Taxon Pgchlamydo Research Articles

The Phytophthora species assemblage and diversity in riparian alder ecosystems of western Oregon, USA

Phytophthora species were systematically sampled, isolated, identified and compared for presence in streams, soil and roots of alder (Alnus species) dominated riparian ecosystems in western Oregon. We describe the species assemblage and evaluate Phytophthora diversity associated with alder. We recovered 1250 isolates of 20 Phytophthora species. Only three species were recovered from all substrates (streams, soil, alder roots): P. gonapodyides, the informally described “P. taxon Pgchlamydo”, and P. siskiyouensis. P. alni ssp. uniformis along with five other species not previously recovered in Oregon forests are included in the assemblage: P.citricola s.l., P. gregata, P. gallica, P. nicotianae and P. parsiana. Phytophthora species diversity was greatest in downstream riparian locations. There was no significant difference in species diversity comparing soil and unwashed roots (the rhizosphere) to stream water. There was a difference between the predominating species from the rhizosphere compared to stream water. The most numerous species was the informally described “P. taxon Oaksoil”, which was mainly recovered from, and most predominant in, stream water. The most common species from riparian forest soils and alder root systems was P. gonapodyides.

Redesignation of Phytophthora taxon Pgchlamydo as Phytophthora chlamydospora sp. nov.

A new species, Phytophthora chlamydospora , is described. P. chlamydospora, previously known informally as P . taxon Pgchlamydo, is found in streams and wet soil worldwide and is a pathogen of some riparian tree species. It is self-sterile, and produces persistent non-papillate sporangia, usually on unbranched sporangiophores. Clamydospores are formed most regularly at warmer temperatures. Phytophthora chlamydospora is classified in ITS Clade 6.

Pathogenicity to alder of Phytophthora species from riparian ecosystems in western Oregon

SummaryDescribed as one of the most destructive pathogens of agricultural crops and forest trees, Phytophthora is a genus of microorganisms containing over 100 known species. Phytophthora alni has caused collar and root disease in alders throughout Europe, and a subspecies has recently been isolated in North America. Reports of canopy dieback in red alder, Alnus rubra, prompted a survey of their overall health and to determine whether P. alni was present in western Oregon riparian ecosystems. Over 1100 Phytophthora isolates were recovered, representing 20 species and 2 taxa. Phytophthora‐type cankers were observed in many trees, and their incidence was positively correlated with canopy dieback. High levels of mortality for red alder were not observed, which suggests these Phytophthora species are not aggressive pathogens. To test this hypothesis, three stem wound inoculations and one root dip were conducted on red alder seedlings using 13 Phytophthora species recovered from the riparian survey. Ten of the 13 Phytophthora species produced significant lesions in at least one pathogenicity test. Phytophthora siskiyouensis produced the largest lesions on red alder from the two stem wound inoculation tests conducted under summer conditions, while P. taxon Pgchlamydo caused the largest lesions during the winter stem wound inoculation test. Phytophthora gonapodyides, P. taxon Pgchlamydo and P. siskiyouensis have previously been found associated with necrotic alder roots and bole cankers in the field, and with the pathogenicity results reported here, we have established these species as causes of Phytophthora root disease and Phytophthora bole canker of alder in Oregon. While none of the Phytophthora species were especially aggressive towards red alder in the pathogenicity tests, they did cause localized disease symptoms. By weakening the root systems or boles of alders, the Phytophthoras could be leaving alders more susceptible to other insects and pathogens.

Phytophthora Taxon Pgchlamydo is a Cause of Shoot Blight and Root and Collar Rot of Viburnum tinus in Italy.

The quarantine pathogen Phytophthora ramorum has recently been found on dying Viburnum tinus in the nursery area of Pistoia, central Italy (43°56'0″ N, 11°1'0″ E) (3). As part of a surveillance program aimed at detecting P. ramorum in this area, the Phytophthora taxon Pgchlamydo was consistently found associated with symptomatic V. tinus. The crowns of these plants were wilted, and some plants also showed root and collar rot and underbark necrosis. Water courses adjacent to the nursery with the infected V. tinus were tested for the pathogen. Samples from seven symptomatic plants were placed on a selective V8A-PARPNH medium within 24 h from sampling. Tissue pieces (2 mm2) of 12 baits (apple fruits) exposed for a week in water bodies were plated on the same medium. Cottony colonies arose after 2 to 3 days of incubation at 23°C in the dark and were transferred to potato dextrose agar (PDA) in purity. Mycelial DNA was extracted with a commercial kit (Sigma-Aldrich). The rDNA ITS region and a portion of the mtDNA cox1 gene were PCR-amplified and the amplicons digested with the restriction enzymes MspI and AluI (for the ITS region) and RsaI (for the cox1 gene region). Isolates R7 from V. tinus, and ES2M5, ES2M11, and ES1M12 from the water bodies belonged to the same taxon based on restriction analysis of both DNA regions coupled with ITS-rDNA sequence homology (GenBank Accession Nos. KJ396773 to 76). A BLAST search in GenBank found that all isolates had a 99% identity in the ITS-rDNA with the Phytophthora ITS Clade 6 member P. taxon Pgchlamydo. Sporangia produced after incubation in filtered pond water for 24 h were mostly ovoid (sometimes obpyriform), non-papillate, non-caducous. Some sporangia were emptied with external proliferation and had hyphal swellings. Thirty sporangia were measured and averaged 42.4 ± 6.2 × 29.9 ± 3.5 μm (range 30.0 to 56.1 × 22.5 to 38.0), with a length/width ratio of 1.4 ± 0.2 (1.2 to 2.0), and exit pores of 11.7 ± 1.5 μm (9.0 to 14.6). Optimum colony growth on V8A at 30°C was 4.4 ± 0.4 mm day-1, and the maximum temperature for growth was 32°C. Inoculation on twigs of Fagus sylvatica and V. tinus produced necrotic lesions of 2.6 ± 0.5 cm (2.1 to 3.5) and 4.7± 0.5 cm (3.8 to 5.6) respectively after 3 weeks of incubation at 23°C in the dark. Inoculation on V. tinus leaves resulted in lesions averaging 3.3 ± 1.1 × 2.1 ± 0.6 cm (range 2 to 5 × 1.5 to 3) after 2 weeks of incubation at 23°C in the dark. Control plant material showed no symptoms.The Phytophthora taxon Pgchlamydo has been reported on several ornamental and woody species, including Arctostaphylos sp., Camellia spp., Laurus nobilis, Buxus sempervirens, Rhododendron sp., Arbutus unedo, Prunus sp., Pseudotsuga sp., and Sequoia sempervirens, in North America and Europe (1,2). This is the first report, to our knowledge, of this taxon on V. tinus in Italy. V. tinus is widely sold in European nurseries, and it is also one of the most common hosts of P. ramorum (4). The fact that V. tinus is a host for both oomycetes, and the two microorganisms induce a similar symptomology (wilt), might complicate the control efforts of the phytosanitary inspection services aimed at restricting P. ramorum foci in Europe.

Phytophthora Community Structure Analyses in Oregon Nurseries Inform Systems Approaches to Disease Management

Nursery plants are important vectors for plant pathogens. Understanding what pathogens occur in nurseries in different production stages can be useful to the development of integrated systems approaches. Four horticultural nurseries in Oregon were sampled every 2 months for 4 years to determine the identity and community structure of Phytophthora spp. associated with different sources and stages in the nursery production cycle. Plants, potting media, used containers, water, greenhouse soil, and container yard substrates were systematically sampled from propagation to the field. From 674 Phytophthora isolates recovered, 28 different species or taxa were identified. The most commonly isolated species from plants were Phytophthora plurivora (33%), P. cinnamomi (26%), P. syringae (19%), and P. citrophthora (11%). From soil and gravel substrates, P. plurivora accounted for 25% of the isolates, with P. taxon Pgchlamydo, P. cryptogea, and P. cinnamomi accounting for 18, 17, and 15%, respectively. Five species (P. plurivora, P. syringae, P. taxon Pgchlamydo, P. gonapodyides, and P. cryptogea) were found in all nurseries. The greatest diversity of taxa occurred in irrigation water reservoirs (20 taxa), with the majority of isolates belonging to internal transcribed spacer clade 6, typically including aquatic opportunists. Nurseries differed in composition of Phytophthora communities across years, seasons, and source within the nursery. These findings suggest likely contamination hazards and target critical control points for management of Phytophthora disease using a systems approach.

Phytophthora Populations in Nursery Irrigation Water in Relationship to Pathogenicity and Infection Frequency of Rhododendron and Pieris.

Phytophthora spp. are waterborne plant pathogens that are commonly found in streams, rivers, and reclaimed irrigation water. Rhododendron and Pieris trap plants at two commercial nurseries were irrigated with water naturally infested with Phytophthora spp. during the 2011 and 2012 growing seasons to assess the frequency of disease. Phytophthora spp. were consistently recovered from water samples at every collection time but detected on only 2 of the 384 trap plants during the two growing seasons. Pathogenicity assays proved that Phytophthora hydropathica and Phytophthora taxon PgChlamydo, commonly recovered taxa in irrigation water at the nurseries, were foliar pathogens of Rhododendron and Pieris; however, neither species was able to cause root rot on these same hosts. Overall, Phytophthora spp.-infested irrigation water did not act as a primary source of infection on Rhododendron and Pieris, even though foliar pathogenic species of Phytophthora were present in the water.

Phytophthora ×stagnum nothosp. nov., a new hybrid from irrigation reservoirs at ornamental plant nurseries in Virginia.

A novel Phytophthora species was frequently recovered from irrigation reservoirs at several ornamental plant production facilities in eastern Virginia. Initial sequencing of the internal transcribed spacer (ITS) region of this species generated unreadable sequences due to continual polymorphic positions. Cloning and sequencing the ITS region as well as sequencing the mitochondrially encoded cytochrome c oxidase 1 and beta-tubulin genes revealed that it is a hybrid between P. taxon PgChlamydo as its paternal parent and an unknown species genetically close to P. mississippiae as its maternal parent. This hybrid has some diagnostic morphological features of P. taxon PgChlamydo and P. mississippiae. It produces catenulate hyphal swellings, characteristic of P. mississippiae, and chlamydospores, typical of P. taxon PgChlamydo. It also produces both ornamented and relatively smooth-walled oogonia. Ornamented oogonia are another important diagnostic character of P. mississippiae. The relatively smooth-walled oogonia may be indicative of oogonial character of P. taxon PgChlamydo. The new hybrid is described here as Phytophthora ×stagnum.

Movement of Phytophthora spp. in Maryland's Nursery Trade.

Phytophthora spp. cause major losses in the nursery industry worldwide. However, a clear demonstration of the route of movement has not been previously shown. A survey of 10 Maryland nurseries was conducted over a 3-year period to investigate the presence of Phytophthora spp. on newly arrived plants, mainly from West Coast suppliers. Local nursery plants, irrigation water, and potting media were also sampled for Phytophthora spp. Isolates were identified using a combination of morphological characteristics and DNA sequencing. Species identified included Phytophthora cactorum, P. cambivora, P. cinnamomi, P. citrophthora, P. drechsleri, P. elongata, P. gonapodyides, P. hydropathica, P. irrigata, P. lacustris, P. multivora, P. nicotianae, P. pini, P. plurivora, and P. syringae. P. taxon pgchlamydo was also isolated from irrigation water. Eight of the abovementioned Phytophthora spp. were isolated in association with incoming material, indicating that the movement of these pathogens continues to occur. Asymptomatic plant material was the main route of introduction of Phytophthora spp. to Maryland nurseries. Results also indicated that several Phytophthora spp. could be found in Maryland nurseries in association with infested potting media of asymptomatic plants. Although P. ramorum was not detected, our surveys underscore the significance of nursery practices that allow introductions of these significant plant pathogens to new geographic locations.

Characterization of Phytophthora hybrids from ITS clade 6 associated with riparian ecosystems in South Africa and Australia

Surveys of Australian and South African rivers revealed numerous Phytophthora isolates residing in clade 6 of the genus, with internal transcribed spacer (ITS) gene regions that were either highly polymorphic or unsequenceable. These isolates were suspected to be hybrids. Three nuclear loci, the ITS region, two single copy loci (antisilencing factor (ASF) and G protein alpha subunit (GPA)), and one mitochondrial locus (cytochrome oxidase c subunit I (coxI)) were amplified and sequenced to test this hypothesis. Abundant recombination within the ITS region was observed. This, combined with phylogenetic comparisons of the other three loci, confirmed the presence of four different hybrid types involving the three described parent species Phytophthora amnicola, Phytophthora thermophila, and Phytophthora taxon PgChlamydo. In all cases, only a single coxI allele was detected, suggesting that hybrids arose from sexual recombination. All the hybrid isolates were sterile in culture and all their physiological traits tended to resemble those of the maternal parents. Nothing is known regarding their host range or pathogenicity. Nonetheless, as several isolates from Western Australia were obtained from the rhizosphere soil of dying plants, they should be regarded as potential threats to plant health. The frequent occurrence of the hybrids and their parent species in Australia strongly suggests an Australian origin and a subsequent introduction into South Africa.

Identification of Phytophthora species baited and isolated from forest soil and streams in northwestern Yunnan province, China

SummaryPhytophthora species were surveyed by collecting soil samples and placing bait leaves in selected streams during June–October in the years 2005, 2006 and 2010 at three sites in oak forests in Diqing Tibetan Autonomous Prefecture of NW Yunnan province, China. Seventy‐three isolates of Phytophthora spp. were recovered from 135 baited leaf samples and 81 soil samples. Eight Phytophthora species were identified by observation of morphological features and ITS1‐5.8S‐ITS2 rDNA sequence analysis. The eight taxa included two well‐known species P. gonapodyides and P. cryptogea, two recently described species P. gregata and P. plurivora, two named but as yet undescribed taxa, P. taxon PgChlamydo and P. taxon Salixsoil, and two previously unrecognized species, Phytophthora sp.1 and P. sp.2. The most numerous species, P. taxon PgChlamydo, and the second most abundant species, P. taxon Salixsoil, were recovered at all three sites. Phytophthora cryptogea was detected only once at site Nixi. Phytophthora gregata and P. sp.2 were isolated from a stream only at site Bitahai, while the other three species were each found at two sites. Phylogenetic analysis revealed that the isolates belonged to three ITS clades, one species including six isolates in clade 2, six species including 66 isolates in clade 6 and one species in clade 8. There was a relatively rich species and genetic diversity of Phytophthora detected in the investigated regions where the forest biotic and abiotic factors affecting the growth and evolution of Phytophthora populations were diverse.

Phytophthora diversity and the population structure of Phytophthora ramorum in Swiss ornamental nurseries

Invasive oomycete pathogens have been causing significant damage to native ecosystems worldwide for over a century. A recent well‐known example is Phytophthora ramorum, the causal agent of sudden oak death, which emerged in the 1990s in Europe and North America. In Europe, this pathogen is mainly restricted to woody ornamentals in nurseries and public greens, while severe outbreaks in the wild have only been reported in the UK. This study presents the results of the P. ramorum survey conducted in Swiss nurseries between 2003 and 2011. In all 120 nurseries subjected to the plant passport system, the main P. ramorum hosts were visually checked for above ground infections. Phytophthora species were isolated from tissue showing symptoms and identified on the basis of the morphological features of the cultures and sequencing of the ribosomal ITS region. Phytophthora was detected on 125 plants (66 Viburnum, 58 Rhododendron and one Pieris). Phytophthora ramorum was the most frequent species (59·2% of the plants), followed by P. plurivora, P. cactorum, P. citrophthora, P. cinnamomi, P. cactorum/P. hedraiandra, P. multivora and P. taxon PgChlamydo. The highest incidence of P. ramorum was observed on Viburnum × bodnantense. Microsatellite genotyping showed that the Swiss P. ramorum population is highly clonal and consists of seven genotypes (five previously reported in Europe, two new), all belonging to the European EU1 clonal lineage. It can therefore be assumed that P. ramorum entered Switzerland through nursery trade. Despite sanitation measures, repeated P. ramorum infections have been recorded in seven nurseries, suggesting either reintroduction or unsuccessful eradication efforts.

First Report of Leaf Spot Caused by Phytophthora taxon Pgchlamydo on Evergreen Nursery Stock in California.

As part of the Phytophthora ramorum testing program from 2005 through 2007, a Phytophthora sp. was isolated on PARP-CMA medium (4) at the CDFA lab in Sacramento, CA, from the margin of necrotic spots and tissue suffering from dieback on Arctostaphylos sp. (manzanita), Camellia spp., Laurus nobilis (bay), Buxus sempervirens (boxwood), Rhododendron sp., Arbutus unedo (strawberry tree), and Sequoia sempervirens (coast redwood). Isolates were collected from Shasta, Contra Costa, San Diego, Solano, Santa Cruz, Alameda, Sacramento, San Joaquin, Monterey, and Los Angeles Counties. Isolates from A. unedo tissue on PARP medium produced apapillate, obovate sporangia 25 to 80 × 15 to 40 μm (48.0 × 26.9 μm average) and a few isolates produced intercalary and terminal chlamydospores at 22°C (30 to 46 μm diameter, 38.9 μm average). The internal transcribed spacer region (ITS) of rDNA was amplified from four isolates using ITS1 and ITS4 primers as described by White et al. (3) and the amplicons sequenced (GenBank Accession Nos. JQ307188 through JQ307191). BLAST analysis of the amplicons showed 99 to 100% identity with the ITS sequence of Phytophthora taxon Pgchlamydo from forest streams in Oregon (GenBank Accession No. HM004224) (1). Pathogenicity tests were performed on B. sempervirens, C. sasanqua, L. nobilis, and A. unedo. Five plants of each species were inoculated with 6-mm plugs taken from the margin of a 7- to 10-day-old culture grown on V8 juice agar. Plant leaves were wounded with a sterile pushpin and two agar plugs were covered with a freezer tube cap filled with sterile dH2O and clipped to the underside of the leaves with a sterile pin-curl clip (4). Inoculated plants were sprayed with water, covered with plastic bags, and incubated for 2 days, when bags and plugs were removed. Five leaves of each isolate plus five control plugs using V8 juice agar alone were inoculated on each plant. Plants were incubated for 12 days at 18°C (16-h photoperiod). Lesions formed on all inoculated plants, ranging in size from approx. 1 mm on B. sempervirens to 9.2 × 10.9 mm average on A. unedo. The lesions on A. unedo grew into and caused the mid-vein to blacken. The lesion sizes on camellia and bay were larger than those formed on B. sempervirens and smaller than those formed on A. unedo, with most lesions surrounded by a dark ring. Phytophthora taxon Pgchlamydo is associated with leaf lesions on rhododendron and dieback of yew in Minnesota (2). To our knowledge, this is the first report of Phytophthora taxon Pgchlamydo causing disease in camellia, bay, strawberry tree, and boxwood in California. Phytophthora taxon Pgchlamydo causes damage that is indistinguishable from the quarantine pest, P. ramorum (4).

New Phytophthoras in Western Australia’s natural ecosystems

Phytophthora spp. are recognised as important plant pathogens. Ten new and genetically diverse species, not previously reported from elsewhere, have recently been described from natural ecosystems in Western Australia (WA): Phytophthora multivora1; P. elongata; P. thermophila, P. gregata, P. gibbosa, P. litoralis; P. arenaria, P. constricta; P. fluvialis; and P. amnicola. They were identified by DNA sequencing of recent and historical isolates from the WA Department of Environment and Conservation (DEC). Several additional new taxa await description. New records for WA of at least eight other Phytophthora taxa that are known overseas, some of them as yet undescribed, have also been confirmed: P. inundata; P. taxon niederhauserii, P. taxon asparagi, P. taxon PgChlamydo, P. taxon personii; P. taxon salixsoil; P. palmivora and P. rosacearum. Furthermore, numerous Phytophthora hybrids have been identified in natural vegetation and waterways in WA. The phylogenetic relationships of the new WA Phytophthora taxa, with their nearest relatives, are shown in Figure 1.

Phytophthora species in forest streams in Oregon and Alaska

Eighteen Phytophthora species and one species of Halophytophthora were identified in 113 forest streams in Alaska, western Oregon and southwestern Oregon that were sampled by baiting or filtration of stream water with isolation on selective media. Species were identified by morphology and DNA characterization with single strand conformational polymorphism, COX spacer sequence and ITS sequence. ITS Clade 6 species were most abundant overall, but only four species, P. gonapodyides (37% of all isolates), P. taxon Salixsoil, P. taxon Oaksoil and P. pseudosyringae, were found in all three regions. The species assemblages were similar in the two Oregon regions, but P. taxon Pgchlamydo was absent in Alaska and one new species present in Alaska was absent in Oregon streams. The number of Phytophthora propagules in Oregon streams varied by season and in SW Oregon, where sampling continued year round, P. taxon Salixsoil, P. nemorosa and P. siskiyouensis were recovered only in some seasons.

Re-evaluation of Phytophthora Species Isolated During 30 Years of Vegetation Health Surveys in Western Australia Using Molecular Techniques.

For 30 years, large-scale aerial photography has been used to map the extent of Phytophthora dieback disease in native forests in the southwest of Western Australia, with validation of the observations involving routine testing of soil and root samples for the presence of Phytophthora cinnamomi. In addition to P. cinnamomi, six morpho-species have been identified using this technique: P. citricola, P. megasperma, P. cryptogea, P. drechsleri, P. nicotianae, and P. boehmeriae. In recent years, many new Phytophthora species have been described worldwide, often with similar morphology to existing species; thus, as many of the isolates collected in Western Australia have been difficult to identify based on morphology, molecular identification of the morpho-species is required. Based on amplification of the internal transcribed spacer (ITS) region of the rDNA gene, sequence data of more than 230 isolates were compared with those of existing species and undescribed taxa. P. inundata, P. asparagi, P. taxon PgChlamydo, P. taxon personii, and P. taxon niederhauserii were identified based on sequence data. Phylogenetic analysis revealed that nine potentially new and undescribed taxa can be distinguished. Several of the new taxa are morphologically indistinguishable from species such as P. citricola, P. drechsleri, and P. megasperma. In some cases, the new taxa are closely related to species with similar morphology (e.g., P.sp.4 and P. citricola). However, the DNA sequences of other new taxa such as P.sp.3 and P.sp.9 show that they are not closely related to morphologically similar species P. drechsleri and P. megasperma, respectively. Most of the new taxa have been associated with dying Banksia spp., while P.sp.2 and P.sp.4 have also been isolated from dying Eucalyptus marginata (jarrah). Some taxa (P.sp.3, 6, and 7) appear to have limited distribution, while others like P.sp.4 are widespread.

Multiple alien Phytophthora taxa discovered on diseased ornamental plants in Spain

The plant trade is unwittingly accelerating the worldwide spread of well‐known and new or undescribed Phytophthora species and creating novel niches for emerging pathogens. The results of a survey carried out from 2001 to 2006 in garden centres and nurseries of the Balearic Islands and eastern Spain combined with the analysis of samples received from ornamental nurseries from northern Spain reflected the extent of this global issue at the local scale. A total of 125 Phytophthora isolates were obtained from 37 different host species and 17 putative species identified on morphological features and direct sequencing of the internal transcribed spacer and four mitochondrial and nuclear genes. Five species, P. ramorum, P. hedraiandra, P. ‘niederhauserii’, P. ‘kelmania’ and P. ‘taxon Pgchlamydo’ were formally unknown to science prior to 2001. In addition, 37 new host/pathogen combinations were first records for Spain, highlighting the risk of non‐coevolved organisms from different biogeographic origins coming into contact under managed environments. The problem generated by new or rare taxa of Phytophthora found in nurseries for which no prior information on natural habitat and ecology is available for pest risk analysis is discussed.

Host Range Investigations of New, Undescribed, and Common Phytophthora spp. Isolated from Ornamental Nurseries in Minnesota.

Eleven woody landscape plants commonly grown in the upper Midwestern United States were inoculated with up to three unnamed Phytophthora taxa (Phytophthora taxon Pgchlamydo, a Phytophthora alni-like isolate [Phytophthora MN14d], and Phytophthora sp. MN1) to explore their host ranges. In addition, P. cactorum, P. citricola, P. citrophthora, P. hedraiandra, and P. nicotianae were used to inoculate plants to further investigate the susceptibilities of plant genera previously found associated with these pathogens, to explore the susceptibility of important landscape plants (i.e., oak) to common ornamental Phytophthora spp., and to prove Koch's postulates. Koch's postulates were completed on fragrant sumac with P. citricola and P. nicotianae and on common lilac with P. citrophthora. A nonwound or wound inoculation technique were used to determine host susceptibility. Phytophthora sp. MN1 caused symptoms on American cranberrybush, bur and red oak, common lilac, fragrant sumac, Norway maple, and 'P.J.M.' rhododendron. The newly described organism P. hedraiandra caused disease on American cranberrybush, common lilac, red oak, and 'Snowdrift' crabapple. Fragrant sumac and common lilac generally were the most susceptible hosts to all Phytophthora spp. This study demonstrated that many ornamental Phytophthora pathogens have larger potential host ranges than previously known. The biology and ecology of P. hedraiandra and Phytophthora sp. MN1 must be further investigated, and methods for rapid identification should be developed.

Phytophthora species from declining Austrocedrus chilensis forests in Patagonia, Argentina

A survey of Phytophthora spp. in declining and healthy Austrocedrus chilensis forest was conducted to obtain an overview of the species that inhabit these forests. Seventeen declining and three healthy stands plus 11 associated streams were surveyed. Five Phytophthora species were recovered. P. syringae was the most common species isolated from soil and/or streams at nine declining sites and one healthy site. P. gonapodyides was isolated from streams only, at five declining sites. P. cambivora was isolated from soil and the undescribed taxa ‘P. taxon Pgchlamydo’ and 22 ‘P. taxon Raspberry’ were isolated from streams at one declining site each. The species were identified by ITS rDNA sequences and morphological features. Brief descriptions of each species and a discussion of their possible relationship with “mal del ciprés” are presented.

Phytophthora species from declining Austrocedrus chilensis forests in Patagonia, Argentina

A survey of Phytophthora spp. in declining and healthy Austrocedrus chilensis forest was conducted to obtain an overview of the species that inhabit these forests. Seventeen declining and three healthy stands plus 11 associated streams were surveyed. Five Phytophthora species were recovered. P. syringae was the most common species isolated from soil and/or streams at nine declining sites and one healthy site. P. gonapodyides was isolated from streams only, at five declining sites. P. cambivora was isolated from soil and the undescribed taxa 'P. taxon Pgchlamydo' and 22 'P taxon Raspberry' were isolated from streams at one declining site each. The species were identified by ITS rDNA sequences and morphological features. Brief descriptions of each species and a discussion of their possible relationship with "mal del ciprés" are presented.

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

Phytophthora isolates associated with Phytophthora major ITS Clade 6 were grouped into 11 phenotypic taxa. These comprised the described morphospecies P. gonapodyides, P. megasperma s. str. and P. humicola; four previously identified but so far undescribed taxa, informally designated here P. sp. O-group, P. sp. Apple-cherry, P. taxon Pgchlamydo, and P. taxon Walnut; and four previously unknown taxa, designated P. taxon Oaksoil, P. taxon Raspberry, P. taxon Forestsoil, and P. taxon Riversoil. With the exception of P. gonapodyides, each phenotypic taxon represented an unique ITS lineage. Two isolates morphologically identical to P. gonapodyides comprised a separate lineage and probably represent another taxon, designated here P. taxon Salixsoil, P. humicola, P. sp. O-group, P. sp. Apple-cherry and P. taxon Walnut grouped together as subclade I. Within subclade II, P. taxon Oaksoil, P. taxon Raspberry, P. taxon Forestsoil, P. taxon Riversoil and P. taxon Pgchlamydo formed a cluster of closely related but phenotypically distinct lineages basal to P. gonapodyides and P. megasperma, P. taxon Salixsoil being the most basal member. The taxonomy, adaptation and breeding systems of Clade 6 taxa are discussed. They show a strong association with forests and riparian ecosystems, only a limited association with agriculture and an ability to tolerate high temperatures. Also, in contrast to most other Phytophthora clades, Clade 6 taxa are predominantly sterile or inbreeding in culture. Only one taxon, P. sp. O-group, appears classically A1/A2 heterothallic.