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Forest Pathology Early View article 12 March 2014

Strategies of attack and defence in woody plant–Phytophthora interactions. Forest Pathology. doi: 10.1111/efp.12096 Oßwald, W., et al.

This review comprises both well-known and recently described Phytophthora species and concentrates on Phytophthora–woody plant interactions. First, comprehensive data on infection strategies are presented which were the basis for three models that explain invasion and spread of Phytophthora pathogens in different woody host plants. The first model describes infection of roots, the second concentrates on invasion of the trunk, and the last one summarizes infection and invasion of host plants via leaves. On the basis of morphological, physiological, biochemical and molecular data, scenarios are suggested which explain the sequences of reactions that occur in susceptible and tolerant plants following infections of roots or of stem bark. Particular emphasis is paid to the significance of Phytophthora elicitins for such host–pathogen interactions. The overall goal is to shed light on the sequences of pathogenesis to better understand how Phytophthora pathogens harm their host plants.

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New Plant Disease article March 2014

Foliar Blight and Shoot Dieback Caused by Phytophthora ramorum on Viburnum tinus in the Pistoia Area, Tuscany, Central Italy

B. Ginetti, S. Carmignani, A. Ragazzi, S. Werres, and S. Moricca Plant Disease 2014 98:3, 423-423
In spring 2013, pot-grown Viburnum tinus plants shipped to an ornamental nursery in Pescia (Pistoia, central Italy, 287 m a.s.l., 43°54′0″ N, 10°41′0″ E) from another local nursery were found to bear disease symptoms. Symptoms included brown to black foliar lesions, later expanding into larger blotches; necrosis of the petioles; shoot wilting and folding; browning of the stems; and necrosis of the cambium. Infected leaves, shoots, and entire plants eventually died. Tissue samples (2 mm2) were cut at the edge of active lesions from tissue of the phloem, the xylem, and the leaves and plated on selective PARPNH V8 agar (V8A) (1). Rose-shaped and finely lobed cottony colonies arose in 2 to 3 days. Mono-hyphal colonies were isolated and transferred to V8A. Square colony pieces (1 cm2) from isolates SB05a and SB05b were placed in filtered pond water after 5 to 7 days. Semipapillate, caducous sporangia with a rounded or conical base were produced within 24 h, individually or in pairs, on each sporangiophore. Sporangia (n = 30 per isolate) were examined: they were 56.2 ± 9.5 × 29.3 ± 4.3 μm (l:b ratio 1.9 ± 0.3). Exit pores averaged 7.0 ± 1.0 μm. Sporangia were ellipsoid (30%), lemon-shaped (28.3%), ovoid (20%), obovoid (16.7%), ampulliform (3.3%), or “peanut-like” (1.7%). Globose chlamydospores, borne intercalarly or terminally, were abundant on both V8A and carrot agar (CA), and were on average 54.7 ± 8.5 μm. Mono-hyphal isolates incubated for 7 days at 23°C were also transferred to CA, corn meal agar (CMA), malt extract agar (MEA), potato dextrose agar (PDA), and V8A. Colonies on these media were identical in shape and appearance to those described in previous reports (2,4). Isolates were identified as Phytophthora ramorum Werres, De Cock & Man in't Veld (4) on the basis of colony type; size, the average l:b ratio and shape of sporangia; and the type and size of the chlamydospores. Isolates were found to be the A1 mating type by pairing them with P. cryptogea BBA 63651 (mating type A2). PCR-amplification of the rDNA ITS region with specific primers Ph1/Ph4 (3) gave fragments of the expected size (GenBank Accession Nos. KF181162 and KF181163). A BLAST search of these ITS sequences in the database found that isolates of P. ramorum were the closest phylogenetically with 100% homology (YQ653034 and HM004221). Pathogenicity tests were conducted on 16 detached V. tinus leaves. A small cut was made aseptically on each of the leaf surfaces and a V8A disc (0.5 cm Ø) with mycelium was placed over the wounds. Control leaves received only sterile V8A discs. Inoculated and control leaves were incubated at 23°C in the dark. Necrotic areas (average 3.5 ± 1.3 cm2) arose on inoculated leaves after 6 days. Control leaves had no symptoms. Re-isolations on PARPNH V8A confirmed P. ramorum as the causal agent. P. ramorum was reported in Italy in 2003 on the exotic Rhododendron yakushimanum (2). This is the first report of the pathogen on a native species (V. tinus) in this country. The Pistoia area is important for nursery gardens and flowers. P. ramorum, which probably arrived on infected plant material, could compromise the export/import trade in stock plants. For this reason, the plant protection services were promptly alerted and the infected plants were destroyed.
 

New Plant Disease article March 2014

Phytophthora cinnamomi as a Contributor to White Oak Decline in Mid-Atlantic United States Forests

M. E. McConnell and Y. Balci Plant Disease 2014 98:3, 319-327

http://dx.doi.org/10.1094/PDIS-06-13-0649-RE

To evaluate Phytophthora cinnamomi as a cause of white oak (Quercus alba) decline in mid-Atlantic forests, sampling was conducted at 102 sites from 2011 to 2012. Soil and roots from healthy and declining white oak trees were collected. Phytophthora spp. were isolated using baiting and CFU of P. cinnamomi quantified using wet-sieving. Fine roots were scanned and measured. Phytophthora spp. were isolated from 43% of the sites. P. cinnamomi was common; six other species were isolated infrequently. Little difference in lesion size existed on white oak seedlings inoculated with 32 isolates of P. cinnamomi; only 13 isolates caused significant mortality. Soils from white oak versus nine other hosts did not have significantly different CFU. P. cinnamomi was restricted to United States Department of Agriculture hardiness zones six and seven and never found in zone five. The presence of Phytophthora spp. in soil can be associated with white oak fine root health. When Phytophthora spp. were present, white oak trees in zones five and six had less fine roots. In mid-Atlantic oak forests, however, environmental conditions appear to play a key role in determining the impact of P. cinnamomi on the root system. P. cinnamomi alone does not appear to be a causal factor of white oak decline.

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Excavator forest mulcher clearing Phytophthora Ramorum infected Larch

YouTube video

Published on Jan 17, 2014 by Justin Kingwell


Diseased larch felling to have 'huge impact' on Manx landscape

BBC News Isle of Man by Ellan Vannin 14 January 2014

Aerial surveys by the Forestry Commission in 2011 showed the affected areas (photo).

Aerial surveys by the Forestry Commission in 2011 showed the affected areas

Work to fell hundreds of thousands of infected larch trees in the Isle of Man will begin this week after an "explosion" of a deadly tree disease.

According to the Manx government about 50% of the island's larch population is currently infected by Phytophthora ramorum.

Forester Jason Bolt said the essential work will have a "huge impact on the island's landscape".

The Forestry Division plans to fell 450 hectares (1,111 acres) of larch.

Senior forester John Walmsley said the disease, first detected on the island in 2010, had "exploded" since March.

In July, a survey by the Manx Forestry Directorate showed a "considerable spread" of the disease in the north of the island.

Since then it has spread to the south, east and west.

'Vital step'

Mr Bolt said: "Larch makes up around 20% of our forests and in the short term it will have a major impact."

Environment Minister Phil Gawne said it was a "vital step" for which "quick action was needed".

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Cork’s Gougane Barra Forest Park closing due to tree fungus

The Irish Times Monday, January 13, 2014 by Barry Roche

Coillte to fell 16,000 trees in major operation to control spread of the disease

Coillte has confirmed it is to close Gougane Barra Forest Park in Co Cork for six months to allow for a major tree-felling operation after the discovery of a tree fungus attack.

According to Coillte forestry productivity manager Padraig Ó Tuama, an outbreak of the fungus phytophthora ramorum has been discovered in the popular forest park near Ballingeary.

Mr Ó Tuama said Coillte had taken the decision to fell about 16,000 trees – primarily Japanese larch – in Gougane Barra to prevent the spread of the disease. “Phytophthora ramorum is a fungus-like disease that can affect a range of trees and other plant species, with Japanese larch particularly susceptible,” he said.

“Coillte have been working closely with the Department of Agriculture, Food and the Marine to detect and prevent the spread of this disease. Regrettably, Gougane Barra is one of 20 Coillte forests where the disease has been confirmed in Japanese larch since first detected on the species in 2010.”

 

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Forest Pathology Early View article 17 Dec 2013

Franceschini, S., Webber, J. F., Sancisi-Frey, S., Brasier, C. M. (2013), Gene × environment tests discriminate the new EU2 evolutionary lineage of Phytophthora ramorum and indicate that it is adaptively different. Forest Pathology. doi: 10.1111/efp.12085

A new evolutionary lineage of the destructive introduced tree pathogen Phytophthora ramorum, EU2 lineage, was recently discovered attacking larch and other hosts in Northern Ireland and south west Scotland, UK. Sixteen ‘medium × agar concentration × incubation temperature’ stress environments were tested to find a rapid and repeatable method to discriminate the known EU2 lineage from the EU1, NA1 and NA2 lineages in culture, in particular from the EU1 already prevalent across the UK; and to investigate whether EU2 might be adaptively different. At 28°C on both Carrot agar and V8 juice agar, the mean radial growth rates of all four lineages were significantly different, with NA2 > EU2 > EU1 > NA1. At this temperature, EU2 colonies were not only phenotypically distinct from EU1 and all other lineages but on average grew three times as fast as EU1. This indicates that EU2 is adaptively different from EU1. Twelve days growth in the environment ‘V8A/2% agar/28°C gave excellent discrimination of all four lineages in three repeat experiments, including clear discrimination of EU2 from EU1. Each lineage exhibited a distinctive colony pattern. The utility of this test environment was examined further by screening fresh UK isolates of unknown lineage from new larch outbreak sites alongside standard isolates. The lineage assignments predicted were corroborated by gene sequencing and RFLP profiling. These results also revealed that the EU2 lineage was present at several new larch sites in south west Scotland, whereas isolates from geographically adjacent areas such as the Isle of Mull, north west Scotland, the Isle of Man and north west England were all of EU1 lineage.

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New Plant Disease article January 2014

Dieback and Mortality of Pinus radiata Trees in Italy Associated with Phytophthora cryptogea

C. Sechi, S. Seddaiu, B. T. Linaldeddu, A. Franceschini, and B. Scanu

Plant Disease 2014 98:1, 159-159

Pinus radiata D. Don is a forest tree species native to the Monterey Baja in California. Due to its rapid growth and desirable lumber and pulp qualities, between 1960 and 1980, about 12,000 ha of P. radiata were planted in Sardinia, Italy. The only disease reported on this conifer species has been Diplodia pinea, which causes tip and branch dieback (3). In January 2012, dieback and mortality of 25-year-old radiata pine trees were observed in a reforestation area of about 20 ha located in northern Sardinia (40°43′N, 9°22′E, 600 m a.s.l.). Symptoms included chlorosis, reddish-brown discoloration of the whole crown or dieback starting in the upper crown and progressing downward through the crown, and necrotic bark tissues at root collar. Approximately 25% of the trees were affected. In a first attempt, a Phytophthora species was consistently isolated from the rhizosphere of 23 symptomatic trees, which included necrotic fine roots using oak leaves as bait (4). Afterwards, it was also isolated from phloem samples taken from the margins of fresh lesions at the stem base and upper roots of affected trees using synthetic mucor agar medium (1). Isolation from soil samples of six healthy pine trees randomly selected in the site did not yield any Phytophthora isolate. On carrot agar (CA), Phytophthora colonies were stellate to slightly radiate with limited aerial mycelium.

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Kauri fightback

The New Zealand Herald  By Geoff Cumming, Nov. 30, 2013

Reports of Tane Mahuta's demise may be premature but death could be just a stray boot away. The dieback disease threatening the forest kings of northern New Zealand is as bad as it gets: once the algae-like microbes infiltrate the kauri's root system, there is no cure. By the time symptoms show - leaf yellowing, canopy loss, withered branches, bleeding lesions and collar rot - it is likely too late.

Talk to scientists and agencies beavering away on the response and the messages are at once frightening and encouraging. The disease is a new species of phytophthora, from the Greek for plant destroyer. Different strains have devastated everything from strawberries, tomatoes and potatoes to forest giants like jarrah in Australia, oak trees in Europe and North American chestnuts.

The soil-borne variety attacking our kauri, known for now as PTA, has spread to 11 per cent of kauri stands in the Waitakere Ranges. It has footholds in the Waipoua Forest, home of Tane Mahuta, on Great Barrier Island (where it was first observed in the 1970s but mis-identified), in the Russell Forest and on private bush lots in Auckland and Northland.

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Christmas Trees Threatened by Root Rot

Sci-Tech Today.com    By Allen G. Breed   December 3, 2013

Phytophthora root rot is a stubborn enemy for some Christmas tree growers this year. With no fungicide yet proven effective to control Phytophthora, many growers are turning to species from Europe, Asia that are more resistant. Researchers at Washington State and other universities are hoping to unlock the secrets to some species' rot resistance.

Jeff Pollard trudged up the steep slope and stopped at a desiccated, rust-brown tree. Two months earlier, workers had tagged this Fraser fir as ready for market.

It was going to be someone's Christmas tree. And now it was dead.

"Never get paid back for this tree," he said with a shrug. "Eleven years of work -- gone."

The culprit: Phytophthora root rot, a water mold that, once in the soil, makes it unfit for production.

Pollard has been growing Fraser fir in these western North Carolina mountains for nearly 40 years. To him, it's "the ultimate tree."

But this persistent problem has him looking to a species from the birthplace of old Saint Nicholas himself for a possible alternative. And he's not alone.
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