Location: Southern Horticultural ResearchTitle: Histological investigation of infection processes of Discula destructiva on leaves of Cornus florida Author
Submitted to: Canadian Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/6/2011
Publication Date: 12/5/2011
Citation: Cheng, Q., Windham, A.S., Klingeman, W.E., Sakhanokho, H.F., Saxton, A.M., Li, Y., Windham, M. 2011. Histological investigation of infection processes of Discula destructiva on leaves of Cornus florida. Canadian Journal of Plant Pathology. 33:525-531. Interpretive Summary: In the late 1970s, high dogwood mortality associated with anthracnose symptoms was reported across the northeastern United States. The causal agent of these symptoms was later identified as the fungus Discula destructiva. Earlier studies suggested that the pathogen invaded the tissues between the cells or through the cells themselves, but the sequence of infection events was not clear. Therefore, the objective of this study was to describe the sequence of events in the infection process of D. destructiva in flowering dogwood (Cornus florida). This objective was achieved, so the sequence of infection events for Discula destructiva on flowering dogwood has now been clearly described, paving the way for the investigation of the mechanisms of resistance interfering with the pathogen’s ability to infect dogwoods.
Technical Abstract: The infection process of Discula destructiva Redlin on Cornus florida L. leaves was studied using histological and microscopic techniques. Penetration of fungal hyphae through natural openings and wounds was not observed, while direct penetration without appressorium formation was demonstrated 3 days after inoculation (DAI). Leaves inoculated with D. destructiva developed symptoms of dogwood anthracnose after 7 to 8 days. At 8 DAI, hyphae were observed in aggregations located between the cuticle and epidermis and also growing intracellularly towards epidermal, palisade, parenchymal and spongy mesophyll cells. At 16 DAI, typical chlorotic and necrotic halos, with a red to purple external border, were formed on the inoculated leaves. Within leaf tissues, at 16 DAI, chloroplasts were intact but decompartmentalized and infection sites were clearly defined. Sporulation and ruptured acervuli (cuticle ruptured and spores released) were first detected at 20 DAI, and had fully developed to rupture the plant cuticle on both adaxial and abaxial leaf surfaces by 24 DAI.