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Early view Forest Pathology article, 12 July 2013

Scanu, B., Hunter, G. C., Linaldeddu, B. T., Franceschini, A., Maddau, L., Jung, T., Denman, S. (2013), A taxonomic re-evaluation reveals that Phytophthora cinnamomi and P. cinnamomi var. parvispora are separate species. Forest Pathology. doi: 10.1111/efp.12064

Between 2008 and 2011, severe dieback associated with root and collar rot was reported on Arbutus unedo in several sites in Sardinia, Italy. Isolations from infected tissues and rhizosphere soil samples consistently yielded a Phytophthora species. It was initially identified as Phytophthora cinnamomi var. parvispora Kröber and Marwitz by comparing morphological features with the original description and the internal transcribed spacer (ITS) sequences with those present in GenBank. A multigene phylogeny based on DNA sequence data from two nuclear (ITS and β-tubulin) and two mitochondrial (cox1 and cox2) gene regions combined with extensive morphological and physiological properties of these isolates, including the ex-type culture of P. cinnamomi var. parvispora, demonstrates that this taxon is unique and it is redesignated here as Phytophthora parvispora sp. nov. Although morphologically similar to P. cinnamomi, P. parvispora differs by its smaller-sized sporangia, chlamydospores, oogonia and oospores, higher oospore wall index, single-celled antheridia, higher minimum and maximum temperatures for growth and faster growth at optimum temperature. In the phylogeny, P. parvispora falls within Phytophthora ITS clade 7a, grouped in a well-supported clade sister to P. cinnamomi. In pathogenicity tests, P. parvispora and P. cinnamomi were equally aggressive towards A. unedo seedlings. The possible geographic origin of P. parvispora is also discussed.

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Early view Journal of Phytopathology article 8 July 2013

Chandelier, A., Heungens, K. and Werres, S. (2013), Change of Mating Type in an EU1 Lineage Isolate of Phytophthora ramorum. Journal of Phytopathology. doi: 10.1111/jph.12150

Abstract

All Phytophthora ramorum EU1 lineage isolates tested are of A1 mating type, except for three rare isolates from 2002 to 2003 from Belgium, which were originally assigned the A2 mating type. In one of these isolates (2338), a switch from A2 to A1 mating type was observed in 2006. This observation initiated a larger study in which all cultures and subcultures of the original three EU1 A2 isolates, maintained in three laboratories under different storage conditions, were checked for mating type change. The A2 to A1 mating type switch was observed in four of seven independently maintained isolates that were derived from isolate 2338 in two laboratories, using different transfer regimes and storage conditions. Following the mating type switch to A1 in these four derived isolates, no reversion back to A2 mating was observed, even after up to 5 years of additional isolate maintenance and several more subculturing events. The three other isolates that were derived from isolate 2338 as well as the other EU1 A2 isolates collected in 2002 and 2003 and stored in the same conditions did not display such mating type change. The potential causes of the mating type conversions as well as their epidemiological implications are discussed.

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Forest must be cleared after Sudden Oak Death disease discovered

Newsletter (Northern Ireland) 13 June 2013

More than 100 hectares of forest in Northern Ireland are to be cleared to help stop the spread of a deadly tree disease.

An outbreak of the infection caused by Phytophthora ramorum - or Sudden Oak Death as it is also known - has been confirmed in larch trees at Castlewellan Forest Park, Co Down, the Forest Service said.

Chief executive Malcolm Beatty said: “We are very disappointed about this outbreak in Castlewellan as it is further evidence that the disease is continuing to spread.

“We will clear over 100 hectares of forest to reduce the risk of the disease spreading to other forest species, and to recover as much of the timber as is possible.”

The disease was identified when many trees that were apparently healthy last autumn showed symptoms during the spring. Many have already died. Action to fell the trees is under way because this is the most effective way of preventing further spread.

Trees develop lesions and their shoots and foliage become wilted.

Visitors to the park have been urged to make sure their feet are clear of soil before visiting other areas to prevent spread of the infection.

 
Natural Resources Wales steps up fight against larch disease

News Wales 25 Jun 2013

Natural Resources Wales has committed more than £2 million into the fight to deal with a disease which is attacking Britain’s larch trees.

The new body, which looks after the Welsh environment, is to invest £500,000 straight away to combat Phytophthora ramorum (P ramorum) by cutting down trees around the edges of infected areas to try to stop it from spreading further.The urgent strategy also includes a groundbreaking trial to see if injecting trees with a common herbicide could be effective in slowing the spread of the disease.

Natural Resources Wales will spend a further £1.7 million to remove infected trees, replant those areas and to build forest roads so that new areas can be cleared.

Trefor Owen from Natural Resources Wales said:“This response shows how concerned we are about this disease because of its impact on timber markets, the landscape, woodland and other habitats.

“We understand the anxiety this is causing the private forestry sector and communities in the affected areas. We are liaising with the Welsh Government and affected forest owners to see how the economic and other impacts can be minimised.”The disease, which spreads through airborne spores from tree to tree, is proving difficult to contain and has moved more quickly than experts expected despite a massive effort to stop it in its tracks.

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Juniper tree disease threatens G&T

The Telegraph Thursday 20 June 2013

Phytophthora austrocedrae has been spotted on juniper bushes in the Lake District and Scotland.

 

The fungus could wipe out the delicate population of native juniper bushes in Britain Photo: ALAMY

 

The fungus could wipe out the delicate population of native juniper bushes in Britain.

The bluey green bushes used to be found around the country but are now confined to a few chalkland sites around the UK.

Many southern English counties have lost 60-70 per cent of their populations of juniper due to loss of habitat.

Now they are even more at risk if the disease spreads.

Some 45 per cent of Scottish trees are at risk of being wiped out by the fungus.

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New Disease Reports article 18 Jun 2013

Grijalba PE, Palmucci HE, Guillin E, Herrera C, 2013. Phytophthora multivora causing leaf spot on rhododendrons in Argentina. New Disease Reports 27, 20. DOI: 10.5197/j.2044-0588.2013.027.020

Rhododendron is a genus belonging to the family Ericaceae and contains over 1000 species commonly known as rhododendrons and azaleas (Dimitri, 1978). Phytophthora multivora is a species that was described in Western Australia in 2008 but before that it was misidentified as . citricola (Scott et al., 2009). During the early spring of 2011, leaf spot symptoms were observed on rhododendrons in two gardens in Tigre (northern Buenos Aires province) and in containers in a nursery near Buenos Aires city. Leaf spots were dark brown to almost black, visible on both sides near the leaf tips and margins, while tissue death continued down the leaf along the midrib (Fig. 1A). The veins under the diseased area of the leaves presented a reddish tint (Fig. 1B). Some leaves became brown and died, while in others the infection remained as spots on leaves.

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Early view Forest Pathology article, 15 June 2013

Mulholland, V., Schlenzig, A., MacAskill, G. A., Green, S. (2013), Development of a quantitative real-time PCR assay for the detection of Phytophthora austrocedrae, an emerging pathogen in Britain. Forest Pathology. doi: 10.1111/efp.12058

A TaqMan real-time PCR assay was developed for Phytophthora austrocedrae, an emerging pathogen causing severe damage to juniper in Britain. The primers amplified DNA of the target pathogen down to 1 pg of extracted DNA, in both the presence and absence of host DNA, but did not amplify any of the non-target Phytophthora and fungal species tested. The assay provides a useful tool for screening juniper populations for the disease.

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Early view Forest Pathology article, 10 April 2013

Than, D. J., Hughes, K. J. D., Boonhan, N., Tomlinson, J. A., Woodhall, J. W., Bellgard, S. E. (2013), A TaqMan real-time PCR assay for the detection of Phytophthora ‘taxon Agathis’ in soil, pathogen of Kauri in New Zealand. Forest Pathology. doi: 10.1111/efp.12034

Kauri Agathis australis, an iconic tree of New Zealand, is under threat from an introduced disease-causing pathogen provisionally named Phytophthora ‘taxon Agathis’ (referred to as PTA). This soilborne, Pythiaceous species belongs to the Chromista and causes a collar rot resulting in yellowing of the foliage and thinning of the canopy, which eventually causes death of the infected tree. The management and containment of this pathogen requires rapid and reliable detection in the soil. The current method for soil detection utilizes a soil bioassay involving lupin baits and soil flooding in a process that takes between ten and twenty days. We describe a real-time PCR assay based on TaqMan chemistry for the specific detection of PTA, which targets the internal transcribed spacer (ITS) region of the nuclear ribosomal DNA. This TaqMan real-time PCR assay could be used with DNA extracted directly from bulk soil samples to enable rapid quantification of PTA within soil. The detection limit was 2 fg of PTA DNA from pure culture, or 20 fg in the presence of DNA extracted from soil. The assay was validated using soil samples taken from a PTA-infested site and soil spiked with a known concentration of oospores. We conclude that the TaqMan real-time PCR assay offers a more time-efficient method for detection of PTA in soil than existing methods.

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March 2013 Biological Invasions article

Challenges in predicting invasive reservoir hosts of emerging pathogens: mapping Rhododendron ponticum as a foliar host for Phytophthora ramorum and Phytophthora kernoviae in the UK. Bethan V. Purse, Philipp Graeser, Kate Searle, Colin Edwards, Catriona Harris. Biological Invasions March 2013, Volume 15, Issue 3, pp 529-545. DOI: 10.1007/s10530-012-0305-y

Abstract: Invasive species can increase the susceptibility of ecosystems to disease by acting as reservoir hosts for pathogens. Invasive hosts are often sparsely recorded and not in equilibrium, so predicting their spatial distributions and overlap with other hosts is problematic. We applied newly developed methods for modelling the distribution of invasive species to the invasive shrub Rhododendron ponticum—a foliar reservoir host for the Phytophthora oomycete plant pathogens, P. ramorum and P. kernoviae, that threaten woodland and heathland habitat in Scotland. We compiled eleven datasets of biological records for R. ponticum (1,691 points, 8,455 polygons) and developed Maximum Entropy (MaxEnt) models incorporating landscape, soil and climate predictors. Our models produced accurate predictions of current suitable R. ponticum habitat (training AUC = 0.838; test AUC = 0.838) that corresponded well with population performance (areal cover). Continuous broad-leaved woodland cover, low elevation (<400 m a.s.l.) and intermediate levels of soil moisture (or Enhanced Vegetation Index) favoured presence of R. ponticum. The high coincidence of suitable habitat with both core native woodlands (54 % of woodlands) and plantations of another sporulation host, Larix kaempferi (64 % of plantations) suggests a high potential for spread of Phytophthora infection to woodland mediated by R. ponticum. Incorporating non-equilibrium modelling methods did not improve habitat suitability predictions of this invasive host, possibly because, as a long-standing invader, R. ponticum has filled more of its available habitat at this national scale than previously suspected.

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Journal of Phytopatholgy early view article 3 April 2013

Tooley, P. W., Browning, M. and Leighty, R. M. (2013), Inoculum density relationships for infection of some eastern US forest species by Phytophthora ramorum. Journal of Phytopathology. doi: 10.1111/jph.12107

Our objectives were to establish inoculum density relationships between P. ramorum and selected hosts using detached leaf and whole-plant inoculations. Young plants and detached leaves of Quercus prinus (Chestnut oak), Q. rubra (Northern red oak), Acer rubrum (red maple), Kalmia latifolia (mountain laurel) and Rhododendron ‘Cunningham's White’ were dip-inoculated with varying numbers of P. ramorum sporangia, and the total number of diseased and healthy leaves recorded following incubation at 20°C and 100% relative humidity. Calibration threshold estimates for obtaining 50% infected leaves based on linear analysis ranged from 36 to 750 sporangia/ml for the five hosts. Half-life (LD50) estimates (the number of spores for which the per cent of diseased leaves reaches 50% of its total) from asymptotic regression analysis ranged from 94 to 319 sporangia/ml. Statistically significant differences (P = 0.0076) were observed among hosts in per cent infection in response to increased inoculum density. Inoculum threshold estimates based on studies with detached leaves were comparable to those obtained using whole plants. The results provide estimates of inoculum levels necessary to cause disease on these five P. ramorum hosts and will be useful in disease prediction and for development of pest risk assessments.

 

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