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Deadly tree disease destroying swathes of Welsh woodland

 WalesOnline - Graham Henry, April 23, 2012

A deadly tree disease that is destroying swathes of Welsh woodland has now spread throughout the country.

The devastating Phytophtora Ramorum disease – known as Sudden Oak Death – prompted mass felling of the scenic Afan Valley forest area of Neath Port Talbot last year, and has now been recorded in North, Mid and West Wales, forestry experts said.

Researchers at Cambridge University have identified South Wales as a particular risk area in the UK if drastic control measures are not taken to control the epidemic.

Dr Matt Castle, a research associate at the University of Cambridge, said around 3,000 hectares of larch had been infected and felled as part of the response – around 2% of British woodland.

 

The risk models produced by the university – which predict the effect of different control measures – showed the greatest risk lay in Wales if no control measures were taken, and in particular the Afan Argoed area near Neath and Port Talbot.

The alternative is widespread felling in infected areas, which could mean large amounts of healthy trees being cut down.

Read More http://www.walesonline.co.uk/news/wales-news/2012/04/23/deadly-tree-disease-destroying-swathes-of-welsh-woodland-91466-30814101/#ixzz1tqzRzqOB

 
WA Flora being rescued from extinction by prior seed banks

Science Network, Western Australia.  April 23, 2012

The Mt Lesueur grevillea (Grevillea batrachioides) in Lesueur National Park is currently known from less than 65 plants. Image: Illawara Grevillea Park

A SEED conservation program is helping to save some of WA’s most threatened plant species from extinction.

Established in late 1992 by the Department of Environment of Conservation (DEC), the program was initially aimed at species affected by the root-rot pathogen Phytophthora cinnamomi (Phytophthora dieback).

Since then, seed collections have targeted species threatened by habitat fragmentation, salinity, weed invasion and, more recently, climate change.

Senior research scientist Anne Cochrane manages the DEC’s Threatened Flora Seed Centre, operating one of the largest and most comprehensive threatened flora translocation programs in Australia.

“Forty-six species are currently being recovered through this program using the seed resources from the centre,” she said.

“Species identified for translocation by DEC scientists have the required numbers of seeds germinated in the seed bank laboratory and the resultant seedlings are then given to the Kings Park-accredited nursery to grow before they are planted in existing or new translocation sites in the wild.

 

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New PLoS ONE article April 18, 2012

Phenotypic Diversification Is Associated with Host-Induced Transposon Derepression in the Sudden Oak Death Pathogen Phytophthora ramorum

Takao Kasuga, Melina Kozanitas, Mai Bui, Daniel Hüberli, David M. Rizz, Matteo Garbelotto

The oomycete pathogen Phytophthora ramorum is responsible for sudden oak death (SOD) in California coastal forests. P. ramorum is a generalist pathogen with over 100 known host species. Three or four closely related genotypes of P. ramorum (from a single lineage) were originally introduced in California forests and the pathogen reproduces clonally. Because of this the genetic diversity of P. ramorum is extremely low in Californian forests. However, P. ramorum shows diverse phenotypic variation in colony morphology, colony senescence, and virulence. In this study, we show that phenotypic variation among isolates is associated with the host species from which the microbe was originally cultured. Microarray global mRNA profiling detected derepression of transposable elements (TEs) and down-regulation of crinkler effector homologs (CRNs) in the majority of isolates originating from coast live oak (Quercus agrifolia), but this expression pattern was not observed in isolates from California bay laurel (Umbellularia californica). In some instances, oak and bay laurel isolates originating from the same geographic location had identical genotypes based on multilocus simples sequence repeat (SSR) marker analysis but had different phenotypes. Expression levels of the two marker genes analyzed by quantitative reverse transcription PCR were correlated with originating host species, but not with multilocus genotypes. Because oak is a nontransmissive dead-end host for P. ramorum, our observations are congruent with an epi-transposon hypothesis; that is, physiological stress is triggered on P. ramorum while colonizing oak stems and disrupts epigenetic silencing of TEs. This then results in TE reactivation and possibly genome diversification without significant epidemiological consequences. We propose the P. ramorum-oak host system in California forests as an ad hoc model for epi-transposon mediated diversification.

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Forest Pathology article February 2012

Detection of mRNA by reverse-transcription PCR as an indicator of viability in Phytophthora ramorum

A. Chimento, S. O. Cacciola, M. Garbelotto

In the last few decades, the use of molecular tools has greatly improved the efficiency of plant disease diagnosis. However, one of the major setbacks of most molecular diagnostic approaches is their inability to differentiate between dead and viable pathogens. We propose a new strategy for the detection of plant pathogens, based on the use of mRNA as a viability marker, on the basis that mRNA degradation in dead cells is significantly more rapid than that of DNA. A real-time reverse-transcription PCR (RT-PCR) assay targeting the mRNA of the subunit I of the cytochrome oxidase gene was designed for Phytophthora ramorum, the causal agent of sudden oak death and ramorum blight. In controlled laboratory tests, the developed RT-PCR assay did not detect the target mRNA a week after the pathogen had been killed by rapid lyophilization, while DNA of the pathogen could still be detected 3 months after the pathogen had died. The RT-PCR assay was then compared with a traditional culturing approach using PARP selective medium and two nested real-time PCR techniques on symptomatic California bay laurel leaves. Samples were either collected in three different sites in July, or in the same site but in three different seasons. Overall, RT-PCR results showed less positive samples than DNA-based nested PCR techniques (p < 0.0001), but more than culturing (p = 0.017). Nested PCR-positive but RT-PCR-negative samples may not be viable. On the other hand, RT-PCR-positive but culture-negative samples may be viable but dormant. A comparative analysis of the results indicated that RT-PCR and culturing provide comparable results when climatic conditions are optimal for the pathogen, but RT-PCR may be the most accurate approach to determine pathogen viability when climatic conditions are less than optimal for the pathogen.

 

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Early view Plant Pathology article April 24, 2012

Survival of Phytophthora ramorum in Rhododendron root balls and in rootless substrates.

A. Vercauteren, M. Riedel, M. Maes, S. Werres, K. Heungens

This study assesses the survival of Phytophthora ramorum in the root ball of Rhododendron container plants as well as in different rootless forest substrates and a horticultural potting medium. Following inoculation of the root balls, the aboveground plant parts stayed symptomless, whilst the pathogen could be recovered with a novel non-destructive baiting assay from the root balls until at least 8 months post-inoculation. Plating of surface-sterilized roots and direct microscopic analysis confirmed the presence of P. ramorum in the roots. Phytophthora ramorum could also be baited from the root balls of symptomless Rhododendron plants from commercial nurseries, even 2 years after acquisition. Survival of P. ramorum in rootless media was assessed after burying disks of infected leaf material below the soil surface in columns filled with four different undisturbed forest substrates or a potting medium, and incubated at an outdoor quarantine facility. Phytophthora ramorum could be recovered at least 33 months after burial from all substrates, with a significant increase in recovery after the winter period. These data suggest the possibility for long-term symptomless presence of P. ramorum in root balls of commercial Rhododendron plants as well as survival in potting medium and different forest substrates under western European climate conditions. Symptomless presence in root balls can contribute to latent spread of this pathogen between nurseries. The novel baiting test, being non-destructive, simple and applicable to a relatively large number of plants, can offer a valuable tool to test plants for the presence of Phytophthora species in root balls.

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Early view Journal of Phytopathology article April 2, 2012

Defining Plant Resistance to Phytophthora cinnamomi: A Standardized Approach to Assessment.
Jane A. Allardyce, James E. Rookes, and David M. Cahill.

Article first published online: 2 APR 2012

Phytophthora cinnamomi is a soil-borne plant pathogen that causes devastating disease in agricultural and natural systems worldwide. While a small number of species survive infection by the pathogen without producing disease symptoms, the nature of resistance, especially under controlled conditions, remains poorly understood. At present, there are no standardized criteria by which resistance or susceptibility to P. cinnamomi can be assessed, and we have used five parameters consisting of plant fresh weight, root growth, lesion length, relative chlorophyll content of leaves and pathogen colonization of roots to analyse responses to the pathogen. The parameters were tested using two plant species, Zea mays and Lupinus angustifolius, through a time course study of the interactions and resistance and susceptibility defined 7 days after inoculation. A scoring system was devised to enable differentiation of these responses. In the resistant interaction with Z. mays, there was no significant difference in fresh weight, root length and relative chlorophyll content in inoculated compared with control plants. Both lesion size and pathogen colonization of root tissues were limited to the site of inoculation. Following inoculation L. angustifolius showed a significant reduction in plant fresh weight and relative leaf chlorophyll content, cessation of root growth and increased lesion lengths and pathogen colonization. We propose that this technique provides a standardized method for plant–P. cinnamomi interactions that could be widely used to differentiate resistant from susceptible species.

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Early view Plant Pathology article 22 March 2012

Effect of electrical conductivity on survival of Phytophthora alni, P. kernoviae and P. ramorum in a simulated aquatic environment. 

P. Kong, J. D. Lea-Cox and C. X. Hong

This study investigated survival of the pathogens Phytophthora ramorum, P. alni and P. kernoviae as zoospores or sporangia in response to an important water quality parameter, electrical conductivity (EC), at its range in irrigation water reservoirs and irrigated cropping systems. Experiments with different strengths of Hoagland’s solution showed that all three pathogens survived at a broad range of EC levels for at least 3 days and were stimulated to grow and sporulate at ECs > 1·89 dS m−1. Recovery of initial populations after a 14-day exposure was over 20% for P. alni subsp. alni and P. kernoviae, and 61·3% and 130% for zoospores and sporangia of P. ramorum, respectively. Zoospore survival of these pathogens at ECs < 0·41 dS m−1 was poor, barely beyond 3 days in pure water; only 0·3% (P. alni), 2·9% (P. kernoviae) and 15·1% (P. ramorum) of the initial population survived after 14 days at EC = 0·21 dS m−1. The variation in rates of survival at different EC levels suggests that these pathogens survive better in cropping systems than in irrigation water. Containment of run-off and reduction in EC levels may therefore be non-chemical control options to reduce the risk of pathogen spread through natural waterways and irrigation systems.

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12,000 trees to be felled near Sabden

Burnley Express. March 23, 2012

 

THOUSANDS of disease-ridden trees are being given the chop at two beauty spots near Sabden.

Forestry workers have moved in to fell 12,000 trees at Black Hill and Churn Clough after a fungus-like infection hit woodland. Phytophthora ramorum is particularly serious in larch trees and hopes are to stop the disease from spreading to other plants and trees.

Harvesters have axed 1,500 trees from Black Hill and removed 300 tonnes of timber. But Lancashire County Council says it is now launching an assault on woodland around Churn Clough Reservoir to bring down 10,000 infected trees over the next six weeks.

Nick Osborne, from Lancashire County Council, said: “Work has begun to remove diseased trees from woodlands near Sabden. Black Hill and Churn Clough have seen an infection spread through the woodlands, meaning an estimated 12,000 larch trees need to be felled to stop it spreading.

“The disease is caused by a fungus-like pathogen and is particularly serious in larch. Once infected, it can pass to other trees and garden plants, most of which will die.

“Work in Black Hill is pretty much complete although there are smaller areas of larch that cannot be reached by the harvesting machine. These will be dealt with over the next few weeks.

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Play it safe to protect kauri from rampant disease

nzherald.co.nz

By Brian Rudman, Monday Mar 12, 2012


Photo / James Shook, Wikimedia

Auckland Council biosecurity experts want 23km of tracks in the Waitakere Regional Park closed in an attempt to stop the spread of the deadly disease sweeping through the kauri population.

Kauri dieback in the Waitakere Ranges began causing concern about five years ago and after a recent census of each kauri in the park, it's believed nearly 1000, or 8 per cent, are visibly infected, with another 3 per cent "doubtful".

Councillors at tomorrow's meeting of the Parks Recreation and Heritage Forum, will be asked to take a "precautionary approach" and quarantine areas of kauri that appear to be healthy until the experts can come up with a possible cure or treatment. A similar approach is being foreshadowed for stands of kauri in the Hunua Ranges regional parks, which appear to have so far escaped the ravages of the killer phytophthora taxon Agathis (PTA).

Jack Craw, AC biosecurity manager says "I call it the HIV for kauri, and where we were three years ago was where they were with HIV 30 years ago. They knew they had something that was killing, but they didn't know what it was or how it spread."

 

He says the organism and how it is spread, have been pinned down, and while they still don't know how to kill it, "we know how to stop it spreading by appropriate behaviours".

In research work over the past three years, not only has the disease been identified as a foreign (almost certain) import that has been lurking around, possibly since the 1950s or longer. It has also been ascertained that its spores hitch a ride on damp soil, or clay - of which the Waitakeres have plenty.

 

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Forest Pathology Early View article 2 March 2012

Behaviour and survival of Phytophthora cambivora inoculum in soil-like substrate under different water regimes
 
Vannini A, Breccia M, Bruni N, Tomassini A, Vettraino AM
 
Phytophthora cambivora is a soil-borne pathogen responsible for root and collar rot of woody species including Castanea spp., on which it causes Ink disease. P. cambivora does not produce chlamydospores, and the prevalence of a single mating type in nature limits the production of oogonia and oospores. Thus, survival of P. cambivora, in the absence of suitable hosts, relies mainly on sporangia, zoospores and mycelium. However, inoculum survival in soils or substrates represents a major factor in disease epidemics and is probably dependant on environmental factors. The aim of this article was to study the behaviour of P. cambivora in a peat-based substrate (PbS) in the absence of a host, under controlled conditions, and by varying the substrate water regimes. Total inoculum in the substrate was quantified by qPCR, using customized rDNA primer sets, whilst zoospores were quantified after elution, and their vitality was determined by a specific staining procedure. Inoculum infectivity was assessed using chestnut root baits. Results indicated that during the initial 48 h after infestation (matric potential, pF 1.2; 70% water content), the inoculum level increased producing microsporangia and mycelium before decreasing, regardless of the water regime applied. The number of free zoospores increased over a period of (maximum) 7 days after substrate inoculation. Vitality of zoospores declined to 45% at day 18, with no statistical differences amongst water regime treatments. Both rDNA and zoospore number increased in flooded samples at day 23, illustrating the vitality of the inoculum. Inoculum was able to infect chestnut root baits up to 45 days at pF 1.2 and 3.5, before and after flooding, but at pF 6.3, only in the absence of flooding. Although based on experiments carried out in microcosms, these results highlight an unexpected resistance of P. cambivora zoospores to environmental constraints. Furthermore, the infectivity ability of the inoculum to survive in PbS over time even in the absence of the host adds relevance to the risk of movement of soil and substrates associated with plant trading worldwide.
 
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