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1.
This review comprises both well‐known and recently described Phytophthora species and concentrates on Phytophthora–woody plant interactions. First, comprehensive data on infection strategies are presented which were the basis for three models that explain invasion and spread of Phytophthora pathogens in different woody host plants. The first model describes infection of roots, the second concentrates on invasion of the trunk, and the last one summarizes infection and invasion of host plants via leaves. On the basis of morphological, physiological, biochemical and molecular data, scenarios are suggested which explain the sequences of reactions that occur in susceptible and tolerant plants following infections of roots or of stem bark. Particular emphasis is paid to the significance of Phytophthora elicitins for such host–pathogen interactions. The overall goal is to shed light on the sequences of pathogenesis to better understand how Phytophthora pathogens harm their host plants.  相似文献   

2.
Phytophthora species secrete several proteins during their interaction with plants. Some of these proteins manipulate host metabolism favouring infection, while others can be recognized by plants thus triggering defence. Elicitins are known to elicit plant defences, leading to resistance. Here, we characterized the elicitin α‐plurivorin and proved that it was essential for the virulence of Phytophthora plurivora towards Fagus sylvatica. The immunodepletion of this peptide impaired its penetration into host tissue and in parallel P. plurivora lost its ability to colonize beech roots. Furthermore, the lack of α‐plurivorin inside the host led to an up‐regulation of several defence‐related genes of both salicylic acid and jasmonate/ethylene pathways, suggesting that α‐plurivorin might act as an effector‐triggered susceptibility during infection. Consequently, plants survived infection with P. plurivora after α‐plurivorin immunodepletion, whereas the majority of the infected control plants had died at the end of the experiment. Because canonical elicitins are ubiquitously secreted by many Phytophthora species, it is possible that these molecules may play a similar role in other susceptible interactions, being a potential target for controlling Phytophthora diseases.  相似文献   

3.
Fagus sylvatica saplings were infected with Phytophthora citricola, Phytophthora cambivora, Phytophthora pseudosyringae and Phytophthora undulata to study the influence of these root pathogens on total belowground and aboveground biomass, on the nutrient distribution within plants, on the concentration of plastid pigments, including tocopherol and on components of the xanthophyll cycle. Phytophthora citricola and P. cambivora infection significantly reduced total biomass of beech when compared with control plants and finally most of these plants died at the end of the experiment. However, beech invaded by the other two Phytophthora spp. did not differ from control plants and none of them was killed. Fine root length as well as the number of root tips of all infected beeches were reduced between 30 and 50%. The excellent growth of beech infected with P. pseudosyringae and P. undulata when compared with control plants was correlated with a strong increase of important root efficiency parameters. Phytophthora citricola and P. cambivora caused a significant reduction in nitrogen concentration of leaves in comparison with control and other infected plants, whereas this nutrient was slightly increased in fine and coarse roots. Furthermore, the phosphorus and potassium concentrations in leaves were impaired after infection with P. citricola. However, foliar concentrations of Ca and Mg were not affected by the different Phytophthora spp., whereas fine and coarse roots were significantly enriched with Ca in beech infected with P. citricola or P. cambivora. The concentrations of α‐tocopherol and xanthophyll cycle pigments were increased in plants infected by P. citricola and P. cambivora, indicating that several reactive oxygen species might be formed in leaves during infection.  相似文献   

4.
Modification in discase-sensibility of forest plants by herbicide treatment. I. Field trials with Lophodermium pinastri. The effect of two herbicides TOP-KH (salt of 2,4,5-T) and Casoron G (Dichlobenil) on incidence of Lophodermium pinastri on Scots pine (Pinus sylvestrií L.) was investigated in field trials with potted plants. Treatment with TOP-KH led to increase in infection with higher herbicide concentrations and to higher numbers of severely infected plants in comparison with controls. Differences were greatest in spring. With Casoron G, however, smaller numbers of sevcrely infected plants were seen in spring and at the end of the growing season the damage was not much greater than in the controls. Possible reasons for changes in degree of infection are discussed as well as effects that could be expected on the epidemiology of pine needle cast.  相似文献   

5.
The primary objective of this research was to determine whether native species of Castilleja and Pedicularis are naturally infected by Cronartium ribicola in whitebark pine ecosystems of the Oregon and Washington Cascade Range, USA. Secondary objectives were to monitor the phenology of aecial and telial hosts to determine whether there is sufficient time for C. ribicola to complete its life cycle within high‐elevation stands and to evaluate the variety of susceptible native host species within these genera through field and growth chamber inoculation. These objectives were approached through fieldwork in 2008 and 2009 in whitebark pine ecosystems at Mt. Rainier, Mt. Adams, Mt. Hood, Mt. Bachelor, Tumalo Mtn. and Crater Lake. Forty‐nine observational study plots were established and monitored. Natural C. ribicola infection was detected on 84 Pedicularis racemosa plants and five Castilleja plants (C. applegatei, C. miniata and C. parviflora). Field observation provided evidence that there is sufficient time for C. ribicola to complete its life cycle on hosts within high‐elevation whitebark pine stands. In 2009, 18 field inoculation plots were established at Mt. Rainier and Crater Lake. Field inoculation confirmed the susceptibility of two additional species within these genera, C. arachnoidea and P. bracteosa. All four Castilleja species inoculated in the growth chamber developed infection, with an overall infection incidence of 62% (167 out of 270 plants). The identity of the rust species on field specimens as C. ribicola was verified through PCR and sequencing of the ITS1‐5.8S‐ITS2 region of DNA. Improved understanding of the role of these newly recognized hosts in white pine blister rust epidemiology should be used to prioritize sites for the restoration of ecologically valuable whitebark pine.  相似文献   

6.
Rosellinia necatrix is a soilborne plant pathogenic fungus belonging to the phylum Ascomycota. The fungus is distributed widely in temperate zones and often causes huge economic losses on numerous crop plants. To determine the potential for wild plants to serve as inoculum reservoirs of white root rot disease, eight woody and two herbaceous plant species belonging to nine families were inoculated with two R. necatrix isolates. The species used were Actinidia polygama, Broussonetia kazinoki, Camellia sinensis, Castanea crenata, Hydrangea serrata, Magnolia obovata, Pteridium aquilinum, Petasites japonicus, Quercus serrata and Rosa multiflora, all common flora in the cool temperate forests of Japan. The mortality of plants varied between species, independent of the effect of fungal isolates. Although some of the plants survived fungal infection, all plant species tested were more or less susceptible, having rotting lesions on the inner bark and cortex. For the woody plants, most of the mycelial strands in the diseased tissues became plumose mycelia, growing compressed between the outer and inner barks. However, mycelia found in diseased tissues of the two herbaceous plants were not in the form of plumose mycelia. All plant species harboured mycelial strands on the surface of their root systems and underground main stem, and the amount of the mycelial strands did not correlate with the mortality of the plants. Even if plants exhibited no external symptoms, some of them harboured abundant mycelial strands. In conclusion, wild plants can serve as alternative host plants for R. necatrix and function as persistent inoculum reservoirs, irrespective of their apparent health status. Thus, assessments of such latent host plants must be considered in the course of managing white root rot.  相似文献   

7.
The aphid transmissibility and within-plant movement of two PVY isolates belonging to PVYO and PVYN strains were studied. Potato plants were infected by Myzus persicae either 1 week after emergence or 30 or 45 days after emergence. Infected leaves, petioles of infected leaves, and different segments of the stems of plants infected 1 week after emergence were ELISA-tested 7, 11 and 14 days after infection. Segments of the plants infected 30 or 45 days after emergence were ELISA tested 30 days after infection. Normalised ELISA values were used for statistical analyses. Virus infection of progeny tubers was assessed by post-harvest inspection. The ability of 15 aphid species to transmit the virus isolates was also examined. There was no difference in the aphid transmissibility of the two isolates 7 or 11 days after exposure to M. persicae. However, normalised ELISA values were significantly affected by both isolate and sampling date 11 and 14 days after M. persicae transmission. The level of infection of different stem segments was significantly affected by both isolate and growth stage of the plant at infection. The proportions of infected leaves, stem segments and progeny tubers were all significantly higher for PVYN than for PVYO. PVYN was more effectively transmitted by a number of different aphid species than was PVYO. Newly described vectors of PVYN include Schizaphis graminum, Aphis fabae cirsiacanthoides, Aphis spiraecola, Myzus ligustri, Aphis fabae, Aphis spiraephaga, Myzus cerasi, Macrosiphum rosae, Diuraphis noxia, Aphis pomi and Rhopalosiphum padi, while those of PVYO include Aphis fabae cirsiacanthoides, Myzus cerasi and Myzus ligustri.  相似文献   

8.
Seven different Phytophthora species were used to test the foliar susceptibility of the common eastern US oak species and understory plants to Phytophthora infection. The Phytophthora species employed were Phytophthora cambivora, Phytophthora cinnamomi, Phytophthora citricola, Phytophthora europaea, Phytophthora quercetorum, Phytophthora quercina‐like and Phytophthora sp1. Inoculation of detached‐leaves with agar plugs containing mycelia of Phytophthora provided an estimate of their relative susceptibility. Lesions were always greater when foliage was wounded and young. On deciduous plants, lesion sizes were considerably reduced with the increasing foliar age, although with evergreen plants lesion sizes remained similar regardless of foliar age when more aggressive isolates were tested. Infections seldom resulted when foliage was not wounded. With young and mature foliage, P. citricola usually produced the largest lesions. Young foliage of Quercus rubra was the most susceptible to infection followed by Castanea dentata for both wounded and non‐wounded inoculations. Mature foliage of Hamamelis virginiana, Kalmia latifolia and Quercus alba were the most susceptible to wound and non‐wound inoculations.  相似文献   

9.
Diplodia corticola is one of the most aggressive fungal pathogens of Quercus species and is involved in the decline of Mediterranean cork oak forests and Californian oaks. Information regarding variation in virulence between strains is scarce. We hypothesize that D. corticola strains differ in virulence and consequently induce different symptoms in infected plants. To test this, infection assays were carried out on Quercus suber half‐sib seedlings with seven strains of D. corticola. Visual symptoms of infection (external lesions, leaf wilting, exudation and others) were recorded in parallel with physiological and biochemical parameters. All strains were able to cause lesions but at differing levels of aggressiveness. We show that internal lesion length did not correlate directly with strain aggressiveness and this agrees with physiological parameters that should be taken into account to infer about strain pathogenicity. Infection by all strains induced an overall negative impact on the net photosynthetic rate and an increase in the oxidative stress status of plants; however, significant differences were found when the effects of different strains were compared. Results also suggest that being under optimum growth conditions, prior to and during infection, allowed plants to respond to the pathogen. At the end of the experiment, some strains of D. corticola established a latent pathogen‐like relationship with cork oak. This is the first study to show that D. corticola virulence is strain‐dependent.  相似文献   

10.
Infection patterns in Scots pine plantations by Armillariella mellea (Vahl.) Karst. Macro- and microscopic analyses of Scots pine root systems in plantations infected by Armillariella mellea are described. Forms of infection and states of penetration are determined and correlated with resistance reactions. Variation of Armillariella attack is discussed in connection with the variation within the population of the host plants and parasites.  相似文献   

11.

Spore germination, growth and appresssoria formation for Melampsora willow rust were studied for compatible and incompatible hosts to elucidate penetration specificity and prehaustorial events in the infection process. Rust originating from Salix dasyclados was inoculated on a compatible (S. dasyclados) and an incompatible (Salix daphnoides) clone and, for comparison, on the non-host plants tomato, tobacco and poplar. The same experimental procedure was also carried out for rust originating from poplar. Rust development was followed for 5 days at 20 h intervals using a microscope with fluorescent equipment. The study showed that the Melampsora rust can develop on, and penetrate, the leaf regardless of whether the rust was inoculated on compatible or incompatible willow plants. However, the fungus was able to infect and reproduce itself only in compatible interactions. For willow rust in the prehaustorial stage, the study indicated that specific recognition mechanisms were unnecessary to start the infection process.  相似文献   

12.
A new inoculation method for testing the resistance of poplars to bacterial canker caused by Xanthomonas populi subsp. populi (Ridé) Ridé & Ridé is discussed. The procedure is based on a more natural infection method and involves spraying plants in spring with bacterial suspensions.  相似文献   

13.
Dwarf mistletoes (Arceuthobium species) are arboreal, hemiparasitic plants of conifers that can change the structure and function of the tree crown. Hemlock dwarf mistletoe (Arceuthobium tsugense subsp. tsugense) principally parasitizes western hemlock (Tsuga heterophylla) and effects 10.8% of all western hemlock trees in Oregon, USA. In this study, we climbed 16 western hemlock trees (age 97–321 years, height 33–54.7 m) across a gradient of infection (0%–100% of branches infected) and measured occurrence of all dwarf mistletoe infections, dwarf mistletoe caused deformities, foliage, branch and crown metrics, and sapwood area. We then modelled over 25 different response variables using linear and generalized linear models with three metrics of severity as explanatory variables: total infection incidence, proportion of all live branches infected, and proportion of all live, infected branches with 33 per cent or more foliage distal to infection. A strong effect of dwarf mistletoe intensification was the reduction of branch foliage and an increase in the proportional amount of foliage distal to infections, with severely infected trees having the majority of foliage distal to infections. Increasing severity led to an apparent crown compaction as crown volumes decreased and became increasingly comprised of deformities. Sapwood area was unrelated to infection severity. Branch length and diameters were unrelated to increasing infection severity despite severely infected branches supporting 1–70 infections. The most severely infected tree had 3,615 individual plants in the crown. Our results suggested that shifts in crown structure and branch deformation, foliage amount, and foliage distal to infection, reflected a likely reduction of capacity for tree growth that coincided with a hypothesized increase in resource demand by dwarf mistletoe plants as infection severity intensified.  相似文献   

14.
Laurel wilt, caused by Raffaelea lauricola, is a lethal, vascular disease of avocado, Persea americana. Its impact on xylem function was examined in artificially inoculated plants of the ‘Simmonds’ cultivar. Three, 7, 14, 21 and 42 days after inoculation (dai), plants were rated externally and internally for disease severity on a subjective one (asymptomatic) to 10 (dead or 100% symptomatic) scale. Stems were then cut under water, 15 cm below the inoculation point, and placed in 0.1% aqueous solutions of acid fuschin in a greenhouse. After 48 h, the percentage of functional xylem was estimated 10 and 5 cm above and below the inoculation point by quantifying acid fuschin‐stained portions of digitized stem cross‐sections. Hydraulic conductivity was determined by placing the proximal end of 5‐cm‐long stem sections, harvested between 5 and 10 cm above the inoculation point, in water and quantifying the volume of water that was drawn over time through the distal end under partial pressure (350 mm Hg). Functional xylem decreased by 3 dai, well before the development of vascular discoloration (7 dai) and wilting of foliage (14 dai). By 14 dai, extensive vascular discoloration had developed and there was a dramatic reduction in functional xylem; plants with internal disease severities of 7 or greater had <20% functional xylem. Hydraulic conductivity decreased exponentially as non‐functional xylem and disease severity increased. In plants with internal severities >7, mean flow rates of water were 0.07 ml?1 min?1 cm?2vs. 42 ml?1 min?1 cm?2 in mock‐inoculated plants. The rapid development of these changes suggests that it may be difficult to manage laurel wilt in avocado once plants are infected by R. lauricola. Better understanding of the temporal and spatial development of infection and how the host responds to infection may assist efforts to select laurel wilt‐tolerant avocado cultivars.  相似文献   

15.
The effects of poplar varietal mixture on infection levels caused by Melampsora larici-populina and on plant growth were studied during two consecutive growing seasons. The varietal mixture consisted of an intimate mixture of three poplar clones, Populus x interamericana‘Boelare’, ‘Rap’ and Populus candicans‘NNT’, expressing different race-specific resistances. Infection levels of M. larici-populina were assessed in monoclonal and polyclonal plots. Plant heights were determined at the end of each growing season. Infection levels in the growing season of the first year were not significantly different between monoclonal and polyclonal plots at the end of the epidemic. During the second growing season, a naturally occurring complex pathotype, able to infect clones ‘Boelare’ and ‘Rap’, invaded some plots prematurely and changed the composition of pathogen population. During this season, four infection assessments were conducted. Infection reduction in polyclonal plots compared with monoclonal plots was observed on ‘Boelare’ and P. candicans plants. Nevertheless, no significant difference was observed for growth between monoclonal and polyclonal plots. Biological factors which may be involved in the reduction of infection levels in polyclonal plots are dilution of susceptible individuals, physical barriers caused by resistant plants and cross-protection. A high auto-infection ratio may have partly hidden the positive effects of the clonal mixture.  相似文献   

16.
Microsite influences on resource allocation related to silvopastoral swards undergoing repeated defoliation are unclear. Defoliating traditional pasture species according to canopy development criteria may not be appropriate when the plants grow as understory crops in woodlots. An experiment using container-grown plants was conducted under field conditions to determine how open (O), shaded woodland (W) and open-to-shaded woodland transition zones (E O, E W), representing the partial shade conditions found in silvopastoral settings, influenced productivity and dry matter allocation in Dactylis glomerata L. Plants established in spring (SP) and late summer (LS) were clipped each time mean sward height reached 20 cm. Dry matter production differed for SP and LS plantings, and was greater in O than W sites. Dry matter allocation to shoots of SP plants indicated some agronomic benefit associated with the E O and E W sites. Leaf mass did not vary with irradiance, but stembase mass did. The SP plants had numerous small tillers whereas LS plants were composed of comparatively fewer but more massive tillers. Plants growing at O, E O and E W were similar, whereas plants in the W site were smaller and had the fewest tillers regardless of planting time. Results suggest that defoliation management for shaded components of silvopastoral systems should be based on some index other than sward height, and that management criteria might change during the growing season. Less intensive removal (e.g., 10-cm rather that 5-cm residue) should be considered for defoliated, shade grown plants, since this could allow more stembase and nonstructural carbohydrate storage tissues to remain. The US Government’s right to retain a royalty-free, non-exclusive copyright is achnowledged.  相似文献   

17.
Seiridium cardinale, the cause of cypress canker disease, was found on Juniperus foetidissima, J. excelsa, J. oxycedrus and J. phoenicea, in a number of natural juniper woodlands in Greece. The presence of infections was sporadic in most cases, with a limited number of plants affected by the pathogen. At one locality in the Prespes Lakes region of northern Greece, however, the incidence of infection was very high, especially on J. foetidissima and J. excelsa. The identity of S. cardinale was confirmed using morphological characters and comparisons of DNA sequences for the β‐tubulin gene region. The pathogenicity of S. cardinale isolates from Juniperus and Cupressus was verified in cross‐inoculation trials on both potted and field grown plants.  相似文献   

18.
Within a research project on quality of plants for forestation of agricultural lands, we studied the aetiology of a late seedling rot affecting holm oak (Quercus ilex ssp. ballota) in two forest nurseries in southern Spain. Major disease symptoms were foliage wilting and necrosis of feeder roots. Phytophthora cinnamomi, Phytophthora cryptogea and Phytophthora drechsleri were isolated from necrotic roots of holm oaks. Selected isolates of the three Phytophthora species were pathogenic to Quercus ilex ssp. ballota and Quercus suber seedlings in artificial inoculations. Soil flooding conditions were essential for infection and root rot development. There was no host specificity among the species, the isolates of P. cinnamomi being the most virulent in all inoculated plants. In these inoculations, Q. ilex ssp. ballota plants were more susceptible than those of Q. suber. This work is the first report of P. cinnamomi, P. drechsleri and P. cryptogea affecting Q. ilex ssp. ballota in forest nurseries.  相似文献   

19.
In September 2013, a canker disease of Ficus nitida and F. benjamina was reported for the first time in Assiut governorate, Egypt. Infected samples were collected from various locations. Pure cultures of a fungus were isolated on potato dextrose agar at 25°C from diseased plants. Morphological investigation and DNA sequencing showed that the causal agent was Neoscytalidium dimidiatum. A pathogenicity test conducted using 2‐year‐old plants of each host gave 70%–80% infection, and the pathogen was reisolated from the inoculated plants. A pure culture of N. dimidiatum was deposited in the culture collection of the Assiut University Mycological Centre (AUMC) under the code AUMC 9293 and the ITS sequence was placed in NCBI under accession number KX985929 .  相似文献   

20.
In Boswellia papyrifera （Del.） Hochst natural stands, we stud- ied the association of parasitic plants with B. papyrifera trees from which frankincense was tapped and marketed for domestic and export markets. Data on the rate of infection of parasitic plants on B. papyrifera was collected in three transects located at separate locations around Baha kar, northern Ethiopia. Each transect had ten circular sample plots of 400 m2 and separated by 100 m. Species composition, DBH, height, crown di- ameter, number of main, secondary and tertiary branches and number of parasitic plants on individual trees were recorded. Sixteen tree species were recorded in the combined sample plots. The parasitic plant associ- ated with B. papyrifera was identified as Tapinanthus globiferus. This parasite infected 38% of Boswellia trees in sample plots. The infection rate of the parasitic plant varied from 1 to 33 per Boswellia tree. The infection of T. globiferus on B. papyrifera was predominantly limited to tertiary small branchlets arising from secondary branches; parasitic plants were absent on thick main and secondary branches. In all plots, infectionof T. globiferus was exclusively limited to Boswellia trees. The influence of T. globiferus parasitism on growth of Boswellia trees and its influence on yield of incense production needs further investigation. Management of natural stands for frankincense production should include measures to reduce infection by T. globiferus.  相似文献   

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