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Phytophthora chlamydospora
... However, despite its abundance in streams, there is generally no evidence of disease in the surrounding vegetation in the study area. In contrast, P. chlamydospora appears to be a pathogen of woody plants and horticulturally valuable species [77], which could have implications for site 1. The other species found in clade 6b of the phylogeny of Yang et al. [22] (P. ...
This work reports the first survey of Phytophthora diversity in the forests soils of Andean Patagonia. It also discusses the role of anthropogenic impact on Phytophthora distribution inferred from the findings on Phytophthora diversity and on the distribution of Phytophthora austrocedri-diseased forests. Invasive pathogen species threaten ecosystems and human activities contribute to their entry and spread. Information on pathogens already established, and early detection of potential invasive ones, are crucial to disease management and prevention. Phytophthora austrocedri causes the most damaging forest disease in Patagonia, affecting the endemic species Austrocedrus chilensis (D. Don) Pic. Sern. and Bizzarri. However, the relationship between anthropogenic impacts and the disease distribution has not been analyzed enough. The aims of this work were: to evaluate Phytophthora diversity in soils of Andean Patagonia using a metabarcoding method, and analyze this information in relation to soil type and land use; to assess the distribution of Austrocedrus disease over time in relation to anthropogenic and abiotic gradients in an area of interest; and to discuss the role of human activities in Phytophthora spread. High throughput Illumina sequencing was used to detect Phytophthora DNA in soil samples. The distribution of Austrocedrus disease over time was assessed by satellite imagery interpretation. Twenty-three Phytophthora species, 12 of which were new records for Argentina, were detected. The most abundant species was P. austrocedri, followed by P. × cambivora, P. ramorum and P. kernoviae. The most frequent was P. × cambivora, followed by P. austrocedri and P. ramorum. Phytophthora richness and abundance, and Austrocedrus disease distribution, were influenced by land use, anthropogenic impact and soil drainage. Results showed several Phytophthoras, including well-known pathogenic species. The threat they could present to Patagonian ecosystems and their relations to human activities are discussed. This study evidenced the need of management measures to control the spread of P. austrocedri and other invasive Phytophthora species in Patagonia.
... Phytophthora chlamydospora is not known as a pathogen of fruit or nut trees in North America but has been reported in Turkey on several perennial orchard species including almond (Türkölmez et al., 2016), and on various ornamentals and forest perennials in the U.S. (Hansen et al., 2018;Hansen et al., 2015). In 2018, we isolated P. chlamydospora from dying almond trees (Prunus dulcis) on Nemaguard seedling rootstock (Prunus persica × P. davidiana) girdled by crown and root rot ( Fig. 1 A, B). ...
Common or English (Persian) walnut (Juglans regia L.) is an important nut crop in Turkey, which is the fourth largest producer of walnut in the world. In August 2015, we observed sudden wilt and subsequent death associated with root rot. Approximately 15% of 2,000 5 to 7-year-old J. regia cv. Chandler trees grafted on wild walnut (J. regia) in waterlogged areas of a commercial walnut orchard in Bingöl province of eastern Turkey were affected. Most fine roots were completely rotted and the inner bark of infected lateral and taproots showed a reddish brown discoloration.Tissue samples taken from the margins of root lesions of 10 symptomatic trees were placed on grated carrot corn meal agar (GCCMA) (Türkölmez et al. 2015) amended with 5 mg of pimaricin, 250 mg of ampicillin, 10 mg of rifampicin, 100 mg of pentachloronitrobenzene, and 50 mg of hymexazol per liter (P5ARPH). Plates were incubated for 5 days at 28°C in the dark. A Phytophthora species was consistently isolated from the tissues. On GCCMA, colonies had a distinct petaloid growth pattern and produced abundant spherical, thin-walled, intercalary and terminal chlamydospores (30 to 46 μm diameter) and hyphal chains of globose to subglobose swellings. After incubation of mycelial disks in non-sterile soil extracts at 25°C, all isolates produced hyaline, non-papillate, non-caducous sporangia of ovoid to obpyriform shape, with internal proliferation, measuring 34.5 to 56.5 μm in length, 27.0 to 39.5 μm wide, with a length/breadth ratio of 1.4 to 1.7, formed on unbranched or sympodial sporangiophores. Growth rate on carrot agar (CA) at 25°C was 3.3 to 3.5 mm d-1; the optimum and maximum temperatures for mycelium growth on CA were 29 and 37°C, respectively. All these characteristics were similar to those described for Phytophthora chlamydospora Brasier and Hansen (Hansen et al. 2015), previously known as P. taxon Pgchlamydo. Genomic DNA was extracted from three representative isolates.The internal transcribed spacer (ITS) region of rDNA and cox2 gene regions were amplified using the ITS6/ITS4 and FMPhy10b/FMPhy8b primer pairs, respectively, and sequenced (GenBank Accession Nos. KU725882, KU725883, KU707216, KX446861, KX446862). BLAST searches of ITS region showed 100% identity to many P. chlamydospora isolates, including the ex-type culture P236 (GenBank Accession No. AF541900) (Brasier et al. 2003), deposited in GenBank and of cox2 gene regions of two isolates had 100% identity with PD_01777_cox2 and PD_00174_cox2 accessions deposited at Phytophthora-ID databases, which confirmed the morphological identification. Pathogenicity of P. chlamydospora was evaluated using the soil infestation method on 10 1-year-old potted J. regia cv. Chandler seedlings by growing P. chlamydospora on sterilized millet seeds for 4 weeks at 29°C and adding infested millet seeds to potting soil at a rate of 3% (wt/vol). In 10 non-inoculated control plants, sterilized millet seeds were added to the potting soil. Both inoculated and control plants were flooded for 24 h at 2 weeks intervals. All inoculated plants showed severe wilting within a month and necrosis on lateral and taproots and rot on fine roots after 2 months of incubation in a greenhouse where air temperatures ranged from 24 to 30°C, while control plants remained asymptomatic. Koch's postulates were satisfied after re-isolating P. chlamydospora, which was identified morphologically, from symptomatic roots of inoculated plants. Phytophthora chlamydospora has been previously recovered from several ornamental and woody species (Blomquist et al. 2012; Brasier et al. 2003; Ginetti et al. 2014), and to our knowledge, this is the first report of P. chlamydospora infection of walnut, which represents a new host for this pathogen.
In June 2015, ∼10% of 10,000 8-year-old almond [Prunus dulcis (Miller) D.A. Webb. cv. Ferragnes] trees grafted on the GF677 rootstock in a commercial almond orchard in Besni of Adıyaman Province, showed wilting and lack of vigor, with severely infected trees dying from root and crown rot. The incidence of infected trees on soils with poor water drainage was greater than that on well-drained soils. Crowns of symptomatic plants had a reddish brown discoloration in the inner bark with a sharp contrast between infected and healthy tissue. Most fine roots were completely rotted and the inner bark of infected larger roots showed similar discoloration. Tissue samples taken from the margins of crown and root lesions were placed on carrot agar (CA) amended with 5 mg of pimaricin, 250 mg of ampicillin, 10 mg of rifampicin, 100 mg of pentachloronitrobenzene, and 50 mg of hymexazol (P5ARPH) per liter. Plates were incubated for 5 days at 28°C in the dark and Phytophthora chlamydospora was consistently isolated from the tissues. Isolates produced petaloid colonies and abundant spherical, thin-walled, intercalary but lateral and terminal chlamydospores (30 to 46 μm diameter, 38.5 μm average). Colonized agar discs were submerged in sterilized deionized water at 25°C. After incubation on submerged discs for 24 h, all isolates produced hyaline, nonpapillate, noncaducous sporangia of ovoid to obpyriform shape, with internal and external proliferation, 34.0 to 56.5 μm long, 26.5 to 39.5 μm wide, with a length/breadth ratio of 1.4 to 1.7, formed on simple, unbranched, occasionally sympodial sporangiophores. Globose to subglobose hyphal swellings in branched chains also formed in water. The optimum and maximum temperatures for mycelium growth on CA were 27 and 37°C, respectively. All these characteristics were similar to those described for P. chlamydospora Brasier and Hansen sp. nov. (Hansen et al. 2015), previously known as P. taxon Pgchlamydo. Genomic DNA was extracted from two representative isolates. The ITS region of rDNA was amplified using the ITS6/ITS4 primer pair and sequenced (GenBank KU647271 and KU647272). BLAST searches showed 99 to 100% identity to P. chlamydospora isolates, including the type isolate P236 (99% identity) (AF541900) (Hansen et al. 2015), deposited in GenBank and Phytophthora-ID databases, which confirmed morphological identification. Primary roots of ten 1-year-old P. dulcis cv. Ferragnes seedlings were wounded with a scalpel, and mycelial disks (3 per plant) of P. chlamydospora grown on CA were placed under the cortical tissue, after removing 10 to 15 cm of soil around the root base. The inoculated and exposed roots were then covered with soil. P. chlamydospora caused severe wilt and browning of leaves within 1 and 2 months and extensive root necrosis and rot after 2 months of incubation in a greenhouse. During this period, soil was kept wet by watering plants daily as required. Koch’s postulates were satisfied after reisolating P. chlamydospora from symptomatic roots of inoculated plants. No disease occurred in 10 controls, similarly inoculated with sterile CA disks, and the pathogen was not recovered from these plants. P. chlamydospora has only rarely been recovered from several ornamental and woody species (Blomquist et al. 2012; Brasier et al. 2003; Ginetti et al. 2014), but not from fruit trees so far. To our knowledge, this is the first report of P. chlamydospora infection of almond, which represents a new host for this pathogen. This is also the first record of P. chlamydospora in Turkey. Within a month, all naturally infected almond trees in this orchard were collapsed and destroyed and the number of infected trees increased dramatically, indicating that it might be a significant threat to almond plantations and orchards, particularly on sites where excess soil water occurs periodically.
Little is currently about the assemblage of Phytophthora species in northeastern North America, representing a gap in our understanding of species incidence. Therefore Phytophthora species were surveyed at 20 sites in Massachusetts, with 16 occurring in the Connecticut River Valley. Many of the sampled waterways were adjacent to active agricultural lands, yet were buffered by mature floodplain forests composed of Acer, Platanus, Populus and Ulmus. Isolates were recovered with three types of baits (rhododendron leaves, pear, green pepper) in 2013 and water filtration in 2014. Overall 457 isolates of Phytophthora were recovered and based on morphological characters and rDNA internal transcribed spacer (ITS), β-tubulin (β-tub) and cytochrome oxidase c subunit I (cox1) sequences, 18 taxa were identified, including three new species, P. taxon intercalaris, P. taxon caryae and P. taxon pocumtuck. In addition, 49 isolates representing five species of Phytopythium also were identified. Water filtration captured a greater number of taxa (18) compared to leaf and fruit baits (12). Of the three bait types rhododendron leaves yielded the greatest number of isolates and taxa, followed by pear and green pepper, respectively. Despite the proximity to agricultural lands, none of the Phytophthora species baited are considered serious pathogens of vegetable crops in the region. However, many of the recovered species are known woody plant pathogens, including four species in the P. citricola s.l. complex that were identified: P. plurivora, P. citricola III, P. pini and a putative novel species, referred to here as P. taxon caryae. An additional novel species, P. taxon pocumtuck, is a close relative of P. borealis based on cox1 sequences. The results illustrate a high level of Phytophthora species richness in the Connecticut River Valley and that major rivers can serve as a source of inoculum for pathogenic Phytophthora species in the northeast.
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).
Phytophthora species are well-known as destructive plant pathogens, especially in natural ecosystems. It is ironic, therefore, how little is known regarding the Phytophthora diversity in South African natural woody ecosystems. In this study, Phytophthora species were isolated using standard baiting techniques from 182 soil and water samples and these were identified based on ITS and coxI sequence data. The 171 resulting Phytophthora isolates resided in 14 taxa including six known species (P. multivora, P. capensis, P. cryptogea, P. frigida, P. cinnamomi, P. cinnamomi var. parvispora), the known but as yet unnamed Phytophthora sp. PgChlamydo, P. sp. emzansi, and P. sp. Kununurra and five novel taxa referred to as P. sp. stellaris, P. sp. Umtamvuna P. sp. canthium, P. sp. xWS, P. sp. xHennops. Four of the new taxa were found exclusively in water and two of these are hybrids. The most commonly isolated species from soil was P. multivora, a species recently described from Western Australia. Phytophthora frigida was isolated for the first time from stream water. With the exception of P. cinnamomi, very little is known regarding the biology, epidemiology or origin of Phytophthora in South Africa.
Schwingle, B. W., Smith, J. A., and Blanchette, R. A. 2007. Phytophthora species associated with diseased woody ornamentals in Minnesota nurseries. Plant Dis. 91:97-102. Phytophthora species are responsible for causing extensive losses of ornamental plants world- wide. Recent international and national surveys for the detection of P. ramorum have led to the finding of previously undescribed Phytophthora species. Since no previous Phytophthora sur- veys have been carried out in Minnesota, surveys of ornamental nurseries were performed over 4 years to isolate and identify the Phytophthora species causing diseases of woody plants in Min- nesota. Species were identified by direct sequencing of internal transcribed spacer (ITS) rDNA, β-tub, and mitochondrial coxI genes. Species associated with diseased ornamental plants include P. cactorum, P. cambivora, P. citricola, P. citrophthora, P. hedraiandra, P. megasperma, P. nico- tianae, and the previously identified but undescribed taxon P. Pgchlamydo. The most common species encountered were P. cactorum, P. citricola, and P. citrophthora. Two additional isolates obtained did not match known species. One was similar to P. alni subsp. alni, and the other ap- peared to be a new species and is referred to as P. sp. MN1. In addition, species are reported for the first time from several hosts. Results indicated that several Phytophthora species were more widespread in the nursery industry than previously thought, and undescribed species were caus- ing disease in Minnesota ornamental nurseries.
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.
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.
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.
During surveys of dying vegetation in natural ecosystems and associated waterways in Australia many new taxa have been identified from Phytophthora ITS Clade 6. For representative isolates, the region spanning the internal transcribed spacer region of the ribosomal DNA, the nuclear
gene encoding heat shock protein 90 and the mitochondrial cox 1 gene were PCR amplified and sequenced. Based on phylogenetic analysis and morphological and physiological comparison, four species and one informally designated taxon have been described; Phytophthora gibbosa, P.
gregata, P. litoralis, P. thermophila and P. taxon paludosa. Phytophthora gibbosa, P. gregata and P. taxon paludosa form a new cluster and share a common ancestor; they are homothallic and generally associated with dying vegetation in swampy or
water-logged areas. Phytophthora thermophila and P. litoralis are sister species to each other and more distantly to P. gonapodyides. Both new species are common in waterways and cause scat tered mortality within native vegetation. They are self-sterile and appear well
adapted for survival in an aquatic environment and inundated soils, filling the niche occupied by P. gonapodyides and P. taxon salixsoil in the northern hemisphere. Currently the origin of these new taxa, their pathogenicity and their role in natural ecosystems are unknown. Following
the precautionary principle, they should be regarded as a potential threat to native ecosystems and managed to minimise their further spread.
Phylogenetic relationships among 50 Phytophthora species and between Phytophthora and other oomycetes were examined on the basis of the ITS sequences of genomic rDNA. Phytophthora grouped with Pythium, Peronospora, and Halophytophthora, distant from genera in the Saprolegniales. Albugo was intermediate between these two groups. Unlike Pythium, Phytophthora was essentially monophyletic, all but three species forming a cluster of eight clades. Two clades contained only species with nonpapillate sporangia. The other six clades included either papillate and semipapillate, or semipapillate and nonpapillate types, transcending traditional morphological groupings, which are evidently not natural assemblages. Peronospora was related to P. megakarya and P. palmivora and appears to be derived from a Phytophthora that has both lost the ability to produce zoospores and become an obligate biotroph. Three other Phytophthoras located some distance from the main Phytophthora-Peronospora cluster probably represent one or more additional genera.
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.
Sour cherry is a very important commercial crop of Turkey. In a newly established orchard in Ankara province of Turkey, some of young sour cherry trees did not leaf out or collapsed after a while turning green in spring, 2014. Lateral and hairy roots of symptomatic trees showed poor growth. Occurrence of necrotic and decay tissues girdling the whole roots resulted in tree mortality. Two Phytophthora spp. were isolated from necrotic tissues on taproots and crowns. The pathogens were identified as Phytophthora chlamydospora and P. megasperma based on morphological characteristics and DNA sequences of the internal transcribed spacer region. Pathogenicity of the isolates was tested by stem inoculation to sour cherry seedlings. P. chlamydospora caused canker lesions and killed the seedlings within 4 weeks, while no cankers occurred on stem of the plants inoculated with P. megasperma and on control plants. Also P. megasperma was found as pathogen on roots of sour cherry seedlings in soil infestation test. This is the first report of P. chlamydospora and P. megasperma causing crown and root rot of sour cherry in Turkey. In addition, P. chlamydospora is a new pathogen of sour cherry grafted on Prunus mahaleb.
In 2013 a survey of Phytophthora diversity was performed in 25 natural and seminatural forest stands and 25 rivers in temperate montane and subtropical lowland regions of Taiwan. Using baiting assays, 10 described species and 17 previously unknown taxa of Phytophthora were isolated from 71.5% of the 144 rhizosphere soil samples from 33 of 40 tree species sampled in 24 forest stands, and from 19 rivers: P. capensis, P. citrophthora, P. plurivora, P. tropicalis, P. citricola VII, P. sp. × botryosa-like, P. sp. × meadii-like and P. sp. occultans-like from Clade 2; P. palmivora from Clade 4; P. castaneae and P. heveae from Clade 5; P. chlamydospora and P. sp. forestsoil-like from Clade 6; P. cinnamomi (Pc), P. parvispora, P. attenuata nom. prov., P. flexuosa nom. prov., P. formosa nom. prov., P. intricata nom. prov., P. × incrassata nom. prov. and P. × heterohybrida nom. prov. from Clade 7; P. sp. palustris and five new hybrid species from Clade 9. The A1 mating type of Pc was widespread in both montane and lowland forests and rarely associated with disease, whereas the A2 mating type was limited to lowland forests and in some cases causing severe dieback. Most other Phytophthora species were not associated with obvious disease symptoms. It is concluded that (i) Taiwan is within the centre of origin of most Phytophthora taxa found, (ii) Pc A2 is an introduced invasive pathogen, and (iii) interspecific hybridizations play a major role in speciation and species radiations in diverse natural ecosystems.
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.
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 mt...
Described 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.
Tanoak (Lithocarpus densiflorus) is a principal host of Phytophthora ramorum, cause of sudden oak death (SOD), in the western United States (1). In the course of SOD surveys in southwestern Oregon, other Phytophthora species were encountered to be causing stem cankers on tanoak that were indistinguishable from those caused by P. ramorum. In Oregon, SOD is subject to quarantine and eradication. Aerial surveys are flown two or more times a year to locate symptomatic tanoaks, which are then examined from the ground to determine the cause of death. Isolations on selective media were attempted from all trees with stem cankers typical of Phytophthora. Phytophthora species were identified by morphological features and DNA sequencing of either internal transcribed spacer (ITS) or the mitochondrial COX spacer region. ITS sequences were compared with validated GenBank records, and COX spacer sequences were compared with known reference isolates in the OSU collection. From 2001 through 2006, Phytophthora spp. were isolated from 482 of 1,057 tanoak stem cankers sampled. P. ramorum was isolated from 359 cankers, P. nemorosa was isolated from 102 cankers, P. gonapodyides was isolated from six cankers, P. cambivora was isolated from four cankers (all A1 mating type), P. siskiyouensis was isolated from four cankers, P. pseudosyringae was isolated from two cankers, P. cinnamomi was isolated from one canker (mating type A2), and P. taxon “Pgchlamydo” was isolated from one canker. Three cankers yielded isolates that were not identified but were closely related to P. pseudosyringae based on ITS sequence. No Phytophthora spp. were cultured from the remaining cankers. One isolate from each species identified (except P. ramorum and P. pseudosyringae) was tested for pathogenicity on tanoak stems (11.4 to 16.0 cm DBH) in the field. A 5-mm-diameter plug from the margin of a V8 agar culture was placed in a hole in the bark, covered with wet cheesecloth, and sealed with aluminum foil and duct tape. Each isolate was inoculated into five different stems. Each stem received three different isolates and an agar control. After 4 weeks, bark was removed to reveal lesion development. Lesions were measured (length by width), and pieces from four points on the lesion margin were plated in selective media to reisolate. P. cambivora, P. cinnamomi, P. gonapodyides, P. nemorosa, P. siskiyouensis and P. taxon “Pgchlamydo” all caused substantial lesions in inoculated tanoak trees (average area 11.5 to 18.6 cm ² ). In all cases, the species used for inoculation was recovered on reisolation from lesion margins. Control inoculations caused necrotic areas averaging 0.2 cm ² . Isolations from these areas were clean. Prior to the recent SOD epidemic, no species of Phytophthora were known as pathogens of tanoak. The discovery of P. ramorum as a pathogen of tanoak in California was quickly followed by the discovery that P. nemorosa and P. pseudosyringae were also associated with tanoak cankers (2). Six years of diagnostic support for survey and detection of P. ramorum in tanoak forests of southwest Oregon has revealed the occurrence, at very low frequency, of at least five additional species of Phytophthora causing stem cankers in tanoak.
References: (1) D. M. Rizzo et al. Ann. Rev. Phytopathol. 43:309, 2005. (2) A. C. Wickland et al. For. Pathol. Online publication. DOI:10.1111/j.1439-0329.2008.00552.x), 2008.
Phytophthora lateralis, a pathogen of Chamaecyparis lawsoniana (Port-Orford cedar or Lawson's cypress), was confirmed in France, but isolates from Germany identified as P. lateralis or “similar to” P. lateralis proved to be P. gonapodyides. Previously, P. lateralis was known only from western North America, where it has been destructive in nurseries, ornamental plantings, and the forest since its introduction about 1920 (1). Reports from other locations have proved to be misidentifications or impossible to confirm. In France, P. lateralis was isolated and identified from C. lawsoniana on two occasions (1996 and 1998) in different parts of the country, probably stemming from a single original infestation of young, potted, greenhouse-propagated cedars in a commercial nursery. German isolates were from an old culture collection and from irrigation water in a nursery growing a wide range of woody ornamentals. Identifications were confirmed by comparison (2) with authentic isolates. P. lateralis isolates from ...
Numerous ornamental nurseries in 32 California Counties were surveyed for leaf spots as part of the California Department of Food and Agriculture mandated surveys targeting Phytophthora ramorum. Tissue collected during the 2005 and 2006 surveys was initially screened by a Phytophthora-specific enzyme-linked immunosorbent assay. All positives samples were further tested using polymerase chain reaction to determine if P. ramorum was present. P ramorum was detected in 1% of the total number of samples taken during the Surveys. A total of 377 isolates were identified as species of Phytophthora other than P. ramorum, and their identify was determined by internal transcriber spacer (ITS) sequences. Subsets of the putative ITS-species were further verified using accepted morphological characters. Thirteen species of Phytophthora Were found: P. cactorum, P cambivora, P citricolo, P. citrophthora. P. cryptogea, P foliorum, P. gonapodyides R hibernalis. P nemorosa, P. 'Pgchldamydo', P pseudosyringae, P syringae, and P. tropicalis. P syringae and P. citricola made up 55% of the total number of isolates. Species thought to be strictly forest pathogens, P. nemorosa and P pseudosyringae, each made up less than 4% of the isolates. To test pathogenicity of acquired isolates'. Subsets of different species of Phytophthora were inoculated onto leaves of selected host plant genera. Of the 66 pathogen-host genera combinations tested, 44 resulted in lesion formation. Disease symptoms appeared as dark, water-Soaked lesions with irregular margins and were similar among phytophthora species.
Phytophthora 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.
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.
Isolates of Phytophthora gonapodyides associated with roots of woody hosts or from aquatic habitats in Britain (10 isolates) and North America (Alaska to California, 12 isolates) were compared. They showed similar characteristics including similar sporangial dimensions, colonies with often distinctive petaloid patterns and a silvery appearance, slow growth rates at 20, 25 and 30 °C, and a maximum temperature for growth of about 35°. Most isolates exhibited a similar protein banding pattern distinct from that of P. cryptogea or P. drechsleri, and including a characteristic band designated the ‘PG band’. Three isolates deviated from this pattern and two of these also produced chlamydospores and chains of swellings in culture. These isolates might be hybrids related to P. gonapodyides or a different taxon, in which case ‘P. gonapodyides’ is polyphyletic.All the isolates were self-sterile. When paired directly or indirectly via polycarbonate membranes with A2 sexual compatibility types of heterothallic species such as P. cambivora, P. megakarya or P. meadii, gametangia were produced which were morphologically characteristic of these species. The range of heterothallic species responding was different from that responding sexually to Trichoderma volatiles. P. gonapodyides isolates may be sterile A1 compatibility types able to produce a compatibility substance which induces selfing in the heterothallic A2s.Three other self-sterile Phytophthora isolates associated with woody hosts in Britain were a distinct group, with a different colony pattern, a distinct 30° growth optimum and an ability to grow at 37°. Their protein banding pattern was different from that of either P. gonapodyides or P. cryptogea/P. drechsleri, but showed similarities to these species. One isolate induced gametangial formation in P. drechsleri A1 types, the two others were sexually neutral. These three isolates might also be species hybrids, possibly with P. gonapodyides and P. cryptogea as parents.
A survey of symptoms of phytophthora root and collar rot of common (Alnus glutinosa) and grey alder (A. incana) in riparian and forest stands in Bavaria was conducted by the Bavarian State Forestry and river authorities. Symptoms were seen in 1041 out of 3247 forest alder stands. The majority of the affected stands (80.9%) were less than 21 years old; 46% of these young stands were growing on nonflooded sites and 92% had been planted. The riparian survey showed that symptoms were widespread along more than 50% of the river systems. Along some rivers the disease incidence exceeded 50%. The 'alder Phytophthora' was recovered from 166 of 185 riparian and forest alder stands with symptoms. In 58 of the 60 rivers and streams investigated in detail, the source of inoculum was traced back to infested young alder plantations growing on the river banks or on forest sites that drain into the rivers. Once introduced to a river system, the 'alder Phytophthora' infects alders downstream. Baiting tests showed that the 'alder Phytophthora' was present in rootstocks of alders from three out of four nurseries which regularly bought in alder plants for re-sale, but not in rootstocks from four nurseries that grew their own alders from seed. In addition, the infected nurseries used water from infested water courses for irrigation. The Bavarian State Ministry for Agriculture and Forestry has developed a code of practice for producing healthy alder plants in forest nurseries. This includes a 3-year fallow period between bare-rooted alder crops because of poor survival of the 'alder Phytophthora' in soil.
Intra- and interspecific isozyme variation was evaluated for 123 isolates assigned to either Phytophthora cryptogea or P. drechsleri, and compared with that of 15 isolates of P. erythroseptica and 11 isolates of P. lateralis. Isolates of P. cryptogea and P. drechsleri were from worldwide sources and displayed a high degree of variability. The majority of these isolates were subsequently divided into ten distinct groups based on numerical analysis of 24 putative enzyme loci. None of the enzyme loci were monomorphic for all ten groups. Analysis of mitochondrial (mt) DNA restriction fragment length polymorphisms of selected isolates from each isozyme group supported the isozyme data. Differences in morphological features of the ten isozyme groups of P. cryptogea and P. drechsleri were not sufficiently distinct to readily distinguish between them. Isozyme analysis of P. erythroseptica revealed that it is a uniform and distinct taxon. The isolates of P. lateralis also formed a homogeneous and discrete group. An interspecific comparison revealed that the variation among the ten isozyme groups of P. cryptogea and P. drechsleri was as great as that observed among P. cinnamomi, P. cambivora, P. lateralis, P. erythroseptica and P. richardiae. The combined results of isozyme and mtDNA analysis indicate that there are at least seven distinct molecular species represented by the 123 isolates of P. cryptogea and P. drechsleri evaluated in this study.
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.
Phytophthora species were surveyed from the end of 1997 through July 1998 in oak forests in NE France. Healthy (Amance) or declining (Illwald) forests were compared. The Phytophthora population in both was diverse and locally abundant. At least eight species were present at Amance and six at Illwald. At Amance Phytophthora species had a localized distribution in water and low-lying soils. At Illwald distribution was more uniform apparently due to flooding events. Most often recovered were P. citricola, P. gonapodyides and. quercina. P. gonapodyides was ubiquitous in water and colonized leaf debris. P. quercina was widely distributed in soil but not abundant, and was found in sites that did not otherwise appear to favor Phytophthora. No correlation was detected between presence of Phytophthora in soil and health of trees. Unusual combinations of environmental factors may be required for resident Phytophthora to have a detrimental impact on oaks. (C) 1999 Editions scientifiques et medicales Elsevier SAS.
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.
Cultural characters, protein patterns and unusual mating behavior of Phytophthora gonapodyides isolates from Britain and North America
- C Blomquist
- L E Yakabe
- M C Soriano
- M A Negrete
- C M Brasier
- P Hamm
- E M Hansen
Blomquist, C.,, L. E. Yakabe, M.C. Soriano, and M.A. Negrete. 2012. First report of leaf spot caused by Phytophthora taxon
Pgchlamydo on evergreen nursery stock in California. Plant Dis. 96:1691. https://doi.org/10.1094/PDIS-02-12-0221-PDN
Brasier, C. M., P. B Hamm and E. M. Hansen. 1993. Cultural characters, protein patterns and unusual mating behavior of
Phytophthora gonapodyides isolates from Britain and North America. Mycol. Res. 97:1287-1298.
http://dx.doi.org/10.1016/S0953-7562(09)80160-3
Identification of Phytophthora spp. known to attack conifers in the Pacific Northwest
- P B Hamm
- E M Hansen
Hamm, P. B. and E. M. Hansen. 1987. Identification of Phytophthora spp. known to attack conifers in the Pacific Northwest.
Northwest Sci. 61:103-109.