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1.
There are three major clonal lineages of Phytophthora ramorum present in North America and Europe named NA1, NA2, and EU1. Twenty‐three isolates representing all three lineages were evaluated for phenotype including (i) aggressiveness on detached Rhododendron leaves and (ii) growth rate at minimum, optimum, and maximum temperatures. Closely related species P. foliorum and P. hibernalis were included in phenotypic tests since these species are encountered in nursery surveys for P. ramorum. Isolates from the NA2 and EU1 lineages were the most aggressive and isolates from the NA1 group were the least aggressive. The NA1 lineage of P. ramorum was the most variable in aggressiveness and growth rate. The variability in the NA1 lineage was due to the presence of non‐wild type (nwt) isolates. There was no significant difference in growth rate among NA1 wild type (wt), NA2, and EU1 lineages at any temperature tested. The difference between wt and nwt P. ramorum isolates is discussed.  相似文献   

2.
During a survey for Phytophthora ramorum undertaken in north‐west Scotland in early 2016, Phytophthora foliorum was found infecting foliage of the invasive shrub Rhododendron ponticum. Prior to this, P. foliorum had only been reported from foliage of hybrid azaleas in nurseries in California and Tennessee and from azalea plants in an ornamental nursery in Spain. No other hosts were known, and much of the behaviour of P. foliorum remained enigmatic. The species is classified in Phytophthora Clade 8c, with closest relatives, P. ramorum and Phytophthora lateralis, both of which are highly damaging tree pathogens. To explore the threat that P. foliorum might pose to trees, its growth–temperature responses on agar media and ability to cause lesions in the living bark of various hosts were contrasted with the behaviours of P. ramorum and P. lateralis. Phytophthora foliorum proved faster growing and more tolerant of temperature extremes than the other Phytophthora species. Comparisons of bark colonization initially focussed on R. ponticum and larch species Larix decidua and Larix kaempferi as all three are significant hosts of P. ramorum in the UK. Further experiments included another P. ramorum host, Fagus sylvatica (European beech), and the main host of P. lateralis, Chamaecyparis lawsoniana (Lawson cypress). Findings suggested that as well as being a significant pathogen of R. ponticum, damage caused by P. foliorum to both species of larch and beech was very similar to that of the EU1 lineage of P. ramorum, although growth in host tissue was also influenced by season.  相似文献   

3.
The zoosporic phase of the pathogen Phytophthora ramorum plays a crucial role in the process of plant infection, yet little is known about the fate of zoospores failing to target their hosts. Here, we describe new stages in the life cycle of P. ramorum concerning the in vitro development of monomorphic diplanetism and microcyclic sporulation in free water. Papillate cysts were formed after zoospore suspensions of isolates of the EU1 and NA1 clonal lineages were vortexed. Cysts usually germinated directly forming an emerging tube, or indirectly by releasing a secondary zoospore, which leaves behind an empty cyst with a short evacuation tube. Germinate cysts frequently developed either an appressorium or a microsporangium both terminally. We also observed microcyclic sporulation, i.e. sporangia indirectly germinated by forming a microsporangium, as in microcyclic conidiation of true fungi. Temporal progress of encysted zoospores in solution showed that percentage of germination varied significantly among and within isolates as well as between experiments, suggesting that germination is partly ruled by internal mechanisms. Diplanetism and microcyclic sporulation in P. ramorum may provide a second opportunity for host infection and may increase the chance of long dispersal in moving water.  相似文献   

4.
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 25°C 1 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/25°C 1 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.  相似文献   

5.
北半球高卢蜜环菌的遗传多样性与分子鉴定   总被引：6，自引：0，他引：6  
从北美、欧洲和中国收集２３个高卢密环菌菌株，ＰＣＲ扩增其rDNA的ＩＧＳ和ＩＴＳ区域，用ＡluI,HaeIII,HinfI和ＴagI四种限制性内切酶进行酶切，同时结合随机扩增微卫生（ＲＡＭＳ）多态性，对北半球的高卢蜜环菌的遗传多样性进行了分析，结果发现了高卢蜜环菌的６种ＩＧＳ－ＲＦＬＰ图谱类型，其中gal(B)和gal(D)是国内外无报道的新的ＩＧＳ－ＲＦＬＰ型，ＲＦＬＰ系统树发现该种有明显的大陆之间的遗传分化，存在中国，欧洲，北美和亚洲４个亚群体，ＲＡＭＳ分析表明北半球高卢蜜环菌存在亚洲，欧洲，北美－中国和北美－欧洲和北美－欧洲等４个高卢蜜环菌发育系，而且不同大陆的高卢蜜环菌具有较近的亲缘关系，而相同大陆的却具有不同的起源，特别是北美的高卢蜜环菌两个发育系异源性很高，北美东部的发育系同欧洲的关系比较近，而北西部的同亚洲关系比较近，同时表明ＲＡＭＳ技术是分析菌物种内遗传多样性的优越方法。  相似文献   

6.
Isolates of the chestnut blight fungus Cryphonectria parasitica were obtained from 44 localities in four provinces in Western Spain and characterized for vegetative compatibility (vc) types, mating types and the presence of Cryphonectria hypovirus 1 (CHV1). Among the 1232 isolates recovered from chestnut blight cankers, 11 vc types were identified: five known vc types included in EU1 to EU74 (EU1, EU11, EU12, EU28 and EU66) and six unknown vc types (CL4, CL5 CL6, CL8, CL9 and CL10). The number of vc types found per province varied between two and seven. The vc type EU11 was present in all provinces and accounted for 48.9% of all isolates. EU1 was detected in three provinces and accounted for 39.1% of the isolates. The vc types EU12, EU66, CL5 and CL6 were present in one or two provinces and comprised between 2.4% and 3% of the isolates. The other vc types were represented by only one or very few isolates. The mating type MAT‐1 was largely dominant in the provinces Leon and Avila, while both mating types MAT‐1 and MAT‐2 were found in Salamanca and Zamora. Fourteen hypovirus‐infected C. parasitica isolates were found, nine were in vc type EU1 and five in EU11, and they were detected only in the province León. All isolates analysed contained the French hypovirus subtype CHV1‐F1.  相似文献   

7.
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.  相似文献   

8.
The distribution of the North American P group of Heterobasidion annosum s.l., recently reported from a Pinus pinea forest in the surroundings of Rome, was studied using mating tests and DNA fingerprinting (mitochondrial DNA, random amplified microsatellite technique and two group‐specific markers). This fungus is present in several forests and small plantations along the Tyrrhenian coast of the Italian peninsula, within an area approximately 100 km long, extending from Fregene in the north to the National Park of Circeo in the south, and 27 km wide including the city of Rome. In pine forests of Castelporziano, Castel Fusano and Anzio, where US troops resided during the Second World War, the North American P group is more frequent than the European P group. The low number of mating alleles in the Italian population of the North American P group supports the hypothesis of its origin from a small number of introductions. The near 100% sexual compatibility between the North American and European P groups, together with inconsistencies in results obtained with different identification methods of these groups, suggests that hybridization between the North American and European P populations occurs occasionally.  相似文献   

9.
We surveyed chestnut stands at 18 sites in 11 locations in Bulgaria in 2005 and 2007 for the presence of chestnut blight. We found chestnut blight in seven locations (Belogradchik, Berkovitsa, Brezhani, Barziya, Govezhda, Petrich and Petrovo) but not in four others (Tsaparevo, Kresna, Dupnica and Botevgrad). We successfully isolated Cryphonectria parasitica from cankers on 606 trees with symptoms of chestnut blight and assayed them for vegetative compatibility (vc) types and mating type. Three vc types were identified among the 606 isolates; all three were among the European vc types with known vegetative incompatibility (vic) genotypes. Vc type EU‐12 was the most common, representing 80% of the isolates, and was found at all locations with blight, with the exception of Belogradchik in north‐west Bulgaria, where all isolates were vc type EU‐2. Only one population (Barziya) had more than one vc type, with a combination of EU‐12 and EU‐10 in almost equal frequencies. Similarly, the diversity of mating types was very low. All but three of 536 isolates assayed were in mating‐type MAT‐1; MAT‐2 was only found in one population in the north‐west (Berkovitsa). We inspected 671 bark samples from chestnut blight cankers with stromata of C. parasitica and found perithecia in only 33, of which 28 were from Berkovitsa where MAT‐2 was present. We did not detect hypoviruses in any of the 270 isolates screened using the standard double‐stranded RNA extraction protocol. Similar to results from previous studies in south‐eastern Europe, the diversity of vc types and mating type of C. parasitica in Bulgaria is low, and reproduction of the fungus is mainly asexual. Unfortunately, naturally occurring hypovirulence was not detected. Nevertheless, we observed a small number of superficial cankers typical of those caused by C. parasitica isolates infected with a hypovirus.  相似文献   

10.
Phytophthora ramorum is the causal agent of the sudden larch death epidemic in Ireland and the UK. Within the EU, it is a quarantine pathogen and eradication measures are required if it is detected in horticultural or forest environments. Eradication measures in forests include the clearance of susceptible tree hosts from the infected stand along with all host known to support pathogen sporulation within a 250‐m buffer zone of the infected stand. Between 2010 and 2016, these measures have affected over 18,000 ha of Larix kaempferi forests in Ireland and the UK, but the epidemic continues to spread. An assessment of the efficacy of the eradication measures has not been published to date. Here, we provide details of the detection frequency of P. ramorum from aerial (rainwater) and terrestrial (soil, watercourses, plant material) sources in three forest locations in Ireland that had significant areas of L. kaempferi affected by P. ramorum before their removal. Monitoring of six plots with differing infection and eradication management histories was carried out from September 2013 to 2015. Presence of P. ramorum was confirmed by plating plant material onto selective media, followed by morphological identification. Phytophthora ramorum was detected in 65 of 1283 samples, in all sample types and in 17 of the 20 months sampled. Only three of the 295 soil samples were positive for P. ramorum, with all of these coming from an area under perennial standing water. The most positive samples came from a plot where symptomatic Larix trees had not been removed and the findings occurred consistently over the 2‐year study. Plots where infected Larix had been removed were rarely positive for P. ramorum across all the sample types indicating a level of success from the eradication measures in reducing pathogen levels on the sites.  相似文献   

11.
Castanea sativa, one of the most precious forest trees in Greece, is affected by the spread of chestnut blight all over the country. Identification and mapping of the vegetative compatibility (vc) types of the fungus Cryphonectria parasitica was carried out and the occurrence of hypovirulence was checked. In 11 chestnut populations distributed all over Greece, 627 isolates were obtained and their vc type was determined. Four vc types were identified by means of tester isolates: EU‐12 was found to be the dominant vc type reaching a percentage of 88%, with EU‐2 (6%), EU‐10 (3%) and EU‐1 (2%) following. EU‐12 was found in all 11 populations investigated whereas EU‐2 was isolated from five populations and EU‐10 and EU‐1 were found only in one population each. Natural hypovirulence was also found in five populations of 11 examined. Perithecia were not found in either population, a finding supported by the fact that all Greek isolates examined belonged to a single mating type, MAT‐1. The low diversity in vc types, the absence of the perithecial stage and the occurrence of natural hypovirulence in some areas support the feasibility of successful application of biological control on the national level in Greece.  相似文献   

12.
Summary The intergenic spacer region 1 (IGS1) of the nuclear ribosomal RNA gene repeat was examined in three European intersterility groups of the wood‐rot fungus Heterobasidion annosum. The IGS1 elements were informative for restriction fragment length polymorphism (RFLP) fingerprinting the fungal intersterility groups following digestion with two different four‐cutter restriction endonucleases. The fingerprints of isolates from the same intersterility group from different localities shared some fragments in common, but also showed specific fragments suggesting that RFLP of the IGS1 region might be used in population studies. RFLP patterns between isolates from different intersterility groups differed more markedly. RFLP were also detected in the IGS1 region of North American strains of H. annosum and in the related species Heterobasidion araucariae. The results indicate that ribosomal IGS1 region fingerprinting could be a useful tool to identify the fungal intersterility group in Heterobasidion annosum.  相似文献   

13.
To investigate the taxonomy of Heterobasidion in Eurasia, 49 specimens belonging to H. annosum sensu lato from Asia were identified with the aid of mating tests. Most of the specimens originated from north‐eastern and south‐western China and from the Altai region in southern Siberia, but a few isolates from Kirghizia, Japan and India were also tested. In addition to mating tests, the material from China was investigated with DNA fingerprinting. Heterobasidion annosum sensu stricto was identified only from the Altai region. Homokaryotic isolates from other specimens, except the Indian ones, were sexually compatible with H. parviporum, but they also showed a high degree of compatibility with H. abietinum and with the North American S group. The isolates from SW China (eastern Himalayas) mated with about equal frequency with the European strains of H. parviporum and H. abietinum. However, the DNA fingerprinting showed that these isolates were more closely related to H. parviporum, and hence they were tentatively included in this species. The North American S group was more distant from these Eurasian taxa. Four old isolates from India mated only weakly with the members of the H. annosum s.lat. According to the species concept presented, the distribution of H. parviporum extends from western Europe through southern Siberia to northern China, Japan and the eastern Himalayas. H. annosum s.str. is so far identified only from the Altai region outside Europe, and H. abietinum only from Europe.  相似文献   

14.
Dothistroma septosporum and D. pini are the causal agents of Dothistroma needle blight (DNB) of Pinus spp. in natural forests and plantations. The main aim of this study was to develop molecular diagnostic procedures to distinguish between isolates within D. septosporum, for use in biosecurity and forest health surveillance programmes. This is of particular interest for New Zealand where the population is clonal and introduction of a new isolate of the opposite mating type could have serious consequences. Areas of diversity in the dothistromin toxin gene clusters were identified in D. septosporum (51 isolates) and D. pini (6 isolates) and used as the basis of two types of diagnostic tests. PCR‐restriction fragment length polymorphism (RFLP) of part of the dothistromin polyketide synthase gene (pksA) enabled distinction between two groups of D. septosporum isolates (A and B) as well as distinguishing D. septosporum and D. pini. The intergenic region between the epoA and avfA genes allowed further resolution between some of the A group isolates in RFLP assays. These regions were analysed further to develop a rapid real‐time PCR method for diagnosis by high‐resolution melting (HRM) curve analysis. The pksA gene enabled rapid discrimination between D. septosporum and D. pini, whilst the epoA–avfA region distinguished the New Zealand isolate from most other isolates in the collection, including some isolates from DNB epidemics in Canada and Europe. Although this study is focused on differences between the New Zealand isolate and other global isolates, this type of diagnostic system could be used more generally for high‐throughput screening of D. septosporum isolates.  相似文献   

15.
Sudden Oak Death, caused by Phytophthora ramorum, poses a serious threat to native American oaks, and is also present in Europe where it has been isolated from numerous European ornamental plant nurseries. Its proven aggressiveness against plants in the Fagaceae and Ericaceae and the damage it has caused in North America have lead to it being assigned quarantine status. The timely and accurate detection of P. ramorum is a critical aid in the study of the epidemiology and biology of this pathogen. As a regulated organism, the availability of a sensitive and reliable assay is essential when attempting to achieve early detection of the pathogen. In this work, new specific hybridization probes for a real‐time PCR amplification method were found to be rapid, robust and labour‐saving, and proved suitable for routine use in a molecular diagnostic laboratory.  相似文献   

16.
Cryphonectria parasitica, the causal agent of chestnut blight, has been responsible for the decline in chestnut in Portugal for the last two decades. In order to improve understanding of C. parasitica diversity, a total of 617 isolates from all affected chestnut‐growing areas in continental Portugal, Madeira and the Azores archipelagos were studied. Nine vegetative compatibility (vc) types were identified among the isolates. EU‐11 was the most widespread vc type comprising 80.2% of the isolates, followed by EU‐12 (7.1%) and EU‐66 (6.6%). Two of the Portuguese vc types could not be assigned to a known European vc type. The diversity of vc types was low in the Portuguese populations of C. parasitica, but comparable with other areas where C. parasitica was introduced recently. The frequent occurrence of perithecia and both mating types of C. parasitica indicates that sexual reproduction of the chestnut blight fungus is common in Portugal. One C. parasitica isolate from Trás‐os‐Montes showed a white culture morphology and contained dsRNA, indicating the presence of hypovirulence in this area.  相似文献   

17.
In this study, we investigated whether birds could be vectors facilitating long‐distance spread of Phytophthora ramorum in Britain. Migratory bird species associated with the main sporangium‐producing host plants and most likely to pick up P. ramorum spores were considered. Swabs were taken from the flank and “feet” of 1,014 birds over a 12‐month period (April 2011–March 2012) in the west of Britain and subsequently analyzed for the presence of P. ramorum using nested PCR. Ten positive samples from 10 birds were identified: three in Cornwall, one in Devon, three in Gloucestershire, two in north Wales and one in Merseyside. Phytophthora ramorum was detected on samples from four species of thrushes (Redwing Turdus iliacus, Fieldfare T. pilaris, Blackbird T. merula and Song Thrush T. philomelos) and one species of warbler (Chiffchaff Phylloscopus collybita). All birds that tested positive were sampled in late autumn and winter (October–February), when long‐distance movements (over 100 km) would have stopped. The low incidence of P. ramorum found using PCR suggests that the incidence of inoculum, whether viable or not, on birds was low. The apparently low incidence of inoculum on birds suggests migratory passerine birds can carry P. ramorum inoculum on their feathers and “feet,” albeit at low frequency. The dates of positive samples indicate that birds would not have been moving long distances at the time but further work is needed to estimate the extent of their contribution to the spread of P. ramorum in Britain.  相似文献   

18.
Phytophthora ramorum is an invasive plant pathogen and the cause of considerable and widespread damage in nurseries, gardens and natural woodland ecosystems of the USA and Europe. It is considered to be a significant plant disease as it could cause biodiversity loss and severe economic losses in plant industries in areas where it is not yet known to exist, such as Australasia. Foliar susceptibility and sporulation potential were tested using detached‐leaf assays for 70 Australian native plant species sourced from established gardens and arboreta in California using a NA2 isolate of P. ramorum. Correa‘Sister Dawn’, Eucalyptus regnans, Isopogon cuneatus, I. formosus, Leptospermum scoparium, L. lanigerum and Melaleuca squamea were identified as potentially highly susceptible host species. Hedycarya angustifolia, Olearia argophylla, Phyllocladus aspleniifolius, Pittosporum undulatum and Podocarpus lawrencei were identified as potentially resistant. All 70 species were able to be infected with P. ramorum, as confirmed by reisolation. Putative sporulating hosts include five members of the Myrtaceae, Agonis flexuosa, Corymbia ficifolia, Eucalyptus haemastoma, E. delegatensis and E. viminalis. As a part of a precautionary strategy, the potentially highly susceptible species found in this study are suitable candidates for targeted surveillance programmes in high‐risk incursion areas of Australia and within the global horticultural trade.  相似文献   

19.
Genomic DNA from 81 isolates of Gremmeniella abietina collected from eleven plantations each of Pinus sylvestris and Pinus contorta in northern Sweden was studied using RAPD markers. The DNA variation between and within populations and the race and type distribution of G. abietina populations, causing symptoms similar to those of the North American race, were studied. The degree of genetic similarity was greater among G. abietina isolates from the same geographical areas than among isolates from different geographical areas, regardless of whether they were isolated from P. sylvestris or P. contorta. RAPD variation was greatest in the central parts of northern Sweden, suggesting that sexual reproduction has been somewhat more important there than further north or south. Only the RAPD fragments characteristic of the EU race of G. abietina were found in the material tested. The RAPD pattern described as characteristic of the northern type within the EU race was identified in 62% of the isolates. Divergence from the expected profile was due to differences in occurrence of fragments OPA12-1400 and 12-1500. This indicates that this part of the RAPD profile cannot be treated as diagnostic for the northern type. A conclusion of practical importance is that there is a considerable risk of G. abietina spreading from infected P. contorta plantations to adjacent areas with indigenous P. sylvestris regeneration, and vice versa, owing to the indicated lack of host-specificity of the pathogen. It is possible, however, that host-specific strains exist, but do not differ in their RAPD profiles.  相似文献   

20.
A new canker disease causing mortality of golden chinquapin trees [Chrysolepis chrysophylla (Dougl.) Hjelmqvist], in Oregon was recently observed. Most of the symptomatic or dead trees were located near roads. The cankers on the lower boles of trees are similar to those caused by species of Phytophthora on other trees in western North America. The cankers in the inner bark were reddish‐orange in colour and extended upward from necrotic roots. Phytophthora cambivora (Petri) Buisman was isolated from the cankers; identity was confirmed by morphological comparison with known isolates and internal transcribed spacer sequence analysis. Pathogenicity was confirmed by inoculation of chinquapin seedlings and mature trees. Seven of nine isolates from chinquapin were A2 mating type; 27 of 28 isolates from other hosts in Oregon and Washington were A1 mating type.  相似文献   

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