| 1. |
- Cleary, Michelle, et al.
(författare)
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First Report of Phytophthora gonapodyides Causing Stem Canker on European Beech (Fagus sylvatica) in Southern Sweden
- 2016
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Ingår i: Plant Disease. - 0191-2917 .- 1943-7692. ; 100, s. 2174-2175
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Tidskriftsartikel (refereegranskat)abstract
- Since 2010, extensive crown transparency of European beech (Fagus sylvatica) has been recorded in southern Sweden, with Phytophthora cambivora, P. plurivora, and P. cactorum as well as associated climatic triggers believed to be the major factors involved. In 2015, a different Phytophthora sp. was isolated from three F. sylvatica trees showing characteristic bleeding canker symptoms in Pildammsparken in Malmö, Sweden. Small sections of inner phloem were dissected at the interface between necrotic and healthy tissue, directly plated onto PAR(PH)-V8 selective medium containing 0.250 g/liter sodium ampicillin, 0.01 g/liter benomyl, 0.05 g/liter hymexazol, 0.1 g/liter PCNB, 0.05 g/liter pimaricin, and 0.01 g/liter rifamycin, and incubated at 20°C in darkness. Growing hyphae were later transferred to PDA and incubated at 20°C in the dark. The colony pattern was stellate. The average radial growth rate at 20°C was 0.6 cm/day. These morphological features are similar to that previously described for P. gonapodyides (Corcobado et al. 2010; Erwin and Ribeiro 1996; Jung et al. 1996). The isolates grown on PDA formed irregularly branched hyphae. Nonpapillate, elongated-ovoid to obpyriform sporangia (∼50 × 40 µm) were produced after 7 days by incubating on V8 agar culture (nonsterile soil water). DNA was extracted from mycelia and the identity of P. gonapodyides was confirmed by sequencing the internal transcribed (ITS) spacer region of the rDNA with the primers ITS4/ITS6 (GenBank accession nos. KX055998, KX055999, and KX056000). BLAST search showed 99 to 100% identity with reference sequences of P. gonapodyides deposited in GenBank. Pathogenicity on F. sylvatica was confirmed in a greenhouse experiment using two different isolates of P. gonapodyides. Mycelial plugs of 3-week-old cultures of each isolate grown on PDA were inoculated on the stems of 1-year-old seedlings at two locations, separated by 20 cm, by aseptically excising a small 5-mm flap of bark, inserting the mycelial plug along the cambium, and adding a droplet of Milliq H2O before sealing the wound with Parafilm. Ten seedlings were inoculated for each isolate. Controls consisted of stem-wound inoculation with a sterile plug of PDA, and no wounding at all. After 7 weeks, lesion length was measured. All seedlings inoculated with P. gonapodyides showed distinct necrotic lesions, whereas control treatments did not show any symptoms of disease. The average cumulative lesion length on seedlings inoculated with P. gonapodyides was significantly higher than on the wounded control treatment (25.4 mm ± 1.66 vs. 0.4 mm ± 0.01; P < 0.0001 for isolate 1 and 28.9 mm ± 1.42 vs. 0.4 mm ± 0.01; P < 0.001 for isolate 2). Koch's postulates were fulfilled by successfully reisolating the pathogen from infected seedlings. To our knowledge, this is the first report of P. gonapodyides causing disease on trees in Sweden. P. gonapodyides has been noted previously in Denmark (Erwin and Ribeiro 1996), and has been traditionally regarded as a weak parasite with saprophytic abilities, usually associated with aquatic environments such as rivers, riparian areas, and wetlands (Brasier et al. 2003). We cannot exclude that recent climatic triggers such as high summer precipitation coupled with mild winter temperatures have favored conditions to multicyclic spread of P. gonapodyides via zoospores, or that increased average age of beech stands has contributed to their higher susceptibility to weaker pathogens. Damage caused by P. gonapodyides however might be underestimated as it also can inhibit seed germination and is known to cause root rot and stem lesions in Quercus robur and Q. ilex (Corcobado et al. 2010; Jung et al. 1996). The newly reported damage caused by P. gonapodyides on F. sylvatica trees in southern Sweden is alarming particularly since beech is a dominant and ecologically important hardwood species that is widely used in forestry and as a planted ornamental in urban and landscape settings. Furthermore, other hosts such as Alnus glutinosa, Q. petraea, Q. robur (Jung et al. 1996), Picea abies, Betula spp., Acer spp., Tilia spp. (Jung et al. 2009), and Salix spp. (Brasier et al. 2003), also common in southern Sweden, may face an increased risk of damages caused by P. gonapodyides in the future.
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| 2. |
- Ghasemkhani, Marjan, et al.
(författare)
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Advanced spectroscopy-based phenotyping offers a potential solution to the ash dieback epidemic
- 2018
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Natural and urban forests worldwide are increasingly threatened by global change resulting from human-mediated factors, including invasions by lethal exotic pathogens. Ash dieback (ADB), incited by the alien invasive fungus Hymenoscyphus fraxineus, has caused large-scale population decline of European ash (Fraxinus excelsior) across Europe, and is threatening to functionally extirpate this tree species. Genetically controlled host resistance is a key element to ensure European ash survival and to restore this keystone species where it has been decimated. We know that a low proportion of the natural population of European ash expresses heritable, quantitative resistance that is stable across environments. To exploit this resource for breeding and restoration efforts, tools that allow for effective and efficient, rapid identification and deployment of superior genotypes are now sorely needed. Here we show that Fourier-transform infrared (FT-IR) spectroscopy of phenolic extracts from uninfected bark tissue, coupled with a model based on soft independent modelling of class analogy (SIMCA), can robustly discriminate between ADB-resistant and susceptible European ash. The model was validated with populations of European ash grown across six European countries. Our work demonstrates that this approach can efficiently advance the effort to save such fundamental forest resource in Europe and elsewhere.
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| 3. |
- Ghasemkhani, Marjan, et al.
(författare)
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Assessment of diversity and genetic relationships of Neonectria ditissima: the causal agent of fruit tree canker
- 2016
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Ingår i: Hereditas. - : Springer Science and Business Media LLC. - 0018-0661 .- 1601-5223. ; 153, s. 11-
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Tidskriftsartikel (refereegranskat)abstract
- Background: Neonectria ditissima is one of the most important fungal pathogens of apple trees, where it causes fruit tree canker. Information about the amount and partitioning of genetic variation of this fungus could be helpful for improving orchard management strategies and for breeding apple cultivars with high levels of genetically determined resistance. In this study single-spore Neonectria isolates originating from both the same and from different perithecia, apple cultivars and apple orchards in Sweden and Belgium, were evaluated for AFLP- and SSR-based genetic similarity and for mating system.Results: Seven SSR loci produced a total of 31 alleles with an average of 4 alleles per locus, while 11 AFLP primer combinations produced an average of 35 fragments per primer combination and 71 % polymorphic fragments. An AFLP-based analysis of molecular variance (AMOVA) revealed that 89 % of the variation was found within orchards and 11 % between orchards. Genetic similarity among the studied isolates was illustrated with a principal coordinate analyseis (PCoA) and a dendrogram. AFLP-based Jaccard's similarity coefficients were the highest when single-ascospore isolates obtained from the same perithecium were compared, medium-high for isolates from different perithecia on the same tree, and lowest when isolates from different trees were compared.Conclusions: Based on the results of PCoA and AMOVA analysis, isolates from the same or geographically close orchards did not group together. Since AFLP profiles differed also when single-ascospore isolates from the same perithecium were compared, the mating system of N. ditissima is most likely heterothallic.
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| 4. |
- Ghasemkhani, Marjan, et al.
(författare)
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Cut-off shoots method for estimation of partial resistance in apple cultivars to fruit tree canker caused by Neonectria ditissima
- 2015
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Ingår i: Acta Agriculturae Scandinavica, Section B - Soil and Plant Science. - : Informa UK Limited. - 0906-4710 .- 1651-1913. ; 65, s. 412-421
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Tidskriftsartikel (refereegranskat)abstract
- Fruit tree canker, caused by the fungus Neonectria ditissima, is an economically devastating disease in apple orchards, especially in north-western Europe. Complete resistance has not yet been reported in apple, but variation in levels of partial resistance has been described and could be valuable in plant breeding programmes. A screening method based on spore inoculation of manually inflicted leaf scars on cut shoots was evaluated for reliability and repeatability in discrimination of 11 apple cultivars during two years - 2012 and 2013 - in two different facilities - biotron and standard greenhouse - and different time periods (February-May). The resulting cankers were counted (infection percentage), first appearance noted (incubation period) and lesion size measured at regular intervals during a period of 25-29 days for comparison of resistance levels. Results of two-way analysis of variance and correlation analyses showed that the area under the disease progress curve yielded the most robust data. This parameter was then applied for screening 30 apple cultivars using the same cut-shoot method. 'Elise' showed very high susceptibility, while the ornamental 'Prairifire' showed the highest level of partial resistance. Results suggested that cut shoots can be used to assess levels of resistance among cultivars, but great care must be taken to provide stable experimental conditions.
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| 5. |
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| 6. |
- Ghasemkhani, Marjan
(författare)
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Genetic basis for resistance against fruit tree canker in apple
- 2012
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Neonectria ditissima (formerly Neonectria galligena, anamorph Cylindrocarpon heteronema) is the causal agent of fruit tree canker which is regarded as a serious economic problem in horticulture. This fungus causes notable damage to apple trees and it is very important in some regions, especially North western Europe, where it can result in death of spur shoots and branches. Although it occurs in a wide range of temperatures, it is associated with wet weather and climate has an important effect on the geographic distribution. The fungus produces conidia and ascospores, both of which are dispersed and cause infection during prolonged periods of rainy weather. Also, spores produced on the infected wood can act as an infection source in the orchards. The fungus can therefore be introduced into new orchards with infected planting material from other orchards or tree nurseries. Chemical and mechanical control like spraying of fungicides, covering wounds with paint, and cutting out infected branches, do not prevent the occurrence of epidemics. Breeding cultivars with a high level of resistance towards canker would be of great help towards the avoidance of this disease. Apple cultivars show variable levels of partial resistance to the fungus, whereas complete resistance has not yet been reported and no major genes have been identified. Therefore, apple genotypes with comparatively high levels of genetically determined partial resistance should be identified for use in apple breeding.
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| 7. |
- Ghasemkhani, Marjan, et al.
(författare)
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Real-time PCR for detection and quantification, and histological characterization of Neonectria ditissima in apple trees
- 2016
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Ingår i: Trees - Structure and Function. - : Springer Science and Business Media LLC. - 0931-1890 .- 1432-2285. ; 30, s. 1111-1125
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Tidskriftsartikel (refereegranskat)abstract
- Neonectria ditissima, the causal pathogen of fruit tree canker, is a sordariomycete fungus that affects apple orchards, especially in north-western Europe. To prevent serious disease epidemics, an accurate, rapid, and sensitive method for detection of N. ditissima is needed for pathogen identification. A quantitative real-time PCR (qPCR) assay was developed for both detection and quantification of this pathogen in infected apple cultivars. Several primer sets were designed from regions of the β-tubulin gene. One primer set passed several validation tests, and the melting curve confirmed species-specific amplification of the correct product. In addition, the N. ditissima biomass could be detected at variable amounts in samples from the infection sites of six different cultivars, with ‘Aroma' having the lowest amount of N. ditissima biomass and ‘Elise' the highest. To complement the qPCR results, tissue from detached shoots and 1-year-old trees of ‘Cox's Orange Pippin' (susceptible) and ‘Santana' (partially resistant) was used in a histopathology study. In both detached shoots and trees, fungal hyphae were found in cells of all tissues. No qualitative differences in the anatomy of the infected samples were observed between the cultivars. In the detached shoot experiment, both cultivars were affected but differences in the rate of disease progression suggest that the partially resistant cultivar could resist the fungus longer. The qPCR assay developed in our study produced reproducible results and can be used for detection of N. ditissima in infected trees.
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| 8. |
- Ghasemkhani, Marjan
(författare)
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Resistance against fruit tree canker in apple : evaluation of disease symptoms, histopathological and RNA-seq analyses in different cultivars, genetic variation of Neonectria ditissima
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Neonectria ditissima (formerly Neonectria galligena, anamorph Cylindrocarpon heteronema) is the causal agent of fruit tree canker, which is regarded as a serious economic problem in apple production. This fungus is closely associated with mild and wet conditions, and climate therefore has an important impact on its geographic distribution. Notable damage to apple trees is especially common in, e.g., North-Western Europe. Complete resistance has not yet been reported. In addition, no major genes have as yet been identified and resistance appears to be controlled mainly by additive gene action. Apple cultivars varied significantly in level of partial resistance towards apple canker after artificial inoculation of detached shoots and/or potted trees with macroconidia of N. ditissima. The inter-specific crabapple hybrid ‘Prairifire’ showed the least damage, indicating that valuable sources of resistance can be found in Malus species. Neonectria ditissima could be detected in artificially infected apple trees using a species-specific β-tubulin gene-based qPCR assay two months after inoculation. When quantified in different cultivars, a positive relationship between N. ditissima biomass and the size of canker-induced lesions was found. Interaction between plant and pathogen was studied using light microscopy of apple woody tissue; fungal hyphae were found in all cell types, and gel formation was observed in both a susceptible and a resistant cultivar but infection appears to progress more rapidly in the susceptible cultivar. Genetic variation among different N. ditissima isolates was investigated using SSR and AFLP markers. Comparatively low levels of genetic differentiation among orchards indicate that gene flow is prominent. Analyses of single-ascospore isolates from the same perithecia suggest that this fungus is heterothallic and therefore outcrossing. Furthermore, a focused genomics approach was applied in order to identify differentially expressed genes in response to fungal attack on apple trees. Obtained data indicate that apple cultivars inoculated with N. ditissima exhibit significant upregulation of defence-related genes and genes involved in detoxification, peroxidase-related reactions, phenylpropanoid metabolism and the lignification process.
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| 9. |
- Ghasemkhani, Marjan, et al.
(författare)
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Screening for Partial Resistance to Fruit Tree Canker in Apple Cultivars
- 2015
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Ingår i: Acta Horticulturae. - 0567-7572 .- 2406-6168. ; 1099, s. 687-690
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Konferensbidrag (refereegranskat)abstract
- Fruit tree canker in apple, caused by the fungus Neonectria ditissima, is considered as a serious economic problem in apple orchards, especially in northwestern Europe. This fungus produces cankers on the wood of branches and trunks, and severe attacks can result in the loss of limbs or whole trees. The fungus produces conidia and ascospores, both of which are dispersed and cause infection during prolonged periods of rainy weather. Apple cultivars show variable levels of partial resistance to the fungus, whereas complete resistance has not yet been reported. Therefore, apple genotypes with high levels of genetically determined resistance should be identified for use in apple breeding. In this study, ten apple cultivars were screened for resistance to N. ditissima. For each cultivar, both potted trees and cut-off shoots in glass bottles were inoculated in a greenhouse. The resulting lesions were measured and disease progression curves were calculated; AUC (area under curve) was used for comparisons of infection severity. Significant differences between cultivars were observed in both experiments. The cultivar 'Rodluvan' showed the highest degree of resistance in both experiments, while the most susceptible were 'Jonathan'(cut shoots) and 'Akero' (potted trees).
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| 10. |
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