What's New

New Phytopathology article accepted for publication
Strong genetic differentiation between North American and European populations of Phytophthora alni subsp. uniformis
Mr. Jaime Aguayo, Dr. Gerard C. Adams, Dr. Fabien Halkett, Dr. Mursel Catal, Mr. Claude Husson, Zoltán Á. Nagy, Dr. Everett Hansen, Dr. Benoit Marçais, and Dr. Pascal Frey
 
Pytopathology 0 0:ja
 
Alder decline caused by Phytophthora alni has been one of the most important diseases of natural ecosystems in Europe during the last 20 years. The emergence of Phytophthora alni subsp. alni (Paa)—the pathogen responsible for the epidemic—is linked to an interspecific hybridization event between two parental species: Phytophthora alni subsp. multiformis (Pam) and Phytophthora alni subsp. uniformis (Pau). One of the parental species, Pau, has been isolated in several European countries and recently in North America. The objective of this work was to assess the level of genetic diversity, the population genetic structure, and the putative reproduction mode and mating system of Pau. Five new polymorphic microsatellite markers were used to contrast both geographical populations. The study comprised 71 isolates of Pau collected from 8 European countries and 10 locations in North America. Our results revealed strong differences between continental populations (Fst=0.88; Rst=0.74), with no evidence for gene flow. European isolates showed extremely low genetic diversity compared to the North American collection. Selfing appears to be the predominant mating system in both continental collections. The results suggest that the European Pau population is most likely alien and derives from the introduction of a few individuals, while the North American population probably is an indigenous population.
 
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Eukaryotic Cell early release article
Sudden Oak Death: interactions of the exotic oomycete Phytophthora ramorum with naïve North American hosts. 
Matteo Garbelotto and Katherine J. Hayden
Eukaryotic Cell EC.00195-12; published ahead of print 21 September 2012, doi:10.1128/EC.00195-12
 
 
 
Ten years after a threatening and previously unknown disease of oaks and tanoaks appeared in coastal California, a significant amount of progress has been made towards the understanding of its causal agent Phytophthora ramorum and of the novel pathosystems associated with this exotic organism. However, a complete understanding of the ecology and epidemiology of this species still eludes us. In part, our inability to fully understand this organism is due to its phylogenetic, phylogeographic, phenotypic, and epidemiological complexity, all reviewed in this paper. Most lines of evidence suggest the high disease severity reported in California is not simply due to a generalized lack of resistance or tolerance in naïve hosts, but also to an innate ability of the pathogen to survive in unfavorable climatic conditions and to reproduce rapidly when conditions become once again favorable.
 
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Wood Focus Magazine, 22 Sep 2012

Tackling larch enemies - genetic analysis of Phytophthora ramorum.

British forestry scientists have identified a new lineage of a deadly tree pathogen that could devastate Japanese larch populations in the UK and oak species in the USA.

The Phytophthora ramorum (P. ramorum) pathogen causes ramorum disease, which is responsible for diseases in more than 120 plant species around the world. Genetic analysis has confirmed the fourth genetically distinct lineage of the pathogen – one that separated from the pathogen’s other strains thousands of years ago.

The California Oak Mortality Task Force in the USA and the UK Forestry Commission are looking to arrest the disease’s progress. Spokesperson for the US organisation, Katharine Palmieri, explains, ‘Each lineage is distant enough from the other that, if reintroduced to one another, unintended consequences could occur, such as mating successfully with each other and creating a hybrid that could be more virulent.’

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Thousands of trees felled in disease outbreak

Get Surrey By Jennifer Maxfield  September 11, 2012

THOUSANDS of trees in Surrey have been felled after a highly destructive disease was found in the south east for the first time.

Ramorum disease, caused by the fungus-like pathogen phytophthora ramorum, has infected woodland near Dorking and it could easily spread to other areas.

Around 7,000 trees in the county have been felled so far while 1,000 have been removed in West Sussex. The Forestry Commission became concerned that trees were showing symptoms during a helicopter survey of the region in June and ground-based checks confirmed their fears

The disease has been responsible for the premature felling of more than three million larch trees in the UK since it was first found in the West Country in 2009.

Most cases have occurred in the wetter, western parts of Britain as well as Ireland and the Isle of Man.

This month’s confirmation that the disease has reached the south east is the first time it has affected the region's larches.

Alison Field, south-east England director for the Forestry Commission, described it as "bitterly disappointing" news.

Evidence of the disease. Pic: Forestry Commission Picture Library/Isobel Cameron

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Fatal juniper fungus spreads to new sites

Sep 10, 2012 The Teesdale Mercury

A DISEASE that is threatening to wipe out Teesdale’s juniper bushes has spread to other areas of the UK. 
The fungus-like phytophthora austrocedrae was first found in juniper trees on Natural England’s Moor House estate in the upper dale last year.

The disease infects the plant through the root system causing the foliage to decline and eventually die.

Now, after investigations by the Food and Environment Research Agency (FERA), the disease has been found at nine new sites.

A spokesperson for Natural England said: “Since we reported the phytophthora outbreak in Moor House and upper Teesdale National Nature Reserve in March, there has been confirmation of a small, isolated infected area on the other side of the River Tees. All other tests over the remaining juniper area were negative and the extent of the restricted area has been reduced following public consultation.”

 As well as the further outbreak in the North East, phytophthora has been found in several sites in Cumbria and at one private garden in Devon. The levels of infected juniper found at the sites range from five per cent to 100 per cent.
 

Steps to contain the disease have been in place in upper Teesdale since the outbreak was identified.
 

 
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USDA, CDFA applaud Dominican research

Dominican Universtiy of California news release
Researchers from National Ornamentals Research Site at Dominican University of California (NORS-DUC) have successfully eliminated Phytophthora ramorum, the pathogen that causes sudden oak death, from the infested soil at a quarantined nursery in California using a non-chemical method that could be used at quarantined sites throughout the state.

Studies conducted at both the NORS-DUC facility in San Rafael and at a commercial nursery in the San Joaquin Valley, which had been under quarantine due to P. ramorum infestation for the past 12 months, show that steaming infected soil at temperatures of 50°C and higher for 30 minutes completely eliminated P. ramorum from previously infected soil.

“This steam treatment research is a giant step toward controlling the serious nursery plant disease Phytophthora ramorum in infested California nurseries,” said Robert Leavitt, the California Department of Food and Agriculture’s director of Plant Health Inspection. “The CDFA is committed to working with the California nursery industry to maintain California's reputation of producing high quality disease-free nursery plants.”

Based on the NORS-DUC results, the USDA has requested that the research team conduct steaming at additional quarantined nurseries in California.

“Our findings support steam as a viable mitigation option in nursery field settings for this pathogen of quarantine significance,” said Dr. Sibdas Ghosh, chair of Dominican’s Department of Natural Sciences and Mathematics Principal Investigator at NORS-DUC.

 

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September 2012 Plant Disease Disease Note

First Report of Phytophthora palmivora Causing Foliar Blight of Pachira aquatica in Florida
A. J. Palmateer, R. A. Cating, P. Lopez, and I. Maguire

Plant Disease 2012 96:9, 1375-1375

 

Pachira aquatica Aubl. is a member of the Bombaceae, indigenous to Central America and northern South America. Known as the money tree within the ornamental plant industry, this tropical species is well adapted to landscapes in south Florida, Hawaii, and milder areas in southern California. Recently, it's become more popular as a potted plant for use in the interiorscape. During August 2011, several local nurseries submitted P. aquatica samples to the Florida Extension Plant Diagnostic Clinic in Homestead, FL. The foliage exhibited dark brown to black water soaked spots that became papery as the disease progressed, and rapidly enlarged and coalesced, resulting in severe leaf blight. Both young and mature leaves were affected. Phytophthora was initially confirmed by serological testing with a commercially available ImmunoStrip test (Agdia, Elkhart, IN). On closer examination, the pathogen was further identified as Phytophthora palmivora by the presence of numerous papillate, deciduous, ellipsoidal to ovoid sporangia with short pedicels. The sporangia averaged 53 × 32 μm with ranges of 48 to 59 × 29 to 35 μm (1). Phytophthora species-specific primers (pal1s and pal2a) targeting part of the 18S rRNA gene, the ITS 1, the 5.8S rRNA gene, and the ITS 2 resulted in a PCR product of 648 bp, testing positive for P. palmivora (2).

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Fourth genetic lineage of Phytophthora ramorum pathogen identified

Issued jointly with the California Oak Mortality Task Force. 

British forestry scientists have identified a fourth genetically distinct lineage of the Phytophthora ramorum (P. ramorum) pathogen which is causing devastating tree diseases in the UK and the USA.

P. ramorum causes ramorum disease of larch trees in the United Kingdom (UK) and Ireland and sudden oak death disease of oak and tanoak trees in the USA, as well as diseases in more than 120 other plant species around the world.

It has been causing dramatic mortality in Japanese larch in the UK, including Northern Ireland and many western parts of Great Britain, especially southwest and north-west England, south Wales and southwest Scotland. The British Forestry Commission uses aerial surveys to detect outbreaks.

The increasing intensity of the P. ramorum outbreaks in the UK led researchers to analyze samples from the new findings further, which resulted in the discovery of a fourth genetically distinct lineage of the pathogen.

Announcing this at the Fifth Sudden Oak Death Symposium in California recently, Clive Brasier, an emeritus professor with the Forestry Commission's Forest Research agency, said he believed, based on genetic analysis, that the previously unknown European Type 2 (EU2) lineage had been recently introduced into south-west Scotland and Northern Ireland.

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New Plant Disease article

Identification and Detection of Phytophthora: Reviewing Our Progress, Identifying Our Needs
Frank N. Martin, Z. Gloria Abad, Yilmaz Balci, and Kelly Ivors

Plant Disease 2012 96:8, 1080-1103

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.

 

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Early view Forest Pathology article July 4, 2012

The destructive invasive pathogen Phytophthora lateralis found on Chamaecyparis lawsoniana across the UK

Green S, Brasier CM, Schlenzig A, McCracken A, MacAskill GA, Wilson M, Webber JF

In 2010–2011, Phytophthora lateralis was isolated from diseased Chamaecyparis lawsoniana exhibiting dieback and mortality at eight geographically separate forest, parkland and shelterbelt locations in England, Scotland and Northern Ireland. In 2011, P. lateralis was also isolated from young symptomatic nursery plants of C. lawsoniana and Thuja occidentalis recently imported into Scotland from mainland Europe. These are the first findings of P. lateralis in the UK. At six of the field sites, only collar and root lesions were observed. However, at two sites, large stem and branch lesions unconnected to the collar region were also observed. Phytophthora lateralis was readily isolated from both aerial and basal lesions. In artificial inoculation experiments, two Scottish isolates of the pathogen caused lesions on C. lawsoniana shoots and were readily reisolated from the lesions, their pathogenicity being comparable to that of P. lateralis isolates originating from outside the UK. Isolates from six field sites and the two nursery interceptions exhibited ITS and coxII sequences identical to published sequences of French and North American isolates. However, the isolates from two field sites shared an ITS sequence with Taiwanese isolates and differed from North American, French and Taiwanese isolates by a single-base substitution in coxII, suggesting a separate evolutionary history. It is clear that P. lateralis now presents a significant threat to C. lawsoniana in Britain. The main source of the outbreaks is likely to be imported infested nursery stock.

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