Submitted to: Journal of Environmental Horticulture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/22/2007
Publication Date: 9/1/2007
Citation: Li, Y.H., Windham, M.T., Trigiano, R.N., Fare, D.C., Spiers, J.M., Copes, W.E. 2007. Evaluation for Resistance to Powdery Mildew in Cornus Species and Hybrids Using a Leafy Disk Assay. Journal of Environmental Horticulture 25:131-133. Interpretive Summary: Cultivars of five dogwood species or species hybrids were evaluated for resistance to the powdery mildew disease based on laboratory tests using leaf disks. Generally, flowering dogwood (C. florida) cultivars were more susceptible than the other species and hybrids. Of the flowering dogwoods, ‘Karen’s Appalachian Blush’ and ‘Worlds Fair’ showed good disease tolerance that was similar to the C. florida × C. kousa hybrid ‘Ruth Ellen’. Kousa dogwoods (C. kousai)and hybrids expressed a high disease tolerance. The laboratory assessments for measuring fungal development in the leaf tissue provide methodology that can be used by scientists. The results of the assay will be usable to plant breeders, ornamental plant retailers, and the general public.
Technical Abstract: Using a leaf disk assay, eight cultivars or/and breeding lines in Cornus florida L., C. kousa (Buerger ex Miq.) Hance, five cultivars in C. kousa × C. florida, one cultivar in C. kousa × C. nuttallii Aud. and one cultivar in (C. kousa × C. nuttallii) × C. kousa were evaluated for resistance to powdery mildew [Erysiphe pulchra (Cooke and Peck) U. Braun & S. Takamatsu (syn. Microsphaera pulchra Cooke and Peck)]. Flowering dogwoods (C. florida) cultivars were more susceptible than the other species and hybrids with the exception of the C. florida × C. kousa hybrid ‘Ruth Ellen’. Resistance in kousa dogwoods and hybrids was manifested as restriction of hyphal growth and inhibition of sporulation. Although mildew colonies and sporulation were detected on leaves of all flowering dogwood cultivars, ‘Karen’s Appalachian Blush’ and ‘Worlds Fair’ were more resistant than other cultivars. These dogwoods had significantly lower values of percent geminated conidia with branched hyphae, infection efficiency, sporulation and delayed latent period. The leaf disk assay provides a laboratory procedure to screen new cultivars and lines of dogwoods for resistance to powdery mildew.