Phytophthora Species and Riparian Alder Tree Damage in Western Oregon
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AN ABSTRACT OF THE DISSERTATION OF Laura L. Sims for the degree of Doctor of Philosophy in Botany and Plant Pathology presented on February 13, 2014. Title: Phytophthora Species and Riparian Alder Tree Damage in Western Oregon Abstract approved: Everett M. Hansen The genus Phytophthora contains some of the most destructive pathogens of forest trees, including the most destructive pathogen of alder in recent times, Phytophthora alni. Alder trees were reported to be suffering from canopy dieback in riparian ecosystems in western Oregon, which prompted a survey of alder health and monitoring for P. alni. In 2010 surveys in western Oregon riparian ecosystems were initiated to gather baseline data on damage and on the Phytophthora species associated with alder. Damage was recorded and analyzed from transects containing alder trees with canopy dieback symptoms according to damage type: (1) pathogen, (2) insect, or (3) wound. Phytophthora species from western Oregon riparian ecosystems were systematically sampled, isolated, identified, stored and compared. Koch’s Postulates were evaluated for three key Phytophthora species recovered: P. alni, P. siskiyouensis and P. taxon Oaksoil, and alder disease in the western United States was described. Then, the ecological role of the most abundant Phytophthora species from streams was evaluated. The data indicated that many of the same agents reported causing damage to alder trees in the western United States were also damaging alder trees in western Oregon including the alder flea beetle, sawflies, flood debris, Septoria alnifolia, and Mycopappus alni. The most important damage correlated with canopy dieback was incidence of Phytophthora cankers, and isolation of Phytophthora siskiyouensis. In the initial systematic survey of Phytophthora species, 1190 individual Phytophthora isolates were recovered but were of many different species. In the survey of alder roots, P. alni subsp. uniformis was one of the species recovered from necrotic red alder roots, but overall incidence was low; it was isolated four times. From the evaluation of Koch’s postulates, Phytophthora canker of alder in the western United States was described, and is a bole canker caused by Phytophthora. Phytophthora canker of alder was only found caused by P. siskiyouensis in nature, and it was isolated 74 times. Isolation was mainly from bole cankers and diseased roots on red and white alder, and from water and alder leaf debris floating in the stream. The most abundant Phytophthora species associated with red alder is an informally described species P. taxon Oaksoil, which appears to be a relatively benign aquatic saprotroph of alder leaf debris. Canopy dieback was more prevalent in riparian alder trees from transects with P. siskiyouensis than from transects with P. taxon Oaksoil but without P. siskiyouensis (70% and 35%, respectively). The informally described P. taxon Oaksoil from western Oregon is formally described here as P. obrutafolium sp. nov., closely related to P. bilorbang from western Australia, and P. taxon Oaksoil ss from an oak forest in France. In summary, other agents besides Phytophthora can damage alder trees in western Oregon. Many Phytophthora species associate with alder in western Oregon but not all of them are important damaging agents of alder. However, Phytophthora canker of alder is widespread in western Oregon. In the United States, Phytophthora canker of alder has only been found to be caused by P. siskiyouensis. ©Copyright by Laura L. Sims February 13, 2014 All Rights Reserved Phytophthora Species and Riparian Alder Tree Damage in Western Oregon by Laura L. Sims A DISSERTATION submitted to Oregon State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy Presented February 13, 2014 Commencement June 2014 Doctor of Philosophy dissertation of Laura L. Sims presented on February 13, 2014. APPROVED: Major Professor, representing Botany and Plant Pathology Head of the Department of Botany and Plant Pathology Dean of the Graduate School I understand that my dissertation will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my dissertation to any reader upon request. Laura L. Sims, Author ACKNOWLEDGEMENTS I sincerely thank my advisor Everett Hansen. I truly appreciate his facilitation of my creative drive and tolerance of my unerring biological curiosity in regards to pathology. I appreciate the time I was allowed to spend on Mary’s Peak with Toby Child’s Poria weirii my first and last summer while obtaining my degree. I would also like to thank both him and Barb for inviting my family to stay in their home, twice. I sincerely thank Ellen Goheen and her U. S. Forest Service crew, which contended with the most difficult terrain of the alder project. I truly appreciate the guidance, cooperation, and direction she gave to the project from the beginning. I truly thank Alan Kanaskie, Michael Thompson, and Jon Laine from the Oregon Department of Forestry for their excellence in fieldwork and for their time. I could not have completed my dissertation project without their assistance. I would also like to thank Mike McWilliams for his enthusiasm and advice about forest pathology. I truly thank Wendy Sutton for her help in processing the seemingly endless stream of samples I brought into the lab for a while. The lab is a very comfortable place to work because of Wendy’s laugh and her great organization. I would also like to thank Paul Reeser for his time, for his patience, and for showing me the art of seeing Phytophthora amongst the myriad of life that I dragged back from the forest. I am grateful to the Oregon State University Botany Department for being a welcoming place while I completed my degree. I truly appreciate the committee that granted me the Anita Summers Fund, which provided a large part of the funding for a work trip conference to Spain. I thank my family for engraining in me the importance of hard work and perseverance. To my sister and brother, Amy and Joe that both accomplished so much while I was completing my degree. To my “Gunny” Sergeant Grandfather, Joe Whealdon, who passed on while I was working on my dissertation, I miss you. Thank you, to the hard working women in my family especially my mother Elisa and my aunt Dawn, who inspired me to stay strong and focused. I would like to thank the Forest Health Monitoring Program of the USDA Forest Service, Pacific Northwest Region, which generously supported survey efforts. I truly appreciate all the financial support for the project, and the opportunities to attend and communicate about my progress at conferences. Particularly I appreciate the opportunity to attend the Western International Forest Disease Work Conference Meetings and the International Union of Forest Research Organization Meeting. I was able to meet and communicate with the forest pathology family. I pray they will keep me. TABLE OF CONTENTS Page CHAPTER 1: Dissertation Introduction …………………………………...........................................1 The Genus Phytophthora …………………...........……………………….……………………....2 Alder…………......................................................................................……………...7 Alder dieback in Oregon ...................................................................................9 Dissertation Objectives ..………........................................................................10 References…..…………………………………………………..…………………………………..…….12 CHAPTER 2: Phytophthora siskiyouensis and other damaging agents of alder trees in western Oregon riparian ecosystems ...…...........................................................……………19 Introduction………………………….……………………………..……...…...…………....…………19 Pathogens……………………………………………………………....…..……………………….24 Insects……………………………………………………………………….………………………….26 Wounds………………………………………………………………………….…………………….28 Materials and Methods…………...……...………….……………...................................29 Transects……………………………….…………………………..………………......……………29 Data Collection…….……..………………………………………………………..................31 Data Analysis……….….……………………..……………………………………..................33 Results………………………………………………..…………..………………………….................36 Canopy Dieback…..…………………………..…………………………………...................36 Pathogens……………..…………………..………………………………………….................38 TABLE OF CONTENTS (Continued) Page Insects…………………………..………………………………………………………...............46 Wounds…………….……………………..………………………………………….................47 Discussion.......................................................................................................49 Canopy Dieback.......................................................................................50 Pathogens................................................................................................50 Insects......................................................................................................52 Wounds...................................................................................................53 Other.......................................................................................................54 Conclusions……..…………….……………………..…………………………………………………...56 References…………………………….…………………………..……………………………………....57 Chapter 3: Phytophthora species from riparian alder ecosystems in western Oregon, USA…..………………………………..………………………………………………………………………………………..63 Introduction……………..…………………..……………………..…………………………………….63 Materials and methods…………………………..………………………………………….……….72 The assemblage