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Early view Forest Pathology article, 19 March 2013

Scanu, B., Linaldeddu, B. T., Franceschini, A., Anselmi, N., Vannini, A., Vettraino, A. M. (2013), Occurrence of Phytophthora cinnamomi in cork oak forests in Italy. Forest Pathology. doi: 10.1111/efp.12039

Summary

An increasing decline and mortality of cork oak trees have been recently observed in central Italy and Sardinia Island. Following surveys conducted in three declining cork oak forests, a Phytophthora species was consistently isolated from soil samples collected from trees displaying different level of decline. Based on morphological features, growth rates at different temperatures and analysis of DNA sequences of the ITS region, all isolates were identified as Phytophthora cinnamomi Rands. This pathogen caused large brownish lesions on inoculated freshly cut branches of cork oak. It was re-isolated from all infected tissues. These findings represent the first report of P. cinnamomi on cork oak trees in Italy.

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Early view Forest Pathology article, 11 March 2013

Pérez-Sierra, A., López-García, C., León, M., García-Jiménez, J., Abad-Campos, P., Jung, T. (2013), Previously unrecorded low-temperature Phytophthora species associated with Quercus decline in a Mediterranean forest in eastern Spain. Forest Pathology. doi: 10.1111/efp.12037

Oak decline has been a serious problem in Europe since the beginning of the twentieth century. In south-west Spain, Quercus ilex and Q. suber are the main affected species, and their decline has been associated with Phytophthora cinnamomi. During the last 10 years, a severe decline of Q. ilex and Q. faginea accompanied by a significant decrease in the production of acorns affecting natural regeneration was observed in the eastern part of the Iberian Peninsula. Therefore, the aim of this study was to investigate the possible involvement of Phytophthora spp. in the decline. A forest in the Natural Park ‘Carrascar de la Font Roja’ in Comunidad Valenciana (eastern Spain), which is dominated by Q. ilex and Q. faginea, was surveyed during 2010–2011. Symptomatic trees showed thinning and dieback of the crown, withering of leaves and death. An extensive loss of both lateral small woody roots and fine roots and callusing or open cankers on suberized roots were observed. Soil samples containing fine roots were baited using both Q. robur leaves and apple fruits. Six Phytophthora species were isolated: P. cryptogea, P. gonapodyides, P. megasperma, P. quercina, P. psychrophila and P. syringae. These are the first records of P. quercina and P. psychrophila on Q. faginea, of P. quercina in Spain and of P. psychrophila in mainland Spain. A soil infestation trial was conducted for 6 months under controlled conditions with 1-year-old seedlings of Q. ilex and Q. faginea. Phytophthora cinnamomi was included in the pathogenicity test for comparison. The results showed that Q. ilex seedlings were generally more susceptible to infection than Q. faginea with P. cinnamomi being the most aggressive pathogen to both oak species. The two most commonly isolated Phytophthora species, P. quercina and P. psychrophila, also proved their pathogenicity towards both Q. ilex and Q. faginea.

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Early view Forest Pathology article, 13 February 2013

Crone, M., McComb, J. A., O'Brien, P. A., Hardy, G. E. S. J.Assessment of Australian native annual/herbaceous perennial plant species as asymptomatic or symptomatic hosts of Phytophthora cinnamomi under controlled conditions.  Forest Pathology. doi: 10.1111/efp.12027

Phytophthora cinnamomi is a necrotrophic pathogen of woody perennials and devastates many biomes worldwide. A controlled perlite–hydroponic system with no other hyphae-producing organisms as contaminants present allowed rapid assessment of ten annual and herbaceous perennial plant species most of which have a wide distribution within the jarrah (Eucalyptus marginata) forest in Western Australia where this pathogen has been introduced. As some annuals and herbaceous perennials have recently been reported as symptomatic and asymptomatic hosts, laboratory screening of some of the field-tested annuals and herbaceous perennials and additional species was used to further evaluate their role in the pathogen's disease cycle. Nine of the species challenged with the pathogen were asymptomatic, with none developing root lesions; however, Trachymene pilosa died. The pathogen produced thick-walled chlamydospores and stromata in the asymptomatic roots. Furthermore, haustoria were observed in the roots, indicating that the pathogen was growing as a biotroph in these hosts.

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Early view Forest Pathology article, 31 January 2013

Jung, T., Colquhoun, I. J., Hardy, G. E. St. J. (2013), New insights into the survival strategy of the invasive soilborne pathogen Phytophthora cinnamomi in different natural ecosystems in Western Australia. Forest Pathology. doi: 10.1111/efp.12025

Despite its importance as one of the most notorious, globally distributed, multihost plant pathogens, knowledge on the survival strategy of Phytophthora cinnamomi in seasonally dry climates is limited. Soil and fine roots were collected from the rhizosphere of severely declining or recently dead specimens of 13 woody species at 11 dieback sites and two dieback spots and from healthy specimens of five woody species at four dieback-free sites in native forests, woodlands and heathlands of the south-west of Western Australia (WA). Phytophthora cinnamomi was recovered from 80.4, 78.1 and 100% of tested soil, fine root and soil–debris slurry samples at the 11 dieback sites, in some cases even after 18-month storage under air-dry conditions, but not from the small dieback spots and the healthy sites. Direct isolations from soil–debris slurry showed that P. cinnamomi colonies exclusively originated from fine roots and root fragments not from free propagules in the soil. Microscopic investigation of P. cinnamomi-infected fine and small woody roots and root fragments demonstrated in 68.8, 81.3 and 93.8% of samples from nine woody species the presence of thick-walled oospores, stromata-like hyphal aggregations and intracellular hyphae encased by lignitubers, respectively, while thin-walled putative chlamydospores were found in only 21.2% of samples from five woody species. These findings were confirmed by microscopic examination of fine roots from artificially inoculated young trees of 10 woody species. It is suggested that (i) the main function of chlamydospores is the survival in moderately dry conditions between consecutive rain events and (ii) selfed oospores, hyphal aggregations, and encased hyphae and vesicles in infected root tissue of both host and non-host species are the major long-term survival propagules of P. cinnamomi during the extremely dry summer conditions in WA.

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Early view Plant Pathology article

Prospero, S., Vercauteren, A., Heungens, K., Belbahri, L. and Rigling, D. (2013). Phytophthora diversity and the population structure of Phytophthora ramorum in Swiss ornamental nurseries. Plant Pathology. doi: 10.1111/ppa.12027

Invasive oomycete pathogens have been causing significant damage to native ecosystems worldwide for over a century. A recent well-known example is Phytophthora ramorum, the causal agent of sudden oak death, which emerged in the 1990s in Europe and North America. In Europe, this pathogen is mainly restricted to woody ornamentals in nurseries and public greens, while severe outbreaks in the wild have only been reported in the UK. This study presents the results of the P. ramorum survey conducted in Swiss nurseries between 2003 and 2011. In all 120 nurseries subjected to the plant passport system, the main P. ramorum hosts were visually checked for above ground infections. Phytophthora species were isolated from tissue showing symptoms and identified on the basis of the morphological features of the cultures and sequencing of the ribosomal ITS region. Phytophthora was detected on 125 plants (66 Viburnum, 58 Rhododendron and one Pieris). Phytophthora ramorum was the most frequent species (59·2% of the plants), followed by P. plurivora, P. cactorum, P. citrophthora, P. cinnamomi, P. cactorum/P. hedraiandra, P. multivora and P. taxon PgChlamydo. The highest incidence of P. ramorum was observed on Viburnum × bodnantense. Microsatellite genotyping showed that the Swiss P. ramorum population is highly clonal and consists of seven genotypes (five previously reported in Europe, two new), all belonging to the European EU1 clonal lineage. It can therefore be assumed that P. ramorum entered Switzerland through nursery trade. Despite sanitation measures, repeated P. ramorum infections have been recorded in seven nurseries, suggesting either reintroduction or unsuccessful eradication efforts.

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Phytophthora ramorum found on larch in east Scotland

31 January 2013

Forestry Commission Scotland is advising woodland managers across Scotland of a confirmed case of Ramorum disease at Glen Dye, south of Banchory.

The outbreak is of concern because the fungus-like pathogen Phytophthora ramorum (‘Ramorum’) which causes the disease has so far been confined to the west coast of Scotland where the wetter climatic conditions are more suited to it.

Hugh Clayden, Tree Health Policy Adviser, for Forestry Commission Scotland, said:

“This outbreak is in a part of the country that is considered to be less climatically suitable for Ramorum - and which is also far from the nearest infected larch crops.

“We are currently investigating how the disease arrived at this location but one possibility is through unintentional transfer on vehicles using the public road. It serves as a timely reminder for everyone to remain alert to the risks to larch from P. ramorum and also highlights why biosecurity has become such an important part of forestry practice.

“Although the western half of Scotland is the most climatically suitable area for P. ramorum, given the right site and micro-climate conditions, coupled with suitable host species, it can occur anywhere. Early detection and rapid action are key to reducing the impacts of this disease and we are therefore most grateful to have received such a prompt and responsible response from the owner and manager of this site in taking swift action to remove the diseased trees.”

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New Annual Review of Phytopathology article

Phytophthora Beyond Agriculture

Everett M. Hansen, Paul W. Reeser, and Wendy Sutton

Vol. 50: 359-378 DOI: 10.1146/annurev-phyto-081211-172946

Little is known about indigenous Phytophthora species in natural ecosystems. Increasing evidence, however, suggests that a diverse, trophically complex Phytophthora community is important in many forests. The number of described species has steadily increased, with a dramatic spike in recent years as new species have been split from old and new species have been discovered through exploration of new habitats. Forest soil, streams, and the upper canopies of trees are now being explored for Phytophthora diversity, and a new appreciation for the ecological amplitude of the genus is emerging. Ten to twenty species are regularly identified in temperate forest surveys. Half or more of this Phytophthora diversity comes from species described since 2000. Taxa in internal transcribed spacer (ITS) Clade 6 are especially numerous in forest streams and may be saprophytic in this habitat. Three ecological assemblages of forest Phytophthora species are hypothesized: aquatic opportunists, foliar pathogens, and soilborne fine-root and canker pathogens. Aggressive invasive species are associated with all three groups.
New Forest Phytophoras Journal article Dec 2012

Riedel, M., Werres, S., Elliott, E., McKeever, K., Shamoun, S.F. 2012. Histopathological investigations of the infection process and propagule development of Phytophthora ramorum on rhododendron leaves. Forest Phytophthoras 2(1). doi: 10.5399/osu/fp.2.1.3036

Abstract

In Europe, cultivated rhododendron is one of the most important hosts for Phytophthora ramorum. To better understand leaf infection and leaf capacity for sporulation, infection studies were carried out. Detached leaves of Rhododendron ‘Catawbiense Grandiflorum ́ and `Brigitte ́ were inoculated with zoospore suspensions of P. ramorum isolates of mating type A1 and A2. ‘Catawbiense Grandiflorum’ developed much more leaf necrosis than ‘Brigitte’ (average necrotic leaf area after 55 days 106.5 mm2 versus 0.12 mm2). The trichomes on the ‘Brigitte’ leaves seemed to prevent the germ tubes from detecting the stomata. P. ramorum germ tubes from encysted zoospores invaded the leaf tissue via the stomata. Appressoria-like structures were observed. On the infected leaves new hyphae grew out of the stomata. Sporangia and chlamydospores developed on the mycelium from germinated zoospore cysts growing on the leaf surface as well as on the hyphae growing out of the stomata after infection. They could be observed mainly on the necrotic leaf areas. Single healthy-looking oospores developed within 12 days on the ‘Brigitte’ leaves. Observation of the infection process on leaves of Rhododendron ‘Cunningham’s White’ with the scanning electron microscope confirmed the various stages of the infection process.

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New Forest Phytophoras Journal article Dec 2012

Hansen, E., Reeser, P., Sutton, W., and Sims, L. 2012. Host and habitat index for Phytophthora species in Oregon. Forest Phytophthoras 2(1). doi: 10.5399/osu/fp.2.1.3026

Abstract

Phytophthora species are abundant in streams in healthy forests and widespread in forest soils causing cryptic diseases, in addition to their more traditional roles as aggressive pathogens. We compiled existing Oregon records from available sources of reliably identified Phytophthora species from forests and forest trees and summarized the results by host and habitat in an interactive online database. Details of documented isolates including locations, available cultures, Genbank acquisition numbers, and citations are in an accompanying supplemental spreadsheet. Thirty-two Phytophthora species have been identified associated with 25 host species from Oregon forests or forest trees. This total includes 19 species recovered from forest streams and 19 from forest soils, generally in the absence of noticeable disease on associated vegetation.

A total of 29 Phytophthora species were identified from the various environments in forests. Fourteen species came from trees or forest shrubs growing in cultivated and urban environments. Only three species were unique to the latter, however, including P. ilicis, from cultivated holly (Ilex), and P. sansomeana and P. taxon ceanothus from forest nurseries. Three species, P. gonapodyides, P. taxon oaksoil, and P. taxon salixsoil were recovered from streams in all surveyed counties. The most widespread species causing root disease or bole cankers of trees was P. lateralis on Port-Orford-cedar in landscape plantings throughout the state as well as on forest trees in its limited native range. P. cambivora and P. cinnamomi were widespread but uncommon on a number of forest trees.
Early view Forest Pathology article, 21 January 2013

Identification of Phytophthora species baited and isolated from forest soil and streams in northwestern Yunnan province, China

W.-x. Huai, G. Tian, E. M. Hansen, W.-x. Zhao, E. M. Goheen, N. J. Grünwald and C. Cheng

Forest Pathology DOI: 10.1111/efp.12015

Phytophthora species were surveyed by collecting soil samples and placing bait leaves in selected streams during June–October in the years 2005, 2006 and 2010 at three sites in oak forests in Diqing Tibetan Autonomous Prefecture of NW Yunnan province, China. Seventy-three isolates of Phytophthora spp. were recovered from 135 baited leaf samples and 81 soil samples. Eight Phytophthora species were identified by observation of morphological features and ITS1-5.8S-ITS2 rDNA sequence analysis. The eight taxa included two well-known species P. gonapodyides and P. cryptogea, two recently described species P. gregata and P. plurivora, two named but as yet undescribed taxa, P. taxon PgChlamydo and P. taxon Salixsoil, and two previously unrecognized species, Phytophthora sp.1 and P. sp.2. The most numerous species, P. taxon PgChlamydo, and the second most abundant species, P. taxon Salixsoil, were recovered at all three sites. Phytophthora cryptogea was detected only once at site Nixi. Phytophthora gregata and P. sp.2 were isolated from a stream only at site Bitahai, while the other three species were each found at two sites. Phylogenetic analysis revealed that the isolates belonged to three ITS clades, one species including six isolates in clade 2, six species including 66 isolates in clade 6 and one species in clade 8. There was a relatively rich species and genetic diversity of Phytophthora detected in the investigated regions where the forest biotic and abiotic factors affecting the growth and evolution of Phytophthora populations were diverse.

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