Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2004
Publication Date: 9/5/2004
Citation: Plant Disease 88:993-999
Interpretive Summary: Sudden oak death is a disease which has killed thousands of trees along the western coast of the U.S. from Big Sur in California to as far north as the State of Oregon. In addition to oaks, the disease affects ornamental nursery crops as a foliar blight. Due to the large-scale movement of known SOD host plants in the nursery trade among states, there is a likelihood the disease could move eastward. It is important to know the levels of susceptibility in eastern nursery species to gain knowledge of the potential impact SOD could have were it to reach the Eastern U.S. We screened 51 ornamental species or varieties for their reactions to the sudden oak death pathogen, Phytophthora ramorum, documented symptoms on each host, and determined their levels of susceptibility. The information, which has been made available to workers in several Eastern states, has been useful as states begin survey work to detect P. ramorum and identify sudden oak death symptoms on nursery plants.
Technical Abstract: We assessed disease reactions of 51 species or varieties of Ericaceous ornamental hosts to two isolates of Phytophthora ramorum, causal agent of sudden oak death. Hosts varied widely in susceptibility, ranging from 0% to over 90% leaf area infected. For only one host were statistically significant differences in disease observed between the two isolates used for inoculations. Numbers of chlamydospores produced by the two isolates varied widely on a subset of host species assessed. Inoculum density studies with two susceptible host species showed that P. ramorum is capable of producing disease symptoms over a wide range of sporangium concentrations and down to 100 sporangia/ml. The results indicate that many ornamental host species and varieties grown in the Eastern U.S. are susceptible to P. ramorum via artificial inoculation. Whether these plants would become infected with P. ramorum in the presence of inoculum under natural conditions is not known.