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- 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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| 2. |
- 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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| 9. |
- Abouhatab, Assem
(författare)
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China
- 2015
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Ingår i: Employability of Erasmus Mundus Graduates in Agriculture on the Chinese Professional Market. - 9788021325791 ; , s. 31-31
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 10. |
- Abouhatab, Assem, et al.
(författare)
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Determinants of import demand for Egyptian potatoes in Germany and the United Kingdom
- 2016
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Ingår i: Acta Horticulturae. - 0567-7572 .- 2406-6168. ; 1132, s. 39-48
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The European Union (EU) is the major import market for Egyptian fresh potatoes. Germany and the United Kingdom (UK) jointly imported about 44% of Egyptian potato exports to the EU during the period 1994-2012. This study sought to identify the determinants of import demand for Egyptian potatoes in these two countries. A general differentiated demand system approach was used to estimate conditional potato import demand per country. For each country, it was assumed that the system of conditional import demand equations for potatoes is specified according to the sources of origin and also depends on all imported potato prices and total import potato expenditure. When estimated econometrically, this import demand model allows conditional price and expenditure elasticities to be derived. The econometric results indicated that with an estimated elasticity of 1.95, Egyptian potato exports responded significantly to total expenditure on imported potatoes by Germany. On the other hand, Egyptian potato exports to Germany did not exhibit significant price responses. In all cases but one, estimated conditional uncompensated price elasticities were not statistically different from zero. However, more interesting results were obtained concerning the price responses of Egyptian potato exports to the UK, whereby the conditional (uncompensated) direct elasticity of potato imports from Egypt to the UK (-0.71) showed an inelastic response to its own price. Furthermore, Egyptian potato exports seemed to compete on the UK market with potatoes originating from Israel and France, while they displayed complementarity with Dutch imports.
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