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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    Disentangling hexaploid genetics : towards DNA-informed breeding for postharvest performance in chrysanthemum
    Geest, Geert van - \ 2017
    Wageningen University. Promotor(en): R.G.F. Visser, co-promotor(en): U. van Meeteren; P.F.P. Arens. - Wageningen : Wageningen University - ISBN 9789463436427 - 142
    chrysanthemum - plant breeding - postharvest quality - hexaploidy - polyploidy - quantitative trait loci - phenotypes - linkage mapping - metabolomics - polymorphism - dna - chrysanthemum - plantenveredeling - kwaliteit na de oogst - hexaploïdie - polyploïdie - loci voor kwantitatief kenmerk - fenotypen - koppelingskartering - metabolomica - polymorfisme - dna

    DNA-informed selection can strongly improve the process of plant breeding. It requires the detection of DNA polymorphisms, calculation of genetic linkage, access to reliable phenotypes and methods to detect genetic loci associated with phenotypic traits of interest. Cultivated chrysanthemum is an outcrossing hexaploid with an unknown mode of inheritance. This complicates the development of resources and methods that enable the detection of trait loci. Postharvest performance is an essential trait in chrysanthemum, but is difficult to measure. This makes it an interesting but challenging trait to phenotype and detect associated genetic loci. In this thesis I describe the development of resources and methods to enable phenotyping for postharvest performance, genetic linkage map construction and detection of quantitative trait loci in hexaploid chrysanthemum.

    Postharvest performance is a complicated trait because it is related to many different disorders that reduce quality. One of these disorders in chrysanthemum is disk floret degreening, which occurs after long storage. In chapter 2, we show that degreening can be prevented by feeding the flower heads with sucrose, suggesting carbohydrate starvation plays a role in the degreening process. To investigate the response to carbohydrate starvation of genotypes with different sensitivity to disk floret degreening, we investigated the metabolome of sugar-fed and carbohydrate-starved disk florets by 1H-NMR and HPAEC. We show that the metabolome is severely altered at carbohydrate starvation. In general, starvation results in an upregulation of amino acid and secondary metabolism. Underlying causes of genotypic differences explaining variation in disk floret degreening in the three investigated genotypes remained to be elucidated, but roles of regulation of respiration rate and camphor metabolism were posed as possible candidates.

    In chapter 3, disk floret degreening was found to be the most important postharvest disorder after 3 weeks of storage among 44 white chrysanthemum cultivars. To investigate the inheritance of disk floret degreening, we crossed two genotypes with opposite phenotypic values of both disk floret degreening and carbohydrate content to obtain a population segregating for disk floret degreening. To phenotype the cultivar panel and the bi-parental population precisely and in a high throughput manner, we developed a method that quantified colour of detached capitula over time. This method was validated with visual observations of disk floret degreening during vase life tests. In a subset of the bi-parental population we measured carbohydrate content of the disk florets at harvest. The amount of total carbohydrates co-segregated with sensitivity to degreening, which shows that the difference in disk floret degreening sensitivity between the parents could be explained by their difference in carbohydrate content. However, the correlation was rather weak, indicating carbohydrate content is not the only factor playing a role.

    In order to develop resources for DNA-informed breeding, one needs to be able to characterize DNA polymorphisms. In chapter 4, we describe the development of a genotyping array containing 183,000 single nucleotide polymorphisms (SNPs). These SNPs were acquired by sequencing the transcriptome of 13 chrysanthemum cultivars. By comparing the genomic dosage based on the SNP assay and the dosage as estimated by the read depth from the transcriptome sequencing data, we show that alleles are expressed conform the genomic dosage, which contradicts to what is often found in disomic polyploids. In line with this finding, we conclusively show that cultivated chrysanthemum exhibits genome-wide hexasomic inheritance, based on the segregation ratios of large numbers of different types of markers in two different populations.

    Tools for genetic analysis in diploids are widely available, but these have limited use for polyploids. In chapter 5, we present a modular software package that enables genetic linkage map construction in tetraploids and hexaploids. Because of the modularity, functionality for other ploidy levels can be easily added. The software is written in the programming language R and we named it polymapR. It can generate genetic linkage maps from marker dosage scores in an F1 population, while taking the following steps: data inspection and filtering, linkage analysis, linkage group assignment and marker ordering. It is the first software package that can handle polysomic hexaploid and partial polysomic tetraploid data, and has advantages over other polyploid mapping software because of its scalability and cross-platform applicability.

    With the marker dosage scores of the bi-parental F1 population from the genotyping array and the developed methods to perform linkage analysis we constructed an integrated genetic linkage map for the hexaploid bi-parental population described in chapter 3 and 4. We describe this process in chapter 6. With this integrated linkage map, we reconstructed the inheritance of parental haplotypes for each individual, and expressed this as identity-by-descent (IBD) probabilities. The phenotypic data on disk floret degreening sensitivity that was acquired as described in chapter 3, was used in addition to three other traits to detect quantitative trait loci (QTL). These QTL were detected based on the IBD probabilities of 1 centiMorgan intervals of each parental homologue. This enabled us to study genetic architecture by estimating the effects of each separate allele within a QTL on the trait. We showed that for many QTL the trait was affected by more than two alleles.

    In chapter 7, the findings in this thesis are discussed in the context of breeding for heterogeneous traits, the implications of the mode of inheritance for breeding and the advantages and disadvantages of polyploidy in crop breeding. In conclusion, this thesis provides in general a significant step for DNA-informed breeding in polysomic hexaploids, and for postharvest performance in chrysanthemum in particular.

    Confituren en zwarte roest
    Zadoks, J.C. - \ 2001
    Gewasbescherming 32 (2001)6. - ISSN 0166-6495 - p. 157 - 157.
    hexaploïdie - triticum aestivum - tarwe - waardplanten - berberis - geschiedenis - vectoren, ziekten - plantenziekteverwekkende schimmels - gewasbescherming - vectorbestrijding - destructie - discussie - hexaploidy - triticum aestivum - wheat - host plants - hosts of plant pests - disease vectors - plant protection - vector control - destruction - berberis - history - discussion
    De berberis als waardplant van zwarte roest in tarwe. Het ruimen van deze waardplant in de 17e eeuw leidde tot een discussie tussen boeren, wetenschappers en de adel
    Fusarium head blight resistance in wheat : using the in vitro androgenic approach
    Bruins, M.B.M. - \ 1998
    Agricultural University. Promotor(en): E. Jacobsen; C.H.A. Snijders. - S.l. : Bruins - ISBN 9789054858638 - 130
    plantenveredeling - ziekteresistentie - plaagresistentie - plantenziekteverwekkende schimmels - deuteromycotina - triticum aestivum - tarwe - hexaploïdie - tuberculariaceae - plant breeding - disease resistance - pest resistance - plant pathogenic fungi - deuteromycotina - triticum aestivum - wheat - hexaploidy - tuberculariaceae

    Wheat ( Triticum aestivum L.) belongs to the three most important food crops in the world. In certain years, the crop can suffer considerable damage as a result of Fusarium Head Blight (FHB), especially as no chemical control is effective against this disease. This disease is mainly caused by the fungi Fusarium culmorum and F. graminearum but in the cooler regions of North-Western Europe, F. culmorum predominates. The pathogen causes a wide range of different damage, of which toxin contamination of the seeds is among the most threatening. These toxins, of which deoxynivalenol (DON), nivalenol (NIV) and acetyldeoxynivalenol (ADON), with the isomers 3-ADON and 15-ADON are most notorious, are capable of inhibiting protein synthesis and are, therefore, extremely hazardous to man and animal. For economic and environmental reasons, host plant resistance is the most appropriate and sustainable disease control method and should be given a high priority in any wheat breeding programme.

    Androgenesis is the outgrowth of the male reproductive cell into a haploid plant. Up until now, for more than 250 plant species haploid plants have been produced via in vitro androgenesis. However, when using the in vitro androgenesis technique there are still specific problems to be solved for the individual crops. The applications and advantages of in vitro androgenesis are for example rapid production of haploid plants evoking a shorter breeding regime, easier genetic analyses both at crossings and at the DNA level and possibilities for genetic modification and in vitro selection. In vitro selection has been used efficiently to find agronomically altered traits and to produce new cultivars. With the use of toxins as selective agent new resistances have been found in wheat, e.g. against Pseudomonas syringae pv. syringae or Helminthosporium sativum . A general overview on Fusarium Head Blight (FHB), on toxicity of the toxins produced by this pathogen, on in vitro androgenesis and in vitro selection is presented in Chapter 1.

    In Chapter 2, the results of a 7x7 full diallel on the inheritance of androgenic ability in wheat anther culture are presented. Seven parental cultivars, differing in both androgenic response and FHB-resistance, together with the 42 F 1 -combinations of the complete diallel were evaluated for several androgenic traits in five replicates. In total 130,000 anthers were cultured, of which 14% responded. Diallel data were analysed by the model of Gardner and Eberhart and it appeared that most of the genetic variation could be explained by additive genetic effects. A total of 17,819 embryos were transferred to MS regeneration medium, of which on average 30% regenerated into plantlets. Of them 11% was green. Except for two combinations, green plants were recovered from all 42 F 1 -combinations. Significant genetic differences were found and genetic effects explained 38%, 48% and 21% of the total variation for the percentage of green regenerants, the percentage of albino regenerants and the percentage of embryos that formed only roots, respectively. Additive effects explained 30%, 65% and 37% of the genetic variation and narrow sense heritabilities were 0.11, 0.32 and 0.08, respectively. Replicate effects were highly significant for the factors percentage albino regenerants and percentage embryos with only root formation. No significant General Combining Ability (GCA) effects were found. Variety heterosis was only significant for the percentage green regenerants and specific heterosis was significant for percentage green- and percentage albino regenerants. No reciprocal effects were found. Large significant differences in Specific Combining Ability (SCA) values were observed, with 13.5% of the F 1 -combinations outyielding the best parent.

    About 2,000 plants were doubled with colchicine and 84% of the doubled haploid (DH) plants could be grown to seed set. For seed set, genetic effects explained 78% of the total variation, but additive effects where responsible for only 4% of the genetic variation and, therefore, the narrow sense heritability was low (0.01). According to heritabilities, for embryo production progress can be rapid, for green plant regeneration it will be important to choose the parents very carefully and for seed set, progress is more hard to make. No correlation between embryo production, plant regeneration or seed set could be found. Over 200,000 seeds were formed on the DH-genotypes.

    A low green plant regeneration is considered to be one of the main bottlenecks for efficient use of the in vitro androgenesis technique in wheat. To study the inheritance of anther culture response and green plant regeneration more specifically, reciprocal crosses were made between the wheat cultivars Ringo Sztar, Ciano 067 and Benoist H77022, each of which had both a good response in anther culture and a high frequency of green plant regeneration (Chapter 3). It was found that, averaged for all genotypes, 23.0% of the anthers responded and a callus induction frequency of 77.8% was observed.

    Furthermore it appeared that of all the embryos, 43.0% developed into plantlets, 25.6% of the regenerants being green, resulting in 3.3 green plants per 100 anthers. It was also found that genotypic effects accounted for 57.7%, 86.3% and 77.5% of the total variance of anther culture response, callus induction frequency and embryo induction frequency, respectively. Additive and dominant gene actions were detected for all androgenesis and regeneration characteristics and no reciprocal differences were found, indicating the absence of cytoplasmic effects. It was concluded that embryo production was primarily correlated with anther culture response and not with the number of embryos produced per plated anther or per responding anther.

    Advantages of in vitro selection compared to in vivo selection are that a larger number of genotypes can be screened under controlled conditions and that a limited amount of space is needed to screen all genotypes. For wheat, resistance against several diseases was reported through in vitro selection with the help of toxins as selective agent. In order to elucidate the phytotoxicity of FHB-produced toxins, effects were studied on four types of wheat plant material i.e. seedlings, coleoptile segments, anther derived callus and anther derived embryos, using different concentrations of DON and 3-ADON (Chapter 4). It appeared that DON inhibited growth of all types of plant material and that the seedling growth response to 4´10 -5M DON of a large set of genotypes did not differentiate between tolerant and sensitive genotypes according to the observed FHB-resistance level in the field. In general, coleoptile segments showed a growth reduction at 10 -5M DON, whereas a concentration of 10 -4M DON appeared to be the optimum concentration to differentiate between haploid wheat calli for DON-tolerance. However, growth analysis data of 40 callus clones did not show any correlation with the known FHB-resistance levels of the original donor genotypes and populations. Regeneration of the anther derived embryos in the embryo selection experiment was decreased 100-fold on DON-containing medium. Averaged across the callus and embryo selection experiments, green plant regeneration showed a decrease of approximately 20-fold on medium containing the toxin.

    Most of the resistance genes against FHB that are known up to now, are located in for European standards considered exotic wheat genotypes and introduction of these genes into varieties requires extensive backcrossing. A haploid step could accelerate the transfer of the genes to cultivars. The final aim of our research was selection for high FHB-resistance in the field and, therefore, crosses were made between resistant and susceptible genotypes for four consecutive years (Chapter 5). Parents, F 1 - or F 2 -populations were used as donor material for anther culture and were, together with the anther culture derived doubled haploid (DH) wheat lines, tested in the field for their FHB-resistance. Percentage infection was measured three and four weeks after artificial inoculation.

    Besides infection, also date of flowering and, during two years, straw length was scored. The observed plant traits within the various DH-lines were stable, homogeneous and no visible segregation occurred. In most cases, the F 1 -, F 2 -populations and the DH-lines were for infection level intermediate between the two parental infection levels, indicating an additive inheritance. However, the infection levels of some of the doubled haploids were significantly lower than the levels of the most resistant parent. In cases where the F 2 -populations were significantly more resistant than the two parents, it was concluded that accumulation of resistance genes of the partially resistant parents had occurred. In cases where the DH-lines, derived from cultivars were significantly more resistant than the cultivars, it was attributed to gametoclonal variation. No evidence was found that a longer callus phase might lead to a higher level of variation. In 1994 infection levels were substantially higher than in the three previous years, probably due to higher maximum temperatures in the inoculation period.

    Microspore culture has several advantages over anther culture, e.g. for in vitro selection experiments, single cells are preferred to multicellular structures as a more uniform selection pressure is secured. The possibility of using isolated microspore culture of wheat for in vitro selection experiments are described in Chapter 6. Experiments were carried out to optimise the isolation and culture of isolated microspores of this recalcitrant crop. It was found that the viability of the microspores was better when co-cultured with wheat ovaries from one cultivar as compared to co-culture with a mixture of wheat ovaries from four cultivars. Furthermore it appeared that co-culture of the microspores with ovaries in culture plate inserts had no significant effect on viability of the microspores, but had, in comparison with culture in agarose rings, a large positive effect on the percentage of swollen microspores. A significant correlation between the number of swollen microspores and the number of multicellular structures was found.

    For future research it will be necessary to analyse the progenies of the diallel-derived DH-regenerants for their FHB-resistance for several generations. It has to be elucidated whether or not the resistance levels of the highly resistant DH-genotypes will also be found in their offspring. Because in some DH-lines accumulation of resistance genes appears to have occurred, these lines will be very useful in breeding for introgression of this trait into commercial varieties.

    Wheat and maize, two of the three most important food crops in the world, are affected by Fusarium head blight. Research on FHB resistance and resistant cultivars are of the utmost importance to ensure an adequate food supply around the world.

    Teelt van wintertarwe
    Darwinkel, A. ; Zwanepol, S. - \ 1997
    Lelystad : Praktijkonderzoek voor de Akkerbouw en de Vollegrondsgroenteteelt (Teelthandleiding 76) - 84
    triticum aestivum - tarwe - hexaploïdie - teelt - cultuurmethoden - winter - akkerbouw - teelthandleidingen - triticum aestivum - wheat - hexaploidy - cultivation - cultural methods - winter - arable farming - cultivation manuals
    Tests of performance of SUCROS-Wheat v4.0 with West-European experimental datasets
    Stol, W. - \ 1997
    Wageningen : AB-DLO (Note / AB-DLO 55) - 19
    triticum aestivum - tarwe - hexaploïdie - groei - gewassen - computersimulatie - simulatie - simulatiemodellen - triticum aestivum - wheat - hexaploidy - growth - crops - computer simulation - simulation - simulation models
    SUCROS97: Simulation of crop growth for potential and water-limited production situations. As applied to spring wheat
    Laar, H.H. van; Goudriaan, J. ; Keulen, H. van - \ 1997
    Wageningen/Haren : AB-DLO, TPE (Quantitative Approaches in Systems Analysis 14) - 52
    groei - gewassen - oogsttoename - oogstverliezen - opbrengsten - water - vochtigheid - droogte - triticum aestivum - tarwe - hexaploïdie - modellen - onderzoek - growth - crops - yield increases - yield losses - yields - water - humidity - drought - triticum aestivum - wheat - hexaploidy - models - research
    Wheat bran glucuronoarabinoxylans : biochemical and physical aspects
    Schooneveld - Bergmans, M.E.F. - \ 1997
    Agricultural University. Promotor(en): A.G.J. Voragen; G. Beldman. - S.l. : Schooneveld-Bergmans - ISBN 9789054857167 - 125
    graansoorten - maling - Triticum aestivum - tarwe - hexaploïdie - voedsel - voedingsmiddelen - koolhydraten - zetmeel - vezel - polysacchariden - structuur - chemische reacties - cereals - milling - Triticum aestivum - wheat - hexaploidy - food - foods - carbohydrates - starch - fibre - polysaccharides - structure - chemical reactions

    Arabinoxylans are present in cereal cell walls and in vitro they have interesting physicochemical properties, such as viscosity and gelation. Although many studies on these properties were reported for wheat flour arabinoxylan, not much research has been directed towards exploitation of these polysaccharides as food gum. For that purpose glucuronoarabinoxylans of wheat bran, a cheap by-product of the cereal industry, were studied with regard to their extractability, their structural and physicochemical properties.

    Approximately 50% of the glucuronoarabinoxylans of wheat bran cell wall material were recovered in high purity by barium hydroxide extraction at 70 to 95°C. Delignification or other treatments to open up the cell wall structure were not effective in increasing the yield. The extracted glucuronoarabinoxylans were very diverse in chemical structure and physicochemical properties. About 30% of them had a low degree of substitution, were easily degradable by xylanolytic enzymes and hardly influenced the viscosity of the solvent as a result of extensive aggregation. Over 50% of them had a high degree of substitution, were supposed to contain dimeric branches of arabinose and xylose, were scarcely degradable by xylanolytic enzymes, gave moderate viscosity to solutions and were very effective in stabilizing emulsions. The structure of these glucuronoarabinoxylans could only be speculated upon and it could not be enzymatically modified as a consequence of its complexity and the lack of appropriate enzymes. The remaining glucuronoarabinoxylans either had an intermediate or very high degree of substitution, of which the latter was presumed to be connected to lignin-fragments.

    Gel-forming glucuronoarabinoxylans were recovered only in low yield by dilute alkali extraction and subsequent purification was necessary. These feruloylated glucuronoarabinoxylans gelled upon addition of oxidative agents, of which peroxide - peroxidase, glucose - glucoseoxidase - peroxidase and ammonium persulphate were investigated. In comparison with wheat flour arabinoxylans, those of wheat bran appeared to give less flexible networks at high concentration, which was ascribed to their high degree of substitution and high ferulic acid content. Of the dimers formed upon cross-linking, the generally known diferulic acid, being a 5-5 coupled dimer, was only present in relatively low amounts. Dimers, in which the 8-position of the ferulic acid residue is involved were preponderant. The distribution of the dimers was not affected by the type of cross- linking agent or the type of arabinoxylan. However, the presence of lignin fragments in the bran extract was presumed to cause a low ferulic acid recovery upon cross-linking.

    Inversion techniques in radar remote sensing of agricultural field : case studies on sugar beet and winter wheat
    Rijckenberg, G.J. - \ 1997
    Agricultural University. Promotor(en): R.A. Feddes; G.P. de Loor. - S.l. : Rijckenberg - ISBN 9789090101460 - 207
    bodemwatergehalte - vloeistoffen (liquids) - absorptie - emissie - omloop - remote sensing - in de grond doordringende radar - scannen - triticum aestivum - tarwe - hexaploïdie - beta vulgaris - suikerbieten - microgolfstraling - soil water content - liquids - absorption - emission - circulation - remote sensing - ground-penetrating radar - scanning - triticum aestivum - wheat - hexaploidy - beta vulgaris - sugarbeet - microwave radiation

    This thesis is an attempt to gain insight in the retrieval of the soil moisture content and the vegetation water content from the radar backscatter of agricultural fields. Two crops have been selected: sugar beet and winter wheat. For a retrieval of the two agricultural parameters two approaches have been adopted.

    The first approach is based on an inversion of existing models, which describe the electromagnetic interaction with a vegetated surface on basis of the radiative transfer theory. A solution to this inversion problem is suggested involving the inversion of the simple Cloud model, which is connected to the complex MIMICS model.

    In the second approach a semi-empirical algorithm is developed, which decomposes the covariance matrix of polarimetric radar data into a vegetation, soil, and vegetation-soil covariance matrix. It is shown how centrical symmetry and the Brewster angle effect can be used in this decomposition technique. The procedure for an assessment of the three covariance matrices has resulted in two solutions for the algorithm. A choice between these solutions can be made by means of three polarimetric tools. A sensitivity analysis reveals that decomposition results at C- and L-band are not always sensitive enough to changes in the agricultural parameters.

    The validity of the two radiative transfer models is examined using backscatter measurements and accompanying ground data. Because of the complex structure of winter wheat the Cloud model has been applied to sugar beet data only. The backscatter of sugar beet and winter wheat at C- and L-band is predicted with MIMICS.

    The performance of the Cloud model could not be tested properly because of two reasons. Firstly the temporal resolution in most of the data sets is too low and secondly a systematic decrease occurred in practically all backscatter data, which complicates the use of the Cloud model.

    The inversion scheme with MIMICS could not be applied to the examined data, because there are disagreements between model predictions and measurements. In particular the predicted extinctions with MIMICS are too low compared with the experimental observations. Polarimetric backscatter is investigated with the three tools. Sugar beet backscatter at C- and L-band exhibits centrical symmetry. A significant Polarimetric Phase Difference ( PPD ) is found in the backscatter of winter wheat at L-band. This PPD can be explained by means of simulations with a radiative transfer model.

    The semi-empirical algorithm has been applied to sugar beet and winter wheat polarimetric backscatter at C- and L-band. The decomposition results so obtained are then considered in relation to trends in the agricultural parameters. The analysis yields promising results since the predicted trends are in agreement with the few available ground data. It appears that the calibration accuracy of the measurements is a limiting factor for the sensitivity of the results for the two agricultural parameters, and for soil moisture content in particular. Of the two frequencies considered the L-band gives the best information.

    The available radar backscatter data could be applied in a vegetation study because of the synergy with optical data. In spite of the large amount of investigated data, there is still a need for detailed experiments, e.g. tower-based measurements. With such experiments the validity of backscatter models can be further evaluated and a better interpretation of phenomena occurring in the polarimetric backscatter becomes possible.

    Bridging the gap between plant physiology and breeding : identifying traits to increase wheat yield potential using systems approaches
    Bindraban, P.S. - \ 1997
    Agricultural University. Promotor(en): R. Rabbinge; H. van Keulen. - S.l. : Bindraban - ISBN 9789054857525 - 135
    triticum aestivum - tarwe - hexaploïdie - oogsttoename - oogstverliezen - opbrengsten - groei - plantenontwikkeling - bladeren - milieufactoren - genetische variatie - modellen - onderzoek - tropen - subtropen - triticum aestivum - wheat - hexaploidy - yield increases - yield losses - yields - growth - plant development - leaves - environmental factors - genetic variation - models - research - tropics - subtropics

    Part of the required increase in wheat production in currently high yielding wheat producing regions, like in the (sub-)tropics (ME1), will have to be obtained primarily by increased genetic wheat yield potential. Progress obtained by breeding to increase yield potential was substantial in the past, but is currently declining. Support from other disciplines to improve breeding efficiency is urgently needed. A systems approach was applied to identify processes that determine wheat growth and yield, and traits that need to be adapted to increase genetic yield potential for ME1 conditions. Increasing biomass through leaf nitrogen affords little opportunity to obtain gains under optimum management conditions. Growth analysis suggested the source capacity of wheat to exceed yield at higher yield levels, while remobilization of stem reserves was needed to supplement grain demand at lower yield levels. The latter aspect was confirmed in an analysis of stem reserve dynamics. Despite sufficient assimilate production, remobilization also occurred at higher yield levels, suggesting other processes, like wasteful respiration and negative feedback on photosynthesis, to become important. Also, higher amounts of residual reserves were found under higher than under lower yield levels. These results indicate that wheat yields under optimum conditions in ME1 are limited by sink capacity, as source capacity is abundant. Sink capacity can be increased by increasing kernel number or weight. Kernel number is determined between early booting and final anthesis, and depends on the duration and the crop growth rate of this period and on the allocation to the spike. Required adjustments to increase kernel number depend on enviromnental conditions. Competition among kernels for carbohydrates limited their growth, in particular those positioned further away from the rachis. This may be due to an inadequate transport system. Without competition, yields were assessed to increase at least one ton per hectare over a wide range of enviromnental conditions. It is concluded that increase in wheat yield potential under ME1 conditions should be obtained by increased sink capacity, which may be realized through the adaptation of the spike morphology. Sufficient genetic variation of this trait is at hand to be incorporated in a breeding program.

    Tarwe bijvoeren aan vleeskuikens: invloed tarweras op resultaten
    Harn, J. van - \ 1996
    Praktijkonderzoek voor de Pluimveehouderij 7 (1996)1. - ISSN 0924-9087 - p. 18 - 21.
    dierhouderij - vleeskuikens - karkassamenstelling - cultivars - ontwikkeling - voer - groei - hexaploïdie - voedingswaarde - productiviteit - rentabiliteit - rassen (taxonomisch) - triticum aestivum - rassen (planten) - tarwe - animal husbandry - broilers - carcass composition - cultivars - development - feeds - growth - hexaploidy - nutritive value - productivity - profitability - races - triticum aestivum - varieties - wheat
    Eén van de vragen bij het bijvoeren van tarwe aan vleeskuikens is welke invloed het tarweras heeft. Het Praktijkonderzoek Pluimveehouderij (PP) heeft twee veel gebruikte tarwerassen, Ritmo en Vivant, vergeleken.
    A simulation study of crop growth and development under climate change
    Peiris, D.E. ; Crawford, J.W. ; Grashoff, C. ; Jefferies, R.A. ; Porter, J.R. ; Marshall, B. - \ 1996
    Agricultural and Forest Meteorology 79 (1996)4. - ISSN 0168-1923 - p. 271 - 287.
    klimaatverandering - hexaploïdie - paleoklimatologie - aardappelen - Schotland - Solanum tuberosum - Triticum aestivum - Vicia faba - tarwe - climatic change - hexaploidy - palaeoclimatology - potatoes - Scotland - Solanum tuberosum - Triticum aestivum - Vicia faba - wheat
    Mycosphaerella graminicola on wheat : genetic variation and histopathology
    Kema, G.H.J. - \ 1996
    Agricultural University. Promotor(en): J.C. Zadoks; C.H. van Silfhout. - S.l. : KEMA - ISBN 9789090094861 - 141
    plantenziekteverwekkende schimmels - triticum aestivum - tarwe - hexaploïdie - dothideales - planten - parasitisme - fysiologie - gastheer parasiet relaties - genetische variatie - mutaties - mycosphaerellaceae - plant pathogenic fungi - triticum aestivum - wheat - hexaploidy - dothideales - plants - parasitism - physiology - host parasite relationships - genetic variation - mutations - mycosphaerellaceae

    The research described in this thesis was focused on a comprehensive understanding of the generation and extent of genetic variation, and its effects on host cultivars in the wheat- Mycosphaerella graminicola pathosystem. Inoculation experiments were conducted in the seedling stage and adult plant stages under field conditions over several years. These experiments encompassed nearly 100 isolates of the pathogen tested on some 50 wheat cultivars. Parametric and non-parametric statistical analyses were employed on large data and very small data sets, and indicated that in all experiments cultivar x isolate interactions were significant. Pathogen isolates originating from bread wheat and durum wheat appeared to be adapted to their hosts, respectively. Molecular analysis of the interternally transcribed spacer regions of isolates from both forms, indicated that these were taxonomically closely related. The inoculation experiments indicated that specificity is an important characteristic of the pathosystem. After having determined the wide genetic variation in the pathosystem, experiments were conducted to elucidate the mating system of the pathogen. The results indicated a bipolar heterothallic mating system and RAPD analyses of progenies showed regular Mendelian inheritance. Furthermore it was shown that the pathogen is able to complete several generative cycles within a season. Hence, genetic recombination appears to be the driving force behind the determined vast genetic variation. Biochemical and histological experiments were conducted involving compatible and incompatible interactions with the host plant in order to elucidate the resistance mechanism of wheat to the pathogen.
    Effects of cultivar, isolate and environment on resistance of wheat to septoria tritici blotch in Kenya
    Arama, P.F. - \ 1996
    Agricultural University. Promotor(en): J.E. Parlevliet; C.H. van Silfhout. - S.l. : Arama - ISBN 9789054855705 - 115
    plantenveredeling - ziekteresistentie - plaagresistentie - triticum aestivum - tarwe - hexaploïdie - plantenziekteverwekkende schimmels - dothideales - planten - kenya - mycosphaerellaceae - plant breeding - disease resistance - pest resistance - triticum aestivum - wheat - hexaploidy - plant pathogenic fungi - dothideales - plants - kenya - mycosphaerellaceae

    The research described in this thesis focused on the characterization of some of the factors that influence disease assessment, development and expression of resistance in wheat cultivars to septoria tritici blotch. Earliness appeared to have a strong effect and tallness a small effect on disease severity (DS). A regression equation derived was used to correct the DS in the entries. Another method that gave good disease assessment was to group the cultivars according to their earliness. It appeared that the disease developed in each earliness group at the same rate. The importance of interplot interference in assessing septoria resistance in wheat was studied. There was no indication of interplot interference. The Nitrogen (N) level is another factor that may affect disease assessment. In Kenya there was an increase in DS on cultivars exposed to more N while in The Netherlands there was no similar increase in DS.

    When an inoculum mixture or single isolates are used for inoculations, the ranking of the cultivars was essentially not affected, indicating that inoculum mixtures can be used effectively in screening wheat genotypes. The correlation coefficients between the DS at the seedling and the adult plant stages was low. Thus resistance assessed at the seedling stage could not fully explain adult plant resistance. Isolates from Kenya and The Netherlands were tested on wheat seedlings. It was concluded that there was variation in virulence (and so in race-specific resistance in the host) of Septoria tritici populations within both countries. The strong cultivar x isolate interactions observed on wheat seedlings was also observed on adult plants in the field.

    F6lines of 36 crosses were evaluated in the field. Transgressive segregation towards more resistance and or more susceptibility occurred in most crosses. It can be said that a fair number of genes operating in an additive manner and epistasis are involved.

    Aanbod en opname van stikstof bij hoge produktieniveaus van wintertarwe op klei- en zavelgrond = Yield level of winter wheat crops in relation to supply and uptake of nitrogen
    Darwinkel, A. - \ 1995
    Lelystad : PAGV (Verslag / Proefstation voor de Akkerbouw en de Groenteteelt in de Vollegrond nr. 205) - 34
    assimilatie - hexaploïdie - nederland - stikstof - triticum aestivum - tarwe - assimilation - hexaploidy - netherlands - nitrogen - triticum aestivum - wheat
    Vruchtwisselingsproef AGM 600 proefboerderij A.G. Mulderhoeve Emmercompascuum 1981 - 1989 : effect van gewasrotaties, organische stof en stikstof op de produktie van aardappelen, suikerbieten, zomertarwe en haver op een veenkoloniale grond
    Wijnholds, K.H. ; Berg, W. van den - \ 1995
    Lelystad : PAGV (Verslag / Proefstation voor de Akkerbouw en de Groenteteelt in de Vollegrond nr. 206) - 129
    avena sativa - beta vulgaris - hexaploïdie - stikstof - haver - organische meststoffen - aardappelen - rotaties - solanum tuberosum - suikerbieten - triticum aestivum - tarwe - nederland - groningen - avena sativa - beta vulgaris - hexaploidy - nitrogen - oats - organic fertilizers - potatoes - rotations - solanum tuberosum - sugarbeet - triticum aestivum - wheat - netherlands - groningen
    Effects of climate change on yield potential of wheat and maize crops in the European Union
    Wolf, J. ; Diepen, C.A. van - \ 1995
    In: Climate change research : evaluation and policy implications : proceedings of the international climate change research conference, Maastricht, The Netherlands, 6 - 9 December 1994 / Zwerver, S., - p. 745 - 750.
    landen van de europese unie - opwarming van de aarde - broeikaseffect - hexaploïdie - maïs - triticum aestivum - tarwe - oogsttoename - oogstverliezen - opbrengsten - zea mays - european union countries - global warming - greenhouse effect - hexaploidy - maize - triticum aestivum - wheat - yield increases - yield losses - yields - zea mays
    Yields of winter wheat, silage maize and grain maize in the main arable areas of the European Union (EU) were calculated with a simulation model, WOFOST, using historical weather data and average soil characteristics. The sensitivity of the model to individual weather variables was determined. Subsequent analyses were made using climate change scenarios with and without the direct effects of increased atmospheric carbon dioxide. The impact of crop management in a changed climate was also assessed. The various climate change scenarios used appear to yield considerably different changes in yield, both for each location and for the EU as a whole.
    Chemische bestrijding van tarwe-opslag in veldbeemdgras
    Baltus, P.C.W. ; Zweep, A.T. - \ 1994
    In: Jaarboek 1993-1996 : verslagen van afgesloten onderzoeksprojecten op de regionale onderzoekcentra en het PAGV. Akkerbouw Lelystad : Proefstation voor de Akkerbouw en de Groenteteelt in de Vollegrond [etc.] (Publikatie / Proefstation voor de Akkerbouw en de Groenteteelt in de Vollegrond, Regionale Onderzoekcentra No. 70a-81A) - p. 148 - 151.
    herbiciden - hexaploïdie - gewasbescherming - poa - triticum aestivum - tarwe - herbicides - hexaploidy - plant protection - poa - triticum aestivum - wheat
    Mechanische bestrijding van tarwe-opslag in veldbeemdgras
    Baltus, P.C.W. ; Zweep, A.T. - \ 1994
    In: Jaarboek 1993-1996 : verslagen van afgesloten onderzoeksprojecten op de regionale onderzoekcentra en het PAGV. Akkerbouw Lelystad : Proefstation voor de Akkerbouw en de Groenteteelt in de Vollegrond [etc.] (Publikatie / Proefstation voor de Akkerbouw en de Groenteteelt in de Vollegrond, Regionale Onderzoekcentra No. 70a-81A) - p. 144 - 147.
    hexaploïdie - mechanische methoden - gewasbescherming - poa - triticum aestivum - tarwe - hexaploidy - mechanical methods - plant protection - poa - triticum aestivum - wheat
    De mechanische bestrijding bestond uit eggen, schoffelen en borstelen
    Bestrijding tarwe-opslag met carvon in graszaad
    Baltus, P.C.W. ; Polman, G.J. ; Bakker, W. - \ 1994
    In: Jaarboek 1993-1996 : verslagen van afgesloten onderzoeksprojecten op de regionale onderzoekcentra en het PAGV. Akkerbouw Lelystad : Proefstation voor de Akkerbouw en de Groenteteelt in de Vollegrond [etc.] (Publikatie / Proefstation voor de Akkerbouw en de Groenteteelt in de Vollegrond, Regionale Onderzoekcentra No. 70a-81A) - p. 137 - 139.
    kiemremmers - herbiciden - hexaploïdie - gewasbescherming - poa - kiemremming - triticum aestivum - tarwe - germination inhibitors - herbicides - hexaploidy - plant protection - poa - sprout inhibition - triticum aestivum - wheat
    Bestrijding tarwe-opslag in veldbeemd met twee typen onkruidbranders
    Baltus, P.C.W. - \ 1994
    In: Jaarboek 1993-1996 : verslagen van afgesloten onderzoeksprojecten op de regionale onderzoekcentra en het PAGV. Akkerbouw Lelystad : Proefstation voor de Akkerbouw en de Groenteteelt in de Vollegrond [etc.] (Publikatie / Proefstation voor de Akkerbouw en de Groenteteelt in de Vollegrond, Regionale Onderzoekcentra No. 70a-81A) - p. 134 - 136.
    verbranden - gecontroleerd branden - brand - vlammenspuiten - hexaploïdie - gewasbescherming - Poa - Triticum aestivum - tarwe - burning - controlled burning - fire - flame cultivators - hexaploidy - plant protection - Poa - Triticum aestivum - wheat
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