Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Biological activity of Pakistani isolate SpltNPV-Pak-BNG in second, third and fourth instar larvae of the leafworm Spodoptera litura
    Ali, Ghulam ; Vlak, Just M. ; Werf, Wopke van der - \ 2018
    Biocontrol Science and Technology 28 (2018)5. - ISSN 0958-3157 - p. 521 - 527.
    biological activity - larval instars - potency - S. litura - Spodoptera litura nucleopolyhedroviruses
    Recently, a novel isolate of the baculovirus Spodoptera litura nucleopolyhedrovirus (SpltNPV) has been isolated from Pakistan, which is distinct from the type species SpltNPV-G2 (ICTV). Here, we examined the biological activity of this isolate (SpltNPV-Pak-BNG) in second (L2), third (L3) and fourth instar (L4) larvae of the leafworm S. litura, more specifically to measure biological properties that are relevant for use of this virus for pest control under field conditions. The median lethal dose for L2 and L3 instar larvae was similar, but significantly lower than for L4 larvae. Likewise, the survival time was similar for L2 and L3 larvae (84 h), but was significantly longer for L4 instar larvae (108 h). Thus, in terms of efficacy, S. litura L2 and L3 instar larvae are the preferred targets for S. litura control with SpltNPV-Pak-BNG in field crops in Pakistan. On the basis of our data spray regimes can be designed to control the leafworm in cotton and vegetable crops targeting L2 and L3 larvae.
    Use of the ES-D3 cell differentiation assay, combined with the BeWo transport model, to predict relative in vivo developmenatl toxicity of antifungal compounds
    Li, H. ; Rietjens, I. ; Louisse, J. ; Blok, M. ; Wang, X. ; Snijders, L. ; Ravenzwaay, B. van - \ 2015
    Toxicology in Vitro 29 (2015)2. - ISSN 0887-2333 - p. 320 - 328.
    dose-response curves - placental perfusion - test est - vitro - toxicology - potency - risk - rat
    We investigated the applicability of the ES-D3 cell differentiation assay combined with the in vitro BeWo transport model to predict the relative in vivo developmental toxicity potencies. To this purpose, the in vitro developmental toxicity of five antifungal compounds was investigated by characterizing their inhibitory effect on the differentiation of ES-D3 cells into cardiomyocytes. The BeWo transport model, consisting of BeWo b30 cells grown on transwell inserts and mimicking the placental barrier, was used to determine the relative placental transport velocity. The ES-D3 cell differentiation data were first compared to benchmark doses (BMDs) for in vivo developmental toxicity as derived from data reported in the literature. Correlation between the benchmark concentration for 50% effect (BMCd50) values, obtained in the ES-D3 cell differentiation assay, with in vivo BMD10 values showed a reasonable correlation (R2 = 0.57). When the ES-D3 cell differentiation data were combined with the relative transport rates obtained from the BeWo model, the correlation with the in vivo data increased (R2 = 0.95). In conclusion, we show that the ES-D3 cell differentiation assay is able to better predict the in vivo developmental toxicity ranking of antifungal compounds when combined with the BeWo transport model, than as a stand-alone assay.
    No significant differences in the breadth of the foot-and-mouth disease serotype A vaccine induced antibody responses in cattle, using different antigens, mixed antigens and different toutes of administration
    Tekleghiorghis, T. ; Weerdmeester, K. ; Hemert-Kluitenberg, F. ; Moormann, R.J.M. ; Dekker, A. - \ 2014
    Vaccine 32 (2014)41. - ISSN 0264-410X - p. 5330 - 5336.
    aluminum hydroxide gel - emergency vaccination - immune-responses - cross-protection - fmd vaccines - virus - elisa - potency - tests - challenge
    Inactivated whole virus foot-and-mouth disease (FMD) vaccines are used worldwide for protection against FMD, but not all vaccines induce protection against all genetic variants of the same FMD virus serotype. The aim of this study is to investigate whether the “breadth” of the antibody response against different strains of the same FMD virus serotype in cattle could be improved by using a different adjuvant, a mix of antigens and/or different routes of administration. To this end, six groups of five cattle were vaccinated with different FMD virus serotype A strain vaccines formulated with Montanide ISA 206 VG adjuvant. Antibody responses for homologous and heterologous cross-reactivity against a panel of 10 different FMD virus serotype A strains were tested by a liquid-phase blocking ELISA. Results of cattle vaccinated with ISA 206 VG adjuvanted vaccine were compared with results obtained in a previous study using aluminium hydroxide-saponin adjuvant. No significant effect of adjuvant on the breadth of the antibody response was observed, neither for mixing of antigens nor for the route of administration (subcutaneous vs. intradermal). Comparison of antigen payload, however, increased both homologous and heterologous titres; a 10-fold higher antigen dose resulted in approximately four times higher titres against all tested strains. Our study shows that breadth of the antibody response depends mainly on the vaccine strain; we therefore propose that, for vaccine preparation, only FMD virus strains are selected that, among other important characteristics, will induce a wide antibody response to different field strains.
    Comparison of test methodologies for foot-and-mouth disease virus serotype A vaccine matching
    Tekleghiorghis, T. ; Weerdmeester, K. ; Hemert-Kluitenberg, F. van; Moormann, R.J.M. ; Dekker, A. - \ 2014
    Clinical and Vaccine Immunology 21 (2014)5. - ISSN 1556-6811 - p. 674 - 683.
    binary ethylenimine - protection - potency - antibodies - cattle - elisa - variability - challenge - evolution - selection
    Vaccination has been one of the most important interventions in disease prevention and control. The impact of vaccination largely depends on the quality and suitability of the chosen vaccine. To determine the suitability of a vaccine strain, antigenic matching is usually studied by in vitro analysis. In this study, we performed three in vitro test methods to determine which one gives the lowest variability and the highest discriminatory capacity. Binary ethylenimine inactivated vaccines, prepared from 10 different foot-and-mouth disease (FMD) virus serotype A strains, were used to vaccinate cattle (5 animals for each strain). The antibody titers in blood serum samples 3 weeks postvaccination (w.p.v.) were determined by a virus neutralization test, neutralization index test, and liquid-phase blocking enzyme-linked immunosorbent assay (ELISA). The titers were then used to calculate relationship coefficient (r1) values. These r1 values were compared to the genetic lineage using receiver operating characteristic (ROC) analysis. In the two neutralization test methods, the median titers observed against the test strains differed considerably, and the sera of the vaccinated animals did not always show the highest titers against their respective homologous virus strains. When the titers were corrected for test strain effect (scaling), the variability (standard error of the mean per vaccinated group) increased because the results were on a different scale, but the discriminatory capacity improved. An ROC analysis of the r1 value calculated on both observed and scaled titers showed that only r1 values of the liquid-phase blocking ELISA gave a consistent statistically significant result. Under the conditions of the present study, the liquid-phase blocking ELISA showed less variation and still had a higher discriminatory capacity than the other tests.
    The development of microbial pest control products for control of arthropods: a critical evaluation and a roadmap to success
    Ravensberg, W.J. - \ 2010
    Wageningen University. Promotor(en): Joop van Lenteren. - [S.l.] : S.n. - ISBN 9789085856788 - 348
    plagen veroorzaakt door geleedpotigen - biopesticiden - ontwikkeling - potentie - screenen - biologische productie - formuleringen - experimenteel veldonderzoek - kwaliteitscontroles - vercommercialisering - planning - toelating van bestrijdingsmiddelen - arthropod pests - microbial pesticides - development - potency - screening - biological production - formulations - field experimentation - quality controls - commercialization - planning - authorisation of pesticides
    Microbial pesticides have been developed for a hundred years, but many of these biological crop protection products have not been successful in the market. This is illustrated in chapter 1 by the history of microbial pest control products and the biopesticide companies producing those. In this thesis I recognize the need for a model that would facilitate the development and commercialization of biopesticides based on entomopathogenic bacteria, fungi, viruses, and nematodes. The aim of this thesis was to develop a rational and structured approach that will increase the chances of achieving success with microbial pest control products for control of arthropods.
    The initial step is finding a microbial pest control agent which has the potential to control the pest (chapter 2). The search for a novel agent is directed by an elaborate description of the pest problem. The first level of selection is the type of entomopathogen: bacteria, fungi, viruses, protozoa, and entomopathogenic nematodes. The second level is at the species and strain level. This study identified three decisive selection criteria for a commercial microbial insecticide: mortality, production efficiency, and safety to humans and the environment. The consecutive steps in the screening process have been identified as the collection of isolates, laboratory screening on efficacy in well-standardized bio-assays, and on production efficiency, assessment of mode of action and toxicological properties, and efficacy in small glasshouse trials. This selection process should deliver determinative information on which one or at the most three to four strains are chosen for further development.
    The next phase is the investigation of the feasibility of economic mass production of the selected strain(s) and the development of a stable product (chapter 3). Two phases are distinguished, the development of the production process, including medium development and downstream processing, and the development of the product, including formulation, packaging and field testing. Mass production is preferably an in vitro process because that offers more control than an in vivo process. Bacteria, fungi and entomopathogenic nematodes are generally produced in vitro, whereas baculoviruses must be produced in vivo. The critical technical and economic factors are identified and evaluated for these four types of pathogens. The goal is to produce the greatest number of infective propagules for the lowest cost.
    A stable product requires a formulation. The four main objectives in formulating the infective propagules are: to stabilize the propagules for reasons of packaging, shelf-life and shipping; to create a user-friendly product that can be effectively delivered to the target; to protect the propagule, once applied, to improve its persistence at the target site; and to minimize risks of exposure to the applicator. Formulation considerations and recommendations are presented per formulation function as well as per type of pathogen.
    Field testing links all steps in the developmental process. It provides information on the efficacy of the selected strain, on the quality of the produced propagules, on the formulation, and on the optimal application strategy. Results from field tests provide a continuous circle of feedback that allows improvement of each of the steps of the entire developmental process.
    The price of a product is an essential element and a cost price model for biopesticides is presented. The model provides a perspective on the makeup of the end-user’s price. Economy of scale, full use of the production capacity, and capacity planning are pivotal factors to keep the costs low. Key elements to successful biopesticides are both production efficiency and product efficacy.
    Quality control (chapter 4) provides feedback on the production and formulation processes, and on the final product. The continuous process of improvements will ultimately decrease costs and improve performance of the production system and the product. Products must meet product specifications. Parameters checked per batch are the number of effective propagules, microbial purity, presence of toxins, technical properties and efficacy. Standardization and comparison with a reference product are prerequisites for proper quality control. Quality control is also required for registration, but standard methods and criteria are lacking. Therefore, guidance documents need to be developed. Biocontrol companies should ensure that product quality is maintained through the whole distribution chain and that end-users receive high quality products. I showed that in that way, both the biocontrol industry and its customers benefit from proper quality control.
    In chapter 5 regulations for microorganisms are reviewed. Microorganisms, except nematodes, need to be registered as plant protection products for crop protection. Registration is perceived as the main hurdle to the development of a biopesticide. The procedures in the EU are presented and difficulties discussed. The issues relate to inappropriate data requirements, lack of guidance for applicants and regulators, testing methods for microbials, lack of experience in regulators, national registration procedures, and the inexperienced small biopesticide companies. Registration is expensive and takes many years. I presented registration cost estimates for each type of entomopathogenic product. Initiatives for improvements from the EU-REBECA project, from the OECD BioPesticides Steering Group, and some national projects are presented. I also provided recommendations for improvements for data requirements and regulatory procedures. New regulations may offer improved procedures in the near future. Various import and export regulations affect the use of microorganisms, and the need for harmonization is emphasized. The Convention of Biodiversity may, through Access and Benefit Sharing, create a further impediment for biocontrol.
    The patentability of an entomopathogen is discussed as well as the criteria for granting a patent: novelty, inventive step, and industrial applicability. I also discussed costs and other considerations whether to apply for a patent for a biopesticide.
    The implementation strategy of the product in an IPM programme is a basic element of the use of any microbial pest control product (chapter 6). Three phases are distinguished: the optimal application strategy of the product, the incorporation of the microbial pest control product in an IPM system, and a carefully designed adoption strategy. Determinative parameters for each phase, and for each type of product are identified. For instance, for a successful use, the compatibility with chemical pesticides and with natural enemies and pollinators needs to be investigated. Furthermore, knowledge transfer and training are pivotal elements. All stakeholders need to participate in this process.
    These phases require a considerable amount of research which should be conducted before market launch. Recommendations are provided for a tiered approach which results in reliable information for commercial conditions. Many companies underestimated or even neglected this part of product development. In my opinion, these phases are paramount for good market introduction. I reported the most relevant requirements for successful use of a microbial pest control product. Successful implementation of a microbial pest control product depends on how well relevant interactions are studied and translated into practical recommendations for the grower. This phase continues after market introduction. It requires a continuous effort from producer, distributor and customer to ensure that product adoption will increase and satisfied customers will remain using the new product in their IPM system.
    In chapter 7, I noted that commercialization is the final and most difficult step in the development and the market introduction of a microbial pest control product. The factors that determine success or failure are identified for a company as well as for a product, and recommendations are provided that will facilitate success.
    Figures on the global biopesticide market are reviewed. The European market is estimated to be €57 million at end-user level, and the market in the Netherlands at €5-6 million. The European biopesticide market comprises less than 1% of the total European crop protection market. Biopesticides are predominantly used in protected crops and in orchards.
    Companies which contemplate the development and commercialization of a biopesticide need realistic data on five key aspects to make their decision: market demand, market size, profit margin, time to market, and time to volume. The biggest mistake companies still make today is a misjudgement of the potential market size and the expected market adoption rate. I proposed the use of a stage-gate process with objective, quantifiable, and transparent tools in decision-making. Examples of scorecards are presented to quantify decisions. The business model that performs best at present seems to be a small company which follows an incremental and manageable growth of the organization. Total developmental costs and time to market are significant factors of a company’s success. Costs amount to € 10-15 million for a company that still needs to be built; while in an existing company, costs may reach € 5-10 million for a biopesticide project. Time to market including registration is five to seven years. I have identified five determinants for successful commercialization: 1) acceptable expenses and time to market; 2) a high quality product; 3) a sufficiently large market; 4) a profit margin that allows expansion in new markets and products; and 5) the appropriate business approach.
    A new product development project is extensive and it is difficult to oversee. In chapter 8 I have made an analysis of the various phases and I highlighted the most important topics in the development and commercialization of a microbial pest control product. This study demonstrated that the development of a microbial pest control product requires a structured project plan. The building blocks of the entire process are defined and essential factors emphasized. From this, I have divided the process in phases and steps, and designed the roadmap to a successful product. Three diagrams illustrate the stepwise approach of the entire process, the selection phase, the product development phase, and the implementation phase. Registration and commercialization are processes that relate to these phases during the entire developmental process.
    A future perspective on the biopesticide market is presented with limiting and promotional factors and trends. The significant drivers for success are food safety concern, changes in the regulatory climate, biodiversity and environmental issues, new research and technology, and the occurrence of new invasive pests. The biopesticide industry has reached a sufficient level of maturity and critical mass to form a base for further expansion. This will allow the biopesticide market to steadily grow. The roadmap proposed in this study will assist developers of biopesticides in accomplishing their goals in a cost- and time-effective way, which will result in successful and sustainable products and expanding biocontrol companies.

    Aardwarmte: duurzame energie met hoge potentie
    Bakker, Sjaak - \ 2007
    energy - geothermal energy - energy sources - comparisons - energy expenditure - potency - greenhouse horticulture - sustainable energy
    Genomic characterization and linkage mapping of the apple allergen genes Mal d 2 (thaumatin-like protein) and Mal d 4 (profilin)
    Gao, Z.S. ; Weg, W.E. van de; Schaart, J.G. ; Arkel, G. van; Breiteneder, H. ; Hoffmann-Sommergruber, K. ; Gilissen, L.J.W.J. - \ 2005
    Theoretical and Applied Genetics 111 (2005)6. - ISSN 0040-5752 - p. 1087 - 1097.
    cross-reactivity - malus-domestica - pollen profilin - heterologous expression - cloning - arabidopsis - family - ige - identification - potency
    Four classes of apple allergens (Mal d 1, ¿2, ¿3 and ¿4) have been reported. By using PCR cloning and sequencing approaches, we obtained genomic sequences of Mal d 2 (thaumatin-like protein) and Mal d 4 (profilin) from the cvs Prima and Fiesta, the two parents of a European reference mapping population. Two copies of the Mal d 2 gene (Mal d 2.01A and Mal d 2.01B) were identified, which primarily differed in the length of a single intron (378 or 380 nt) and in one amino acid in the signal peptide. Both Mal d 2.01A and Mal d 2.01B were mapped at identical position on linkage group 9. Genomic characterization of four Mal d 4 genes (Mal d 4.01A and B, Mal d 4.02A and Mal d 4.03A) revealed their complete gDNA sequences which varied among genes in length from 862 to 2017 nt. They all contained three exons of conserved length: 123, 138, and 135 nt. Mal d 4.01 appeared to be duplicated in two copies and located on linkage group 9. Mal d 4.02A and Mal d 4.03A were single copy genes located on linkage group 2 and 8, respectively
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