What's New

New Plant Pathology article Jan 2020

Phytophthora agathidicida: research progress, cultural perspectives and knowledge gaps in the control and management of kauri dieback in New Zealand.

Bradshaw, RE, Bellgard, SE, Black, A, Burns, BR, Gerth, ML, McDougal, RL, Scott, PM, Waipara, NW, Weir, BS, Williams, NM, Winkworth, RC, Ashcroft, T, Bradley, EL, Dijkwel, PP, Guo, Y, Lacey, RF, Mesarich, CH, Panda, P, Horner, IJ.

Plant Pathology (2020) 69, 3–16, https://bsppjournals.onlinelibrary.wiley.com/doi/full/10.1111/ppa.13104

Kauri (Agathis australis), which is one of the world's largest and longest‐living conifer species, is under threat from a root and collar dieback disease caused by the oomycete pathogen Phytophthora agathidicida. The noted incidence of kauri dieback has increased in the past decade, and even trees >1000 years old are not immune. This disease has profound effects on both forest ecosystems and human society, particularly indigenous Māori, for whom kauri is a taonga or treasure of immense significance. This review brings together existing scientific knowledge about the pathogen and the devastating disease it causes, as well as highlighting important knowledge gaps and potential approaches for disease management. The life cycle of P. agathidicida is similar to those of other soilborne Phytophthora pathogens, with roles for vegetative hyphae, zoospores and oospores in the disease. However, there is comparatively little known about many aspects of the biology of P. agathidicida, such as its host range and disease latency, or about the impact on the disease of abiotic and biotic factors such as soil health and co‐occurring Phytophthora species. This review discusses current and emerging tools and strategies for surveillance, diagnostics and management, including a consideration of genomic resources, and the role these play in understanding the pathogen and how it causes this deadly disease. Key aspects of indigenous Māori knowledge, which include rich ecological and historical knowledge of kauri forests and a holistic approach to forest health, are highlighted.

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New Environmental Science & Policy article Nov. 2019

Global biogeography and invasion risk of the plant pathogen genus Phytophthora

Peter Scott; Martin K.-F. Bader; Treena Burgess; Giles Hardy; Nari Williams

New Environmental Science & Policy Volume 101, November 2019, Pages 175-182

Abstract: A global database of the pathogen genus Phytophthora, comprising ca. 12,500 disease reports over 142 years, was collated to benchmark and examine the genus-wide distribution and invasiveness. Rarefaction was used to estimate global Phytophthora species richness. We applied a framework, leveraging geographically and economically biased pathogen data against environmental and socioeconomic metrics to model their distribution. Hierarchical clustering of host and country range allowed characterisation of invasion potential. Phytophthora descriptions rose to 86 by the year 2000, surging to over 180 species to date driven primarily by novel molecular techniques, resulting in a species richness estimate of 326 (95% CI: 274–378). Countries with diverse ecosystems and entrenched agricultural and forestry industries supported by intensive research programmes reported the highest diversity. Constructing principal components from enviro-socioeconomic factors highlighted national data deficits, showing that two-thirds of trading nations have reported lower-than-predicted species numbers. Phytophthora species clustered into two main invasiveness groups as either cosmopolitan generalists or specialists, historically tied to agriculture. Further spread and detection of Phytophthora pathogens are inevitable with increasing global trade, especially in developing and emerging economies. Adoption of best practice diagnostics and enhanced resource and data sharing are crucial for coordinated global pathogen surveillance and biosecurity.

This research aimed to test the following hypotheses:

•The global distribution of Phytophthora species is associated with environmental, social and economic traits of different country’s.
•Models for Phytophthora diversity, incorporating environmental, social and economic characteristics, can be used to predict a countries trade risk.
Phytophthora species biogeography and host range can be used to predict invasiveness and a country’s conduciveness to infection.

 


New Plant Disease article September 2019

Variation in Susceptibility of Tanoak to the NA1 and EU1 Lineages of Phytophthora ramorum, the Cause of Sudden Oak Death

Kelsey L. Søndreli, Alan Kanaskie, Susanna Keriö, and Jared M. LeBoldus

Plant Disease https://apsjournals.apsnet.org/doi/10.1094/PDIS-04-19-0831-RE

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Abstract: Phytophthora ramorum, the cause of sudden oak death (SOD), kills tanoak (Notholithocarpus densiflorus) trees in southwestern Oregon and California. Two lineages of P. ramorum are now found in wildland forests of Oregon (NA1 and EU1). In addition to the management of SOD in forest ecosystems, disease resistance could be used as a way to mitigate the impact of P. ramorum. The objectives of this study were to (i) characterize the variability in resistance of N. densiflorus among families using lesion length; (ii) determine whether lineage, isolate, family, or their interactions significantly affect variation in lesion length; and (iii) determine whether there are differences among isolates and among families in terms of lesion length. The parameters isolate nested within lineage (isolate[lineage]) and family × isolate(lineage) interaction explained the majority of the variation in lesion length. There was no significant difference between the NA1 and EU1 lineages in terms of mean lesion length; however, there were differences among the six isolates. Lesions on seedlings collected from surviving trees at infested sites were smaller, on average, than lesions of seedlings collected from trees at noninfested sites (P = 0.0064). The results indicate that there is potential to establish a breeding program for tanoak resistance to SOD and that several isolates of P. ramorum should be used in an artificial inoculation assay.


New Plant Disease article July 2019

A qPCR Assay for the Detection of Phytophthora cinnamomi Including an mRNA Protocol Designed to Establish Propagule Viability in Environmental Samples | Plant Disease

Manisha B. Kunadiya, William D. Dunstan, Diane White, Giles E. St. J. Hardy, Andrew H. Grigg, and Treena I. Burgess

Plant Disease Vol. 103, No. 9, https://doi.org/10.1094/PDIS-09-18-1641-RE

Abstract: Phytophthora cinnamomi causes root and collar rot in many plant species in natural ecosystems and horticulture. A species-specific primer and probe PCIN5 were designed based on a mitochondrial locus encoding subunit 2 of cytochrome c oxidase (cox2). Eight PCR primers, including three forward and five reverse, were designed and tested in all possible combinations. Annealing temperatures were optimized for each primer pair set to maximize both specificity and sensitivity. Each set was tested against P. cinnamomi and two closely related clade 7 species, P. parvispora and P. niederhauseri. From these tests, five primer pairs were selected based on specificity and, with a species-specific P. cinnamomi probe, used to develop quantitative real-time PCR (qPCR) assays. The specificity of the two most sensitive qPCR assays was confirmed using the genomic DNA of 29 Phytophthora isolates, including 17 isolates of 11 species from clade 7, and representative species from nine other clades (all except clade 3). The assay was able to detect as little as 150 ag of P. cinnamomi DNA and showed no cross-reaction with other Phytophthora species, except for P. parvispora, a very closely related species to P. cinnamomi, which showed late amplification at high DNA concentrations. The efficiency of the qPCR protocol was evaluated with environmental samples including roots and associated soil from plants artificially infected with P. cinnamomi. Different RNA isolation kits were tested and evaluated for their performance in the isolation of RNA from environmental samples, followed by cDNA synthesis, and qPCR assay. Finally, a protocol was recommended for determining the presence of P. cinnamomi in recalcitrant environmental samples.

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New Phytopathology article

Promise and Pitfalls of Endemic Resistance for Cultural ResourcesThreatened by Phytophthora ramorum.  Richard C. Cobb, Noam Ross, Katherine J. Hayden, Catherine A. Eyre, Richard S. Dodd, Susan J. Frankel, Matteo Garbelotto, and David M. Rizzo.

Phytopathology2019109:760-769https://doi.org/10.1094/PHYTO-04-18-0142-R

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First Look Phytopatholgy article 6 May 2019

A microsatellite analysis identifies global pathways of movement of Phytophthora cinnamomi and the likely sources of wildland infestations in California and Mexico. https://apsjournals.apsnet.org/doi/10.1094/PHYTO-03-19-0102-R

Maria Socorro Serrano, Todd Osmundson, Alejandra Almaraz-Sanchez, Peter JP Croucher, Ted Swiecki, Dionisio Alvarado, and Matteo Garbelotto

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New Plant Disease article August 2018

First Report of Phytophthora ramorum Causing Japanese Larch Dieback in France.

N. Schenck, C. Saurat, C. Guinet, C. Fourrier-Jeandel, L. Roche, A. Bouvet, C. Husson, F.-X. Saintonge, C. Contal, and R. Ioos

Plant Disease 0 0:0, PDIS-02-18-0288-PDN

Phytophthora ramorum Werres, De Cock & Man in’t Veld, an oomycete known in the United States as the causal agent of sudden oak death, has spread across Europe since the early 2000s. It is responsible for damage and death to a wide range of plant species, including mature trees. In 2009 it was identified on Japanese larch (Larix kaempferi) in southwest England (Webber et al. 2010), and since then it has caused severe damage and losses to Larix spp. in the United Kingdom and the Republic of Ireland. There are two lineages of the oomycete, EU1 and EU2, found in Europe (King et al. 2015), EU2 being the more aggressive. The symptoms on larch include necrosis and loss of needles, wilting of shoots, dieback of branches, and death, often with abundant resin bleeding on trunks and branches. As sporulating hosts, Larix spp. may disperse P. ramorum over long distances. In May 2017, wilting, yellowing/reddening needles, and branch mortality were observed on mature Larix kaempferi (about 50 years old) in the forest of Saint-Cadou, Finistère, in the far northwestern part of France (3°59′49.2″ W; 48°22′22.4″ N)....

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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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