Emergence of the sudden oak death pathogen Phytophthora ramorum.
Grünwald NJ, Garbelotto M, Goss EM, Heungens K, Prospero S.
Trends Microbiol. 2012 Mar;20(3):131-8. Epub 2012 Feb 9.
Reference...
What's New
Newly published article in Trends Microbiol.
Are grey squirrels implicated in spreading P. ramorum?
From The Forestry Commision, Great Britain, 10 February 201
Is the spread of ramorum disease linked to grey squirrels?
Helicopter aerial surveys are being used to detect symptoms of dieback or crown colour change in trees. The cause of the symptoms then has to be established with ground surveys and, in the case of P. ramorum, is usually then confirmed by laboratory analysis.
The surveys have concentrated mainly on larch in the western region of Britain, where the climatic conditions favour P. ramorum. Ground surveys have confirmed that much of the dieback detected in larch through the aerial surveys is due to squirrel bark stripping damage.
No sites were confirmed infected by P. ramorum as well as damaged by squirrels. On a few sites (11 out of 317, or 3.5%) there are suggestions of the co-occurrence of squirrel damage and Phytophthora infection. However, this does not demonstrate cause and effect, and we should be very cautious about presuming or suggesting a link between damage by squirrels (grey or red) and Phytophthora disease.
The results from the aerial surveys demonstrate the usefulness of this as a tool to identify areas of dieback. They have identified the presence of extensive squirrel damage on larch in some areas, but because the surveys are regionally focused, this is not a country-wide view of where squirrel damage to larch is occurring.
Does P. ramorum enter trees via a wound such as might be made by squirrel damage?
Plant Pathology Early View article 17 Feb 2012
Response of selected South Australian native plant species to Phytophthora cinnamomi
Kueh KH, McKay SF, Facelli E, Facelli JM, Velzeboer RMA, Able AJ, Scott ES
10.1111/j.1365-3059.2012.02593.x
Thirty-seven South Australian native plant species from 11 families, including 15 threatened species in the state (of which six are listed as threatened under the federal Environment Protection and Biodiversity Conservation Act 1999) were assessed for response to infection by Phytophthora cinnamomi. Seedlings, 3-6 months old and grown in a greenhouse, were inoculated by placing infested pine wood plugs in the potting mix, maintained in moist conditions and assessed for mortality and disease symptoms for between 3 and 10 months. Thirty species were found to be susceptible, of which nine were highly susceptible, 15 moderately susceptible and six slightly susceptible. Three species were found to be resistant and results for four species were inconclusive. Six of the 15 threatened, rare or locally endangered species tested (Eucalyptus viminalis var. viminalis, Correa aemula, C. calycina, Olearia pannosa ssp. pannosa, Pomaderris halmaturina ssp. halmaturina and Prostanthera eurybioides) were moderately susceptible, while two (Allocasuarina robusta and Pultenaea graveolens) were highly susceptible.Significant populations of at least five of the threatened species susceptible to the disease are located close to confirmed or suspected Phytophthora-infested areas or growing in areas conducive for P.cinnamomi. An effective management strategy is therefore required to avoid extinction of such species due to infection by the phytophthora dieback pathogen.
P. austrocedrae - New disease identified in native juniper trees in Upper Teesdale
Forestry Commission, 9 February 2012
A damaging plant disease that was until recently almost unknown in Britain has been confirmed in rare native juniper bushes at the Moor House-Upper Teesdale National Nature Reserve in the North Pennines of England.
The disease is caused by Phytophthora austrocedrae, a fungus-like organism that infects the plant through the root system and causes the foliage to decline and eventually die.
Juniper is a native conifer and a member of the Cypress (Cupressaceae) family of plants. P. austrocedrae infection was only confirmed in the UK last year on other trees from this family, at two sites in Scotland.
The source of the infection is unknown: P. austrocedrae is difficult to identify because it is rare, and there is only limited information available about it. However, the Forestry Commission scientists who identified it believe it can be transmitted in ground water, infected plant material and contaminated soil, making further spread very difficult to prevent.
It is especially serious because juniper is quite rare in the UK. The Teesdale juniper population is the second largest in the UK and is protected as part of a Special Area of Conservation (SAC).
First report of Phytophthora alni subsp. uniformis on black alder in Spain
Mrs. Cristina Pintos Varela, Miss Cristina Rial Martínez, Dr. Olga Aguín Casal, Dr. José Pedro Mansilla Vázquez, and Miss Aitana Ares Yebra
Plant Disease 2012
Phytophthora alni is the causal organism responsible for devastating losses occurring on riparian alder stands in Europe. This emergent hybrid pathogen has multiple variants that have been placed in three subspecies (1). P. alni subsp. uniformis and P. alni subsp. multiformis are reported to be less aggressive than P. alni subsp. alni, though both are considered pathogenic (2, 3). In Spain, P. alni subsp. alni was detected for the first time in 2009 in Galicia (NW Spain) causing root and collar rot on riparian alder populations (3,4), but other subspecies had not been identified. In April 2011 a survey along the Deza river in Galicia was carried out in order to clarify the Phytophthora species associated with the alder decline. Thirty riparian A. glutinosa stands from both sides of the river, were surveyed. Samples of bark and roots of 18 alders stands that showed symptoms of Phytophthora rot, and soil from all the thirty stands, were collected.
8 Species Added to P. ramorum Host List
FEDERAL ORDER
Domestic quarantine for Phytophthora ramorum
DA-2012-03
January 25, 2012
This Federal Order is issued pursuant to the regulatory authority provided by the Plant Protection Act of June 20, 2000, as amended, Section 412(a), 7 U.S.C. 7712(a), which authorizes the Secretary of Agriculture to prohibit or restrict the movement in interstate commerce of any plant, plant part, or article, if the Secretary determines the prohibition or restriction is necessary to prevent the dissemination of a plant pest within the United States and is likewise issued pursuant to the regulations promulgated under the Plant Protection Act found at 7 CFR §301.92 et seq.
The Administrator of the Animal and Plant Health Inspection Service (APHIS) considers it necessary in order to prevent the spread and dissemination of P. ramorum, to add eight new plant species to the list of associated plant taxa. Additionally, the APHIS administrator has determined it is necessary to move one currently regulated species Cinnamomum camphora from the list of associated plant taxa to the list of proven host plant taxa. The movement of nursery stock of these plant taxa from the States of California, Oregon, and Washington will now be regulated in accordance with this Federal Order and the P. ramorum regulations located at 7 CFR §301.92. Nurseries in the regulated states containing these newly listed plants must operate under a compliance agreement.
The State Regulatory Agencies in the United States, Canadian Food Inspection Agency (CFIA), and the United Kingdom’s Department for Environment, Food, and Rural Affairs, Food and Environment Research Agency (DEFRA /FERA) have identified additional plants associated with P. ramorum that were not previously recorded. Details on these detections are as follows:
Newly published Forest Pathology article, February 2012
Phytophthora ramorum is a generalist plant pathogen with differences in virulence between isolates from infectious and dead-end hosts
D. Hüberli and M. Garbelotto
Volume 42, Issue 1, pages 8–13, February 2012
Variation in virulence was examined among isolates of Phytophthora ramorum from epidemiologically important or infectious (non-oak) and transmissive dead-end (oak) hosts from North America. Twelve isolates representative of the genetic, geographic and host range of P. ramorum in the western United States were inoculated on leaves of Umbellularia californica (bay laurel or bay) and stems of Quercus agrifolia (coast live oak). In spite of extreme genetic similarity among the isolates employed, and even within the same genotype, significant differences in lesion size were measured, suggesting virulence in this pathogen is also controlled by epigenetic factors. A strong positive correlation between lesion size on bay laurel and coast live oak provides experimental evidence P. ramorum is a generalist pathogen that lacks host specificity. Isolates from non-transmissive oaks were significantly less pathogenic both on oaks and bays than isolates from infectious hosts. These results are essential to further our understanding of the epidemiology and evolutionary potential of this pathogen. A quantitative differential in virulence of isolates from hosts with different epidemiological roles has been described for many animal diseases, but is a novel report for a plant disease.Forest Pathology
Detour keeps walkers away from sick kauri
Auckland Now, North Shore Times, by Maryke Penman 26/01/2012
A soil and water borne disease has ravaged kauri trees along the Okura bush walk, forcing a realignment of the popular track.
Phytophthora taxon agathis (PTA) infects the roots of kauri trees causing the yellowing of foliage, canopy thinning and lesions in the bark that bleed resin.
Most infected kauri die as a result and the disease, found in microscopic spores in soil, has killed thousands of trees since it was discovered in 2008.
In December the Conservation Department began the track upgrade at Okura from Haigh Access Rd to Dacre Cottage in Karepiro Bay.
DOC spokesman Peter Smith says the upgrade will ensure the track can be used all year round and it should reduce the spread of kauri dieback to the remaining healthy trees.
The upgrade covers 4.5km of the Okura bush walkway and is due to be completed by the end of February.
"In recent years the track has deteriorated and in winter becomes unusable for all but the hardiest trampers and runners," Mr Smith says.
DYING OFF: An example of a dieback lesion where resin
bleeds from the lower part of the trunk.
- © Fairfax NZ News
Plant Pathology Early View article 16 Jan 2012
Alteration of physiological parameters of Austrocedrus chilensis by the pathogen Phytophthora austrocedrae
M. L. Vélez, P. V. Silva, O. A. Troncoso, A. G. Greslebin
DOI: 10.1111/j.1365-3059.2011.02585.x
The effect of the pathogen Phytophthora austrocedrae on tree physiology of Austrocedrus chilensis in Patagonia was studied in a 4-week study. In the first week, stem-inoculated saplings showed a significant decrease in photosynthesis (A) without alteration of stomatal conductance (gs) or stem-specific hydraulic conductivity (Ks). From the second week on, progressive decreases in A, gs and Ks were observed, concomitantly with development of significant stem lesions. Water use efficiency (WUE) increased in the second week and declined progressively from the third week. Hyphae and resinous materials were observed in tracheids and rays below lesions. Necrosis of parenchyma ray cells and blockage of tracheids torus were observed. Healthy xylem showed no resinous materials or tracheid blockage, but abundant starch in rays, which was absent in altered xylem. The culture filtrate (CF) of the pathogen was shown to induce changes in extracellular pH and conductivity, and increased necrosis in tissues of leaves and stem challenged with CF in vitro. Similar results were obtained in leaf tissues of the inoculated saplings in vivo. CF injection into xylem of saplings induced a decline in A and disturbance of leaf tissue integrity, without altering gs, WUE or Ks. The decrease of A correlated with changes in tissue integrity. A possible mechanism of A. chilensis decline induced by P. austrocedrae is discussed.
More insidious hybrids of Phytophthora discovered
ScienceNetwork, Western Autralia
Written by Nic White Saturday, 14 January 2012
Scientists have discovered numerous new species of the water-mould Phytophthora in WA’s forests, heathland and waterways, some of which could pose a threat similar to the deadly Phytophthora cinnamomi, the most well-known cause of Phytophthora Dieback.
The new species include Phytophthora multivora, elongata, thermophila, fluvialis, arenaria, constricta, litoralis, gibbosa and gregata, which had not previously been found anywhere else, and eight exotic species never recorded before in WA.
The new species were identified using recent DNA technology that enabled them to be distinguished from similar species.
WA Department Environment and Conservation research scientist Mike Stukely says P.thermophila and P.constricta are among the most destructive and have been associated with “devastating” plant mortality in coastal heathlands following heavy summer rainfall.