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1.
Phlomis purpurea (Lamiaceae), found in Quercus suber and Quercus ilex ssp. rotundifolia forest habitats in southern Portugal, is a non-host for the oomycete Phytophthora cinnamomi, the main biotic factor involved in cork oak and holm oak decline in the Iberian Peninsula. The effect of P. purpurea crude ethanol root extract was evaluated in vitro on P. cinnamomi mycelial growth, sporangial production, zoospore release and germination as well as on chlamydospore production and viability. The protection of cork oak against infection by the pathogen was also evaluated in planta. At 10 mg ml?1, in vitro inhibition of the pathogen structures was 85–100 %. In addition, P. purpurea plants were shown to protect Q. suber and Q. ilex from P. cinnamomi infection and to reduce the inoculum potential in glasshouse trials, indicating the ability to reduce root infection by the pathogen. The results suggest that P. purpurea has the potential to reduce disease spread and that their root extracts could provide candidate substances for control of the important pathogen, P. cinnamomi.  相似文献   

2.
The virulence of two wild type (PA45 and PA37) and two genetically modified (13C: hygromycin resistant; FATSS: hygromycin resistant and β-cin knock-down) Phytophthora cinnamomi strains towards cork oak (Quercus suber) was assessed via a quantitative evaluation of disease symptoms arising from a soil infestation assay, and by a histological analysis of root colonization. Comparison of virulence, as expressed by symptom severity, resulted in the following ranking: highly virulent (wild type strains), medium virulence (strain 13C) and weakly virulent (FATSS). Both transgenic strains were compromised in their virulence, as expressed by symptom severity, but strain 13C was much less affected than FATSS. Microscopic observation showed that the FATSS strain was unable to effectively invade the root, while 13C and the two wild type strains were all able to rapidly colonize the whole root, including the vascular tissue. These results strengthen the notion that elicitins are associated, either directly or indirectly, with the infection process of Phytophthora.  相似文献   

3.
In Portugal, the oak pinhole borer Platypus cylindrus and its mycobiota have been associated with cork oak (Quercus suber) death, but no knowledge exists regarding the associated bacterial community. However, it is known that some bacteria are important for ambrosia beetle symbiosis and play a role in oak tree health. To explore the bacteria associated with this beetle and its host, with the ultimate goal of highlighting potential roles in oak decline, this study used a culture-dependent approach for strain isolation and phylogenetic identification using 16S rRNA gene sequencing and multilocus sequence analysis (MLSA). The bored galleries of different cork oak trees from a cork stand in Alentejo, together with the body and mycangia of adult beetles, were investigated. The samples revealed a diverse community comprising 500 isolates with 64 distinct types of bacterial colonies. Sixty-eight strains were selected for sequencing and used for phylogenetic analysis, 40 from wood galleries and 28 from beetles. Thirty-two genera of bacteria were identified, 18 of which were described for the first time within oak–beetle interactions. Major taxonomic groups were Actinobacteria in beetles and Enterobacterales in wood galleries. Although specific oak bacterial pathogens were not detected, a group of distinct strains detected in wood galleries, potentially belonging to a new Pectobacteriaceae species, were able to produce mild symptoms on cork oak plantlets. This study reports for the first time the biodiversity of culturable bacteria associated with the Q. suber–P. cylindrus interaction, their relevance to both organisms and the possible contribution to oak decline.  相似文献   

4.
In Australia, Phytophthora cinnamomi is the only species reported as the causal agent of stem canker and root rot in macadamia. In other countries, five Phytophthora species have been reported to cause diseases in macadamia, which led us to question if more than one Phytophthora species is responsible for poor tree health in macadamia orchards in Australia. To investigate this, samples were collected from the rhizosphere, stem, and root tissues of trees with and without symptoms, nurseries, and water sources from 70 commercial macadamia orchards in Australia. Phytophthora isolates were identified based on morphological characteristics and DNA sequencing. P. cinnamomi was the most predominant and widely distributed species, and was obtained from the different types of samples including symptomless root tissues. In addition to P. cinnamomi, only P. multivora was isolated from diseased tissue (stem canker) samples. Six other Phytophthora species were obtained from the rhizosphere samples: P. pseudocryptogea, P. citrophthora, P. nicotianae, P. gondwanense, P. sojae, and a new Phytophthora taxon. Only P. cinnamomi was obtained from macadamia nursery samples, while five Phytophthora species were obtained from water sources. Of the heterothallic Phytophthora species, mating type A2 isolates were dominant in P. cinnamomi isolates, whereas only mating type A1 isolates were obtained for P. nicotianae, P. pseudocryptogea, and P. citrophthora. Pathogenicity assays revealed that P. cinnamomi and P. multivora caused significantly larger stem and leaf lesions than P. citrophthora, P. nicotianae, and P. pseudocryptogea. Phytophthora sp. and P. sojae were nonpathogenic towards leaves and stems.  相似文献   

5.
Based on the observation that the root disease caused by P. cinnamomi on Q. ilex has a low incidence and severity in soils with medium-high Ca2+ content, we studied the ability of Ca2+ fertilizers to induce soil suppressiveness to the pathogen. Studies on cultures of P. cinnamomi exposed to different Ca2+ fertilizers in vitro showed significant inhibition of sporangial, chlamydospore and zoospore production at millimolar concentrations while mycelial growth was mainly unaffected. Experiments performed with artificially infested soil showed that some Ca2+ fertilizers induce a significant decrease on chlamydospore viability. Additionally, greenhouse experiments using artificially infested soils showed a significant reduction of foliar and root symptom severities in Holm oak seedlings growing in soils amended with Ca2+ fertilizers. We suggest that limestone amendments in oak rangelands could enhance the suppressiveness of soils to P. cinnamomi, and it is likely that the inhibition of sporangial production was the main mechanism involved.  相似文献   

6.
Forest declines are usually complex multifactorial phenomena that involve interactions between different factors. The possible interaction between different types of mycelial pathogens was investigated through artificial inoculation of oak seedlings, involving two root rot basidiomycetes, Collybia fusipes and Armillaria mellea, and two Phytophthora species, P. cinnamomi and P. cambivora. These pathogens were inoculated onto young Quercus robur saplings in greenhouse conditions, either alone or combining a root rot basidiomycete with a Phytophthora species. Three out of the four Phytophthora spp.*root rot basidiomycete combinations tested resulted in significantly greater damage to the oak host than the sum of the damages induced by the individual pathogens. This positive interaction could be significant in oak decline syndrome.  相似文献   

7.
Arabidopsis thaliana (Arabidopsis) Col-0 was inoculated with Phytophthora cinnamomi to assess the interaction and defence responses involved. Pathogen ingress and asexual reproduction occurred on root tissue but not leaf tissue. The colonisation of root tissue did not cause disease symptoms or plant death, indicating that Arabidopsis Col-0 was tolerant of the infection. The induction of several plant defence responses including the expression of defence-related genes were found, with differences displayed between inoculated root and leaf tissue. Arabidopsis defence-related gene mutant/over-expressing lines were also inoculated with P. cinnamomi but none of the lines tested exhibited a marked increase in susceptibility to the pathogen.  相似文献   

8.
Quercus ilex is one of the European forest species most susceptible to root rot caused by the oomycete Phytophthora cinnamomi. This disease contributes to holm oak decline, a particularly serious problem in the ‘dehesas’ ecosystem of the southwestern Iberian Peninsula. This work describes the host–pathogen interaction of Q. ilex and P. cinnamomi, using new infection indices at the tissue level. Fine roots of 6‐month‐old saplings inoculated with P. cinnamomi were examined by light microscopy and a random pool of images was analysed in order to calculate different indices based on the measured area of pathogen structures. In the early stages of invasion, P. cinnamomi colonizes the apoplast and penetrates cortical cells with somatic structures. On reaching the parenchymatous tissues of the central cylinder, the pathogen develops different reproductive and survival structures inside the cells and then expands through the vascular system of the root. Some host responses were identified, such as cell wall thickening, accumulation of phenolic compounds in the middle lamella of sclerenchyma tissues, and mucilage secretion blocking vascular cells. New insights into the behaviour of P. cinnamomi inside fine roots are described. Host responses fail due to rapid expansion of the pathogen and a change in its behaviour from biotrophic to necrotrophic.  相似文献   

9.
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10.
Biscogniauxia mediterranea is one of the most frequent fungal pathogens involved in cork oak decline in the Mediterranean Basin, causing charcoal canker. In Portugal, this disease is widespread on adult declining trees but nowadays it increasingly affects young trees and exhibits atypical symptoms, leading to the hypothesis that some change in the fungus may have occurred. In order to evaluate the genetic diversity and phylogenetic relationship of B. mediterranea associated with cork oak, 102 isolates were obtained from young and adult trees of Quercus suber and other hosts species with different disease expression, from several Mediterranean countries. The collection of isolates was analyzed by individual and multigene phylogenies using Maximum-Likelihood approach based on nucleotide sequences of the internal transcribed spacers of ribosomal DNA, translation elongation factor 1-α and β-tubulin genes, and by microsatellite-primed PCR profiles. Sequence analyses separated the Mediterranean isolates from those from other regions, while MSP-PCR analysis revealed relevant but unstructured diversity among the Mediterranean isolates under study, making this a monophyletic but diverse population. Considering the adaptive capacity of the fungus in the Mediterranean-climate ecosystems and the present climatic change scenario, all conditions are gathered to favor aggravation of the disease in cork oak stands.  相似文献   

11.
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12.
Ultrastructural aspects of host–parasite interactions were investigated in fruits and leaves of citrus (satsuma mandarin) infected with Elsinoe fawcettii. Fungal infection induced host tissues to form cork layers bordering the necrotic areas below the infected sites. The cork layers were composed of compact host cells with convoluted cell walls and alternating lamellations, indicating ligno–suberized tissues in the wound periderm. No host tissues below the cork layers were invaded by hyphae. Hyphae grew intercellularly and intracellularly, often causing hypertrophy and compartmentalization of infected host cells. Also, host cells adjacent to invading hyphae showed accumulation of electron-dense materials and the formation of host cell wall protuberances in intercellular spaces. Hyphae had concentric bodies that showed an electron-transparent core surrounded by an electron-dense layer with radiating filamentous structures on their surface. One or more intrahyphal hyphae were found in the cytoplasm of intercellular or intracellular hyphae. These results suggest that the ligno–suberized cork layers in the wound periderm of citrus act as a protective barrier, which leads to restricted growth of E. fawcettii in bordered scab lesions. The fungus is thought to form concentric bodies and intrahyphal hyphae as a survival mechanism against the water- and nutrient-deficient environments that occur in the cork layers of necrotic host parts.  相似文献   

13.
The pathogenicity of some Phytophthora species recently described from Western Australia, together with P. cinnamomi as a control, was tested against seven Western Australian native plant species in the glasshouse. Host species were Banksia grandis, B. littoralis, B. occidentalis, Casuarina obesa, Corymbia calophylla, Eucalyptus marginata and Lambertia inermis. Twenty‐two Phytophthora species were grown on a vermiculite, millet seed and V8 substrate and used as soil inoculum when the plant hosts were approximately 3 months old. Pathogenicity was assessed after 6 weeks and plants were scored for death, root damage, and percentage reduction of shoot growth compared with control plants. The pathogenicity of P. cinnamomi was confirmed. Phytophthora niederhauserii was shown to be similar to P. cinnamomi in pathogenicity and of concern ecologically. Other species that killed one or more hosts were P. boodjera, P. constricta, P. elongata, P. moyootj and P. rosacearum, while P. condilina, P. gibbosa, P. gregata, P. litoralis and P. ‘personii’ caused significant reduction to shoot and/or root growth, but did not kill plants. Host species susceptible to the highest number of Phytophthora species were B. grandis, B. littoralis, B. occidentalis and E. marginata. No Phytophthora species tested killed C. calophylla.  相似文献   

14.
ABSTRACT Phytophthora ramorum, causal agent of sudden oak death, is responsible for widespread oak mortality in California and Oregon, and has the potential to infect 100 or more species. Symptoms range from stem girdling and shoot blight to leaf spotting. In this study, we examined the physiological impacts of P. ramorum infection on Rhododendron macrophyllum. In stem-inoculated plants, photosynthetic capacity (V(cmax)) significantly declined by approximately 21% 3 weeks after inoculation in visibly asymptomatic leaves. By 4 weeks, after the development of significant stem lesions and loss in water transport capacity, water stress led to stomatal closure and additional declines in photosynthetic capacity. We also report the isolation, characterization, and biological activity of two P. ramorum elicitins. Both elicitins were capable of inducing a hypersensitive-like response in one incompatible (Nicotiana tabacum SR1) and three compatible hosts (R. macrophyllum, Lithocarpus densiflorus, and Umbellularia californica). Infiltration of leaves from all three compatible hosts with both P. ramorum elicitins caused significant declines in chlorophyll fluorescence (F(v) /F(m)). For all four species, the loss of photosynthetic capacity was directly proportional to H(+) uptake and ethylene production, two common components of the hypersensitive response. This is the first report of elicitins causing photosynthetic declines in compatible hosts independent of plant water stress.  相似文献   

15.
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16.
The genetic diversity of Phytophthora spp. was investigated in potted ornamental and fruit tree species. A metabarcoding approach was used, based on a semi‐nested PCR with Phytophthora genus‐specific primers targeting the ITS1 region of the rDNA. More than 50 ITS1 sequence types representing at least 15 distinct Phytophthora taxa were detected. Nine had ITS sequences that grouped them in defined taxonomic groups (P. nicotianae, P. citrophthora, P. meadii, P. taxon Pgchlamydo, P. cinnamomi, P. parvispora, P. cambivora, P. niederhauserii and P. lateralis) whereas three phylotypes were associated to two or more taxa (P. citricola taxon E or III; P. pseudosyringae, P. ilicis or P. nemorosa; and P. cryptogea, P. erythroseptica, P. himalayensis or P. sp. ‘kelmania’) that can be challenging to resolve with ITS1 sequences alone. Three additional phylotypes were considered as representatives of novel Phytophthora taxa and defined as P. meadii‐like, P. cinnamomi‐like and P. niederhauserii‐like. Furthermore, the analyses highlighted a very complex assemblage of Phytophthora taxa in ornamental nurseries within a limited geographic area and provided some indications of structure amongst populations of P. nicotianae (the most prevalent taxon) and other taxa. Data revealed new host–pathogen combinations, evidence of new species previously unreported in Italy (P. lateralis) or Europe (P. meadii) and phylotypes representative of species that remain to be taxonomically defined. Furthermore, the results reinforced the primary role of plant nurseries in favouring the introduction, dissemination and evolution of Phytophthora species.  相似文献   

17.
The purpose of this research was to identify the pathogens causing root and crown rot in major pomegranate-growing areas of Iran. Infected tissue samples were collected from trees with symptoms from 49 pomegranate orchards in four provinces of Iran: Fars, Markazi, Isfahan, and Kohgiluyeh va Boyer-Ahmad. In total, 23 Phytophthora spp. isolates were obtained, which were identified as P. cryptogea species complex (12 isolates) and P. cinnamomi (11 isolates) based on morphological characters. Molecular confirmation of identification was performed by inference of phylogeny of ITS-rDNA regions, β-tubulin gene, and the mitochondrial gene cytochrome c oxidase subunit 1. The results of our phylogenetic analysis confirmed the morphological identification of P. cinnamomi isolates and placed them in Clade 7c of Phytophthora. In addition, the P. cryptogea species complex isolates, despite morphological similarities, were in fact four distinct species including P. cryptogea sensu stricto (two isolates), P. pseudocryptogea (one isolate), P. sp. kelmania (one isolate), and P. erythroseptica (six isolates). This is the first report of pomegranate root and crown rot caused by P. cinnamomi and P. cryptogea species complex.  相似文献   

18.
The mechanisms by which Phytophthora cinnamomi zoospores infect inundated, above‐ground woody stem tissue are described. Using 4–6‐ and 18‐month‐old jarrah seedlings, the infection courts were identified and the invasion of the stems at sites of zoospore cyst binding were described. Stems were inoculated with a suspension of motile zoospores on the green stem/young periderm region. Light microscopy was used to examine penetration at sites of taxis, and fluorescent microscopy was used to examine penetration sites of seedlings with intact periderm. Two main infection courts were identified on stems: the emerging axillary shoot and the region of stem immediately surrounding an axillary shoot, where the periderm was thin or discontinuous. Invasion also occurred at sites where the developing shoot had not yet emerged but was at the stem surface. At these sites the pathogen also directly invaded through the thin‐walled phellem of the periderm surrounding the shoot. Zoospores of P. cinnamomi were not attracted to stomata on mature leaves or green stems. Penetration of the epidermal cell layer of the axillary bud leaf primordia was inter‐ and intra‐cellular; growth of hyphae in the periderm surrounding the shoot was intercellular; while in collenchyma it was inter‐ and intra‐cellular, being intercellular between polyphenolic‐rich cells. Exposed stem collenchyma was also directly invaded immediately adjacent to the young axillary shoot. Zoospores demonstrated taxis to sites of discontinuous periderm, similar to wounded areas where the outer protective layers of the plant are breached. This study presents the first evidence that P. cinnamomi is capable of intercellular penetration of suberized periderm.  相似文献   

19.
The genus Phytophthora contains species that are major pathogens worldwide, affecting a multitude of plant species across agriculture, horticulture, forestry, and natural ecosystems. Here, we concentrate on those species that are dispersed through soil and water, attacking the roots of the plants, causing them to rot and die. The intention of this study was to compare the soil baiting protocol developed by the Centre for Phytophthora Science and Management (CPSM) with two other baiting methods used in Australia. The aim was to demonstrate the effectiveness of each protocol for soil baiting Phytophthora species in different substrates. Three experiments were conducted: the first to test the sensitivity of each method to detect Phytophthora cinnamomi, the second to test the effect of substrate type (sand or loam), and the third to test the detection of species (P. cinnamomi, P. multivora, or P. pseudocryptogea). The specificity of different plant species baits was compared within and between the methods. Substrate type influenced isolation in all methods; however, the CPSM method was superior regardless of substrate, albeit slower than one of the other methods for one substrate. Comparing bait species between the three methods, Quercus ilex was the most attractive bait for P. cinnamomi, particularly in the CPSM method. The choice of protocol affected the isolation associated with each bait type. Overall, the multiple bait system used by CPSM was shown to provide the most sensitive and reliable detection of Phytophthora species from soil samples.  相似文献   

20.
Resistant annual and herbaceous perennial plant species were identified as key hosts which allow Phytophthora cinnamomi to persist on severely impacted black gravel sites within the Eucalyptus marginata (jarrah) forest of southwest Western Australia. Of the annual and herbaceous perennial plant species present on black gravel sites, 15 out of 19 species were found to be hosts of P. cinnamomi, and 10 of these were symptomless hosts. In particular, the native annual Trachymene pilosa and the two native herbaceous perennials Stylidium diuroides and Chamaescilla corymbosa were commonly found to be hosts of the pathogen. Species from 12 new genera including three from new families (Crassulaceae, Droseraceae and Primulaceae) are reported for the first time to be hosts of P. cinnamomi. The species from which P. cinnamomi was recovered were the native species: Chamaescilla corymbosa, Crassula closiana, Drosera erythrorhiza, Hydrocotyle callicarpa, Levenhookia pusilla, Paracaleana nigrita, Podotheca angustifolia, Pterochaeta paniculata, Rytidosperma caespitosum, Siloxerus multiflorus, Stylidium diuroides and Trachymene pilosa, and the introduced annual weeds Hypochaeris glabra, Lysimachia arvensis and Pentameris airoides.  相似文献   

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