| 1. |
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| 2. |
- Didon, Ulla, et al.
(författare)
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Cover Crop Residues-Effects on Germination and Early Growth of Annual Weeds
- 2014
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Ingår i: Weed Science. - 0043-1745 .- 1550-2759. ; 62, s. 294-302
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Tidskriftsartikel (refereegranskat)abstract
- There is an increasing interest in the use of cover crops in agriculture, in Sweden mainly for the use as catch crops to reduce nitrogen leakage. Some of these crops are known for their allelopathic abilities, which may play a role in the control of weeds and contribute to reduced herbicide use. This study aimed to explore the possible suppressive effect of the cover crop species white mustard, fodder radish, rye, and annual ryegrass on the early growth of the weed species silky windgrass, shepherd's-purse, and scentless false mayweed. In a greenhouse experiment using fresh cover crop residues, white mustard was the only crop that showed an effect. It reduced both seedling establishment, by 51 to 73%, and biomass, by 59 to 86%, of shepherd's-purse and scentless false mayweed. In contrast, in a growth chamber experiment using frozen material, mean germination time of silky windgrass was extended by 20 to 66% by all cover crops. Also, three out of four cover crops reduced root growth in scentless false mayweed by 40 to 46%, and two out of four cover crops reduced root growth in shepherd's-purse by 13 to 61%. However, considering seedling survival, white mustard was the most prominent cover crop, reducing survival by 21 to 57% in shepherd's-purse and scentless false mayweed. In this paper we provide evidence that different weed species show different response to different cover crops under climatic conditions prevailing in Scandinavia. Such results emphasize the importance of understanding weed cover crop interactions as necessary for developing cropping systems that can utilize cover crops to suppress local weed flora.
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| 3. |
- Hossain, Shakhawat, et al.
(författare)
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Aphanomyces pea root rot disease and control with special reference to impact of Brassicaceae cover crops
- 2012
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Ingår i: Acta Agriculturae Scandinavica, Section B - Soil and Plant Science. - : Informa UK Limited. - 0906-4710 .- 1651-1913. ; 62, s. 477-487
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Tidskriftsartikel (refereegranskat)abstract
- Pea root rot disease caused by the pathogen Aphanomyces euteiches deserves increased attention, since peas are an important cash crop and also improve the N balance in temperate agriculture. However, due to pea root rot it is difficult to cultivate peas as frequently and successfully as desired. In the search for biological measures to overcome this problem, attention has been drawn to the use of Brassicaceae plants as cover crops between main crops, since these can be effective catch crops for nutrients and also exert allelopathic effects. Many species within the Brassicaceae contain glucosinolates (GSLs). Their hydrolysis products, the volatile isothiocyanates (ITCs), have been shown to suppress soil-borne plant pathogens such as A. euteiches. In addition, Brassicaceae biomass releases water-soluble toxic substances such as oxazolidine-2-thione and supplies nutrients and organic matter. Overall, this influences the soil microbial community and the final suppression of pathogens. Due to the unpredictability of the control effect of Brassicaceae biomass incorporation into soil on the pathogen, there is a need to define the mechanisms behind suppression in the field situation. This review focuses on how incorporation of Brassicaceae biomass suppresses A. euteiches under field conditions and the effect on the emerging pea. Different factors influencing the severity of field pea (Pisum sativum L.) root rot disease are also discussed. One conclusion is that suppression of pea root rot depends on the quality and quantity of incorporated Brassicaceae biomass.
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| 4. |
- Hossain, Shakhawat, et al.
(författare)
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Brassicaceae cover crops reduce Aphanomyces pea root rot without suppressing genetic potential of microbial nitrogen cycling
- 2015
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Ingår i: Plant and Soil. - : Springer Science and Business Media LLC. - 0032-079X .- 1573-5036. ; 392, s. 227-238
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Tidskriftsartikel (refereegranskat)abstract
- Brassicaceae cover crops can be used to suppress soil-borne pathogens. The aim was to investigate the effect of different brassicas with different glucosinolate profiles on the development of Aphanomyces pea root rot in subsequent pea plants, and the genetic potential of free-living N-2-fixing bacteria and ammonia oxidising bacteria (AOB) and archaea (AOA) performing key soil ecosystem services.The Brassicaceae species Brassica juncea and Sinapis alba and non-Brassicaceae species Secale cereale were grown for 11-weeks in Aphanomyces euteiches infested soil at low and high nitrogen (N) fertiliser doses. After removing both shoots and roots of the cover crops, peas were grown as a bioassay to evaluate Aphanomyces pea root rot development. Soil was sampled before harvesting the cover crops and at the end of the bioassay. Volatile compounds were collected in the root-soil environment before harvesting the Brassicaceae cover crops to determine the concentration of isothiocyanates. The abundance of genes involved in N-2-fixing bacteria and ammonia oxidation in AOA and AOB were assessed.Pea root rot disease severity was reduced in Brassicaceae grown soil at the high N fertiliser dose. This was associated with increased growth of the cover crops. The growth of Brassicaceae did not suppress the abundance of N-cycling microbial communities, but rather increased the AOB at the end of the bioassay, most likely due to increased N availability. The disease suppressive effect was higher with S. alba than with B. juncea, and this coincided with a more diverse composition and higher concentration of aliphatic ITCs released from S. alba roots. Fewer nodules were formed after the Brassicaceae crops, especially Sinapis alba.Brassicaceae cover crops, particularly S. alba, can be used to control soil-borne pathogens without major side effects on the genetic potential of beneficial soil microorganisms involved in N cycling. However, less nodule formation after brassicas indicates an effect on rhizobium activity.
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| 5. |
- Hossain, Shakhawat, et al.
(författare)
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Concentration- and time-dependent effects of isothiocyanates produced from Brassicaceae shoot tissues on the pea root rot pathogen Aphanomyces euteiches
- 2014
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Ingår i: Journal of Agricultural and Food Chemistry. - : American Chemical Society (ACS). - 0021-8561 .- 1520-5118. ; 62, s. 4584-4591
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Tidskriftsartikel (refereegranskat)abstract
- Isothiocyanates (ITCs) hydrolyzed from glocosinolates (GSLs) in Brassicaceae tissue are toxic to soil organisms. In this study, the effect of aliphatic and aromatic ITCs from hydrated dy Brassicaceae shoot tissues on the mycelium and oospores of the pea root rot pathogen Aphanomyces euteiches was investigated. The profile and concentrations of GSLs in two test Brassicaceae species, Sinapis alba and Brassica juncea, and the ITCs from the dominant hydrolyzed parent GSLs were monitored. The concentrations of dominant ITCs and pathogen exposure time were evaluated in in vitro experiments. The greatest effect on the pathogen was observed from aliphatic ITCs hydrolyzed from B. juncea tissue, and the effect depended on the ITS concentration and exopsure time. ITCs were more effectively hydrolyzed from B. juncea GSLs than from S. alba GSLs; i.e., the ITC/GSL ratio was higher in B. juncea than in S. albatissue, giving a different release pattern. The release of phenylethyl isothiocyanate, which was common to both species, followed a pattern similar to that of the dominant ITC in each crop speices. This suggests that trait other than GSL content, e.g., plant cell structure, may affect the release of ITCs ans should therefore influence the choice of speices used for biofumigation purposes.
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| 6. |
- Jögi, Annika, et al.
(författare)
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Modulation of Basic Helix-Loop-Helix Transcription Complex Formation by Id Proteins during Neuronal Differentiation.
- 2002
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Ingår i: Journal of Biological Chemistry. - 1083-351X. ; 277:11, s. 9118-9126
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Tidskriftsartikel (refereegranskat)abstract
- It is assumed that the Id helix-loop-helix (HLH) proteins act by associating with ubiquitously expressed basic HLH (bHLH) transcription factors, such as E47 and E2-2, which prevents these factors from forming functional hetero- or homodimeric DNA binding complexes. Several tissue-specific bHLH proteins, including HASH-1, dHAND, and HES-1, are important for development of the nervous system. Neuroblastoma tumors are derived from the sympathetic nervous system and exhibit neural crest features. In differentiating neuroblastoma cells, HASH-1 is down-regulated, and there is coincident up-regulation of the transcriptional repressor HES-1, which is known to bind the HASH-1 promoter. We found that the three Id proteins expressed in neuroblastoma cells (Id1, Id2, and Id3) were down-regulated during induced differentiation, indicating that Id proteins help keep the tumor cells in an undifferentiated state. Studying interactions, we noted that all four Id proteins could dimerize with E47 or E2-2, but not with HASH-1 or dHAND. However, the Id proteins did complex with HES-1, and increased levels of Id2 reduced the DNA binding activity of HES-1. Furthermore, HES-1 interfered with Id2/E2-2 complex formation. The ability of Id proteins to affect HES-1 activity is of particular interest in neuronal cells, where regulation of HES-1 is essential for the timing of neuronal differentiation.
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| 7. |
- Karlsson, Ida, et al.
(författare)
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Agricultural factors affecting Fusarium communities in wheat kernels
- 2017
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Ingår i: International Journal of Food Microbiology. - : Elsevier BV. - 0168-1605 .- 1879-3460. ; 252, s. 53-60
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Tidskriftsartikel (refereegranskat)abstract
- Fusarium head blight (FHB) is a devastating disease of cereals caused by Fusarium fungi. The disease is of great economic importance especially owing to reduced grain quality due to contamination by a range of mycotoxins produced by Fusarium. Disease control and prediction is difficult because of the many Fusarium species associated with FHB. Different species may respond differently to control methods and can have both competitive and synergistic interactions. Therefore, it is important to understand how agricultural practices affect Fusarium at the community level.Lower levels of Fusariwn mycotoxin contamination of organically produced cereals compared with conventionally produced have been reported, but the causes of these differences are not well understood. The aim of our study was to investigate the effect of agricultural factors on Fusarium abundance and community composition in different cropping systems. Winter wheat kernels were collected from 18 organically and conventionally cultivated fields in Sweden, paired based on their geographical distance and the wheat cultivar grown. We characterised the Fusarium community in harvested wheat kernels using 454 sequencing of translation elongation factor 1-alpha amplicons. In addition, we quantified Fusariwn spp. using real-time PCR to reveal differences in biomass between fields.We identified 12 Fusariwn operational taxonomic units (OTUs) with a median of 4.5 OTUs per field. Fusarium graminearum was the most abundant species, while F. avenaceum had the highest occurrence. The abundance of Fusariwn spp. ranged two orders of magnitude between fields. Two pairs of Fusariurt species co-occurred between fields: F. poae with F. tricinctwn and F. culmorwn with F. sporofrichoides. We could not detect any difference in Fusariwn communities between the organic and conventional systems. However, agricultural intensity, measured as the number of pesticide applications and the amount of nitrogen fertiliser applied, had an impact on Fusariwn communities, specifically increasing the abundance of F. tricinctwn. There were geographical differences in the Fusarium community composition where F. graminearwn was more abundant in the western part of Sweden. The application of amplicon sequencing provided a comprehensive view of the Fusarium community in cereals. This gives us better opportunities to understand the ecology of Fusarium spp., which is important in order to limit FHB and mycotoxin contamination in cereals.
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| 8. |
- Karlsson, Ida, et al.
(författare)
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Genus-Specific Primers for Study of Fusarium Communities in Field Samples
- 2016
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Ingår i: Applied and Environmental Microbiology. - 0099-2240 .- 1098-5336. ; 82, s. 491-501
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Tidskriftsartikel (refereegranskat)abstract
- Fusarium is a large and diverse genus of fungi of great agricultural and economic importance, containing many plant pathogens and mycotoxin producers. To date, high-throughput sequencing of Fusarium communities has been limited by the lack of genus-specific primers targeting regions with high discriminatory power at the species level. In the present study, we evaluated two Fusarium- specific primer pairs targeting translation elongation factor 1 (TEF1). We also present the new primer pair Fa+7/Ra+6. Mock Fusarium communities reflecting phylogenetic diversity were used to evaluate the accuracy of the primers in reflecting the relative abundance of the species. TEF1 amplicons were subjected to 454 high-throughput sequencing to characterize Fusarium communities. Field samples from soil and wheat kernels were included to test the method on more-complex material. For kernel samples, a single PCR was sufficient, while for soil samples, nested PCR was necessary. The newly developed primer pairs Fa+7/Ra+6 and Fa/Ra accurately reflected Fusarium species composition in mock DNA communities. In field samples, 47 Fusarium operational taxonomic units were identified, with the highest Fusarium diversity in soil. The Fusarium community in soil was dominated by members of the Fusarium incarnatum-Fusarium equiseti species complex, contradicting findings in previous studies. The method was successfully applied to analyze Fusarium communities in soil and plant material and can facilitate further studies of Fusarium ecology.
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| 9. |
- Karlsson, Ida, et al.
(författare)
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Organic farming increases richness of fungal taxa in the wheat phyllosphere
- 2017
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Ingår i: Molecular Ecology. - : Wiley. - 0962-1083 .- 1365-294X. ; 26, s. 3424-3436
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Tidskriftsartikel (refereegranskat)abstract
- Organic farming is often advocated as an approach to mitigate biodiversity loss on agricultural land. The phyllosphere provides a habitat for diverse fungal communities that are important for plant health and productivity. However, it is still unknown how organic farming affects the diversity of phyllosphere fungi in major crops. We sampled wheat leaves from 22 organically and conventionally cultivated fields in Sweden, paired based on their geographical location and wheat cultivar. Fungal communities were described using amplicon sequencing and real-time PCR. Species richness was higher on wheat leaves from organically managed fields, with a mean of 54 operational taxonomic units (OTUs) compared with 40 OTUs for conventionally managed fields. The main components of the fungal community were similar throughout the 350-km-long sampling area, and seven OTUs were present in all fields: Zymoseptoria, Dioszegia fristingensis, Cladosporium, Dioszegia hungarica, Cryptococcus, Ascochyta and Dioszegia. Fungal abundance was highly variable between fields, 10(3)-10(5) internal transcribed spacer copies per ng wheat DNA, but did not differ between cropping systems. Further analyses showed that weed biomass was the strongest explanatory variable for fungal community composition and OTU richness. These findings help provide a more comprehensive understanding of the effect of organic farming on the diversity of organism groups in different habitats within the agroecosystem.
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| 10. |
- Kolseth, Anna-Karin, et al.
(författare)
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Dispersal paaterns of F. graminearum and possible implications for disease development in the field
- 2012
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Ingår i: NJF Report. - 1653-2015. ; 8, s. 33-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Focusing on F. graminearum, results from two studies on inter species interactions of Fusarium will be discussed. The two studies have different inoculation strategies, one using inoculated sterilized kernels placed at sowing depth as inoculum, and the other using spray inoculation of dissolved conidia on the panicle, at flowering stage. Both studies were performed in growth chambers with oat as a host but they differed considering the choice of Fusarium species studied. The first study, with inoculum at sowing depth used F. graminearum, F. culmorum and F. langsethiae as models, while the spray inoculation study focused on F. graminearum, F. avenaceum and F. langsethiae. In both studies Fusarium inoculations were performed with both single species and different combinations of species mixtures. Infection development in both studies was quantified using real-time PCR. When placing inoculum at sowing depth, following the development of fungal infection over time, F. culmorum was detected earlier during plant development compared to F. graminearum in roots, stem bases and first nodes (DC 60). At a later stage (DC 90), F. graminearum had caught up, but the two species did show a different colonization pattern. While a large proportion of sampled plants had detectable F. culmorum DNA in roots, stem bases and first nodes (23 of 50 plants inoculated with F. culmorum), no infection of this species was found in the panicles. In comparison, F. graminearum was found in roots, stem bases and first nodes in only 3 of 38 plants inoculated with F. graminearum. It had on the other hand spread and contaminated pots with other inoculation treatments, and was found in almost all panicles in the growth chamber irrespective of inoculation treatment. Infection of F. langsethiae was not detectable using real-time PCR in any sampled material in any growth stage. Pots inoculated with F. langsethiae at sowing depth showed a lower cross contamination of F. graminearum in roots, stem bases and first nodes compared to the control pots, but no difference was found in F. graminearum panicle infections, comparing uninoculated control pots with F. langsethiae inoculated pots. Applying inoculum directly to the panicle using spray inoculation, following the development of the infection over 2 weeks (sampling 2, 6, 10 and 14 days after inoculation), reveals an effect of the two other species on F. graminearum. When F. graminearum was co-inoculated with either F. avenaceum or F. langsethiae or both, F. graminearum did show a lower infection rate at all time-points compared to when it was inoculated singly. Results imply that F. graminearum has a preference for air dispersal entering the plant in to the panicle. Results also imply that this species is poor at interference competition in planta. Recent outbreaks of F. graminearum in Scandinavia may be explained by an optimal seasonal climate, but can the dispersal pattern of F. graminearum also be of importance? By being good at dispersal it may be the first one to establish on the host, and thereby gain a competitive advantage over other Fusarium species.
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