Location: Floral and Nursery Plants ResearchTitle: An evaluation of yellow-flowering magnolias and magnolia rootstocks Author
Submitted to: HortTechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/20/2016
Publication Date: 12/2/2016
Citation: Fare, D.C. 2016. An evaluation of yellow-flowering magnolias and magnolia rootstocks. HortTechnology. 27:291-295.
Interpretive Summary: Deciduous magnolias are popular landscape plants because of their striking spring flowers. There has been interest in breeding for deciduous yellow-flowering magnolias since the 1950s.ARS scientists in McMinnville, TN conducted a comprehensive replicated evaluation of yellow-flowering magnolias in one location. The study revealed differences in flower color (from pale to bright yellow), bloom time, growth rate, and disease incidence. Time of flowering is critical for plants in US Hardiness zones 6 and 7 due to early spring frosts; this study will provide information on which cultivars can be grown in this hardiness zone. The study also showed differences in rootstock, with some bud incompatibility observed. In time, more valuable information will be collected as the plants mature and bud incompatibility becomes more pronounced. This study will benefit magnolia connoisseurs, the nursery industry and prospective plant breeders.
Technical Abstract: Yellow-flowering magnolias were evaluated for flower color, bloom duration and growth rate in USDA Hardiness Zone 6b. Of the thirty selections evaluated, all were reported to have yellow blooms; however, tepal color ranged from light pink with some yellow coloration, to creamy yellow to dark yellow. ‘Daphne’, ‘Judy Zuk’ and ‘Yellow Bird’ had the darkest yellow tepals and usually bloomed last. ‘Gold Star’, ‘Golden Gala’, ‘Stellar Acclaim’, ‘Sun Spire’ and ‘Sundance’ had the lightest yellow tepal color. ‘Goldfinch’, ‘Butterflies’ and ‘Elizabeth’ were the earliest to bloom and ‘Elizabeth’ had one of the longest flowering periods. ‘Carlos’ and ‘Gold Star’ were the tallest selections at 7 m each after ten years in the evaluation. ‘Golden Gala’, ‘Gold Star’, ‘Carlos’, ‘Lois’, and ‘Yellow Lantern’ had the largest trunk diameters and averaged over 2.5 cm growth per year. ‘Sun Spire’ had one of the smallest trunk diameters and showed an annual increase of about 1.5 cm per year. Powdery mildew, caused by Phyllactinia corylea and Microsphaera alni, was observed on all selections; however, ‘Golden Sun’, ‘Solar Flair’, ‘Stellar Acclaim’, ‘Sunburst’, ‘Sunsation’ and ‘Yellow Bird’ had greater than 40% of the leaf area affected with mildew with over 60% of the canopy affected by late summer. Powdery mildew was significantly less on ‘Banana Split’, ‘Carlos’, ‘Elizabeth’ and ‘Sun Spire’. An evaluation of rootstocks revealed that ‘Leonard Messel’ resulted in more height growth of scions than scionss budded onto other rootstocks. Scions budded on to ‘Wada’s Memory’ rootstock had the smallest height growth. Rootstocks ‘Wada’s Memory’ and ‘Ballerina’ produced the smallest scion trunk diameter growth. After five years, bud incompatibility was observed on rootstocks ‘Ballerina’ and ‘Leonard Messel’ as indicated in the difference of growth between the rootstock and the scion.