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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    The fatter the better : selecting microalgae cells for outdoor lipid production
    Dominguez Teles, I. - \ 2016
    Wageningen University. Promotor(en): Rene Wijffels, co-promotor(en): Maria Barbosa; Dorinde Kleinegris. - Wageningen : Wageningen University - ISBN 9789462578821 - 164
    algae - chlorococcum - lipids - lipogenesis - fat - production - phenotypes - inoculum - diameter - cells - sorting - algen - chlorococcum - lipiden - lipogenese - vet - productie - fenotypen - entstof - diameter - cellen - sorteren

    In chapter 1 we introduce microalgae, photosynthetic microorganisms with potential to replace commodities (such as food, feed, chemicals and fuels). Production costs are still high, reason why microalgae are still only economically feasible for niche markets. We suggest to borrow the concept of plant domestication to select industrial microalgae cells. Two approaches can be successfully used to domesticate microalgae: adaptive laboratory evolution (ALE) and fluorescence assisted cell sorting (FACS). ALE takes advantage of the natural adaptability of microorganisms to different environments, while FACS actually select cells with specific phenotypes. This thesis aimed to select cells of Chlorococcum littorale with improved phenotypes, assuming that these cells could establish new populations with increased industrial performance.

    In Chapter 2 we wanted to know what happened during time to biomass and lipid productivities of Chlorococcum littorale repeatedly subjected to N-starvation. We tested 2 different cycles of N-starvation, short (6 days) and long (12 days). Short cycles didn’t affect lipid productivity, highlighting the potential of C. littorale to be produced in semi-continuous cultivation. Repeated cycles of N-starvation could have caused adaptations of the strain. Hence, we also discussed the implications of using repeated N-starvation for adaptive laboratory evolution (ALE) experiments. Chapter 3 introduces a method to detect and to select microalgae cells with increased lipid content. The method requires only the fluorescence dye Bodipy505/515 dissolved in ethanol, and the method was designed to maintain cellular viability so the cells could be used to produce new inoculum. In chapter 4 we evaluated a question that emerged while deciding which criteria to use to sort lipid-rich cells: does cellular size affects lipid productivity of C. littorale? We hypothesized that cells with different diameters have different division rates, which could affect lipid productivity. Therefore, we assessed the influence of cell diameter, as a sorting parameter, on both biomass and lipid productivity of Chlorococcum littorale (comparing populations before and after sorting, based on different diameters). Results showed that the size of vegetative cells doesn’t affect the lipid productivity of C. littorale. In chapter 5 we present a strategy to sort cells of C. littorale with increased TAG productivity using the method developed at chapter 3. Both the original and the sorted population with the highest lipid productivity (namely, S5) were compared under simulated Dutch summer conditions. The results confirmed our data from experiments done under continuous light: S5 showed a double TAG productivity. Our results showed also that the selected phenotype was stable (1.5 year after sorting) and with potential to be used under industrial conditions. In chapter 6 we extrapolated our results (indoor and outdoor) to other climate conditions. We ran simulations changing the light conditions to four different locations worldwide (the Netherlands, Norway, Brazil and Spain) to estimate both biomass and TAG productivities. Results indicated that biomass yields were reduced at locations with higher light intensities (Brazil/Spain) when compared with locations with lower light intensities (Norway/Netherlands). Hence, the choice of location should not be based on light intensity, but on how stable irradiation is. Chapter 7 is the general discussion of the thesis, demonstrating that both ALE and FACS are effective approaches to select industrial microalgae cells. We also present our view on how ALE and FACS could further improve microalgae strains for industry.

    Dynamics of pear-pathogenic Stemphylium vesicarium in necrotic plant residues in Dutch pear orchards
    Köhl, J. ; Jong, P.F. de; Kastelein, P. ; Groenenboom-de Haas, B.H. de; Anbergen, R.H.N. ; Balkhoven, H. ; Wubben, J.P. - \ 2013
    European Journal of Plant Pathology 137 (2013)3. - ISSN 0929-1873 - p. 609 - 619.
    brown spot - causal agent - inoculum - disease
    Brown spot disease on pear caused by Stemphylium vesicarium may affect leaves and fruits. Inoculum sources present on orchard floors play an important role in the epidemiology of pear brown spot. The pathogen can overwinter on plant residues and multiply and spread on the residues during the growing season. In the Netherlands, brown spot characteristically occurs only in a fraction of the orchards per season. Until now, no tools are available for Dutch pear growers to predict the risk of brown spot in specific orchards. As a consequence, preventive fungicide sprayings are common. The concentration of DNA of pear-pathogenic S. vesicarium was quantified by a specific TaqMan-PCR assay for various types of plant residues present on orchard floors to evaluate their importance as potential inoculum source. The pathogen was often found in residues of pear leaves, grasses and weeds, but only occasionally in mummies and prunings. Studies of the population dynamics showed that S. vesicarium decreased in dead pear leaves during early winter whereas pathogen populations developed with irregular pattern during the growing season on residues of weeds and grasses. Based on DNA concentrations of S. vesicarium in plant residue samples taken in 78 to 106 orchards in the springs of 2010, 2011 and 2012, the risk of brown spot development could be predicted for individual orchards. Such a risk prediction will allow growers to adapt their fungicide spray schedules to avoid unnecessary sprays in low-risk orchards. © 2013 KNPV.
    Effects of preservation conditions of canine feces on in vitro gas production kinetics and fermentation end-products
    Bosch, G. ; Wrigglesworth, D.J. ; Cone, J.W. ; Pellikaan, W.F. ; Hendriks, W.H. - \ 2013
    Journal of Animal Science 91 (2013)1. - ISSN 0021-8812 - p. 259 - 267.
    protein fermentation - fiber sources - rumen fluid - microflora - inoculum - time - compartments - intestine - digestion - tract
    This study investigated the effect of chilling and freezing (for 24 h) canine feces on in vitro gas production kinetics and fermentation end-product profiles from carbohydrate-rich (in vitro run 1) and protein-rich substrates (in vitro run 2). Feces were collected from 3 adult Retriever-type dogs fed a canned diet for at least 2 wk. Each fecal sample was divided in 3 portions; 1 portion was used immediately as an inoculum (fresh), whereas the other 2 portions were used after either chilling to 5°C for 30 min and storage in crushed ice for 23.5 h (chilling) or freezing to -20°C for 30 min and storage in a pre-frozen (-20°C) container for 23.5 h (freezing). The medium solution for run 1 contained N, whereas that for run 2 was N-free. Substrates included fructooligosaccharide (FOS), sugar beet pulp, and wheat middlings in run 1 and soybean meal, poultry meat meal, and feather meal in run 2. Gas production kinetics were calculated from cumulative gas production data measured for 72 h. After incubation, fermentation liquids were analyzed for short-chain fatty acids, NH3, and aromatic compounds. For both in vitro runs, chilling feces did not affect gas production kinetics and end-product profiles of substrates compared to inocula from fresh feces. Freezing feces decreased the maximum rate of gas production in phase 2 for FOS (P <0.001) and across substrates increased gas produced (P = 0.005) and time of maximum gas production in phase 2 (P <0.001). Furthermore, compared to fresh fecal inocula, inocula from frozen feces resulted in increased overall indole concentrations in run 1 (P = 0.006) and indole concentrations from soybean meal and poultry meat meal in run 2 (P <0.001). In run 2, phenol concentrations were greater (P = 0.015) for frozen feces than for fresh feces (P = 0.015). In conclusion, freezing canine feces for 24 h slightly altered fermentative characteristics of fecal inoculum, whereas chilling feces in crushed ice for 24 h maintained fermentative characteristics. Chilling feces in crushed ice is a practical method to preserve feces during transport between laboratories within 24 h for in vitro fermentation studies evaluating dietary ingredients.
    Loofresistentie tegen Phytophthora infestans in aardappel : effecten van isolaatkeuze en proefontwerp op resistentiecijfers
    Kessel, G.J.T. ; Bosch, G.B.M. van den; Forch, M.G. ; Evenhuis, B. ; Flier, W.G. - \ 2010
    Wageningen : Plant Research International, Business Unit Biointeracties en Plantgezondheid (Rapport / Plant Research International 358) - 34
    solanum tuberosum - aardappelen - phytophthora infestans - ziekteresistentie - rassen (planten) - rassenproeven - entstof - solanum tuberosum - potatoes - phytophthora infestans - disease resistance - varieties - variety trials - inoculum
    Gedurende de periode 2002 tot en met 2004 werden veld- en laboratoriumproven uitgevoerd naar de effecten van de toetsmethode en isolaatkeuze op het resulterende Phytophthoraloofresisentiecijfer voor 30 economisch belangrijke rassen in nederland. Twee methodieken, de CGO methode en een alternatieve methode, werden vergeleken. Daarnaast werden de effecten van drie verschllende inocula die in meer of mindere mate representatief waren voor de Nederlandse P. infestans populatie vergeleken.
    The role of crop waste and soil in Pseudomonas syringae pathovar porri infection of leek (Allium porrum)
    Overbeek, L.S. van; Nijhuis, E.H. ; Koenraadt, H. ; Visser, J.H.M. - \ 2010
    Applied Soil Ecology 46 (2010)3. - ISSN 0929-1393 - p. 457 - 463.
    bacterial leaf-spot - pv lachrymans - pisum-sativum - survival - blight - epidemiology - california - inoculum - disease - field
    Pseudomonas syringae pv. porri, the causal agent of bacterial blight of leek, is a current threat for leek (Allium porrum) production in the Netherlands. The roles of post-harvest crop waste and plant invasion from soil in leek plant infection was investigated with the purpose to gain better understanding on the ecology and epidemiology of this pathogen. In a survey done over 167 leek fields, P. syringae pv. porri was present in 101 fields. About a tenfold higher P. syringae pv. porri average infection rate was recorded in leek plants from fields where post-harvest crop waste was returned than in those from fields where no waste was returned. P. syringae pv. porri could survive for at least 1 month in shredded plant material made from infected plants (mimicking crop waste in practice). Field experiments done over three successive years revealed that leek plants that were treated with crop waste at the nursery and production growth stages consistently showed higher infection rates than plants that remained untreated. Plants that were treated with crop waste only at one of both stages revealed intermediate infection rates. In a plant-soil microcosm study, it appeared that P. syringae pv. porri strain P55R colony numbers in the leek rhizosphere were approximately 4 orders in magnitude higher than in corresponding bulk soils. P. syringae pv. porri was shown to colonize leek roots and cells of the pathogen were also present in the leaves. It was concluded that post-harvest crop waste play an important role in the epidemiology of P. syringae pv. porri in leek production. The following route for primary infection of leek plants is proposed, from crop plant residues via soil to leek roots and plants. (C) 2010 Elsevier B.V. All rights reserved.
    Quantitative detection of pear-pathogenic Stemphylium vesicarium in orchards
    Köhl, J. ; Groenenboom-de Haas, B.H. de; Kastelein, P. ; Rossi, V. ; Waalwijk, C. - \ 2009
    Phytopathology 99 (2009)12. - ISSN 0031-949X - p. 1377 - 1386.
    brown spot disease - causal agent - epidemiology - infection - inoculum
    Isolates of Stemphylium vesicarium causing brown spot of pear can be distinguished from nonpathogenic isolates of S. vesicarium from pear or from other hosts on the basis of distinctive amplified fragment length polymorphism fingerprinting profiles. DNA fragments specific for isolates pathogenic to pear were identified and a quantitative polymerase chain reaction (PCR) was developed on the sequence from one of these specific DNA loci. This TaqMan PCR has a high sensitivity with a dynamic range for reliable quantification between 1 ng and 100 fg of DNA. The method detected pear-pathogenic isolates of S. vesicarium originating from four different European countries and various regions within those countries. No cross-reaction was found with either the nonpathogenic isolates of S. vesicarium tested or isolates belonging to other Stemphylium spp. or related fungi. The pathogen was detected on leaves with brown-spot symptoms originating from six different locations in The Netherlands, Italy, and Spain. Pear-pathogenic S. vesicarium populations were monitored on crop residues in two Dutch orchards between October 2007 and October 2008. Brown spot had been observed at both orchards at the end of the growing season of 2007. In one location, pear-pathogenic S. vesicarium was detected only sporadically on crop residues and no brown-spot symptoms were observed on fruit in 2008. At the other location, a pathogenic population was found on fallen pear leaves and on other crop residues but this population decreased during winter. From the beginning of the growing season in 2008 onward, the pathogen population could not be detected and the disease incidence was only 0.6%. The TaqMan PCR will allow more detailed studies on epidemiology of brown spot and on the effect of disease control measures.
    Pathogenicity of Stemphylium vesicarium from different hosts causing brown spot in pear
    Köhl, J. ; Groenenboom-de Haas, B.H. ; Goossen-van de Geijn, H.M. ; Speksnijder, A.G.C.L. ; Kastelein, P. ; Hoog, S. de; Ende, B.G. van den - \ 2009
    European Journal of Plant Pathology 124 (2009)1. - ISSN 0929-1873 - p. 151 - 162.
    pleospora-allii - causal agent - leaf-spot - disease - alternaria - california - infection - botryosum - inoculum - alfalfa
    Stemphylium vesicarium (teleomorph: Pleospora herbarum) is the causal agent of brown spot disease in pear. The species is also able to cause disease in asparagus, onion and other crops. Saprophytic growth of the fungus on plant debris is common. The objective of this study was to investigate whether isolates of S. vesicarium from different hosts can be pathogenic to pear. More than hundred isolates of Stemphylium spp. were obtained from infected pear fruits, dead pear leaves, dead grass leaves present in pear orchard lawns as well as from necrotic leaf parts of asparagus and onion. Only isolates originating from pear orchards, including isolates from dead grass leaves, were pathogenic on pear leaves or fruits in bioassays. Non-pathogenic isolates were also present in pear orchards. Stemphylium vesicarium from asparagus or onion, with one exception, were not pathogenic to pear. Analysis of the genetic variation between isolates using Amplified Fragment Length Polymorphism (AFLP) showed significant concordance with host plants. Isolates from asparagus or onion belonged to clusters separate from the cluster with isolates from pear or grass leaves collected in pear orchards. Multilocus sequencing of a subset of isolates showed that such isolates were similar to S. vesicarium.
    Prediction of Deoxynivalenol Content in Dutch Winter Wheat
    Franz, E. ; Booij, K. ; Fels-Klerx, H.J. van der - \ 2009
    Journal of Food Protection 72 (2009)10. - ISSN 0362-028X - p. 2170 - 2177.
    fusarium head blight - small-grain cereals - gibberella-zeae - previous crop - mycotoxins - models - inoculum - plots - graminearum - netherlands
    Predictive models for the deoxynivalenol (DON) content in wheat can be a useful tool for control authorities and the industry to avoid or limit potential food and/or feed safety problems. The objective of this study was to develop a predictive model for DON in mature Dutch winter wheat. From 2001 to 2007, the concentration of DON was measured in winter wheat samples taken just before harvest from 264 fields throughout The Netherlands. Agronomic and climatic variables were obtained for each field for a 48-day period, centered on the heading date. Multiple regression was used to determine the most important variables and to construct the predictive model. The first model (model 1) was based on 24-day pre- and postheading periods, while the second model (model 2) was based on eight time blocks of 6 days around the heading date. Although both models showed good statistical evaluations and predictive performance, model 1 showed the highest performance (R2 of 0.59 between observed and predicted values, fraction samples correctly below or above the 1,250 µg/kg threshold of 92%, and sensitivity of 63%). With both models, the predicted DON level increased with a higher average temperature, increased precipitation, and higher relative humidity, but decreased with increased number of hours with the temperature above 25°C. We observed a strong regional effect on the levels of DON, which could not be explained by differences in the recorded agronomic and climatic variables. It is suggested that future model improvement might be realized by indentifying and quantifying the mechanism underlying the region effect.
    Genetic structure and pathogenicity of populations of Phytophthora infestans from organic potato crops in France, Norway, Switzerland and the United Kingdom
    Flier, W.G. ; Kroon, L.P.N.M. ; Hermansen, A. ; Raaij, H.M.G. van; Speiser, B. ; Tamm, L. ; Fuchs, J.G. ; Lambion, J. ; Razzaghian, J. ; Andrivon, D. ; Wilcockson, S. ; Leifert, C. - \ 2007
    Plant Pathology 56 (2007)4. - ISSN 0032-0862 - p. 562 - 572.
    late blight - genotypic diversity - foliar aggressiveness - toluca valley - mating-type - resistance - cultivars - netherlands - inoculum - finland
    Genetic variation and pathogenicity of Pbytophthora infestans isolates collected from organic potato crops of the susceptible cv. Bintje and the moderately resistant cv. Sante were assessed in France, Norway, and the United Kingdom in 2001 and in Switzerland in 2001 and 2002. Population structures differed considerably between the four P. infestans populations. Those from France, Switzerland and the UK were mainly clonal populations showing restricted levels of genetic diversity, whilst those from Norway were mixed A1 and A2 mating type populations with high levels of genetic diversity, suggesting periodical sexual reproduction. Isolates collected from cv. Bintje were on average more aggressive than or comparable to isolates from cv. Sante. Race complexity varied considerably between the regional P. infestans populations, with isolates from France and Switzerland showing the highest number of virulence factors. In all pathogen samples but the French, isolates collected from cv. Sante were more complex than isolates collected from cv. Bintje. No directional selection towards increased aggressiveness towards the more resistant cultivar Sante was observed. This suggests that there is no shift towards increased levels of pathogenicity in P. infestans populations following the large-scale introduction of more resistant potato varieties in organic production systems in Europe.
    Veldresistentie en bemonsteringsmethode van wratziekte (Synchytrium endobioticum)
    Lamers, J.G. ; Been, T.H. ; Bonants, P.J.M. ; Gent-Pelzer, M.P.E. van; Wander, J.G.N. - \ 2007
    synchytrium endobioticum - entstof - bemonsteren - plaagresistentie - synchytrium endobioticum - inoculum - sampling - pest resistance
    Vraag is aan welk niveau van veldresistentie voldaan moet worden om ook in de toekomst de vermeerdering van S. endobioticum en daarmee verspreiding van inoculum tegen te gaan. Bovendien is een goede bemonsteringsmethode belangrijk. De Hendrickx Centrifuge geeft goede uitslagen, maar de bemonsteringstechniek is nog niet onderzocht
    The effect of sample grinding procedures after processing on gas production profiles and end-product formation in expander processed barley and peas
    Azarfar, A. ; Poel, A.F.B. van der; Tamminga, S. - \ 2007
    Journal of the Science of Food and Agriculture 87 (2007)5. - ISSN 0022-5142 - p. 855 - 864.
    in-vitro fermentation - fatty-acid production - cumulative gas - ruminant feeds - pressure transducer - particle-size - rumen fluid - kinetics - digestion - inoculum
    Grinding is a technological process widely applied in the feed manufacturing industry and is a prerequisite for obtaining representative samples for laboratory procedures (e.g. gas production analysis). When feeds are subjected to technological processes other than grinding (e.g. expander treatment), grinding afterwards may disturb the effect of processing, both in practice and when laboratory techniques are applied. Therefore, this study aimed to establish the possible effects of different grinding procedures and sample preparation on the degradative behaviour of expander processed barley and peas. Samples of expander processed barley and peas were subjected to six different sample preparation procedures (intact sample, dissolved sample, samples ground stepwise over 6 and 3 mm sieves, samples ground stepwise over 6, 3 and 1 mm sieves, samples ground over a 3 mm sieve and samples ground over a 1 mm sieve). The patterns of gas production in these samples were studied over a period of 72 h incubation using an automated in vitro gas production system. The particle size distribution determined by dry sieve analysis and the Coulter counter method changed due to the different grinding procedures. Grinding the samples of expander processed barley and peas changed the kinetics of gas production and led to a faster degradation, most pronounced after stepwise grinding. However, the formation of the fermentation end-product was not affected by the method of sample preparation. In expander processed barley, the difference in the degradation pattern due to the different grinding procedures was small.
    Effects of integrated control measures on earthworms, leaf litter and Venturia inaequalis infection in two European apple orchards
    Holb, I.J. ; Heijne, B. ; Jeger, M.J. - \ 2006
    Agriculture, Ecosystems and Environment 114 (2006)2-4. - ISSN 0167-8809 - p. 287 - 295.
    fungicide use - scab - disease - urea - wint - netherlands - populations - management - ascospores - inoculum
    Two-, three-year studies were conducted to determine the effect of combining chemical (fungicide and urea) and non-chemical (leaf shredding) sanitation treatments on earthworm populations, leaf litter density (LLD), and leaf and fruit infections caused by Venturia inaequalis in Dutch and Hungarian integrated apple orchards from 2000 to 2002 and 2001 to 2003, respectively. The combined sanitation treatment included urea and captan sprays applied to the tree and to the orchard floor and the shredding of fallen leaves in the previous autumn and winter. The earthworm numbers were significantly higher in the sanitation treatment compared to the treatment without sanitation in 2001 and 2002 (P <0.05) at Randwijk (The Netherlands) and in 2002 and 2003 (P <0.05) at Derecske (Hungary). LLD decreased continuously from leaf fall in late autumn to mid-May the following spring at Randwijk, which was explained well by a linear function fitted to the LLD data, with R 2 values ranging from 0.82 to 0.99. Model coefficients for the sanitation plots were significantly different (P <0.05) from those of the non-sanitized plots in 2001 and 2002. At Derecske, LLD started to clearly decrease in both treatments from February 2001 and 2002 and from March 2003 to late spring, and this was explained well by an exponential function fitted to the LLD data, with R 2 values ranging from 0.80 to 0.97. Model coefficients for the sanitation plots were significantly different (P <0.05) from those of the non-sanitized plots only in 2002. In most years and at both sites, the sanitation treatment resulted in significantly lower (P <0.05) scab incidence on spur-leaf clusters compared to the treatment without sanitation. However, the sanitation effect on scab levels on older leaves and fruits was low and varied by year and location. The results are discussed in connection with the environmental conditions in the two countries.
    In vitro cumulative gas production techniques: history, methodological considerations and challenges
    Rymer, C. ; Huntington, J.A. ; Williams, B.A. ; Givens, D.I. - \ 2005
    Animal Feed Science and Technology 123-124 (2005)1. - ISSN 0377-8401 - p. 9 - 30.
    temperature dried grass - rumen microorganisms - pressure transducer - fermentation characteristics - production profiles - ruminal bacteria - energy content - invitro - inoculum - feeds
    Methodology used to measure in vitro gas production is reviewed to determine impacts of sources of variation on resultant gas production profiles (GPP). Current methods include measurement of gas production at constant pressure (e.g., use of gas tight syringes), a system that is inexpensive, but may be less sensitive than others thereby affecting its suitability in some situations. Automated systems that measure gas production at constant volume allow pressure to accumulate in the bottle, which is recorded at different times to produce a GPP, and may result in sufficiently high pressure that solubility of evolved gases in the medium is affected, thereby resulting in a recorded volume of gas that is lower than that predicted from stoichiometric calculations. Several other methods measure gas production at constant pressure and volume with either pressure transducers or sensors, and these may be manual, semi-automated or fully automated in operation. In these systems, gas is released as pressure increases, and vented gas is recorded. Agitating the medium does not consistently produce more gas with automated systems, and little or no effect of agitation was observed with manual systems. The apparatus affects GPP, but mathematical manipulation may enable effects of apparatus to be removed. The amount of substrate affects the volume of gas produced, but not rate of gas production, provided there is sufficient buffering capacity in the medium. Systems that use a very small amount of substrate are prone to experimental error in sample weighing. Effect of sample preparation on GPP has been found to be important, but further research is required to determine the optimum preparation that mimics animal chewing. Inoculum is the single largest source of variation in measuring GPP, as rumen fluid is variable and sampling schedules, diets fed to donor animals and ratios of rumen fluid/medium must be selected such that microbial activity is sufficiently high that it does not affect rate and extent of fermentation. Species of donor animal may also cause differences in GPP. End point measures can be mathematically manipulated to account for species differences, but rates of fermentation are not related. Other sources of inocula that have been used include caecal fluid (primarily for investigating hindgut fermentation in monogastrics), effluent from simulated rumen fermentation (e.g., `Rusitec¿, which was as variable as rumen fluid), faeces, and frozen or freeze-dried rumen fluid (which were both less active than fresh rumen fluid). Use of mixtures of cell-free enzymes, or pure cultures of bacteria, may be a way of increasing GPP reproducibility, while reducing reliance on surgically modified animals. However, more research is required to develop these inocula. A number of media have been developed which buffer the incubation and provide relevant micro-nutrients to the microorganisms. To date, little research has been completed on relationships between the composition of the medium and measured GPP. However, comparing GPP from media either rich in N or N-free, allows assessment of contributions of N containing compounds in the sample.
    Phytosanitary risk assessment of composts
    Termorshuizen, A.J. ; Rijn, E. van; Blok, W.J. - \ 2005
    Compost Science & Utilization 13 (2005)2. - ISSN 1065-657X - p. 108 - 115.
    yellow vein virus - plant-pathogens - macrophomina-phaseolina - anaerobic-digestion - survival - potato - soil - inactivation - waste - inoculum
    Assessment of phytosanitary risks associated with application of composts in agriculture generally has focused on the sanitation (self-heating) phase during composting when most plant pathogens are inactivated due to lethal temperatures. However, a few plant pathogens are heat resistant and they may survive a properly monitored and controlled composting process. To assess the phytosanitary risks associated with compost utilization, several additional factors need to be considered which all relate to a tracing-and-tracking principle. It includes the composition of the original waste and several aspects related to compost utilization. The following parameters are considered to be key-factors: 1) the proportion of host biomass relative to the total quantity of biowaste, 2) the proportion of host infected with a pathogen, 3) the density of infected host material, 4) the proportion of propagules of a pathogen that survived the process, and 5) the threshold density of a pathogen in soil above which disease of the host is expected to develop. While the first two parameters may be rather easy to estimate and information on survival of many plant pathogens can be obtained from the literature, little knowledge exists on the density of the pathogens in host materials or on threshold values. This applies particularly to virus diseases. The phytosanitary risk of several types of plant pathogens is discussed in some detail in this paper. Recommendations are given for testing of a composting process for phytohygienic safety.
    Mycorrhizaschimmels: een rol in gewasbescherming?; thema bodemweerbaarheid
    Baar, J. - \ 2005
    Gewasbescherming 36 (2005)5. - ISSN 0166-6495 - p. 222 - 224.
    gewasbescherming - mycorrhizaschimmels - ectomycorrhiza - vesiculair-arbusculaire mycorrhizae - wortels - bodemschimmels - symbiose - worteloppervlak - plantenziekteverwekkers - entstof - plant protection - mycorrhizal fungi - ectomycorrhizas - vesicular arbuscular mycorrhizas - roots - soil fungi - symbiosis - rhizoplane - plant pathogens - inoculum
    In de grond kunnen bij planten specifieke bodemschimmels voorkomen. Dit zijn de zogeheten mycorrhizaschimmels. Kenmerkend voor mycorrhizaschimmels is dat deze schimmels met planten in een gebalanceerde symbiose leven. Van zo'n symbiose hebben zowel de planten als de schimmels profijt. In dit artikel wordt ingegaan op de achtergrond van de twee belangrijkste groepen mycorrhizaschimmels, de ecto- en arbusculaire mycorrhizaschimmels, en hun mogelijke rol in de gewasbescherming
    Effects of mushroom and herb polysaccharides, as alternatives for an antibiotic, on growth performance of broilers
    Guo, F.C. ; Kwakkel, R.P. ; Williams, B.A. ; Li, W.K. ; Li, H.S. ; Luo, J.Y. ; Li, X.P. ; Wei, Y.X. ; Yan, Z.T. ; Verstegen, M.W.A. - \ 2004
    British Poultry Science 45 (2004)5. - ISSN 0007-1668 - p. 684 - 694.
    normal microbial flora - in-vitro fermentation - virginiamycin - chickens - inoculum - tract - pigs
    1. This in vivo trial was conducted to study the effects of polysaccharide extracts of two mushrooms, Lentinus edodes (LenE) and Tremella fuciformis (TreE), and a herb, Astragalus membranaceus (AstE) on growth performance, and the weights of organs and the gastrointestinal tract (GIT) of broiler chickens. 2. Three extracts (LenE, TreE and AstE) were supplemented at inclusion rates of 0·5, 1, 2, 3 and 4 g/kg from 7 to 14 d of age and compared with an antibiotic treatment group (20 mg/kg, virginiamycin (VRG) as well as a group of non-supplemented birds. 3. Body weight (BW) gain, feed intake and feed conversion ratio (FCR) of the extract-supplemented groups were not significantly different from those of the antibiotic group. Significant effects of type of extract and concentration on growth performance were found from 7 to 28 d of age. Generally, birds fed with LenE showed higher BW gain and lower FCR from 7 to 28 d of age than those fed with TreE and AstE and 2 g/kg LenE was considered the optimal inclusion rate for enhanced broiler growth. However, the extracts had no significant effect on the relative weights of organs and GIT compared with the antibiotic group. 4. The birds fed the extracts showed better growth performance than the non-supplemented birds, but were not significantly different from those fed VRG. Of the three extracts, LenE appeared to be a potential growth promoter. Future studies are needed to investigate whether the extracts can be used as alternatives for antibiotic growth promoters in challenged birds, and to elucidate the mechanisms for potentially enhanced growth performance in poultry.
    Dormancy, activation and viability of Rhizopus oligosporus sporangiospores
    Thanh, N.V. - \ 2004
    Wageningen University. Promotor(en): Frans Rombouts; [No Value] Tran Phuoc Duong, co-promotor(en): Rob Nout. - Wageningen : s.n. - ISBN 9789085040989 - 114
    rhizopus microsporus - schimmelsporen - sporangia - slaaptoestand - levensvatbaarheid - entstof - zuursels - aminozuren - tempé - rhizopus microsporus - fungal spores - sporangia - dormancy - viability - inoculum - starters - amino acids - tempeh
    Biological nitrogen fixation of soybean in acid soils of Sumatra, Indonesia
    Waluyo, S.H. - \ 2000
    Agricultural University. Promotor(en): W.M. de Vos; L. 't Mannetje; L.T. An. - S.l. : S.n. - ISBN 9789058082954 - 151
    glycine max - sojabonen - bodembiologie - stikstoffixatie - stikstofbindende bacteriën - rhizobium - bradyrhizobium - inoculatie - entstof - biochemische technieken - dna-fingerprinting - stamverschillen - stammen (biologisch) - zaadbehandeling - omhullen - zure gronden - bodemaciditeit - bekalking - sumatra - indonesië - glycine max - soyabeans - soil biology - nitrogen fixation - nitrogen fixing bacteria - rhizobium - bradyrhizobium - inoculation - inoculum - biochemical techniques - dna fingerprinting - strain differences - strains - seed treatment - pelleting - acid soils - soil acidity - liming - sumatra - indonesia

    The aim of this study is to improve soybean cultivation in transmigration areas, especially in Sitiung, West Sumatra. However, these soils are very acid, and have a high P-fixing capacity. To reduce the amounts of fertilisers, normally 5 - 7 ton lime ha -1 and 100 kg P as TSP, seed, pelleted with lime (60 kg ha -1 ) and TSP (10 kg ha -1 ), was introduced. In this way only 2 ton lime ha -1 are required.

    Soybean can fix nitrogen (BNF) in symbiosis with ( Brady ) Rhizobium bacteria. However, these acid soils in general, have low numbers of ( Brady ) Rhizobium . By inoculating the soils with ( Brady ) Rhizobium , BNF of soybean, and yield, were considerably improved.

    A study was made of the indigenous ( Brady ) Rhizobium population in view of the following:

      Although at the beginning the numbers may be low, by repeated soybean cultivation, the numbers will increase, and they may interfere with inoculation of effective ( Brady ) Rhizobium strains.These indigenous ( Brady ) Rhizobium are adapted to local stress conditions, and they may be useful for the improvement of strains, to be used as inoculants.

    Using molecular techniques, indigenous strains derived from soil samples from old soybean areas (Java) and from new soybean areas (Sumatra) were classified in more detail. Most likely B. japonicum is the dominant strain in Java while in Sumatra B. elkanii is more present. A Sinorhizobium fredii -like strain was isolated from one soil sample from Java.

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