| 1. |
- Blumenstein, Kathrin, et al.
(author)
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Diversidad de endófitos del olmo y relación con la resistencia a la grafiosis
- 2013
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Conference paper (other academic/artistic)abstract
- Los endófitos activan en sus hospedantes mecanismos defensivos similares a los activados por patógenos. Se plantea la hipótesis de que estos mecanismos limitan el establecimiento de endófitos en olmos resistentes a la grafiosis. Asimismo, ciertos endófitos proporcionan a sus hospedantes mecanismos epigenéticos de protección ante patógenos. Planteamos como segunda hipótesis que determinados endófitos están implicados en la resistencia ambiental a la grafiosis. Se ha estudiado la frecuencia y diversidad de endófitos en olmos genéticamente resistentes a la grafiosis y se ha comparado con la encontrada en olmos susceptibles. Además, se han aislado endófitos de olmos que en campo muestran resistencia fenotípica a la grafiosis, pese a que son susceptibles a la enfermedad. Su antagonismo hacia la grafiosis se ha evaluado mediante ensayos in vitro e in vivo. Olmos resistentes muestran una menor frecuencia y diversidad de endófitos en el xilema, lo que confirma la primera hipótesis. Ciertos endófitos produjeron metabolitos extracelulares que inhibieron el crecimiento del hongo de la grafiosis in vitro. El efecto protector de los tratamientos con endófitos ante la grafiosis ha sido en general poco notable, si bien ciertas cepas mostraron un efecto significativo, aunque dependiente del genotipo de olmo.
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| 2. |
- Blumenstein, Kathrin
(author)
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Endophytic fungi in elms : implications for the integrated management of Dutch elm disease
- 2015
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Doctoral thesis (other academic/artistic)abstract
- Integrated pest management calls for new biocontrol solutions in management of forest diseases. Endophytic fungi that are commonly found in tree tissue may have potential in biocontrol. However, the links between endophyte status and disease tolerance are still unclear, and we know little about the mechanisms by which the endophytes can influence tree pathogens. The first goal of the thesis was to compare the endophyte status in elm (Ulmus spp.) trees with low vs. high susceptibility to Dutch elm disease (DED), caused by Ophiostoma fungi, and to find correlations between endophytes and the susceptibility pattern of the trees. The second goal was to investigate the potential mechanisms of antagonism by the endophytes towards the pathogen. Thus, endophytes were isolated from leaves, bark and xylem of elms that differed in DED susceptibility. The isolates were screened for their potential to counteract the pathogen in dual cultures. Selected strains were investigated using Phenotype MicroArrays to obtain the substrate utilization profiles that reflect the endophytes’ ability to compete with the pathogen for a nutritional niche. To test for a protective effect against the disease, promising isolates were injected into young elms. Preliminary analyses were done to identify the extracellular chemicals that some of the endophytes released into the growth medium. The results showed that the frequency and diversity of endophytes was higher in xylem of elms with high susceptibility to DED. Some endophytes deadlocked the pathogen with extracellular chemicals in vitro, while others had a faster growth rate. Several endophytes were able to utilize substrates more effectively than the pathogen. A preventive treatment with endophytes protected elms against DED, but the effect was unstable across years. Bioactive fungal extracts had a complex chemical profile, and the individual compounds in the extracts remain to be identified. Because endophytes antagonized the pathogen through different mechanisms, I suggest that an endophyte-based biocontrol of DED could be best achieved through a synergistic effect of several endophyte strains.
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| 3. |
- Blumenstein, Kathrin, et al.
(author)
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Nutritional niche overlap potentiates the use of endophytes in biocontrol of a tree disease
- 2015
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In: BioControl (Dordrecht). - : Springer Science and Business Media LLC. - 1386-6141 .- 1573-8248. ; 60:5, s. 655-667
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Journal article (peer-reviewed)abstract
- Asymptomatic endophytic fungi are often regarded as potent biocontrol agents in plants, but the competitive interactions between endophytes and other microbes within the same host plant are poorly understood. We tested a hypothesis that as compared to asymptomatic endophytes, an aggressive pathogen inhabiting the same host is able to utilize carbon substrates more efficiently. Using phenotype microarray, we determined the carbon utilization profiles of the highly virulent Dutch elm disease (DED) pathogen Ophiostoma novo-ulmi, and four asymptomatic elm (Ulmus spp.) endophyte isolates that were selected based on their differential association to the DED-susceptibility pattern of the host elms. The competitive interactions between isolates were evaluated using a niche overlap index. In contrast to our hypothesis, the studied endophytes exhibited extensive niche overlap with the pathogen, suggesting that some endophyte strains might protect elms against DED-pathogen through competition for substrates and provide new tools for biocontrol of DED.
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| 4. |
- Blumenstein, Kathrin, et al.
(author)
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Phenotype MicroArrays as a complementary tool to next generation sequencing for characterization of tree endophytes
- 2015
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In: Frontiers in Microbiology. - : Frontiers Media SA. - 1664-302X. ; 6
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Journal article (peer-reviewed)abstract
- There is an increasing need to calibrate microbial community profiles obtained through next generation sequencing (NGS) with relevant taxonomic identities of the microbes, and to further associate these identities with phenotypic attributes. Phenotype MicroArray (PM) techniques provide a semi-high throughput assay for characterization and monitoring the microbial cellular phenotypes. Here, we present detailed descriptions of two different PM protocols used in our recent studies on fungal endophytes of forest trees, and highlight the benefits and limitations of this technique. We found that the PM approach enables effective screening of substrate utilization by endophytes. However, the technical limitations are multifaceted and the interpretation of the PM data challenging. For the best result, we recommend that the growth conditions for the fungi are carefully standardized. In addition, rigorous replication and control strategies should be employed whether using pre-configured, commercial microwell-plates or in-house designed PM plates for targeted substrate analyses. With these precautions, the PM technique is a valuable tool to characterize the metabolic capabilities of individual endophyte isolates, or successional endophyte communities identified by NGS, allowing a functional interpretation of the taxonomic data. Thus, PM approaches can provide valuable complementary information for NGS studies of fungal endophytes in forest trees.
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| 5. |
- Martín, Juan A, et al.
(author)
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Resistance to Dutch elm disease reduces presence of xylem endophytic fungi in Elms (Ulmus spp.)
- 2013
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In: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 8:2
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Journal article (peer-reviewed)abstract
- Efforts to introduce pathogen resistance into landscape tree species by breeding may have unintended consequences for fungal diversity. To address this issue, we compared the frequency and diversity of endophytic fungi and defensive phenolic metabolites in elm (Ulmus spp.) trees with genotypes known to differ in resistance to Dutch elm disease. Our results indicate that resistant U. minor and U. pumila genotypes exhibit a lower frequency and diversity of fungal endophytes in the xylem than susceptible U. minor genotypes. However, resistant and susceptible genotypes showed a similar frequency and diversity of endophytes in the leaves and bark. The resistant and susceptible genotypes could be discriminated on the basis of the phenolic profile of the xylem, but not on basis of phenolics in the leaves or bark. As the Dutch elm disease pathogen develops within xylem tissues, the defensive chemistry of resistant elm genotypes thus appears to be one of the factors that may limit colonization by both the pathogen and endophytes. We discuss a potential trade-off between the benefits of breeding resistance into tree species, versus concomitant losses of fungal endophytes and the ecosystem services they provide.
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| 6. |
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| 7. |
- Witzell, Johanna, et al.
(author)
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Ecological aspects of endophyte-based biocontrol of forest diseases
- 2014
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In: Advances in Endophytic Research. - New Delhi : Springer India. - 9788132215745 ; , s. 321-333
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Book chapter (other academic/artistic)abstract
- Recent studies have shown that the asymptomatic fungal endophytes may influence the outcome of forest trees' interactions with pathogens and herbivores, raising a promise that endophytes might be utilized as biocontrol agents in integrated pest and disease management. However, practical applications for forest protection based on endophytes are still rare, in particular in the case of the economically and ecologically important large trees and their diseases. A better understanding of the ecological and biological background of the protection provided by endophytes may help to design new forest protection strategies that utilize endophytes in control of tree diseases. More information is also needed regarding the effects of silvicultural methods on endophyte communities at the level of single trees and forest stands. In this chapter, we discuss the motivation for continued research on endophyte-based biocontrol of forest tree diseases and some ecological aspects related to the topic.
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| 8. |
- Witzell, Johanna, et al.
(author)
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Resistance to Dutch elm disease reduces xylem endophytic fungi presence in elms (Ulmus spp.)
- 2013
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In: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 8
-
Journal article (peer-reviewed)abstract
- Efforts to introduce pathogen resistance into landscape tree species by breeding may have unintended consequences for fungal diversity. To address this issue, we compared the frequency and diversity of endophytic fungi and defensive phenolic metabolites in elm (Ulmus spp.) trees with genotypes known to differ in resistance to Dutch elm disease. Our results indicate that resistant U. minor and U. pumila genotypes exhibit a lower frequency and diversity of fungal endophytes in the xylem than susceptible U. minor genotypes. However, resistant and susceptible genotypes showed a similar frequency and diversity of endophytes in the leaves and bark. The resistant and susceptible genotypes could be discriminated on the basis of the phenolic profile of the xylem, but not on basis of phenolics in the leaves or bark. As the Dutch elm disease pathogen develops within xylem tissues, the defensive chemistry of resistant elm genotypes thus appears to be one of the factors that may limit colonization by both the pathogen and endophytes. We discuss a potential trade-off between the benefits of breeding resistance into tree species, versus concomitant losses of fungal endophytes and the ecosystem services they provide.
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| 9. |
- Witzell, Johanna, et al.
(author)
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Strong in vitro antagonism by elm xylem endophytes is not accompanied by temporally stable in planta protection against a vascular pathogen under field conditions
- 2015
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In: European Journal of Plant Pathology. - : Springer Science and Business Media LLC. - 0929-1873 .- 1573-8469. ; 142, s. 185-196
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Journal article (peer-reviewed)abstract
- Some endophytic fungi provide their host plants with protection against abiotic and biotic stressors, including pathogens. Endophyte-mediated mechanisms might be behind the environmental resistance shown in the field by some adult Ulmus minor trees to the Dutch elm disease (DED) pathogen, Ophiostoma novo-ulmi. We isolated and characterized seven endophyte fungi from the xylem of three adult U. minor trees that have survived the DED epidemics within areas in Spain ravaged by the disease. The antagonism of the isolated endophytes towards O. novo-ulmi was evaluated in vitro by means of dual culture assays. Six of the studied endophytes hindered the pathogen growth through antibiosis, competition for the substrate, or a combination of both mechanisms. Four of these endophytes were selected for in vivo tests where their protective effect was evaluated in field experiments during three successive years (2011-2013). The conditioning inoculation of two endophytes (Monographella nivalis and Alternaria tennuissima) reduced DED symptoms in 2011 and 2012, respectively. However, the same isolates did not show any prophylactic effect in 2013, which suggests that the repeatability of the treatments is low. A significant treatment x clone interaction was found, showing that the effectiveness of the treatments depended on the tree clone. The future use of endophytes in biocontrol strategies might be oriented towards taking into consideration the whole fungal microbiome in forest breeding programs rather than the external application of particular endophyte strains.
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