PARENT SESSION
Oral Session #59: Conservation Ecology: Terrestrial Biodiversity. Presiding: K. Schulz.
Thursday, August 9, 2001. 8:00 AM to 12:15 PM. Madison Ballroom D.
Recently discovered Phytophthora species may underlie epidemic oak mortality in California.
RIZZO, DAVID1, GARBELOTTO, MATTEO2, DAVIDSON, JENNIFER1, SLAUGHTER, GAREY1, KOIKE, STEVEN3, 1 2 3
ABSTRACT- Over the past five years, elevated mortality of tanoak (Lithocarpus densiflorus), coast live oak (Quercus agrifolia), and black oak (Quercus kelloggii) has been reported from coastal areas of central California. This epidemic has been referred to as "Sudden Oak Death" in the press. Initial surveys suggest that up to 40% of trees may be affected within some stands, posing a serious threat to California woodlands. In spite of increased attention, a causal agent for the disease was unknown until July, 2000, when we isolated an undescribed Phytophthora species (a fungal-like pathogen) from oak cankers. Subsequently, the pathogen has been isolated from diseased oaks at 27 sites spread over 300 km of the coastal ranges. We confirmed pathogenicity of the Phytophthora species novus through inoculation experiments on coast live oak and tanoak. Analysis of the internal transcribed spacer (ITS) region of DNA showed that the Phytophthora sp. nov. is most closely related to Phytophthora lateralis, an introduced pathogen of native Port-Orford cedar (Chamaecyparis lawsoniana) in California. As such, the Phytophthora sp. nov. may also be exotic. The recent finding of the Phytophthora sp. nov. infecting ornamental Rhododendron spp. in Europe and northern California suggests a possible host vector for introduction. Current research focuses on the origin and transmission biology of the Phytophthora sp. nov. in hopes of providing management solutions for disease control.
KEY WORDS: plant pathogen, forest disease, forest pathology, disease management