Hansen, E., Reeser, P., Sutton, W., and Sims, L. 2012. Host and habitat index for Phytophthora species in Oregon. Forest Phytophthoras 2(1). doi: 10.5399/osu/fp.2.1.3026 Host and Habitat Index for Phytophthora Species in Oregon
• Everett Hansen • Paul Reeser • Wendy Sutton • Laura Sims
Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331 USA
Corresponding author: [email protected] 1. Introduction
Phytophthora species are known as pathogens of agricultural crops or invasive pathogens destroying forests, and their prominent inclusion in various host-pathogen-indices reflects this importance. It is increasingly evident, however, that Phytophthora species are abundant in streams in healthy forests and widespread in forest soils causing cryptic diseases, in addition to their more traditional roles as aggressive pathogens. While their ecology in non-agricultural ecosystems remains poorly understood, we now know that a numerous and diverse, nutritionally complex community of Phytophthora species is present in a variety of associations with forests and forest trees.
In this contribution we compile existing records from available sources of reliably identified Phytophthora species from forests and forest trees in Oregon, USA. The results are summarized by host and habitat in Tables 1-3. A searchable version of this information may be found in the Forest Phytophthoras of the World Disease Finder (select USA-Oregon). Details of specifically documented isolates, including locations and available cultures and Genbank acquisitions, as well as citations are included in the supplemental spreadsheet. We have included isolations from soil and streams in forests that are often not associated with any specific disease symptoms. Our goal is to inventory forest Phytophthora species, not forest diseases. On the other hand, we have included records from forest trees growing outside the forest, as Christmas trees or in the urban landscape, for example. The result is, we hope, a more accurate representation of the ecological amplitude of Phytophthora species and a more complete record of the sources from which they may be spread. 2. Sources
For this report we attempted to compile all reliable records from all sources. Most records were from three large programs or projects. The OSU Plant Disease Clinic database extends across many years and includes records from all hosts and the entire state. Most samples to the Clinic came from diseased plants grown as agricultural or horticultural crops, and many Phytophthora isolations were identified only to genus; these were not included here. Those from forest related sources with specific identification were included, however, and identified by “Pc”. Another major source continues to be the Sudden Oak Death control program in this state. While diagnosis focused on P. ramorum, and was concentrated in one county in the SW corner of the state, all Phytophthora species encountered in plants, soil, and streams were cultured and identified, leading to many new records. Many of theseresults were published and sources are cited here. The third main source of records was an ongoing survey of the Phytophthora species associated with declining alder trees along streams in western Oregon. This has resulted in several thousand Phytophthora isolates from alder roots and stems as well as associated soil and adjacent streams. This work is not yet published. In addition, there were many reports from systematic surveys of Phytophthora species in forest tree nurseries and Christmas tree plantations. Unfortunately, morphological identification methods available at the time could not distinguish problem species reliably and many of these records were thus excluded. 3. Criteria for Inclusion
Phytophthora species: All records are based on isolations in culture, and identifications of all problematic species were confirmed with molecular sequencing methods. Older records of species that lack distinctive morphology were not included unless confirmed by recent sequencing of original isolates. Many records originally identified as P. drechsleri, P. citricola, P. cryptogea, and P. megasperma in particular were thus excluded. This especially affected the host and location records from forest tree nurseries, since nursery pathology research in Oregon largely predated availability of molecular tools.
Species concepts in Phytophthora continue to evolve. The range of variability in morphology as well as DNA sequence is not clearly established for many species. We have adopted a population based phylogenetic species concept that is tolerant of minor variations in sequence and morphology, so long as isolates are consistent with norms for the species, and in the same terminal DNA sequence clade. Sometimes single isolates or even populations of isolates differ from named species in more troublesome ways. In this work, these are named for the closest established relative, but a “note” is added in the appendix Table. In a few cases it is clear that a population represents an as yet undescribed species. These are designated P. taxon xxxx. P. taxon ceanothus, for example, would be identified as P. citrophthora based on ITS sequence alone, but isolates are homothallic.
Habitats and Hosts: All records are from western Oregon (west of the crest of the Cascade Mountains). We have not deliberately excluded the eastern 2/3 of the state; there simply are no forest Phytophthora records from that part of the state. There are extensive forests on the ‘eastside,’ but these are drier forests with fewer hardwoods, and there have been no stream surveys in these areas as yet. “Forest” in our usage is a plant community dominated by trees at maturity. We include records from all plant species growing in the forest, as well as from forest soil and forest streams. “Forests” are often disturbed and may be found at various stages of ecological succession. In Oregon, many forests originated from planting after harvest of the previous stand. They are almost always comprised of species native to Oregon. “Christmas tree plantations” and “Seed orchards” are cultivated plantations of forest tree species managed for specific products. The “Urban” habitat refers to trees planted in cities, usually in parks or as street trees. In some cases the host species are not native to Oregon.
In forest nurseries trees, and sometimes shrubs and other native plants, are intensively managed to produce stock for transplanting to forest sites for regeneration of the forest after harvest or other disturbance. In general, we have not included records from horticultural nurseries, regardless of the plant species. The decision is rather arbitrary and the distinction is sometimes vague, however. Chamaecyparis lawsoniana illustrates the ambiguity. We have included landscape records for this species that is widely planted as an ornamental, but we have not included horticultural nursery records despite the role of the horticultural nurseries in the establishment and spread of Phytophthora lateralis in the state. 4. Results and Discussion
Thirty-two Phytophthora species, including described but not formally named taxa, have been identified associated with 25 host species from Oregon forests or forest trees (Tables 1 and 2). This total includes 19 species recovered from forest streams, and 19 from forest soils, generally in the absence of noticeable disease on associated vegetation. A total of 29 Phytophthora species were identified from the various environments in forests (Table 3). Fourteen species came from cultivated and urban environments. Only three species were unique to the latter, however, including P. ilicis, known only from cultivated holly (Ilex), P. sansomeana and P. taxon ceanothus from forest nurseries (Table 3).
The sampling that produced these lists is not systematic, however, and very uneven. Only in tanoak forests of Curry County was the full range of habitats sampled. Two large studies focused on forest stream sampling, so the list from that habitat is perhaps most complete, but this work still covers only a small portion of the state, including streams in 12 of the 19 counties in western Oregon. Three species, P. gonapodyides, P. taxon oaksoil, and P. lacustris (Nechwatal et al. 2012) were recovered from streams in 13 counties. The most widespread species causing root disease or bole cankers was P. lateralis on Port Orford cedar in landscape plantings throughout the state as well as on forest trees in its limited native range (Tucker and Milbrath 1942), and P. cambivora, which is widespread but uncommon on a number of forest trees (Saavedra et al. 2007). Other widespread species were P. ilicis, only on holly in commercial plantations and landscapes (Buddenhagen and Young 1957), and P. cinnamomi on several hosts, although uncommon. In contrast, eleven species are reported from only 1 county. Some, such as P. ramorum on Notholithocarpus are locally abundant (Hansen et al. 2008), while others seem to be rare, known only from one or a few records. The overall forest Phytophthora record reflects the relative health of Oregon forests despite the potential susceptibility of the tree species evident from the records from nurseries and Christmas tree plantations.
Douglas-fir (Pseudotsuga menziezii) provides an interesting example. It is by far the most important forest tree in Oregon, dominating forest sites in much of the state including the 19 counties in western Oregon that were most regularly sampled in these surveys. Only one Phytophthora species (P. ramorum) is reported from this host growing in forests, although in nurseries and Christmas tree plantations at least five other species cause disease. In contrast, tanoak (Notholithocarpus densiflorus) is host to at least 11 Phytophthora species in the forests of SW Oregon where it grows (Reeser et al. 2008, Reeser et al. 2011a)
a Number of counties with reports. There are 19 counties in western Oregon covered by this index.
Table 1. Hosts and habitats of Phytophthora species identified Number Plant from Oregon Hosts Habitats of Oregon Parts forest trees and Countiesa forests.
Phytophthora Species P. alni uniformis Alnus rubra forest root 1 Christmas Abies procera, tree Ceanothus bole plantation, integerrimus, leaf/twig, P. cactorum forest, forest 3 Ceanothus velutinus, root, soil, native Notholithocarpus stem plant densiflorus nursery Christmas Abies procera, Alnus tree sp., Chrysolepis plantation, chrysophylla, Fagus P. cambivora forest, forest bole 9 grandifolia, soil, forest Notholithocarpus stream, densiflorus urban Abies procera, Christmas P. cinnamomi Chamaecyparis tree bole, root 6 lawsoniana, plantation, Notholithocarpus forest, forest densiflorus, soil, forest Pseudotsuga menziezii tree nursery, urban forest soil forest seed orchard, Pinus lambertiana, P. cryptogea forest soil, root 2 Pseudotsuga menziesii forest tree nursery forest P. europaea 1 stream forest, forest P. gallica Alnus rubra soil, forest root 2 stream Alnus rhombifolia, forest, forest Alnus rubra, soil, forest bole, P. gonapodyides Notholithocarpus stream, leaf/twig, 13 densiflorus, forest tree root Pseudotsuga menziesii nursery forest, forest P. gregata Alnus rubra soil, forest root 1 stream P. hydropathica Alnus sp. forest root 4 plantation, P. ilicis Ilex aquifolium leaf/twig 6 landscape forest, forest Chamaecyparis research lawsoniana, Taxus nursery, P. lateralis root 12 brevifolia, Thuja forest tree occidentalis nursery, landscape Christmas tree plantation, Abies procera, P. megasperma forest bole, root 4 Pseudotsuga menziezii stream, native tree nursery P. multivora forest soil 1
forest, forest Notholithocarpus soil, forest densiflorus, bole, P. nemorosa stream, 1 Umbellularia leaf/twig urban forest californica soil forest P. nicotianae 1 stream forest stream, P. pini Ceanothus sanguineus root 3 native plant nursery forest soil, P. plurivora forest 7
stream Alnus rubra, forest soil, bole, leaf P. pseudosyringae Notholithocarpus forest /twig, 5 densiflorus stream root Christmas tree Pinus monticola, plantation, P. pseudotsugae root 5 Pseudotsuga menziesii forest soil, forest tree nursery Notholithocarpus P. psychrophyla forest leaf/twig 1 densiflorus Notholithocarpus densiflorus, Pseudotsuga menziezii, Rhamnus purshiana, Rhododendron forest, forest bole, P. ramorum macrophyllum, Rhus stream, 1 leaf/twig diversiloba, Rubus forest soil spectabilis, Umbellularia californica, Vaccinium ovatum, Vaccinium parviflorum forest P. riparia 5 stream forest tree P. sansomeana Pseudotsuga menziesii root 1 nursery Alnus rhombifolia, Alnus rubra, forest, forest leaf Notholithocarpus P. siskiyouensis soil, forest /twig, 5 densiflorus, stream bole, root Umbellularia californica forest P. syringae stream, 2
forest soil Ceanothus integerrimus, P. taxon native plant root, Ceanothus 1 ceanothus nursery Stem sanguineus, Ceanothus velutinous P. taxon morella Morella californica forest leaf/twig 1 forest, forest Notholithocarpus bole, P. taxon pluvialis soil, forest 4 densiflorus leaf/twig stream forest, forest P. taxon oaksoil Alnus rubra soil, forest root 13 stream Christmas tree Abies procera, Alnus plantation, P. taxon rubra, forest, forest bole, root 9 pgchlamydo Notholithocarpus soil, forest densiflorus stream, urban forest soil Alnus rhombifolia, P. lacustris forest root 13 Alnus rubra, Alnus sp.
Includes Christmas tree plantations, seed orchards, landscape plantings, forest tree and native plant restoration nurseries, and urban forests.
Table 2. Phytophthora species identified from Oregon forest Phytophthora Plant trees and forests by hosts and Habitats species Parts habitats.
Host<> Christmas tree Abies procera P. cactorum bole plantation Christmas tree P. cambivora bole, root plantation Christmas tree P. cinnamomi bole, root plantation Christmas tree plantation, P. megasperma bole, root forest tree nursery P. taxon Christmas tree root pgchlamydo plantation Alnus rhombifolia P. gonapodyides forest root P. siskiyouensis forest root
P. lacustris forest root
Alnus rubra P. alni uniformis forest root P. gonapodyides forest root
P. gregata forest root
P. forest root pseudosyringae P. siskiyouensis forest root
P. taxon oaksoil forest root
P. taxon forest root pgchlamydo P. lacustris forest root
P. gallica forest root
P. siskiyouensis forest bole
Alnus sp. P. cambivora forest root P. hydropathica forest root
P. lacustris forest root
native plant Ceanothus integerrimus P. cactorum stem nursery P. taxon native plant root ceanothus nursery native plant Ceanothus sanguineus P. pini root nursery P. taxon native plant stem ceanothus nursery Ceanothus velutinus P. cactorum native plant root nursery P. taxon native plant root, ceanothus nursery stem forest tree Chamaecyparis lawsoniana P. cinnamomi root nursery forest, P. lateralis Landscape root
plantings Chrysolepis chrysophylla P. cambivora forest bole Fagus grandifolia P. cambivora urban bole Landscape Ilex aquifolium P. ilicis leaf/twig plantings holly plantations leaf/twig
Morella californica P. taxon morella forest leaf/twig Notholithocarpus densiflorus P. cactorum forest leaf/twig P. cambivora forest bole
P. cinnamomi forest bole
bole, P. gonapodyides forest leaf/twig bole, P. nemorosa forest leaf/twig P. bole, forest pseudosyringae leaf/twig P. psychrophyla forest leaf/twig
bole, leaf P. ramorum forest /twig P. siskiyouensis forest bole
bole, P. taxon pluvialis forest leaf/twig P. taxon forest bole pgchlamydo forest seed Pinus lambertiana P. cryptogea root orchard forest tree Pinus monticola P. pseudotsugae root nursery forest tree Pseudotsuga menziesii P. cinnamomi root nursery forest tree P. cryptogea root nursery forest tree P. gonapodyides root nursery forest tree P. megasperma root nursery forest tree P. pseudotsugae root nursery Christmas tree root plantation P. ramorum forest leaf/twig
forest tree P. sansomeana root nursery Rhamnus purshiana P. ramorum forest leaf/twig Rhododendron macrophyllum P. ramorum forest leaf/twig Rhus diversiloba P. ramorum forest leaf/twig Rubus spectabilis P. ramorum forest leaf/twig Taxus brevifolia P. lateralis forest root Thuja occidentalis P. lateralis landscape root Umbellularia californica P. nemorosa forest leaf/twig P. ramorum forest leaf/twig
P. siskiyouensis forest leaf/twig
Vaccinium ovatum P. ramorum forest leaf/twig Vaccinium parviflorum P. ramorum forest leaf/twig
a Includes Christmas tree plantations, seed orchards, landscape plantings, forest tree and native plant restoration nurseries, and urban forests.
Table 3. Phytophthora species identified from Oregon forest plants, forest soils, and forest streams, or Forest Forest Forest Cultivated from various cultivated and urban plants soil stream and Urban a forest environments.
P. alni uniformis X
P. cactorum X X X
P. cambivora X X X X P. cinnamomi X X X
P. cryptogea X X
P. europaea X
P. gallica X X X
P. gonapodyides X X X X P. gregata X
P. hydropathica X X X
P. ilicis X
P. megasperma X X
P. lateralis X X
P. multivora X
P. nemorosa X X X X P. nicotianae X
P. pini X X
P. plurivora X X
P. pseudosyringae X X X
P. pseudotsugae X X
P. psychrophyla X
P. ramorum X X X
P. riparia X
P. sansomeana X
P. siskiyouensis X X X
P. syringae X X
P. taxon morella X
P. taxon ceanothus X
P. taxon oaksoil X X X
P. taxon pgchlamydo X X X X P. taxon pluvialis X X X
P. lacustris X X X
Acknowledgements
We thank the Oregon Department of Forestry and the USDA Forest Service, Pacific Southwest Experiment Station and Southwest Oregon Forest Insect and Disease Center for participation in, and support of, this work. Literature Cited
Brasier CM, Cooke DEL, Duncan JM, Hansen EM. 2003. Multiple new phenotypic taxa from trees and riparian ecosystems in Phytophthora gonapodyides-P. megasperma ITS Clade 6, which tend to be high-temperature tolerant and either inbreeding or sterile. Mycological Research 107:277– 290. doi:10.1017/S095375620300738X Buddenhagen IW. 1954. A Phytophthora-induced disease of English holly, Ilex aquifolium L. MS Thesis, Oregon State College.
Buddenhagen IW, Young RA. 1957. A leaf and twig disease of English holly caused by Phytophthora ilicis n.sp. Phytopathology 47:95–101.
Chastagner GA, Hamm PB, Riley KL. 1995. Symptoms and Phytophthora spp. associated with root rot and stem canker of noble fir Christmas trees in the Pacific Northwest. Plant Disease 79:290–293. doi: 10.1094/PD-79-0290.
Cooke DEL, Drenth A, Duncan JM, Wagels G, Brasier CM. 2000. A molecular phylogeny of Phytophthora and related oomycetes. Fungal Genetics and Biology 30:17 – 32. doi:10.1006/fgbi.2000.1202
Davidson JM, Werres S, Garbelotto M, Hansen EM, Rizzo DM. 2003. Sudden oak death and associated diseases caused by Phytophthora ramorum. Plant Health Progress. doi:10.1094/PHP-2003-0707-01-DG
Gallegly ME, Hong C. 2008. Phytophthora: identifying species by morphology and DNA fingerprints. St. Paul, Minn: APS Press. 158 pp.
Goheen EM, Hansen EM, Kanaskie A, McWilliams MG, Osterbauer N, Sutton W. 2002. Sudden oak death caused by Phytophthora ramorum in Oregon. Plant Disease 86:441–441. doi:10.1094/PDIS.2002.86.4.441C
Hamm PB, Hansen EM. 1982. Pathogenicity of Phytophthora species to Pacific Northwest conifers. European Journal of Forest Pathology 12:167–174. doi:10.1111/j.1439-0329.1982.tb01390.x
Hamm PB, Hansen EM. 1983. Phytophthora pseudotsugae, a new species causing root rot of Douglas-fir. Canadian Journal of Botany 61:2626–2631. doi:10.1139/b83-289
Hamm PB, Hansen EM. 1984. Improved method for isolating Phytophthora lateralis from soil. Plant Disease 68:517–519. doi:10.1094/PD-68-517
Hansen EM, Brasier CM, Shaw DS, Hamm PB. 1986. The taxonomic structure of Phytophthora megasperma: evidence for emerging biological species groups. Transactions of the British Mycological Society 87:557– 573. doi:10.1016/S0007-1536(86)80097-3
Hansen EM, Hamm PB, Julis AJ, Roth LF. 1979. Isolation, incidence and management of Phytophthora in forest tree nurseries in the Pacific Northwest [USA]. Plant Disease Reporter 63:607.
Hansen EM, Kanaskie A, Prosper S, McWilliams M, Goheen EM, Osterbauer N, Reeser P, Sutton W. 2008. Epidemiology of Phytophthora ramorum in Oregon tanoak forests. Canadian Journal of Forest Research 38:1133–1143. doi: 10.1139/X07-217
Hansen EM, Maxwell DP. 1991. Species of the Phytophthora megasperma complex. Mycologia 83:376–381.
Hansen EM, Parke JL, Sutton W. 2005. Susceptibility of Oregon forest trees and shrubs to Phytophthora ramorum: a comparison of artificial inoculation and natural infection. Plant Disease 89:63– 70. doi:10.1094/PD-89-0063
Hansen EM, Reeser PW, Davidson JM, Garbelotto M., Ivors K, Douhan L, Rizzo DM. 2003. Phytophthora nemorosa, a new species causing cankers and leaf blight of forest trees in California and Oregon, USA. Mycotaxon 88:129–138.
Hansen EM, Wilcox WF, Reeser PW, Sutton W. 2009. Phytophthora rosacearum and P. sansomeana, new species segregated from the Phytophthora megasperma “complex”. Mycologia 101:129– 135. doi:10.3852/07-203
Ivors K, Garbelotto M, Vries IDE, Ruyter-Spira C, Hekkert BT, Rosenzweig N, Bonants P. 2006. Microsatellite markers identify three lineages of Phytophthora ramorum in US nurseries, yet single lineages in US forest and European nursery populations. Molecular Ecology 15:1493–1505. doi:10.1111/j.1365- 294X.2006.02864.x
Ivors KL, Hayden KJ, Bonants PJM, Rizzo DM, Garbelotto M. 2004. AFLP and phylogenetic analyses of North American and European populations of Phytophthora ramorum. Mycological Research 108:378– 392. doi:10.1017/S0953756204009827
Martin FN, Tooley PW. 2003. Phylogenetic relationships of Phytophthora ramorum, P. nemorosa, and P. pseudosyringae, three species recovered from areas in California with sudden oak death. Mycological Research 107:1379–1391. doi:10.1017/S0953756203008785
McWilliams MG. 2000. Port-Orford-cedar and Phytophthora lateralis: grafting and heritability of resistance in the host, and variation in the pathogen. Ph.D. Thesis, Oregon State University. 101 pp.
Mills SD, Coffey MD, Forster H. 1991. Taxonomic structure of Phytophthora cryptogea and P. drechsleri based on isozyme and mitochondrial DNA analyses. Mycological research 95:31–48. doi: 10.1016/S0953- 7562(09)81359-2
Nechwatal, J, Bakonyi J, Cacciola SO, Cooke DEL, Jung T, Nagy ZÁ, Vannini Á, Vettraino AM, Brasier CM. 2012. The morphology, behaviour and molecular phylogeny of Phytophthora taxon Salixsoil and its redesignation as Phytophthora lacustris sp. nov. Plant Pathology:Early view. doi:10.1111/j.1365- 3059.2012.02638.x
Oh E, Hansen EM. 2007. Histopathology of infection and colonization of susceptible and resistant Port- Orford-Cedar by Phytophthora lateralis. Phytopathology 97:684–693. doi:10.1094/phyto-97-6-0684
Pratt RG, Roth LF, Hansen EM, Ostrofsky WD. 1976. Identity and pathogenicity of species of Phytophthora causing root rot of Douglas-fir in the Pacific Northwest. Phytopathology 66:710–714. doi: 10.1094/Phyto- 66-710
Putnam M, Serdani M, Curtis M, Angima S. 2011. Phytophthora leaf blight - a new disease of California wax- myrtle (Morella californica) in Oregon, USA caused by a Phytophthora species. New Zealand Journal of Forestry Science 41 Suppl.:S57–S63.
Reeser PW, Hansen EM, Sutton W. 2007. Phytophthora siskiyouensis, a new species from soil, water, myrtlewood (Umbellularia californica) and tanoak (Lithocarpus densiflorus) in southwestern Oregon. Mycologia 99:639–643. doi:10.3852/mycologia.99.5.639
Reeser PW, Hansen EM, Sutton W. 2008. Phytophthora species causing tanoak stem cankers in southwestern Oregon. Plant Disease 92:1252–1252. doi:10.1094/PDIS-92-8-1252B
Reeser PW, Sutton W, Hansen EM. 2011a. Phytophthora species in tanoak trees, canopy drip, soil, and streams in the sudden oak death epidemic area of southwestern Oregon, USA. New Zealand Journal of Forestry Science 41 Suppl.:S65–S73.
Reeser PW, Sutton W, Hansen EM, Remigi P, Adams GC. 2011b. Phytophthora species in forest streams in Oregon and Alaska. Mycologia 103:22–35. doi:10.3852/10-013
Robideau GP, De Cock AWAM, Coffey MD, Voglmayr H, Brouwer H, Bala K, Chitty DW, Désaulniers N, Eggertson QA, Gachon CMM. 2011. DNA barcoding of oomycetes with cytochrome c oxidase subunit I and internal transcribed spacer. Molecular Ecology Resources 11:1002–1011. doi:10.1111/j.1755- 0998.2011.03041.x
Saavedra A, Hansen EM, Goheen DJ. 2007. Phytophthora cambivora in Oregon and its pathogenicity to Chrysolepis chrysophylla. Forest Pathology 37:409 – 419. doi:10.1111/j.1439-0329.2007.00515.x
Sims L. Phytophthora species associated with declining alder trees in riparian areas of western Oregon. Ph.D. thesis (in preparation). Oregon State University. Sutton W, Hansen EM, Reeser PW, Kanaskie A. 2009. Stream monitoring for detection of Phytophthora ramorum in Oregon tanoak forests. Plant Disease 93:1182–1186. doi:10.1094/PDIS-93-11-1182
Torgeson,DC 1953. Epiphytology and etiology of a Phytophthora-induced root rot diseases of Chamaecyparis in Oregon. PhD thesis, Oregon State College.
Trione EJ. 1974. Sporulation and germination of Phytophthora lateralis. Phytopathology 64:1531– 1533. doi:10.1094/Phyto-64-1531
Tucker CM, Milbrath JA. 1942. Root rot of Chamaecyparis caused by a species of Phytophthora. Mycologia 34:94–103.