Development of Tubakia dryina on host tissue
Excised leaves of Quercus rubra were inoculated with suspensions of conidia of Tubakia dryina and the development of the fungus on the leaf tissue was observed by scanning electron and light microscopy. Conidial germination was 2% after 6 h, 53% after 12 h, and 54% after 24 h. Germ tubes formed appressorium-like structures directly on the leaf cuticle or over stomata, or entered stomata directly. Development of conidiomata was first evident 24–72 h after inoculation. Conidiomata first appeared as a small mass of hyphal cells, which then proliferated in a radial fashion, with simultaneous formation of conidia. Conidiogenous cells later ceased to form conidia and became thick walled and pigmented, forming a dark scutellum. Conidiogenous cells continued to proliferate ventrally to the scutellum, producing a ring of conidia embedded in a sticky matrix, surrounding the conidioma. Leaf tissue colonized by the fungus became water soaked, and later turned brown and necrotic. Key words: Actinopelte, leaf spot, oak, pycnothyrium.