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.

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    Purple witchweed (Striga hermonthica) germination and seedbank depletion under different crops, fallow, and bare soil
    Mourik, T.A. van; Stomph, T.J. ; Murdoch, A.J. - \ 2011
    Weed Biology and Management 11 (2011)2. - ISSN 1444-6162 - p. 100 - 110.
    long-term management - strategy evaluation - population-model - longevity - sorghum - banks - seeds
    Seedbank density is an important aspect that determines the amount of damage that the parasitic weed, purple witchweed (Striga hermonthica; hereafter, called “Striga”), causes on its crop hosts. The seedbank depletion of Striga was measured in Mali and Niger during the 2004 rainy season under the host crops, pearl millet and sorghum, the non-host crops, cowpea and sesame, the intercrops of pearl millet or sorghum with cowpea or sesame, and fallow with or without weeding. Two methods were used and compared; namely, a seed bag method and a soil-sampling method. The fate of the seeds was assessed by a seed press test. Seed germination, as determined by the presence of empty seed coats, contributed most to the seedbank depletion of Striga under a variety of crop covers and fallow. The highest seedbank depletion was found under the monocultures of the host crops. The intercrops of the host and non-host crops caused less seedbank depletion, followed by the monocultures of the non-host crops, fallow, and bare soil. The seed bag method and the soil-sampling method yielded similar percentages of seedbank depletion, while the former allowed for distinguishing between the germinated and diseased seeds. The results suggest that, although all the tested crop species can cause the seed germination and seedbank depletion of Striga, management by using host cereal crops causes the highest amount of germination and has the highest potential to deplete the soil seed bank, provided that seed production is prevented
    Organic matter and seed survival of Striga hermonthica - Mechanisms for seed depletion in the soil
    Ayongwa, G.C. ; Stomph, T.J. ; Belder, P. ; Leffelaar, P.A. ; Kuyper, T.W. - \ 2011
    Crop Protection 30 (2011)12. - ISSN 0261-2194 - p. 1594 - 1600.
    long-term management - strategy evaluation - ethylene production - fusarium-oxysporum - population-model - del. benth. - germination - decomposition - stimulation - longevity
    Seed survival of Striga hermonthica is influenced by amendments of organic matter; however, the role of organic matter quality (C:N ratio) and mechanisms for enhanced seed decay are inadequately understood. In a field experiment, plots received a single dose of 6 t organic matter per hectare but with large differences in quality in terms of C:N ratio. Soil moisture, soil temperature and soil ethylene concentrations were measured, while buried nylon seed bags were periodically withdrawn from the soil and assayed for seed viability and germination. Organic matter amendments incorporated in the soil significantly depressed S. hermonthica seed survival. The effect was strongest with organic matter of high quality. Organic matter of low-quality enhanced soil water content during the first five days after a rainfall event and resulted in a 0.5 °C lower soil temperature. The highest observed ethylene concentrations in the soil were between 2 and 3 ppm, high enough to stimulate S. hermonthica seed germination. Maximal seed germination in vitro was obtained after 48 h of exposure to 1 ppm ethylene. However, observed changes in seed germination and viability of retrieved seed batches (seed survival) did not correlate with soil ethylene concentrations. The latter in turn did not differ between qualities of the applied organic matter. Seed survival decreased with increasing time of burial, especially after 4–8 weeks. As S. hermonthica attachment mainly occurs during the first four weeks of the cropping season the observed effect of seed decay may hardly be beneficial for the on-going cropping season. Nutrient release through decomposition of organic matter, enhancing decay of S. hermonthica seeds, is proposed as the probable cause of seed depletion in the soil.
    Authenticity of old cultivars in genebank collections: a case study on lettuce
    Wouw, M.J. van de; Treuren, R. van; Hintum, T.J.L. van - \ 2011
    Crop Science 51 (2011)2. - ISSN 0011-183X - p. 736 - 746.
    genenbanken - slasoorten - aflp - oude plantenrassen - ex-situ conservering - cultivarauthenticiteit - lactuca sativa - rassen (planten) - cultivars - gene banks - lettuces - amplified fragment length polymorphism - old varieties - ex situ conservation - cultivar authenticity - lactuca sativa - varieties - cultivars - genetic diversity - maintenance - accessions - longevity - level - l.
    Ex situ collections in genebanks conserve many old cultivars that had disappeared from mainstream agriculture before modern genebanks were established. The collections incorporated cultivars from many sources, such as botanical gardens and working collections, sometimes with little further information on their origin. Many old cultivars with identical or synonymous names are maintained in multiple collections and often more than once within collections. This research investigates the authenticity of old cultivars in genebanks using a large lettuce (Lactuca sativa L.) collection as a case study. Accessions presumed to be identical, based on the cultivar names accompanying the accessions, were compared for their DNA marker profiles, based on amplified fragment length polymorphisms (AFLPs). Using the genetic similarity of these accessions, the probability of authenticity of the old cultivars maintained in the collection was estimated. Separate analyses were done for different classes of cultivars, on the basis of the year of release or the donor history of the cultivar. The two largest cultivar groups within the collection, Sans Rivale à Graine Blanche and Maikönig, were analyzed in detail. Nonauthenticity of the investigated cultivars appeared to be high. This was especially true for the oldest cultivars, but even for the cultivars released from the 1960s to 1990 it was estimated that approximately 10% was not authentic. Recommendations to improve authenticity of cultivars in ex situ collections were presented
    Heritability of foot conformation and its relationship to sports performance in a Dutch warmblood horse population.
    Ducro, B.J. ; Bovenhuis, H. ; Back, W. - \ 2009
    Equine Veterinary Journal 41 (2009)2. - ISSN 0425-1644 - p. 139 - 143.
    swedish warmblood - racehorses - parameters - longevity - dressage - balance - traits - health
    Reasons for performing study: Warmblood horse studbooks aim to breed horses with a conformation that will enable elite future performance, but reduce the risk of injuries and lameness. Negative conformational traits, such as asymmetrical or 'uneven' forefeet would possibly diminish performance. Objectives: To assess the prevalence and heritability of uneven feet and its genetic relationship to other conformation traits as well as to sporting performance later in life in Warmblood riding horses. Methods: The databases of the Royal Dutch Warmblood Studbook (KWPN, n = 44,840 horses) and Royal Dutch Equestrian Sports Federation (KNHS, n = 33,459 horses in dressage and n = 30,474 horses in showjumping) were linked through the unique number of each registered horse. Therefore, heritabilities and genetic and phenotypic correlations could be estimated from the scores of the jury at studbook admission and the sports performance of that population in dressage and jumping over the period 1990-2002. Results: The prevalence of uneven feet was 5.3% on average, and increased from under 4.5% during the first 3 years of recording to over 8% in the years from 2000 onwards. Heritability estimates of foot conformation traits were moderate and ranged from 0.16 for heel height to 0.27 for hoof shape. The genetic correlation between the trait of uneven feet and performance in competition was negative but weak: -0.09 with dressage and -0.12 with showjumping. Conclusions: Predisposition to uneven feet can be reduced by selection. Because of weak genetic correlations, the increased prevalence is not directly associated with selection for better sports performance or higher conformation grade. If the trait 'uneven feet' arises from a disproportionate relationship between height at the withers and neck length, then selection on conformation grade might result in development of uneven feet. In general, limb conformation has a moderate genetic relationship to conformation grade and foot conformation traits have a genetic relationship to sporting performance. Reducing occurrence of uneven feet by selection is possible, without limiting progress in sport performance.
    Nectar exploitation by herbivores and their parasitoids is a function of flower species and relative humidity
    Winkler, K. ; Wäckers, F.L. ; Kaufman, L.V. ; Larraz, V. ; Lenteren, J.C. van - \ 2009
    Biological Control 50 (2009)3. - ISSN 1049-9644 - p. 299 - 306.
    diadegma-insulare hymenoptera - diamondback moth lepidoptera - biological-control - nutritional state - floral resources - field conditions - honeydew sugars - aphid honeydew - longevity - ichneumonidae
    In conservation biological control, diversification of the agro ecosystem with flowering vegetation is seen as an important tool to support the broad range of predators and parasitoids that require nectar and pollen sources to survive and reproduce. In order to identify flowering plants that provide suitable food sources for natural enemies without supporting the pest species, we analyzed the exploitation of 19 flowering plants by two important lepidopteran cabbage pests, Pieris rapae and Plutella xylostella, and their hymenopteran parasitoids, Cotesia glomerata and Diadegma semiclausum. The experiments were conducted at 90% r.h., while Pieris rapae was tested both at 45% r.h. and at 90% r.h. At 45 ± 5% r.h., corresponding with field conditions at which P. rapae is predominantly active, the butterfly was unable to feed on a number of exposed floral nectar sources whose nectar was successfully exploited at 90% r.h. The broader nectar exploitation by P. rapae at the high humidity is presumably explained by the resulting decrease in nectar viscosity. When comparing D. semiclausum and its herbivorous host P. xylostella, the herbivore exploited a broader range of plants. However, those plants that benefited both the parasitoid and the herbivore had a much stronger effect on the longevity of the parasitoid. The results from the accessibility bioassay suggest that flowers where nectar is not accessible can have a negative impact on insect survival presumably by stimulating foraging without providing accessible nectar. Our results underline the importance of considering species-specific environmental conditions when fine-tuning the choice of nectar sources to be used in conservation biological control programs.
    Influence of foot conformation on length of competitive life in a Dutch warmblood horse population.
    Ducro, B.J. ; Gorissen, B.M.C. ; Eldik, P. van; Back, W. - \ 2009
    Equine Veterinary Journal 41 (2009)2. - ISSN 0425-1644 - p. 144 - 148.
    swedish warmblood - longevity - traits
    Reasons for performing study: Warmblood horse studbooks aim to breed horses with a conformation that will enable elite future sports performance, but reduce the risk of early retirement due to lameness. Negative conformational traits, such as asymmetrical or 'uneven' forefeet may possibly shorten the career of sporthorses. Objectives: To investigate the significance of foot conformation at young age to duration of the career of sporthorses. Methods: Databases of the Royal Dutch Warmblood Studbook (KWPN) and of the Royal Dutch Equestrian Sports Federation (KNHS) were matched and resulted in a dataset comprising 23,116 records of horses for which their conformation scores and duration of their sports career were available. Survival analysis was used to determine which of the conformation traits had a significant effect on duration of sports career in dressage and jumping at basic and elite level.Results: Duration of competitive life was shorter for jumping than for dressage. A different set of risk factors was found for each level and discipline. The trait 'uneven feet' tended to shorten the competitive life in dressage, but was a significant risk factor at the elite level of jumping. Conclusions: Limb conformation and, in particular, the conformation of the distal limb, are important for duration of competitive life. From the prevalence of uneven feet in sports disciplines, it may be concluded that this is an undesirable trait, particularly at the elite level of jumping, since uneven feet have a detrimental effect on the duration of competitive life in a sporthorse population. Potential relevance: This study provided evidence that the conformation trait uneven feet has a negative effect on Warmblood jumping performance and, therefore, breeders should be encouraged to avoid this phenomenon at foal age.
    Breeding for robustness in cattle
    Klopcic, M. ; Reents, R. ; Philipsson, J. ; Kuipers, A. - \ 2009
    Wageningen : Wageningen Academic Publishers (EAAP publication no. 126) - ISBN 9789086860845 - 281
    rundvee - bos - dierveredeling - fokkerijmethoden - gebruiksduur - ziekteresistentie - melkvee - rundveerassen - vruchtbaarheid - genetische variatie - prestatiekenmerken - cattle - bos - animal breeding - animal breeding methods - longevity - disease resistance - dairy cattle - cattle breeds - fertility - genetic variation - performance traits
    Effects of flower attractiveness and nectar availability in field margins on biological control by parasitoids
    Bianchi, F.J.J.A. ; Wackers, F.L. - \ 2008
    Biological Control 46 (2008)3. - ISSN 1049-9644 - p. 400 - 408.
    habitat management - natural enemies - arthropod pests - sugar analysis - weed strips - food - longevity - hosts - wasps - hymenoptera
    Flowering plants have been shown to differ with regard to their attractiveness to parasitoids and nectar accessibility. These floral traits are likely to affect the foraging performance of parasitoids in agricultural landscapes. Using a spatially explicit simulation model we explore how the attractiveness and nectar availability of flowering field margins affects their impact on parasitoids and ultimately on pest populations in crops. The model simulates the movement, nectar feeding and parasitism of parasitoids in an agroecosystem composed of a crop and adjacent flower margin. The perception of olfactory cues emitted by flowers and host-infestcd plants drives the movement of the parasitoid. Its preference for floral nectar or hosts is described as a function of its internal energy status. Model validation reveals that simulations and measurements of the spatial distribution and energy status of parasitoids are generally in good agreement. Model simulations suggest that aggregation of parasitoids at flower strips are caused by a prolonged longevity of parasitoids feeding on floral nectar as well as by attraction of parasitoids from the surrounding area. We found no indication for depletion of parasitoids in the field interior as a result of migration towards flower strips. Simulations further suggest that the attractiveness of flowers is an important characteristic that should be taken into account for the selection of flowering plants. This study implies that tailoring nectar supply to the requirements of parasitoids holds potential to increase their effectiveness as biological control agents.
    A mitochondrial mutator plasmid that causes senescence under dietary restricted conditions
    Maas, M.F.P.M. ; Hoekstra, R.F. ; Debets, A.J.M. - \ 2007
    BMC Genetics 8 (2007)9. - ISSN 1471-2156 - p. 1 - 12.
    podospora-anserina - linear plasmids - neurospora-intermedia - calorie restriction - dna-sequences - genomic dna - longevity - mutant - pal2-1 - amplification
    Background Calorie or dietary restriction extends life span in a wide range of organisms including the filamentous fungus Podospora anserina. Under dietary restricted conditions, P. anserina isolates are several-fold longer lived. This is however not the case in isolates that carry one of the pAL2-1 homologous mitochondrial plasmids. Results We show that the pAL2-1 homologues act as 'insertional mutators' of the mitochondrial genome, which may explain their negative effect on life span extension. Sequencing revealed at least fourteen unique plasmid integration sites, of which twelve were located within the mitochondrial genome and two within copies of the plasmid itself. The plasmids were able to integrate in their entirety, via a non-homologous mode of recombination. Some of the integrated plasmid copies were truncated, which probably resulted from secondary, post-integrative, recombination processes. Integration sites were predominantly located within and surrounding the region containing the mitochondrial rDNA loci. Conclusion We propose a model for the mechanism of integration, based on innate modes of mtDNA recombination, and discuss its possible link with the plasmid's negative effect on dietary restriction mediated life span extension.
    Afvoerleeftijd geen betrouwbare maat voor duurzaamheid
    Ouweltjes, W. - \ 2006
    V-focus 3 (2006)1. - ISSN 1574-1575 - p. 18 - 19.
    melkveehouderij - melkkoeien - melkproductie - productieve levensduur - gebruiksduur - duurzaamheid (sustainability) - kuddes (flocks) - selectie - agrarische bedrijfsvoering - meting - dairy farming - dairy cows - milk production - productive life - longevity - sustainability - flocks - selection - farm management - measurement
    Niet een hoge afvoerleeftijd maar een laag celgetal (in relatie tot de leeftijd) duidt op een bovengemiddelde duurzaamheid. Dit betekent dat bij het beoordelen van het tankmelkcelgetal rekening moet worden gehouden met de leeftijd van de veestapel.Het rekenmodel voor het vervangingsbeleid gaat ervan uit dat er steeds vervangende vaarzen voorhanden zijn. In de praktijk is dat lang niet altijd het geval. Veel boeren fokken zelf hun vaarzen op en daarmee is de jongveeopfok sterk bepalend voor het vervangingsbeleid. Door minder jongvee op te fokken wordt de afvoerleeftijd wel hoger, maar daarmee wordt de veestapel nog niet duurzamer. Op het LageKostenbedrijf (LKB) bleek uit de ziekteregistratie en de vruchtbaarheidsgegevens dat de duurzaamheid van de oude veestapel te wensen overliet. Omdat er weinig jongvee instroomde, is steeds getracht zoveel mogelijk dieren opnieuw drachtig te krijgen. Ook het gemiddelde geometrische celgetal van de afgevoerde dieren was hoog, namelijk 333.000 cellen/ml. Daarnaast zijn jaarlijks enkele dieren vanwege acute gezondheidsproblemen afgevoerd. De lage vervanging kon alleen worden behaald door extra kosten te maken voor diergezondheid. Zou er wel ruimte zijn geweest voor vrijwillige vervanging, dan zouden bij een gelijkblijvende duurzaamheid, dieren sneller zijn afgevoerd waardoor de afvoerleeftijd zou zijn gedaald. De afvoerleeftijd is dan ook geen betrouwbare maat voor duurzaamheid. Een betere indicatie van de duurzaamheid van een veestapel wordt waarschijnlijk verkregen als naast de afvoerleeftijd, ook de kosten voor diergezondheid en vruchtbaarheid worden meegenomen. Of dat zo is, wordt het komende jaar nader onderzocht.
    Infection of the malaria mosquito Anopheles gambiae with the entomopathogenic fungus Metarhizium anisopliae reduces blood feeding and fecundity
    Scholte, E.J. ; Knols, B.G.J. ; Takken, W. - \ 2006
    Journal of Invertebrate Pathology 91 (2006)1. - ISSN 0022-2011 - p. 43 - 49.
    schistocerca-gregaria - desert locust - destruxins - reduction - flavoviride - consumption - longevity - culicidae - pathogen - survival
    The entomopathogenic fungus Metarhizium anisopliae is being considered as a biocontrol agent against adult African malaria vectors. In addition to causing significant mortality, this pathogen is known to cause reductions in feeding and fecundity in a range of insects. In the present study we investigated whether infection with M. anisopliae affected blood feeding and fecundity of adult female malaria vectors Anopheles gambiae Giles sensu stricto. Mosquitoes were contaminated with either a low or a moderately high dose of oil-formulated conidia of M. anisopliae, and offered a single human blood meal 48, 72, or 96 h later to assess feeding propensity and individual blood meal size. In a second experiment, individual fungus-infected females were offered a blood meal every third day (to a total of 8 gonotrophic cycles), and allowed to oviposit after each cycle in order to quantify feeding propensity and fecundity. Infected females took smaller blood meals and displayed reduced feeding propensity. It was found that mosquitoes, inoculated with a moderately high dose of fungal conidia, exhibited reduced appetite related to increasing fungal growth. Of the fungus-infected females, the proportion of mosquitoes taking the second blood meal was reduced with 51%. This was further reduced to 35.3% by the 4th blood meal. During 8 feeding opportunities, the average number of blood meals taken by uninfected females was 4.39, against 3.40 (low dose), and 2.07 (high dose) blood meals for the fungus-infected females. Moreover, infected females produced fewer eggs per gonotrophic cycle and had a lower life-time fecundity. Epidemiological models show that both blood feeding and fecundity are among the most important factors affecting the likelihood of a mosquito transmitting malaria, which suggests that this fungus may have potential as biocontrol agent for vector-borne disease control
    Cloning of DOG1, a quantitative trait locus controlling seed dormancy in Arabidopsis
    Bentsink, L. ; Jowett, J. ; Hanhart, C.J. ; Koornneef, M. - \ 2006
    Proceedings of the National Academy of Sciences of the United States of America 103 (2006)45. - ISSN 0027-8424 - p. 17042 - 17047.
    natural allelic variation - thaliana l heynh - abscisic-acid - gibberellin biosynthesis - embryo development - germination - mutants - gene - longevity - maintenance
    Genetic variation for seed dormancy in nature is a typical quantitative trait controlled by multiple loci on which environmental factors have a strong effect. Finding the genes underlying dormancy quantitative trait loci is a major scientific challenge, which also has relevance for agriculture and ecology. In this study we describe the identification of the DELAY OF GERMINATION 1 (DOG1) gene previously identified as a quantitative trait locus involved in the control of seed dormancy. This gene was isolated by a combination of positional cloning and mutant analysis and is absolutely required for the induction of seed dormancy. DOG1 is a member of a small gene family of unknown molecular function, with five members in Arabidopsis. The functional natural allelic variation present in Arabidopsis is caused by polymorphisms in the cis-regulatory region of the DOG1 gene and results in considerable expression differences between the DOG1 alleles of the accessions analyzed
    Effect of seed maturity on sensitiviy of seed towards physical sanitation treatments
    Groot, S.P.C. ; Birnbaum, Y.E. ; Rop, N. ; Jalink, H. ; Forsberg, G. ; Kromphardt, C. ; Werner, S. ; Koch, E. - \ 2006
    Seed Science and Technology 34 (2006)2. - ISSN 0251-0952 - p. 403 - 413.
    zaadproductie - plantenziekten - brassica oleracea - daucus carota - heetwaterbehandeling - rijpheid - seed production - plant diseases - brassica oleracea - daucus carota - hot water treatment - maturity - chlorophyll fluorescence - brassica-oleracea - borne pathogens - aerated steam - humid air - hot - longevity
    Physical sanitation methods are used by the seed industry to prevent transmission of seed-borne diseases, but sensitivity varies between seed lots. The effect of seed maturity on the sensitivity to hot water, aerated steam and electron treatments was studied. Two Brassica oleracea L. and two Daucus carota L. seed lots from commercial production were selected for containing relatively large amounts of less mature seeds. Each seed lot was sorted into three maturity fractions based on the levels of chlorophyll fluorescence of individual seeds. Less mature B. oleracea and D. carota seeds were more susceptible to hot water treatments and less mature B. oleracea seeds to the aerated steam treatment. Seed maturity did not influence the sensitivity to the applied electron seed treatments. Seed lots were not selected for infections with seed-borne pathogens, however the less mature seeds were observed to be more frequently infected. It would be advisable to harvest seeds as mature as possible and to remove less mature seeds during seed processing. Sorting seeds by their level of chlorophyll fluorescence provides a useful method of sorting B. oleracea and D. carota seed lots. This would result in more efficient physical sanitation of seed lots
    Life expectancy in a follow-up study of a birth cohort of boxer dogs from post weaning to 10-years of age
    Hagen, M.A.E. van; Ducro, B.J. ; Knol, B.W. - \ 2005
    American Journal of Veterinary Research 66 (2005)9. - ISSN 0002-9645 - p. 1646 - 1650.
    survival analysis - insured dogs - mortality - longevity - breeds - death - heritability - puppies - sweden
    Objective-To determine mortality rate over time, risk factors for death, and heritability of life expectancy in Boxers. Animals-1,733 purebred Boxers born in The Netherlands between January 1994 and March 1995. Procedure-Dogs were followed up from weaning (ie, 49 days of age) to 10 years of age through use of a written questionnaire sent to owners every 6 months. Mortality rate over time, risk factors potentially associated with death, and heritability of life expectancy were examined by use of a proportional hazards model based on the Weibull distribution. Results Estimated mortality rate during the 10-year study period for this birth cohort of Boxers was 45%. The probability of surviving to 5 years of age was 88%; the probability of surviving to 10 years of age was 55%. Estimated effective heritability of life expectancy was 0.076, meaning that in this population, an estimated 76% of the observed variation in life expectancy could be attributed to genetic differences among dogs that were passed from parents to their offspring. Conclusions and Clinical Relevance-Results suggest that cumulative incidence of death from weaning to 10 years of age among this birth cohort of Boxers was 45%. The estimated heritability of life expectancy suggested that life expectancy can be improved by use of selective breeding.
    Root infection of sugar beet by Cercospora beticola in a climate chamber and in the field
    Vereijssen, J. ; Schneider, J.H.M. ; Termorshuizen, A.J. - \ 2005
    European Journal of Plant Pathology 112 (2005)3. - ISSN 0929-1873 - p. 201 - 210.
    gray leaf-spot - north-carolina - zeae-maydis - dispersal - tillage - conidia - soil - longevity - survival - release
    Sugar beet root infection by Cercospora beticola, the causal agent of Cercospora leaf spot (CLS), was studied in a climate chamber and in the field. In the climate chamber, root incubation of susceptible seedlings with a conidial suspension resulted in disease incidences that were significantly different for two sugar beet cultivars (Auris: 0.8 ± 0.14 and A00170: 0.5 ± 0.18; P <0.05) with regard to the control treatment 35 days after root incubation in a standard potting soil-fine river sand mixture. In a field trial with susceptible cv. Savannah with soil-incorporated CLS-infested leaf material, disease developed four weeks earlier in the infested plots than in the control plots. The probability that disease develops in the field was significantly higher for the infested than for the control plots (P <0.05). Symptomless plants from infested field plots transferred to the glasshouse to induce leaf spot symptoms showed a significantly higher probability to induce symptom development (0.4 ± 0.08), than plants from control plots (0.02 ± 0.02) (P 20°C) and high relative humidity (> 95) in our climate chamber or after canopy closure in the field. Quantification of root infection and long term survival in soil is necessary to assess its contribution to the epidemiology and life cycle of Cercospora beticola. Cultural methods such as a wider crop rotation, management of crop debris and ploughing systems may provide control strategies alternative to or reducing fungicide input.
    Breeding for longevity in Italian Chianina cattle
    Forabosco, F. - \ 2005
    Wageningen University. Promotor(en): Johan van Arendonk, co-promotor(en): Piter Bijma; R. Bozzi. - Wageningen : - ISBN 9789085042662 - 153
    chianina - vleesvee - gebruiksduur - productieve levensduur - fenotypen - rundvleesproductie - genetische analyse - lineaire modellen - overleving - rentabiliteit - kenmerken - selectief fokken - genetische verbetering - chianina - beef cattle - longevity - productive life - phenotypes - beef production - genetic analysis - linear models - survival - profitability - traits - selective breeding - genetic improvement

    The objective of this thesis was to evaluate genetic aspects of longevity (LPL) in the Chianina beef cattle population in order to define how to include this trait in selection criteria. The Chianina breed has been raised for over twenty-two centuries inItalyand today this breed is present in different countries across Europe, South and Central America,Australia,Canada and the USA. Its characteristics of somatic gigantism and rapid growth are combined with enormous resistance to harsh environmental conditions, great ease of calving and an excellent meat quality. In this breed longevity was recorded as the length of productive life (LPL), defined as years from the age at the insemination that resulted in the birth of the first calf to the date of culling or censoring. Six mo were added after the last date of calving to account for the time that the calf remains with the cow. The LPL was equal to 5.97 years on average. Heritability was equal to 0.11 when both censored and uncensored data were included to estimate longevity with the survival analysis. Type traits were used as an early predictor of profitability and muscularity traits were the most important parameters for longevity among the factors studied. Cows with approximately one calf per year remained in the herd longer than cows with fewer calves.Cows with a long LPL were more profitable than cows with short LPL. The final score could be used as an early predictor of profitability. An increase of one day unit in LPL was associated with an increase of +0.19 /cow per year and +1.65 /cow on a lifetime basis. Including longevity in both the Chianina breeding index and breeding goal either using empirical or economical weights has the positive effect of increasing the response (+2.97 and +4.92 days/year respectively). Beef breeding organizations should consider the opportunity to include longevity in a future breeding scheme to increase profit and to promote the well-being and welfare of the cows.

    Responses to stress of Caenorhabditis elegans populations with different reproductive strategies
    Alda Alvarez, O. ; Jager, T. ; Kooijman, S.A.L.M. ; Kammenga, J.E. - \ 2005
    Functional Ecology 19 (2005)4. - ISSN 0269-8463 - p. 656 - 664.
    sperm competition - toxicity tests - life-cycle - sex - fertilization - recombination - longevity - genetics - cadmium - growth
    Hermaphroditic and gonochoric reproduction are essentially different reproductive strategies that may lead to diverging population responses to adverse environmental conditions. Each strategy implies different physiological mechanisms, which affect life-history traits and represent different ways of dealing with stress. We studied the performance of hermaphroditic vs gonochoric strains in the nematode Caenorhabditis elegans exposed to cadmium stress at the individual and population level. Under control conditions, the gonochoric strain started reproduction earlier than the hermaphroditic strain at a smaller size. This was due to an earlier switch from sperm to oocyte production triggered by male sperm availability. Under cadmium stress hermaphrodites showed a decrease in the size at onset of reproduction, presumably as a strategy to maintain a high population growth rate. In contrast the body size of gonochoric nematodes was not affected. A process-based model (DEBtox) was used as a tool for analysing life-history data and calculating population growth rates. The model fitted the data well using physiologically relevant parameters such as ageing, survival or reproduction related parameters. The simultaneous fit of all life-history traits was used to obtain populations growth rate estimates. The differences between the two C. elegans strains were reflected at the population level. Lower population growth rates, as calculated by DEBtox, were found in the gonochoric strain, largely determined by the proportion of males in the offspring. From the overall results we suggest that the differences found between both populations are due to the reproductive strategy. Under control conditions, CB strain (with gonochoric reproduction) does not favour population growth rates in the short term due to faster ageing and copulation costs on survival. Furthermore, in response to stress this strain also showed lower performance than the N2 hermaphroditic strain, mainly due to a higher sensitivity of survival to the stressor
    Relationship between profitability and type traits and derivation of economic values for reproduction and survival traits in Chianina beef cows
    Forabosco, F. ; Bozzi, R. ; Boettcher, P. ; Filippini, F. ; Bijma, P. ; Arendonk, J.A.M. van - \ 2005
    Journal of Animal Science 83 (2005). - ISSN 0021-8812 - p. 2043 - 2051.
    restricted maximum-likelihood - spanish holstein cows - dairy-cattle - animal-model - herd life - variance-components - genetic evaluation - profit equations - longevity - selection
    The objectives of this study were 1) to propose a profit function for Italian Chianina beef cattle; 2) to derive economic values for some biological variables in beef cows, specifically, production expressed as the number of calves born alive per year (NACY), age at the insemination that resulted in the birth of the first calf (FI), and length of productive life (LPL); and 3) to investigate the relationship between the phenotypic profit function and type traits as early predictors of profitability in the Chianina beef cattle population. The average profit was 196/(cow·yr) for the length of productive life (LPL) and was obtained as the difference between the average income of 1,375/(cow·yr) for LPL and costs of 1,178/(cow·yr) of LPL. The mean LPL was equal to 5.97 yr, so the average total phenotypic profit per cow on a lifetime basis was 1,175. A normative approach was used to derive the economic weights for the biological variables. The most important trait was the number of calves born alive (+4.03·cow¿1·yr¿1 and +24.06/cow). An increase of 1 d in LPL was associated with an increase of +0.19/(cow·yr) and +1.65/cow on a lifetime basis. Increasing FI by 1 d decreased profit by 0.42/(cow·yr) and 2.51/cow. Phenotypic profit per cow had a heritability of 0.29. Heritabilities for eight muscularity traits ranged from 0.16 to 0.23, and for the seven body size traits between 0.21 and 0.30. The conformation trait final score can be used as an early predictor of profitability. The sale price of the animal and differences in the revenue and costs of offspring due to muscularity should be included in a future profit function
    Survival and vigour of ultra-dry seeds after ten years of hermetic storage
    Hong, T.D. ; Ellis, R.H. ; Astley, D. ; Pinnegar, A.E. ; Groot, S.P.C. ; Kraak, H.L. - \ 2005
    Seed Science and Technology 33 (2005)2. - ISSN 0251-0952 - p. 449 - 460.
    zaadkieming - groeikracht - uitdrogingstolerantie - daucus carota - aardnoten - koolzaad - allium cepa - opslag van zaden - seed germination - vigour - desiccation tolerance - daucus carota - groundnuts - rape - allium cepa - seed storage - moisture-content limit - logarithmic relation - theoretical basis - longevity - temperatures - groundnut - protocols - lettuce
    Seeds of carrot, groundnut, lettuce, oilseed rape and onion were stored hermetically in laminated aluminium foil packets in four environments (dry or ultra-dry moisture contents combined factorially with temperatures of 20 degrees C or -20 degrees C), replicated at several sites. After ten years' hermetic storage, seed moisture content, equilibrium relative humidity, viability (assessed by ability to germinate normally in standard germination tests) and vigour were determined. After a decade, the change in seed moisture content of samples stored at -20 degrees C was small or nil. Except for groundnut and lettuce (where loss in viability was about 8 and 3%, respectively), no loss in viability was detected after 10 years' hermetic storage at -20 degrees C. In all cases, there was no difference in seed survival between moisture contents at this temperature (P > 0.25). Comparison of seed vigour (root length and rate of germination) also confirmed that drying to moisture contents in equilibrium with 10-12% r.h. had no detrimental effect to longevity when stored at -20 degrees C: the only significant (P <0.05) differences detected were slightly greater root lengths for ultra-dry storage of four of the six seed lots. Seed moisture content had increased after a decade at 20 degrees C (generally to the level in equilibrium with ambient relative humidity). Hence, sub-zero temperature storage helped maintain the long-term integrity of the laminated aluminium foil packets, as well as that of the seeds within.
    Why high seed densities within buried mesh bags may overestimate depletion rates of soil seed banks
    Mourik, T.A. van; Stomph, T.J. ; Murdoch, A.J. - \ 2005
    Journal of Applied Ecology 42 (2005)2. - ISSN 0021-8901 - p. 299 - 305.
    striga-hermonthica - weed seeds - longevity - emergence - viability - dynamics - rotation - dormancy - losses - fields
    1. Estimates of seed bank depletion rates are essential for modelling and management of plant populations. The seed bag burial method is often used to measure seed mortality in the soil. However, the density of seeds within seed bags is higher than densities in natural seed banks, which may elevate levels of pathogens and influence seed mortality. The aim of this study was to quantify the effects of fungi and seed density within buried mesh bags on the mortality of seeds. Striga hermonthica was chosen as the study species because it has been widely studied but different methods for measuring seed mortality in the soil have yielded contradictory estimates. 2. Seed bags were buried in soil and exhumed at regular time intervals to monitor mortality of the seeds in three field experiments during two rainy seasons. The effect of fungal activity on seed mortality was evaluated in a fungi exclusion experiment. Differences in seed-to-seed interaction were obtained by using two and four densities within the seed bags in consecutive years. Densities were created by mixing 1000 seeds with 0, 10, 100 or 1000 g of coarse sand. 3. The mortality rate was significantly lower when fungi were excluded, indicating the possible role of pathogenic fungi. 4. Decreasing the density of seeds in bags significantly reduced seed mortality, most probably because of decreased seed-to-seed contamination by pathogenic fungi. 5. Synthesis and applications. Models of plant populations in general and annual weeds in particular often use values from the literature for seed bank depletion rates. These depletion rates have often been estimated by the seed bag burial method, yet seed density within seed bags may be unrealistically high. Consequently, estimates of seed mortality rates may be too high because of an overestimation of the effects of soil or seed-borne pathogens. Species that have been classified from such studies as having short-lived seed banks may need to be re-assessed using realistic densities either within seed bags or otherwise. Similarly, models of seed bank dynamics based on such overestimated depletion rates may lead to incorrect conclusions regarding the seed banks and, perhaps, the management of weeds and rare species
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