| 1. |
- Albrectsen, Benedicte R, 1960-, et al.
(författare)
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Large scale geographic clines of parasite damage to Populus tremula L
- 2010
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Ingår i: Ecography. - : Wiley. - 0906-7590 .- 1600-0587. ; 33:3, s. 483-493
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Tidskriftsartikel (refereegranskat)abstract
- In conclusion, clines of Phyllocnistis were stronger and more persistent compared to Melampsora, which showed contrasting clines of varying strength. Our data thus support the assumption of the GMTC model that clines exist in the border between hot and cold spots and that they may be less persistent for parasites with an elevated gene flow, and/or for parasites which cover relatively larger hot spots surrounded by fewer cold spots.
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| 2. |
- Bengtsson, Therese, et al.
(författare)
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Activation of defence responses to Phytophthora infestans in potato by BABA
- 2014
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Ingår i: Plant Pathology. - : Wiley. - 0032-0862 .- 1365-3059. ; 63, s. 193-202
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Tidskriftsartikel (refereegranskat)abstract
- Late blight caused by Phytophthora infestans is one of the most devastating diseases of the potato crop. Resistance breeding and current fungicides are unable to control the rapidly evolving P. infestans and new control strategies are urgently needed. This study examined mechanisms of dl-β-aminobutyric acid (BABA)-induced resistance (IR) in the potato-P. infestans system. Leaves from two cultivars that differ in their degree of resistance, Bintje and Ovatio, were analysed after foliar treatment with BABA. Rapid activation of various defence responses and a significant reduction in P. infestans growth were observed in leaves treated with BABA. In the more resistant cultivar, Ovatio, the activation was both faster and stronger than in Bintje. Microscopic analysis of leaves treated with BABA revealed induction of small hypersensitive response (HR)-like lesions surrounded by callose, as well as production of hydrogen peroxide (H2O2). Molecular and chemical analyses revealed soluble phenols such as arbutin and chlorogenic acid and activation of PR-1. These results show a direct activation of defence responses in potato, rather than priming as reported for other plant species. They also show that the efficiency of BABA-IR differs between cultivars, which highlights the importance of taking all aspects into consideration when establishing new methods for disease management.
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| 3. |
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| 4. |
- Blumenstein, Kathrin, et al.
(författare)
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Diversidad de endófitos del olmo y relación con la resistencia a la grafiosis
- 2013
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)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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| 5. |
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| 6. |
- Farnier, Kevin, et al.
(författare)
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Novel bioassay demonstrates attraction of the white potato cyst nematode Globodera pallida (Stone) to non-volatile and volatile host plant cues
- 2012
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Ingår i: Journal of Chemical Ecology. - : Springer. - 0098-0331 .- 1573-1561. ; 38:6, s. 795-801
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Tidskriftsartikel (refereegranskat)abstract
- Potato cyst nematodes (PCNs) are a major pest of solanaceous crops such as potatoes, tomatoes, and eggplants and have been widely studied over the last 30 years, with the majority of earlier studies focusing on the identification of natural hatching factors. As a novel approach, we focused instead on chemicals involved in nematode orientation towards its host plant. A new dual choice sand bioassay was designed to study nematode responses to potato root exudates (PRE). This bioassay, conducted together with a traditional hatching bioassay, showed that biologically active compounds that induce both hatching and attraction of PCNs can be collected by water extraction of incised potato roots. Furthermore, our results demonstrated that PCN also were attracted by potato root volatiles. Further work is needed to fully understand how PCNs use host plant chemical cues to orientate towards hosts. Nevertheless, the simple attraction assay used in this study provides an important tool for the identification of host-emitted attractants.
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| 7. |
- Jensen, Anna M., et al.
(författare)
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Effects of competition and indirect facilitation by shrubs on Quercus robur saplings
- 2012
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Ingår i: Plant Ecology. - : Springer. - 1385-0237 .- 1573-5052. ; 213:4, s. 535-543
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Tidskriftsartikel (refereegranskat)abstract
- Indirect facilitation by shrubs has been suggested as a cost-effective way of regenerating oaks in forests of conservation interest. In this study, we tested whether shrubs can enhance growth in pedunculate oak (Quercus robur) by suppressing herbaceous competitors. We studied interactions between young oaks, shrubs, and/or herbaceous vegetation in an open-field experiment, in southern Sweden, over the first 3 years after planting. Oak saplings were grown in four competition treatments: no competing vegetation; with herbaceous vegetation; with shrubs; and with both herbaceous vegetation and shrubs. Competition from shrubs and herbaceous vegetation both reduced stem diameter and biomass accumulation, but they affected biomass partitioning differently. Saplings grown with competition from shrubs partitioned biomass primarily into height growth, while those saplings exposed to competition from herbaceous vegetation invested a relatively higher proportion in root growth. Competition between shrubs and herbaceous vegetation reduced the above-ground biomass of the herbaceous vegetation, resulting in an indirect facilitative effect for the oaks during the first 2 years after planting. However, during the third year, shrubs had a negative effect on biomass accumulation. In summary, results from this study suggest that shrubs indirectly facilitate biomass accumulation of oak saplings by suppressing herbaceous vegetation, possibly by reducing competition for below-ground resources. However, owing to the relatively short duration of positive net outcome for the oak, we recommend that a longer-term assessment of the interaction between oak regeneration and neighboring shrubs be made before the outcome of this study is applied to practical forestry.
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| 8. |
- Martín, Juan A, et al.
(författare)
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Resistance to Dutch elm disease reduces presence of xylem endophytic fungi in Elms (Ulmus spp.)
- 2013
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 8:2
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Tidskriftsartikel (refereegranskat)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. |
- Schiebe, Christian, et al.
(författare)
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Inducibility of chemical defenses in Norway spruce bark is correlated with unsuccessful mass attacks by the spruce bark beetle
- 2012
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Ingår i: Oecologia. - : Springer Science and Business Media LLC. - 0029-8549 .- 1432-1939. ; 170:1, s. 183-198
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Tidskriftsartikel (refereegranskat)abstract
- Secondary attraction to aggregation pheromones plays a central role in the host colonization behavior of the European spruce bark beetle Ips typographus. However, it is largely unknown how the beetles pioneering an attack locate suitable host trees, and eventually accept or reject them. To find possible biomarkers for host choice by I. typographus, we analyzed the chemistry of 58 Norway spruce (Picea abies) trees that were subsequently either (1) successfully attacked and killed, (2) unsuccessfully attacked, or (3) left unattacked. The trees were sampled before the main beetle flight in a natural Norway spruce-dominated forest. No pheromones were used to attract beetles to the experimental trees. To test the trees' defense potential, each tree was treated in a local area with the defense hormone methyl jasmonate (MeJ), and treated and untreated bark were analyzed for 66 different compounds, including terpenes, phenolics and alkaloids. The chemistry of MeJ-treated bark correlated strongly with the success of I. typographus attack, revealing major chemical differences between killed trees and unsuccessfully attacked trees. Surviving trees produced significantly higher amounts of most of the 39 analyzed mono-, sesqui-, and diterpenes and of 4 of 20 phenolics. Alkaloids showed no clear pattern. Differences in untreated bark were less pronounced, where only 1,8-cineole and (-)-limonene were significantly higher in unsuccessfully attacked trees. Our results show that the potential of individual P. abies trees for inducing defense compounds upon I. typographus attack may partly determine tree resistance to this bark beetle by inhibiting its mass attack.
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| 10. |
- Torp, Mikaela, 1978-, et al.
(författare)
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Snow-induced changes in dwarf birch chemistry increase moth larval growth rate and level of herbivory
- 2010
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Ingår i: Polar Biology. - : Springer. - 0722-4060 .- 1432-2056. ; 33:5, s. 693-702
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Tidskriftsartikel (refereegranskat)abstract
- Changes in snow cover might influence arctic ecosystems to the same extent as increased temperatures. Although the duration of snow cover is generally expected to decrease in the future as a result of global warming, the amounts of snow might increase in arctic areas where much of the elevated precipitation will fall as snow. We examined the effects of an increased snow cover, as a result of a snow fence treatment, on soil nitrogen mineralization, plant phenology, plant chemistry (nitrogen and potential defense compounds), the level of invertebrate herbivory, and performance of invertebrate herbivores in an arctic ecosystem, using dwarf birch (Betula nana) and the autumnal moth (Epirrita autumnata) as study organisms. An enhanced and prolonged snow cover increased the level of herbivory on dwarf birch leaves. Larvae feeding on plants that had experienced enhanced snow cover grew faster and pupated earlier than larvae fed with plant material from control plots, indicating that plants from enhanced snow-lie plots produce higher-quality food to herbivores. The increased larval growth rate was strongly correlated with higher leaf nitrogen concentration in plants subjected to snow manipulation, and also to certain phenolic acids. Snow manipulation did not change net nitrogen mineralization rates in the soil or total carbon concentration in leaves, but it altered the within-season fluctuating pattern of leaf phenolic compounds. This study demonstrates a positive relationship between increased snow cover and level of herbivory on deciduous shrubs, thus proposing a negative feedback on the climate-induced dwarf shrub expansion in arctic areas.
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| 11. |
- Torp, Mikaela, 1978-, et al.
(författare)
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The effect of snow on plant chemistry and invertebrate herbivory : Experimental manipulations along a natural snow gradient
- 2010
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Ingår i: Ecosystems (New York. Print). - : Springer. - 1432-9840 .- 1435-0629. ; 13:5, s. 741-751
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Tidskriftsartikel (refereegranskat)abstract
- Changing snow conditions have strong effects onnorthern ecosystems, but these effects are rarelyincorporated into ecosystem models and our perceptionof how the ecosystems will respond to awarmer climate. We investigated the relationshipsbetween snow cover, plant phenology, level ofinvertebrate herbivory and leaf chemical traits inBetula nana in four different habitats located along anatural snow cover gradient. To separate the effectof snow per se from other differences, we manipulatedthe snow cover with snow fences in threehabitats. The experimentally prolonged snow coverdelayed plant phenology, but not as much as expectedbased on the pattern along the natural gradient.The positive effect of the snow treatment onplant nitrogen concentration was also weaker thanexpected, because plant nitrogen concentrationclosely followed plant phenology. The level ofherbivory by leaf-chewing invertebrates increasedin response to an increased snow cover, at least atthe end of the growing season. The concentrationof phenolic substances varied among habitats,treatments and sampling occasions, indicating thatB. nana shrubs were able to retain a mosaic ofsecondary chemical quality despite altered snowconditions. This study shows that the effect of thesnow cover period on leaf nitrogen concentrationand level of herbivory can be predicted based ondifferences between habitats, whereas the effect ofa changed plant phenology on plant nitrogenconcentration is better explained by temporaltrends within habitats. These results have importantimplications for how northern ecosystemsshould respond to future climate changes.
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| 12. |
- Witzell, Johanna, et al.
(författare)
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Almsjuka – en berest skadesvamp på långbesök
- 2013
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Ingår i: Ekbladet. - 0283-4839. ; :28, s. 13-19
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- Alm är en uppskattad komponent i stadsmiljöer och rekreationsskogar och ett potentiellt betydelsefullt trädslag för skogsbruket. Almar hyser ett stort antal rödlistade insekter, svampar, mossor och lavar, och är därmed ytterst värdefulla för den biologiska mångfalden i svenska ädellövsskogar. Alla våra almar, och samtidigt de arter som är beroende av dem, hotas dock allvarligt av almsjukan.
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| 13. |
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| 14. |
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| 15. |
- Witzell, Johanna
(författare)
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Antifungal effect and reduction of Ulmus minor symptoms to Ophiostoma novo-ulmi by carvacrol and salicylic acid
- 2010
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Ingår i: European Journal of Plant Pathology. - : Springer Science and Business Media LLC. - 0929-1873 .- 1573-8469. ; 127, s. 21-32
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Tidskriftsartikel (refereegranskat)abstract
- There are still no effective means to control Dutch elm disease (DED), caused by the vascular fungi Ophiostoma ulmi and O. novo-ulmi. Plant phenolics may provide a new strategy for DED control, given their known antifungal activity against pathogens and their involvement in plant defence mechanisms. The in vitro antifungal activity of salicylic acid, carvacrol, thymol, phenol, o-cresol, m-cresol, p-cresol, and 2,5-xylenol against the DED pathogens was tested. Also, the protective effect of watering Ulmus minor seedlings with these compounds was tested against O. novo-ulmi. Salicylic acid, carvacrol, and thymol showed the strongest antifungal in vitro activity, while carvacrol and salicylic acid provided the strongest in vivo protection against O. novo-ulmi (63 and 46% reduction of leaf wilting symptoms with respect to controls, respectively). The effect of the treatments on tree phenology was low, and a significant negative relation was observed between the number of days to bud burst and the leaf wilting symptoms after inoculation, probably determined by genetic differences among the elm tree progenies used. The treatments with salicylic acid, carvacrol and thymol induced the highest shift in phenolic metabolite profile with respect to control trees. The protective effect of carvacrol and salicylic acid is discussed in terms of their combined activity as antifungal compounds and as inductors of tree defence responses.
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| 16. |
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| 17. |
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| 18. |
- Witzell, Johanna, et al.
(författare)
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Does temperature regime govern the establishment of Heterobasidion annosum in Scandinavia?
- 2011
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Ingår i: International journal of biometeorology. - : Springer. - 0020-7128 .- 1432-1254. ; 55:3, s. 275-284
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Tidskriftsartikel (refereegranskat)abstract
- We explored the reasons underlying the biogeographic distribution patterns of the economically important, wood-rotting basidiomycete Heterobasidion annosum in Sweden. Despite the commonness of suitable host trees, Heterobasidion annosum has not been recorded in the north of Sweden, whereas its relative, H. parviporum, is present throughout the country. To test the hypothesis that H. annosum has not spread to the north because of the effect of climate, mainly differences in the general temperature regime, we inoculated Norway spruce stumps and standing trees with H. annosum and H. parviporum at six field sites, three in the south and three in the north of Sweden. Three strains of both species were used in random combinations, so that each selected stump and tree was inoculated with both species at the same time. At 2 and 10 months after the inoculations, we compared the frequencies of detection of H. annosum and H. parviporum colonies at different distances from inoculation points in the stumps and in trees. The H. annosum colonies were detected only infrequently on disks cut from the inoculated stumps (0-4% of re-isolations) in both areas, whereas H. parviporum was detected much more frequently (26-47% of re-isolations). In standing trees, colonies belonging to H. annosum could be detected up to 210 cm (south) and 80 cm (north) and those belonging to H. parviporum up to 210 cm (south) and 140 cm (north) above the inoculation points. Our results suggest that difference in temperature regime does not provide an explanation for the distribution limit of H. annosum.
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| 19. |
- Witzell, Johanna, et al.
(författare)
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Ecological aspects of endophyte-based biocontrol of forest diseases
- 2014
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Ingår i: Advances in Endophytic Research. - New Delhi : Springer India. - 9788132215745 ; , s. 321-333
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Bokkapitel (övrigt vetenskapligt/konstnärligt)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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| 20. |
- Witzell, Johanna
(författare)
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Ecological factors in Dutch elm disease complex in Europe – a review
- 2010
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Ingår i: Broadleaved Forests in Southern Sweden: Management for Multiple Goals. ; :53, s. 209-224
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Bokkapitel (refereegranskat)abstract
- The current Dutch elm disease (DED) pandemic, caused by the vascular fungus Ophiostoma novo-ulmi Brasier, is devastating the global elm communities. The reasons for the great success of this disease are many. Since ancient times, humans have intensively manipulated the European elms resulting in a progressive reduction of their genetic diversity. This has facilitated the spread of DED in Europe, particularly at the beginning of the current pandemic. However, DED is a result of complex and dynamic interactions between multiple factors: elms, fungi, insect vectors, humans, and other organisms that interact with these factors in different ways. In addition, abiotic environment is likely to directly or indirectly regulate these interactions. Along with the urgent need to conserve the remaining genetic diversity of elms and to progress with elm breeding efforts for resistance, we thus also need to better understand the ecological factors behind the DED complex. This understanding could be useful also in managing other similar disease complexes in broadleaved trees, in particular in oaks and ash. A better understanding of environment-genotype interactions could also help informing sustainable disease management strategies for other clonally propagated tree species, such as poplars, whose massive clonal propagation in Europe could increase their vulnerability to emerging forest diseases, In this paper, we summarize current knowledge of some ecological factors that affect the success of the DED in the nemoral and temporal broadleaved forests of Europe, and discuss how alterations in the global climate could push the ecological balance in DED complex to a different position from where it is today
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| 21. |
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| 22. |
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| 23. |
- Witzell, Johanna, et al.
(författare)
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Resistance to Dutch elm disease reduces xylem endophytic fungi presence in elms (Ulmus spp.)
- 2013
-
Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 8
-
Tidskriftsartikel (refereegranskat)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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| 24. |
- Witzell, Johanna, et al.
(författare)
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Sugar beet extract induces defence against Phytophthora infestans in potato plants
- 2013
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Ingår i: European Journal of Plant Pathology. - : Springer Science and Business Media LLC. - 0929-1873 .- 1573-8469. ; 136, s. 261-271
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to find a natural and cheap agent that could induce defence responses in potato plants to combat Phytophthora infestans, which causes late blight disease that is one of the most devastating plant pathogens in agriculture. We tested whether a sugar beet extract (SBE), derived through a simple extraction procedure from a large-scale plant waste product, induced resistance under green-house conditions. In three potato genotypes differing in their level of resistance to P. infestans (two susceptible genotypes: Desiree and Bintje and one partially resistant: Ovatio), treatment with SBE resulted in significant reduction of the size of the infection lesions in a pattern similar to that seen with application of a known defence-inducing compound, beta-aminobutyric acid (BABA). Lower sporangial production was also observed on SBE-treated leaves, but the reduction in sporangial production was more pronounced after BABA treatment. SBE had no apparent toxic effect on the hyphal growth of the pathogen or on the germination of sporangia. Instead, SBE triggered pathogenesis-related protein (PR-1 and PR-2) induction which suggests that the protection conferred by SBE could be via induced resistance. An array of phenolic metabolites was found in the SBE that may contribute to the defence response.
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| 25. |
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