Edwin R. Florance1
A major question regarding the biology of Phytophthora ramorum is the pathway through which the fungus enters the plant in order to establish an infection. Two possible points of entry are stem lenticels and leaf stomata. Stem and leaf tissue samples of Umbellularia californica, Quercus spp. and Rhododendron macrophyllum infected with P. ramorum were collected in both California and Oregon. Samples were fixed immediately in buffered 4% glutaraldehyde, followed by 1% osmium tetroxide, and prepared for both scanning electron and light microscopic analysis. Major tissues of the plants were observed. Data indicate that both lenticels and stomata can serve as points of entry for the hyphae of P. ramorum. Hyphae were also observed growing in the vascular tissues of the stem.
