An evaluation of yellow-flowering magnolias and magnolia rootstocks

Abstract

Yellow-flowering magnolias were evaluated for flower color, bloom duration and growth rate in USDA Hardiness Zone 6b. Of the 30 selections evaluated, all were reported to have yellow blooms; however, tepal color ranged from light pink with some yellow coloration, creamy yellow to dark yellow. 'Daphne', 'Judy Zuk', and 'Yellow Bird' have the darkest yellow tepals and would often be the last to bloom. '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' are the tallest selections at 7 m each after 10 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' has one of the smallest trunk diameters and shows an annual increase of about 1.5 cm per year. Powdery mildew incidence, 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 'Leonard Messel' had more height growth occur with scions than selections budded onto other rootstocks in comparison to scions budded on to 'Wada's Memory' rootstock which produced the smallest height growth. Rootstocks 'Wada's Memory' and 'Ballerina' produced the smallest scion trunk diameter growth. After 5 years, bud incompatibility was observed on rootstocks 'Ballerina' and 'Leonard Messel' as indicated in the difference of growth between the rootstock and the scion.