Location: Southern Horticultural ResearchTitle: Comparison of Resistant and Susceptible Flowering Dogwoods in Pathogenesis of Discula destructiva) Author
Submitted to: Southern Nursery Association Research Conference
Publication Type: Abstract only
Publication Acceptance Date: 1/15/2009
Publication Date: 2/12/2009
Citation: Cheng, Q., Windham, A., Klingeman, W., Sakhanokho, H.F., Li, Y., Windham, M. 2009. Comparison of Resistant and Susceptible Flowering Dogwoods in Pathogenesis of Discula destructiva. Southern Nursery Association Research Conference. 54:54-56. Interpretive Summary:
Technical Abstract: Flowering dogwood (Cornus florida L.) is one of the most popular ornamental trees in eastern United States. Flowering dogwood has been severely impacted by dogwood anthracnose since the disease first appeared in 1976 and significant mortality has occurred in the southeastern United States. Differences in levels of disease resistance were observed among flowering dogwood lines. Understanding the mechanism of the resistance in flowering dogwood is essential in order to determine breeding strategies and manage the disease. Thus, it is very essential to understand early stages of the pathogenesis. Cultures of Discula destructiva were isolated from infected dogwood twigs and leaves. Terminal leaves were wounded and inoculated with a conidial suspension. Each inoculated leaf was enclosed in Petri dishes with moistened filter paper, which were placed at 20° with a 12/12h light/dark cycle. One-centimeter leaf segments were harvested 2, 3, 4 days after inoculation (dai). Leaf segments were then placed into a clearance solution (0.15% trichloroacetic acid [wt/vol] in ethyl alcohol/chloroform, 4:1 [vol/vol]) to stop the growth of the fungi and to remove all chlorophyll. The solution was exchanged once during the next 48 h. To stain fungal structures for light microscopy, leaf segments were stained in a freshly prepared Coomassie blue solution (0.6% Coomassie brilliant blue R 250 [wt/vol] in methanol/15% trichloroacetic acid [wt/vol] in H2O, 1:1 [vol/vol]) for 15 s, washed in water and mounted in 50% glycerol [vol/vol], examined under a light microscope. At the same time, the percentages of germinated conidia were calculated in 1 and 2 DAI under the light microscope. At 24 h after inoculation, the percentage of germinated conidia was not significantly different on leaves of susceptible and resistant cultivars. At 48 h after inoculation, the percentage of germinated conidia on susceptible and resistant leaves was significantly different, which implies that the cuticle is less compatible for conidia germination on ‘Appalachian Spring’. Furthermore, the growth of germ tube was also significantly suppressed on ‘Appalachian Spring’. This type of inhibition of hyphal growth on resistant cultivars has been reported for powdery mildew of dogwood and sweat peas. This strategy decreases inoculum potential of dogwood anthracnose. Further research will focus on how the host resistance histologically affects the infection events of D. destructiva on flowering dogwood.