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A taxonomic re-evaluation reveals that Phytophthora cinnamomi and P. cinnamomi var. parvispora are separate species
Abstract
Between 2008 and 2011, severe dieback associated with root and collar rot was reported on Arbutus unedo in several sites in Sardinia, Italy. Isolations from infected tissues and rhizosphere soil samples consistently yielded a Phytophthora species. It was initially identified as Phytophthora cinnamomi var. parvispora Krober and Marwitz by comparing morphological features with the original description and the internal transcribed spacer (ITS) sequences with those present in GenBank. A multigene phylogeny based on DNA sequence data from two nuclear (ITS and b-tubulin) and two mitochondrial (cox1 and cox2) gene regions combined with extensive morphological and physiological properties of these isolates, including the ex-type culture of P. cinnamomi var. parvispora, demonstrates that this taxon is unique and it is redesignated here as Phytophthora parvispora sp. nov. Although morphologically similar to P. cinnamomi, P. parvispora differs by its smaller-
sized sporangia, chlamydospores, oogonia and oospores, higher oospore wall index, single-celled antheridia, higher minimum and maximum temperatures for growth and faster growth at optimum temperature. In the phylogeny, P. parvispora falls within Phytophthora ITS clade 7a, grouped in a well-supported clade sister to P. cinnamomi. In pathogenicity tests, P. parvispora and P. cinnamomi were equally aggressive towards A. unedo seedlings. The possible geographic origin of P. parvispora is also discussed.
... Sequences of ITS and cox1 were trimmed to the same length and combined to result in a total of 1488 positions in the final concatenated dataset. All sequences of Phytophthora species used for the phylogenetic analysis were shown by Scanu, Hunter [17]. The phylogenetic analyses were conducted using MEGA X [18]. ...
... ON573332, ON573333, and ON573334) also showed high identity to P. parvispora. The identity of the three isolates was further validated by aligning the concatenated sequences of ITS and cox1 with reference sequences of related Phytophthora species in the Phytophthora clade 7 [17] and conducting a maximum likelihood analysis. The phylogenetic tree grouped VN-Oo03, VN-Oo04, and VN-Oo10 with the ex-type strain (CBS 132772) and other reference strains of P. parvispora with 100% support (Fig. 2). ...
... Previously, P. parvispora was first elevated to species status from a reevaluation of P. cinnamomi var. parvispora in 2014 [17]. P. parvispora and P. cinnamomi are very morphologically similar, except that P. parvispora has significantly smaller sizes of sporangia, chlamydospores, oogonia, and oospores and single-celled antheridia compared with two-celled antheridia in P. cinnamomi. ...
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In 2021, pomelo (Citrus grandis) trees grown in Tuyen Quang and Phu Tho in northern Vietnam suffered from leaf yellowing, gummosis on stems, brown rot on fruit, and black rot on roots. Based on morphological and sequence analysis of the ITS and cox1 gene regions, the pathogen causing gummosis and root rot of citrus trees was identified as Phytophthora parvispora. Pathogenicity assays using mycelial plugs and zoospore suspension showed that P. parvispora induces disease symptoms on both the upper and lower parts of various citrus trees, including pomelo, orange (C. sinensis), and lime (C. aurantiifolia). This is the first report of P. parvispora as the causative agent of gummosis and root rot on various citrus trees in South-East Asia as well as in Vietnam. Further, P. parvispora was sensitive to all tested fungicides, including mancozeb, chlorothalonil, fosetyl aluminium, potassium phosphonate, and dimethomorph. These findings will have important implications for the effective management of gummosis and root rot disease of citrus trees.
... Culture characteristics: Colonies always white with chrysanthemum, petallate, petaloid, radiate, stellate, striate, rosaceous, dendroid or uniform patterns; on V8-juice agar (V8A) and carrot agar (CA) appressed, felty, or with limited to fluffy aerial mycelium, in some species umbonate in the centre of the colony, with round or irregular margins; largely submerged on CMA; on PDA and MEA often with slow growth, felty to cottony aerial mycelium, and round to irregular, sometimes submerged margins (Brasier & Griffin 1979, Erwin & Ribeiro 1996, Jung et al. 1999, 2011, b, 2021, Brasier et al. 2004, Jung & Burgess 2009, Rea et al. 2010, 2011, Bertier et al. 2013a, Henricot et al. 2014, Scanu et al. 2014a, Burgess et al. 2018. ...
... V8A, CA prepared from grated carrots or carrot juice and -for Phy. infestans -rye agar at 20 °C in the dark to stimulate the production of gametangia (Brasier 1967, Erwin & Ribeiro 1996, Jung et al. 1999, Scanu et al. 2014a which, depending on the Phytophthora species, predominantly occurs in the centre of the colony, confined to fertile patches of dense mycelium or at the margins of the colony close to the Petri dish walls. Chlamydospores and hyphal swellings frequently differentiated at the margins of the colony. ...
... thermophila and Phy. versiformis (Mchau & Coffey 1995, Erwin & Ribeiro 1996, Abad et al. 2008, Jung et al. 2002, 2011, 2016, c, 2018a, b, 2020, Brasier et al. 2003b, de Cock & Lévesque 2004, Rea et al. 2010, 2011, Nechwatal et al. 2013, Henricot et al. 2014, Scanu et al. 2014a, Paap et al. 2017, Burgess et al. 2018 (Brasier & Griffin 1979, Erwin & Ribeiro 1996, Aragaki & Uchida 2001, Grünwald et al. 2008, Jung & Burgess 2009, Panabières et al. 2016, Jung et al. 2018a). The emerging pathogens Phy. ...
This paper is the fourth contribution in the Genera of Phytopathogenic Fungi (GOPHY) series. The series provides morphological descriptions and information about the pathology, distribution, hosts and disease symptoms, as well as DNA barcodes for the taxa covered. Moreover, 12 whole-genome sequences for the type or new species in the treated genera are provided. The fourth paper in the GOPHY series covers 19 genera of phytopathogenic fungi and their relatives, including Ascochyta , Cadophora , Celoporthe , Cercospora , Coleophoma , Cytospora , Dendrostoma , Didymella , Endothia , Heterophaeomoniella , Leptosphaerulina , Melampsora , Nigrospora , Pezicula , Phaeomoniella , Pseudocercospora , Pteridopassalora , Zymoseptoria , and one genus of oomycetes, Phytophthora . This study includes two new genera, 30 new species, five new combinations, and 43 typifications of older names.
... Based on unwanted Phytophthora ITS1 in the control samples, an unusually stringent minimum abundance threshold just over 2000 copies was used (meaning with a median of almost 60,000 reads per sample, accepted unique ITS1 sequences typically represent at least 3% of a sample). Species identification was based on the THAPBI PICT v0.6.1 Phytophthora ITS1 curated database and a local database containing sequences of ex-type or key isolates from published studies [8,30,38,68,[71][72][73]. ASVs were assigned to a species when their sequences were at least 99% identical to a reference isolate. ...
... Seven-day-old cultures grown at 22 • C in the dark on V8-agar were used to group all isolates from each sampling site into morphotypes based on their growth pattern. Morphological features of sporangia; oogonia; antheridia; chlamydospores; hyphal swellings and aggregations were also checked (data not shown) [7] in relation to species already described in the literature [5,15,72,73,78,79]. Species' identification was confirmed by the amplification and analysis of the Internal Transcribed Spacer (ITS) regions of the ribosomal DNA (rDNA). ...
... The relatively high number of new records from the botanical garden confirms that plant diversity conservation sites, such as botanical gardens, arboretums and nature reserves hosting so called 'sentinel trees', may have a crucial role in surveillance programs aimed at preventing the introduction of exotic plant pathogens [85][86][87]. Eleven of the 21 recorded Phytophthora taxa, including P. asparagi; P. bilorbang; P. cactorum; P.citrophthora; P. cryptogea; P. multivora; P. nicotianae; P. plurivora; P. pseudocryptogea; P. parvispora and P. syringae, are considered exotic pathogens for European countries [6,37,40,72,78,88,89]. In contrast, Phytophthora psychrophila and P. quercina are considered endemic to Europe and proposed to originate from species radiation following adaptation to different Fagaceae hosts [7,90]. ...
Isolation techniques supplemented by sequencing of DNA from axenic cultures have provided a robust methodology for the study of Phytophthora communities in agricultural and natural ecosystems. Recently, metabarcoding approaches have emerged as new paradigms for the detection of Phytophthora species in environmental samples. In this study, Illumina DNA metabarcoding and a conventional leaf baiting isolation technique were compared to unravel the variability of Phytophthora communities in different environments. Overall, 39 rhizosphere soil samples from a natural, a semi-natural and a horticultural small-scale ecosystem, respectively, were processed by both baiting and metabarcoding. Using both detection techniques, 28 out of 39 samples tested positive for Phytophthora. Overall, 1,406,613 Phytophthora internal transcribed spacer 1 (ITS1) sequences and 155 Phytophthora isolates were obtained, which grouped into 21 taxa, five retrieved exclusively by baiting (P. bilorbang; P. cryptogea; P. gonapodyides; P. parvispora and P. pseudocryptogea), 12 exclusively by metabarcoding (P. asparagi; P. occultans; P. psycrophila; P. syringae; P. aleatoria/P. cactorum; P. castanetorum/P. quercina; P. iranica-like; P. unknown sp. 1; P. unknown sp. 2; P. unknown sp. 3; P. unknown sp. 4; P. unknown sp. 5) and four with both techniques (P. citrophthora, P. multivora, P. nicotianae and P. plurivora). Both techniques complemented each other in describing the variability of Phytophthora communities from natural and managed ecosystems and revealing the presence of rare or undescribed Phytophthora taxa.
... From olive trees Phytophthora isolations were mostly made from necrotic bark lesions on stems, collars, and roots. Small pieces from the margins of fresh lesions were cut aseptically and plated onto synthetic mucor agar (SMA) [15]. Soil and fine roots of infected trees were also collected and baited with Rhododendron sp. and citrus leaves using the method originally described by Jung et al. [16]. ...
... From C. spinosa, D. zibethinus, J. oxycedrus, and Z. spina-christi seedlings, Phytophthora isolates were obtained by both direct isolation from stem lesions, infected roots, and collar tissues and baiting of the rhizosphere soil using fresh cork oak and citrus leaves as baits and selective SMA and CMA-PARP agar [17]. Any colonies developing from infected tissues and leaf baits on selective media were subcultured onto carrot agar (CA; Oxoid ® n°3 agar 16 g L −1 , CaCO3 3 g L −1 , blended carrots 200 g L −1 ) and cornmeal agar (CMA; Oxoid ® ground corn extract 40 g L −1 , agar 15 g L −1 ), incubated at 20 °C and examined within 4 days using morphological characters for identification [15]. ...
... The sexual compatibility type of all P. heterospora isolates was determined in dual culture with known A1 and A2 tester strains of P. cinnamomi (P904, P1889) on CA [15]. Selfed gametangia of the six representative isolates were induced on 35 mm plates containing 10 mL CA in polycarbonate membrane tests (Whatman Nuclepore™ Track-Etched Membranes, Sigma-Aldrich, St. Louis, Missouri, USA) with opposite mating type tester strains of P. palmivora (CBS 179.26). ...
Since 1999, an unusual Phytophthora species has repeatedly been found associated with stem lesions and root and collar rot on young olive trees in Southern Italy. In all cases, this species was obtained from recently established commercial plantations or from nursery plants. Morphologically , the Phytophthora isolates were characterized by the abundant production of caducous non-papillate conidia-like sporangia (pseudoconidia) and caducous papillate sporangia with a short pedicel, resembling P. palmivora var. heterocystica. Additional isolates with similar features were obtained from nursery plants of Ziziphus spina-christi in Iran, Juniperus oxycedrus and Capparis spinosa in Italy, and mature trees in commercial farms of Durio zibethinus in Vietnam. In this study, morphology, breeding system and growth characteristics of these Phytophthora isolates with peculiar features were examined, and combined mitochondrial and nuclear multigene phylogenetic analyses were performed. The proportion between pseudoconidia and sporangia varied amongst isolates and depended on the availability of free water. Oogonia with amphigynous antheridia and aplerotic oospores were produced in dual cultures with an A2 mating type strain of P. palmivora, indicating all isolates were A1 mating type. Phylogenetically, these isolates grouped in a distinct well-supported clade sister to P. palmivora; thus, they constitute a separate taxon. The new species, described here as Phytophthora heterospora sp. nov., proved to be highly pathogenic to both olive and durian plants in stem inoculation tests.
... Recent studies have revealed a very high diversity of Phytophthora species in ornamental nurseries [47,48]. This is linked both to the widespread presence of invasive and ubiquitous species such as P. nicotianae and P. palmivora, but also of new species, such as P. parvispora, a cryptic species closely related to P. cinnamomi [48,49]. At the same time, the discovery of rare species on nursery plants, such as Phytophthora pistaciae, characterized by a limited geographic distribution points out the risks posed by nursery material to the conservation and integrity of natural ecosystems in the new areas [50]. ...
... It is plausible that different agronomical practices including sanitation, water management, origin and treatment of seeds as well as host plant diversity could have a role in the differences observed in terms of Phytophthora assemblages. Some species such as P. parvispora and P. pistaciae have confirmed a specificity towards some plant hosts already reported in other studies [49,50]. Phytophthora parvispora, long considered a variety of P. cinnamomi, is closely linked to Arbutus unedo plants in both nursery and natural areas of the Mediterranean Basin [49]. ...
... Some species such as P. parvispora and P. pistaciae have confirmed a specificity towards some plant hosts already reported in other studies [49,50]. Phytophthora parvispora, long considered a variety of P. cinnamomi, is closely linked to Arbutus unedo plants in both nursery and natural areas of the Mediterranean Basin [49]. It has also recently been reported in North American nurseries associated with seedlings destined for reforestation programmes and in pomegranate orchards in Turkey [63,64]. ...
Monitoring surveys of Phytophthora related diseases in four forest nurseries in Italy revealed the occurrence of fourteen Phytophthora species to be associated with collar and root rot on fourteen plants typical of Mediterranean and alpine regions. In addition, a multilocus phylogeny analysis based on nuclear ITS and ß-tubulin and mitochondrial cox1 sequences, as well as micromorphological features, supported the description of a new species belonging to the phylogenetic clade 7c, Phytophthora mediterranea sp. nov. Phytophthora mediterranea was shown to be associated with collar and root rot symptoms on myrtle seedlings. Phylogenetically, P. mediterranea is closely related to P. cinnamomi but the two species differ in 87 nucleotides in the three studied DNA regions. Morphologically P. mediterranea can be easily distinguished from P. cinnamomi on the basis of its smaller sporangia, colony growth pattern and higher optimum and maximum temperature values. Data from the pathogenicity test showed that P. mediterranea has the potential to threaten the native Mediterranean maquis vegetation. Finally, the discovery of P. cinnamomi in alpine nurseries, confirms the progressive expansion of this species towards cold environments, probably driven by climate change.
... Previous results obtained by Perez-Sierra et al. [20] suggest these species are well adapted to the Mediterranean climate and may act as fine root nibblers, the incidence of which varies depending on the occurrence of extreme climatic events, such as recurrent drought and wet seasons [60]. Both P. psychrophila and P. quercina are already reported in Sardinia from declining Q. ilex trees, while P. syringae is associated with dieback and mortality of Juniperus phoenicea on Caprera Island [28]. Due to their low maximum temperature for growth (around 25 • C), typical of Phytophthora species from cool temperate regions, a potential seasonal activity, as suggested for P. cinnamomi and other cool-temperature pathogens, may occur [61][62][63][64]. ...
... Similarly, P. pseudocryptogea from clade 8 was the only species obtained from QS5 and QS38; otherwise, it co-occurred with P. cinnamomi or other species. It is noteworthy that all the previous isolates identified as Phytophthora cryptogea in Sardinia from forest trees, including oaks and Pinus radiate, are indeed P. pseudocryptogea [28,37,48,67]. Phytophthora pseudocryptogea was recently reported as one of the most widespread species in riparian thermo-Mediterranean forest stands and from five rivers in Sicily [66]. ...
... Phytophthora gonapodyides occurred in all investigated sites, followed by P. bilorbang, P. lacustris, and P. chlamydospora isolated from five, four, and two watercourses, respectively. Both P. bilorbang and P. gonapodyides have been previously reported in Sardinia on Caprera Island, detected from both rhizosphere soil beneath declining Mediterranean maquis vegetation and holm oak trees [28]. In Italy, P. bilorbang has also been reported from riparian ecosystems of Alnus glutinosa, in Sardinia, and on 15-year-old olive trees in Calabria [75,76], while P. gonapodyides is generally encountered in Mediterranean forest ecosystems, including holm oak [20,44,45]. ...
Cork oak forests are of immense importance in terms of economic, cultural, and ecological value in the Mediterranean regions. Since the beginning of the 20th century, these forests ecosystems have been threatened by several factors, including human intervention, climate change, wildfires, pathogens, and pests. Several studies have demonstrated the primary role of the oomycete Phytophthora cinnamomi Ronds in the widespread decline of cork oaks in Portugal, Spain, southern France, and Italy, although other congeneric species have also been occasionally associated. Between 2015 and 2019, independent surveys were undertaken to determine the diversity of Phytophthora species in declining cork oak stands in Sardinia (Italy). Rhizosphere soil samples were collected from 39 declining cork oak stands and baited in the laboratory with oak leaflets. In addition, the occurrence of Phytophthora was assayed using an in-situ baiting technique in rivers and streams located throughout ten of the surveyed oak stands. Isolates were identified by means of both morphological characters and sequence analysis of internal transcribed spacer (ITS) regions of ribosomal DNA. In total, 14 different Phytophthora species were detected. Phytophthora cinnamomi was the most frequently isolated species from rhizosphere soil, followed by P. quercina, P. pseudocryptogea, and P. tyrrhenica. In contrast, P. gonapodyides turned out to be the most dominant species in stream water, followed by P. bilorbang, P. pseudocryptogea, P. lacustris, and P. plurivora. Pathogenicity of the most common Phytophthora species detected was tested using both soil infestation and log inoculation methods. This study showed the high diversity of Phytophthora species inhabiting soil and watercourses, including several previously unrecorded species potentially involved in the decline of cork oak forests.
... Phytophthora parvispora (Sub-clade 7c) was considered to be a variety of P. cinnamomi prior to Scanu et al. (2014) redesignating it as a unique taxon, based on a multigene phylogeny and examination of morphological and physiological properties. Scanu et al. (2014) suggested that almost all findings of P. parvispora are linked to the trade in plants-for-planting, with current known outbreaks confined to plants in cultivated settings. ...
... Phytophthora parvispora (Sub-clade 7c) was considered to be a variety of P. cinnamomi prior to Scanu et al. (2014) redesignating it as a unique taxon, based on a multigene phylogeny and examination of morphological and physiological properties. Scanu et al. (2014) suggested that almost all findings of P. parvispora are linked to the trade in plants-for-planting, with current known outbreaks confined to plants in cultivated settings. This includes the report of Bezuidenhout et al. (2010), who found P. parvispora during surveys of diseased Agathosma in nurseries and fields of cultivated Agathosma in the Western Cape Province of South Africa. ...
The genus Phytophthora contains many destructive and globally important plant pathogens. In the last decade, targeted sampling efforts have resulted in a dramatic increase in the number of known species, as well as a better understanding of their global distribution. Routine activities undertaken in botanical gardens, combined with great numbers of local and international visitors, place botanical gardens at risk to the accidental introduction and establishment of pathogens such as Phytophthora spp. In this study, the occurrence of Phytophthora was investigated in two botanical gardens in the KwaZulu-Natal Province of South Africa. Symptomatic collar and stem tissues were collected, and root and rhizosphere soil samples were taken from trees exhibiting symptoms of decline. Standard baiting techniques and direct plating of symptomatic tissues revealed the presence of seven species of Phytophthora residing in four phylogenetic clades. Five of these species, P. cinnamomi, P. citrophthora, P. multivora, P. parvispora and the informally designated taxon Phytophthora sp. stellaris were known to be present in South Africa and P. aquimorbida was recorded for the first time. Of these, P. citrophthora represented a novel host-pathogen association causing bleeding cankers on indigenous Celtis africana. A multilocus phylogenetic analysis based on ITS, βtub, cox1 and hsp90 sequences showed the presence of an undescribed species belonging to the Phytophthora ITS Clade 5. This species is described here as Phytophthora mammiformis sp. nov. This study highlights the importance of monitoring botanical gardens for the detection and discovery of pathogens and emphasises their value as sites for the discovery of novel host-pathogen associations.
... Any growing colonies developed on SMA were subcultured and stored on carrot agar [47] (CA) at 20 • C. Isolates obtained were first grouped based on morphological analyses, and then representative morphotypes (8) were subjected to molecular analyses as described by Scanu and Webber [48]. DNA extraction, amplification, purification, sequencing, and analysis of the ITS sequences were performed as described by Scanu et al. [49]. All sequences were deposited at GenBank (http://www.ncbi.nlm.nih. ...
... Lesion development by P. cinnamomi may have been due to the higher temperatures during experiment 2, where, with a mean temperature of 25 • C, P. cinnamomi caused extensive lesions (av. 2 cm length per day) on untreated stems. This is consistent with the optimum temperature for pathogen growth in vitro, which is shown to be around 27 • C [49]. In a scenario of climate change, with an expected rise in the mean temperature in the following decades [69], the spread and impact of P. cinnamomi on chestnut stands will most likely increase in Mediterranean areas [70,71]. ...
Ink disease, caused by Phytophthora spp., represents a serious threat to sweet chestnuts throughout their distribution area. Among the control strategies, new perspectives have been offered by using potassium phosphonate, which indirectly controls Phytophthora diseases by acting on both host physiology and host-pathogen interactions. In this study, we tested in planta the effectiveness of trunk injection with K-phosphonate against seven different Phytophthora species associated with ink disease. For the two most aggressive species, P. cinnamomi and P. ×cambivora, the treatments were repeated at two different environmental conditions (a mean temperature of 14.5 °C vs. 25 °C) and tree phenology stages. The results obtained in this study demonstrated that K-phosphonate could contain the development of Phytophthora infection in phloem tissues. However, its effectiveness varied based on the concentration applied and the Phytophthora species tested. A concentration of 280 g/L of K-phosphonate was the most effective, and in some cases, callus formation around the necrotic lesion was detected. Overall, this study broadens the knowledge of endotherapic treatments with K-phosphonate as an effective measure for managing chestnut ink disease. Interestingly, the increase in mean temperature had a positive impact on the development of P. cinnamomi lesions on chestnut phloem tissues.
... According to our experience, the rose petals have been excellent bait for Phytophthora spores (Fig.1). After 3 to 5 days of incubation at room temperature, leaves showing necrotic lesions were carefully dried on sterile filter paper, cut into small squares (0.5x0.5 cm), and placed on a selective medium (Synthetic Mucor Agar) (Scanu et al., 2014). Then, plates were incubated at 20 °C in the dark and monitored daily for any growth. ...
... For some oomycetes, a sporulation technique has been implemented to produce sporangia: for each isolate, 4 to 5 squares of 1 cm2 were taken and placed in a petri dish containing about 10 ml of non-sterile distilled water as used by several authors (Scanu et al., 2014;Smahi et al., 2017b). The plats are incubated at laboratory temperature under permanent light to accelerate the appearance of sporangia, otherwise daylight. ...
Fungi play a central role in most ecosystems and seem to dominate the microbial biomass in soil habitats, where they are important decomposers and occupy a notable position in the natural carbon, nitrogen and phosphorus cycles. Despite the fact that fungal species have been studied in several contexts, the diversity of some soil fungal species in nurseries is still unknown. This study aimed to explore the diversity of fungal species occurring in nursery soil of Tlemcen province (North-west of Algeria) and to test the antagonist effect of some isolates of Trichoderma sp. on species of the genus Pythium and those of Diplodia. Soil and root samples from young seedlings showing symptoms of oomycete infection and other fungal were collected in three nurseries of Tlemcen region. Following a soil baiting using fresh ornamental leaves, three Phytophthora species were isolated and identified based on morphology and microscopic observation. About the others groups, the dilution method using physiological water, revealed the presence of significant fungal biodiversity on the PDA medium. Twelve fungal species and five oomycetes have been isolated and identified, namely: D. sapinea, Lasio. exigua, F. oxysporum, Aspergillus sp., Penicellium sp., Mucor sp., Trichoderma sp., Alternaria sp. P. cinnamomi, P. gonapodyides, P. ramorum, Py. ultimum and Py. Polare. Significant antagonist activity was recorded for isolates of Trichoderma sp. against Pythium sp. and Diplodia sp.
... Phytophthora parvispora is very closely related and morphologically similar to P. cinnamomi. It has been reported as a pathogen of a few plant species (Scanu et al., 2014). Phytophthora niederhauserii, only identified in one nursery, is known as a pathogen of ornamentals, fruit trees and native trees. ...
... Phytophthora niederhauserii, only identified in one nursery, is known as a pathogen of ornamentals, fruit trees and native trees. Nursery material has especially been implicated in the distribution of both species world-wide (Scanu et al., 2014;Abad et al., 2014). ...
Soilborne oomycetes, including species within the genera Phytophthora, Pythium, and Phytopythium, are fungus-like microbes that contain species that can either stimulate
or have no effect on plant growth, or destroy tree crops. In South Africa, Phytophthora cinnamomi is regarded as the only soilborne oomycete pathogen of macadamia, which causes both root rot and stem canker. However, in Australia, additional Phytophthora species have recently been reported as pathogens. Worldwide, the role of Pythium and
Phytopythium species as pathogens of macadamia is mostly unknown.
... The Phytophthora isolates were grown on Petri dishes containing CA medium, covered with sterile cellophane paper, at 25 ± 2 • C for 3-5 days (Scanu et al., 2014). The mycelial growth was collected using a sterile toothpick and deposited in 1.5 mL microtubes containing 50 µL of Tris-EDTA (TE) buffer, four metal beads (2.8 mm), and 600 µL of Nuclei Lysis Solution (Promega R ). ...
... The colony growth rates were determined, for representative isolates of P. theobromicola sp. nov., P. citrophthora, and P. palmivora, on clarified 20% V8 juice-agar (V8A), 2% MEA, PDA, and CA during 7 days at 20 ± 1 • C (Erwin and Ribeiro, 1996;Scanu et al., 2014;Ruano-Rosa et al., 2018). The radial colony growth was recorded daily along two perpendicular lines that intersected the center of the initial inoculum (mycelial plugs of 5 mm in diameter). ...
Black pod disease, caused by Phytophthora species, is among the main limiting factors of cacao (Theobroma cacao L.) production. High incidence levels of black pod disease have been reported in Brazil, being induced by Phytophthora capsici, Phytophthora citrophthora, Phytophthora heveae, and Phytophthora palmivora. To assess the diversity of Phytophthora species affecting cacao in Brazil, 40 new isolates were obtained from cacao pods exhibiting symptoms of black pod disease collected in different smallholder farms in 2017. Further, ten cacao-infecting isolates morphologically identified as P. citrophthora and P. palmivora were molecularly characterized. The genomic regions beta-tubulin, elongation factor 1 alpha, heat shock protein 90, and internal transcribed spacer, and the mitochondrially encoded cytochrome c oxidase I and II genes were PCR-amplified and Sanger-sequenced from the cacao-infecting Phytophthora isolates. The morphological characterization and evaluation of the mycelial growth rates for the Phytophthora isolates were performed in vitro. Based on the molecular analysis and morphological comparisons, 19 isolates were identified as P. palmivora (clade 4). Interestingly, 31 isolates grouped together in the phylogenetic tree and were placed apart from previously known species in Phytophthora clade 2. Therefore, these isolates are considered as a new species herein referred to as Phytophthora theobromicola sp. nov., which produced papillate, semipapillate, and persistent sporangia on simple sporangiophores. The P. palmivora isolates were identified as A1 mating type by pairing each isolate with known A1 and A2 tester strains of P. capsici, but no oogonia/antheridia were observed when P. theobromicola was paired with the different tester strains. The P. theobromicola and P. citrophthora isolates showed higher mycelial growth rates, when compared to P. palmivora, on different media at 10, 15, and 20°C, but similar values were observed when grown on clarified CA media at 25 and 30°C. The pathogenicity tests carried out on pods of four cacao clones (CCN51, PS1319, Cepec2004, and CP49) showed significant variability among the isolates of both Phytophthora species, with P. theobromicola inducing higher rates of necrotic lesion expansion, when compared to P. palmivora. Here, two Phytophthora species were found associated with black pod disease in the state of Bahia, Brazil, and the previously undescribed P. theobromicola seems to be prevalent in field conditions. This is the first report of P. theobromicola on T. cacao. Also, these findings are crucial to improve the disease control strategies, and for the development of cacao materials genetically resistant to Phytophthora.
... Bacteria were cultured in BHI broth or BHI agar (Microbiol, Cagliari, IT) and incubated at 37°C for 24 h, while Phytophthora spp. were cultured on carrot agar (CA) (Scanu et al., 2014), and incubated at 20°C for 24-48 h. ...
... The antifungal properties of the biofilm against Phytophthora spp. was also tested using the dual culture method. A mycelial plug (5 mm diameter) were cut from the margin of actively growing 5-day-old colony, using a flamed cork borer, and placed on one side of a Petri dish containing 20 ml of CA (Scanu et al., 2014). Meanwhile a 10 mm disk of Pectin/LDH-cinnamate 10 wt% was placed on the opposite side of the plate, with a 30 mm of distance between the two plugs. ...
This paper reports the preparation of green pesticides based on nano-hybrids composed of a Layered Double Hydroxide (LDH) with cinnamate anion. The dispersion into a pectin matrix was obtained using high energy ball milling in wet conditions. Structure and physical properties of the fillers and the composites films were evaluated. Controlled release of cinnamate was followed using UV spectrophotometry and the release kinetics were found to be dependent on the filler loading. The experimental results were analyzed by the Gallagher-Corrigan model. Antimicrobial activity was evaluated on different bacterial strains, as well as plant pathogens belonging to the genus Phytophthora using modified agar diffusion, broth microdilution and dual culture methods, respectively. Experimental results suggested the possibility to use the analyzed composites as green protective coatings for crops’ protection.
... Phytophthora cinnamomi was isolated from R. alaternus showing severe dieback and wilting and together with its closest relative P. parvispora, this pathogen was also isolated from A. unedo, another common species in Mediterranean maquis ecosystems (Scanu et al. 2014a). Also in Portugal, P. cinnamomi has been isolated from declining and wilting A. unedo plants in Mediterranean maquis vegetation (T. ...
... The frequent detection of P. cinnamomi from Mediterranean plant species in recent years indicates that this pathogen is currently spreading into the maquis vegetation ecosystems. Against the background of a predicted increase of P. cinnamomi activity under current climate change projections (Brasier & Scott 1994, Burgess et al. 2017, the severe destructions of the root system caused by P. cinnamomi in pathogenicity tests on A. unedo, E. umbellata, J. phoenicea and P. lentiscus (Acedo et al. 2013, Scanu et al. 2014a suggest that this polyphagous pathogen has the potential to threaten the native maquis vegetation in the Mediterranean basin on a large scale. ...
Most members of the oomycete genus Phytophthora are primary plant pathogens. Both soil- and airborne Phytophthora species are able to survive adverse environmental conditions with enduring resting structures, mainly sexual oospores, vegetative chlamydospores and hyphal aggregations. Soilborne Phytophthora species infect fine
roots and the bark of suberized roots and the collar region with motile biflagellate zoospores released from sporangia during wet soil conditions. Airborne Phytophthora species infect leaves, shoots, fruits and bark of branches and stems with caducous sporangia produced during humid conditions on infected plant tissues and dispersed by rain and wind splash. During the past six decades, the number of previously unknown Phytophthora declines and diebacks of natural and semi-natural forests and woodlands has increased exponentially, and the vast majority of them are driven by introduced invasive Phytophthora species. Nurseries in Europe, North America and Australia show high
infestation rates with a wide range of mostly exotic Phytophthora species. Planting of infested nursery stock has proven to be the main pathway of Phytophthora species between and within continents. This review provides insights into the history, distribution, aetiology, symptomatology, dynamics and impact of the most important canker, decline and dieback diseases caused by soil- and airborne Phytophthora species in forests and natural ecosystems of Europe, Australia and the Americas.
... parvispora (Scanu et al., 2014). This species has since been detected in Californian nursery stock where it was determined to be pathogenic on Choisya ternata (Rooney-Latham et al., 2019). ...
The oomycete genus Phytophthora includes plant pathogens that pose significant threats to agricultural systems, natural ecosystems and urban forests. Urban forests are increasingly recognized for their role in mitigating climate change impacts and urban greening initiatives are underway worldwide. However, research suggests that the urban forest is also a reservoir of Phytophthora diversity, acting as bridgeheads for the introduction of these pathogens into production and natural ecosystems. The source of Phytophthora in urban forests is linked to anthropogenic factors, with the live plant trade the primary pathway. This study focused on the incidence and diversity of Phytophthora in amenity tree nursery stock in eastern Australia, primarily New South Wales, with one nursery from Victoria. The findings revealed a high incidence of Phytophthora in nursery stock destined for urban greening projects, having an overall positive rate of 22.1%, with incidence in individual nurseries ranging from 2.5% to 32%. The study detected 13 described Phytophthora species that are considered polyphagous on woody hosts and three lineages that potentially represent novel species. In addition, the detection of P . mediterranea and P . heterospora represent first reports for Australia, with P . mediterranea considered a biosecurity concern. The study highlights the substantial risk associated with the live plant trade as a source of Phytophthora introduction into urban forests and beyond. These findings underscore the urgent need to strictly implement clean nursery management practices to reduce the economic and environmental risks associated with Phytophthora in urban greening programmes.
... The core of the analysis involves data reduction to unique marker sequences termed amplicon sequence variants (ASVs) which are then processed against dynamic thresholds based on control samples on the Illumina flow cell. Then ASVs are classified against a curated reference database of THAPBI PICT Phytophthora ITS1 and a local Phytophthora Research Centre database containing sequences of ex-type or key isolates from published studies (Aghighi et al., 2012;Cooke et al., 2000;Jung et al., 2019Jung et al., , 2020Riolo et al., 2020;Safaiefarahani et al., 2015;Santilli et al., 2020;Scanu et al., 2014) using BioEdit. ASVs were assigned to a species when their sequences were at least 99% identical to a reference sequence. ...
Phytophthora diversity was examined in eight forest and ornamental nurseries in the Czech Republic. A leaf baiting isolation technique and, in two nurseries, also Illumina DNA metabarcoding were used to reveal the diversity of Phytophthora in soil and irrigation water and compare the efficacy of both approaches. In total, baiting revealed the occurrence of 12 Phytophthora taxa in 59.4% of soil samples from seven (87.5%) nurseries. Additional baiting of compost was carried out in two nurseries and two Phytophthora species were recovered. Irrigation water was examined in three nurseries by baiting or by direct isolation from partially decomposed floating leaves collected from the water source, and two Phytophthora species were obtained. Illumina sequencing of soil and water samples was done in two and one nurseries, respectively. Phytophthora reads were identified as 45 Phytophthora taxa, 15 of them previously unknown taxa from Clades 6, 7, 8 and 9. Another 11 taxa belonged to known or undescribed species of the oomycete genera Globisporangium , Hyaloperonospora , Nothophytophthora , Peronospora and Plasmopara . Overall, with both techniques 50 Phytophthora taxa were detected with five taxa ( P. taxon organica, P. plurivora, P. rosacearum, P. syringae and P. transitoria ) being exclusively detected by baiting and 38 only by DNA metabarcoding. Particularly common records in DNA barcoding were P. cinnamomi and P. lateralis which were not isolated by baiting. Only seven species were detected by both techniques. It is recommended to use the combination of both techniques to determine true diversity of Phytophthora in managed or natural ecosystems and reveal the presence of rare or unknown Phytophthora taxa.
... The core of the analysis involves data reduction to unique marker sequences termed amplicon sequence variants (ASVs) which are then processed against dynamic thresholds based on control samples on the Illumina flow cell. Then ASVs are classified against a curated reference database of THAPBI PICT Phytophthora ITS1 and a local Phytophthora Research Centre database containing sequences of ex-type or key isolates from published studies (Aghighi et al., 2012;Cooke et al., 2000;Jung et al., 2019Jung et al., , 2020Riolo et al., 2020;Safaiefarahani et al., 2015;Santilli et al., 2020;Scanu et al., 2014) using BioEdit. ASVs were assigned to a species when their sequences were at least 99% identical to a reference sequence. ...
Phytophthora diversity was examined in eight forest and ornamental nurseries in the Czech Republic. A leaf baiting isolation technique and, in two nurseries, also Illumina DNA metabarcoding were used to reveal the diversity of Phytophthora in soil and irrigation water and compare the efficacy of both approaches. In total, baiting revealed the occurrence of 12 Phytophthora taxa in 59.4% of soil samples
from seven (87.5%) nurseries. Additional baiting of compost was carried out in two nurseries and two Phytophthora species were recovered. Irrigation water was examined in three nurseries by baiting or by direct isolation from partially decomposed floating
leaves collected from the water source, and two Phytophthora
species were obtained. Illumina sequencing of soil and water samples was done in two and one nurseries, respectively. Phytophthora reads were identified as 45 Phytophthora taxa, 15 of them previously unknown taxa from Clades 6, 7, 8 and 9.
Another 11 taxa belonged to known or undescribed species of the oomycete genera Globisporangium, Hyaloperonospora, Nothophytophthora, Peronospora and Plasmopara. Overall, with both techniques 50 Phytophthora taxa were detected with five taxa (P. taxon organica, P. plurivora, P. rosacearum, P. syringae and P. transitoria) being exclusively detected by baiting and 38 only by DNA metabarcoding. Particularly common records in DNA barcoding were P. cinnamomi and P. lateralis which were not isolated by baiting. Only seven species were detected by both techniques. It is recommended to use the combination of both techniques to determine true diversity of Phytophthora in managed or natural ecosystems and reveal the presence of rare or unknown Phytophthora taxa.
... Its impact spans forestry, horticulture, and nursery industries [3,4]. With a host range encompassing approximately 5,000 woody plant species across 70 countries, P. cinnamomi poses a substantial threat [5][6][7][8]. ...
Phytophthora cinnamomi is a devastating soil-borne plant pathogen. The primary source of P. cinnamomi infection is the soil, where the pathogen can persist for long periods. Effective prevention and management of this pathogen in tree crops require an early and reliable detection method. In this study, we develop a simple, fast, reliable, and sensitive method based on real-time quantitative PCR (qPCR) for P. cinnamomi detection and quantification directly in plant or soil samples. Primers were developed targeting the nuclear single-copy ras-related protein gene Ypt1, suitable for Phytophthora-specific PCR. The specificity of the assay was confirmed by testing it against genomic DNA from 50 isolates across 8 different Phytophthora clades, including very similar P. parvispora. The efficiency and reliability of the qPCR protocol were evaluated on challenging environmental samples, such as plant tissue of different host trees (walnut, chestnut, oak) and naturally infected soils in walnut orchards. The main outcome was the development of a qPCR method for the specific identification and quantification of P. cinnamomi in natural soil samples. Additionally, this study established a systematic and repeatable soil sampling method and developed an efficient soil DNA extraction technique to apply the developed qPCR in naturally infested soils of walnut orchards.
... For all isolates, single hyphal tip cultures were produced under the stereomicroscope at ×20 from the margins of fresh cultures on V8-juice agar (V8A; 16 g agar, 3 g CaCO 3 , 100 mL Campbell's V8 juice, 900 mL distilled water; Jung et al. 1999). Stock cultures were maintained on V8A and carrot juice agar (CA; 20 g agar, 3 g CaCO 3 , 100 mL organic carrot juice from the company DM in Karlsruhe, Germany, 900 mL distilled water; Scanu et al. 2014) at 10 °C in the dark. All isolates of the 43 new Phytophthora spp. ...
During 25 surveys of global Phytophthora diversity, conducted between 1998 and 2020, 43 new species were detected in natural ecosystems and,
occasionally, in nurseries and outplantings in Europe, Southeast and East Asia and the Americas. Based on a multigene phylogeny of nine nuclear and four
mitochondrial gene regions they were assigned to five of the six known subclades, 2a–c, e and f, of Phytophthora major Clade 2 and the new subclade 2g.
The evolutionary history of the Clade appears to have involved the pre-Gondwanan divergence of three extant subclades, 2c, 2e and 2f, all having disjunct
natural distributions on separate continents and comprising species with a soilborne and aquatic lifestyle and, in addition, a few partially aerial species in
Clade 2c; and the post-Gondwanan evolution of subclades 2a and 2g in Southeast/East Asia and 2b in South America, respectively, from their common
ancestor. Species in Clade 2g are soilborne whereas Clade 2b comprises both soil-inhabiting and aerial species. Clade 2a has evolved further towards an
aerial lifestyle comprising only species which are predominantly or partially airborne. Based on high nuclear heterozygosity levels ca. 38 % of the taxa in
Clades 2a and 2b could be some form of hybrid, and the hybridity may be favoured by an A1/A2 breeding system and an aerial life style. Circumstantial
evidence suggests the now 93 described species and informally designated taxa in Clade 2 result from both allopatric non-adaptive and sympatric adaptive
radiations. They represent most morphological and physiological characters, breeding systems, lifestyles and forms of host specialism found across the
Phytophthora clades as a whole, demonstrating the strong biological cohesiveness of the genus. The finding of 43 previously unknown species from a single
Phytophthora clade highlight a critical lack of information on the scale of the unknown pathogen threats to forests and natural ecosystems, underlining the
risk of basing plant biosecurity protocols mainly on lists of named organisms. More surveys in natural ecosystems of yet unsurveyed regions in Africa, Asia,
Central and South America are needed to unveil the full diversity of the clade and the factors driving diversity, speciation and adaptation in Phytophthora.
... Taxonomic re-evaluation of P. cinnamomi Rands and P. cinnamomi var. parvispora Kröber and Marwitz (Scanu et al. 2014) (analysing ITS, β-tubulin, cox1 and cox2), and P. cryptogea Pethybr. and Laff. ...
... Ultimamente, purtroppo, anche la macchia mediterranea, che sembrava rappresentare una cenosi in buon equilibrio con le avversità (Mazzaglia et al., 2005), sta andando incontro, soprattutto in Sardegna, ad inquietanti attacchi di Phytophthora spp. (Scanu et al., 2011(Scanu et al., , 2014a(Scanu et al., , 2014b, con preoccupati danni ecologici e paesaggistici. Da ricordare anche l'ulteriore recente reperimento, su piante di viburno seppur in vivaio, della temuta Phytophthora ramorum (Ginetti et al., 2014). ...
... : H. avicennae isolate BD697 from the estuary of Rio Guadiana; H. brevisporangia isolate BD658 from a tidal pond in a salt marsh of the Ria Formosa at Quelfes; H. celeris isolate BD646 and H. macrosporangia isolate BD645 from a tidal channel in a salt marsh of the Ria Formosa at Santa Luzia; H. frigida isolate BD675 from a coastal lagoon of the Ria de Alvor; H. lateralis isolate BD680 from a coastal lagoon of the Ria Formosa at Almancil; H. lusitanica isolate BD632 and H. thermoambigua isolate BD631 from the estuary of Rio Séqua at Tavira; and H. sinuata isolate BD656 (=CBS 147237) from a tidal pond in a salt marsh of the Ria Formosa at Santa Luzia. Stock cultures were maintained on carrot juice agar (CA) at 10 • C in the dark[45]. ...
In this study, mycelia of eight recently described species of Halophytophthora and H. avicennae collected in Southern Portugal were analysed for lipids and fatty acids (FA) content to evaluate their possible use as alternative sources of FAs and understand how each species FAs profile relates to their phylogenetic position. All species had a low lipid percentage (0.06% in H. avicennae to 0.28% in H. frigida). Subclade 6b species contained more lipids. All species produced monounsaturated (MUFA), polyunsaturated (PUFA) and saturated (SFA) FAs, the latter being most abundant in all species. H. avicennae had the highest FA variety and was the only producer of γ-linolenic acid, while H. brevisporangia produced the lowest number of FAs. The best producer of arachidonic acid (ARA) and eicosapentaenoic acid (EPA) was H. thermoambigua with 3.89% and 9.09% of total FAs, respectively. In all species, palmitic acid (SFA) was most abundant and among the MUFAs produced oleic acid had the highest relative percentage. Principal component analysis (PCA) showed partial segregation of species by phylogenetic clade and subclade based on their FA profile. H. avicennae (Clade 4) differed from all other Clade 6 species due to the production of γ-linolenic and lauric acids. Our results disclosed interesting FA profiles in the tested species, adequate for energy (biodiesel), pharmaceutical and food industries (bioactive FAs). Despite the low amounts of lipids produced, this can be boosted by manipulating culture growth conditions. The observed interspecific variations in FA production provide preliminary insights into an evolutionary background of its production.
... For example, although the mycelial growth of our P. cinnamomi isolates occurred within the broad range of 20 to 33°C described by Zentmyer et al. (1976), most of our isolates had a lower T opt for mycelial growth (25.3°C) than the range of 26 to 30°C reported in several other studies (Chee and Newhook 1965;Phillips and Weste 1985;Sánchez et al. 2002;Scanu et al. 2014). Our Fig. 3. Sporulation intensity by of Phytophthora spp. ...
Temperature is an important environmental variable affecting Phytophthora species biology. It alters the ability of species to grow, sporulate, and infect their plant host, and it is also important in mediating pathogen responses to disease control measures. Average global temperatures are increasing as a consequence of climate change. Yet, there are few studies that compare the effects of temperature on Phytophthora species that are important to the nursery industry. To address this, we conducted a series of experiments to evaluate how temperature affects the biology and control of three soilborne Phytophthora species prevalent in the nursery industry. In the first set of experiments, we evaluated the mycelial growth and sporulation of several P. cinnamomi, P. plurivora, and P. pini isolates at temperatures ranging from 4 to 42°C for different amounts of time (0-120 h). In the second set of experiments, we evaluated the response of three isolates of each species to the fungicides mefenoxam and phosphorous acid at temperatures ranging from 6 to 40°C. Results showed that each species responds differently to temperature, with P. plurivora having the greatest optimal temperature (26.6°C), P. pini the least (24.4°C), and P. cinnamomi between the two (25.3°C). P. plurivora and P. pini had the lowest minimum temperatures (~2.4°C) compared to P. cinnamomi (6.5°C), while all three species had a similar maximum temperature (~35°C). When tested against mefenoxam, all three species were generally more sensitive to mefenoxam at cool temperatures (6-14°C) than at warmer temperatures (22-30°C). P. cinnamomi was also more sensitive to phosphorous acid at cool temperatures 6-14°C. However, both P. plurivora and P. pini tended to be more sensitive to phosphorous acid at warmer temperatures (22-30°C). These findings help define the temperatures at which these pathogens will be the most damaging and help delineate the temperatures at which fungicides should be applied for maximum efficacy.
... A total of 204 P. cinnamomi isolates were collected from Africa The isolates were obtained from rhizosphere soil samples using different baiting approaches or, less frequently, by direct plating of infected root or bark tissue onto Phytophthora-selective agar media (Arentz & Simpson, 1986;Dobrowolski et al., 2003;Jung et al., 1996Jung et al., , 2013Jung et al., , 2017Jung & Dobler, 2002;Linde et al., 1997;Scanu et al., 2014). P. cinnamomi isolates from the US were primarily sampled from Rhododendron in ornamental nurseries in Oregon (Parke et al., 2014;Weiland et al., 2020). ...
Various hypotheses have been proposed regarding the origin of the plant pathogen Phytophthora cinnamomi. P. cinnamomi is a devastating, highly invasive soilborne pathogen associated with epidemics of agricultural, horticultural and forest plantations and native ecosystems worldwide. We conducted a phylogeographic analysis of populations of this pathogen sampled in Asia, Australia, Europe, southern and northern Africa, South America, and North America. Based on genotyping‐by‐sequencing, we observed the highest genotypic diversity in Taiwan and Vietnam, followed by Australia and South Africa. Mating type ratios were in equal proportions in Asia as expected for a sexual population. Simulations based on the index of association suggest a partially sexual, semi‐clonal mode of reproduction for the Taiwanese and Vietnamese populations while populations outside of Asia are clonal. Ancestral area reconstruction provides new evidence supporting Taiwan as the ancestral area, given our sample, indicating that this region might be near or at the center of origin for this pathogen as speculated previously. The Australian and South African populations appear to be a secondary center of diversity following migration from Taiwan or Vietnam. Our work also identified two panglobal, clonal lineages PcG1‐A2 and PcG2‐A2 of A2 mating type found on all continents. Further surveys of natural forests across Southeast Asia are needed to definitively locate the actual center of origin of this important plant pathogen.
... parvispora are separated species (reviewed in SCANU et al. 2014). The study conducted by Scanu and collaborators used multigene phylogeny based on DNA sequences from internal transcribed spacer (ITS) and β-tubulin (nuclear gene regions) and, cox1 and cox2 (mitochondrial gene regions) combined with the study of morphological and physiological properties revealed that Phytophthora parvispora is a unique taxon [9]. A similar situation occurs with the P. cinnamomi var. ...
The Phytophthora genus is composed, mainly, of plant pathogens. This genus belongs to the Oomycete class, also known as "pseudo-fungi", within the Chromista Kingdom. Phytophthora spp. is highlighted due to the significant plant diseases that they cause, which represents some of the most economically and cultural losses, such as European chestnut ink disease, which is caused by P. cinnamomi. Currently, there have been four genome assemblies placed at the National Center for Biotechnology Information (NCBI), although the progress to understand and elucidate the pathogenic process of P. cinnamomi by its genome is progressing slowly. In this review paper, we aim to report and discuss the recent findings related to P. cinnamomi and its genomic information. Our research is based on paper databases that reported probable functions to P. cinnamomi proteins using sequence alignments, bioinformatics, and biotechnology approaches. Some of these proteins studied have functions that are proposed to be involved in the asexual sporulation and zoosporogenesis leading to the host colonization and consequently associated with pathogenicity. Some remarkable genes and proteins discussed here are related to oospore development, inhibition of sporangium formation and cleavage, inhibition of flagellar assembly, blockage of cyst germination and hyphal extension, and biofilm proteins. Lastly, we report some biotechnological approaches using biological control, studies with genome sequencing of P. cinnamomi resistant plants, and gene silencing through RNA interference (iRNA).
... Phytophthora species were identified by examining the morphological characters of sporangia, oogonia, antheridia, chlamydospores and hyphal swellings under the light microscope at ×320 magnification, and comparing them together with colony growth patterns on V8A and carrot agar (CA) [55] and cardinal temperatures of growth on V8A with descriptions in the Literature [48,[56][57][58][59]. Sporangia were produced by cutting discs (15 mm diam) from the growing edge of a 5-7 days old culture grown on V8A at 20 • C in the dark, and immersing them in non-sterile soil extract water [44]. In case the classical species identification was ambiguous, the isolates were identified using ITS DNA sequence analysis according to [60,61]. ...
A severe decline and dieback of European beech (Fagus sylvatica L.) stands have been observed in Austria in recent decades. From 2008 to 2010, the distribution and diversity of Phytophthora species and pathogenic fungi and pests were surveyed in 34 beech forest stands in Lower Austria, and analyses performed to assess the relationships between Phytophthora presence and various parameters, i.e. root condition, crown damage, ectomycorrhizal abundance and site conditions. In total, 6464 trees were surveyed, and Phytophthora-associated collar rot and aerial bark cankers were detected on 133 trees (2.1%) in 25 stands (73.5%). Isolations tests were performed from 103 trees in 27 stands and seven Phytophthora species were isolated from bleeding bark cankers and/or from the rhizosphere soil of 49 trees (47.6%) in 25 stands (92.6%). The most common species were P. ×cambivora (16 stands) followed by P. plurivora (eight stands) and P. cactorum (four stands), while P. gonapodyides, P. syringae, P. psychrophila and P. tubulina were each found in only one stand. Geological substrate had a significant effect on the distribution of P. ×cambivora and P. plurivora while P. cactorum showed no site preferences. In addition, 21 fungal species were identified on beech bark, of which 19 and five species were associated with collar rot and aerial bark cankers, respectively. Four tested fine root parameters showed differences between declining and non-declining beech trees in both Phytophthora-infested and Phytophthora-free stands. In both stand categories, ectomycorrhizal frequency of fine root tips was significantly higher in non-declining than in declining trees. This study confirmed the involvement of Phytophthora species in European beech decline and underlines the need of more research on the root condition of beech stands and other biotic and abiotic factors interacting with Phytophthora infections or causing beech decline in absence of Phytophthora.
... In this survey, it was recovered from the rhizosphere of willow (S. pedicellata Desf.) in a riparian semi-aquatic environment. In a previous study, it had been reported as a pathogen of strawberry tree (Arbutus unedo) in Sardinia (central Italy) and described as a new species distinct from P. cinnamomi [86]. The first record of this species in Italy dates back to 2010 and was from ornamental plants in nursery [87]. ...
Research Highlights: Protected natural areas are a reservoir of Phytophthora species and represent the most suitable sites to study their ecology, being less disturbed by human activities than other environments. Background and Objectives: The specific objective of this study was to correlate the diversity and distribution of Phytophthora species with the vegetation in aquatic, riparian and terrestrial habitats within a protected area in Eastern Sicily, Southern Italy. Materials and Methods: Environmental samples (water and soil) were sourced from two streams running through the reserve and six different types of vegetation, including Platano-Salicetum pedicellatae, the Sarcopoterium spinosum community, Myrto communis-Pistacietum lentisci, Pistacio-Quercetum ilicis,Oleo-Quercetum virgilianae and a gallery forest dominated by Nerium oleander (Natura 2000 classification of habitats). Phytophthora species were recovered from samples using leaf baiting and were classified on the basis of morphological characteristics and sequencing of internal transcribed spacer (ITS) regions of ribosomal DNA (rDNA). Results: As many as 11 Phytophthora species, within five different ITS clades, were identified, including P. asparagi, P. bilorbang, P. cryptogea, P. gonapodyides, P. lacustris, P. multivora, P. nicotianae, P. oleae, P. parvispora, P. plurivora and P. syringae. No Phytophthora species were found in the Sarcopoterium spinosum comm. Phytophthora asparagi, P. lacustris and P. plurivora were the prevalent species in the other five plant communities, but only P. plurivora was present in all of them. Overall aquatic species from clade 6 (100 out of 228 isolates) were the most common; they were recovered from all five types of vegetation, streams and riparian habitats. Phytophthora populations found in the Platano-Salicetum pedicellatae and Oleo-Quercetum virgilianae show the highest diversity, while no correlation was found with the physicochemical characteristics of the soil. Conclusions: The vegetation type and the aquatic or terrestrial habitat were identified as major environmental factors correlated with the diversity of Phytophthora communities in this reserve.
... Phytophthora species of regulatory concern [16,29,30], such as P. parvispora, P. chrysanthemi, and P. sojae, were identified in this study. P. sojae was detected in PA in 1995 and 2010 ( Figure S17) as a part of severe outbreaks on Glycine max [31]. ...
The increasing movement of exotic pathogens calls for systematic surveillance so that newly introduced pathogens can be recognized and dealt with early. A resource crucial for recognizing such pathogens is knowledge about the spatial and temporal diversity of endemic pathogens. Here, we report an effort to build this resource for Pennsylvania (PA) by characterizing the identity and distribution of Phytophthora species isolated from diverse plant species in PA nurseries and greenhouses. We identified 1137 Phytophthora isolates cultured from clinical samples of >150 plant species submitted to the PA Department of Agriculture for diagnosis from 1975 to 2019 using sequences of one or more loci and morphological characteristics. The three most commonly received plants were Abies, Rhododendron, and Pseudotsuga. Thirty-six Phytophthora species identified represent all clades, except 3 and 10, and included a distinct subgroup of a known species and a prospective new species. Prominent pathogenic species such as P. cactorum, P. cinnamomi, P. nicotianae, P. drechsleri, P. pini, P. plurivora, and P. sp. kelmania have been found consistently since 1975. One isolate cultured from Juniperus horizontalis roots did not correspond to any known species, and several other isolates also show considerable genetic variation from any authentic species or isolate. Some species were isolated from never-before-documented plants, suggesting that their host range is larger than previously thought. This survey only provides a coarse picture of historical patterns of Phytophthora encounters in PA nurseries and greenhouses because the isolation of Phytophthora was not designed for a systematic survey. However, its extensive temporal and plant coverage offers a unique insight into the association of Phytophthora with diverse plants in nurseries and greenhouses.
... were identified primarily on the basis of their morphological characteristics. The morphological identification of isolates was based on colony morphology, the presence of hyphal swellings, chlamydospores, or sexual structures (oogonium, antheridium, oospor) and morphological features of sporangia according to Erwin and Ribeiro (2005), Brasier et al. (2003), Gallegly and Hong (2008), Hansen et al. (2009), Jung et al. (2011, Abad et al. (2014) and Scanu et al. (2014). To stimulate sporangial production, when half surface of a Petri dish was covered with a colony, 5-Eur J Plant Pathol mm-diameter agar plugs were cut from the growing edge of the colonies grown on CA or V8 juice agar at 24°C in the dark, and placed in 6-cm-diameter Petri dishes previously flooded with 7 ml of 1.5% non-sterile soil extract. ...
Pomegranate (Punica granatum) is an important fruit-tree at southwestern Turkey, as this region (Antalya and Muğla provinces) produces and exports the great majority of the pomegranate fruits of the country. Pomegranate orchards showing severe dieback and tree mortality in the region were surveyed to determine the role of Phytophthora spp. in symptom development. Root (from 51 trees) and soil (from 136 trees) samples were collected from symptomatic trees in 113 commercial pomegranate orchards, covering 170 ha. A total of 98 isolates were obtained from the roots of 19 trees and soil samples of 79 trees, using selective medium and soil baiting. Species isolated were identified by morphological characteristics and ITS sequencing. The most frequently isolated species were P. nicotianae (37 isolates) and P. palmivora (26 isolates), followed by P. parvispora (14 isolates), P. inundata (six isolates), P. cryptogea (four isolates), P. niederhauserii (four isolates), P. taxon walnut (two isolates) and P. rosacearum (one isolate), and four unidentified species. Twelve orchards were infected with more than one species. Disease incidence and prevalence were 4.59% and 69.91%, respectively. Pathogenicity tests by soil infestation, revealed that the isolates caused root and collar rot, reducing root weights of pomegranate seedlings. Phytophthora palmivora and P. nicotianae were the most virulent species. This is the first report of any species other than P. palmivora causing root and collar rot of pomegranate trees worldwide.
... The studies of Erwin et al. (1963Erwin et al. ( , 1983 and Caten (1971) revealed the problem of inherent variation within the genus which led to difficulties in accurate describing of species. With the advent of molecular approaches many unsolved questions within Phytophthora could be adressed and complexes of morphologically similar Phytophthora species were sorted out (Jung et al. 2003(Jung et al. , 2011(Jung et al. , 2017cJung and Burgess 2009;Scanu et al. 2014). Alongside morphological characters, the internal transcribed spacer region of the nuclear rDNA (ITS) and the mitochondrial cox1 gene region are now used as barcodes for the identification of Phytophthora species. ...
... Previous molecular detection assays of P. cinnamomi were developed based on conventional PCR [22][23][24][25][26], real-time PCR [27][28][29], and isothermal amplification assays [28,30]. However, many of these assays have failed in differentiating P. cinnamomi from P. parvispora [31], the species most closely related to P. cinnamomi within the genus Phytophthora [32][33][34]. ...
Phytophthora cinnamomi is a devastating pathogen causing root and crown rot and dieback diseases of nearly 5000 plant species. Accurate and rapid detection of P. cinnamomi plays a fundamental role within the current disease prevention and management programs. In this study, a novel effector gene PHYCI_587572 was found as unique to P. cinnamomi based on a comparative genomic analysis of 12 Phytophthora species. Its avirulence homolog protein 87 (Avh87) is characterized by the Arg-Xaa-Leu-Arg (RxLR) motif. Avh87 suppressed the pro-apoptotic protein BAX-and elicitin protein INF1-mediated cell death of Nicotiana benthamiana. Furthermore, a recombinase polymerase amplification-lateral flow dipstick detection assay targeting this P. cinnamomi-specific biomarker was developed. While successfully detected 19 P. cinnamomi isolates of a global distribution, this assay lacked detection of 37 other oomycete and fungal species, including P. parvispora, a sister taxon of P. cinnamomi. In addition, it detected P. cinnamomi from artificially inoculated leaves of Cedrus deodara. Moreover, the RPA-LFD assay was found to be more sensitive than a conventional PCR assay, by detecting as low as 2 pg of genomic DNA in a 50-µL reaction. It detected P. cinnamomi in 13 infested soil samples, while the detection rate was 46.2% using PCR. Results in this study indicated that PHYCI_587572 is a unique biomarker for detecting P. cinnamomi. Although PHYCI_587572 was identified as an effector gene based on the RxLR motif of Avh87 and the avirulence activity on Nicotiana, its exact genetic background and biological function on the natural hosts of P. cinnamomi warrant further investigations.
... Pure cultures were obtained by transferring single hyphal tips from the edge of the colonies onto V8A. Stock cultures were maintained on carrot agar (CA) [45] at 10 • C in the dark. ...
In 2016 and 2017, surveys of Phytophthora diversity were performed in 25 natural and semi-natural forest stands and 16 rivers in temperate and subtropical montane and tropical lowland regions of Vietnam. Using baiting assays from soil samples and rivers and direct isolations from naturally fallen leaves, 13 described species, five informally designated taxa and 21 previously unknown taxa of Phytophthora were isolated from 58 of the 91 soil samples (63.7%) taken from the rhizosphere of 52 of the 64 woody plant species sampled (81.3%) in 20 forest stands (83.7%), and from all rivers: P. capensis, P. citricola VII, VIII, IX, X and XI, P. sp. botryosa-like 2, P. sp. meadii-like 1 and 2, P. sp. tropicalis-like 2 and P. sp. multivesiculata-like 1 from Phytophthora major phylogenetic Clade 2; P. castaneae and P. heveae from Clade 5; P. chlamydospora, P. gregata, P. sp. bitahaiensis-like and P. sp. sylvatica-like 1, 2 and 3 from Clade 6; P. cinnamomi (Pc), P. parvispora, P. attenuata, P. sp. attenuata-like 1, 2 and 3 and P. ×heterohybrida from Clade 7; P. drechsleri, P. pseudocryptogea, P. ramorum (Pr) and P. sp. kelmania from Clade 8, P. macrochlamydospora, P. sp. ×insolita-like, P. sp. ×kunnunara-like, P. sp. ×virginiana-like s.l. and three new taxa, P. sp. quininea-like, P. sp. ×Grenada 3-like and P. sp. ×Peru 4-like, from Clade 9; and P. sp. gallica-like 1 and 2 from Clade 10. The A1 and A2 mating types of both Pc and Pr co-occurred. The A2 mating type of Pc was associated with severe dieback of montane forests in northern Vietnam. Most other Phytophthora species, including Pr, were not associated with obvious disease symptoms. It is concluded that (1) Vietnam is within the center of origin of most Phytophthora taxa found including Pc and Pr, and (2) Phytophthora clades 2, 5, 6, 7, 8, 9, and 10 are native to Indochina.
... Among eight evaluated assays, only three were specific to P. cinnamomi (Kunadiya et al. 2017). The other five assays failed in differentiating P. cinnamomi from Phytophthora parvispora (Kunadiya et al. 2017), a species closely related to P. cinnamomi (Scanu et al. 2014;Yang et al. 2017). ...
Phytophthora cinnamomi is an ecologically and agriculturally significant plant pathogen. Early and accurate detection of P. cinnamomi is paramount to disease prevention and management. In this study, a loop-mediated isothermal amplification (LAMP) assay utilizing a new target gene Pcinn100006 identified from genomic sequence data was developed and evaluated for the detection of P. cinnamomi. This Pcinn100006 LAMP assay was found highly specific to P. cinnamomi. All 10 tested isolates of P. cinnamomi yielded positive results, whereas 50 isolates belonging to 16 other Phytophthora species, Globisporangium ultimum, and 14 fungal species lacked detection. This assay was 10 times more sensitive (100 pg in a 25-µl reaction mixture) than a conventional PCR assay (2 ng in a 50-µl reaction mixture) for detecting the genomic DNA of P. cinnamomi. In addition, it detected P. cinnamomi from artificially inoculated leaves of Cedrus deodara. Moreover, detection rates of P. cinnamomi using environmental DNAs extracted from 13 naturally infested rhizosphere samples were 100% in the Pcinn100006 LAMP assay versus 46% in the conventional PCR assay. Considering its higher accuracy and shorter time span, this Pcinn100006 LAMP assay is a promising diagnostic tool to replace conventional PCR-based and culture-dependent assays for screening of P. cinnamomi in regions at risk of infection or contamination.
... The pr es en ce of exotic, potentially invasive Phytophthora species often represents a threat for the survival of native plant species and may alter the stability of the entire ecosystem. In Sardinia, a survey in the National Park of the La Maddalena archipelago demonstrated the involvement of exotic Phytophthora species in the widespread mortality of Quercus ilex trees and Mediterranean maquis vegetation [25,27,28]. Outplanting of infected nursery stock is considered a primary pathway for the introduction of non-native Phytophthora species into forest ecosystems [10,[29][30][31][32][33][34][35][36]. ...
: The aim of this study was to investigate the occurrence, diversity, and distribution of Phytophthora species in Protected Natural Areas (PNAs), including forest stands, rivers, and riparian ecosystems, in Sicily (Italy), and assessing correlations with natural vegetation and host plants. Fifteen forest stands and 14 rivers in 10 Sicilian PNAs were studied. Phytophthora isolations from soil and stream water were performed using leaf baitings. Isolates were identified using both morphological characters and sequence analysis of the internal transcribed spacer (ITS) region. A rich community of 20 Phytophthora species from eight phylogenetic clades, including three new Phytophthora taxa, was recovered (17 species in rhizosphere soil from forest stands and 12 species in rivers). New knowledge about the distribution, host associations, and ecology of several Phytophthora species was provided.
... Genetically, P. parvispora is very closely related to P. cinnamomi and was originally considered a variety of P. cinnamomi when it was first detected causing stem rot of Beaucarnea spp. in Germany (Kröber and Marwitz 1993). It was also recently found to cause severe dieback including root and collar rot on Arbutus unedo L. in Italy (Scanu et al. 2014). In our study, P. parvispora was found with P. nicotianae causing crown rot of a nonnative host, C. ternata. ...
Phytophthora tentaculata was detected for the first time in North America in 2012 in a nursery on sticky monkeyflower plant (Diplacus aurantiacus) and again in 2014 on outplanted native plants. At that time, this species was listed as a federally actionable and reportable pathogen by the USDA. As a result of these detections, California native plant nurseries were surveyed to determine the prevalence of Phytophthora on native plant nursery stock. A total of 402 samples were collected from 26 different native plant nurseries in California between 2014 and 2016. Sampling focused on plants with symptoms of root and crown rot. Symptomatic tissue was collected and tested by immunoassay, culture, and molecular techniques (PCR). Identifications were made using sequences from the internal transcribed spacer (ITS) rDNA region, a portion of the trnM-trnP-trnM, or the atp9-nad9 mitochondrial regions. Phytophthora was confirmed from 149 of the 402 samples (37%), and from plants in 22 different host families. Phytophthora tentaculata was the most frequently detected species in our survey, followed by P. cactorum and members of the P. cryptogea complex. Other species include P. cambivora, P. cinnamomi, P. citricola, P. hedraiandra, P. megasperma, P. multivora, P. nicotianae, P. niederhauserii, P. parvispora, P. pini, P. plurivora, and P. riparia. A few Phytophthora sequences generated from mitochondrial regions could not be assigned to a species. Although this survey was limited to a relatively small number of California native plant nurseries, Phytophthora species were detected from three quarters of them (77%). In addition to sticky monkeyflower, Phytopthora tentaculata was detected from seven other hosts, expanding the number of associated hosts. During this survey, Phytophthora parvispora was detected for the first time in North America from symptomatic crowns and roots of the non-native Mexican orange blossom (Choisya ternata). Pathogenicity of P. parvispora and P. nicotianae was confirmed on this host. These findings document the widespread occurrence of Phytophthora spp. in native plant nurseries and highlight the potential risks associated with outplanting infested nursery grown stock into residential gardens and wildlands.
... A total of 204 P. cinnamomi isolates were collected from Africa The isolates were obtained from rhizosphere soil samples using different baiting approaches or, less frequently, by direct plating of infected root or bark tissue onto Phytophthora-selective agar media (Arentz & Simpson, 1986;Dobrowolski et al., 2003;Jung et al., 1996Jung et al., , 2013Jung et al., , 2017Jung & Dobler, 2002;Linde et al., 1997;Scanu et al., 2014). P. cinnamomi isolates from the US were primarily sampled from Rhododendron in ornamental nurseries in Oregon (Parke et al., 2014;Weiland et al., 2020). ...
Phytophthora cinnamomi is a heterothallic, broad host range plant pathogen causing dieback and root rots of more than 3000 plant species. Several independent studies have suggested the existence of clonal lineages, primarily of the A2 mating type, and rarely sexual reproduction. However, a rigorous study of population diversity at a global scale is currently lacking. We analyzed 197 isolates of P. cinnamomi sampled from 11 countries. Genotyping by sequencing was performed using two restriction enzymes (PstI and MspI) and sequenced on the Illumina HiSeq 3000 platform. Raw reads were mapped to the P. cinnamomi reference genome using bowtie2 and variants were called with the GATK HaplotypeCaller. We tested the hypothesis of clonal reproduction in P. cinnamomi populations. A neighbor-joining tree based on 1,027 variants indicated that populations of P. cinnamomi from Southeast Asia (Taiwan & Vietnam) consisting of A1 and A2 mating type isolates were highly diverse whereas most isolates from the remaining countries formed two distinct clonal lineages of the A2 mating type. A1 mating type isolates from Papua New Guinea, South Africa and Australia grouped within the diverse Taiwanese and Vietnamese populations which were inferred to be partially sexual based on the index of association. This suggests that Southeast Asia might be a candidate center of origin for P. cinnamomi as speculated previously. These results provide novel insights into the existence of both mating types in Southeast Asia and probably sexual reproduction that could potentially give rise to novel aggressive genotypes or lineages.
... Meanwhile, we did not observe whether PparvAvh214 enhance GmSKRPs induced susceptibility. Another possibility is that SKPRs have natural variations in different plants, thus it is possible that SKRP in the host of P. parvispora, such as A. unedo (Scanu et al., 2013), is quite different from soybean SKRP. The interaction of PparvAvh214 with its natural host will be important for an in-depth physiological dissection and analysis of its function. ...
PsAvr3c is an effector identified from oomycete plant pathogen Phytophthora sojae that causes soybean root and stem rot disease. Earlier studies have demonstrated that PsAvr3c binds to a novel soybean spliceosomal complex protein, GmSKRP, to reprogram the splicing of hundreds of pre-mRNAs and consequently subvert host immunity. PsAvr3c family genes are present in some other Phytophthora species, but their function remains unknown. Here, we characterized the functions of PsAvh27b (PsAvr3c paralog from P. sojae), ProbiAvh89 and PparvAvh214 (orthologs from P. cinnamomi var. robiniae and Phytophthora parvispora, respectively). The study reveals that both PsAvh27b and ProbiAvh89 interact with GmSKRPs in vitro, and stabilize GmSKRP1 in vivo. However, PparvAvh214 cannot interact with GmSKRPs proteins. The qRT-PCR result illustrates that the alternative splicing of pre-mRNAs of several soybean defense-related genes are altered in PsAvh27b and ProbiAvh89 when over-expressed on soybean hairy roots. Moreover, PsAvr3c family members display differences in promoting Phytophthora infection in a SKRP-dependent manner. Overall, this study highlights that the effector-mediated host pre-mRNA alternative splicing occurs in other pathosystems, thus providing new probes to further dissect SKRP-mediated plant susceptibility.
... Tissues were first surface disinfested (1 min in 0.5% NaOCl, 30 s in 70% EtOH), then dried for 30 to 60 s in a laminar flow hood before plating onto PARP, a semiselective medium for Pythiaceious species (Kannwischer and Mitchell 1978). Isolates were identified using DNA sequence from the internal transcribed spacer (ITS) region and were 99 to 100% identical to sequences from type or extype isolates: P. cinnamomi (KC478663 and FJ801806), Py. cryptoirregulare (AY907893), and P. plurivora (FJ665225) (Garzon et al. 2007;Jung and Burgess 2009;Martin and Coffey 2012;Scanu et al. 2014). ...
Rhododendrons are an important crop in the ornamental nursery industry, but are prone to Phytophthora root rot. Phytophthora root rot is a continuing issue on rhododendrons despite decades of research. Several Phytophthora species are known to cause root rot, but most research has focused on P. cinnamomi, and comparative information on pathogenicity is limited for other commonly encountered oomycetes, including Phytophthora plurivora and Pythium cryptoirregulare. In this study, three isolates each of P. cinnamomi, P. plurivora, and Py. cryptoirregulare were used to inoculate rhododendron cultivars Cunningham's White and Yaku Princess at two different inoculum levels. All three species caused disease, especially at the higher inoculum level. P. cinnamomi and P. plurivora were the most aggressive pathogens, causing severe root rot, whereas Py. cryptoirregulare was a weak pathogen that only caused mild disease. Within each pathogen species, isolate had no influence on disease. Both P. cinnamomi and P. plurivora caused more severe disease on Cunningham's White than on Yaku Princess, suggesting that the relative resistance and susceptibility among rhododendron cultivars might be similar for both pathogens. Reisolation of P. cinnamomi and P. plurivora was also greater from plants exhibiting aboveground symptoms of wilting and plant death and belowground symptoms of root rot than from those without symptoms. Results show that both P. cinnamomi and P. plurivora, but not Py. cryptoirregulare, are important pathogens causing severe root rot in rhododendron. This study establishes the risks for disease resulting from low and high levels of inoculum for each pathogen. Further research is needed to evaluate longer term risks associated with low inoculum levels on rhododendron health and to explore whether differences among pathogen species affect disease control.
... Pure cultures were obtained by transferring single hyphal tips from the edge of the colonies onto V8A (Jung & Nechwatal, 2008). Stock cultures were maintained on carrot juice agar (CA; Scanu et al., 2014) at 10°C in the dark. ...
... The closest published related sequences that were obtained in the initial BLAST search were also included in the phylogenetic analyses. For Phytophthora, the reference sequences were (i) the type isolates of P. cinnamomi, P. citricola, P. melonis, P. mengei, P. multivora, P. niederhauserii and P. plurivora; (ii) sequences published by Cooke et al. (2000) for P. cactorum, P. cambivora, P. capsici, P. infestans, P. megakarya, P. multivesiculata, P. nicotianae and P. palmivora; (iii) sequences published by Robideau et al. (2011) for P. alni and P. tropicalis; and (iv) the sequence published by Scanu et al. (2014) for P. parvispora. For Phytopythium, the sequences used as references were taken from Cooke et al. (2000), Lévesque and De Cock (2004) (Bala et al., 2010), was also included. ...
Root rot, caused by Phytophthora cinnamomi, is the most important disease of avocado, but few studies have determined whether other Phytophthora or oomycete species are involved in crop decline. Avocado orchards in the Canary Islands were surveyed for the presence of Phytophthora and Phytophthora-like oomycetes. Isolates obtained were identified morphologically and by sequence analysis of their internal transcribed spacer (ITS) regions, and their pathogenicity was tested by root and stem inoculation of avocado seedlings. Phytophthora species were isolated in 41 of 99 orchards sampled, and 10% of orchards were infected with more than one species. The species most frequently isolated was P. cinnamomi, which was detected in 26 orchards. In addition, P. multivora (ten orchards), P. niederhauserii (four orchards), P. nicotianae (four orchards), P. palmivora (one orchard) and Phytopythium vexans (20 orchards) were isolated. Phytophthora nicotianae and P. palmivora have been previously reported as pathogens of avocado, but P. niederhauserii, P. multivora and Pp. vexans are reported for the first time to be associated with this host. Phytophthora niederhauserii was the most virulent of these species. It was isolated from declining trees, and root rot severity was comparable to that caused by P. cinnamomi in two independent pathogenicity tests. In addition, P. niederhauserii caused cankers after stem inoculation. The pathogenicity results for P. multivora and Pp. vexans varied depending on isolates and pathogenicity tests. This study increases the knowledge of oomycetes associated with avocado, highlighting the potential threat posed by P. niederhauserii to this important fruit crop.
... Isolates were paired with A1 and A2 mating type of P. cinnamomi and P. cambivora tester strains to stimulate production of oogonia. Isolates of P. cinnamomi used as tester were PRC-102 (A1, Mycological Collection of Reggio Calabria, Italy) and CBS 144.22 (A2, ex-type isolate, Scanu et al. 2014) isolates; for P. xcambivora IMI 229178 (A1) and CBS 141.218, (A2) (Jung et al. 2017b) isolates were used. A 5 mm plug was taken from each isolate and transferred to the edge of four 90 mm Petri dishes on V8A. ...
During a survey of forest stands of holm oak (Quercus ilex) in the Salento peninsula, Apulia region (southern Italy), the oomycete Phytophthora cinnamomi was found to be consistently associated with tree decline and mortality in 7 municipalities of the province of Lecce. The pathogen was recovered directly from roots using a selective medium and from rhizosphere soil samples with leaf baits and subsequent isolation on the same selective medium used for direct isolation from roots. It was identified on the basis of morphological characters and by sequencing of the internal transcribed spacer (ITS) regions of the rDNA after amplification with conventional PCR. All P. cinnamomi isolates were A2 mating type and proved to be highly aggressive on seedlings of evergreen Mediterranean oak species, including holm oak. cork oak (Q. suber) and kermes oak (Q. coccifera). P. cinnamomi is a well know pathogen of several forest trees worldwide and on the basis of its widespread and consistent occurrence in forest stands of the Lecce province it was assumed to be the primary causal agent of holm oak decline in this area. Options for the management of this phytosanitary environmental emergence are discussed.
Phytophthora cinnamomi is an important soilborne pathogen causing root rot and stem cankers on macadamia in South Africa and other countries. It is unknown whether a temporal pattern exists in the colonization of macadamia tree roots by P . cinnamomi . To investigate this, three macadamia orchards were studied bimonthly for 2 years. The study also examined whether two types of feeder roots contained varying levels of P. cinnamomi DNA. A new sensitive P. cinnamomi ‐specific quantitative real‐time PCR (qPCR) assay was used to conduct the assessments. Only symptomatic trees were studied in two of the orchards (ZC and ZD), while symptomatic and asymptomatic trees were assessed in the third orchard (ZA). In the ZC and ZD orchards, white non‐suberized feeder roots from a new root flush had higher levels of P. cinnamomi DNA than suberized feeder roots. In orchard ZD, autumn and winter yielded the highest P. cinnamomi root quantities in suberized roots. The symptomatic and asymptomatic trees in orchard ZA generally contained higher P. cinnamomi root quantities in winter than in summer. However, in orchard ZC, no significant temporal pattern was evident, although a trend was noticeable towards higher P. cinnamomi root colonization in autumn, winter and spring. Principal component analyses supported autumn and winter as the months yielding the highest P. cinnamomi root colonization levels. The study has contributed to a better understanding of the temporal nature of P. cinnamomi root colonization, and feeder root types that are optimal for qPCR quantifying the pathogen in macadamia.
Environmental changes are occurring on a global scale, but their effects are most pronounced in climate change hotspot zones, such as the Mediterranean basin. Within this area Italy, extending from its southern coasts in the core of the Mediterranean Sea to its northernmost pre-Alpine and Alpine regions, is characterized by a variety of climatic conditions and vegetation types. Surveys conducted in 2018-2022 in forest formations of Central-Northern Italy revealed that the enhanced warming trend and irregular distribution of precipitations are strongly impacting the health of Fraxinus species, with some pathogenic fungi and oomycetes being important contributing factors to the decline of the three main ash species growing there: common ash (Fraxinus excelsior), flowering ash (Fraxinus ornus) and narrow-leaved ash (Fraxinus angustifolia). Isolation from symptomatic plant material collected countrywide under different site conditions and pathogenicity tests revealed a complex phytopathological framework, with several pathogenic species in addition to Hymenoscyphus fraxineus involved with a prominent role in the ash dieback aetiology. Key microbial taxa included the fungal and oomycete pathogens Botryosphaeria dothidea, Diplodia fraxini, Diplodia subglobosa, Phytophthora acerina and Phytophthora plurivora. The disease impact was higher on sites where ash trees grew under environmental stress (i.e. areas characterized by mild dry winters, hot summers with intense and prolonged drought) and exhibited reduced vigour, also as a consequence of anthropogenic interference (i.e. silvicultural management and fires). The identified causative agents are emerging pathogens that thrive under warmer conditions, their impact in the investigated areas being prevalent compared to H. fraxineus, which appears to be restricted on the Italian peninsula to the cooler and wetter valleys of the Alps and Central-Northern Apennines.
Eucalypt, mostly Eucalyptus globulus, is the exotic tree species occupying the largest area of Portuguese planted forest. Eucalypts were introduced in the country more than one hundred years ago, but it was only in the second half of the twentieth century that the area of plantations grew with the onset of their use in the paper and pulp industry. As an exotic species, it was free from pests and diseases but gradually the number of insects and pathogens affecting these plants increased. In recent year, a new disease causing root rot and dieback has been detected with increasing frequency. In this work, two Phytophthora species, P. cinnamomi and P. alticola, were identified associated with these symptoms. Koch’s postulates were fulfilled, proving that these two species are pathogenic to E. globulus. This is the first report of P. alticola outside South Africa. Although presently unknown, the possible factors associated with the increased occurrence of this disease are discussed.
During extensive surveys of global Phytophthora diversity 14 new species detected in natural ecosystems in Chile, Indonesia, USA (Louisiana), Sweden, Ukraine and Vietnam were assigned to Phytophthora major Clade 10 based on a multigene phylogeny of nine nuclear and three mitochondrial gene regions. Clade 10 now comprises three subclades. Subclades 10a and 10b contain species with nonpapillate sporangia, a range of breeding systems and a
mainly soil- and waterborne lifestyle. These include the previously described P. afrocarpa, P. gallica and P. intercalaris and eight of the new species: P. ludoviciana, P. procera, P. pseudogallica, P. scandinavica, P. subarctica, P. tenuimura, P. tonkinensis and P. ukrainensis. In contrast, all species in Subclade 10c have papillate sporangia and are self-fertile (or homothallic) with an aerial lifestyle including the known P. boehmeriae, P. gondwanensis, P. kernoviae and P. morindae and the new species P. celebensis, P. chilensis, P. javanensis, P. multiglobulosa, P. pseudochilensis and P. pseudokernoviae. All new Phytophthora species differed from each other and from related species by their unique combinations of morphological characters, breeding systems, cardinal temperatures and growth rates. The
biogeography and evolutionary history of Clade 10 are discussed. We propose that the three subclades originated via the early divergence of pre-Gondwanan ancestors > 175 Mya into water- and soilborne and aerially dispersed lineages and subsequently underwent multiple allopatric and sympatric radiations during their global spread.
To document the distribution of potentially harmful Phytophthora spp. within Pennsylvania (PA), the PA Department of Agriculture collected 89 plant, 137 soil, and 48 water samples at 64 forested sites from 2018 to 2020. In total, 231 Phytophthora strains were isolated using baiting assays and identified based on morphological characteristics and sequences of nuclear and mitochondrial loci. Twenty-one Phytophthora spp. in nine clades and one unidentified species were present. Phytophthora abietivora, a recently described clade 7a species, was recovered from diseased tissue of 10 native broadleaved plants and twice from soil from 12 locations. Phytophthora abietivora is most likely endemic to PA based on pathogenicity tests on six native plant species, intraspecific genetic diversity, wide distribution, and recoveries from Abies Mill. and Tsuga Carrière plantations dating back to 1989. Cardinal temperatures and morphological traits are provided for this species. Other taxa, in decreasing order of frequency, include P. chlamydospora, P. plurivora, P. pini, P. cinnamomi, P. xcambivora, P. irrigata, P. gonapodyides, P. cactorum, P. pseudosyringae, P. hydropathica, P. stricta, P. xstagnum, P. caryae, P. intercalaris, Phytophthora ‘bitahaiensis’, P. heveae, P. citrophthora, P. macilentosa, P. cryptogea, and P. riparia. Twelve species were associated with diseased plant tissues. This survey documented 53 new plant-Phytophthora associations and expanded the known distribution of some species.
An emerging soil-borne disease resembling Phytophthora stem rot was observed on mung bean plants grown in Anhui, China. To identify the causal agent, diseased plants and soil samples from 13 fields were collected to isolate the pathogen. Twenty-two Phytophthora isolates were recovered from the samples and conducted for detailed identification. Based on morphological and molecular characterizations, all the isolates were consistently identified as Phytophthora vignae. Phylogenetic analysis using eight nuclear loci sequences of the internal transcribed spacer (ITS) region, rRNA gene large subunit (LSU), a partial sequence of the beta-tubulin (β-tubulin) gene, the translation elongation factor 1 alpha (EF1-α), the 60S ribosomal protein L10 (60SL10), enolase (Enl) gene, the heat shock protein 90 (HSP90), and the triose phosphate isomerase/glyceraldehyde-3-phosphate dehydrogenase (TigA) and a mitochondrial locus cytochrome c oxidase subunit I (cox1) revealed that the mung bean isolates group in the same clade as P. vignae and its two formae speciales, P. vignae f. sp. adzukicola and P. vignae f. sp. vignae. A host specificity test showed that the mung bean isolates of P. vignae are pathogenic towards mung bean with a much stronger virulence and towards adzuki bean with a relatively weak virulence, but non-pathogenic to the other tested legume crops, soybean, cowpea, pea, common bean, faba bean, and chickpea. The host range of mung bean isolates significantly differs from that of the P. vignae f. sp. adzukicola and f. sp. vignae, based on our results and the previous studies. Thus, the pathogen causing Phytophthora stem rot of mung bean is proposed as a new forma specialis of P. vignae, designated as P. vignae f. sp. mungcola.
A number of fir species, (Abies), are produced as Christmas trees around the world. In particular, Fraser fir (Abies fraseri (Pursh) Poir.), is popular as it yields high-quality Christmas trees in temperate North America and Europe. A Phytophthora sp. causing root rot on Fraser fir was isolated from a Christmas tree farm in Connecticut, USA, and found to be new to science according to morphological and molecular phylogenetic analysis using multi-locus DNA sequences from ITS, Cox1, β-Tub, Nadh1, and Hsp90 loci. Thus, it was described and illustrated as Phytophthora abietivora. An informative Koch’s postulates test revealed that P. abietivora was the pathogen causing root rot of Fraser fir.
Nursery stocks and irrigation water are important sources of Phytophthora spp. In this study, twenty irrigation water reservoirs and ten avocado nurseries were surveyed in the Canary Islands between 2013 and 2015 to investigate their potential role in disseminating pathogenic species in avocado orchards. Phytophthora multivora was isolated from one of the irrigation reservoirs, whereas, in two surveys conducted in nurseries, Phytophthora cinnamomi, the primary pathogen in avocado, was detected in addition to other Phytophthora species (P. lacustris, P. multivora, P. nicotianae, P. niederhauserii, P. palmivora) and Phytopythium vexans. The species recovered from nurseries were isolated mostly from propagated plants but also from nursery irrigation water, soil used for substrate preparation and soil samples collected in orchards that supply seeds for seedling propagation. Species recovered from nurseries correlated with those found in avocado orchards in a previous study, except for P. lacustris, suggesting that nurseries could be involved in their dissemination in avocado orchards. The improved sanitary status of nurseries resulted in the reduced incidence in the second survey, indicating the importance of nursery monitoring to reduce infestations.
Soil infestation by Phytophthora spp. is widespread but affects timber production only in the mixed species eucalypt forests in Victoria and the Eucalyptus marginata (jarrah) forest in Western Australia. It also affects water production in Western Australia. As Phytophthora spp. have a very wide host range, site infestation leads to vegetation changes which reduce the conservation value of indigenous forests and similar plant communities in southern Australia. -from Authors
The morphological and physiological characteristics of Phytophthora cinnamomi isolates including two from citrus and one each from soil, pineapple, and avocado from Taiwan, one from camellia from California, and one from macadamia from Hawaii, were studied. Only PCiC1 and PCiC11 from citrus made slight growth at 36 C and failed to produce chlamydospores in any media tested. The average length: breadth ratio of sporangia was 1.5-1.8 for all isolates except for PCiC1 which produced nearly spherical sporangia with the average length: breadth ratio of 1.2. Only PT6 from soil was capable of producing sporangia on 5% V-8 agar. Both PCiC1 and PCiC11 are A1 mating type and belong to sexuality type 2. PT5, the avocado PCiA, and the macadamia 64F are A2 mating type belonging to sexuality type 4. The pineapple PCiP, and the camellia PC97 are A1 mating type belonging to sexuality type 1. All of these fungi have identical protein patterns.
Phytophthora isolates with deciduous long-pedicellate sporangia can be separated into two groups by isozyme analyses, but an apparent overlap in morphological characteristics was previously deemed as sufficient justification for inclusion of both groups in P. capsici with an expanded description of the species. However, the occurrence of two morphologic groups in a species is unsettling, prompting a reexamination of the taxon. Comparative morphological and cultural studies of 100 Phytophthora isolates with deciduous, long-pedicellate sporangia which have been referred to P. capsici, revealed that they were separable into two taxa: Phytophthora capsici with broad sporangia, sporangial length to diameter ratio less than 1.8, predominately round sporangial bases, absence of chlamydospores, good growth at 35 C, and pathogenicity to Capsicum; and Phytophthora tropicalis sp. nov., distinguished from P. capsici by narrow sporangia less than 26 μm in diameter, sporangial length to diameter ratio of more than 1.8, predominately tapered sporangial bases, production of chlamydospores by most isolates, poor or no growth at 35 C, and weak or no virulence to Capsicum.
The niches of three co-dominant Banksia shrub species were determined by examining their water relations, architecture and vegetative phenology. Dawn and dusk xylem pressure potentials were similar in the three species, decreasing almost three fold from early summer to mid-autumn. All species showed similar daily patterns of stomatal conductance. Peak conductances decreased almost three fold over the summer period, corresponding with increased aerial and edaphic water deficits. The horizontal and vertical root patterns were similar, providing equal access to soil-stored water, with much intermingling of root systems. Vegetative growth of the three species occurred almost exclusively in summer even though surface root growth was restricted to winter-spring. Despite marked differences in life history and leaf sizes, no variations in water use patterns that might promote co-existence of the three species were evident. It is concluded that co-occurrence of these species cannot be attributed to their differential partitioning of this apparently limiting resource.
Approximately 150,000 potted mandevillas (Apocynaceae) are produced each year in the Etna District of eastern Sicily. Since 2004, leaf chlorosis, wilt, and sudden collapse of the entire plant associated with root and basal stem rot of 6- to 12-month-old potted mandevillas, including Mandevilla × amabilis ‘Alice du Pont’, M. splendens, and M. sanderi ‘Alba’, ‘My Fair Lady’, and ‘Scarlet Pimpernel’, have been observed in six nurseries. Incidence of affected plants varied from 5 to 40%. Four Phytophthora species were consistently isolated from rotted roots and stems on a selective medium (2). Pure cultures of the first species produced colonies with a camellia pattern on potato dextrose agar and grew between 10 and 37°C with an optimum of 27°C. On V8 juice agar they produced ellipsoid to obpyriform (length/breadth [l/b] 1.45:1), nonpapillate sporangia with internal proliferation, coralloid, spherical hyphal swellings and both terminal and intercalary chlamydospores. In dual cultures with A1 and A2 isolates o...
The morphology of Pc40 (A2) and Pc97 (A1) isolates of Phytophthora cinnamomi was studied with light and scanning electron microscopy. While confirming the findings of previous workers, some interesting features were observed, hitherto undescribed. Encysted zoospores germinated either by germ tubes or "repeated emergence" of zoospores. Microsporangia or miniature sporangia and appressoria were sometimes produced by germ tubes. Bicellular antheridia were present in both Pc40 selfing and in Pc40 × Pc97. They were longer than the unicellular type and occurred less frequently. The amphigynous antheridium was presumably brought about by the penetration of an antheridium initial by the oogonium initial. A fertilization tube was clearly demonstrated within the oogonium stalk. Oogonia and oospores from Pc40 selfing were larger than those from Pc40 × Pc97. Isolate Pc40 produced more sporangia than Pc97 and the Pc40 sporangia tended to be longer and limoniform. The significance of the bicellular antheridium and the use of scanning electron microscopy in the taxonomy of Phytophthora are discussed.
With the increased attention given to the genus Phytophthora in the last decade in response to the ecological and economic impact of several invasive species (such as P. ramorum, P. kernoviae, and P. alni), there has been a significant increase in the number of described species. In part, this is due to the extensive surveys in historically underexplored ecosystems (e.g., forest and stream ecosystems) undertaken to determine the spread of invasive species and the involvement of Phytophthora species in forest decline worldwide (e.g., oak decline). The past decade has seen an approximate doubling in the number of described species within the genus Phytophthora, and the number will likely continue to increase as more surveys are completed and greater attention is devoted to clarifying phylogenetic relationships and delineating boundaries in species complexes. The development of molecular resources, the availability of credible sequence databases to simplify identification of new species, and the sequencing of several genomes have provided a solid framework to gain a better understanding of the biology, diversity, and taxonomic relationships within the genus. This information is much needed considering the impact invasive or exotic Phytophthora species have had on natural ecosystems and the regulatory issues associated with their management. While this work is improving our ability to identify species based on phylogenetic grouping, it has also revealed that the genus has a much greater diversity than previously appreciated.
Estimates of the susceptibility of plant species in Banksia woodland to Phytophthora cinnamomi Rands were obtained by determining the incidence of plant death and frequency of isolation of the pathogen, among species occurring in 46 disease centres on the Swan Coastal Plain south of Perth, Western Australia. In the disease centres, dicotyledons outnumbered monocotyledons. About half of all species occurring in the disease centres were from four families of dicotyledons, with the largest number of species from the Myrtaceae, Proteaceae and Papilionaceae. The greatest number of species of monocotyledons were from the Anthericaceae and Cyperaceae. No deaths were recorded for 47% of species found in three or more disease centres. These species were mainly from the Cyperaceae, Haemodoraceae, Myrtaceae and Papilionaceae. The species that tended to die frequently in disease centres were mainly from the Papilionaceae, Proteaceae, Epacridaceae, Xanthorrhoeaceae and the Zamiaceae. Phytophthora cinnamomi was isolated from 26 of the 95 species occurring in three or more disease centres. For most species, the frequency of isolation of P. cinnamomi from recently dead plants was much less than the frequency of dead plants sampled. Isolation from plants was less frequent than from adjacent soil. The pathogen was isolated from recently dead plants or soil mainly for species of the Proteaceae, Myrtaceae, Papilionaceae, Dasypogonaceae, Iridaceae and Xanthorrhoeaceae. Cross-tabulation of species by incidence of plant death and isolation of P. cinnamomi from plant and soil, provided the opportunity to classify the response of plant species to infection by P. cinnamomi.
Incidence of Phytophthora blight in bell pepper fields that were sprayed for the first time with Ridomil Gold (mefenoxam) according to labeled recommendations was higher in North Carolina in 1997 than in previous years. Mefenoxam is the more active enantiomer contained in the racemic fungicide metalaxyl. A total of 150 isolates were obtained from 17 fields at eight grower locations. Among isolates from all locations, 30% were classified as sensitive, 10% as intermediate, and 59% were resistant to mefenoxam. Mefenoxam-resistant isolates were found in 82% of the fields sampled (14 of 17 fields). The proportion of resistant isolates in individual fields ranged from 28 to 100%. The mean effective concentration (EC50) values for mefenoxam-sensitive isolates was 0.568 μg ml-1 (ranging from 0.12 to 1.1 μg ml-1), whereas the mean EC50 value for mefenoxam-resistant isolates was 366.5 μg ml-1 (ranging from 3 to 863 μg ml-1). The mean EC50 value for metalaxyl-sensitive isolates was 0.27 μg ml-1 (ranging from 0.00002 to 1.3 μg ml-1) and for metalaxyl-resistant isolates was 470.34 μg ml-1 (ranging from 10 to 966 μg ml-1). The greatest proportion of resistant isolates came from fields where mefenoxam was used alone rather than in combination with other fungicides. Both mating types were found among resistant isolates, suggesting that these isolates may persist in soil in subsequent years. Field isolates of Phytophthora capsici resistant to mefenoxam on pepper have not been reported previously and now pose new challenges for management of this important disease.
The pattern of invasion and the histological changes in primary root tissues after infection by Phytophthora cinnamomi are described from the following species: Xanthorrhoea australis, X. resinosa, Theme da australis, Eucalyptus marginata, E. sieberi, and Acacia melanoxylon (susceptible); A. pulchella, E. calophylla, E. maculât a, Gahnia r adula, Juncus bufonius, Zea mays, and Triticum aestivum var. cappelle (resistant). Zoospores germinated on and penetrated the roots of all species, and lesions formed within 8-16 hr after invasion at 20-24 C. Root growth ceased within 24 hr of inoculation but resumed within 48 hr in resistant species, usually from a lateral branch. In susceptible species, progressive symptom development included water soaking of tissues, lesion extension through the root to the hypocotyl, and root death. This was accompanied by wilting and chlorosis of the leaves, die-back of shoots, and plant death. Sporulation occurred between 24 and 72 hr after inoculation on all but the most resistant species. In resistant species, lesions were contained well before they extended to the hypocotyl. Deposition of phenolic materials, granulation of the cytoplasm, shrinkage of the protoplast, and cell wall distortion and disruption accompanied infection in all species. Lignification of cell walls, deposition of phenolics, and the formation of callosic papillae were more commonly observed in the resistant species but occurred in some susceptible species. No specific anatomical feature or histological change was consistently associated with resistance. Although the species examined were classed as either resistant or susceptible on the basis of their field response, examination of the anatomical and histological changes that followed infection showed a gradient in which the fully susceptible and most resistant types represent the extremes.
This study compares, for the first time, variation in estimates of susceptibility of native flora to Phytophthora cinnamomi Rands among four databases and proposes an estimate of the proportion of the flora of the South-West Botanical Province of Western Australia that is susceptible to the pathogen. Estimates of the susceptibility of south-western native flora to P. cinnamomi infection were obtained from databases for Banksia woodland of the Swan Coastal Plain, jarrah (Eucalyptus marginata Donn. ex Smith) forest, the Stirling Range National Park and Rare and Threatened Flora of Western Australia. For the woodland, forest and national park databases, hosts were naturally infected in uncontrolled diverse natural environments. In contrast, threatened flora were artificially inoculated in a shadehouse environment. Considerable variation occurred within taxonomic units, making occurrence within family and genus poor predictors of species susceptibility. Identification of intra-specific resistance suggests that P. cinnamomi could be having a strong selection pressure on some threatened flora at infested sites and the populations could shift to more resistant types. Similar estimates of the proportion of species susceptible to P. cinnamomi among the databases from the wide range of environments suggests that a realistic estimate of species susceptibility to P. cinnamomi infection in the south-western region has been obtained. The mean of 40% susceptible and 14% highly susceptible equates to 2284 and 800 species of the 5710 described plant species in the South-West Botanical Province susceptible and highly susceptible to P. cinnamomi, respectively. Such estimates are important for determining the cost of disease to conservation values and for prioritising disease importance and research priorities. P. cinnamomi in south-western Australia is an unparalleled example of an introduced pathogen with a wide host range causing immense irreversible damage to unique, diverse but mainly susceptible plant communities.
This book begins with an account of the early history of Phytophthora research and the tumultuous events setting the genus in motion. In keeping with its controversial inception, the chapter on taxonomy and phylogeny makes a compelling case that our current notion of Phytophthora as a genus is illusory. This chapter sets the stage for the importance of molecular tools on these enigmatic pathogens. The following chapters discuss species identification, population-level investigation, interspecific hybrids and the impact of diverse Phytophthora species on crops, forests, nurseries, greenhouses and natural areas worldwide.
This book begins with an account of the early history of Phytophthora research and the tumultuous events setting the genus in motion. In keeping with its controversial inception, the chapter on taxonomy and phylogeny makes a compelling case that our current notion of Phytophthora as a genus is illusory. This chapter sets the stage for the importance of molecular tools on these enigmatic pathogens. The following chapters discuss species identification, population-level investigation, interspecific hybrids and the impact of diverse Phytophthora species on crops, forests, nurseries, greenhouses and natural areas worldwide.
Isozyme analysis and cytochrome oxidase sequences were used to examine whether differentiation of P. fragariae var. fragariae and P. fragariae var. rubi at the variety level is justified. In isozyme studies six strains of both P. fragariae varieties were analyzed with malate dehydrogenase (MDH), glucose phosphate isomerase (GPI), aconitase (ACO), isocitrate dehydrogenase (IDH) and phosphogluconate dehydrogenase (PGD), comprising altogether seven putative loci. Five unique alleles (Mdh-1A, Mdh-2 B, Gpi A, AcoB and Idh-1B) were found in strains of P. fragariae var. fragariae, whereas five unique alleles (Mdh-1B, Mdh-2 A, GpiB, Aco A and Idh-1A) were present in strains of P. fragariae var. rubi. It was inferred from these data that there is no gene flow between the two P. fragariae varieties. Cytochrome oxidase I (Cox I ) sequences showed consistent differences at 15 positions between strains of Fragaria and Rubus respectively. Based on isozyme data, cytochrome oxidase I sequences, and previously published differences in restyriction enzyme patterns of mitochondrial DNA, sequences of nuclear and mitochondrial genes, AFLP patterns and pathogenicity, it was concluded that both specific pathogenic varieties of P. fragariae are reproductively isolated and constitute a distinct species. Consequently strains isolated from Rubus idaeus are assigned to Phytophthora rubi comb. nov.
Phytophthora cinnamomi continues to cause devastating disease in Australian native vegetation and consequently the disease is listed by the Federal Government as a process that is threatening Australia’s biodiversity. Although several advances have been made in our understanding of how this soil-borne pathogen interacts with plants and of how we may tackle it in natural systems, our ability to control the disease is limited. The pathogen occurs widely across Australia but the severity of its impact is most evident within ecological communities of the south-west and south-east of the country. A regional impact summary for all states and territories shows the pathogen to be the cause of serious disease in numerous species, a significant number of which are rare and threatened. Many genera of endemic taxa have a high proportion of susceptible species including the iconic genera Banksia, Epacris and Xanthorrhoea. Long-term studies in Victoria have shown limited but probably unsustainable recovery of susceptible vegetation, given current management practices. Management of the disease in conservation reserves is reliant on hygiene, the use of chemicals and restriction of access, and has had only limited effectiveness and not provided complete control. The deleterious impacts of the disease on faunal habitat are reasonably well documented and demonstrate loss of individual animal species and changes in population structure and species abundance. Few plant species are known to be resistant to P. cinnamomi; however, investigations over several years have discovered the mechanisms by which some plants are able to survive infection, including the activation of defence-related genes and signalling pathways, the reinforcement of cell walls and accumulation of toxic metabolites. Manipulation of resistance and resistance-related mechanisms may provide avenues for protection against disease in otherwise susceptible species. Despite the advances made in Phytophthora research in Australia during the past 40 years, there is still much to be done to give land managers the resources to combat this disease. Recent State and Federal initiatives offer the prospect of a growing and broader awareness of the disease and its associated impacts. However, awareness must be translated into action as time is running out for the large number of susceptible, and potentially susceptible, species within vulnerable Australian ecological communities.
Taiwanese isolates of Phytophthora cinnamomi were examined for genetic diversity by the random amplified polymorphic DNA assay. The amount of genetic variation was evaluated by polymerase chain reaction amplification with a set of nine random 10-mer primers. All amplifications revealed scorable polymorphisms among the isolates, and a total of 217 band positions was scored for the nine primers tested. Genetic distances between each of the isolates were calculated and cluster analysis was used to generate a dendrogram showing relationships between them. Isolates did not cluster into groups corresponding to their mating types. Primer OPS-13 did produce one 2.7 kb hand for all isolates of A1 mating type, but not for A2 isolates. Moreover, primer OPE-06 amplified one 1.3 kb band for all A1 mating type isolates, while that was absent in A2 isolates except for three isolates obtained from avocado roots. Genetic differentiation often isolates obtained from the same location between two mating types was significantly high, indicating that no hybridization occurred between A1 and A2 mating types in that situation. Primer OPE-4 amplified a 680 bp fragment which was only observed in three isolates obtained from avocado roots. Also, genetic differentiation between isolates from avocado and those from other sources was significantly strong (distance between 0.262 and 0.412). These results suggest host specified races might occur in P cinnamomi and the RAPD technique could be used to differentiate races within P. cinnamomi.
This oomycete genus includes >50 morphological species, most being plant pathogens. Phytophthora have a genetic system more akin to that of higher organisms than to other fungi, possessing a range of reproductive mechanisms. Major sections of this review are: the genetic system (including heterothallism, ie production of gametangia in single culture); natural variation (including fitness characters); and the role of the genetic system in the generation of variation. -P.J.Jarvis
Water samples were collected from effluent holding ponds at one northern and two southern California nurseries that practice the capture and recirculation of irrigation runoff water. Nursery effluent samples were collected approximately monthly over a 12-mo period and aliquots filtered through 0.45-µm Millipore filters. Filter residues were resuspended and dispersed onto selective agar media in petri dishes to estimate the numbers of viable propagules of Phytophthora spp. or total pythiacious fungi. Propagule numbers varied greatly from month to month at each nursery location. Pythium propagules were consistently the most numerous, ranging from 500 lo 1,500 per liter, whereas the number of Phytophthora spp. propagules ranged from 0 to 400 per liter. At the northern California nursery, propagule numbers were lowest during winter months and highest during warm seasons. Seasonal fluctuations in inoculum load were not apparent in the southern California nurseries. P. ciirophthora was the most commonly detected Phytophthora sp. Other species frequently recovered included P. citricola, P. cinnamomi, and P. cryptogea. Isolates of P. parasitica, P. megasperma, and P. syringae were recovered less frequently. Water samples also were tested for Phytophthora spp. using commercially available ELIS A tests. The ELIS A reaction intensity of filter pad extracts was correlated with the numbers of propagules estimated to be on the filters, but the correlation was stronger at some times than at others. This is believed to reflect temporal differences in water sample quality or species mixtures.
The taxonomic status of Phytophthora mirabilis, one of six host-specific, foliar pathogens in Phytophthora group IV, has been uncertain. At various times this taxon has been given three different names: P. infestans var. mirabilis; P. mirabilis; and P. infestans forma specialis mirabilis. Which of these names is correct depends on the degree of reproductive isolation between this taxon and the closely related species, P. infestans. The purpose of this paper was to evaluate the hypothesis that P. infestans and P. mirabilis are conspecific using a large battery of molecular markers. Analyses of one isozyme, 44 DNA fingerprint, and 85 presumed RAPD loci revealed little, if any, gene flow between P. infestans and P. mirabilis. Thus, host specificity apparently functions as an effective pre- and postmating reproductive isolating mechanism in nature. Gene flow analysis indicated that these two taxa are as reproductively isolated from each other as they are from the other four species in Phytophthora group IV. There were 26 fixed differences between P. infestans and P. mirabilis that only could have developed in the absence of gene flow. Attempts to obtain F<sub>2</sub> progeny from F<sub>1</sub> interspecific hybrids failed, indicating the existence of genetic mechanisms of reproductive isolation in addition to host specificity. Despite the differences between P. infestans and P. mirabilis, growth rate on seven commonly used laboratory media could not be used to separate them in the laboratory. These data clearly reject the hypothesis that P. infestans and P. mirabilis are conspecific. Therefore, two of the three names given to this taxon, P. infestans var. mirabilis and P. infestans forma specialis mirabilis, are invalid. We propose that the correct name for this species is P. mirabilis.
1. Survival, growth, and water relations of first-year seedlings of the shrub species Banksia attenuata, B. leptophylla, and B. hookeriana, were compared in scrub-heath and sand-mine rehabilitation sites. 2. Survival and growth of the broad-leaved B. hookeriana and B. attenuata were lower in the rehabilitation site than in two contrasting natural areas, but the needle-leaved species, B. leptophylla, survived and grew equally well in all three sites. 3. Root system development was poorer in the rehabilitation site: tap-roots stopped at the topsoil/subsoil boundary at 0.1 m in the rehabilitation site, while they reached 2 m at the natural sites. 4. Seedlings in the rehabilitation site had much lower pre-dawn xylem pressure potentials (XPP) and stomatal conductance. 5. Soil water potentials (ψ) in the top 0.5 m of the soil profile were generally lowest at the natural sites, and almost always lower than XPP. At these sites, seedlings must have been obtaining water over summer - autumn from deeper in the soil via their well-developed tap-roots. Topsoil ψ in the rehabilitation site was more similar to XPP than the much higher values in the subsoils, which rarely contained roots. 6. Impedance of the rehabilitation soils was significantly greater than that for soils at the two natural sites. It appeared to explain the poor root development and dependence of seedlings on soil water stored near the surface; the consequent lower xylem potentials, stomatal conductances and growth rates; and the ultimately higher mortality levels.
Isolations were made from blighted pigeon-pea (Cajanus cajan) plants from different locations in India. A species of Phytophthora was consistently obtained from these locations and was proved to be the causal organism involved in the disease. Based on the sporangium shape and size, oogonium and oospore formation, temperature requirements, and pathogenicity tests, we have classified these isolates as P. drechsleri f. sp. cajani. The use of formae speciales was considered appropriate because of the specificity of these isolates to pigeon pea and Atylosia spp., wild relatives of the pigeon pea.
Despite its importance as one of the most notorious, globally distributed, multihost plant pathogens, knowledge on the survival strategy of Phytophthora cinnamomi in seasonally dry climates is limited. Soil and fine roots were collected from the rhizosphere of severely declining or recently dead specimens of 13 woody species at 11 dieback sites and two dieback spots and from healthy specimens of five woody species at four dieback-free sites in native forests, woodlands and heathlands of the south-west of Western Australia (WA). Phytophthora cinnamomi was recovered from 80.4, 78.1 and 100% of tested soil, fine root and soil–debris slurry samples at the 11 dieback sites, in some cases even after 18-month storage under air-dry conditions, but not from the small dieback spots and the healthy sites. Direct isolations from soil–debris slurry showed that P. cinnamomi colonies exclusively originated from fine roots and root fragments not from free propagules in the soil. Microscopic investigation of P. cinnamomi-infected fine and small woody roots and root fragments demonstrated in 68.8, 81.3 and 93.8% of samples from nine woody species the presence of thick-walled oospores, stromata-like hyphal aggregations and intracellular hyphae encased by lignitubers, respectively, while thin-walled putative chlamydospores were found in only 21.2% of samples from five woody species. These findings were confirmed by microscopic examination of fine roots from artificially inoculated young trees of 10 woody species. It is suggested that (i) the main function of chlamydospores is the survival in moderately dry conditions between consecutive rain events and (ii) selfed oospores, hyphal aggregations, and encased hyphae and vesicles in infected root tissue of both host and non-host species are the major long-term survival propagules of P. cinnamomi during the extremely dry summer conditions in WA.
Resistant annual and herbaceous perennial plant species were identified as key hosts which allow Phytophthora cinnamomi to persist on severely impacted black gravel sites within the Eucalyptus marginata (jarrah) forest of southwest Western Australia. Of the annual and herbaceous perennial plant species present on black gravel sites, 15 out of 19 species were found to be hosts of P. cinnamomi, and 10 of these were symptomless hosts. In particular, the native annual Trachymene pilosa and the two native herbaceous perennials Stylidium diuroides and Chamaescilla corymbosa were commonly found to be hosts of the pathogen. Species from 12 new genera including three from new families (Crassulaceae, Droseraceae and Primulaceae) are reported for the first time to be hosts of P. cinnamomi. The species from which P. cinnamomi was recovered were the native species: Chamaescilla corymbosa, Crassula closiana, Drosera erythrorhiza, Hydrocotyle callicarpa, Levenhookia pusilla, Paracaleana nigrita, Podotheca angustifolia, Pterochaeta paniculata, Rytidosperma caespitosum, Siloxerus multiflorus, Stylidium diuroides and Trachymene pilosa, and the introduced annual weeds Hypochaeris glabra, Lysimachia arvensis and Pentameris airoides.
Abstract During the period 1997–2007, a comprehensive study of the occurrence and distribution of Phytophthora species was conducted on Hainan Island of South China. To date, 14 species of Phytophthora have been recovered and their distribution determined. Phytophthora nicotianae (=P. parasitica) is the most important species attacking a wide variety of crops, followed by Phytophthora capsici and Phytophthora citrophthora. In contrast to Phytophthora colocasiae attacking taro leaves throughout the entire island, Phytophthora cyperi was found only once on Digitaria ciliaris in Danzhou. It is of interest to note that Phytophthora heveae, Phytophthora katsurae and Phytophthora insolita are commonly found in forest soil/water of protected mountains without causing any plant diseases. Although Phytophthora species are usually terrestrial or found in fresh water, one isolate of Phytophthora resembling closely the asexual isolates of P. insolita in Hainan was obtained from decaying Rhizophora leaves submerged in seawater. An unidentified Phytophthora species producing non-papillate; internally proliferating sporangia was isolated from the soil in which Ceriops tagel and Bruguiera serangula were growing in a salt water shrimp farm.
Gas chromatographic-mass spectrometric (GC-MS) analysis of the aroma fraction isolated from several strawberry tree blossom honey samples showed a marked predominance of norisoprenoids. Some were identified or tentatively identified as C-9, C-10, and C-13 compounds. For this aspect, the honey is similar to that: from another plant of the Ericaceae family, heather, but is distinguishable from it due to different concentrations of the compounds common to both and the uniqueness of several substances, whose tentative structures have been attributed with the support of GC-Fourier Transform Infrared (FTIR) spectra. Some interesting C-10 aldehyde structures are proposed. Most compounds could be interrelated in degradation processes, starting from the compounds with the highest molecular weight. Among the samples from different areas of Sardinia, there were important quantitative differences in some of the most abundant compounds.
In different areas of Extremadura, Western Spain, soil samples were taken at the bottom of holm oak (Quercus ilex) trees that were showing decline symptoms. Half of each sample was sterilized, and acorns were sown in both sterilized and nonsterilized soil samples. The resulting seedlings were used as baits for the isolation of fungi. Seedlings growing on the natural, nonsterilized substrate were characterized by having a lower vegetative growth than the ones growing on the sterilized soil samples, and most of them died. Phytophthora dnnamomi was consistently isolated from their roots. Fusarium oxysporum was also isolated as well as different species of Pythium, although to a lesser extent. Pathogenicity tests were performed on holm oak seedlings with five different isolates of P. chinnamomi, with F. oxysporum, Pythium and with a mixture of the three fungi. All the inoculated seedlings with P. chinnamomi developed root rot and grew slowly, and 35.7% of them died up to the end of the experiments. P. chinnamomi was consistently isolated from their roots, indicating that this fungus is the causal agent of holm oak decline. However, F. oxysporum caused similar symptoms on oak seedlings as P. chinnamomi, and was isolated also from the roots, although its frequency was lower than that of. P. cinnamomi.
This research identifies the root pathogen Phytophthora cinnamomi as the primary cause of mortality in a 300-ha disease center of mixed oak trees in a native forest in southern Mexico. In increasing order of apparent field resistance to the disease, the major oak species are Quercus glaucoides, Q. peduncularis, and Q. salicifolia. P. cinnamomi was isolated from soil in the affected area from symptomatic trees and was successfully used to perform Koch's postulates on these three oak species. Artificial and natural infections produced vertically elongated discolorations in the outer xylem and distinctive phloem canker lesions with a sharp demarcation line between healthy and affected tissues. In Q. glaucoides there is little evidence that this oak species is able to resist the girdling effects of the phloem lesions, but in Q. peduncularis, and especially in Q. salicifolia, increased production of callus tissue around the phloem canker lesions suggests an active resistance mechanism that may allow these infected trees to survive somewhat longer. This particular incident is unlike other recent reports in other parts of the world of oak mortality caused by P. cinnamomi because the initial appearance of disease in this area is known (just prior to 1987), and it has subsequently expanded to the present area of 300 ha (in 1999) as a distinctive infection locus with periodically advancing infection fronts. This incident is also another dramatic illustration of the potential environmental damage that can result when P. cinnamomi is introduced into a simple forest ecosystem where the major overstory trees are susceptible to infection and are killed.
