Sudden Oak Death — Abstract of Paper


Phytophthora ramorum and Sudden Oak Death in California: II. Transmission and Survival
Jennifer M. Davidson,¹ David M. Rizzo,² Matteo Garbelotto,³ Steven Tjosvold,⁴ and Garey W. Slaughter²


The newly discovered Phytophthora ramorum canker disease of oak (Sudden Oak Death Syndrome) threatens millions of acres of California woodlands where coast live oak (Quercus agrifolia), tanoak (Lithocarpus densiflorus), or black oak (Quercus kelloggii) are dominant species. An important step in controlling this disease involves understanding how it is spread. The presence of diseased oaks at all elevations on hillsides and the above-ground nature of the disease suggest wind-blown rain or rain splash as a common mechanism for movement of spores. Although viable spores have yet to be found on infected oak tissue, other hosts may serve as sources of rain-dispersed inoculum. In the laboratory, abundant sporangia form on moistened leaves of infected bay (Umbellularia californica) and Rhododendron spp. within 72 hours. These sporangia break off and easily disperse in water. Chlamydospores were also observed on the surface of moistened bay leaves. Consistent with these results, P. ramorum has been recovered from rain, soil, litter, and stream water from woodlands with infected oak and bay trees. Spores of P. ramorum do not survive drying, but in moist conditions can survive for at least one month.