Edwin Florance

Professor Emeritus of Biology

department: Biology
office: 210 Bodine Hall
phone: 503-768-7515
e-mail: florance@lclark.edu, florance@comcast.net
Web: http://www.lclark. edu/~florance

The following scanning electron micrographs show the various ultrastructural features of Phytophthora ramorum, the organism that causes Sudden Oak Death.

Images 1 - 3:  The ultrastructural morphology of P. ramorum Zoospores from pure culture. Note the biflagellation, reniform shape, longitudinal groove, and pitted surface.

Figures 4,5,& 6 show mature Zoosporangia. In figure 4 the papillate morphology can be observed and in bothe figures 4 and 5 the pedicel at the base of the sporangium can be seen. Figure 6 not only shows the pedicel but zoospore release is occurring.

The arrows identify a structure known as the pedicel.

Figure 7 demonstrates zoospore release. Zoospores are motile and swim away from the zoosporangium.

Once zoospores are released they will remian motile for varying periods of itme depending on the specific conditions in the immediate environment. Eventually, they encyst. This process involves loss or retraction of the flagella, becoming more spherical, and forming a thicker more resistant cell wall. Cysts eventually germinate and produce hyphae.

Figures 8, 9 & 10 show cysts and cyst germination.

Figure 11 shows the morphology of hyphae from Phytophthora ramorum. The hyphae are nodose, branched, and grow on or in suitable substrates.

Figure 12. As the Phytophthora ramorum colony continues to grow eventually it will produce asexual reproductive structures called Chlamydospores (white arrow). Chlamydospores are approximately 5 to 7 times larger than cysts or zoospores. They have very thick cell walls and can remain dormant for extended periods. The chlamydospores of Phytophthora ramorum are relatively smooth and lack distinguishing ornamentation.