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Title:   Author  item
                                            SWIECKI, TEDMUND - Phytosphere Researchitem
                                            ARAM, KAMYAR - University Of Californiaitem
                                            Kasuga, Takaoitem
                                            Bui, Maiitem
                                            RIZZO, DAVID - University Of Californiaitem
                                            BERNHARDT, ELIZABETH - Phytosphere Research
  Submitted to: Plant Health Progress
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 12/15/2015
                                    Publication  Date: 2/18/2016
                                    Citation: Swiecki, T., Aram, K., Kasuga, T., Bui, M.Q., Rizzo, D., Bernhardt, E. 2016. Phytophthora ramorum causes cryptic bole cankers in Canyon line Oak. Plant Health Progress. 17:20-26.Interpretive Summary: Unusual mortality of large canyon live oaks was observed in natural stands in San Mateo, and we suspected it was caused by the Sudden Oak Death pathogen, Phytophthora ramorum. We found that symptomatic trees were spatially associated with California bay, the primary source of P. ramorum spores in this forest type; however, the pathogen could not be isolated from affected trees. Artificial inoculation of logs, and later, trees, confirmed that P. ramorum caused cankers on canyon live oak, but cankers showed either no or minuscule external bleeding. Tree declines associated with similarly cryptic Phytophthora cankers could remain undiagnosed or misdiagnosed for many years, thwarting detection and management efforts.
                                Technical Abstract: Unusual mortality of large canyon live oaks was observed in natural stands in San Mateo, California starting in 2007. A survey of affected stands showed that symptomatic trees were spatially associated with California bay, the primary source of Phytophthora ramorum spores in this forest type. Trunk canker symptoms on affected trees were similar to late-stage symptoms caused by Phytophthora ramorum on other oak hosts, but the pathogen could not be isolated from affected trees. Artificial inoculation of logs, and later, trees, confirmed that P. ramorum caused phloem cankers on canyon live oak, but cankers showed either no or minuscule external bleeding. Knowledge of early bark symptom appearance facilitated successful isolations from naturally-infected trees. Tree declines associated with similarly cryptic Phytophthora cankers could remain undiagnosed or misdiagnosed for many years, thwarting detection and management efforts.


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