The Phytophthora Species Assemblage and Diversity in Riparian Alder Ecosystems of Western Oregon, USA

The Phytophthora species assemblage and diversity in riparian alder ecosystems of western Oregon, USA Sims, L. L., Sutton, W., Reeser, P., & Hansen, E. M. (2015). The Phytophthora species assemblage and diversity in riparian alder ecosystems of western Oregon, USA. Mycologia, 107(5), 889-902. doi:10.3852/14-255 10.3852/14-255 Mycological Society of America Version of Record http://cdss.library.oregonstate.edu/sa-termsofuse Mycologia, 107(5), 2015, pp. 889–902. DOI: 10.3852/14-255 # 2015 by The Mycological Society of America, Lawrence, KS 66044-8897 Issued 13 OCTOBER 2015 The Phytophthora species assemblage and diversity in riparian alder ecosystems of western Oregon, USA Laura Lee Sims1 (Alnus rhombifolia Nutt.) is less frequent in the same Oregon State University, Department of Botany and riparian ecosystems (Johnson 1968). In 2009 an Plant Pathology, Corvallis, Oregon 97330, and unusual amount of alder mortality was observed University of California, Berkeley, Department of along the Smith River in Douglas County, Oregon. Environmental Science, Policy and Management, Berkeley, California 94704 Alder trees with Phytophthora-type cankers and canopy dieback were reported and a preliminary survey of Wendy Sutton above ground symptoms suggested the dieback might Paul Reeser be more widespread (Sims et al. 2014). In Europe Everett M Hansen (Gibbs et al. 1999, Streito et al. 2002, Webber et al. Oregon State University, Department of Botany and 2004), in Australia (Smith et al. 2006) and in the Plant Pathology, Corvallis, Oregon 97330 United States (Rooney-Latham et al. 2007) alarming new diseases of alder caused by species of Phy- tophthora recently had been reported. Abstract: Phytophthora species were systematically Phytophthora species rank prominently in lists of sampled, isolated, identified and compared for threats to forest tree health (Hansen 2007). Examples presence in streams, soil and roots of alder (Alnus include oak (Hansen and Delatour 1999, Jung et al. species) dominated riparian ecosystems in western 2005) and alder decline (Gibbs 1995, Brasier et al. Oregon. We describe the species assemblage and 2004, Jung and Blaschke 2004) in Europe, oak evaluate Phytophthora diversity associated with alder. decline in eastern North America (Hwang et al. We recovered 1250 isolates of 20 Phytophthora species. 2008) and sudden oak death in the western United Only three species were recovered from all substrates States (Werres et al. 2001, Goheen et al. 2002, Rizzo et (streams, soil, alder roots): P. gonapodyides,the al. 2002). Nevertheless Phytophthora species also may informally described “P. taxon Pgchlamydo”, and P. be present, even abundant, without causing signifi- siskiyouensis. P. alni ssp. uniformis along with five cant disease (Hansen et al. 2012a). Phytophthora other species not previously recovered in Oregon species in Oregon forest streams and in tanoak forests are included in the assemblage: P.citricola s.l., (Notholithocarpus densiflorus) stands in southwestern P. gregata, P. gallica, P. nicotianae and P. parsiana. Oregon have been surveyed (Sutton et al. 2009; Phytophthora species diversity was greatest in down- Reeser et al. 2011a, b; Hansen et al. 2012b). However, stream riparian locations. There was no significant Phytophthora species associated with alder in Oregon difference in species diversity comparing soil and unwashed roots (the rhizosphere) to stream water. forests have not been examined and there has been There was a difference between the predominating no systematic attempt to relate the Phytophthora species from the rhizosphere compared to stream assemblage in streams to the species present in soil water. The most numerous species was the informally and roots (Hansen 2012a). described “P. taxon Oaksoil”, which was mainly Ten lineages and at least 100 species are now recovered from, and most predominant in, stream recognized within Phytophthora (Hansen et al. 2012a, water. The most common species from riparian forest Kroon et al. 2012).The lineages are recognized based soils and alder root systems was P. gonapodyides. on DNA sequence similarity in the ITS (internal Key words: ecology, forest pathogens, hardwoods, transcribed spacer) regions of the nuclear ribosomal microorganisms in streams, oomycetes genes (Cooke et al. 2000). These lineages may reflect natural relationships because the composition of clades are generally unchanged when additional gene INTRODUCTION sequences are analyzed to accompany ITS (Blair et al. In western Oregon red alder (Alnus rubra Bong. 2008). The 10-clade system is now widely accepted, Betulaceae) is the most common hardwood. It is and in some cases clades have been associated with ecologically important and an economically valuable particular life histories (Kroon et al. 2012). The timber species (Harrington et al. 1994). White alder mitochondrial chromosome in Phytophthora, Pythium and many plant species include the cytochrome c Submitted 30 Sep 2014; accepted for publication 26 Jun 2015. oxidase subunit 1 (Cox 1) and subunit 2 (Cox 2) gene 1 Corresponding author. E-mail: [email protected] cluster (Martin et al. 2007). The spacer region 889 890 MYCOLOGIA between Cox 1 and Cox 2 is useful for sequence-based initiated an examination of alder trees exhibiting identification of many Phytophthora species (Kang et dieback along streams in western Oregon. Bole al. 2010). A rapid species diagnosis can be made with cankers, similar to those caused by P. alni in Europe, isolate sequence data for this region (Gru¨nwald et al. were observed and were associated with canopy 2011). dieback. P. siskiyouensis was isolated several times Species from three ITS clades (2, 6, 7) are reported from this type of canker (Sims et al. 2015) and was causing alder disease. Phytophthora clade 2 includes identified as the causal agent of bark cankers on alder three species: P. pini, P. plurivora and P. siskiyouensis in western Oregon (Sims et al. 2013, Navarro et al. reported from Oregon streams (Reeser et al. 2011b), 2015). The following year a subset of the 2010 two of which have been reported causing disease transects was revisited focusing on Phytophthora symptoms in alder. P. plurivora is a pathogen of species from surface-sterilized diseased red alder European hardwoods including black alder roots. Here we examine the soil, roots and stream (A. glutinosa L. Gaertn.) (Jung and Burgess 2009). water within riparian alder ecosystems to describe the P. siskiyouensis was recovered from the trunks of assemblage and diversity of Phytophthora species and dying black alders in Melbourne Australia (Smith et clades from 88 riparian forest transects. The study al. 2006); it causes root collar cankers and kills Italian focused on Phytophthora species in stream water and alders (Alnus cordata Desf.) in California (Rooney- from soil and unwashed roots (the alder rhizo- Latham et al. 2007, 2009) and most recently was sphere). We were ecologically motivated to answer described as the causal agent of alder bark cankers in questions about Phytophthora species in riparian alder western Oregon (Sims et al. 2013, Navarro et al. ecosystems of western Oregon: (i) is the Phytophthora 2015). Clade 6 Phytophthora species were associated species assemblage widespread or limited? (ii) how with forests, streams and riparian areas in multiple many Phytophthora species will we find? and (iii) are studies (Vettraino et al. 2001, Winton and Hansen there particular substrate (stream water, soil, roots) 2001, Balci and Halmschlager 2003, Brasier et al. determinants of species composition? (iv) does di- 2003, Greslebin et al. 2005, Sutton et al. 2009, Hwang versity change along streams or across substrates? 2009, Remigi et al. 2009, Reeser et al. 2011b, Jung et Finally we hoped to discuss how the assemblage and al. 2011, Randall 2011, Hansen et al. 2012a). Clade 6 diversity compared to that found in similar studies. P. gonapodyides was reported as causing a twig dieback We hypothesized that (i) the Phytophthora species of alder in Denmark (Petersen 1910, Erwin and assemblage from diseased alder stands would be Ribiero 1999). Clade 7 Phytophthora species often are widespread, because forests have evolved with patho- aggressive forest pathogens (Erwin and Ribeiro 1996, gens including Phytophthora species (Hansen et al. Vettraino et al. 2001, Saavedra et al. 2007, Robin et al. 2015); (ii) that diversity and species richness would 2012). P. alni is a clade 7 species and in particular is change along streams and across substrates because considered a threat to alder health around the world. these environs differs so much themselves; (iii) that It is an emergent hybrid, soil- and waterborne Phytophthora alni would be recovered from the soil, pathogen, causing lethal collar rot of alder in Europe. roots and streams around diseased alder because this Spread of the pathogen has been facilitated through continual association with all aspects of the substrates streamside planting of contaminated nursery stock surrounding alder is what is found for the alder (Jung et al. 2009). Once introduced the pathogen pathogen P. alni across Europe. This work provides spreads naturally with streams, floods and drainage a baseline of information on Phytophthora species in water, and the pathogen negatively affects natural alder-dominated riparian ecosystems in western Ore- alder stands (Gibbs et al. 1999). The species was gon and furthers our understanding of the determi- divided into three subspecies. The most aggressive is nants of the composition

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