Three New Cultivars of Cornus kousa: Empire, Pam’s Mountain Bouquet, and Red Steeple

Abstract

The genus Cornus contains 58 species of trees, shrubs, and herbs that are mostly distributed throughout the northern hemisphere (Xiang et al., 2006). Flowering dogwood (C. florida), kousa dogwood (C. kousa), and their interspecific hybrids are considered the most popular and economically significant members of the genus in the nursery and landscape industries. These deciduous trees are valued for their spring display of pink, red, or white bracts, brilliant-red fall foliage, and exfoliating bark. Retail and wholesale sales of dogwood in the United States account for over $30 million dollars annually with 73.1% of these sales coming from eight states [Maryland, Minnesota, New Jersey, North Carolina, Ohio, Oregon, Pennsylvania, and Tennessee (U.S. Dept. of Agriculture–National Agricultural Statistics Service, 2010)]. Sales in Tenneessee account for 21.9% of total sales of deciduous flowering trees, making it an important crop for the state’s economy. Additionally, six counties in Tennessee produce substantial amounts of 1-year-old liners that are sold to out-of-state nurseries for finishing and resale. In nursery production, a liner refers to a small tree that is transplanted and allowed to become a larger tree for sale by wholesale or retail outlets. These liners ultimately supply 80% of the country’s dogwoods (Simmons, 2002). Large-bracted dogwoods are widely grown throughout midtemperate regions of eastern North America, both in the wild and as coveted ornamental trees in urban and suburban landscapes. Across this range, flowering dogwoods have been severely affected by dogwood anthracnose [Discula destructiva (Redlin, 1991)] and powdery mildew [Erysiphe pulchra (Li et al., 2009)]. Because of the importance of dogwoods to the U.S. agricultural economy, an improvement program was initiated over 20 years ago at the University of Tennessee to develop disease-resistant cultivars of dogwoods. These efforts have resulted in the release of the first flowering dogwood cultivar (Appalachian Spring) with resistance to dogwood anthracnose (Windham et al., 1998) and three powdery mildew resistant cultivars: Jean’s Appalachian Snow, Karen’s Appalachian Blush, and Kay’s Appalachian Mist (Windham et al., 2003). Cornus kousa is more tolerant to anthracnose and powdery mildew than C. florida (Holmes and Hibben, 1989; Ranney et al., 1995). Hybrids between these two species are generally more vigorous than typical plants of either parent species and have field resistance or tolerance to dogwood anthracnose and powdery mildew (Ranney et al., 1995). There are over 100 named cultivars of C. kousa and many cultivars are the result of either selection of open-pollinated seedlings or spontaneous sports rather than systematic breeding (Cappiello and Shadow, 2005). The objective of this project was to evaluate 400 seedlings of C. kousa for disease resistance and horticultural traits such as color, degree of overlap, size of bracts, tree form, and bark and leaf characteristics. From these, three genotypes were selected for development and release.