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1.
J. Diez  L. Gil 《Forest Pathology》1998,28(6):399-407
Cell cultures of callus tissue cultures obtained from four elm genotypes (Ulmus minor; Ulmus minor×Ulmus pumila; [Ulmus carpinifolia×Ulmus glabra] × [Ulmus wallichiana×Ulmus glabra]; and Ulmus pumila), either susceptible or resistant to Dutch elm disease (DED) were exposed to culture filtrates of Ophiostoma ulmi and Ophiostoma novo-ulmi. Elm cells were largely affected by crude culture filtrate incorporated into the media. However, the correlation between ‘in vivo’ cell resistance and growth in the presence of culture filtrate was poor: the effects of fungal media components were greater than that exerted by fungal exotoxins. Therefore, it is concluded that these ‘in vitro’ assays cannot be used to evaluate resistance sources to DED in elms, or to assess specific pathogenicity of fungal isolates.  相似文献   

2.
Differences in elm susceptibility against Ophiostoma novo‐ulmi have been related with differences in timing and degree of the tree defence responses. In this study, we used Fourier transform‐infrared spectroscopy, coupled with chemometric methods, to detect progressive changes in the metabolic profile of Ulmus minor and U. minor × U. pumila xylem tissues after inoculation with O. novo‐ulmi. Differences between control and inoculated trees were detected at 30 and 60 days post‐inoculation (dpi) in U. minor, and at 15, 30 and 60 dpi in U. minor × U. pumila. These differences were related with increased levels of lignin in the xylem tissues, suggesting an earlier defence response to the infection in the hybrids.  相似文献   

3.
In 1995 a clone bank of elms from across Italy was created at Antella (Florence, I) under a European Union project. In 1998 an experimental planting of some clones from this source was established in Antella together with material from a similar clone bank in France and two reference clones: Commelin (relatively susceptible) and Lobel (relatively resistant). In May 2001, the elms were inoculated with Ophiostoma novo‐ulmi and disease development was assessed throughout that summer and the next. Significant differences in susceptibility were found between taxonomic groups, with putative natural hybrids between Ulmus minor and Ulmus pumila being the most resistant and Ulmus glabra the most susceptible. Significant differences were also found within U. minor, some clones being as resistant as Lobel. For U. minor, a statistically significant relation was found with latitude, southerly clones showing less disease than more northerly ones. Relationships were also found between disease severity and times to bud burst, these relationships applying both to the different taxonomic groups and within U. minor. Relationships between growth increment and disease severity were inconsistent. These results are discussed in relation to the intrinsic genetically‐controlled differences that exist between elms and to differences in susceptibility that occur as the growing season proceeds and as a consequence of environmental influences.  相似文献   

4.
The cellulolytic activity (exoglucanase, endoglucanase and β‐glucosidase) of Ophiostoma ulmi (four isolates), O. novo‐ulmi (19 isolates) and ‘fast‐waxy’ (five isolates) was determined in growth media containing carboxymethylcellulose (CMC) and cellulose powder. Differences in enzyme activities were observed among isolates, irrespective of the species and substrate used. Inoculation experiments on Ulmus minor with randomly selected isolates of O. ulmi (two isolates), O. novo‐ulmi (five isolates) and ‘fast‐waxy’ (two isolates) were also performed. Disease was assessed as the percentage of leaves showing yellowing and browning. Ophiostoma novo‐ulmi and ‘fast‐waxy’ isolates exhibited a great variability in their capacities to cause the disease. In the presence of CMC, a significant correlation between the activity of exoglucanase and β‐glucosidase in vitro and virulence was found.  相似文献   

5.
One hundred and eight Ophiostoma ulmi sensu lato isolates were collected from field elm trees with symptoms in 14 Prefectures of Greece. The purpose of this study was to assign Greek isolates to species and afterwards subspecies of the DED fungi and to analyse the genetic variability within the Greek populations of these pathogens. Isolates were compared with six reference strains belonging to O. ulmi and the two subspecies of O. novo‐ulmi. The structure of the population has been analysed by means of morpho‐physiological features (growth rates, colony morphology and fertility responses) and by DNA sequencing and PCR‐RFLP amplification of the cerato‐ulmin (cu) and the colony type (col1) gene regions. According to fertility tests, both subspecies of O. novo‐ulmi were detected in Greece, but none of the isolates collected was identified as O. ulmi. O. novo‐ulmi ssp. novo‐ulmi occurred more frequently than ssp. americana (73 and 35 isolates, respectively) and their ranges overlapped. All isolates that behaved as ssp. novo‐ulmi in the fertility tests had the cu, as well as the col1 profile of ssp. novo‐ulmi. Surprisingly, all isolates that behaved as O. novo‐ulmi ssp. americana in the fertility test had the cu, as well as the col1 (with one exception) profile of O. novo‐ulmi ssp. novo‐ulmi. A possible explanation for this inconsistency could be the occurrence of hybridization between the two subspecies in Greece.  相似文献   

6.
Experiments were conducted to test whether Fourier transform‐infrared (FT‐IR) spectroscopy, coupled with chemometric methods, can distinguish healthy xylem tissues collected from elms known to differ significantly in their susceptibility to Ophiostoma novo‐ulmi Brasier. Twig samples from resistant Ulmus pumila L., susceptible U. minor Mill. and resistant U. minor clones were harvested on 1 May, 15 May, 1 June, 1 July and 1 September 2004, and subjected to FT‐IR analysis. The application of principal component analysis to the spectral data, followed by discriminant function analysis, discriminated between the three groups of samples in all harvesting dates. The examination of the DF‐loading plots allowed the identification of key regions within the spectra for the separation between clusters. The chemical assignments of these key regions allowed the following interpretations to be made: (i) U. pumila tissues contained enhanced levels of starch, cellulose and lignin with respect to U. minor tissues and (ii) resistant U. minor tissues contained enhanced levels of starch, cellulose and pectic polysaccharides with respect to susceptible U. minor tissues. The possible roles of the compositional differences in disease resistance, as well as the potential use of FT‐IR spectroscopy and chemometrics as a tool for screening resistant elms are discussed.  相似文献   

7.
Dutch Elm Disease (DED) is a vascular wilt disease of Ulmus species (elms) incited in North America primarily by the exotic fungus Ophiostoma novo‐ulmi. The pathogen is transmitted via root grafts and elm bark beetle vectors, including the native North American elm bark beetle, Hylurgopinus rufipes and the exotic smaller European elm bark beetle, Scolytus multistriatus. The banded elm bark beetle, Scolytus schevyrewi, is an exotic Asian bark beetle that is now apparently the dominant elm bark beetle in the Rocky Mountain region of the USA. It is not known if S. schevyrewi will have an equivalent vector competence or if management recommendations need to be updated. Thus the study objectives were to: (i) determine the type and size of wounds made by adult S. schevyrewi on branches of Ulmus americana and (ii) determine if adult S. schevyrewi can transfer the pathogen to American elms during maturation feeding. To determine the DED vectoring capability of S. schevyrewi, newly emerged adults were infested with spores of Ophiostoma novo‐ulmi and then placed with either in‐vivo or in‐vitro branches of American elm trees. The inoculation of trees via feeding wounds was successful 30% of the time for in‐vivo trials and 33% for in‐vitro trials. Although the infection rate of DED has declined in Colorado over the past 10 years, the disease is still present in urban elms. While it appears that S. schevyrewi is another vector of the DED pathogens, it appears that S. schevyrewi is no more efficient than S. multistriatus. Thus, management programs that remove elm bark beetle breeding sites, rapidly remove DED‐infected elms and include the planting of DED‐resistant elms should continue to be effective management tactics.  相似文献   

8.
Inoculation experiments on Ulmus procera, U. glabra and U. pumila with isolates of Ceratocystis ulmi from Canada, the United States, England, France, the Netherlands and Iran confirmed earlier work on the correlation between cultural characters and pathogenicity. Inocula-  相似文献   

9.
The antagonist ability of four fungal endophytes isolated from elms (Trichoderma atroviride GF13, Diaporthe eres GF2, Diplodia ulmi GF5 and Alternaria alternata GF6) and two fungi from a collection (Trichoderma harzianum and Trichoderma virens) was evaluated against six strains of Ophiostoma novo‐ulmi (1, 10, 19, 32, 43 and O‐Va), the causal agent of Dutch elm disease. Dual culture tests were established in PDA and MA culture media to test the interactions between pathogenic fungi and potential antagonist ones. The fungi showed varying levels of antagonist capacity against O. novo‐ulmi. Among them, T. atroviride and T. harzianum had the greatest inhibiting effect (around 50%). Culture filtrates and previously inoculated cellophane discs from T. harzianum and T. atroviride also caused growth inhibition of O. novo‐ulmi, with less intensity in strains 10 and 19. The control mechanisms involved in the process were competition, mycoparasitism and the production of soluble and diffusible antifungal metabolites. The new isolate T. atroviride GF13 was efficient as antagonist. It showed antagonist ability against non‐elm‐derived fungi such as Verticillium, Fusarium, Aspergillus, Rhizopus and Penicillium. These results suggest interesting application possibilities in the biological control of Dutch elm disease.  相似文献   

10.
The intact yeast phase spores of Ophiostoma ulmi and O. novo‐ulmi isolates were analysed by matrix‐assisted‐laser‐desorption/ionization time‐of‐flight/time‐of‐flight mass spectrometry. The results clearly showed that isolates of O. ulmi and O. novo‐ulmi have different mass peak profiles. The specific mass in m/z may vary slightly. One of the peaks from m/z 7623 to 7630 dominated (in high intensity) mass spectra for all isolates of O. novo‐ulmi tested in this study. This specific peak is believed to be CU (cerato‐ulmi) protein. However, no specific m/z peak can be found to distinguish between the isolates of ssp. novo‐ulmi and ssp. americana. On the contrary, all isolates of O. ulmi tested possessed one of a dominate peak at m/z 7337 to 7342, but none around m/z 7626 as shown in O. novo‐ulmi isolates.  相似文献   

11.
Dutch elm disease (DED) spread across Europe and North America in the 20th century killing most natural elm populations. Today, breeding programmes aim at identifying, propagating and studying elm clones resistant to DED. Here, we have compared the physiology and biochemistry of six genotypes of Ulmus minor of variable DED resistance. Leaf gas exchange, water potential, stem hydraulic conductivity and biochemical status were studied in 5‐year‐old trees of AB‐AM2.4, M‐DV2.3, M‐DV2 × M‐CC1.5 and M‐DV1 and 6‐year‐old trees of VA‐AP38 and BU‐FL7 before and after inoculation with Ophiostoma novo‐ulmi. Leaf water potential and net photosynthesis rates declined, while the percentage loss of hydraulic conductivity (PLC) increased after the inoculation in susceptible trees. By the 21st day, leaf predawn and midday water potential, stomatal conductance to water vapour and net photosynthesis rates were lower, and PLC was higher in trees of susceptible (S) genotypes inoculated with the pathogen than in control trees inoculated with water, whereas no significant treatment effect was observed on these variables in the resistant (R) genotypes. Fourier transform infrared spectroscopy analyses revealed a different biochemical profile for branches of R and S clones. R clones showed higher absorption peaks that could be assigned to phenolic compounds, saturated hydrocarbons, cellulose and hemicellulose than S clones. The differences were more marked at the end of the experiment than at the beginning, suggesting that R and S clones responded differently to the inevitable wounding from inoculation and repeated sampling over the experimental course. We hypothesize that a weak activation of the defence system in response to experimental wounding can contribute to the susceptibility of some genotypes to O. novo‐ulmi. In turn, the decline in shoot hydraulic conductivity and leaf carbon uptake caused by the infection further exacerbates tree susceptibility to the fungus.  相似文献   

12.
A. SOLLA  L. GIL 《Forest Pathology》2002,32(2):123-134
An investigation has been carried out to study the relationship between the susceptibility of Ulmus minor to Ophiostoma novo‐ulmi and the diameter of its xylem vessels. Vessel diameters have been analysed in seven Spanish elms of known susceptibility, taking measurements from second and third year rings in 3‐year‐old branches. In the second year rings no relationship could be observed between the vessel diameters and the susceptibility of the trees. In the third year rings the mean diameter and the percentage of vessels larger than 100 μm were found to be significantly greater for the group of elms of high susceptibility. In the third year rings the vessel transectional area (VTA) and the theoretical hydraulic conductance (THC) were calculated. The decrease in VTA and THC became increasingly noticeable in the group of high susceptibility elms as vessels of larger diameter were excluded from the calculation. Xylem vessel diameters and the proportion of large vessels were correlated with the susceptibility of U. minor to Dutch elm disease. How these properties influence the dispersal of the fungus, the sap flow and the tree's ability to compartmentalize the disease is discussed.  相似文献   

13.
This paper describes the chemical and biochemical properties of exopolysaccharides (EPS) produced by Ophiostoma ulmi and O. novo‐ulmi isolates, the Dutch elm disease (DED) fungi. Some of EPS have been considered as pathogenicity factor in the DED complex. The selected isolates grow well and produce EPS in a medium containing various types of carbon and nitrogen sources. EPS obtained from potato dextrose broth (PDB) medium appeared to be opaque, firm and stained purple blue with iodine‐potassium iodide solution, whereas those from yeast extract (YE) medium were less opaque, jelly‐like and remained unchanged in iodine solution. The selected fungal isolates produced much higher molecular weight EPS from the medium containing YE than from PDB. The results of this study suggest that high molecular weight compounds produced by O. ulmi (W9) and O. novo‐ulmi (R136) are not involved in DED pathogenesis. Spectrometric analysis of acid‐digested EPS obtained from PDB and YE revealed the presence of a monomer similar to glucose used as a standard. Thin layer chromatography indicated that glucan‐1,4‐α‐glucosidase (glucoamylase) only hydrolyses EPS from PDB media and releases glucose. The results strongly indicate that isolates of O. ulmi and O. novo‐ulmi produce starch‐like EPS from PDB medium. The EPS obtained from YE medium lacked this characteristic. The biological significance and the potential use of these EPS are discussed.  相似文献   

14.
Degradation of cell walls in elm wood tissue (Ulmus americand) by aggressive and non-aggressive isolates of Ophiostoma ulmi was studied by scanning electron microscopy. Xylem vessel walls were much more affected after infection with the aggressive isolate than after infection with the non-aggressive one.  相似文献   

15.
This study describes the first observation of Botryodiplodia canker in the Western Carpathians in south‐eastern Poland caused by Botryodiplodia hypodermia (Sacc.) Petr. (syn. Sphaeropsis hypodermia, S. ulmicola). The canker occurred on an approximately 17‐year‐old Ulmus glabra sapling in a mixed conifer/deciduous stand with elm trees severely damaged by Dutch elm disease. This paper describes disease symptoms and provides information on the macro‐ and micromorphology of the fungus isolated from the cankered tissues. The results of BLAST search using DNA sequences obtained for our cultures and subsequent phylogenetic positioning of the fungus among closely related Botryosphaeriaceae indicate that the species is much more closely related to Phaeobotryon than to the other Botryodiplodia or Sphaeropsis species. Moreover, a total of 16 polymorphisms within the ITS region were detected between S. ulmicola associated with Botryodiplodia canker in North America and B. hypodermia associated with the canker observed in Poland. Thus, the “European” variant of “Sphaeropsis” ulmicola can now be easily identified with our barcode sequences. The Botryodiplodia canker is much less prevalent in Europe than in North America. Differences in virulence of “American” and “European” linages and differences in susceptibility of various elm species may be the reason for the higher prevalence of the disease in North America.  相似文献   

16.
Five cultivars and two populations of wild‐type seedlings of American elm (Ulmus americana), 3 and 4 years old, were examined for differences in their abilities to compartmentalize and resist infection by artificially inoculating with Ophiostoma novo‐ulmi. Morphological characteristics of tree defence, often referred to as the compartmentalization of decay in trees model, were used as a conceptual framework, with particular emphasis on the limiting of tangential spread of infection within the xylem and barriers that limit spread outwards to cells formed after infection. To investigate the change in functional xylem over time, 3‐year‐old trees were assessed at multiple time points following inoculation for hydraulic conductivity. Three and four‐year‐old cut trees were placed in 0.1% w/v safranin O for 18 to 24 hr to indicate functional xylem. Transverse sections of the stained stems were used to calculate per cent of sap‐conducting xylem area and the per cent of circumference conducting of first formed cells and later formed cells. At each collection time, trees were assessed for disease severity on a 1–12 scale, based on the percentage of permanent wilt in the crown. There was considerable variation between cultivars in disease severity and their capacity to localize and resist infection. “Prairie Expedition,” which had the lowest disease severity rating in 2015 and the second lowest in 2016, consistently limited the spread of infection into newly formed xylem and had functional xylem around the entire circumference of the stem at 90 days post‐inoculation. “Valley Forge” in 2016 had the lowest overall disease severity rating and was the only cultivar to consistently limit the tangential spread of infection within extant xylem. This research identifies key characteristics that some cultivars have to resist and limit infection and provides new information that can be used in disease screening programmes to evaluate other cultivars and older plant material.  相似文献   

17.
The structure of the Ophiostoma ulmi and Ophiostoma novo-ulmi population of Switzerland was analysed. 79 Swiss isolates were compared to reference strains from various countries. A dendrogram from RAPD profiles was produced. O. ulmi and O. novo-ulmi were clearly separated into two major clusters. O. novo-ulmi was further divided into the EAN and NAN races. This classification is consistent with subgroups by taxonomic parameters (growth rate, culture aspect, fertility barriers). The variation detected within the EAN and NAN races indicates a post-epidemic situation in Switzerland. A clonal population is present only in a restricted area in mid-eastern Switzerland, indicating a still active disease front.  相似文献   

18.
American beech (Fagus grandifolia) is the target of a newly emerging disease in North America called beech leaf disease (BLD) that affects and disfigures leaves and which can lead to tree mortality. Beech leaf disease may be caused by a newly recognized subspecies of the anguinid nematode Litylenchus crenatae subsp. mccannii, but the associations of this nematode with bacterial and fungal taxa are unknown. We examined microbial communities associated with beech leaves affected by BLD in a 16‐year‐old American beech plantation using molecular methods. We detected L. crenatae subsp. mccannii in anywhere from 45% to 90% of leaves depending on the degree of visual BLD symptoms. Approximately 37% of asymptomatic leaves contained L. crenatae subsp. mccannii, whereas 90% of buds associated with symptomatic leaves contained L. crenatae subsp. mccannii. We found that fungal communities on leaves and buds were unaffected by BLD, but bud and leaves had significantly different fungal communities. Bacterial communities on buds also were unaffected by BLD, but bacterial communities were significantly different between symptomatic and asymptomatic leaves suggesting that the nematode could be altering the community of bacteria on the leaves. Clone libraries indicate that Wolbachia, an intracellular endosymbiont of arthropods, was found only on symptomatic leaves and buds associated with either symptomatic or asymptomatic leaves. In addition, only symptomatic leaves contained taxa in the genus Mucilaginibacter, which previous studies suggest could produce exopolysaccharides. These bacterial taxa could represent a marker for the vector of L. crenatae subsp. mccannii that enables spread between trees and a possible endosymbiont that could facilitate nematode feeding and establishment on nematode infested leaves. Our results are the first to examine changes to the leaf microbiome of this newly emerging pest and may aid identification of mechanisms associated with the spread and success of L. crenatae subsp. mccanni.  相似文献   

19.
Three scolytid species consistently associated with Dutch elm disease were assessed and compared for their effectiveness as vectors of Ophiostoma ulmi. Assessments were based on the number of beetles within a sample carrying any detectable O. ulmi, the number of O. ulmi spores carried by individual beetles and the number of discrete gallery systems colonised by O. ulmi.  相似文献   

20.
Elm (Ulmus sp.) shoots from in vitro micropropagated plants were tested with Ophiostoma ulmi culture filtrates, at different dilutions to determine the susceptibility of different host clones to Dutch elm disease (DED). ‘Commelin’, a susceptible Dutch hybrid, showed a high wilting index but that of American elm was higher. Although U. pumila × japonica (Sapporo gold 2) was the most tolerant to spore inoculation, its wilting index was as high as that of ‘Commelin’. The absorption capacity and wilting index of the elm shoots showed consistent correlation to isolate effectiveness (as determined by inoculation experiments), to production of toxin (cerato-ulmin) and to filtrate dilution. This method could be used to assess the effectiveness of the different O. ulmi isolates and for the detection of elm genotypes that are highly susceptible to Dutch elm disease.  相似文献   

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