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Phytophthora ramorum Werres et al., 2001
causes important forest diseases in North America, like the lethal canker disease sudden oak death. It infects mainly tanoak (Lithocarpus densiflora), coast live oak (Quercus agrifolia) and Californian black oak (Quercus kelloggii). This species has killed millions of trees. In 2005 more than 200,000 dead standing trees were found in the Big Sur region of California alone. It also causes sudden larch death in the U.K. as well as leaf blights (ramorum blight) and diebacks on various other plants, e.g. in Rhododendron. It appears that P. ramorum is native to Europe and has spread to California around 1990, possibly via infected ornamentals.
Asexual reproduction involves the formation of 1) spindle-shaped sporangia, approximately 50 x 25 µm large, containing ~30 mobile zoospores, as well as 2) durable chlamydospores. Short distance transmission occurs by rain splashes through the air. The pathogen persists in leaf litter and plant debris. Long distance transmission involves the spread through rivers, transport of infected plant material, as well as contaminated footwear and vehicle tires. Sexual reproduction and the formation of oospores is possible in the presence of the two mating types A1 and A2. In Europe, only A1 has been found with some rare exceptions, while both types occur in North America.
For details see the respective page in Wikipedia.
The literature database currently contains 240 publications for Phytophthora ramorum. (See box above/on left.)