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July 2018 Plant Disease article

An Overview of Canadian Research Activities on Diseases Caused by Phytophthora ramorum: Results, Progress, and Challenges.

Simon Francis Shamoun, Danny Rioux, Brenda Callan, Delano James, Richard C. Hamelin, Guillaume J. Bilodeau, Marianne Elliott, C. André Lévesque, Elisa Becker, Dan McKenney, John Pedlar, Karen Bailey, S. C. Brière, Kurt Niquidet, and Eric Allen

Plant Disease 2018 102:7, 1218-1233

International trade and travel are the driving forces behind the spread of invasive plant pathogens around the world, and human-mediated movement of plants and plant products is now generally accepted as the primary mode of their introduction, resulting in huge disturbance to ecosystems and severe socio-economic impact. These problems are exacerbated under the present conditions of rapid climatic change. We report an overview of the Canadian research activities on Phytophthora ramorum. Since the first discovery and subsequent eradication of P. ramorum on infected ornamentals in nurseries in Vancouver, British Columbia, in 2003, a research team of Canadian government scientists representing the Canadian Forest Service, Canadian Food Inspection Agency, and Agriculture and Agri-Food Canada worked together over a 10-year period and have significantly contributed to many aspects of research and risk assessment on this pathogen. The overall objectives of the Canadian research efforts were to gain a better understanding of the molecular diagnostics of P. ramorum, its biology, host-pathogen interactions, and management options. With this information, it was possible to develop pest risk assessments and evaluate the environmental and economic impact and future research needs and challenges relevant to P. ramorum and other emerging forest Phytophthora spp.

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Early View Forest Pathology article

Susceptibility to the rare Phytophthora tentaculata and to the widespread Phytophthora cactorum is consistent with host ecology and history. Early View article 2018. Laura Sims and Matteo Garbelotto.

We evaluated the susceptibility of three California endemic plant species Heteromeles arbutifolia, Platanus racemosa and Quercus agrifolia to the two congeneric soilborne pathogen species: Phytophthora tentaculata and Phytophthora cactorum. These pathogens were recently introduced in ecosystems east of the San Francisco Bay, where the three plant species above are dominant. Phytophthora cactorum has a worldwide distribution inclusive of California, and a broad host range. Phytophthora tentaculata, in contrast, is suspected to be a “new” exotic to California and has been described on relatively few hosts. By separately challenging the roots and the stems of the three plant species above, we show that: (a) Both were equally pathogenic, but the type of disease differed based on host; (b) disease was consistent with host ecology and with previous disease reports, even if caused by different Phytophthora spp. and; (c) there were intraspecific differences in virulence. This study provides the following significant information regarding the management and early modelling of polyphagous soilborne Phytophthoras: (a) Endemic species can be as problematic as recently introduced exotics. (b) Multiple introductions should be avoided due to varying virulence levels among genotypes. (c) Riparian species like P. racemosa may develop disease tolerance in their root systems, but remain susceptible in their aerial portions, and thus, diseases could be facilitated by flooding or splash of infectious structures of soilborne pathogens onto aerial plant portions.

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Early View Forest Pathology article

Diversity of Phytophthoraspecies in Valdivian rainforests and association with severe dieback symptoms.

The Valdivian rainforest, one of the global hotspots of biodiversity, is a temperate rainforest originating as a Tertiary relic from the supercontinent Gondwana. In November 2014, a survey of Phytophthora diversity was performed in 13 natural forest stands and 20 forest streams and rivers in two protected areas near Valdivia and in a temperate montane forest in the Concepción area. One planted stand each of the introduced tree species Castanea sativa and Fagus sylvatica were also included. Using baiting assays, eight described species and four previously unknown taxa of Phytophthora were isolated from 86% of the 50 rhizosphere soil samples from seven of the eight tree species sampled in 12 forest stands, and from 20 streams: P. chlamydospora, P. cinnamomi, P. kernoviae, P. lacustris, P. plurivora, P. pseudosyringae, P. ×cambivora, P×stagnum, P. valdiviana nom. prov. from Clade 2b, P. madida nom. prov. from Clade 8a, and P. chilensis nom. prov. and P. pseudokernoviae nom. prov. The latter two species are the closest relatives of P. kernoviae from Clade 10. Phytophthora pseudokernoviae nom. prov. was also isolated from necrotic leaves of Drimys winteri. From the Valdivia river, a swarm of three Clade 6 hybrids was recovered. Each hybrid isolate resulted from multiple reticulation events with P. thermophila as maternal and both P. amnicola and P. chlamydospora as paternal parents. In addition, three previously unknown and recently described Nothophytophthora species, N. caduca, N. chlamydospora and N. valdiviana, were isolated from several forest streams. Phytophthora cinnamomi, the most common and widespread species in soils of native forests, was associated with severe dieback of Valdivian rainforest trees, in particular D. winteri, Luma apiculata, Nothofagus dombeyi and the endangered Saxegothaea conspicua. A first pathogenicity test demonstrated high aggressiveness of P. cinnamomi to several native tree species, including N. dombeyi, Blepharocalyx cruckshanksii and Gevuina avellana.

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New Plant Disease article
J. M. LeBoldus, K. L. Sondreli, W. Sutton, P. Reeser, S. Navarro, A. Kanaskie, and N. J. Grünwald

Plant Disease 2018 102:2, 455-455

Sudden oak death (SOD) is caused by the introduced oomycete pathogen Phytophthora ramorum S. Werres, A. W. A. M. de Cock & W. A. Man in’t Veld. This fungus-like organism has four clonal lineages: NA1, NA2, EU1, and EU2 (Grünwald et al. 2016; Prospero et al. 2007). Until recently, the NA1 lineage was the only clonal lineage of P. ramorum reported in wildland forests in the western United States. In contrast, EU1, NA1, and NA2 have all been found in U.S. nurseries (Grünwald et al. 2012). In the winter of 2015, a symptomatic Notholithocarpus densiflorus Manos, Cannon & S.H.Oh (tanoak) was identified during a SOD helicopter survey in Curry County, OR. P. ramorum was isolated from symptomatic bark tissue. Subsequently, the isolate was determined to be of the EU1 lineage based on 14 microsatellite loci (Grünwald et al. 2016).....

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New Plant Disease article posted Dec. 2017

First report of alder Phytophthora closely related to P. uniformis on Alnus glutinosa seedling in Finland. 

A. Poimala, S. Werres, T. Pennanen, and J. Hantula' Plant Disease 0 0:0, PDIS-03-17-0322-PDN
 
The allotriploid Phytophthora × alni (Brasier & S.A. Kirk) Husson, Ioos & Marcais and its progenitors, the diploid P. uniformis (Brasier & S.A. Kirk) Husson, Ioos & Aguayo and the allotetraploid P. × multiformis (Brasier & S.A. Kirk) Husson, Ioos & Frey are the causal agents of alder decline in Europe. In June 2015, a dark, ∼40 mm stem lesion was found on one out of 100 inspected Alnus glutinosa (L.) Gaertn seedlings in Mäntyharju, Finland. Surface wood pieces from the lesion edges were plated onto malt agar. Cultures on carrot piece agar (CPA) showed an appressed colony with woolly aerial mycelium. Oogonia (Ø mean 44.8 µm, n = 50) and oospores (Ø mean 40.0 µm, n = 50) developed after 7 days at 20°C in the dark. They were commonly smooth walled, and 49 out of 50 of the amphigynous antheridia were single celled. Sporangia (21.7 × 18.1 µm, n = 50) were produced on pea broth, with 2-day flooding with soil extract, and they were commonly unpapillate and obpyriform-ellipsoidal. DNA was extracted, and the internal transcribed spacer (ITS) rDNA was amplified (ITS6 and ITS4; Cooke et al. 2000). The PCR products were then cloned because of double peaks in the sequence. Among 33 clones, four alleles with five polymorphic bases were obtained (A1, 55%; A2, 6%; A3, 15%; and A4, 24%; these were deposited in GenBank as accession nos. MF356294, MF356295, MF356296, and MF356297, respectively). The closest match to the ITS allele sequences in GenBank was the very closely related species P. cambivora AF087479 (differences, 7 to 9 bases). All other sequenced regions showed single alleles. The mitochondrial cox spacer (MF356298; amplified by FMPhy8 and FMPhy10, Martin et al. 2004) matched 100% with P. cambivora P1431 (GU221955) and P. alni P16202 (GU221933) in GenBank. A partial beta tubulin gene (MF356299; amplified by 901F and 1401R, Bilodeau et al. 2007) matched 100% with P. uniformis ALN58 (KU899249). ASF-like, GPA1, RAS-Ypt, and TRP1 genes were amplified with primers by Ioos et al. (2006). GPA1 (MF356301) matched 100% with P. uniformis PAU84 (DQ092849), and RAS-Ypt (MF356302) had exact matches with four P. uniformis isolates in GenBank (e.g., PANM53 and EU371549). The TRP1 gene (MF356303) differed by 1 base from P. uniformis alleles PAU60 (DQ202480) and PAU89 (DQ202481). The ASF-like gene (MF356300) matched 100% with PAU84 (DQ092815). Nine 1-year-old seedlings of A. glutinosa and of Betula pendula Roth were inoculated with plugs from 10-day-old mycelial culture on CPA after making a bark incision. Nine control seedlings of each species received a sterile CPA plug. Inoculations were wrapped in damp cotton wool, and the plants were kept outdoors at 10 to 22°C. After 15 days, eight out of nine (89%) A. glutinosa seedlings had developed lesions (mean length 22 mm), as well as six out of nine (67%) B. pendula seedlings (mean length 4 mm). No lesions were observed in control seedlings. The pathogen was reisolated from two symptomatic seedlings of both hosts. This is the first report of an alder Phytophthora in Finland. The sequence data suggested the isolate to be closely related but dissimilar to P. uniformis. The morphology corresponded to that previously reported for P. uniformis (Brasier et al. 2004), except for the antheridia, which were almost all single celled. Multiple ITS alleles could also refer to the initially reported P. uniformis karyotype 2n+2 (Brasier et al. 2004). These findings add to our knowledge on the variation among the alder Phytophthora group. Furthermore, they demonstrate the risk that the pathogen could be transported in new hosts.
 
 

New Phytopathology article December 2017

Morphological and Genetic Analyses of the Invasive Forest Pathogen Phytophthora austrocedri Reveal that Two Clonal Lineages Colonized Britain and Argentina from a Common Ancestral Population

Béatrice Henricot, Ana Pérez-Sierra, April C. Armstrong, Paul M. Sharp, and Sarah Green. Phytopathology 2017. 107:12, 1532-1540 https://apsjournals.apsnet.org/doi/abs/10.1094/PHYTO-03-17-0126-R
 
Phytophthora austrocedri is causing widespread mortality of Austrocedrus chilensis in Argentina and Juniperus communis in Britain. The pathogen has also been isolated from J. horizontalis in Germany. Isolates from Britain, Argentina, and Germany are homothallic, with no clear differences in the dimensions of sporangia, oogonia, or oospores. Argentinian and German isolates grew faster than British isolates across a range of media and had a higher temperature tolerance, although most isolates, regardless of origin, grew best at 15°C and all isolates were killed at 25°C. Argentinian and British isolates caused lesions when inoculated onto both A. chilensis and J. communis; however, the Argentinian isolate caused longer lesions on A. chilensis than on J. communis and vice versa for the British isolate. Genetic analyses of nuclear and mitochondrial loci showed that all British isolates are identical. Argentinian isolates and the German isolate are also identical but differ from the British isolates. Single-nucleotide polymorphisms are shared between the British and Argentinian isolates. We concluded that British isolates and Argentinian isolates conform to two distinct clonal lineages of P. austrocedri founded from the same as-yet-unidentified source population. These lineages should be recognized and treated as separate risks by international plant health legislation.
 

Forest Phytophthoras volume 7 Special Issue: Sudden Oak Death Management

Forest Phytophthoras vol. 7 can be viewed and downloaded at:
http://journals.library.oregonstate.edu/ForestPhytophthora

This special issue of Forest Phytophthoras contains five peer-reviewed articles on management of sudden oak death in California and Oregon (USA) with a foreward by Susan J. Frankel, guest editor. It serves as part of the proceedings from the Sixth Sudden Oak Death Science Symposium held June 21 - 23, 2016 at Fort Mason Center in San Francisco, CA, USA.


Proceedings for the 8th IUFRO meeting in Viet Nam available

Phytophthora in Forests and Natural Ecosystems, Proceedings of the 8th Meeting of the International Union of Forest Research Organizations (IUFRO) Working Party S07-02-09 are available for download at http://forestphytophthoras.org/proceedings


Early view Phytopathology article July 2017

 Morphological and genetic analyses of the invasive forest pathogen Phytophthora austrocedri reveal two clonal lineages colonised Britain and Argentina from a common ancestral population.

Béatrice Henricot, Ana Pérez-Sierra, April Armstrong, Paul Sharp, and Sarah Green

Phytopathology, Vol. 0, No. ja http://apsjournals.apsnet.org/doi/abs/10.1094/PHYTO-03-17-0126-R

Phytophthora austrocedri is causing widespread mortality of Austrocedrus chilensis in Argentina and Juniperus communis in Britain. The pathogen has also been isolated from J. horizontalis in Germany. Isolates from Britain, Argentina and Germany are homothallic with no clear differences in the dimensions of sporangia, oogonia or oospores. Argentinian and German isolates grew faster than British isolates across a range of media and had a higher temperature tolerance although most isolates regardless of origin grew best at 15°C and all isolates were killed at 25°C. Argentinian and British isolates caused lesions on both hosts when inoculated onto A. chilensis and J. communis; however the Argentinian isolate caused longer lesions on A. chilensis than on J. communis and vice versa for the British isolate. Genetic analyses of nuclear and mitochondrial loci showed that all British isolates are identical. Argentinian isolates and the German isolate are also identical but differ from the British isolates. Single nucleotide polymorphisms are shared between the British and Argentinian isolates. It is concluded that British isolates and Argentinian isolates conform to two distinct clonal lineages of P. austrocedri founded from the same as-yet unidentified source population. These lineages should be recognised and treated as separate risks by international plant health legislation.


Early view Phytopathology article
Ms. Justine Beaulieu, Mr. Blain B Ford, and Dr. Yilmaz Balci. Phytopathology 0 0:ja
 
Genetic diversity of two Phytophthora species, P. cinnamomi (102 isolates) and P. plurivora (186), commonly encountered in Maryland nurseries and forests in the Mid-Atlantic United States was characterized using amplified fragment length polymorphism (AFLP). Expected heterozygosity and other indices suggested a lower level of diversity among P. cinnamomi than P. plurivora. Hierarchical clustering showed P. cinnamomi isolates separated into four clusters, and two of the largest clusters were closely related, containing 80% of the isolates. In contrast, P. plurivora isolates separated into six clusters, one of which included approximately 40% of the isolates. P. plurivora isolates recovered from the environment (e.g. soil, water) were genotypically more diverse than those found causing lesions. For both species, isolate origin (forest vs. nursery or among nurseries) was a significant factor of heterozygosity. Clonal groups existed within P. cinnamomi and P. plurivora and included isolates from both forest and nurseries, suggesting that a pathway from nurseries to forests or visa verse exists.
 

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