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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    Identification and functional characterization of putative (a)virulence factors in the fungal wheat pathogen Zymoseptoria tritici
    Mirzadi Gohari, A. - \ 2015
    Wageningen University. Promotor(en): Pierre de Wit, co-promotor(en): Gert Kema; Rahim Mehrabi. - Wageningen : Wageningen University - ISBN 9789462575912 - 159
    triticum aestivum - wheat - plant pathogenic fungi - mycosphaerella graminicola - virulence factors - genetic analysis - pathogenesis - bioinformatics - triticum aestivum - tarwe - plantenziekteverwekkende schimmels - mycosphaerella graminicola - virulente factoren - genetische analyse - pathogenese - bio-informatica

    Zymoseptoria tritici (Desm.) Quaedvlieg & Crous (previously known as Mycosphaerella graminicola) is the causal agent of septoria tritici blotch (STB), which is a devastating foliar wheat disease worldwide. It is responsible for significant yield losses occurring annually in all major wheat-growing areas and threatens global food security. Z. tritici is a hemi-biotrophic fungal pathogen that, after stomatal penetration, establishes a stealthy biotrophic and symptomless relation with its host plant that is followed by a sudden switch to a necrotrophic growth phase coinciding with chlorosis that eventually develops in large necrotic blotches containing many pycnidia producing asexual splash-borne conidia. Under natural conditions - once competent mating partners are present and conditions are conducive- pseudothecia are formed producing airborne ascospores. Disease management of STB is primarily achieved through fungicide applications and growing commercial cultivars carrying Stb resistance genes. However, the efficacy of both strategies is limited as strains resistant to fungicides frequently develop and progressively dominate natural populations, which hampers disease management; also the deployed Stb genes are often overcome by existing or newly developed isolates of the fungus. Hence, there is a need for discovery research to better understand the molecular basis of the host-pathogen interaction that enables breeders to identify and deploy new Stb genes, which will eventually contribute to more sustainable disease control.

    Chapter 1 introduces the subject of the thesis and describes various aspects of the lifestyle of Z. tritici with emphasis on dissecting the various stages and physiological processes during pathogenesis on wheat. In addition, it includes a short summary and discussion of the current understanding of the role of (a)virulence factors in the Z. tritici–wheat pathosystem.

    Chapter 2 describes new gateway technology-driven molecular tools comprising 22 entry constructs facilitating rapid construction of binary vectors for functional analyses of fungal genes. The entry vectors for single, double or triple gene deletion mutants were developed using hygromycin, geneticin and nourseothricin resistance genes as selection markers. Furthermore, these entry vectors contain the genes encoding green fluorescent (GFP) or red fluorescent (RFP) protein in combination with the three selection markers, which enables simultaneous tagging of gene deletion mutants for microscopic analyses. The functionality of these entry vectors was validated in Z. tritici and described in Chapters 3, 4 and 5.

    Chapter 3 describes the functional characterization of ZtWor1, the orthologue of Wor1 in the fungal human pathogen Candida albicans. ZtWor1 is up-regulated during initiation of colonization and fructification, and regulates expression of candidate effector genes, including one that was discovered after comparative proteome analysis of Z. tritici wild-type and ΔZtWor1 strains. Cell fusion and anastomosis occurred frequently in ΔZtWor1 strains, which is reminiscent of mutants of MgGpb1, the β-subunit of the heterotrimeric G protein. Comparative expression profiling of ΔZtWor1, ΔMgGpb1 and ΔMgTpk2 (the catalytic subunit of protein kinase A) strains, suggests that ZtWor1 is downstream of the cyclic adenosine monophosphate (cAMP) pathway that is crucial for pathogenicity of many fungal plant pathogens.

    Chapter 4 describes combined bioinformatics and expression profiling studies during pathogenesis in order to discover candidate effectors of  Z. tritici important for virulence. In addition, a genetic approach was followed to map quantitative trait loci (QTLs) in Z. tritici carrying putative effectors. Functional analysis of two top effector candidates, small-secreted proteins SSP15 and SSP18, which were selected based on their expression profile in planta, showed that they are dispensable for virulence of Z. tritici. These analyses suggest that generally adopted criteria for effector discovery, such as protein size, number of cysteine residues and up-regulated expression during pathogenesis, should be taken with caution and cannot be applied to every pathosystem, as they likely represent only a subset of effector genes.

    Chapter 5 describes the functional characterization of ZtCpx1 and ZtCpx2 encoding a secreted and a cytoplasmic catalase-peroxidase (CP) in Z. tritici, respectively. Gene replacement of ZtCpx1 resulted in mutant strains that were sensitive to exogenously added H2O2 and in planta phenotyping showed they are significantly less virulent compared to wild-type. All mutant phenotypes could be restored to wild-type by complementation with the wild-type allele of ZtCpx1 driven by its native promoter. Additionally, functional analysis of ZtCpx2 confirmed that this gene encodes a secreted CP and is, however, dispensable for virulence of Z. tritici on wheat. However, we showed that both genes act synergistically, as the generated double knock-out strain showed a significantly stronger reduction in virulence than the individual single knock-out strains. Hence, both genes are required by Z. tritici for successful infection and colonization of wheat.

    In Chapter 6 I discuss and summarize the genetic approaches used in this study, reflect on the major findings and bottlenecks encountered, and propose new strategies to identify effectors of Z. tritici in the future.

    Towards an improved variety assortment for the Dutch organic sector : case studies on onion and spring wheat
    Osman, A.M. - \ 2014
    Wageningen University. Promotor(en): Edith Lammerts van Bueren; Paul Struik, co-promotor(en): Conny Almekinders. - Wageningen : Wageningen University - ISBN 9789462570689 - 212
    allium cepa - uien - triticum aestivum - zomertarwe - biologische landbouw - rassen (planten) - cultivars - rassenproeven - rasreacties - classificatie van rassen - plantenveredeling - allium cepa - onions - triticum aestivum - spring wheat - organic farming - varieties - cultivars - variety trials - varietal reactions - variety classification - plant breeding

    Key words:

    organic farming; principles of organic agriculture; food production chain;

    plant breeding; genetic correlation; plant traits; farmers’ preferences;

    variety testing; Value for Cultivation and Use; EU seed legislation;

    onion; Allium cepa; spring wheat; Triticum aestivum; baking quality

    Variety choice is an important component of organic crop management. The organic sector pursues to produce healthy, nutritious food without using synthetic inputs and excessive amounts of natural resources. Access to varieties that are able to cope with weeds, diseases and pests, and thrive well under an organic fertility management regime, allows actors in the organic food production chain to achieve these aspirations. In this thesis I analyse how the current breeding, variety assessment and registration process should be changed to provide varieties that fulfil the needs of organic farmers, traders and processors. The research is based on the cases of two crops, onion (Allium cepa) and spring wheat (Triticum aestivum), that differ in key issues that influence the options for change: breeding and variety registration aspects; organic seed and crop production issues; destination of the harvest; and composition of and relations between actors in the production chain.

    Variety trials, in which we evaluated onion and spring wheat varieties for traits prioritized by organic stakeholders, revealed that the variety assortment displayed important weaknesses when grown and processed organically. In the case of onion, farmers needed varieties with improvements for resistances against main diseases, root system, storability and erect plant types in combination with high yield. For spring wheat, weed suppressiveness and baking quality were the key traits that required improvements.

    Interviews with conventional onion breeders showed that they focussed on yield and post-harvest traits (storability, bulb quality). In addition to these traits, breeding for the organic sector would require breeders to pay more attention to the selection of field traits like partial resistance against leaf diseases and a better root system. To improve key traits for organic growers, selection should take place in a growing environment without the fungicides and herbicides that are typically applied in conventional nurseries.

    Interviewing conventional wheat breeders made clear that selection for the organic market would conflict with achieving the high yield demanded by conventional growers. Breeders have achieved high yields by increasing the harvest index, which goes at the expense of baking quality through a relative decrease in protein content. Based on a literature review, we propose two alternative approaches to improve yield and protein content simultaneously: selection for increased total biomass or/and selection for protein quality. The first approach would deliver taller, leafier varieties that are also more competitive against weeds. Improving protein quality would require selection under low nitrogen input or organic growing conditions as protein composition is strongly influenced by soil nitrogen availability. Analysis of data of our own conventional and organic variety trials, together with datasets from other European countries showed that for other important traits (e.g., yield, disease resistance, plant length) selection for the organic sector could also be conducted in non-organically managed breeding nurseries, which typically refrain from fungicides and growth regulator applications, as genetic correlations for these traits were high (0.8 -1.0).

    Conducting variety trials in organic fields and evaluating these for traits prioritized by the stakeholders make results more relevant for the latter. In the specific case of Value for Cultivation and Use (VCU) testing, that is part of the official variety registration procedure of field crops in the EU, adapting the research protocol proved crucial to provide market access to varieties better adapted to organic production. The organic spring wheat VCU testing resulted in the inclusion of varieties in an organic section of the Dutch Recommended List of Varieties, showing that the statutory variety testing system is flexible to address new needs. However, procedures are costly and not in proportion to market size and in this way prohibit the release of varieties for organic and other small markets.

    Although specifically wheat breeders proved to be open to consider adaptations in their programme, the relatively small market prevents conventional private sector breeders from investing in selecting varieties specifically targeted at the organic sector. Therefore we elaborate options to set up a way of breeding that is in line with organic principles and overcomes this economic barrier.

    Diversity of different farmer and modern wheat varieties cultivated in contrasting organic farming conditions in Western Europe and implications for European seed and variety legislation
    Serpolay, E. ; Dawson, J.C. ; Chable, V. ; Lammerts Van Bueren, E. ; Osman, A.M. ; Pino, S. ; Goldringer, I. - \ 2011
    Organic Agriculture 1 (2011)3. - ISSN 1879-4238 - p. 127 - 145.
    rassenproeven - tarwe - triticum aestivum - biologische landbouw - landrassen - oude plantenrassen - rassen (planten) - west-europa - akkerbouw - variety trials - wheat - triticum aestivum - organic farming - landraces - old varieties - varieties - western europe - arable farming
    The importance of genetic diversity in cultivated varieties for organic and low-input agriculture has attracted increasing attention in recent years, with a need to identify relevant sources of diversity and strategies for incorporating diversity in plant breeding for organic systems. However, the regulatory system in many countries, particularly in the European Union, restricts the varieties available to farmers to those registered in an official catalogue, and most countries require varieties to go through official tests under conventional management, which has resulted in a lack of suitable varieties available to organic farmers. This study characterized a sample of wheat (Triticum aestivum L.) landraces, historic varieties and varietal mixtures currently of interest to organic farmers in a diverse range of organic conditions on farms in Italy, France and the Netherlands. These varieties were assessed for individual plant and spike characteristics and compared to modern registered wheat varieties grown under the same on-farm conditions. Significant differences in mean values were found among varieties for many plant and spike traits, as well as significant variety-by-environment interactions. There were often similar levels of intra-varietal variability between farmer and modern varieties, indicating that the strong selection for genetic homogeneity to meet regulatory criteria has little impact on the phenotypic variability of certain traits when assessed on-farm. Several farmer varieties had high values of traits related to productivity outside their region of origin, which underlines the need for experimentation with diverse types of varieties in order to find and develop appropriate varieties for organic systems
    Genome structure and pathogenicity of the fungal wheat pathogen Mycosphaerella graminicola
    M'Barek, S. Ben - \ 2011
    Wageningen University. Promotor(en): Pierre de Wit, co-promotor(en): Gert Kema. - [S.l.] : S.n. - ISBN 9789085859970 - 229
    triticum aestivum - triticum turgidum - tarwe - mycosphaerella graminicola - plantenziekteverwekkende schimmels - genoomstructuur - eiwitexpressieanalyse - pathogeniteit - pathogenesis-gerelateerde eiwitten - genomen - plasticiteit - plant-microbe interacties - triticum aestivum - triticum turgidum - wheat - mycosphaerella graminicola - plant pathogenic fungi - genomic structure - proteomics - pathogenicity - pathogenesis-related proteins - genomes - plasticity - plant-microbe interactions

    The phytopathogenic fungus Mycosphaerella graminicola (Fuckel) J. Schröt. in Cohn (asexual stage: Zymoseptoria tritici (Desm.) Quaedvlieg & Crous) causes septoria tritici leaf blotch (STB) in wheat and is one of the most important diseases of this crop worldwide. However, STB control, mainly based on the use of resistant cultivars and fungicides, is significantly hampered by the limited understanding of the genetic and biochemical bases of pathogenicity, and mechanisms of infection and resistance in the host. M. graminicola has a very active sexual cycle under field conditions, which is an important driver of STB epidemics. Moreover, it results in high genetic diversity of field populations that causes a major challenge for the development and sustainable management of resistant cultivars and the discovery of new antifungal compounds. Understanding the role of the sexual and asexual life cycles on genome composition of this versatile pathogen and its infection strategy is crucial in order to develop novel control methods.

    Chapter 1 is an introduction to the biology and pathogenicity of M. graminicola. In addition, it shortly describes the impact of improved and novel technologies on the speed, scope and scale of comparative genomics research.

    Chapter 2 provides detailed genetic analyses of two M. graminicola mapping populations, using mainly DArT markers, and the analysis of the meiotic transmission of unequal chromosome numbers. Polymorphisms in chromosome length and number were frequently observed in progeny isolates, of which 15–20% lacked one or more chromosomes despite their presence in one or both parents, but these had no apparent effect on sexual and pathogenic fitness. M. graminicola has up to eight so called dispensable chromosomes that can be easily lost - collectively called the dispensome - which is, so far, the highest number of dispensable chromosomes reported in filamentous fungi. They represent small-sized chromosomes and make up 38% of the chromosome complement of this pathogen. Much of the observed genome plasticity is generated during meiosis and could explain the high adaptability of M. graminicola in the field. The generated linkage map was crucial for finishing the M. graminicola genome sequence.

    Chapter 3 describes the M. graminicola genome sequence with highlights on genome structure and organization including the eight dispensable chromosomes. The genome comprises a core set of 13 chromosomes and a dispensome, consisting of eight chromosomes that are distinct from the core chromosomes in structure, gene and repeat content. The dispensome contains a higher frequency of transposons and the genes have a different codon use. Most of the genes present one the dispensome are also present on the core chromosomes but little synteny is observed neither between the M. graminicola dispensome and the core chromosomes nor with the chromosomes of other related Dothideomycetes. The dispensome likely originates from ancient horizontal transfer(s) from (an) unknown donor(s).

    Chapter 4 shows a global analysis of proteins secreted by M. graminicola in apoplastic fluids during infection. It focuses mainly on fungal proteins secreted in a compatible interaction. The study showed that many of the annotated secreted proteins have putative functions in fungal pathogenicity, such as cell wall degrading enzymes and proteases, but the function of a substantial number of the identified proteins is unknown. During compatible interactions proteins are primarily secreted during the later stages. However, many pathogenesis-related host proteins, such as PR-2, PR-3 and PR-9, accumulated earlier and at higher concentrations during incompatible interactions, indicating that fungal effectors are recognized by resistant plants and trigger resistant gene-mediated defence responses, though without a visible hypersensitive response.

    Chapter 5 further details the initial identification and characterization of necrosis-inducing proteins that are produced in culture filtrates (CFs) of M. graminicola. The necrosis-inducing activity of CFs is light dependent and inactivated by proteinase K and heat treatment (100C). This is reminiscent of the necrosis-inducing properties of host selective toxins of other Dothideomycete pathogens such as Stagonospora nodorum and Pyrenophora tritici-repentis. Subsequent purifications of CFs and mass spectrometry identified several candidate proteins with necrosis-inducing activity. Heterologous expression of the two most prominent proteins in Pichia pastoris produced sufficient quantities for infiltration assays in a panel of wheat cultivars that showed differential responses, suggesting specific recognition.

    Chapter 6 provides a general discussion of the thesis and puts the results obtained in a broader perspective with a focus on the genome structure of M. graminicola and its function. In addition, aspects of the hemi-biotrophic lifestyle, the relevance of secreted proteins for the wheat-M. graminicola pathosystem in relation to gene-for-gene models and the potential implications for resistance breeding strategies are discussed.

    Efficacy and mapping of resistance to Mycosphaerella graminicola in wheat
    Tabib Ghaffary, M.S. - \ 2011
    Wageningen University. Promotor(en): Richard Visser, co-promotor(en): Gert Kema. - S.l. : s.n. - ISBN 9789085859284 - 233
    triticum aestivum - tarwe - plantenziekteverwekkende schimmels - mycosphaerella graminicola - ziekteresistentie - genetische kartering - genetische analyse - plantenveredeling - plant-microbe interacties - triticum aestivum - wheat - plant pathogenic fungi - mycosphaerella graminicola - disease resistance - genetic mapping - genetic analysis - plant breeding - plant-microbe interactions

    Wheat is the most important food and feed crop, contributing about 19% of the required human dietary energy. The annual growth rate of the global cereal production -including wheat- is below one per cent. This is due to biotic and biotic constraints – including diseases – such that production falls short of meeting future food demands. Thus more wheat should be produced and the best way to achieve that is to produce and release cultivars with better disease resistance. Septoria tritici blotch (STB) is Europe’s major foliar wheat disease and is caused by the fungus Mycosphaerella graminicola that reduces yields to at least 50% under conducive conditions. STB management relies mostly on chemical control, but the continuously increasing incidence of fungicide resistant strains in fungal populations has resulted in a growing awareness of the importance of host resistance. However, the number of identified resistance genes to STB is very low compared to the number of known resistance genes for other wheat diseases. Moreover, these genes are not very effective and therefore of limited practical value. The aim of this research was to discover new genes for resistance and to develop tools facilitating their deployment in modern breeding programs. Three new resistance genes were detected on chromosomes 3DL, 5AL and 6DS that were designated as Stb16, Stb17 and Stb18, respectively. Stb17 was only expressed in adult plants, which is new for this disease, Stb18 is effective to a limited suite of isolates, but Stb16 has an extremely broad resistance that is of great interest to the commercial breeding industry. However, the impact of an individual gene depends strongly of the genetic make-up of a cultivar. Along with improved testing protocols these results are important for the successful commercial deployment of Stb genes in European wheat breeding programs.

    Aanvullend onderzoek mineralenconcentraten 2009-2010 op bouwland en grasland : rapportage van de resultaten van de veldproeven in wintertarwe (klei), zomergerst (zand) en zetmeelaardappelen (dalgrond) in NO-Nederland in 2010
    Wijnholds, K.H. - \ 2011
    Wageningen : Praktijkonderzoek Plant & Omgeving B.V. - 34
    solanum tuberosum - aardappelen - zetmeelgewassen - hordeum vulgare - gerst - triticum aestivum - tarwe - mineralen - concentraten - stikstofrespons - solanum tuberosum - potatoes - starch crops - hordeum vulgare - barley - triticum aestivum - wheat - minerals - concentrates - nitrogen response
    Het in 2009 gestarte onderzoek met MC (Mineralenconcentraat) is in 2010 op vergelijkbare wijze voortgezet. In de verschillende proeven met zetmeelaardappelen op dalgrond, zomergerst op zandgrond en wintertarwe op zware klei was gedurende het groeiseizoen een duidelijke stikstofwerking zichtbaar. In de proeven was de stikstofwerking van MC praktisch 100 % en waren de resultaten van de verschillende beoordelingen en de opbrengst en kwaliteit vergelijkbaar met de vergelijkbare stikstofhoeveelheden op basis van KAS. Oppervlakkige toediening, uitgevoerd bij de proeven in zomergerst en wintertarwe, had een negatieve invloed op de stikstofwerking. Op basis van de verschillende proeven van 2009 en 2010 zal de werkingscoëfficiënt op uniforme worden berekend. Het veldonderzoek wordt in 2011 op vergelijkbare wijze voortgezet
    Bestrijding van Fusarium in wintertarwe
    Spits, H.G. ; Jansen, D. ; Schepers, H.T.A.M. - \ 2010
    Lelystad : Praktijkonderzoek Plant & Omgeving, Sector AGV
    triticum aestivum - tarwe - plantenziekteverwekkende schimmels - fusarium culmorum - gibberella avenacea - gibberella zeae - plantenziektebestrijding - beslissingsmodellen - beslissingsondersteunende systemen - wintertarwe - akkerbouw - triticum aestivum - wheat - plant pathogenic fungi - fusarium culmorum - gibberella avenacea - gibberella zeae - plant disease control - decision models - decision support systems - winter wheat - arable farming
    Bestrijding van Fusarium is een complexe aangelegenheid. Het voorkomen van aantasting door Fusarium (en de vorming van het mycotoxine DON) moet een samenspel zijn van maatregelen. Te denken valt aan: ruime vruchtwisseling, een kerende grondbewerking, teelt van resistente rassen en een fungicide bespuiting tijdens de bloei. Fungiciden zijn beperkt werkzaam tegen deze schimmels; ook als ze op het juiste tijdstip worden gespoten. Echter, een bespuiting met fungicide is niet altijd nodig/zinvol, daar de belangrijkste factor voor aantasting het weer is. Is de periode vóór en tijdens de bloei niet gunstig dan zal de aantasting door Fusarium niet groot zijn. Het voorspellen van deze omstandigheden is lastig. Hierbij kunnen beslissingsondersteunde systemen zeer behulpzaam zijn. In dit project is op basis van (internationale) literatuur en proefgegevens een opzet gemaakt voor een beslissingondersteunend systeem voor Fusarium in wintertarwe en getest in veldproeven en in praktijkpercelen.
    Fusarium in wintertarwe (2007 en 2008). Inventarisatie, identificatie en kwantificering van nieuwe soorten
    Waalwijk, C. ; Köhl, J. ; Vries, P.M. de; Lee, T. van der - \ 2009
    Wageningen : Plant Research International (Rapport / Plant Research International 272)
    triticum aestivum - tarwe - schimmelziekten - fusarium - identificatie - mycotoxinen - eu regelingen - gezondheid - diergezondheid - nederland - duitsland - frankrijk - triticum aestivum - wheat - fungal diseases - fusarium - identification - mycotoxins - eu regulations - health - animal health - netherlands - germany - france
    Fusarium-aarziekte of kalfjesrood is vanwege de opbrengstderving een probleem in granen. Feitelijk wordt Fusarium-aarziekte veroorzaakt door een complex van schimmels dat in steeds andere samenstelling het gewas belaagt. Van recenter datum is de zorg over het vermogen van verschillende Fusariumsoorten om mycotoxinen te produceren. Deze secundaire metabolieten vormen reeds in geringe hoeveelheden een bedreiging voor de gezondheid van mens en dier. De Europese Commissie heeft daarom actielimieten vastgesteld voor een aantal mycotoxinen, terwij; voor enkele andere deze regels aanstaande zijn (Verordening (EG) nr. 1881/2006; Verordening (EG) nr. 1126/2007). Vanwege de steeds strengere normen voor diverse mycotoxinen in voedsel en voer zijn bji ongunstige teeltcondities partijen niet vermarktbaar en kan een tekort aan het te verwerken graanproduct ontstaan
    Tarwe na tarwe?
    Lamers, J.G. - \ 2008 2008 (2008)23 okt.
    tarwe - akkerbouw - cultuurmethoden - triticum aestivum - wheat - arable farming - cultural methods - triticum aestivum
    Tarwe na tarwe is alleen goed mogelijk op die percelen waar meer dan 50% tarwe, gerst of rogge in het bouwplan zit. Met verwijzingen naar meer informatie over dit onderwerp.
    Productivity and resource use in cotton and wheat relay intercropping
    Zhang, L. - \ 2007
    Wageningen University. Promotor(en): Huub Spiertz, co-promotor(en): Wopke van der Werf. - [S.l.] : S.n. - ISBN 9789085047599 - 198
    gossypium - triticum aestivum - teeltsystemen - estafetteteelt (relay cropping) - tussenteelt - gebruiksefficiëntie - stikstof - plant-water relaties - simulatiemodellen - china - gossypium - triticum aestivum - cropping systems - relay cropping - intercropping - use efficiency - nitrogen - plant water relations - simulation models - china
    Keywords: Grain yield; lint yield; phenological delay; light use; nitrogen use; resource use efficiency; modelling; profitability; water productivity. From the early 1980s onwards, farmers in the Yellow River cotton producing region intercropped cotton and winter wheat; currently on more than 60% of the total cotton acreage. The driving force for intercropping was the need to increase household income by producing a cash crop, while maintaining the production of a major staple food. This study aims at analyzing the productivity and resource use of cotton-wheat relay intercropping systems. Wheat is sown in strips with interspersed bare soil in October and harvested in June of the next year, while cotton is sown in the interspersed space in the wheat crop in April and harvested before the next wheat sowing in October. Crop growth, phenology, productivity, quality, resource use efficiencies and profitability of mono- and intercrops were studied at the plant, field and system levels. The measurements were carried out in field experiments during three consecutive years with monocultures of wheat and cotton and four intercropping designs differing in strip and path width as well as number of rows per strip. The intercrop systems were identified by the number of rows per strip of wheat and cotton, as 3:1, 3:2, 4:2 and 6:2, respectively. All intercropping systems showed an advantage in land productivity compared to growing of monocrops. The fiber quality of cotton was not affected by intercropping. The land equivalence ratio was 1.39 in the 3:1, 3:2 and 4:2 systems, and significantly lower, 1.28, in the 6:2 system. All systems thus provide a substantial land use advantage. Resource (light and nitrogen) use efficiencies of intercropped wheat were similar to the monoculture; however, the resource capture decreased, because part of the land space was assigned to cotton. For intercropped cotton, light use efficiencies were similar to the monoculture; the amount of light intercepted decreased due to a delay in development and growth during the seedling stage and by the extent of canopy closure after the wheat harvest. The relative nitrogen yield total of intercrops was higher than the land equivalence ratio. Nitrogen use efficiency of cotton was decreased. The analysis of the N balance sheet showed that in the intercropping systems N was considerably more prone to losses than in the sole cotton. Conventional N-management in intercrops results in high N-surpluses that pose an environmental risk. Water productivity, both of wheat and cotton, was lower for the intercrops than for monocultures. The lower WP in the intercropping systems compared to the sole crop is a concern for the sustainability of these systems; water productivity needs to be enhanced. A simple mechanistic model for cotton (SUCROS-Cotton) was developed to explore the prospects to optimize intercropping systems. This model simulates cotton development as well for intercrops as for monoculture. The findings suggest that the productivity and resource use efficiencies of cotton-wheat intercropping can be improved by modifying the conventional management practices and by system optimization. It is concluded that the intercropping systems increase farmers’ income under a wide range of wheat and cotton prices.
    Heat-shock effects on photosynthesis and sink-source dynamics in wheat (Triticum aestivum L.)
    Schapendonk, A.H.C.M. ; Xu, H.Y. ; Putten, P.E.L. van der; Spiertz, J.H.J. - \ 2007
    NJAS Wageningen Journal of Life Sciences 55 (2007)1. - ISSN 1573-5214 - p. 37 - 54.
    hittetolerantie - weerstand van huidmondjes - fluorescentie - veroudering - tarwe - triticum aestivum - genotypische variatie - fotosynthese - gewasopbrengst - heat tolerance - stomatal resistance - fluorescence - senescence - wheat - triticum aestivum - genetic variance - photosynthesis - crop yield - high-temperature stress - grain-growth - irrigated environment - yield - cereals - quality - traits - productivity - limitations - maturation
    To assess the mechanisms causing genotypic differences in heat tolerance of wheat (Triticum aestivum L.), physiological responses to a heat shock in a vegetative (`end of tillering¿) or a reproductive (`early grain filling¿) stage were studied. Three cultivars ¿ Lavett, Ciano-79 and Attila ¿ differing in adaptation to heat were grown in a glasshouse at a day/night temperature regime of 15/10 °C and a 12-h daylength from sowing to `end of tillering¿ and next at two day/night regimes of 25/20 and 18/13 °C under natural daylength. The heat-shock treatment consisted of an exposure of plants to temperatures raised gradually over a time-span of 12 hours to above 30 °C with a maximum of 38 °C during three hours at midday for three days either at the `end of tillering¿ or at `grain filling¿. A heat shock at the `end of tillering¿ strongly reduced the rate of leaf photosynthesis. A similar heat shock during `grain filling¿ decreased both rate of photosynthesis (source) and grain growth (sink). The rate of leaf photosynthesis was decreased by 40 to 70%, depending on cultivar and developmental stage. Photosynthesis fully recovered within 4 days after the heat-shock treatment was ended. The effects of the heat shock on biomass yield were more pronounced for treatments at `early grain filling¿ than at `end of tillering¿. However, the impact of a 3-day heat shock on biomass yield was less than the effects of the pre- and post-treatment growing temperature.
    Signaling pathways involved in pathogenicity and development of the fungal wheat pathogen Mycosphaerella graminicola
    Mehrabi, R. - \ 2006
    Wageningen University. Promotor(en): Pierre de Wit, co-promotor(en): Gert Kema; M.A. de Waard. - [S.l.] : S.n. - ISBN 9789085044093 - 176
    mycosphaerella graminicola - signaaltransductie - pathogeniteit - genetische analyse - regulator-genen - genexpressie - triticum aestivum - tarwe - septoria - triticum aestivum - wheat - mycosphaerella graminicola - septoria - signal transduction - pathogenicity - genetic analysis - regulatory genes - gene expression
    Mycosphaerella graminicola(Fuckel) J. Schröt is the causal agent of septoria tritici leaf blotch, which is the major foliar wheat disease in most temperate areas.Direct losses and the cost of control strategies contribute to the huge economical importance of this disease. M. graminicolais a dimorphic fungal pathogen that grows in yeast-like or filamentous fashion depending on the environmental conditions. Filamentation is required for pathogenicity of this non-appressorium forming pathogen, which has a hemibiotrophic lifestyle characterized by an initial biotrophic phase (about 10 days) that is followed by a necrotrophic phase during which numerous asexual and eventually sexual fructifications are produced. 

    This thesis is part of an ongoing research program aimed at understanding the genetic and molecular control of pathogenicity. The research was initiated with the generation of EST and genomic sequence data of the pathogen. This thesis describes the functional analyses of 10 genes encoding proteins involved in signal transduction pathways operating in M. graminicola when grown in vitro and in planta . Chapter one gives an introduction to the research topic. In chapter two, the role of the mitogen-activated protein kinase (MAPK)-encoding gene, MgFus3 , the ortholog of Fus3 controlling mating in Saccharomyces cerevisiae , is described. Disruption of this gene prevented melanization of mycelia and formation of pycnidia in vitro. MgFus3 mutants are non-pathogenic. This is ascribed to impaired penetration of stomata, possibly due to inability of the mutants to recognize stomata. 

    Chapter threedescribes the MAPK-encoding gene, MgSlt2 . This is the ortholog of Slt2 in S. cerevisiae that regulates cell wall biosynthesis. In M. graminicola , MgSlt2 plays a role in cell wall integrity since MgSlt2 mutants were affected in polarized growth and showedprogressive autolysis during aging. They were also hypersensitive to glucanase and several fungicides and did not produce aerial mycelium or melanin on potato dextrose agar (PDA). Pathogenicity assays revealed that virulence of MgSlt2 mutants was severely reduced. Electron microscopy and histopathological analyses showed that MgSlt2 mutants penetrated wheat stomata regularly, but were unable to establish invasive growth and did not produce asexual fructifications. BecauseMgSlt2 is involved in cell wall integrity, MgSlt2 mutants are probably more sensitive to hitherto unknown plant defense compounds, which might explain the compromised colonization of mesophyll tissue.

    Chapter fourdescribes characterization of MAPK-encoding gene, MgHog1 , and the p21-activated kinase (PAK)-encoding gene, MgSte20 .MgHog1 mutants were osmosensitive, highly resistant to the fungicides fludioxonil, fenpiclonil and iprodione did not melanize and were unable to switch from yeast-like to filamentous growth. As a result of the impaired dimorphic switch, MgHog1 mutants were unable to establish infectious germ tubes and therefore failed to penetrate wheat leaves. This demonstrates that dimorphic transition is a key factor in pathogenicity of M. graminicola. Phenotypes of MgSte20 mutants were identical to the wild-type isolate in all tested conditions.

    Fructification of M. graminicola is a complex process requiring differentiation of the infectious hyphae in the substomatal cavities during the latter stages of infection. In Chapter five, functional analyses of genes encoding the catalytic ( MgTpk2 ) and the regulatory ( MgBcy1 ) subunits of PKA showed that these genes are essential for asexual fructification. MgTpk2 and MgBcy1 mutants were able to germinate, penetrate and colonize mesophyll tissue, but were unable to differentiate pycnidia. Our data provide evidence that the cAMP pathway regulates filamentation through MgTpk2 and MgBcy1 . Disruption of MgTpk2 impaired filamentation. In addition, the MgTpk2 mutants became melanized faster and secreted a dark-brown pigment into yeast glucose broth medium (YGB), whereas MgBcy1 mutants showed delayed melanization on PDA and were osmosensitive. Overall, the divergent functions of the regulatory and the catalytic subunits of PKA indicate that proper regulation of PKA activity is required for various physiological processes including differentiation, filamentation, osmoregulation and melanization. 

    Chapter sixdescribes the characterization of three Gaprotein-encoding genes ( MgGpa1, MgGpa2 and MgGpa3 ) and one Gbprotein-encoding gene ( MgGpb1 ) in M. graminicola . Phylogenetic comparisons and sequence analyses of Gaproteins of M. graminicola revealed that MgGPA1 and MgGPA3 can be categorized as homologs of the mammalian Gaiand Gasfamilies, respectively, whereas MgGPA2 is unrelated to mammalian Gaproteins. MgGpa1 , MgGpa3 and MgGpb1 mutants exhibited different phenotypes when grown on PDA at 20 °C that were not observed when the temperature was raised to 28 °C. Melanization did not occur in the MgGpa1 and MgGpb1 mutants, and the former formed fluffy mycelia in YGB and hardly produced spores. MgGpb1 mutants showed a nested type of growth on PDA that resulted from hampered filamentation, numerous cell fusions and increased anastomosis. Therefore, we concluded that MgGpa1 negatively regulates filamentation, which is positively regulated by MgGpa3 and MgGpb1 . Interestingly, unlike the response of the MgGpa1 mutants, exogenous cAMP restored the phenotype of the wild-type in the MgGpb1 and MgGpa3 mutants, indicating a stimulating function for MgGPB1 and MgGPA3 and an inhibitory function for MgGPA1 in the regulation of the cAMP pathway. Pathogenicity assays revealed that MgGpa1 , MgGpa3 and MgGpb1 are required for virulence of M. graminicola whereas MgGpa2 is dispensable.

    Finally, in chapterseven the results described in this thesis are discussed in a broader perspective. The roles of the various kinases as well as G proteins during development in vitro and in planta for fungal pathogenesis in general and for M. graminicola in particular are highlighted. Also, the potential of M. graminicola as a new model fungus is addressed. The power of comparative genomics can be fully exploited once the genomic sequence of the fungus is available.
    Aspects of sexual reproduction in Mycosphaerella species on wheat and barley : genetic studies on specificity, mapping, and fungicide resistance
    Ware, S.B. - \ 2006
    Wageningen University. Promotor(en): Pierre de Wit, co-promotor(en): Gert Kema; M.A. de Waard. - [S.l.] : S.n. - ISBN 9789085045274 - 190
    triticum aestivum - tarwe - hordeum vulgare - gerst - mycosphaerella graminicola - geslachtelijke voortplanting - plantenziekteverwekkende schimmels - septoria - gastheerspecificiteit - genetische kartering - resistentie tegen pesticiden - virulentie - pathogeniteit - ziekteresistentie - overleving - triticum aestivum - wheat - hordeum vulgare - barley - mycosphaerella graminicola - septoria - sexual reproduction - survival - plant pathogenic fungi - host specificity - virulence - pathogenicity - genetic mapping - pesticide resistance - disease resistance

    Mycosphaerella species are haploid ascomycetes that cause major economic losses in crops that include cereals, citrus fruits, and bananas, among others. Two organisms in this genus are Mycosphaerella graminicola (Fuckel) .I. Schröt (anamorph Sepioria tritici) and Septoriapasserinii. M graminicola is the causal agent of septoria tritici blotch of both bread wheat and durum wheat species, and S. passerinii causes septoria speck!ed 1eaf blotch of barley. M. graminicola is a heterothaliic fungus with a very active sexual cycle, while no sexual cycle has been reported for S. passerinii.

    This thesis inciudes studies on mating and genetics of both M. graminicola and S. passerinii. Chapter 1 gives an introduction to these pathogens and an overview of the research topics. In Chapter 2. we studied the possibility of in planta generation of sexual progeny of the fungal wheat pathogen M graminicola when one of the parents was avirulent on a resistant host. We found that avirulent isolates are able to survive and even increase in biomass after inoculation onto resistant wheat cultivars and can complete sexual cycles on resistant cultivars to yield viable ascospores as long as the other parent is virulent. To our knowledge, this is the first time such a phenomenon has been described, and the possibility to generate such crosses opened the door for studies in Chapters 3 and 4.

    Chapter 3 describes the construction of two high-density genetic linkage maps of M graminicola using Diversity Arrays Technology (DArT) and the integration of these into a core map with common markers due to a common parental isolate. One of the maps was constructed based on segregations of progeny of two bread wheat-derived isolates, IPO323 and IPO94269, and the other was constructed from segregations of progeny of IPO323 and the durum wheat-derived isolate IPO95052. In total, 1,144 markers made up the integrated core map. Analyses from this study revealed that progeny had translocations, diploid and partial diploid linkage groups, and loss of entire linkage groups.

    Although M. graminicola causes disease on both bread wheat and durum wheat, isolates within the population show clear distinctions in either virulence on bread wheat or on durum wheat (host specificity)- In Chapter 4, we studied the genetic basis of host specificity in M. graminicola using 163 progeny from crosses between the Dutch bread wheat-derived 1PO323 and the Algerian durum wheat-derived TPO95052. Phenotyping of progeny was performed on a set of seven differential cultivars, and progeny crossed on either bread wheat or durum wheat could infect cultivars of bread wheat, durum wheat, both, or neither. These results were used to map nine quantitative trait loci (QTLs) on seven linkage groups in the high-densiry genetic linkage map from Chapter 3. One of these loci was previously mapped for cultivar specificity of IPO323in bread wheat, and the same locus was now mapped for host specificity of IPO323 to durum wheat. Our results show that the reported host specificity is probably the result of combinations of a number of independently inherited avirulence factors.

    In addition to avirulence genes, fungi can inherit other traits for survival. One such heritable trait is a point mutation in the mitochondrial genome that conveys resistance to strobilurin fungicides. Chapter 5 describes a study on the inheritance of strobilurin resistance. Resistant and sensitive isolates of M. graminicola were crossed on wheat seedlings that were both untreated and preventively treated with various concentrations of azoxystrobin (Amistar™), and progeny were analyzed to determine the rate of inheritance of the aforementioned mutation. Preventive rates from 3.125-200% Amistar™ resulted in completely resistant progeny populations despite the fact that the segregation of nuclear genes confirmed regular meiotic behavior. We conclude that sensitive isolates overcome the disruption of mitochondrial respiration and participate in sexual reproduction even under high fungicide pressure and that fungicide stress induces or results in preferential mating in M. graminicola.

    The barley pathogen S. passerinii clusters closely to M. graminicola in phylogenetic studies based on ITS sequences, and a high degree of genetic variation among isolates is found in nature. However, no teleomorph has been reported for this S. passerinii, and hence, it was considered to be asexual. Nevertheless, mating type idiomorphs were recently detected and isolated. In Chapter 6, we studied the possibility of a Mycosphaerella teleomorph associated with S. passerinii. Isolates with opposite mating types were co-inoculated onto barley cultivars, and leaves were monitored for the discharge of ascospores. Characterization of a segregating population by both molecular and phenotypic analyses confirmed that we successfully generated the hitherto unknown Mycosphaerella teleomorph of S. passerinii.

    Finally, the results of this thesis are discussed in a broader perspective in Chapter 7 in relation to epidemiology, co-evolution, and durability of resistance in the wheat-M. graminicola pathosystem. The proven ability of avirulent isolates of M. graminicola to generate sexual progeny on resistant cultivars represents a new dynamic in population genetics that has not'previously been considered in epidemiology. Resu!ts from this thesis emphasize the complex ways in which the sexual cycle contributes to the overall success of M. graminicola on wheat.

    Tillering in spring wheat : a 3D virtual plant modelling study
    Evers, J.B. - \ 2006
    Wageningen University. Promotor(en): Paul Struik, co-promotor(en): Jan Vos; B. Andrieu. - Wageningen : s.n. - ISBN 9789085043775 - 159
    triticum aestivum - tarwe - plantenontwikkeling - uitstoeling - plantenmorfologie - modellen - licht - verrood licht - lichtrelaties - optische eigenschappen - bladoppervlakte-index - grondbedekking - triticum aestivum - wheat - plant development - tillering - plant morphology - models - light - far red light - light relations - optical properties - leaf area index - ground cover - cum laude
    cum laude graduation (with distinction)
    Patrel en Anthus nieuwe wintertarwerassen
    Brink, L. van den; Paauw, J.G.M. - \ 2005
    Boerderij/Akkerbouw 91 (2005)19. - ISSN 0169-0116 - p. 16 - 17.
    wintertarwe - tarwe - triticum aestivum - rassen (planten) - rassenproeven - kwaliteit - gewasopbrengst - ziekteresistentie - winter wheat - wheat - triticum aestivum - varieties - variety trials - quality - crop yield - disease resistance
    Wintertarwe is in najaar 2004 onder tamelijk goede omstandigheden gezaaid. Afgelopen winter vroor het niet genoeg om de rassen op winterhardheid te beoordelen. Conclusies uit het jaarlijkse rassenonderzoek
    Zomertarwerassen voor de bioteelt
    Osman, A.M. ; Brink, L. van den; Paauw, J.G.M. - \ 2005
    Boerderij/Akkerbouw 90 (2005)1. - ISSN 0169-0116 - p. 12 - 13.
    triticum aestivum - tarwe - rassen (planten) - cultivars - biologische landbouw - opbrengsten - eigenschappen - bakkwaliteit - triticum aestivum - wheat - varieties - cultivars - organic farming - yields - properties - baking quality
    De Rassenlijst heeft nu voor het eerst een rubriek biologische zomertarwe. Hierin zijn rassen opgenomen die meer dan 3 jaar onder biologische teeltomstandigheden onderzocht zijn
    Changes in Nuclear Structure During Wheat Endosperm Development
    Wegel, E. - \ 2005
    Wageningen University. Promotor(en): Maarten Koornneef, co-promotor(en): Hans de Jong; P.J. Shaw. - - 75
    triticum aestivum - endosperm - tarwe - celkernen - celstructuur - plantenontwikkeling - cytologie - modellen - chromatine - cytogenetica - dna - triticum aestivum - endosperm - wheat - nuclei - cell structure - plant development - cytology - models - chromatin - cytogenetics - dna
    This thesis is an investigation into the structure of wheat endosperm nuclei starting with nuclear divisions and migration during syncytium formation followed by the development of nuclear shape and positioning of chromosome territories and ending with changes in subchromosomal structure during the activation of a transgene locus.

    At the level of the whole endosperm we have developed a method for modelling in 3D the formation of the syncytium that characterises early endosperm development. After the initial nuclear division of the first endosperm nucleus three groups of nuclei form in the original central cell: a stem-like group of nuclei close to the zygote and connected to a single layer of nuclei in the dorsal periphery and another, unconnected single layer in the ventral periphery. By two days post anthesis (dpa) both the ventral and dorsal groups of nuclei have developed into plates of nuclei. The dorsal plate then merges with the ventral plate through synchronous nuclear divisions. By 4 dpa the entire periphery of the central cell is surrounded by a layer of nuclei and the syncytium is complete.

    Wheat endosperm is initially triploid and during its development a percentage of the nuclei increase their DNA-content to 6C and 12C. 3D modelling of nuclei with DNA contents of 3C, 6C and 12C allowed us to visualise progressive changes in nuclear shape and chromosome positioning. With increasing C content, nuclear volumes increase predominantly in two directions, thereby changing the shape of the nuclei into a disc-like structure. Wheat chromosomes in interphase nuclei have a typical Rabl configuration with centromeres and telomeres arranged at opposite poles. The majority of centromeres and telomeres are found at or close to the nuclear membrane, some also in the middle of the nucleus and in rare instances a telomere can be observed at the centromere pole and vice versa. This means that centromeres and telomeres are not or only transiently anchored to the nuclear membrane. Both centromeres and telomeres show a degree of non-homologous associations, which for centromeres remains constant through increases in ploidy, while telomere associations increase with higher C-values.

    The wheat line we used has a 1RS / 1BS ( Secale cereale ) chromosome arm substitution. Fluorescence in situ hybridisation detection of the rye arm substitution with total genomic DNA as probe revealed the following: during endosperm development chromosomes are able to change their position in all three dimensions and as the C-content increases in nuclei that have stopped dividing chromosome arrangements become progressively distorted. The vast majority of 12 C nuclei show six rye chromosome arms, but a few show three groups of associated rye chromosome arms. This means that during endosperm development wheat nuclei increase their ploidy through both polyploidisation and polytenisation.

    The final part analyses the chromatin structure of active and inactive gene loci. The High Molecular Weight (HMW) glutenin genes in wheat are developmentally activated in the endosperm at about 8 dpa. I have investigated the physical changes that occur in these genes in two transgenic lines containing about 20 and 50 copies respectively of the HMW glutenin genes together with their promoters. Fluorescence in situ hybridisation (FISH) and confocal imaging data show that in non-expressing tissue each transgene locus consists of one or two highly condensed sites that decondense into many foci upon activation of transcription in endosperm nuclei. Initiation of transcription can precede decondensation but not vice versa. In one of the lines, cytoplasmic transcript levels are high after onset of transcription, but disappear by 14 dpa, while siRNAs, indicative of post-transcriptional gene silencing (PTGS), are detected at this stage. However, the transcript levels remain high at the transcription sites, the great majority of the transgene copies are transcriptionally active and transcriptional activity in the nucleus ceases only with cell death at the end of endosperm development.
    The Russian wheat aphid (Diuraphis noxia Mord.): damage on Kenyan wheat (Triticum aestivum L.) varieties and possible control through resistance breeding
    Kiplagat, O. - \ 2005
    Wageningen University. Promotor(en): P. Stam, co-promotor(en): I. Bos; H.A. Rheenen. - Wageningen : S.n. - ISBN 9789085041757 - 141
    triticum aestivum - tarwe - insectenplagen - diuraphis noxia - rassen (planten) - plaagresistentie - plantenveredeling - triticum aestivum - wheat - insect pests - diuraphis noxia - varieties - pest resistance - plant breeding
    We studied the effect of the Russian wheat aphid (RW A) (Diuraphis noxia) infestation on seedlings and adult plants of eight Kenyan wheat (Triticum aestivum L.) varieties. The Kenyan varieties were 91B33, Fahari, Kwale, Mbuni, Chiriku, Kongoni, Nyangumi and Mbega. Two RW A resistant wheats, Halt and PI 294994, were also tested against Kenyan isolates of the aphid. All the Kenyan varieties were susceptible to RW A when compared with the resistant line PI 294994. Halt, which is a resistant variety developed in the USA, was susceptible to Kenyan isolates of RW A. This indicates that the Kenyan RW A isolates are different from the USA ones. In seedlings, the RW A damage was expressed mainly as leaf chlorosis and leaf rolling, with damage scores increasing with time. Differences among the Kenyan varieties in the extent of leaf chlorosis were observed. The most devastating effect of RW A infestation of adult plants of the Kenyan varieties was the reduction in seed set. The tight rolling of flag leaves caused by the aphid delayed ear emergence, leading to floret sterility. Infestation also reduced the quality of the seeds produced, as shown by increased rate of seed deterioration under accelerated ageing conditions, and reduced seedling vigour. The effect of infestation on seed quality was more pronounced under dry conditions. Morphological and genetic variations within PI 294994 were identified. The PI 294994 plants tested could be separated into three distinct groups, all of which had equally high resistance to Kenyan RW A. One PI 294994 derived line, designated P3, was discovered to require no vernalization and therefore to be suitable for use in a Kenyan breeding programme. Segregation in the Fz populations indicated that resistance in two PI 294994 derived lines (PI and P2) was controlled by two genes (one dominant and one recessive). For P3, the results were inconclusive since in one Fz population the segregation indicated that the resistance was controlled by one dominant gene, whereas in another population the segregation indicated that resistance was due to one dominant and one recessive gene. Work to identify molecular markers linked to RW A resistance genees) in P3 was initiated.
    Granen bron van onkruidvervuiling? : onkruiden in graan verdienen meer aandacht
    Weide, R.Y. van der; Lotz, B. ; Groeneveld, R. - \ 2004 2004 (2004)15 juli.
    biologische landbouw - cultuurmethoden - duurzaamheid (sustainability) - triticum aestivum - tarwe - onkruiden - onkruidbestrijding - gewasbescherming - wintertarwe - organic farming - cultural methods - sustainability - triticum aestivum - wheat - weeds - weed control - plant protection - winter wheat
    Op biologische bedrijven werden in tarwe vaak meer onkruiden geteld dan in de andere gewassen. Zaadproductie van onkruid in wintertarwe kan wel oplopen tot duizend zaden per plant. Onderzoekers van PPO en PRI benadrukken het gevaar van onopvallende veronkruiding vanuit het graangewas en de mogelijkheden om deze veronkruiding tegen te gaan
    Zeven teelten in praktijk : teelthandleidingen voor biologisch geteelde gewassen
    Sukkel, W. ; Leeuwen, W.K. van; Balen, D.J.M. van; Holwerda, J. - \ 2004
    Lelystad : Praktijkonderzoek Plant & Omgeving B.V. (PPO 321) - 94
    solanum tuberosum - aardappelen - triticum aestivum - tarwe - lactuca sativa - slasoorten - daucus carota - penen - allium porrum - preien - brassica oleracea var. capitata - koolsoorten - brassica oleracea var. gemmifera - spruitjes - kostenanalyse - biologische landbouw - landbouwplantenteelt - akkerbouw - vollegrondsteelt - teelthandleidingen - vollegrondsgroenten - cultuurmethoden - nederland - solanum tuberosum - potatoes - triticum aestivum - wheat - lactuca sativa - lettuces - daucus carota - carrots - allium porrum - leeks - brassica oleracea var. capitata - cabbages - brassica oleracea var. gemmifera - brussels sprouts - cost analysis - organic farming - crop husbandry - arable farming - outdoor cropping - cultivation manuals - field vegetables - cultural methods - netherlands
    Teelthandleidingen voor biologisch geteelde consumptieaardappelen, granen, ijsbergsla, peen, prei, sluitkool en spruitkool. Het laatste hoofdstuk van het boek bestaat uit saldoberekeningen voor pootaardappel uit kleigebieden, vroege aardappelen, consumptieaardappelen uit kleigebieden, wintertarwe uit kleigebieden, zomertarwe uit kleigebieden, wintergerst uit kleigebieden, zomergerst uit kleigebieden, haver uit zandgebieden, winterrogge uit zandgebieden, triticale uit zandgebieden, ijssla (zomerteelt), bospeen (zomerteelt), grove peen (b-peen, bewaring), prei (vroeg herfst), witte kool (bewaring), witte kool (industrie), rode kool (bewaring), rode kool (industrie) en spruitkool (middenvroeg).
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