ARS | Publication request: DEVELOPMENT OF POWDERY MILDEW ON RESISTANT AND SUSCEPTIBLE DOGWOOD CULTIVARS

Submitted to: Southern Nursery Association Research Conference
Publication Type: Proceedings
Publication Acceptance Date: August 15, 2005
Publication Date: February 1, 2006
Citation: Li, Y.H., Windham, M.T., Trigiano, R.N., Fare, D.C., Spiers, J.M., Copes, W.E. 2006. Development of powdery mildew on resistant and susceptible dogwood cultivars. Southern Nursery Association Research Conference 50:247-250.

Interpretive Summary: This is the first report that evaluates disease resistance of flowering dogwood lines to powdery mildew using detached leaf disks in a laboratory. This technique documented partial plant resistance components that reduced four developmental stages of the fungal pathogen: incomplete structure development on the leaf surface, poor success infecting the outer cells of a leaf, slowed development within the leaf tissue, and reduced production of wind-borne infection propagules on the leaf surface. This simple screening technique documented two of the four development stages were involved in field resistance exhibited by 'Karen's Appalachian Blush', a dogwood cultivar. This information will help research scientists and extension specialists develop and document disease resistance, which will help producers market disease resistant dogwood cultivars.

Technical Abstract: Differences in resistance to powdery mildew were observed on detached leaf disks of six flowering dogwood lines inoculated with conidia of Erysiphe pulchra. Significant differences (P < 0.02) in germinated conidia with branched hyphae, infection efficiency, latent period and sporulation were detected among dogwood lines. However, percentages of spore germination (P = 0.0745) and secondary appressorium formation (P = 0.2661) were not significantly different among lines. In addition to sporulation, infection efficiency and latent period were major differentiable components between highly susceptible and moderately susceptible lines and between moderately susceptible and resistant lines, respectively. Similar to infection efficiency, percentages of germinated conidia with branched hyphae on highly susceptible lines were significantly greater than on resistant and moderately susceptible lines. A recently released flowering dogwood cultivar, ‘Karen’s Appalachian Blush’, expressed significantly higher levels of resistance to powdery mildew than ‘Cherokee Brave’ in latent period and sporulation. Laboratory assays using detached leaf disks could be useful for screening dogwood selections and cultivars for resistance to powdery mildew.