Phytophthora Austrocedri Research Articles

Utility of decision tools for assessing plant health risks from management strategies in natural environments.

Increased imports of plants and timber through global trade networks provide frequent opportunities for the introduction of novel plant pathogens that can cross-over from commercial to natural environments, threatening native species and ecosystem functioning. Prevention or management of such outbreaks relies on a diversity of cross-sectoral stakeholders acting along the invasion pathway. Yet, guidelines are often only produced for a small number of stakeholders, missing opportunities to consider ways to control outbreaks in other parts of the pathway. We used the infection of common juniper with the invasive pathogen Phytophthora austrocedri as a case study to explore the utility of decision tools for managing outbreaks of plant pathogens in the wider environment. We invited stakeholders who manage or monitor juniper populations or supply plants or management advice to participate in a survey exploring their awareness of, and ability to use, an existing decision tree produced by a coalition of statutory agencies augmented with new distribution maps designed by the authors. Awareness of the decision tree was low across all stakeholder groups including those planting juniper for restoration purposes. Stakeholders requested that decision tools contain greater detail about environmental conditions that increase host vulnerability to the pathogen, and clearer examples of when management practices implicated in pathogen introduction or spread should not be adopted. The results demonstrate the need to set clear objectives for the purpose of decision tools and to frame and co-produce them with many different stakeholders, including overlooked groups, such as growers and advisory agents, to improve management of pathogens in the wider environment.

Silviculture of South American temperate native forests

Background: South America has the largest area of temperate forests in the Southern Hemisphere, which grow in diverse site conditions. The aim of this paper is to review the practices of silviculture applied and recommended for these temperate forests, and to discuss prospects to develop new silvicultural proposals to improve sustainability, adaptation and in-situ conservation of forest ecosystems. Methods: We reviewed the silviculture knowledge in four major forest types: 1) The Nothofagus-dominated forests of south-central Chile; 2) the Angiosperm-dominated evergreen forests; 3) the Nothofagus and Austrocedrus chilensis (D.Don) Pic. Serm. & Bizzarri forests in the Argentinean Northern Patagonia; and 4) the Cool temperate Nothofagus forests and Magellanic rainforests. Results: In Chile, both Nothofagus-dominated and Angiosperm-dominated evergreen forests are diverse in tree species, and mixed-species silviculture with commercially valuable species of variable shade tolerance is most promising. Some secondary forests can reach growth rates as high as 20 m3ha-1yr-1. After thinnings, stands with 35–60% of residual densities have shown the best responses in growth. Even-aged silvicultural methods have shown a rapid reorganization and development of new cohorts, although, where Chusquea species are conspicuous, regeneration establishment requires controlling competing vegetation. Preliminary results also show interesting prospects for single-tree selection cuts in uneven-aged forests. East of the Andes, in Argentina, mixed Nothofagus forests and pure and mixed Nothofagus and A. chilensis forests occur. The shelterwood method has been the most practised and successful in the mixed Nothofagus forests, with abundant regeneration, and good growth rates. For A. chilensis forests, an adaptive management approach is proposed, conditioned by the cypress disease attack (e.g., Phytophthora austrocedri). Conversion of pure A. chilensis to mixed A. chilensis–N. dombeyi forests could increase growth considerably. Finally, in the cool temperate Nothofagus forests and Magellanic rainforests, shared by Chile and Argentina, the regular shelterwood cuts have been the most common silvicultural method, with massive regeneration a decade after the regeneration felling. Since the two major Nothofagus species in these forests regenerate well in gaps, uneven-aged silviculture seems also promising. Conclusions: There is abundant knowledge about the silviculture of these forest types. However, there are opportunities for several silvicultural systems to better contribute to sustainable forest management, reverse forest degradation, and cope with climate change challenges, primarily through developing mixed and single-species productive and carbon-rich forests, with greater adaptive capacity.

Investigating the Role of Restoration Plantings in Introducing Disease—A Case Study Using Phytophthora

Translocating plants to natural habitats is a long-standing conservation practice but is growing in magnitude to deliver international targets to mitigate climate change and reverse biodiversity loss. Concurrently, outbreaks of novel plant pests and pathogens are multiplying with increased global trade network connectivity and larger volumes of imported plants, raising concerns that restoration plantings may act as introductory disease pathways. We used UK common juniper, subject since ~1995 to conservation plantings and now experiencing significant mortality from the non-native pathogen Phytophthora austrocedri Gresl. & E. M. Hansen, as an example species to explore the availability of monitoring data that could be used to assess disease risks posed by planting. We compiled spatial records of juniper planting including qualitative data on sources of planting material, propagation settings and organization types that managed planting projects. We found that juniper planting activity expanded every decade since 1990 across the UK and while not all planting resulted in outbreaks, 19% of P. austrocedri detections were found within 2 km of a known planting. We highlight the scale and diversity of organizations raising and planting juniper, as well as the lack of source material traceability, and suggest that cross-sector collaboration and changes in practice are required to reduce the risks of pathogen introduction posed by restoration planting.

Evidence for natural resistance in Juniperus communis to Phytophthora austrocedri

Phytophthora austrocedri is a recently invasive pathogen causing widespread mortality of the ecologically important native conifer, Juniperus communis, in northern Britain. Observations of disease symptoms at severely infected woodlands revealed the presence of individual, apparently healthy trees in areas of high mortality. This study was undertaken to test the hypothesis that these ‘survivor’ trees have greater resistance to P. austrocedri. Rooted cuttings were obtained from seventeen putatively resistant J. communis clones at two heavily infected natural woodlands. Inoculation of excised stems from three putatively resistant clones with P. austrocedri provided initial data to support the hypothesis of resistance. A larger trial was conducted in which whole J. communis plants representing seventeen putatively resistant clones and a known susceptible clone were inoculated with two isolates of P. austrocedri. This trial revealed variation in resistance, with at least six clones exhibiting a high degree of resistance to the pathogen. One surprising finding given the lack of genetic diversity in UK P. austrocedri isolates was that one of the clones was resistant to one isolate and susceptible to the other, warranting further investigation. The next steps are to ascertain whether this natural resistance in J. communis is heritable and exploitable for population recovery.

Phytophthora austrocedri in Argentina and Co-Inhabiting Phytophthoras: Roles of Anthropogenic and Abiotic Factors in Species Distribution and Diversity

This work reports the first survey of Phytophthora diversity in the forests soils of Andean Patagonia. It also discusses the role of anthropogenic impact on Phytophthora distribution inferred from the findings on Phytophthora diversity and on the distribution of Phytophthora austrocedri-diseased forests. Invasive pathogen species threatening ecosystems and human activities contribute to their entry and spread. Information on pathogens already established, and early detection of potential invasive ones, are crucial to disease management and prevention. Phytophthora austrocedri causes the most damaging forest disease in Patagonia, affecting the endemic species Austrocedrus chilensis (D. Don) Pic. Sern. and Bizzarri. However, the relationship between anthropogenic impacts and the disease distribution has not been analyzed enough. The aims of this work were: to evaluate Phytophthora diversity in soils of Andean Patagonia using a metabarcoding method, and analyze this information in relation to soil type and land use; to assess the distribution of Austrocedrus disease over time in relation to anthropogenic and abiotic gradients in an area of interest; and to discuss the role of human activities in Phytophthora spread. High throughput Illumina sequencing was used to detect Phytophthora DNA in soil samples. The distribution of Austrocedrus disease over time was assessed by satellite imagery interpretation. Twenty-three Phytophthora species, 12 of which were new records for Argentina, were detected. The most abundant species was P. austrocedri, followed by P. × cambivora, P. ramorum and P. kernoviae. The most frequent was P. × cambivora, followed by P. austrocedri and P. ramorum. Phytophthora richness and abundance, and Austrocedrus disease distribution, were influenced by land use, anthropogenic impact and soil drainage. Results showed several Phytophthoras, including well-known pathogenic species. The threat they could present to Patagonian ecosystems and their relations to human activities are discussed. This study evidenced the need of management measures to control the spread of P. austrocedri and other invasive Phytophthora species in Patagonia.

Anthropogenic Factors Control the Distribution of a Southern Conifer Phytophthora Disease in a Peri-Urban Area of Northern Patagonia, Argentina

Several mid-sized urban areas have established boundaries overlapping with the distribution of Austrocedruschilensis (D.Don) Pic.Serm. & Bizzarri forests in Patagonia. These forests suffer a disease whose primary cause is the aggressive pathogen Phytophthora austrocedri. This study analyzes the factors related to Austrocedrus disease in an urban and peri-urban environment, showing that anthropogenic factors related to Phytophthora dispersion predominantly influence the disease distribution. The study was developed in urban and suburban areas of San Carlos de Bariloche county (Río Negro Province, Argentina). A database of requests to fell A. chilensis trees, from the Forest Department of Río Negro Province, was cleaned up and improved through satellite images analysis and field sampling. Data were analyzed in order to set up a layer of Austrocedrus disease presence. From this layer, and from anthropogenic and environmental layers (distance to houses, distance to roads, precipitation, slope, aspect, altitude, distance to water courses), a risk model was developed using the Maximum Entropy (MaxEnt) algorithm. In turn, data from the field sampling were assessed by contingency tables and chi square analysis. The results show that disease occurrence in San Carlos de Bariloche county is associated with the insertion of the urban network over areas of native forests. Distance to houses, distance to roads and distance to gardens with irrigation were the most important variables associated with the disease occurrence. A risk model was generated for the study area, which shows the current risk situation for the disease. Urbanization’s advance over the forest modifies key variables related to Phytophthora dispersion, such as the distance from cypress trees to houses and roads, thus progressively increasing the area at risk of becoming diseased. Based on these results, plausible measures and actions are proposed.

Rhizospheric microorganisms as potential biocontrol agents against Phytophthora austrocedri

Austrocedrus chilensis [D.Don] Pic. Serm. et Bizarri (Pinales: Cupressaceae) is a keystone tree species in South America. Mortality of A. chilensis has been reported over most of its distribution in Argentina, and Phytophthora austrocedri has been identified as the causal agent. The aim of this work was to evaluate rhizospheric microorganisms present in A. chilensis roots as biocontrol agents against P. austrocedri. Mycelial growth of P. austrocedri was inhibited by seven fungal and four bacterial isolates in vitro. Interaction among isolates and P. austrocedri was microscopically studied. Isolates with high in vitro fungistatic or fungicide performance were molecularly identified and inoculated in plants to evaluate their ability to reduce the effect of the pathogen. Two of the bacterial isolates were able to reduce the symptoms in A. chilensis seedlings inoculated with P. austrocedri. These findings are promising since they may contribute to the development of a biocontrol strategy for the disease.

Small scale variability in soil moisture drives infection of vulnerable juniper populations by invasive forest pathogen

The oomycete plant pathogen, Phytophthora austrocedri, is an aggressive killer of cypress trees causing severe mortality of Chilean cedar (Austrocedrus chilensis) in Argentina since the 1940 s and now of common juniper (Juniperus communis s.l.) in the UK. Rapid mortality of key UK juniper populations was first observed in the early 2000 s. The causal agent of mortality was confirmed as P. austrocedri in 2012 and the pathogen has now been widely detected - but is not ubiquitous - in juniper populations across Scotland and England. Although juniper has a broad distribution across the northern hemisphere, the UK incidence of P. austrocedri remains the only confirmed infection of juniper populations globally. Juniper is an important species for biodiversity, so it is imperative to understand the abiotic and biotic drivers of emergent P. austrocedri infection to inform detection, containment and conservation strategies to manage juniper populations across the full extent of its range.As management of UK juniper populations is primarily conducted at a local level, we investigated field scale drivers of disease – in three, geographically separate populations with different infection histories. Variation in the proportion of juniper showing symptoms - discoloured or dead foliage – was measured using stratified sampling across along key environmental gradients within each 100-hectare population. Potential predictors of infection included altitude, slope, distance to nearest watercourse, soil moisture (mean percentage volumetric water content), area of red deer browsing damage and area of commonly associated vascular plant species. We assessed support in the data for alternative models explaining the spatial distribution of P. austrocedri symptoms using full subset covariate selection and Deviance Information Criteria (DIC). Despite differences in environmental gradients and infection histories between populations, area of juniper symptomatic for P. austrocedri increased with waterlogging, increasing with soil moisture in sites where soils had higher peat or clay contents, and decreasing with proximity to watercourses where sites had shallower, sandier soils. Furthermore, we identified common taxa in the associated plant community that correlated with increased area of symptoms and could be used by land managers as indicators to identify microsites at high risk of infection, enabling site-specific tailoring of disease management strategies. Such strategies could include prioritising detection inspections in microsites with high water tables and high grazing pressure (guided by indicator taxa), limiting soil disturbance in wet microsites and creating sites for natural regeneration in drier microsites, to minimise pathogen spread and maximise the resilience of existing juniper populations.

Detection and spread of Phytophthora austrocedri within infected Juniperus communis woodland and diversity of co‐associated Phytophthoras as revealed by metabarcoding

AbstractPhytophthora austrocedri is a recently invasive soilborne pathogen which is causing widespread mortality of Juniperus communis in northern Britain. The pathways by which a single genotype of P. austrocedri has spread to infect such a geographically dispersed range of woodland sites within a relatively short timeframe are unknown. This study examined the detectability of P. austrocedri in soil and water within infected J. communis woodland using qPCR to gain a better understanding of the pathogen's key mechanisms of spread. A Phytophthora metabarcoding method was also applied to investigate the wider diversity of Phytophthora species present in water at one of the sites. qPCR analyses of P. austrocedri in soil samples at a J. communis woodland exhibiting low‐to‐moderate levels of disease suggested a slow natural spread of the pathogen in soil, requiring high moisture conditions. However, the ubiquity of P. austrocedri DNA in soil samples collected across a heavily infected J. communis site suggests that once established at a site the pathogen can be spread readily in soil locally, most likely vectored by animal movements and/or human activities. The hypothesis that P. austrocedri is aerially transmitted in rainwater was not adequately proven, and an alternative hypothesis for the widespread distribution of the pathogen on J. communis in northern Britain is presented. Metabarcoding identified DNA from a diverse range of Phytophthora species in river and rainwater samples although the main target pathogen, P. austrocedri, was not amplified which disagreed with some of the qPCR findings. Possible reasons for this are discussed.

Two conifer species native to Patagonia threatened by Phytophthora austrocedri

AbstractPhytophthora austrocedri is a pathogen of Austrocedrus chilensis causing “Mal del Ciprés” (cypress sickness) in Patagonia and killing Juniperus communis in Britain, along with other species in the Cupressaceae. The evident association of the pathogen with members of the Cupressaceae makes it necessary to study the susceptibility of other species related to A. chilensis to prevent the emergence of new diseases. The present study tested the pathogenicity of P. austrocedri to three native and endemic conifers in South America: Fitzroya cupressoides, Pilgerodendron uviferum and Araucaria araucana. The results showed that F. cupressoides and P. uviferum were highly susceptible to P. austrocedri. Since these are endangered tree species, the outcome of this study is crucial for governmental agencies, policymakers and stakeholders.

Trabeculae in Patagonian mountain cypress (Austrocedrus chilensis) associated with Phytophthora austrocedri infection

ABSTRACT Phytophthora austrocedri is a straminipilous (heterokonta) organism that causes mortality of Austrocedrus chilensis, an endemic Cupressaceae from the Patagonian Andes forest in temperate South America. This soil pathogen colonizes and kills the roots and extends up to the stem causing necrosis of cambium, phloem and xylem ray parenchyma. An anatomical study of affected tissues was conducted in order to better understand the process of pathogen colonization and tree response. It was found that tracheids of the xylem of affected trees showed large numbers of trabeculae, both rod- and plate-shaped. The occurrence of these structures was clearly associated with the necrotic lesion area, since the trabeculae were rare in healthy tissues above the necrotic lesion. Trabeculae occurred in a variety of arrangements: solitary or in long files, single, double or triple. Our results could indicate that trabeculae proliferation in tracheids of A. chilensis trees is induced by the stress generated by the P. austrocedri invasion. Whether this is triggered by a nonspecific stress response or in direct response to the pathogen remains to be tested.

Trabeculae in Patagonian mountain cypress (Austrocedrus chilensis) associated with Phytophthora austrocedri infection

Phytophthora austrocedri is a straminipilous (heterokonta) organism that causes mortality of Austrocedrus chilensis, an endemic Cupressaceae from the Patagonian Andes forest in temperate South America. This soil pathogen colonizes and kills the roots and extends up to the stem causing necrosis of cambium, phloem and xylem ray parenchyma. An anatomical study of affected tissues was conducted in order to better understand the process of pathogen colonization and tree response. It was found that tracheids of the xylem of affected trees showed large numbers of trabeculae, both rod- and plate-shaped. The occurrence of these structures was clearly associated with the necrotic lesion area, since the trabeculae were rare in healthy tissues above the necrotic lesion. Trabeculae occurred in a variety of arrangements: solitary or in long files, single, double or triple. Our results could indicate that trabeculae proliferation in tracheids of A. chilensis trees is induced by the stress generated by the P. austrocedri invasion. Whether this is triggered by a nonspecific stress response or in direct response to the pathogen remains to be tested.

Morphological and Genetic Analyses of the Invasive Forest Pathogen Phytophthora austrocedri Reveal that Two Clonal Lineages Colonized Britain and Argentina from a Common Ancestral Population.

Phytophthora austrocedri is causing widespread mortality of Austrocedrus chilensis in Argentina and Juniperus communis in Britain. The pathogen has also been isolated from J. horizontalis in Germany. Isolates from Britain, Argentina, and Germany are homothallic, with no clear differences in the dimensions of sporangia, oogonia, or oospores. Argentinian and German isolates grew faster than British isolates across a range of media and had a higher temperature tolerance, although most isolates, regardless of origin, grew best at 15°C and all isolates were killed at 25°C. Argentinian and British isolates caused lesions when inoculated onto both A. chilensis and J. communis; however, the Argentinian isolate caused longer lesions on A. chilensis than on J. communis and vice versa for the British isolate. Genetic analyses of nuclear and mitochondrial loci showed that all British isolates are identical. Argentinian isolates and the German isolate are also identical but differ from the British isolates. Single-nucleotide polymorphisms are shared between the British and Argentinian isolates. We concluded that British isolates and Argentinian isolates conform to two distinct clonal lineages of P. austrocedri founded from the same as-yet-unidentified source population. These lineages should be recognized and treated as separate risks by international plant health legislation.

First report of Phytophthora austrocedri causing phloem lesions and bronzing on Cupressus sempervirens in northern Iran

In 2016, the Qazvin Agricultural and Natural Resources Research Center received reports of foliage bronzing of Italian cypress (Cupressus sempervirens) in a public park in Qazvin city, Iran. Symptomatic, fully-bronzed foliage of trees had an orange-brown colored lesion in the phloem around the stem collar (Figs. 1-2). Phloem samples taken from the lesion edges (Green et al., 1) were plated on a Phytophthora-selective medium (synthetic mucor agar) and incubated at a temperature of 17–27°C in the dark. Resulting mycelial growth was transferred to V8 agar medium. The colony on V8 agar was white with coralloid hyphae (Fig. 3) and very slow growing (less than 0.5 mm per day). Formation of sporangia appeared on V8 agar with a width and length (μm) of (28.4) 31.5-44.7 (46.1) and (39.9) 46.7-73.5 (79.7), respectively. Homothallic oospores appeared on corn meal agar with a diameter (μm) of (21.7) 24.1–40.2 (46.5). The internal transcribed spacer region was amplified using ITS1/ITS4 primers (White et al., 5) and sequences of a representative strain were compared with related species retrieved from GenBank, resulting in 99% sequence identity with Phytophthora austrocedri (GenBank Accession Nos. JQ346530 and KJ49066; Green et al., 2 & 1). The ITS sequence of our isolate was deposited in GenBank (MF480422). According to colony morphology and sequencing of the ITS region, the isolate was identified as P. austrocedri (syn=P. austrocedrae; Greslebin et al., 3). Pathogenicity tests were performed using 15 replicate shoots (c. 40 cm long) of Italian cypress. Mycelia plugs (roughly 5 mm), derived from the margins of an actively growing 20-day-old culture of the P. austrocedri isolate on V8 agar, were used to inoculate the shoots by placing the plug on wounded points under the bark. In order to maintain humidity, inoculation points (centre of each shoot) were coated with paraffin film and wrapped with aluminum foil. The shoots were incubated at 17°C in the dark after placing in sealed plastic bags containing a damp cotton wall ball. Fifteen shoots were inoculated with sterile V8 agar as controls. After ten weeks, orange-brown phloem lesions ranging from 20-100 mm in length appeared on the inoculated shoots. The pathogen was reisolated from all of the infected shoots, whereas control shoots remained symptom-free. Phytophthora austrocedri has been reported to be a pathogen on Juniperus communis and Chamaecyparis spp. (Green et al., 2). To the authors' knowledge, this is the first report of P. austrocedri causing lesions in the phloem on Cupressus sempervirens in northern Iran or Cupressus species worldwide. The origin of P. austrocedri in Iran is unknown. As Italian cypress is only planted in Iran in parks, the potential of this pathogen spreading to nurseries and orchards around of Qazvin city is not high. However, the host range of P. austrocedri has not been studied extensively and there is concern that other economically important species, such as surrounding pistachio gardens could be at risk, since they are susceptible to other Phytophthora spp. (Saremi et al., 4). Studies will need to be conducted to determine if these local hosts are susceptible.

Action of fosetyl‐al and metalaxyl against Phytophthora austrocedri

SummaryFosetyl‐Al and metalaxyl, the most commonly used systemic fungicides against Phytophthora, were evaluated for their efficacy to control Phytophthora austrocedri, the pathogen that causes a serious disease at the Austrocedrus chilensis forests in Patagonia. The effect of the chemicals on pathogen development in vitro and in planta was analysed. Both chemicals were shown to protect plants from the pathogen. In vitro assays showed that asexual reproduction was sensitive to both chemicals. However, mycelial growth and sexual reproduction, which were clearly sensitive to metalaxyl, were sensitive only to high concentrations of fosetyl‐Al. Fosetyl‐Al and metalaxyl had almost the same efficacy when applied preventively by soil drench to seedlings. This difference between in vitro and in planta results can be attributed to the dual action of fosetyl‐Al, not only inhibiting the pathogen but also stimulating host defence. In adult trees, preventive and curative treatments were tested, but only the fosetyl‐Al preventive treatment was effective in the assayed conditions. Interestingly, seedlings pretreated with both fungicides were less susceptible to the effectors secreted by the pathogen. Our results indicate that fosetyl‐Al and metalaxyl provide some resistance to the plant besides the fungistatic direct action on the pathogen. Further studies to elucidate a possible resistance‐inducing activity of these chemicals and the mechanisms involved are underway.

Phytophthora austrocedri Elicitates Changes in Diterpene Profile of Austrocedrus chilensis.

The populations of the Andean Cupressaceae Austrocedrus chilensis have been severely affected by a disease caused by the phytopathogenic fungus Phytophthora austrocedri. A study was undertaken to disclose changes in the resin composition of P. austrocedri-infected individuals, including naturally infected and artificially inoculated trees, compared with healthy A. chilensis trees. GC-MS and 1H-NMR studies showed a clear differentiation among healthy and infected resins, with the diterpene isopimara-8(9),15-dien-19-ol as a relevant constituent in resins from infected trees. The effect of resin fractions from P. austrocedri infected trees on the pathogen was assessed by measuring the mycelial growth in agar plates. The most active fractions from resin obtained from infected trees inhibited fungal growth by nearly 50% at 1 mg/dish (35.37 µg/cm2). The main constituent in the active fractions were 18-hydroxymanool and the aldehyde torulosal. Both compounds are oxidation products of manool and can be a chemical response of the tree to the pathogen or be formed from the pathogen as a biotransformation product of manool by microbial oxidation. While the diterpene profiles from A. chilensis tree resins can easily differentiate healthy and P. austrocedri infected individuals, the possible conversion of manool to the antifungal derivatives 4 and 6 by the microorganism remains to be established.

Diagnostics of Tree Diseases Caused by Phytophthora austrocedri Species.

We present methods for the detection and quantification of four Phytophthora species which are pathogenic on trees; Phytophthora ramorum, Phytophthora kernoviae, Phytophthora lateralis, and Phytophthora austrocedri. Nucleic acid extraction methods are presented for phloem tissue from trees, soil, and pure cultures on agar plates. Real-time PCR methods are presented and include primer and probe sets for each species, general advice on real-time PCR setup and data analysis. A method for sequence-based identification, useful for pure cultures, is also included.