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ARS Home » Northeast Area » Washington, D.C. » National Arboretum » Floral and Nursery Plants Research » Research » Publications at this Location » Publication #400541

Research Project: Genetic Improvement of Nursery Crops through Functional Genomics and Breeding

Location: Floral and Nursery Plants Research

Title: Tree architecture and powdery mildew resistance of yellow-flowering magnolias in Tennessee, USA

item PARAJULI, MADHAV - Tennessee State University
item LIYANAPATHIRANAGE, PRABHA - Tennessee State University
item NEUPANE, KRISHNA - Tennessee State University
item Shreckhise, Jacob - Jake
item FARE, DONNA - Former ARS Employee
item Moore, Benjamin
item BAYSAL-GUREL, FULYA - Tennessee State University

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/12/2023
Publication Date: 2/23/2023
Citation: Parajuli, M., Liyanapathiranage, P., Neupane, K., Shreckhise, J.H., Fare, D., Moore, B.T., Baysal-Gurel, F. 2023. Tree architecture and powdery mildew resistance of yellow-flowering magnolias in Tennessee, USA. HortScience.

Interpretive Summary: Yellow-flowering magnolias are underutilized in U.S. landscapes, partially owing to their susceptibility to powdery mildew which reduces the marketability of susceptible varieties if they are not repeatedly treated with expensive fungicides. USDA-ARS scientists teamed up with Tennessee State University to conduct a two-year evaluation of 26 yellow-flowering magnolia cultivars to measure their relative resistance or susceptibility to powdery mildew and their canopy form at 10 to 11 years after planting. The researchers found marked differences in powdery mildew susceptibility among cultivars, with ‘Sundance’, ‘Sun Spire’, ‘Sun Ray’, and ‘Gold Cup’ being most resistant. Tree form also varied among cultivars; some had a round canopy and were about as wide as they were tall (e.g., ‘Gold Star’ and ‘Sundance’) whereas others had an upright oval canopy and were three times as tall as they were wide (e.g., ‘Gold Cup’ and ‘Sun Spire’). Powdery mildew-resistant cultivars identified from this research may be used in magnolia breeding programs to incorporate powdery-mildew resistance into new varieties. In addition, as powdery mildew resistance was found in cultivars across the spectrum of canopy forms, this research indicates that disease-resistant yellow-flowering magnolias may have broad applicability in landscape design.

Technical Abstract: Magnolias (Magnolia sp.) are economically important woody ornamental plants; however, plant damage associated with frost and powdery mildew (Microsphaera alni and Phyllactinia corylea) disease is a major production challenge. To understand the tree architecture and powdery mildew resistance, twenty-six yellow-flowering magnolias (Magnolia sp.) were evaluated in McMinnville, TN (USDA Plant Hardiness Zone 6b), USA. One-year-old containerized trees were planted in a field plot in Mar. 2006 with 4.6 m plant-to-plant and 3.7 m row-to-row spacing. The experiment was a completely randomized block design with three single-plant replications. Plant height and canopy diameter were measured on Dec. 2016 and Feb. 2018 and apical dominance ratio (i.e., indicating tree architecture) was calculated by dividing height by canopy diameter. Plants were evaluated for powdery mildew severity and defoliation on a scale of 0% to 100% of total plant canopy affected or defoliated, respectively, from Aug. to Oct. of 2016 and 2017. Area under the disease progress curve (AUDPC) was calculated for the evaluation period of each year. The plant apical dominance ratio ranged from 1 to 3, with ‘Gold Cup’ and ‘Sun Spire’ having the highest and ‘Lois’, ‘Gold Star’, ‘Golden Gala’, ‘Solar Flair’, ‘Stellar Acclaim’, ‘Sun Ray’, ‘Sunburst’, and ‘Sundance’ having the lowest value (i.e., relatively round shape). Out of the 26 cultivars, Sundance, Sun Spire, Sun Ray, and Gold Cup showed the lowest powdery mildew severity (10% to 33% in 2016 and 40% to 60% in 2017), AUDPC, and defoliation. Cultivars, Anilou, Gold Star, Golden Pond, Golden Rain, Golden Sun, Green Bee, Honey Liz, Judy Zuk, Koban Dori, Lois, Solar Flair, Stellar Acclaim, and Yellow Bird were highly susceptible to powdery mildew (>80% disease severity) and had the highest AUDPC values. Results from this research may aid breeders, nursery producers, and landscapers in selecting yellow-flowering magnolia cultivars with desirable tree architecture and resistance to powdery mildew.