Submitted to: Plant Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/15/2008
Publication Date: 12/1/2005
Citation: Li, Y.H., Windham, M.T., Trigiano, R.N., Fare, D.C., Spiers, J.M., Copes, W.E. 2005. Spore germination, infection structure formation and colony development of erysiphe pulchra on dogwood leaves and glass slides. Plant Disease 89:1301-1304. Interpretive Summary: Flowering dogwood (Cornus florida L.) is a valuable landscape tree that has increasingly experienced powdery mildew leaf blight since 1995. A rapid laboratory testing method is needed to correlate pathogen development and host mechanisms of disease resistance. In the present study, we described in detail the developmental time course for E. pulchra on dogwood leaf disks and glass slides. Development of branched hyphae indicated that the pathogen had successful infected the plant, and lack of branched hyphae indicated the resistance mechanisms of the plant had interrupted the infection process of the pathogen. These results provide useful information for investigating mechanisms of resistance to powdery mildew in flowering dogwood that will benefit plant breeders and nursery propagators.
Technical Abstract: Spore germination, infection structure formation, and colony development of Erysiphe pulchra on glass slides and leaf disks of a susceptible flowering dogwood line were examined using light and scanning electron microscopy. On both glass slides and leaf disks, conidia germinated within 2 h after inoculation (hai). One to four germ tubes grew from two poles of a conidium, one or two of the germ tubes formed initial appressoria, and only one of the germ tubes with an initial appressoria formed a secondary appressoria. However, formation of initial and secondary appressorium was delayed on glass slides (48 and 72 hai, respectively) compared to that on dogwood leaf disks (3 and 4 hai, respectively). Branching hyphae did not grow from germinated conidia on glass slides. However, on dogwood leaf disks, branched hyphae were observed 48 hai. In epidermal cells, the fungus formed compact and globose haustoria. Conidia formation on conidiophores started on leaf disks 7 days after inoculation. Conidia germinated and formed initial and secondary appressoria on glass slides without establishing a parasite relationship, but food sources in conidia could not provide enough energy and nutrition for growth of branched hyphae. Growth of branched hyphae could be used as a sign of successful parasite relationship of pathogen and host cells.