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1.
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.  相似文献   

2.
Phytophthora ramorum and Phytophthora kernoviae are recently discovered invasive Phytophthoras causing leaf necrosis and shoot tip dieback mostly on ornamental and forest understorey species, but also cause bleeding cankers on stems of a wide range of tree species. Sporulation occurs only on infected shoots or fruits and foliage so foliar hosts are central to the disease epidemiology. In field trials to assess infection in trap plants exposed to natural inoculum of P. ramorum and P. kernoviae on rhododendron in south west England, it was discovered that leaves of the trap plants ( Rhododendron 'Cunninghams White') and holm oak ( Quercus ilex ) were asymptomatically infected and supported sporulation of both pathogens. More than half the rhododendron trap plants exposed to inoculum of P. kernoviae became infected compared with approximately a third of those exposed to P. ramorum in a natural situation. Approximately one third of the infections were detected from asymptomatic foliage for both pathogens. The significance of these findings for plant health regulation based on visual inspection as a measure to prevent introduction and dissemination of both these pathogens is explored and research gaps identified.  相似文献   

3.
Phytophthora ramorum came to the Netherlands in 1993. Despite initially not seeming to pose a high risk, findings in California showed its potential destructive impact on ecosystems. A programme began in the Netherlands to eliminate P. ramorum from nurseries and surveys in the natural environment were held to obtain information to determine a strategy for dealing with the disease. About 1100 nurseries are inspected annually by NAKtuinbouw under the auspices of the Plant Protection Service and measures are taken according to EC directives. The percentage of infected nurseries decreased steadily during recent years, from 4% in 2002/2003 to 0.5% in 2004/2005. Surveys in the natural environment show that P. ramorum occurs on 2% of the sites with Rhododendron and therefore it was concluded that an elimination scenario is not realistic. A programme based on containment measures supported by an extension programme was put into place with its effects being monitored by the Plant Protection Service. 12 years of observing P. ramorum show that the risk for indigenous trees and shrubs in the Netherlands is very limited. Spread from infected rhododendrons to other potential hosts, even at heavily infected Rhododendron sites, hardly takes place although some infected Quercus rubra trees have been found. Recently several new Phytophthora species were found in natural environments in Europe and California, mainly as a result of intensive P. ramorum surveys. As well as P. ramorum, the Phytophthora spp. P. kernoviae, P. numerosa and P. pseudosyringae pose risks, indicating the need for a more general approach against Phytophthora diseases. As a result, a new protocol for detection and identification of Phytophthora spp. both as a group and individually is being developed and workers are asking whether these Phytophthora species could be managed together.  相似文献   

4.
D. R. Tracy 《EPPO Bulletin》2009,39(2):161-167
Phytophthora ramorum and P. kernoviae were first identified in Great Britain (GB) in 2002 and 2003 respectively, although both are believed to have been present for perhaps 10–20 years. Public gardens have been badly affected by these pathogens, but British woodlands are also considered at risk as a number of tree species have been found to be susceptible to the pathogens. The principal host of both Phytophthoras in GB is Rhododendron ponticum , which is arguably our most invasive weed species. It is found extensively in GB, especially along the west coast which has ideal climatic conditions for its growth and spread. In 2004 the Forestry Commission surveyed 1479 woodlands where R. ponticum was present, and in 2008 both infected and non-infected R. ponticum were cleared from approximately 1200 ha of woodlands in England and Wales where P. ramorum had been found. No clearance to date has taken place in Scotland. In the case of a positive finding in a garden or woodland, all woodlands with rhododendron within a 3 km radius of such a finding are to be surveyed. As both pathogens are notifiable any positives must be eradicated or contained through the serving of an official phytosanitary notice. Ministerial approval has now been given to a joint Defra and Forestry Commission initiative to undertake inter alia the removal of host plants (primarily rhododendrons) infected with these sporulating pathogens in woodlands and the wider environment in England and Wales. A similar programme will be effected in Scotland where the Forestry Commission is working with the Scottish Government's Rural Payments and Inspections Directorate.  相似文献   

5.
Phytophthora crown rot, caused primarily by Phytophthora cambivora, has caused considerable losses in almond orchards in the Willunga and northern plains areas approximately 50 km north and south of Adelaide (AU), respectively. Other Phytophthora species including P. citrophthora, P. cryptogea, P. megasperma and P. syringae have also been associated with diseased trees. Tree losses have been associated with P. cactorum isolated from trunk cankers on scaffold limbs on trees in the Riverland almond-growing area approximately 350 km north-east of Adelaide. The Al mating type of P. cambivora was the most pathogenic to almond seedlings. Cvs Mission and Chellaston, which are commonly used as rootstocks, were highly susceptible to crown rot whereas peach cv. Nemaguard was resistant. An excised twig assay has been developed to screen micropropagated shoots for resistance to P. cambivora. Metalaxyl applied at 5 g active substance per tree in spring, winter and autumn in a shallow trench close to the trunk prevented the development of trunk cankers. Foliar sprays of phosphonate (H3PO3) at 2 g active substance per litre in autumn and spring also inhibited canker development.  相似文献   

6.
Phytophthora root rot of sweet pepper   总被引：1，自引：0，他引：1  
Phytophthora capsici proved to be the causal agent of a root and crown rot of sweet pepper in the Netherlands.P. capsici was pathogenic on sweet pepper, tomato and sometimes on eggplant but not on tobacco Xanthi. Of these test plants only tomato was infected byP. nicotianae.No different symptoms in plants infected with eitherP. capsici orP. nicotianae were found. Dipping the roots of tomato and sweet pepper plants in a suspension ofP. capsici resulted in a more severe attack than pouring the suspension on the stem base.Resistance in tomato toP. nicotianae did not include resistance toP. capsici. A method to distinguishP. capsici fromP. nicotianae after isolation from soil is described. Both species were able to infect green fruits of tomato and sweet pepper.p. capsici survived in moist soil in the absence of a host for at least 15 months.Samenvatting Phytophthora capsici bleek de oorzaak te zijn van een voet-en wortelrot in paprika op twee bedrijven in 1977 in Nederland.P. capsici was pathogeen op paprika, tomaat en soms op aubergine maar niet op tabak Xanthi.P. nicotianae tastte van deze toetsplanten alleen tomaat aan. Verschillen in symptomen tussenP. nicotianae enP. capsici werden bij tomaat niet waargenomen.Het dompelen van de wortels in eenP. capsici suspensie gaf een ernstiger aantasting dan het begieten van de wortelhals met deze suspensie.Resistentie in tomaat tegenP. nicotianae bleek geen resistentie tegenP. capsici in te houden. P. capsici kan in grond worden aangetoond door groene paprikavruchten als vangsubstraat te gebruiken.P. capsici enP. nicotianae kunnen beide zowel vruchten van tomaat als paprika aantasten. P. capsici overleefde een periode van 15 maan den in vochtige grond waarop geen waardplant werd geteeld.  相似文献   

7.
ABSTRACT A real-time fluorescent polymerase chain reaction (PCR) detection method for the sudden oak death pathogen Phytophthora ramorum was developed based on mitochondrial DNA sequence with an ABI Prism 7700 (TaqMan) Sequence Detection System. Primers and probes were also developed for detecting P. pseudosyringae, a newly described species that causes symptoms similar to P. ramorum on certain hosts. The species-specific primer-probe systems were combined in a multiplex assay with a plant primer-probe system to allow plant DNA present in extracted samples to serve as a positive control in each reaction. The lower limit of detection of P. ramorum DNA was 1 fg of genomic DNA, lower than for many other described PCR procedures for detecting Phytophthora species. The assay was also used in a three-way multiplex format to simultaneously detect P. ramorum, P. pseudosyringae, and plant DNA in a single tube. P. ramorum was detected down to a 10(-5) dilution of extracted tissue of artificially infected rhododendron 'Cunningham's White', and the amount of pathogen DNA present in the infected tissue was estimated using a standard curve. The multiplex assay was also used to detect P. ramorum in infected California field samples from several hosts determined to contain the pathogen by other methods. The real-time PCR assay we describe is highly sensitive and specific, and has several advantages over conventional PCR assays used for P. ramorum detection to confirm positive P. ramorum finds in nurseries and elsewhere.  相似文献   

8.
In laboratory tests, mycelium and sporangia of Phytophthora meadii survived in soil for about 3 weeks, whereas chlamydospores survived for 12 weeks. When petioles of rubber (Hevea brasiliensis) colonized by P. meadii were buried in soil, chlamydospores formed in the tissues after about 2 weeks and P. meadii could be reisolated up to 22 weeks after burial. Colonized petioles buried in soil in a rubber plantation decayed more rapidly than those in laboratory tests, and attempts to reisolate P. meadii after 18 weeks were unsuccessful, although chlamydospores were still visible. P. meadii was isolated most readily from soil in a rubber plantation during epidemics of pod and leaf disease, suggesting that sporangia from these sources maintained soil inoculum at a high level. Inoculum detected in soil before pod and leaf infection may have arisen from subclinical infections or from chlamydospores surviving in petioles from the previous season.  相似文献   

9.
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10.
Forty eight isolates of Phytophthora cinnamomi from various host plants in France (35 isolates) and in other countries were tested for pathogenicity. Seedlings of chestnut, northern red oak, pine and eucalyptus were infected by soil contamination. Taproots, stems and bark strips of plants of chestnut and different oak species were inoculated with mycelium agar disks. Results of the different experiments were in good agreement. All isolates appeared pathogenic to all the different test species but with variable levels of virulence. Isolates with consistent low or high level of virulence, which could be used as standards in further studies, were identified. Interaction between P. cinnamomi isolates and host plant species was significant in terms of lesion lengths. These interactions could not be related to host from which P. cinnamomi was isolated. Consistent with this, in Quercus rubra, the isolate-provenance interaction was not significant. This feature is encouraging for provenance screening for resistance to P. cinnamomi in this species. The variation in virulence was not related to other isolate characteristics (mating type, electrophoretic type, age).  相似文献   

11.
Eighty-nine Phytophthora isolates from rubber throughout the world were examined critically. Five species were distinguished: P. palmivora morphological form I (MF1), P. meadii, P. botryosa, P. citricola, P. citrophthora and one currently designated P. palmivora (MF4). P. citrophthora is reported for the first time from rubber in the Ivory Coast and Indonesia, and mating types are given.  相似文献   

12.
Temperature and exposure time effects on Phytophthora kernoviae and Phytophthora ramorum viability were examined in flasks of compost and in a large‐scale composting system containing plant waste. Cellophane, rhododendron leaf and peat‐based inoculum of P. kernoviae and P. ramorum isolates were used in flasks; naturally infected leaves were inserted into a large‐scale system. Exposures of 5 and 10 days respectively at a mean temperature of 35°C in flask and large‐scale composts reduced P. kernoviae and P. ramorum inocula to below detection limits using semi‐selective culturing. Although P. ramorum was undetectable after a 1‐day exposure of inoculum to compost at 40°C in flasks, it survived on leaves exposed to a mean temperature of 40·9°C for 5 days in a large‐scale composting system. No survival of P. ramorum was detected after exposure of infected leaves for 5 days to a mean temperature of ≥41·9°C (32·8°C for P. kernoviae) or for 10 days at ≥31·8°C (25·9°C for Phytophthora pseudosyringae on infected bilberry stems) in large‐scale systems. Fitted survival probabilities of P. ramorum on infected leaves exposed in a large‐scale system for 5 days at 45°C or for 10 days at 35°C were <3%, for an average initial infection level of leaves of 59·2%. RNA quantification to measure viability was shown to be unreliable in environments that favour RNA preservation: high levels of ITS1 RNA were recovered from P. kernoviae‐ and P. ramorum‐infected leaves exposed to composting plant wastes at >53°C, when all culture results were negative.  相似文献   

13.
Phosphate was shown to reverse the in vitro activity of phosphonate ions against P. capsici (strain 375) more efficiently in liquid than in solid media. Phosphonate transport by mycelia incubated in aqueous solutions was enhanced by a previous phosphate starvation and the presence of K+ cations. The intracellular phosphonate concentration reached a constant level and this concentration, which is a function of the external concentration, fits a hyperbolic relationship. Phosphonate transport was greatly stimulated when mycelia were incubated in modified Ribeiro's medium. In the absence of any phosphorus source in the growth medium, the phosphate content of mycelia at stationary phase of growth decreased. This sign of phosphate deficiency was intensified in the presence of phosphonate.  相似文献   

14.
Invasive Phytophthora species are responsible for severe tree diseases in many forest ecosystems in Europe. In Hungary, the symptoms were first noted when P. alni infection led to a serious decline and mortality of alder stands in the late 1990s. Between 2001 and 2009, over 300 soilborne Phytophthora isolates were collected from declining broadleaf forests in Hungary, and 10 Phytophthora species identified based on morphological traits and the molecular characteristics of the internally transcribed spacer (ITS) regions of the nuclear ribosomal DNA. The most diverse species spectrum, found in diseased alder stands, included P. gonapodyides, P. gregata, P. inundata, P. lacustris, P. megasperma, P. plurivora, one informally designated taxon: P. taxon hungarica, and one unnamed species P. sp.1. P. cactorum and P. plurivora isolates were prevalent in the soil of a declining eastern black walnut forest, and three species, P. gonapodyides, P. multivora and P. plurivora were recovered from a declining oak stand. More than one ITS-based genotype was identified for four species, including six genotypes for P. gonapodyides, and two each for P. cactorum, P. plurivora and P. inundata. The high genetic diversity of the P. gonapodyides isolates may indicate that the species is indigenous to the region. In contrast, the frequently recovered, widely distributed P. lacustris with a single ITS genotype may represent a recent colonizer. The P. multivora isolates are, to date, the first reported from a European native forest.  相似文献   

15.
Mycelial growth, polyamine concentrations and the activities of enzymes of polyamine biosynthesis and catabolism were examined in Phytophthora infestans and Pythium ultimum grown in the presence of difluoromethylornithine (DFMO), an inhibitor of omithine decarboxylase (ODC), and difluoro-methylarginine (DFMA), an inhibitor of arginine decarboxylase (ADC). Growth of P. infestans was reduced by DFMO and a mixture of DFMO + DFMA, but was increased by DFMA at concentratiotis of 5 MM and greater, Polyamine concentrations and ODC activity were significantly reduced in P. infestans grown on all inhibitor treatments. In contrast, growth, polyamine concentrations and enzyme activities were not affected in P, ultimum exposed to the inhibitors.
It seems unlikely that P. infestans and P. uttimum possess ADC activity, as neither of the products of ADC activity (agmatine and putrescine) could be detected in ADC assays. Although ODC from P. infestans was sensitive to DFMO, ODC from P. uttimum was insensitive to the inhibitor. Moreover, uptake of DFMO by P. infestans was three times greater than that observed by P. ultimum.  相似文献   

16.
ABSTRACT Phytophthora cinnamomi isolates collected from 1977 to 1986 and 1991 to 1993 in two regions in South Africa were analyzed using isozymes. A total of 135 isolates was analyzed for 14 enzymes representing 20 putative loci, of which four were polymorphic. This led to the identification of nine different multilocus isozyme genotypes. Both mating types of P. cinnamomi occurred commonly in the Cape region, whereas, predominantly, the A2 mating type occurred in the Mpumalanga region of South Africa. A2 mating type isolates could be resolved into seven multilocus isozyme genotypes, compared with only two multilocus isozyme genotypes for the A1 mating type isolates. Low levels of gene (0.115) and genotypic (2.4%) diversity and a low number of alleles per locus (1.43) were observed for the South African P. cinnamomi population. The genetic distance between the Cape and Mpumalanga P. cinnamomi populations was relatively low (D(m) = 0.165), and no specific pattern in regional distribution of multilocus isozyme genotypes could be observed. The genetic distance between the "old" (isolated between 1977 and 1986) and "new" (isolated between 1991 and 1993) P. cinnamomi populations from the Cape was low (D(m) = 0.164), indicating a stable population over time. Three of the nine multilocus isozyme genotypes were specific to the "old" population, and only one multilocus isozyme genotype was specific to the "new" population. Significant differences in allele frequencies, a high genetic distance (D(m) = 0.581) between the Cape A1 and A2 mating type isolates, significant deviations from Hardy-Weinberg equilibrium, a low overall level of heterozygosity, and a high fixation index (0.71) all indicate that sexual reproduction occurs rarely, if at all, in the South African P. cinnamomi population.  相似文献   

17.
The newly described Phytophthora kernoviae (previously known as P. taxon C) was first found in the UK in October 2003 and has been subject to emergency European Community phytosanitary legislation since 2004. Since the first finding, P. kernoviae has been found on a limited number of shrub hosts in the UK. The majority of observations have been on Rhododendron ponticum where both leaves and stems may be affected. Symptoms range from slight necrosis of leaf tips through to extensive leaf lesions, stem cankers, defoliation and apparent death of the bush. Diagnosis of P. kernoviae begins in the field with the use of generic lateral flow test kits and is completed in the laboratory using cultural and molecular techniques. To date, the organism has been detected at 29 UK sites, mainly in the South West of England. DNA profiling has shown that isolates are related with no distinct groups or clusters based on host, geographical distribution or place of origin.  相似文献   

18.
Infection with Likubin bacterium (LB) followed by Phytophthora parasitica increased the mortality of sour orange and pummelo seedlings, and enhanced the P. parasitica-induced root rot in all the four types of citrus tested. The LB-induced enhancement of root infection by P. parasitica was apparent within 1h of exposure to zoospore suspension. The enhancement of P. parasitica-induced root rot was affected by the infection sequence. Inoculation of sour orange seedlings with LB before P. parasitica was more effective in increasing P. parasitica-induced root rot than LB and P. parasitica concomitantly or LB after P. parasitica. Grafting P. parasitica susceptible scions of ponkan (Citrus reticulata) onto P. parasitica-tolerant rootstocks of sour orange greatly increased the susceptibility of rootstocks to P. parasitica. Results also demonstrate the enhancement of LB-induced symptoms by P. parasitica in citrus plants.  相似文献   

19.
Antiserum (anti-PfM) raised against mycelial suspensions of Phytophthora fragariae isolates reacted strongly with antigens from several Phytophthora species. Some cross-reactions with antigens from Pythium species were decreased by fractionating on an affinity column of Sepharose 4B bound to extracts of Fragaria vesca roots infected with P. fragariae. The affinity-purified anti-PfM retained its high cross-reactivity with the various Phytophthora species tested. It also detected infection of raspberry and strawberry roots by some Phytophthora species. This antiserum could, therefore, prove useful as a broad-spectrum Phytophthora-detecting antiserum.
Anti-PfM could not be made specific for P. fragariae because it was raised against components shown to be antigenically similar in all Phytophthora species tested. However, immunoblotting with the affinity-purified anti-PfM produced distinct patterns for P. fragariae, P. erythroseptica and P. cactorum: three serotypes were identified for the latter species. This antiserum might therefore prove useful in classifying Phytophthora species.  相似文献   

20.
ABSTRACT Phytophthora root rot of citrus in Florida is caused by Phytophthora nicotianae and P. palmivora. A naturally occurring isolate of P. nicotianae (Pn117) was characterized as hypovirulent on citrus roots. Pn117 infected and colonized fibrous roots, but caused significantly less disease than the virulent isolates P. nicotianae Pn198 and P. palmivora Pp99. Coincident inoculation of rootstock seedlings of Cleopatra mandarin (Citrus reticulata) or Swingle citrumelo (C. paradisi x Poncirus trifoliata) with the hypovirulent Pn117 and the virulent isolates Pn198 and Pp99 did not reduce the severity of disease caused by the virulent Phytophthora spp. When either rootstock was inoculated with the hypovirulent Pn117 for 3 days prior to inoculation with virulent isolates, preinoculated seedlings had significantly less disease and greater root weight compared with seedlings inoculated with the virulent isolates alone. Recovery of the different colony types of Phytophthora spp. from roots of sweet orange (C. sinensis) or Swingle citrumelo was evaluated on semiselective medium after sequential inoculations with the hypovirulent Pn117 and virulent Pp99. Pn117 was isolated from roots at the same level as the Pp99 at 3 days post inoculation. Preinoculation of Pn117 for 3 days followed by inoculation with Pp99 resulted in greater recovery of the hypovirulent isolate and lower recovery of the virulent compared with coincident inoculation.  相似文献   

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