2015; Molnar 2016). Together, sales of C. kousa and C. florida cultivars yield about $30 million in sales each year (Nowicki et al. 2018; US Department of Agriculture National Agricultural Statistics Service 2012, 2020). Both dogwood species and hybrids are primarily produced in Tennessee and New Jersey, USA, and sold as 1-year-old “liners” (Wadl et al. 2014).
Origin
‘Melissa’s Mountain Snowfall’ (PP32706 P3) and ‘Sarah’s Mountain Pixie’ were both developed alongside ‘Pam’s Mountain Bouquet’ (Wadl et al. 2014) and were selected from a plot of 30-year-old trees at the University of Tennessee Forest Resources AgResearch and Education Center, Oak Ridge, TN, USA. The original plot was selected from ∼400 seedlings for pathogen resistance screening as described in Augé et al. (2002). Specifically, the seeds were produced via open pollinated ‘Big Apple’, ‘Snowbird’, ‘Steeple’, and an unnamed accession by Polly Hill of Barnard’s Inn Farm, MA, USA in 1989. In 1994, all the seedlings were evaluated for resistance to fungi causing dogwood anthracnose and powdery mildew and those exhibiting disease resistance were planted at the University of Tennessee Forest Resources AgResearch and Education Center in Oak Ridge, TN, USA (US Department of Agriculture Hardiness Zone 7a). Dogwoods were planted on 10-foot centers (∼3 m) according to Witte et al. (1996). The trees at the site have been continuously monitored to the present date for disease and insect presence as well as unique physical characteristics.
‘Melissa’s Mountain Snowfall’ Description
‘Melissa’s Mountain Snowfall’ (PP32706 P3) is a multistem tree that develops an inverted pyramidal shape growing 16 to 20 feet (5 to 6 m) high and ∼23 feet (7 m) wide (Fig. 1A). Exfoliating bark on the main stem is bicolored: Greyed-Orange Group 198B and Green Group 143C and exfoliating areas are Greyed-Brown 190–199D (all colors for the cultivars are made with comparison with those provided by the Royal Horticultural Society 2001 Color Chart) and gives the trunks an exaggerated textured appearance (Fig. 1B). Leaves (Green Group 137D) are obovate-shaped, nonrolling, and average ∼3.5 (∼8.7 cm) inches long by ∼2 inches (∼4.4 cm) wide. The major veins are Yellow-Green 145B (Fig. 1C). Peak fall foliage is Red Group 46A. The four bracts are pure white and variously fused (2 to 4) (Fig. 1C). Globose fruit (1.2 inches or 3 cm diameter) are muted red (Red-Purple Group 60D–61A) in the fall and often subtended by a “collar” of fused bracts encircling the fruit pedicle (Fig. 1D). ‘Melissa’s Mountain Snowfall’ (PP32706 P3) is perhaps a half-sibling of ‘Pam’s Mountain Bouquet’ (PP25,575 P3) because of the fused bracts characteristic (Moreau 2022; Wadl et al. 2014). All C. kousa cultivars developed by the University of Tennessee contain “Mountain” in the cultivar name.
‘Melissa’s Mountain Snowfall’. (A) Reversed pyramidal form of the 30-year-old tree. (B) Multiple stems and exfoliating bark. (C) Variously fused bracts. (D) Fall fruit with “collar” of fused bracts subtending and circling the pedicle of the fruit.
Citation: HortScience 59, 1; 10.21273/HORTSCI17489-23
‘Sarah’s Mountain Pixie’ Description
‘Sarah’s Mountain Pixie’ is a short, bushy, single trunk, Grey Group (201A) tree, growing only 12 to 15 feet (4 to 5 m) in 30 years (Fig. 2A). The widely ovate leaves are green (Green Group 137D) with 3 inches (∼7 cm) wide. The wide leaves have Yellow-Green 151D major veins (Fig. 2B). The pure white, small (2 inches or 5 cm) bracts are spade-shaped, taper to a point, slightly overlapping but never fused (Fig. 2C). The large (mean 1.5 inches or 3.8 cm in diameter, but often larger) fruits are a bright red-purple (Red-Purple Group 58C) when mature in the fall.
‘Sarah’s Mountain Pixie’. (A) Bushy tree form of ‘Sarah’s Mountain Pixie’. (B) Large leaves. (C) Spade-shaped bracts. (D) Large fruits in the fall.
Citation: HortScience 59, 1; 10.21273/HORTSCI17489-23
Molecular Identification (Genetic Analyses) of Cultivars Using Microsatellite Markers
Microsatellite markers [simple sequence repeats (SSRs)] were used to compare ‘Melissa’s Mountain Snowfall’ and ‘Sarah’s Mountain Pixie’ to other closely related cultivars and unnamed accessions in the University of Tennessee Forest Resources AgResearch and Education Center planting (Table 1) (Wadl 2009; Wadl et al. 2008). ‘Melissa’s Mountain Snowfall’ and ‘Sarah’s Mountain Pixie’ were compared with eight trees at seven loci from the same plot and two commercially available cultivars. Data were analyzed using Qiagen ScreenGel (Qiagen, Germantown, MD, USA) and binned using the method of Amos et al. (2007). The raw data from the SSR analyses is presented in Table 2. ‘Sarah’s Mountain Pixie’ and ‘Melissa’s Mountain Snowfall’ differ greatly at these loci (Table 2) and were easily differentiated from all other samples included in the study when comparing the data from only two SSR markers (Fig. 3).
Primers used to analyze cultivars and accession of Cornus kousa.
Characterization of Cornus florida cultivars using simple sequence repeats. Numbers are base pairs in alleles.
Separation of Cornus kousa cultivars and unnamed accessions (PHKxxx) using simple sequence repeats (SSRs). ‘Mountain Snowfall’ and ‘Mountain Pixie’ are identifiable using two SSRs.
Citation: HortScience 59, 1; 10.21273/HORTSCI17489-23
Availability.
For additional information and availability of the cultivars, contact R. N. Trigiano (rtrigian@utk.edu).
References Cited
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