Spatial distribution of disease caused by Phytophthora ramorum in coast live oak woodlands
Jennifer M. Davidson1, Allison C. Wickland2, Andrea C. Morse2, Camille E. Jensen2, Rebecca G. Albright2, Shannon C. Lynch2, Justin Tse3, Garey Slaughter2, Matteo Garbelotto3, and David M. Rizzo2
We established three one hectare plots in coast live oak woodlands infested with Phytophthora ramorum to study the spatial distribution and spread of disease among all hosts of P. ramorum. On each plot, all individuals greater than 1 cm dbh were tagged, mapped, and visually assessed for disease symptoms due to P. ramorum. For all hosts except madrone, tissue samples were taken from symptomatic plants for isolation of P. ramorum on selective medium (PARP). Because madrone is a difficult host from which to culture P. ramorum, molecular diagnostics were used to test for the presence of P. ramorum. In addition, failed culturing for coast live oak, big leaf maple, toyon, coffeeberry, honeysuckle, and hazelnut were also subjected to molecular testing. In total, 1533 plants were censused on the three plots. Two of the three plots (Fairfield Osborn Preserve (FOP), Sonoma Co. and Napa Skyline Wilderness County Park, Napa) were dominated by coast live oak and bay. Coast live oak and bay accounted for 38.7% (164/424) and 45.0% (191/424) of the tagged species at FOP, and 45% (241/535) and 40.6% (217/535) of the tagged species at Skyline, respectively. In the third plot in Pacheco Hills, Marin Co., coast live oak and madrone were the dominant tree species, comprising 58.0% (333/574) and 29.6% (170/574) of the individuals, respectively. Identification of infected individuals on these plots via molecular analysis is still in progress. Final data will be analyzed for spatial distribution of disease on coast live oak versus other hosts. Future work will monitor how infection spreads on each of the plots, especially in years of high versus low rainfall.
1Pacific Southwest Research Station, USDA Forest Service, P.O. Box 245, Berkeley, CA 94701; jmdavidson@ucdavis.edu
2Department of Plant Pathology, One Shields Ave., University of California, Davis, CA 95616
3Department of Environmental Science, Policy and Management, Ecosystem Science Division, 151 Hilgard Hall, University of California, Berkeley, CA 94720
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