| 1. |
- Bakys, Remigijus, et al.
(författare)
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Investigations concerning the role of Chalara fraxinea in declining Fraxinus excelsior
- 2009
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Ingår i: Plant Pathology. - : Wiley. - 0032-0862 .- 1365-3059. ; 58, s. 284-292
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Tidskriftsartikel (refereegranskat)abstract
- A study was carried out to clarify the role of the fungus Chalara fraxinea in decline of Fraxinus excelsior, which is observed on a large scale in central and northern Europe with high incidence of tree mortality. The aims of this work were: (i) to check for the presence of C. fraxinea in various tissues of declining F. excelsior by agar culture isolations and by direct analysis of plant tissues using molecular techniques (DNA extraction, ITS-PCR, cloning, ITS sequencing and T-RFLP); (ii) to study fungal communities inhabiting tissues with symptoms; and (iii) to test the pathogenicity of C. fraxinea to F. excelsior. Chalara fraxinea was isolated from 93% of stem cankers, 91% of necrotic leaf stalks, 27-28% of bark wounds and 30% of visually healthy leaf stalks. Molecular analyses of necrotic leaves, leaf stalks and bark revealed the presence of 25 different fungal taxa, 14 of which were detected in all three types of tissue sample. Chalara fraxinea was the second most common species (61% of samples), and only Cryptococcus foliicola occurred more often (70%). All eight of the tested C. fraxinea isolates induced necroses in bark and cambium on each of 86 inoculated trees, and all controls remained healthy. Average length of necroses caused by different C. fraxinea strains varied from 4.2 to 8.9 cm, but the differences were statistically insignificant. Instead, differences in resistance of individual trees to C. fraxinea were observed.
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| 2. |
- Bakys, Remigijus, et al.
(författare)
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Occurrence and pathogenicity of fungi in necrotic and non-symptomatic shoots of declining common ash (Fraxinus excelsior) in Sweden
- 2009
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Ingår i: European Journal of Forest Research. - : Springer Science and Business Media LLC. - 1612-4669 .- 1612-4677. ; 128, s. 51-60
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Tidskriftsartikel (refereegranskat)abstract
- Currently, massive dieback of Fraxinus excelsior is observed in countries of eastern, northern and central Europe, and the reasons for it are unclear. The aims of the present work were (a) to study fungal communities in declining F. excelsior crowns; (b) to clarify role of fungi in the decline. Shoots from symptomatic crowns were collected in four localities in central Sweden, and distributed into the following categories: (a) visually healthy; (b) initial necroses; (c) advanced necroses; (c) dead tops. The most frequently isolated fungi were Gibberella avenacea, Alternaria alternata, Epicoccum nigrum, Botryosphaeria stevensii, Valsa sp., Lewia sp., Aureobasidium pullulans and Phomopsis sp., and these taxa were consistently found in shoots of all four symptomatic categories. Forty-eight taxa of other fungi were isolated, and fungal diversity was not exhausted by the sampling effort. The same taxa of fungi were dominant in F. excelsior shoots of different symptomatic categories, and moderate to high similarity of fungal communities was observed in shoots despite the symptoms. Forty-four isolates from 24 fungal taxa were used for artificial inoculations of 277 1-year-old F. excelsior seedlings in bare root nursery. After 2 years, only four fungi caused symptomatic necroses of bark and cambium: A. alternata, E. nigrum, Chalara fraxinea and Phomopsis sp. The most pathogenic was C. fraxinea, inducing symptoms on 50% of inoculated trees, while three other fungi caused necroses on 3-17% of inoculated trees. Infection biology of C. fraxinea and environmental factors determining susceptibility of F. excelsior to decline deserve future investigations.
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| 3. |
- Barklund, Pia, et al.
(författare)
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Fler och fler insekter på lärk
- 2016
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Ingår i: Lustgården. - 0349-0033. ; 96, s. 49-52
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Tidskriftsartikel (populärvet., debatt m.m.)
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| 4. |
- Bengtsson, Stina, et al.
(författare)
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Detection of Chalara fraxinea from tissue of Fraxinus excelsior using species-specific ITS primers
- 2010
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Ingår i: Forest Pathology. - : Wiley. - 1437-4781 .- 1439-0329. ; 40, s. 111-115
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Tidskriftsartikel (refereegranskat)abstract
- P>Chalara fraxinea (teleomorph: Hymenoscyphus albidus) is known as a serious pathogen of Fraxinus excelsior, causing massive dieback of trees in Europe. The fungus is able to cause latent infections, and has been previously detected as an endophyte in asymptomatic tissues. Chalara fraxinea is a slow grower in culture, and is thus likely to be overgrown by faster growing fungi whenever pure culture isolations are being attempted. This study reports species-specific ITS primers allowing fast and reliable detection of the pathogen directly from infected tissues of F. excelsior.
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| 5. |
- Bengtsson, Stina, et al.
(författare)
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Seasonal Pattern of Lesion Development in Diseased Fraxinus excelsior Infected by Hymenoscyphus pseudoalbidus
- 2014
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Ash dieback is a recent widespread disease on ash (Fraxinus sp.) that is causing important economic and ecological losses throughout Europe. The disease is initiated by the ascomycetous fungus Hymenoscyphus pseudoalbidus (anamorph Chalara fraxinea). The main aim of this study was to investigate seasonal pattern of lesion development associated with ash dieback. We present data on the spread of 324 natural lesions in ash shoots, branches and stems surveyed over a 32 month period. Most lesions were active and showed the greatest rate of growth during the summer; however, lesions were active throughout the year. Tree mortality was high, with more than a third of the surveyed trees dying during the study. Although many lesions permanently ceased to develop, the rate at which new lesions emerged was greater than the rate at which lesions entered a resting phase. The most common cause for a lesion going into a permanent state of rest was that it had encountered a branch-base. Genotype analysis showed that multiple infections can occur in a single tree given that different genotypes were identified in different lesions as well as in single lesions. A weak positive correlation was noted between tree health and tree size and a weak negative correlation was noted between tree overall health and lesion activity. The lower limit for H. pseudoalbidus growth in culture was between 4.0 degrees C and 0.5 degrees C.
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| 6. |
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| 7. |
- Eshete, Getachew, et al.
(författare)
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Wood biomass functions for Acacia abyssinica trees and shrubs and implications for provision of ecosystem services in a community managed exclosure in Tigray, Ethiopia
- 2013
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Ingår i: Journal of Arid Environments. - : Elsevier BV. - 0140-1963 .- 1095-922X. ; 94, s. 80-86
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Tidskriftsartikel (refereegranskat)abstract
- In the Ethiopian highlands, remarkable recovery of vegetation has been achieved using exclosures, protecting vegetation against livestock browsing and firewood harvesting. But these emerging forest resources require tools for sustainable use, implying knowledge on biomass stocks and growth. In this study we developed biomass functions estimating total, stem and branch biomass from diameter at stump height (DSH) and tree height (H) for an 11-year old exclosure in Tigray, Ethiopia. In a systematic grid of 55 plots, DSH and H of all trees and shrubs were recorded. 40 Acacia abyssinica trees were selected for destructive sampling. Allometric relationships using a natural log-log model were established between aboveground biomass, DSH and H. Models with only DSH were found best with R-2 between 0.95 and 0.98. The functions were 10 fold cross-validated and R-2_cv ranged from 0.94 to 0.97, indicating good model performance. The models were found well in range with those of other seasonal forests in East Africa. Total aboveground biomass was estimated 25.4 ton ha(-1) with an annual production of 2.3 ton ha(-1), allowing sustainable wood fuel use for 4 persons ha(-1). The presented predictive functions help to harmonize between ecological and societal objectives and are as such a first step towards an integrated planning tool for exclosures. (C) 2013 Elsevier Ltd. All rights reserved.
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| 8. |
- Njuguna, Jane Wangu, et al.
(författare)
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A canker and dieback disease threatening the cultivation of Grevillea robusta on small-scale farms in Kenya
- 2011
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Ingår i: African Journal of Agricultural Research. - 1991-637X. ; 6, s. 748-756
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Tidskriftsartikel (refereegranskat)abstract
- A canker and dieback disease was recently reported on Grevillea robusta in east Africa but little was known about its magnitude, distribution and associated pathogens. In our survey of the disease approximately 36% of 17,994 G. robusta trees assessed showed canker and dieback symptoms. Disease index increased from the humid zone (18%) and to the semi-arid zones (67%). Tree mortality increased from 0.3 to 20% respectively on the same scale and was highest in trees less than 7 years old in all zones. Disease index and tree mortality showed positive correlations with drought period which increased from an average of 0.7 months (humid) to 7 months (semi-arid zones). Both variables showed negative correlations with farm altitude. Disease index was higher in the woodlots compared to other types of tree planting in all zones. Two Botryosphaeriaceae species, Neofusicoccum parvum and Lasiodiplodia theobromae known to be pathogenic on G. robusta were highly abundant in severely diseased stems and branches and their occurrence also showed positive correlations with disease severity. From the results of this study, it was recommended that G. robusta should not be planted in the semi arid zones of Kenya, due to its susceptibility to the canker and dieback disease.
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| 9. |
- Persson, Torgny, et al.
(författare)
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The inheritance of resistance to Scots pine blister rust in Pinus sylvestris
- 2024
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Ingår i: Forest Ecology and Management. - : Elsevier. - 0378-1127 .- 1872-7042. ; 568
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Tidskriftsartikel (refereegranskat)abstract
- Scots pine blister rust is a rust fungal pathogen that has become more noticeable in recent years and has increased in recorded incidence in Northern Scandinavia. This has prompted an initiation of resistance breeding to the fungus in the Northern Swedish pine breeding program. To accomplish this, it is necessary to evaluate the breeding potential for increased resistance and putative impact on other breeding objective traits that may have genetic correlations to resistance. To assess the potential of the trait to be included in the breeding program we examined half sibling families in four trials of which two had high incidence of Scots pine blister rust in a range of 25.4–42.1 %. We assessed vitality and height in one year and rust lesion frequency at two later time points. We found that rust resistance had a narrow sense heritability of 0.36–0.41, while vitality reached 0.17 and height 0.25. We found a high genetic correlation between sites in rust resistance and no genetic correlation between rust resistance and either vitality or height. This means that breeding for increased resistance in Scots pine can be done effectively without risking a negative impact on established breeding objective traits and that resistance is stable across environments.
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| 10. |
- Samils, Berit, et al.
(författare)
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New genetic markers for identifying Cronartium flaccidum and Peridermium pini and examining genetic variation within and between lesions of Scots pine blister rust in Sweden
- 2011
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Ingår i: Fungal Biology. - : Elsevier BV. - 1878-6146. ; 115, s. 1303-1311
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Tidskriftsartikel (refereegranskat)abstract
- Microsatellite markers were developed as an identification tool and for analysis of the genetic variation in the pathogens Cronartium flaccidum and Peridermium pini, causing Scots pine blister rust in Pinus spp. Six reference aeciospore samples from Finland were used to examine genetic differences between the two pathogens. Genetic variation within and between 27 lesions on Scots pines from seven locations in Sweden was also investigated. Aeciospores were collected from single aecia within the lesions. Reference samples from P. pini were homozygous for all seven microsatellite loci investigated, while the three C. flaccidum samples contained heterozygous loci. These results confirm previous studies, where homozygous aeciospores were indicated to be characteristic for P. pini. The majority of aeciospores had two nuclei in both heterozygotic and homozygotic samples. Five of the Swedish lesions contained only homozygotic aecia, while the aecia in the remaining 22 lesions were heterozygotic. All lesions with homozygotic aecia contained only one single multilocus genotype, while many of the lesions with heterozygotic aecia contained several genotypes. The latter indicates the occurrence of multiple matings within a lesion between the resident spermogonia and alien fertilizing spermatia. (C) 2011. British Mycological Society. Published by Elsevier Ltd. All rights reserved.
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