‘Appalachian Joy’ is a supernumery, white-bracted cultivar of cornus florida resistant to powdery mildew

Authors: TRIGIANO, ROBERT - University Of Tennessee; WINDHAM, ALAN - University Of Tennessee; WINDHAM, MARK - University Of Tennessee; Wadl, Phillip

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/25/2016
Publication Date: 6/9/2016
Citation: Trigiano, R.N., Windham, A.S., Windham, M.T., Wadl, P. 2016. ‘Appalachian Joy’ is a supernumery, white-bracted cultivar of cornus florida resistant to powdery mildew. HortScience. 51(5):592-594.

Interpretive Summary: Nursery sales in Tennessee are over $200 million annually and flowering dogwood sales are in excess of $50 million, making the tree an important ornamental species. The fungal diseases, dogwood anthracnose and powdery mildew, have increased production costs for nursery growers and has forced many small growers to cease production of dogwoods. There is limited host resistance available for these diseases, with the cultivar Appalachian Spring having strong resistance to dogwood anthracnose and four cultivars available with resistance to powdery mildew. The goal of scientists at the University of Tennessee and the United States Department of Agriculture Agricultural Research Service was to identify sources of powdery mildew resistance in flowering dogwoods. After visually screening over 20,000 flowering dogwood seedlings that had been naturally infected with powdery, a cultivar named Appalachian Joy was identified and a United States Plant Patent was awarded to scientists at the University of Tennessee for the discovery. The tree is about 4-5 m tall and broadly columnar after 10-15 years of growth and has multiple white-bracts that make the floral display spectacular in the spring. This study demonstrates the need for screening of wild plant material for the discovery of new sources of disease resistance and we expect adoption of this tree by growers and homeowners to reduce reliance on chemical control of powdery mildew.

Technical Abstract: The wholesale nursery industry in Tennessee contributes more than $200 million to the annual economy of the state and are in excess of $50 million annually for flowering dogwood (Cornus florida). Two fungal diseases, dogwood anthracnose and powdery mildew (Discula destructiva and Erysiphe pulchra, respectively) have threatened commercial production of dogwoods during the past 20 years. Both diseases can be treated with fungicide applications, but are very costly and has forced many small nursery growers to abandon production. Host resistance for these diseases is limited. ‘Appalachian Spring’, the only documented cultivar with strong resistance to dogwood anthracnose and four cultivars with resistance to powdery mildew. This germplasm notes reports the discovery of C. florida ‘Appalachian Joy’ PP 18238 as supernumery, white-bracted tree resistant to powdery mildew. The tree is about 4-5 m tall and broadly columnar after 10-15 years of growth. Discovery of the tree resulted after a screening of 20,922 seedlings that were naturally infested with powdery mildew. Powdery mildew on the leaves of ‘Appalachian Joy’ has occasionally been observed on individuals planted in the landscape and stock blocks over the last ten years, but only as small lesions affecting less than 2% of the foliage. Despite this very low level of disease incidence, ‘Appalachian Joy’ is the only documented white, multibracted flowering dogwood cultivar with strong resistant to powdery mildew.