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Title: New relationships among the sudden oak death pathogen, bark and ambrosia beetles, and fungi colonizing coast live oaks

Author: Erbilgin, Nadir; McPherson, Brice A.; Bonello, Pierluigi; Wood, David L.; Nelson, Andrew J.;

Date: 2008

Source: In: Frankel, Susan J.; Kliejunas, John T.; Palmieri, Katharine M., tech. coords. 2008. Proceedings of the sudden oak death third science symposium. Gen. Tech. Rep. PSW-GTR-214. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station. pp. 355-356

Publication Series: General Technical Report (GTR)

   Note: This article is part of a larger document. View the larger document

Description: Sudden oak death (SOD) has had devastating effects on several oak species in many California coastal forests. Phytophthora ramorum has been identified as the primary causal agent of sudden oak death. While the pathogen may be capable of killing mature trees, it is likely that in nature opportunistic organisms play significant roles in the decline and death of infected trees. For example, we have found elevated landing rates of bark and ambrosia beetles (Coleoptera: Scolytidae) on mechanically inoculated coast live oaks (Quercus agrifolia) in California. The tunneling activity of these beetles in bleeding cankers on P. ramorum-infected coast live oaks may accelerate mortality and may contribute to catastrophic failures, even while diseased trees retain asymptomatic canopies. The objective of this study was to determine the role of bark and ambrosia beetle infestation in the introduction and/or stimulation of decay fungi associated with tree mortality and breakage. We inoculated coast live oaks with P. ramorum in two forested sites in Marin County in March 2005 and monitored them for signs and symptoms of P. ramorum infection. An additional group of asymptomatic trees was felled to allow colonization by bark and ambrosia beetles. In January and July of 2006, we randomly selected and harvested three P. ramorum inoculated trees and three asymptomatic trees from each of the sites. Trees selected for fungal culturing were in the following categories: (1) Asymptomatic trees; (2) Live symptomatic trees exhibiting only bleeding without obvious beetle attacks; (3) Live symptomatic trees exhibiting bleeding with beetle attacks; 4. Dead symptomatic trees with beetle attacks; (5) Dead asymptomatic trees without beetle attacks; (6) Dead asymptomatic trees with beetle attacks. Trees were cut a minimum of 30 cm below the point of inoculation, generating bolts approximately 70 cm long. Each bolt was cut into 15 cm thick disks. Wood samples (5 to 10 mm wide, four per disk) were collected along cross-sectional transects from the upper surface of each disk and divided into four sections. Each section was placed on one of several types of media: potato dextrose agar, malt extract agar and water agar. We separated and purified morphologically distinct fungal colonies (morphotypes) and amplified the internal transcribed spacer ITS) region of the rDNA operon. Amplicons were sequenced and blasted in GenBank (http://www.ncbi.nlm.nih.gov). The principal taxa isolated from wood samples are described below.

Keywords: Phytophthora ramorum, sudden oak death, bark and ambrosia beetles, decay fungi, coast live oak

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Erbilgin, Nadir; McPherson, Brice A.; Bonello, Pierluigi; Wood, David L.; Nelson, Andrew J. 2008. New relationships among the sudden oak death pathogen, bark and ambrosia beetles, and fungi colonizing coast live oaks. In: Frankel, Susan J.; Kliejunas, John T.; Palmieri, Katharine M., tech. coords. 2008. Proceedings of the sudden oak death third science symposium. Gen. Tech. Rep. PSW-GTR-214. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station. pp. 355-356

 


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