| 1. |
- Jensen, Anna M
(författare)
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Effects of facilitation and competition on oak seedlings : using shrubs as nurse-plants to facilitate growth and reduce browsing from large herbivores
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Plant–plant interactions have been indicated as a potential means to facilitate oak seedling establishment and reduce herbivory when restoring oak forests. The aim of this thesis was to investigate mechanisms and outcomes of competitive and indirectly facilitative interactions between oak (Quercus robur and Q. petraea) seedlings and neighboring plants, primarily shrubs. The associational resistance of planted oak seedlings to larger herbivores provided by naturally occurring shrubs was tested in ten temperate broadleaved forests across southern Sweden. The results showed that shrubs reduced ungulate browsing frequency and intensity by concealing the oak seedlings and by sharing enemies (i.e. ungulate herbivores) with surrounding and more preferred shrub species, thus providing numeric dilution and associational plant refuges. The occurrence of naturally regenerated oak seedlings, five years after a conservation-oriented thinning, was negatively influenced by the presence of tall ground vegetation and positively influenced by high soil moisture. For oak seedlings planted in an open field, shrubs indirectly facilitated biomass accumulation by reducing competition from herbaceous vegetation. However, shrubs became net competitors three years after planting. The oak seedling response, in terms of biomass accumulation, transpiration and photosynthesis, to competition from shrubs was proportional to resource availability. Aboveground competition for light had a greater effect on oak seedling growth than belowground competition. Nevertheless, oak seedlings were able to produce a second shoot flush, over-topping the shrub canopy. This periodic flushing enabled light-acclimation in a stratified light environment. In conclusion, management of shrubs has the potential to reduce browsing and herbaceous competitors during oak regeneration, particularly during the first years after planting. Although shrubs alone may not replace fences as an effective means of reducing browsing on oaks, they provide a complement to improve the growth of seedlings during the early stages of establishment.
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| 2. |
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| 3. |
- Lamei, Sepideh
(författare)
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The effect of honeybee-specific lactic acid bacteria on american foulbrood disease of honeybees
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The honeybee, Apis mellifera, is one of the most economically important pollinators and highly valued for its honey and wax production. Managed honeybees occupy an increasingly critical role in agricultural productivity and food security. American foulbrood (AFB) is a highly contagious and destructive bacterial honeybee brood disease caused by Paenibacillus larvae that affects beekeeping worldwide. However, only a minority of bacteria associated with honeybees are harmful. Honeybee-specific Lactic Acid Bacteria (hbs-LAB), a defined group of beneficial bacteria inhabiting the honey crop, have strong antimicrobial properties important for honey production and honeybee health that could be exploited for combating diseases such as AFB. The aim of this thesis was to investigate the effect of hbs-LAB on P. larvae and AFB, both in culture, in individual larval bioassays, and at colony level. First we showed that the laboratory cultivation of the 13 distinct hbs-LAB was significantly improved by the addition of L-cysteine and fructose to the medium and optimized a culture-independent molecular technique for the detection and identification of the individual hbs-LAB species. Secondly the effect of the cell free supernatant, the secretome, from a culture mix of the 13 hbs-LAB species was investigated on P. larvae growth and associated larval mortality. The results showed that this secretome strongly inhibited the multiplication of P. larvae vegetative cells but that spore germination appeared to be unaffected, and that it decreased the mortality of P. larvae infected larvae. Finally it was shown that oral administration of hbs-LAB supplement to honeybee colonies had no influence on colony-level P. larvae spore levels or colony strength. Furthermore, the results showed that although the antibiotic tylosin decreased AFB symptoms in colonies, it had no effect on P. larvae spore levels. In conclusion, the colony-level results do not contradict the antagonistic effects observed in individual larvae in laboratory studies, but rather suggest that supplementary administration of live bacteria may not be the most effective way to harness such effects in a useful application.
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| 4. |
- Nilsson, Kerstin
(författare)
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To work or not to work in an extended working life? Factors in working and retirement decisions
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In most of the industrialised world, the proportion of older and retired people in the population is continuously increasing. This will have budgetary implications for maintaining the welfare state, because the active working section of the population must fund the non-active and old population. Aim: The overall aim of this thesis was to obtain knowledge about older workers’ work and life situation in association with their planning and decision to retire from working life. Method: The thesis includes one qualitative and three quantitative studies conducted in Sweden. Result: Self-rated health was found to be a better measure than diagnosed disease of whether older workers believed they could work until 65 years or beyond. Health seems not to be a general impediment to working in old age if older workers are satisfied with their work situation and have enough time and opportunities to recover from fatigue. In one of Sweden’s most hazardous work environments, older workers were not injured significantly more often than younger workers. Good mental and physical work environment, moderate working pace and working time, and the right competence and possibility for skills development were factors determining whether older workers believed they can extend their working life. Attitude to older workers in the organisation, motivation and work satisfaction were factors determining whether older workers want to extend working life. Health, personal economic incentives, family/leisure pursuits and attitude to pension in society affected both whether people believed they can and wanted to extend their working life. In their final retirement decision, older workers considered: i) their possibility to balance and adapt functional ageing and health to a sustainable work situation; ii) their economic situation; iii) possibilities for social inclusion and coherence; and iv) possibilities for meaningful activities. Whether these requirements were best fulfilled in or outside working life determined the decision to continue working or to retire. Conclusion: If it is desirable for society that people will to extend their working life, both the “can work” and the “want to work” factors need to be met. It is important to provide a good fit inside working life. This requires a focus not only on older workers, but also on organisations and managers in order to provide incentives that keep older workers in the work force.
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| 5. |
- Aballay, Erwin
(författare)
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Rhizobacteria associated to Vitis vinifera and their effect on the control of Xiphinema index, Meloidogyne ethiopica and Vitis growth
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Plant-parasitic nematodes are one of the most important pests affecting the growth of vineyards due to the destruction of new roots. Several species are associated with this problem, the most important being the ectoparasite Xiphinema index and the endoparasite Meloidogyne ethiopica. The search for new pest and disease control methods based on bioantagonist microorganisms is an important aspect of modern agriculture and the development of tools based on the use of rhizobacteria is becoming a widely evaluated alternative. The present study on suppressive soils started with a survey undertaken in productive Chilean vineyards to explore the younger roots of grapevines and identify the presence of rhizobacteria. More than 1800 soils were surveyed and a set of 11 vineyards were selected and considered suitable for bacteria isolation, as they showed low densities of plant-parasitic nematodes. A total of 400 bacterial isolates in 25 genera were obtained using tryptic soy broth agar and identified with fatty acid profiling. Two of the most frequently isolated species were Pseudomonas putida (35.1%) and P. fluorescens (6.1%). The effect of these isolates on the parasitism and reproduction of X. index was assessed through assays using potted vine plants (cv. Thompson Seedless) and a bacterial suspension containing 1×106 CFU/mL. Some isolates from Bacillus megaterium, B. brevis, B. mycoides, B. sphaericus, B. thuringiensis, Pseudomonas corrugata, P. putida, P. alcaligenes, P. savastanoi, P. fluorescens, P. pseudoalcaligenes, P. viridiflava, Stenotrophomonas maltophilia, Serratia plymuthica, Cytophaga johnsonae, Rahnella aquatilis, Stenotrophomonas sp., Variovorax paradoxus and Curtobacterium flaccumfaciens reduced root damage and suppressed populations. Isolates of B. brevis, Comamonas acidovorans, B. megaterium, Pantoea agglomerans and P. savastanoi increased plant growth or root weight, but did not control nematodes. Most of the culture filtrates obtained from isolates from four vineyards were effective in killing X. index and decreasing egg hatching, which was not related to damage or population control. It was estimated that 89, 32 and 16% of the isolates were effective against X. index under supernatant conditions, in potted plants growing in sterile substrate and in potted plants growing in field soil, respectively. Sixteen bacterial isolates previously assessed were also evaluated on M. ethiopica in vine cv. Chardonnay. Seven isolates (Serratia marcescens, C. acidovorans, P. agglomerans, Sphingobacterium spiritivorum, B. mycoides, Alcaligenes piechaudii and S. plymuthica) decreased damage or reproduction, showing that different species of nematodes can respond differently to a particular isolate.
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| 6. |
- Abd El-Daim, Islam Ahmed Moustafa
(författare)
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Use of rhizobacteria for the alleviation of plant stress
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Plant growth promoting rhizobacteria are beneficial microbes able to induce plant stress tolerance and antagonise plant pathogens. The present study showed that wheat seedlings pre-treated with Bacillus thuringiensis AZP2 had better tolerance to severe drought stress and showed 78% greater plant biomass and five-fold higher survivorship compared to wheat seedlings not treated with the bacterium. The effect of B. thuringiensis AZP2 also resulted in improved net assimilation and reduced emission of stress volatiles. The study investigated the effect of the inactivation of sfp-type phosphopantetheinyl transferase in plant growth promoting bacterium Paenibacillus polymyxa A26. The inactivation of the sfp gene resulted in loss of NRP/PK production such fusaricidins and polymyxins. In contrast to the former Bacillus spp. model the mutant strain compared to wild type showed greatly enhanced biofilm formation ability. Its biofilm promotion is directly mediated by NRP/PK, as exogenous addition of the wild type metabolite extracts restores its biofilm formation level. Further, increased biofilm formation was connected with enhanced ability of the sfp inactivated strain to remarkably protect wheat seedlings by improving its survival and biomass under severe drought stress conditions compared to wild type. Fusarium graminearum and F. culmorum are the causing agents of a destructive disease known as Fusarium head blight (FHB). The disease is the leading cause of contamination of grain with Fusarium mycotoxins that are severe threat to humans and animals. Biological control has been suggested as one of the integrated management strategies to control FHB causing agents. The present study showed that P. polymyxa A26 is a potent antagonistic agent against F. graminearum and F. culmorum. In order to optimize strain A26 production, formulation and application strategies traits important for its compatibility need to be revealed. Hence, a toolbox comprising of dual culture plate assays and wheat kernel assays including simultaneous monitoring of the FHB causing pathogens, A26 and mycotoxins produced was developed in the present study. Using this system results showed that, besides the involvement of lipopeptide antibiotic production by P. polymyxa in the antagonism process, biofilm formation ability may play a crucial role in the case of A26 F. culmorum antagonism.
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| 7. |
- Aboshady, Hadeer Moursy
(författare)
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Genomic variation and molecular mechanisms of the host response to gastrointestinal nematodes in small ruminants
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Gastrointestinal nematode (GIN) infections are one of the major constrains for sheep and goat production worldwide. One of the promising control strategies is the genetic selection for resistant animals as there are no issues due to anthelmintic resistance and it aligns to demands for chemical-free food. Exploring possible phenotypic and genomic markers that could be used in breeding scheme besides understanding the mechanisms responsible for resistance were the main goals of this thesis. Thesis consists of General introduction, a brief description of GIN biology and methods to control GIN with focus on phenotypic and genomic markers, four papers and General discussion. In paper Ⅰ, a systematic review and meta-analysis were conducted to re-analyse and summarize the findings on immunoglobulins response to GIN in the literature and discuss the potential to use immunoglobulins as biomarkers of the host resistance. A conceptual model summarizing the role of immunoglobulins in resistance to GIN is proposed. In paper Ⅱ, transcriptome profiling of the abomasal mucosa and lymph node tissues were compared between non-infected, resistant and susceptible Creole goats experimentally infected with Haemonchus contortus. Results indicated that the maintenance of the integrity of the mucosa has probably the priority for the host at late infection stage. In paper Ⅲ, the dynamics of the response of the abomasal mucosa of resistant and susceptible Creole goats experimentally infected with H. contortus were compared. The immune response was activated through many relevant pathways including the Th1 immune response at different time post-infection. Interestingly, the results showed a simultaneous time series activation of Th2 related genes in resistant compared to susceptible kids. In paper Ⅳ, the genomic variants of Creole goats resistant and susceptible to H. contortus were discovered from RNAsequencing data at four different times post-infection. Single nucleotide polymorphisms, insertions and deletions that distinguish the resistant and the susceptible groups were identified and characterized through functional analysis. The T cell receptor signalling pathway was one of the top significant pathways that distinguish the resistant from the susceptible group with genomic variants in 78% of genes in this pathway.
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| 8. |
- Abrahamsson, Malin
(författare)
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Patterning during embryo development in Pinus : with special emphasis on somatic embryogenesis in Scots pine (Pinus sylvestris L.)
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Somatic embryogenesis is an attractive method to propagate conifers vegetatively. However, many species belonging to Pinus are recalcitrant to somatic embryo development. The overall aim of this thesis has been to gain a better understanding of the developmental pathway leading to cotyledonary somatic embryos of Scots pine (Pinus sylvestris). By comparing the developmental pathway of somatic embryos in a normal and in an abnormal cell line, differences between the cell lines were identified. An important difference was the high ratio of early and late embryos carrying supernumerary suspensor cells in the abnormal cell line compared to embryos in the normal cell line. This unbalanced ratio between the embryonal mass and the suspensor is at least partly caused by a disturbed polar auxin transport. Furthermore, a high proportion of early and late embryos degenerated in both cell lines. The degenerating embryos in the normal cell line were eliminated in a similar way as subordinate embryos in the seed. Contrastingly, the degenerating embryos in the abnormal cell line were not eliminated; instead the degenerated embryos started to differentiate new embryos creating a loop of embryo degeneration and embryo differentiation. During initiation of embryogenic tissue, the protruding early zygotic embryo(s) started to degenerate before a proliferating embryogenic culture was established, indicating that the initiation of embryogenic cultures is not a direct continuation of cleavage polyembryony. The results further suggest that there is a high risk that cell lines initiated from early zygotic embryos at the stage of cleavage develop abnormally. To be able to use more differentiated tissues as explants for initiation of embryogenic cultures, more knowledge is needed about totipotence and embryogenic potential. Treatment with the histone deacetylase inhibitor trichostatin A (TSA) during maturation of somatic embryos of Norway spruce inhibited the maturation progression of the embryos. Furthermore, although TSA-treatment maintained the embryogenic potential in germinating somatic embryos, it did not enable the embryos to regain embryogenic potential after it was lost. By analysing global changes in gene expression during early zygotic embryo development in Scots pine, we identified genes and processes that might be important for regulating the cleavage process and for the development of a dominant embryo. Together these results contribute to the knowledge that in turn can lead to improved protocols for large scale propagation of Pinus species via somatic embryos.
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| 9. |
- Abrahamsson, Sara
(författare)
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Genetic dissection of quantitative traits in Scots pine
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The phenotypic expressions of Scots pine, have been extensively studied over the years, but the gene regulation behind the traits has only just begun to be elucidated. The overall aim of this thesis was to start dissecting the genetics behind a number of adaptive traits in Scots pine and examine how they are influenced by relatedness using different molecular tools. In a full-sib family of Scots pine the genetic variation in autumn frost hardiness and height growth was revelead by measuring open-pollinated offspring. A significant genetic variation for both traits was found, a prerequisite to identify quantitative trait loci (QTL). A conceptual statistical model in the Bayesian framework for identifying QTLs in dynamic traits i.e. traits that vary over time, was developed and applied in a QTL study based on a full-sib family of 250 trees. A set of 160 AFLPs were utilized. QTLs for three latent traits were identified: one for the slope (growth) and two for the quadratic term (growth cessation). As a tool to identify candidate genes for the study of quantitative adaptive traits, gene regulation under continuous red (cR) and far-red (cFR) light was studied in hypocotyls from open-pollinated seeds from a natural population in northern Sweden using microarray technology. The gene expression patterns for the light response pathway in Scots pine under cFR show clear differences from those of angiosperms, wherein we observed up-regulation of cryptochrome1. This gene has, therefore, become a strong candidate gene that deserves further studies to elucidate the genetics behind Scots pine adaptation. Not knowing the genetic relationship and inbreeding of trees, and how it influences the phenotypic expression, can lead to over- or underestimation of additive genetic values resulting in biased heritability estimates. A natural population of Scots pine, earlier identified as being highly inbreed, was used to investigate the influence of inbreeding by the correlation between heterozygosity and propotion of sound seed (PSS), average seed weight and proportion of rare alleles (PRA). Heterozygosity fitness correlation (HFC) was found positive for PSS and negative for PRA most likely due to recessive deleterious alleles purged in homozygotes. The study provided evidence that, as predicted by theory, inbreeding enhances HFC in a species with high outbreeding rate and high number of lethal equivalents as Scots pine.
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| 10. |
- Abro, Rani
(författare)
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Digestion and metabolism of carbohydrates in fish
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with the digestion and metabolism of carbohydrates in Arctic charr, Eurasian perch and tilapia. Two sources of carbohydrates, native starch (wheat) and chitin (zygomycete biomass), were evaluated. Gut tissue of Arctic charr displayed significant chitinase activity, of both endo- and exo-chitinase forms. Moreover, the distribution pattern along the gastrointestinal tract of Arctic charr differed between endo-chitinase and exo-chitinase. The endo-chitinase activity in stomach tissue and in the distal intestine was several hundred-fold higher than the exo-chitinase activity in stomach tissue. The greatest exo-chitinase activity was found in the distal intestine fed a zygomycete-based diet. Disturbed intestinal integrity and increased uptake rate of the amino acid lysine were observed in the distal, but not proximal, intestine of fish fed the zygomycete-based feed. A ¹HNMR metabolomics approach revealed no differences in metabolic profile in liver tissues of Arctic charr fingerlings fed a zygomycete-based diet and a fish-meal based diet. The inclusion of wheat starch did not affect α-amylase activity in gut tissue of Arctic charr and Eurasian perch. Overall, α-amylase activity was correlated with the trends obtained for starch digestibility. The apparent digestibility (AD) of crude protein, starch, crude fat and energy differed between the fish species, with on average higher values for all parameters in Eurasian perch than in Arctic charr. Within fish species, dietary starch level had no effect on AD of dry matter, crude protein, crude fat and energy. Studies of the metabolic response to wheat starch inclusion in Arctic charr and tilapia using ¹HNMR base metabolomics indicated metabolic effects in tilapia, while inclusion of starch in the diet of Arctic charr resulted in partial or negligible metabolism effects. Thus there are species-related differences in the metabolic response to dietary starch inclusion.
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