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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    Regio heeft grote invloed op levensvatbaarheid
    Pellikaan, F. ; Ouweltjes, W. ; Windig, J.J. ; Muskens, J. ; Linden, R. van der; Pelt, M.L. van; Calus, M.P.L. - \ 2014
    Veeteelt 31 (2014)14. - ISSN 0168-7565 - p. 10 - 13.
    melkveehouderij - kalveren - levensvatbaarheid - geboorte - vaarzen - grote landbouwbedrijven - bedrijfsgrootte in de landbouw - landbouwstatistieken - bedrijfsvergelijking in de landbouw - invloeden - dairy farming - calves - viability - birth - heifers - large farms - farm size - agricultural statistics - farm comparisons - influences
    Een afname van zes procent levend geboren kalveren van vaarzen tussen 1995 en 2010 was aanleiding voor nieuw sectoronderzoek. Uit de inventarisatie blijkt dat naast bekende factoren als draagtijd en geboorteverloop de regio waar het bedrijf is gehuisvest en het seizoen van afkalven zorgen voor opmerkelijke verschillen in levensvatbaarheid van kalveren.
    FutMon activiteiten in Nederland in 2009 en 2010
    Oldenburger, J. ; Briel, J. van den; Bleeker, A. ; Rietra, R.P.J.J. - \ 2011
    Wageningen : Stichting Probos - 47
    bossen - luchtverontreiniging - levensvatbaarheid - monitoring - nederland - forests - air pollution - viability - monitoring - netherlands
    Dit rapport geeft een overzicht en beschrijving van de activiteiten die in 2009 en 2010 in Nederland zijn uitgevoerd in het kader van het Life+ project Future of Forest Monitoring (FutMon). FutMon is het vervolg op Forest Focus en wordt gecoördineerd door het Johann Heinrich von Thünen Institute in Hamburg en de resultaten worden gebruik door ICP Forest om mogelijke effecten van luchtvervuiling op de vitaliteit van de bossen in Europa te bepalen. ICP Forest is in 1985 opgericht onder het Verdrag voor Grensoverschrijdende Luchtverontreiniging Over Lange Afstand van de UNECE.
    Farm viability in the European Union : assessment of the impact of changes in farm paymen
    Vrolijk, H.C.J. ; Bont, C.J.A.M. de; Blokland, P.W. ; Soboh, R.A.M.E. - \ 2010
    Den Haag : LEI Wageningen UR (Report / LEI : Research area Agriculture & entrepreneurship ) - ISBN 9789086153992 - 67
    landbouwbedrijven - levensvatbaarheid - inkomen van landbouwers - bedrijfsresultaten in de landbouw - subsidies - europese unie - internationale vergelijkingen - farms - viability - farmers' income - farm results - subsidies - european union - international comparisons
    Farm viability is an important issue in the European Union. Farm payments contribute to the viability of farms. This study analyses the differences in farm payments within Europe and analyses the possible impacts of reductions in farm payments in the viability of farms in Europe.
    Keizersnee eikenprocessierups oktober 2009
    Vliet, A.J.H. van - \ 2009
    Wapserveen : Biocontrole
    thaumetopoea processionea - ontwikkelingsstadia - levensvatbaarheid - insectenplagen - rupsen - thaumetopoea processionea - developmental stages - viability - insect pests - caterpillars
    Om te bepalen hoe ver de eikenprocessierupsjes in recent gevonden eipakketjes ontwikkeld zijn is op 3 oktober 2009 een 'keizersnede' uitgevoerd. Het blijkt dat de rupsen al volledig levensvatbaar zijn. Dit kan betekenen dat in warme jaren een tweede generatie van de eikenprocessierupsen mogelijk is. Meer informatie over de ontwikkeling van de eikenprocessierups in Nederland is te vinden op www.natuurbericht.nl of op www.natuurkalender.nl
    Relationship between variation in quality of individual seeds and bulk seed quality in common bean (Phaseolus vulgaris L.) seed lots
    Muasya, R.M. ; Lommen, W.J.M. ; Auma, E.O. ; Struik, P.C. - \ 2006
    NJAS Wageningen Journal of Life Sciences 54 (2006)1. - ISSN 1573-5214 - p. 5 - 16.
    phaseolus vulgaris - peulvruchten - zaadkwaliteit - gewaskwaliteit - kieming - levensvatbaarheid - elektrische geleidbaarheid - statistiek - gemiddelden - statistische analyse - variantie-analyse - correlatieanalyse - phaseolus vulgaris - grain legumes - seed quality - crop quality - germination - viability - electrical conductivity - statistics - averages - statistical analysis - analysis of variance - correlation analysis - pod fractions - maturity - growth - vigor - crops
    The variation in individual seed electrical conductivity (EC) (µS cm¿¹ g¿¹) of 24 seed lots of two common bean cultivars produced at two locations was quantified using the parameters mean ¿ median, standard deviation (SD), and the range 0¿75%. Also coefficient of variation (CV) was tested, which was regarded not to be a good indicator of this type of variation. Bulk seed lot quality of this material with a very high germination percentage was determined using EC and percentage viable seeds. At physiological maturity (PM), a low variation in individual seed EC as quantified by mean ¿ median, SD and the range 0¿75% was associated with good quality as measured by a low bulk EC and a high percentage of viable seeds. At harvest maturity, associations were less clear than at PM, partly because individual seed variation was smaller and also because bulk EC values differed only slightly among most seed lots. The relationships between individual seed variation and bulk quality were different for the two sites, as shown by a statistically significant improvement of the adjusted R² of the regression when site was included in the regression model, but the relationships were not affected by cultivar. No relationship was found between CV for individual seed EC and bulk quality.
    Dormancy, activation and viability of Rhizopus oligosporus sporangiospores
    Thanh, N.V. - \ 2004
    Wageningen University. Promotor(en): Frans Rombouts; [No Value] Tran Phuoc Duong, co-promotor(en): Rob Nout. - Wageningen : s.n. - ISBN 9789085040989 - 114
    rhizopus microsporus - schimmelsporen - sporangia - slaaptoestand - levensvatbaarheid - entstof - zuursels - aminozuren - tempé - rhizopus microsporus - fungal spores - sporangia - dormancy - viability - inoculum - starters - amino acids - tempeh
    Haalbaarheidsonderzoek naar de herkolonisatie van de bever in het bekken van de Schelde en Dijle
    Niewold, F.J.J. - \ 2003
    Wageningen : Alterra (Alterra-rapport 705) - 93
    Castor fiber - habitats - populaties - levensvatbaarheid - haalbaarheidsstudies - geïntroduceerde soorten - monitoring - België - natuurtechniek - schelde - vlaanderen - Castor fiber - habitats - populations - viability - feasibility studies - introduced species - monitoring - Belgium - ecological engineering - river scheldt - flanders
    In opdracht van de afdeling Natuur van de Vlaamse Gemeenschap is een haalbaarheidsonderzoek uitgevoerd naar mogelijkheden voor terugkeer van de bever in het Dijle-Scheldebekken in Vlaanderen. Hier zijn veel natuur(ontwikkelings)gebieden aanwezig en erzijn plannen tot uitbreiding daarvan. De Europese bever Castor fiber, die op de rode lijst van de IUCN als bedreigd staat vermeld, wordt bij natuurontwikkeling een sleutelrol toebedacht en afwezigheid wordt als een gemis ervaren. Er is op de middellange termijn (10-25 jaar) geen zicht op autonome vestiging van bevers vanuit aangrenzende populaties, terwijl het aantal reeds aanwezige dieren te gering is voor een succesvolle uitbreiding. Herstel van de populaties kan alleen gebeuren door herintroductie. Op basis van criteria en voorwaarden voor beverleefgebieden zijn binnen het onderzoeksgebied voldoende leefgebieden aanwezig voor een levensvatbare, samenhangende populatie van minstens 40 beverfamilies (ca. 160 dieren). Er zijn geen grote knelpunten aanwezig, maar de stad Leuven vormt in de Dijlevallei een belangrijke hindernis voor dispergerende bevers. Voor een aantal kleinere problemen worden oplossingen en verbeteringen voorgesteld. Daarnaast worden aanbevelingen gedaan voor uitvoering van herintroductie op basis van ervaringen bij de goed gecontroleerde herintroducties elders. Belangrijke aspecten daarbij zijn de keuze van bronpopulaties en de monitoring.
    Suspensions or biofilms : and other factors that affect disinfectant testing on pathogens
    Luppens, S.B.I. - \ 2002
    Wageningen University. Promotor(en): F.M. Rombouts; T. Abee. - S.l. : S.n. - ISBN 9789058086143 - 102
    voedselmicrobiologie - desinfectie - listeria monocytogenes - staphylococcus aureus - benzalkoniumchloride - biofilms - levensvatbaarheid - food microbiology - disinfection - listeria monocytogenes - staphylococcus aureus - benzalkonium chloride - biofilms - viability

    Disinfectants are very important for the maintenance of proper hygiene in the food industry. In Europe, candidate disinfectants have to be tested on suspended bacteria in so called suspension tests, before they can be approved as disinfectants. In the food industry bacteria usually are attached to surfaces, where they may form biofilms. This mode of growth makes them less susceptible to disinfectants than free-living (suspended) bacteria. Thus, disinfectant testing would greatly profit from a biofilm disinfectant test. The aim of the research described in this thesis was to improve the current European disinfectant tests. To achieve this goal we studied factors that influence the efficacy of disinfectants and alternatives for viability assessment by plate counting. Furthermore, we developed a biofilm disinfectant test.

    The bacteria used in this study were the biofilm forming pathogens Listeria monocytogenes and Staphylococcus aureus . The disinfectants were benzalkonium chloride (BAC), sodium hypochlorite (NaOCl), hydrogen peroxide, and dodecylbenzene sulphonic acid.

    The growth phase of cells grown in suspension had a large influence on their susceptibility to disinfectants. S. aureus cells grown according to the prescription of the European suspension test were phenotypically not the most disinfectant resistant cells of all the cell types tested. Thus, in suspension tests, cells that are grown differently and have a higher phenotypic resistance than the cells currently used for disinfectant testing could be used.

    Fluorescent labeling could be used as a rapid alternative for viability assessment by plate counting, for both free-living cells and biofilm cells, provided the proper fluorescent probes were selected. Thus, for rapid screening of candidate disinfectants, fluorescent probes in combination with flow cytometry may be used instead of plate counting.

    In the biofilm disinfectant test, S. aureus biofilm formation and biofilm disinfection by BAC and NaOCl were reproducible and a genuine biofilm was produced. To improve disinfectant testing in general, the biofilm disinfectant test developed in this thesis can be added to the set of tests that are used currently. The biofilm test will show which currently used or new disinfectants are the most effective against biofilm cells. In the end, this will contribute to food safety and food quality and the control of cleaning costs in the food industry.

    Accounting for water : institutional viability and impacts of market-oriented irrigation interventions in Central Mexico
    Kloezen, W.H. - \ 2002
    Wageningen University. Promotor(en): L.F. Vincent; C. Garcés-Restrepo. - S.l. : S.n. - ISBN 9789058086570 - 291
    irrigatie - bedrijfsvoering - institutionele opbouw - instellingen - levensvatbaarheid - impact - beoordeling - mexico - irrigation - management - institution building - institutions - viability - impact - assessment - mexico

    During the past decade, many countries throughout the world have attempted to improve their generally poor performance record of agency-managed irrigation systems by designing and implementing institutional policy programs. This thesis analyses the institutional viability and the local impact on irrigation performance of two such institutional intervention programs. This is done in the context of the Alto Río Lerma irrigation district (ARLID), a large-scale irrigation system with a command area of more than 112,000 hectares located in the State of Guanajuato, Central Mexico. The central notion that runs through this study is the recognition that new institutional arrangements do not necessarily follow institutional design principles and top-down directives from policy makers and government interveners, but rather are created in a process of local negotiation between water users, farmer leaders and irrigation managers. This requires detailed observations on local practices, strategies and interactions on how users, leaders and managers cope with building and transforming irrigation institutions.

    The first intervention program analyzed in this thesis aims to transfer management responsibilities from the irrigation agency (CNA) to local newly established water user organizations (WUAs) and to make them responsible for cost-recovery. The neoliberal belief behind this program is that greater farmer involvement in irrigation management and financing would eventually lead to a reduction in public investments in irrigated agriculture as well as to higher levels of irrigation performance. The second institutional intervention program that is analyzed in this thesis deals with the introduction of water markets, aiming at re-allocating water use to uses of higher economic value. Both intervention programs clearly embark on the 'less state, more market' approach to design and implement institutional arrangements for more use and cost-effective management of scarce resources such as water and funds. The central theme of this thesis is to study how water users and local water managers deal with the problems that result from these interventions and arrangements.

    In 1992, ARLID was one of the first of Mexican districts were irrigation management transfer (IMT) was introduced. The Mexican IMT program is worldwide considered to be the most successful and ambitious institutional programs in its kind, both because of its scale and the speed with which the policy was designed and implemented. The claims on the successes of these and similar programs are generally ideologically driven, and empirical evidence to support the policy claim that these institutional interventions have achieved these goals remain largely undocumented. This thesis fills some of this empirical void.

    This thesis comprises ten chapters. After the conceptual and methodological introduction in chapter 1, two contextual chapters follow. Chapter 2 introduces the research site, and chapter 3 presents the political economic history and context in which the institutional interventions took place. Chapter 4 to 9 provide the empirical data from the intensive case study in ARLID. Chapter 10 evaluates the main empirical, conceptual and methodological findings and discusses possible implications for policy and research orientations.

    The first chapter provides a review of the conceptual approaches and methodologies used to study the viability of new institutional arrangements in the context of market-oriented reforms. This thesis explores the kind of conditions, processes and mechanisms that help to create viable institutions. These mechanisms do not only refer to institutional and economic relationships, but also to the relationship between institutions, and water scarcity and irrigation technology. In that sense the thesis follows the notion that irrigation technology is a sociotechnical phenomenon, with institutional requirements for use.

    A key concept used for analyzing the viability of new irrigation institutions is accountability. This study shows that four forms of accountability can be separated: operational, financial, political and administrative accountability. Studying these forms of accountability (and the relationship between them ) demonstrates that practices and strategies of decision making in water management are only partly influenced by rational choice and (economic) incentives for utility maximization. They are also influenced by socio-political factors.

    The methodological concern of this thesis is to develop a set of tools and indicators that help to assess the impacts of institutional interventions, both in terms of changes in irrigation performance levels, and in qualitative terms of processes of institutional viability. Two sets of performance indicators are presented. The first set comprises indicators that measure actual performance against set performance targets. The second set compares performance levels over time and across different system levels. The field work for this thesis comprised a wide set of methods and research techniques, ranging from intensive observations of practices and strategies for coping with the new institutional arrangements, to daily measurements of water flows in two selected WUA areas and several canals and fields in the irrigation district. Field research took place during the period from early 1995 to mid-1998.

    Chapter 2 provides background information on the location, history, water availability and layout of ARLID. It also introduces the two main groups of farmers that now jointly are organized in the new WUA: ejidatarios and private growers. It shows how these two groups have historically and economically been separated for almost 70 years. The chapter also provides a brief description of the Cortazar and Salvatierra module areas, their canals and WUAs that were selected for the intensive case study.

    Two important notions form the basis of the chapter 3, in which a detailed description of the historical and political economic context of IMT and water marketing is given. The first notion is that the legitimization for institutional interventions should be viewed in the political economic context of privatizing the Mexican country-side through dramatic constitutional revisions in the way distribution of land and water rights are organized. These reforms and revisions were started in the 1980 as a result of both a political and an economic crisis and were accompanied by wave of programs on the liberalization, decentralization and technocratization of the economy. Institutional intervention programs like the Mexican IMT program do not come on their own, but are preceded, accompanied and followed by other intervention programs that share the same neoliberal legitimization for restructuring the political and economic control over resources. The second notion is that to achieve the economic goals of these neolibral programs, the Salinas and subsequent administrations needed intervention policies such as IMT and water marketing as these would help to recover costs from the users. However, to improve greater involvement of farmers in water management, neoliberal programs are not a necessity.

    Chapter 4 shows how IMT and water markets were implemented, both at the national level and in ARLID. The IMT program is a typical example of institutional engineering, comprising detailed prescriptions on institutional design and a top-down approach for implementing these designs. Yet, farmers and local managers do not fully disregard these proposed arrangements. Rather than using them as prescriptive dictates, the new principles and arrangements served as a strategic starting point for the WUAs for negotiating irrigation fee levels, water marketing, mode of user representation, maintenance programs, and redistribution of O&M responsibilities between the WUAs and CNA. Local recipients have partly adopted and accommodated the new institutional arrangements. The IMT program allowed local irrigation managers, new leaders of WUAs and farmers to jointly create room and institutional flexibility to alter the proposed arrangements. This was made possible mainly because from the initial stage of implementation, CNA officials in ARLID have shown to users that they are credible and willing to share knowledge and information in a transparent way. Credibility, transparency, institutional flexibility and probity were among the most important factors to explain how operational accountability from CNA to WUAs, and from WUAs to water users, was earned in a continuous process of negotiating institutional arrangements. Furthermore, given the wider set of market-oriented reforms and constitutional revisions that farmers had become familiar with, they realized that they could hardly resist IMT.

    Chapter 5 provides a detailed analysis of practices, results and operational accountability for local water management. It demonstrates that official post-transfer arrangements for O&M in ARLID do not always reflect actual irrigation practices. As result, outputs of these practices in terms of relative water supply and land and water productivity remained unchanged after IMT. The main reason for this is the conflict in forms of accountability, which could not be resolved under the new institutional arrangements. Rather than adhering to new principles of using water as an economic good, farmers and local managers adhered to pre-IMT arrangements and practices of distributing water. Daily measurements of water flows and observation of irrigation practices revealed that ditch tenders (who are now employed by the WUAs) generally report planned water deliveries rather than actually supplied volumes. In that sense, they continued the practice of being administratively accountable to both users and CNA. This runs counter to the idea of encouraging efficient water use through water pricing and cost-recovery and hence being both financially and operationally accountable. Comparison of water use per hectare or per m 3of water across the 11 module areas in ARLID, shows that although water is the limiting factor in ARLID, the irrigation management strategy chosen by farmers is to maximize returns per hectare rather than increasing returns per m 3of water. As a result, water deliveries per hectare of irrigated land are generally very high. The chapter also provides some evidence that existing irrigation technology and water management regimes do not always match with the institutional capacity of the new WUAs to operate the system. The chapter also explores some ideas of approaching issues of relative water scarcity in the context of conjunctive use and in a wider setting of the entire water basin.

    Chapter 6 gives a detailed account of how practices, processes and mechanisms of user representation, leadership election and conflict resolution affect political accountability and institutional viability. Detailed analysis of election procedures and processes over a period of two WUA administrations demonstrate that the de jure distribution of farmer representation in the boards and assemblies of WUAs is well organized. However, the de facto control over decision making remains in the hands of a few farmer leaders. These leaders have developed several strategies to reproduce this control. These include political coercion to become re-elected; favoritism in the employment of board members and irrigation staff; corruption; and extending economic and political networks. Particularly in the case of Salvatierra WUA, these strategies have caused that accountability was hardly created. Farmers use two strategies in their trying to counter-balance these mechanisms that weaken accountability. First, they refuse to pay higher fees to signal their dissatisfaction with th WUA's management policies. Second, they call for CNA to resolve disputes over illicit payments and the performance of the WUA leadership.

    In chapter 7 an analysis is made of how mechanisms of financial accountability influence the institutional viability of the post-transfer institutional arrangements for irrigation management. WUAs in ARLID succeeded to boost cost-recovery and to become financially autonomous. In that sense IMT has been very instrumental to achieving the government goal of reducing public investments in irrigation. However, improved cost-recovery and financial autonomy have also helped WUAs to create room for negotiating the reformulation of important institutional arrangements such as the percentages of total revenue that had to be paid to CNA; the level of water pricing; and the conditions and prices for water trading. Financial transparency, the use of computers and external auditing helped the WUAs to become financially accountable to fee payers. Moreover, particularly in the case of Cortazar, leaders showed that they were credible when they started to use revenues from fee payments to dramatically improve canal maintenance. They also showed their willingness to fire irrigation staff that had proved to be corrupt. Yet, financial viability is threatened in two ways. First, as a result of lack of political accountability (such as in the case of Salvatierra). Second, because of the WUAs' total dependency on water availability to generate income.

    In chapter 8 the focus of analysis is shifted towards issues of water marketing. WUAs in ARLID indeed have used the now legal opportunity to market water with other WUAs within the district. However, unlike the common belief among neoliberal advocates of water marketing, trading is not used to price water at opportunity cost levels. Rather, the process of water marketing is used to create solidarity among the WUAs. This solidarity is needed to be able to work together in the new federation of WUAs, which has opted to take over from CNA maintenance responsibilities for the main canal system. Water trading is also used by WUAs to show their members that they are credible in the sense that they will try to deliver water at any time; even when they have to buy it from other WUAs during times of water scarcity. As a result, prices of traded water are generally lower than water prices paid for normal water deliveries during times of sufficient water availability.

    Chapter 9 returns to the official objectives of the IMT program and assesses the program's impact on water management. By applying a set of comparative indicators, it is shown that the result of IMT and water marketing in terms of changes in performance levels are disappointing. With the exception of improvements in cost-recovery and maintenance, there is no evidence that water is used more efficiently or that IMT has resulted in higher levels of productivity per hectare or per m 3of water.

    Chapter 10 first provides a full synthesis of the empirical findings discussed bove. It subsequently revisits some of the conceptual and methodological tools used for this study. This shows that the conceptual notion of social requirements for use of irrigation technology should be further elaborated to institutional requirements for use. An important notion in this respect is that institutional arrangements are a mixture of formal prescriptive arrangements, existing arrangements and newly negotiated arrangements. Existing and new institutions are the result of a continuous process of creating, negotiating, earning, and maintaining accountability. This explains why institutions manifest themselves as being contingent rather than proposed static structures that follow designed institutional principles.

    A revisit of the accountability concept shows that it is useful to separate different forms of accountability. This separation helps to analyze accountability mechanisms that go beyond those related to providing mere O&M services or cost-recovery; it also helps to unravel in what way providers of services are accountable, or not; and it helps to recognize in what way different forms of accountability can compete with each other. This is particularly of interest in the case of joint WUA-agency management of irrigation system, where different organizations can have competing management values and targets, and hence try to be accountable in different ways.

    The methodological revisit on the different sets of impact assessment tools shows that comparative indicators are useful to assess changes over time as a result from institutional interventions. Yet, they are limited in the sense that they exclusively focus on economic and productivity output oriented results. Furthermore, applying these indicators was more time and resource consuming than assumed. The reason for this are the complexity and amount of secondary data needed as well as the difficult process it takes to deconstruct the meaning of these data.

    This study has several implications for market-oriented policies, both in and outside of Mexico. Because of its unique political economic and constitutional context, the 'Mexican IMT model' cannot simply be copied to other countries where similar attempts of planned institutional changes are underway. Particularly the fact that IMT and water marketing in Mexico were supported by political commitment at the highest levels and by dramatic constitutional revisions and other agrarian reforms, explains why the new institutional arrangements for water management could be speedily implemented on such a wide scale. This study also suggests that institutional 'modernization' programs (such as IMT and water marketing) and physical modernization programs in irrigation should be better matched. Although physical improvement programs are often used to sell institutional reforms (and the consequent burden) to water users, they hardly ever are matched in such a sense that the proposed new technology matches with the proposed new institutional arrangements to use this technology.

    Chapter 10 ends with a discussion on why to orient research on institutional interventions in water management to the level of entire water basin rather than irrigation systems. Also, irrespective that universities and international research institutes need to do research in the context of a globalizing world and with globalized research agendas, a plea is made to not shift too frequently to doing extensive, quantitative and comparative studies during a short period of time. Understanding institutional change processes and their impacts at the local level requires intensive and qualitative case studies over longer periods of time. Only in this way collaboration with local research partners can fully develop, resulting in the level of creation of institutional research memory that is needed for this understanding.

    Effecten van vernatting op de groei en vitaliteit van eik, beuk en douglas in Roden, Leende en Gees
    Olsthoorn, A.F.M. ; Tolkamp, G.W. ; Koch, M.J. - \ 2001
    Wageningen : Alterra (Alterra-rapport 276) - 54
    quercus - fagus sylvatica - pseudotsuga menziesii - grondwaterspiegel - grondwaterstand - plant-water relaties - bomen - mortaliteit - levensvatbaarheid - bosschade - nederland - bodemwater - groei - drenthe - beuk - boomvitaliteit - bosbouw - eik - douglasspar - verdroging - vernatting - Brabant - quercus - fagus sylvatica - pseudotsuga menziesii - water table - groundwater level - soil water - growth - plant water relations - trees - mortality - viability - forest damage - netherlands - drenthe
    In het verleden is in grote delen van Nederland verdroging opgetreden. Om de natuurwaarde te herstellen probeert men nu om het water langer in het gebied vast te houden, zodat het grondwater weer op het oorspronkelijke niveau komt. In drie veldlocaties met volwassen bomen is onderzoek gedaan naar de effecten van deze vernatting op de vitaliteit van de bomen. Door de stijging van het grondwater in de afgelopen periode bleek dat inderdaad wortelsterfte is opgetreden, afhankelijk van de vernatting. Dezebleek goed te relateren aan de bovengrondse vitaliteit. Er waren verschillen in reactie te vinden tussen de drie onderzochte boomsoorten. Op gronden die in het verleden diep vergraven zijn, bijvoorbeeld in de werkverschaffing, bleken onnatuurlijke wortelprofielen voor te komen met soms meer dan 50% van de wortels dieper dan 40 cm (wortels < 5mm). Dit levert meer risico's op voor de bomen bij vernatting. Deze vergravenheid komt veel voor in het Nederlandse bos en hiermee dient dus rekening gehouden te worden bij het plannen van vernattingsmaatregelen. Meestal is het aanbevelenswaardig om vernatting in niet te grote stappen uit te voeren en om een ondiep slotenstelsel open te houden om in een nat voorjaar voldoende wortelruimte te houden.
    Fluorescence techniques to detect and to assess viability of plant pathogenic bacteria
    Chitarra, L.G. - \ 2001
    Wageningen University. Promotor(en): F.M. Rombouts; R.W. van den Bulk; T. Abee. - S.l. : S.n. - ISBN 9789058083890 - 101
    clavibacter michiganensis subsp. michiganensis - xanthomonas campestris pv. campestris - plantenziekteverwekkende bacteriën - doorstroomcytometrie - levensvatbaarheid - fluorescentie - technieken - clavibacter michiganensis subsp. michiganensis - xanthomonas campestris pv. campestris - plant pathogenic bacteria - flow cytometry - viability - fluorescence - techniques

    Plant pathogenic bacteria cause major economic losses in commercial crop production worldwide every year. The current methods used to detect and to assess the viability of bacterial pathogens and to test seed lots or plants for contamination are usually based on plate assays or on serological techniques. Plating methods provide information about cell viability, but are generally laborious and time-consuming. Serological techniques, such as immunofluorescence microscopy (IF) and enzyme-linked immunosorbent assay (ELISA), are much faster than most of the plating assays. However, they provide the user only with semi-quantitative information, which for various tests is not satisfactory, and they do not distinguish between viable and non-viable cell. Flow cytometry (FCM) is a rapid, reliable, and sensitive technique that has been successfully applied to detect and to assess the viability of several microorganisms in the field of veterinary science, medicine, and microbiology, and it could be worth exploring in the field of plant pathology. The research described in this thesis focused on the development of a rapid, reliable, and accurate method for the detection and assessment of viability of the seed-borne organisms Xanthomonascampestris pv. campestris (Xcc), the causal agent of black rot on cabbage, and Clavibacter michiganensis subsp. michiganensis (Cmm), the cause of bacterial canker of tomato, by applying fluorescent probes in combination with flow cytometry or spectrofluorometry.

    The viability of Cmm cells was first determined by measuring the intracellular pH (pH in ), as a parameter for viability, applying the fluorescent probe 5(and 6-)-carboxyfluorescein succinimidyl ester (cFSE) in combination with fluorescence spectrofluorometry or flow cytometry. The growth of Cmm cells in Glucose-Nutrient-Broth medium supplemented with potassium chloride in the absence and presence of the ionophore nigericin was evaluated to determine the minimum pH in value at which cells are able to grow. In the presence of nigericin (0.1 µmol -1 ), which equilibrates the intracellular and the extracellular pH out (pH in = pH out ), Cmm was not able to grow at pH 5.5 and below. Therefore, viable cells should maintain their intracellular pH above this pH value. The pH in of Cmm cells exposed to acid treatments, 0.1, 0.2 or 0.6 mol l -1 of HCl for 1 hour, was determined using fluorescence spectrofluorometry. In HCl treated cells no pH gradient could be detected (pH in = pH out ). Fluorescence microscopy revealed that these cells were poorly labeled with cFSE, either due to a low esterase activity in the cytoplasm or due to an increased efflux of cFSE resulting from the damage caused by the acid treatment. The spectrofluorometry analysis for pH in measurements was not able to detect the signal of these weakly stained cells and only a small percentage of HCl treated cells (0.001%) could be recovered on plate. For cells exposed to elevated temperatures, 40, 45 or 50 °C for 1 hour, the pH in was determined using cFSE in combination with flow cytometry and fluorescence spectrofluorometry. A good correlation (r 2 ≥0.80) was found between the number of colony-forming units per ml (CFU ml -1 ) determined by plate counting and the magnitude of the pH gradient (pH out - pH in ) determined with spectrofluorometry for the heat-treated populations. However, with the spectrofluorometry technique the analysis is based on the whole cell population and the sensitivity of this technique was found to be rather low. In our experiments, cell numbers of at least 10 7 CFU ml -1 were needed for the analysis. Using flow cytometry, which measures fluorescence intensity of individual cells, heat-treated and non-treated Cmm cells could be distinguished based on differences in the fluorescence ratios (pH gradients) after labeling with cFSE. From the FL1/FL2 dot plots the ratio of the green and the orange signals (FL1/FL2) could be calculated (after back transformation from log to linear mode). From this ratio the intracellular pH was calculated. The heat-treated cells had a low fluorescence ratio (no pH gradient) and could not be recovered on plates, whereas the ratio of live cells was significantly higher (pH gradient present). The major advantages of flow cytometry when compared with spectrofluorometry were its sensitivity and speed, because the analysis could be performed in two hours.

    The fluorescent enzyme activity probes Calcein acetoxy methyl ester (Calcein AM) and carboxyfluorescein diacetate (cFDA), and the nucleic acid probe propidium iodide (PI), were evaluated for assessing the viability of Cmm cells when applied in combination with flow cytometry. Heat-treated (80 °C for 30 minutes) and viable (non-treated) Cmm cells were mixed in different ratios, 100/0, 50/50, 20/80, and 0/100% respectively, to create populations varying in viability. Non-treated and heat-treated Cmm cells labeled with Calcein AM, cFDA, PI, or combinations of Calcein AM and cFDA with PI, could be distinguished based on their fluorescence intensity in flow cytometry analyses. Non-treated cells showed relatively high green fluorescence intensity levels, as the result of staining with Calcein AM or cFDA. Once inside the cell, Calcein AM and cFDA are cleaved (hydrolysed) by non-specific esterases to release fluorescein, a polar fluorescent compound which is retained inside the cells. Thus, the ability of the cell to accumulate fluorescein due to esterase activity is used as a parameter for viability. Damaged cells (heat-treated) showed high red fluorescence intensity levels, as the result of PI entering the cells with damaged cell membranes, intercalating into RNA and DNA. Flow cytometry allowed a rapid quantification and separation of viable Cmm cells labeled with Calcein AM or cFDA from heat-treated cells labeled with PI. The results showed a good correlation (r 2 ≥0.95) between the percentage of non-treated cells present in the samples and the flow cytometry counts for Cmm cells labeled with Calcein AM or cFDA. A linear relation (r 2 ≥0.80) was also found between the percentage of heat-treated cells in the samples and the flow cytometry counts for Cmm cells labeled with PI. However, when PI was applied as a single stain, it was able to stain 18 to 56% of non-treated Cmm cells. These results suggest that PI cannot be considered a good viability indicator for viable Cmm cells when applied alone. However, itt was shown to be a good indicator for dead or damaged cells. Therefore, the application of flow cytometry in combination with fluorescent probes appears to be a promising technique for assessing viability of Cmm cells in suspensions when cells are labeled with Calcein AM or the combination of Calcein AM with PI.

    Flow cytometry was also evaluated for the rapid detection of Xcc cells labeled in pure suspensions and in suspensions containing mixtures of Xcc and the common saprophyte Pseudomonas fluorescens (Psf) with a specific FITC-labeled monoclonal antibody (Mab). The concentration of Mab affected the sensitivity of the flow cytometry measurements. This is based on the concept that the optimal concentration of Mab is the one that gives the greatest discrimination between the fluorescently stained target cells and cells stained as the result of non-specific binding. However, the Mab concentrations tested do not seem to be a limiting factor for the detection of Xcc by flow cytometry. A limitation, however, is the concentration of cells present in the samples. Xcc cells labeled with FITC-conjugated monoclonal antibodies could rapidly be detected at low numbers, i.e 10 3 colony-forming units per ml in pure suspensions and in suspensions containing both Xcc and saprophytic Psf cells. The detection limit for Xcc applying other serological techniques, such as immunoflorescence microscopy (IF) and enzyme-linked immunosorbent assay (ELISA), is approximately 10 3 and 10 5 CFU ml -1 , respectively. A good correlation (r 2 ≥0.95) was observed between the flow cytometry counts and plate counts, although flow counts were always higher than plate counts due to the fact that antibodies do not discriminate between viable and non-viable cells. The number of Psf cells, relative to the number of Xcc cells, did not interfere, neither in the flow cytometry measurements nor in plate counts. Thus, flow cytometry in combination with Xcc specific FITC-labeled monoclonal antibodies may provide a novel tool for rapid detection and quantification of this plant pathogenic bacterium.

    The flow cytometry method applied to bacterial suspensions was evaluated as a tool for a rapid detection of Xcc cells, labeled with a mixture of three specific FITC-monoclonal antibodies (18G12, 2F4, and 20H6), in crude seed extracts. Flow cytometry allowed a rapid detection and quantification of Xcc cells labeled with FITC-monoclonal antibodies in both artificially and naturally Xcc-contaminated samples tested. Flow cytometry was able to detect the labeled Xcc cells in the seed extracts based on their high green fluorescence levels. No cross-reactions were observed with related Xanthomonads or other microorganisms present in artificially contaminated samples. In conclusion, the application of the flow cytometry technique in combination with specific, FITC-labeled monoclonal antibodies was shown to be a rapid and reliable alternative for the detection and quantification of Xcc cells in seed extracts.

    The work described in this thesis showed that flow cytometry in combination with fluorescent probes can be a promising technique to detect and to assess viability of plant pathogenic bacteria. Nonetheless, the application of flow cytometry as a routine method to test seed lots or plants for contamination with bacteria has to be further explored, especially combining detection with viability assessment in the same assay.

    Crop physiological analysis of seed quality variation in common bean (Phaseolus vulgaris L.)
    Muasya, R.M. - \ 2001
    Wageningen University. Promotor(en): P.C. Struik; W.J.M. Lommen. - S.l. : S.n. - ISBN 9789058084699 - 169
    phaseolus vulgaris - plantenfysiologie - zaden - zaadkwaliteit - levensvatbaarheid - rijpheid - groeifasen, rijp - groeikracht - phaseolus vulgaris - plant physiology - seeds - seed quality - viability - maturity - maturity stage - vigour

    Keywords : Physiological maturity, harvest maturity, earliness, common bean, Phaseolus vulgaris L., morphological markers, variation, moisture content, dry weight, viability, vigour, electrical conductivity, tetrazolium, seed lot, seed filling, maturation drying, temperature, rainfall.



    Common bean yield is low in Kenya and use of poor quality seed by small-scale farmers has been identified as a major yield constraint. This research project aimed at increasing insight into development of common bean seed quality and its variation during crop production and into how conditions during production affect these.

    In experiments involving bean cultivars Rosecoco and Mwezi Moja, physiological maturity (PM), i.e. the moment of maximum seed dry weight, was achieved at 58% seed moisture content. Harvest maturity (HM) was defined to occur at 20% moisture content. At PM, the percentage viable seeds as measured by tetrazolium test was still increasing. It became maximum closer to HM implying that seed development does not stop at PM. Seed vigour as measured by electrical conductivity (EC) was maximum at PM and remained constant until HM.

    Seeds in pods of different earliness and seeds of the whole crop all achieved maximum viability at the same moment beyond PM. The maximum viability achieved also was the same in all seed classes. Maximum seed vigour was achieved at PM in individual seed classes and was achieved earlier in seeds from earlier pods than from later pods. The vigour of seeds from the individual earliness classes at their optimum moment of harvesting was higher than the vigour of seeds from all pods combined. Individual seed variation in dry weight, moisture content and EC over time was lower in seeds from earlier pods than from all pods combined.

    Seed lots produced under different weather conditions and at two sites differed in quality within and between seed lots. Within seed lots, variation in individual seed quality as quantified by mean - median, range 0 - 100%, variance and standard deviation (SD) in individual seed EC was high when there were seeds with extremely high values deviating from the bulk of the seeds. Seed lots with deviating values did not necessarily have large variation in the bulk of the seeds, as quantified by the ranges 0 - 75% and 25 - 75%. Low variation in individual seed EC as quantified by mean - median, SD and the range 0 - 75%, was associated with good quality as measured by low bulk EC and/or high percentage viable seeds. Associations were clearer at PM than at HM. Relationships between individual seed variation and bulk quality were different at the two sites implying both the degree of variation and the level of individual seed quality can determine bulk quality. No relationship was found between CV% in individual seed EC and bulk quality.

    High temperature and less rainfall both could reduce seed quality. Over the ranges studied, high temperature was more detrimental than limited rainfall. Weather conditions seemed to reduce seed quality mainly through reducing the maximum quality attainable during crop development. Quality deterioration "in planta" was less important. Variations in weather conditions during production did not lead to lower quality seed lots through increasing variation within the crop, as measured by duration of flowering or pod set or plant-to-plant variation in number of flowers. Production conditions conducive to low seed yield or low individual seed weights were also conducive to low percentage of viable seeds. However, high seed yield does not guarantee high percentage viable seeds.

    Although the moment all seeds within a crop or crop fraction achieve the final red purple colour pattern was identified as a good indicator of PM, practically the use of pod and seed colour changes was an unreliable method for determining when to harvest. Results imply that processes determining the changes in colour and those determining changes in seed moisture content are differentially affected by external conditions. Based on the results of this research, picking pods from individual pod classes based on 20% seed moisture content could improve the uniformity within the harvested seeds and subsequently the final quality of the seeds harvested. This was shown for seeds from early pods.

    Duurzaam functioneren van populatienetwerken in de stad
    Snep, R.P.H. ; Opdam, P.F.M. ; Kwak, R.G.M. - \ 2000
    De Levende Natuur 101 (2000)6. - ISSN 0024-1520 - p. 189 - 192.
    steden - stedelijke gebieden - stadsomgeving - natuurbescherming - ecologie - habitats - milieu - ruimtelijke verdeling - geografische verdeling - populaties - populatie-ecologie - landschapsecologie - modellen - duurzaamheid (sustainability) - levensvatbaarheid - vogels - biodiversiteit - biotopen - natuur - populatiebiologie - ecologische hoofdstructuur - habitatfragmentatie - towns - urban areas - urban environment - nature conservation - ecology - habitats - environment - spatial distribution - geographical distribution - populations - population ecology - landscape ecology - models - sustainability - viability - birds - biodiversity - biotopes - nature - population biology - ecological network - habitat fragmentation
    In een case-studie voor een deel van het Rotterdamse havengebied is voor enige vogelsoorten onderzocht in hoeverre habitatnetwerken van populaties (metapopulaties) duurzaam kunnen functioneren in het stedelijk gebied. Daarvoor is gebruik gemaakt van het model LARCH (Landschapsecologische Analyse en Ruimtelijke Configuratie van Habitat). De factoren die de draagkracht en duurzaamheid van habitat- en populatienetwerken bepalen en de toepasbaarheid van ruimtelijke modellen in het stedelijk natuurbeleid komen aan de orde
    Vernattingsonderzoek in bossen: 1998 ideaal jaar
    Olsthoorn, A.F.M. - \ 1999
    Nederlands Bosbouwtijdschrift 71 (1999)4. - ISSN 0028-2057 - p. 155 - 156.
    bossen - bosbouw - onderzoek - onderzoeksprojecten - grondwaterstand - grondwater - grondwaterspiegel - inundatie - stagnatie - bomen - gezondheid - schade - waterrelaties - plant-water relaties - wortels - bodem - achteruitgang, bossen - levensvatbaarheid - verdroging - drogen - natuurbescherming - herstel - forests - forestry - research - research projects - groundwater level - groundwater - water table - flooding - stagnation - trees - health - damage - water relations - plant water relations - roots - soil - forest decline - viability - desiccation - drying - nature conservation - rehabilitation
    Effect van grondwaterstandverhoging op de vitaliteit van boomsoorten. Opzet van het vernattingsonderzoek op hydrologisch proefveld Geestmerambacht en drie locaties in volwassen bos verspreid over Nederland, en een eerste indruk van de resultaten
    Speeltjes weerhouden kalkoenen niet van pikkerij: onacceptabel veel beschadigingen en hoge uitval.
    Veldkamp, T. ; Kiezebrink, M.C. - \ 1998
    De Pluimveehouderij 28 (1998)44. - ISSN 0166-8250 - p. 8 - 10.
    kalkoenen - snavelkappen - huisvesting, dieren - dierenwelzijn - sociaal gedrag - diergezondheid - lichtregiem - groei - levensvatbaarheid - turkeys - debeaking - animal housing - animal welfare - social behaviour - animal health - light regime - growth - viability
    Onderzoek wijst uit dat het niet-behandelen van de bovensnavels van kalkoenen leidt tot meer uitval en beschadigingen door pikkerij. Het verlagen van de lichtsterkte en het instellen van een licht-donkerschema, alsmede de aanwezigheid van speelobjecten in de stal kon de uitval en beschadigingen niet tot een aanvaardbaar niveau terugbrengen
    Assessment of the exposure and loads of acidifying and eutrophying pollutants and ozone, as well as their harmful influence on the vitality of the trees and the Speulder forest ecosystem as a whole
    Erisman, J.W. ; Draaijers, G.P.J. ; Steingröver, E. ; Dijk, H. van; Boxman, A. ; Vries, W. de - \ 1998
    Water Air and Soil Pollution 105 (1998)3/4. - ISSN 0049-6979 - p. 539 - 571.
    zure regen - bosbouw - zure depositie - levensvatbaarheid - eutrofiëring - acid rain - forestry - acid deposition - viability - eutrophication
    Eerste opname van de ondergroei in het Meetnet Bosvitaliteit
    Dobben, H.F. van; Vocks, M.J.M.R. ; Bouwma, I.M. - \ 1997
    Wageningen : IBN-DLO (IBN - rapport 321) - 29
    bosbouw - grondbedekking - grasbestand - mossen - korstmossen - milieu - verontreiniging - monitoring - achteruitgang, bossen - levensvatbaarheid - nederland - onderlaag - forestry - ground cover - herbage - mosses - lichens - environment - pollution - monitoring - forest decline - viability - netherlands - understorey
    Invloed van milieubedreigingen op de natuurwaarden van het Nederlandse bos. Basisdocument voor Natuurverkenning '97
    Hendriks, C.M.A. ; Jansen, P.C. ; Schotman, A.G.M. ; Vries, F. de; Kemmers, R.H. ; Olsthoorn, A.F.M. ; Schaap, W. - \ 1997
    Wageningen : SC-DLO (Rapport / DLO-Staring Centrum 413) - 104
    bosbouw - achteruitgang, bossen - levensvatbaarheid - synecologie - milieu - verontreinigende stoffen - verontreiniging - nadelige gevolgen - verdroging - drogen - neerslag - chemische eigenschappen - zuurgraad - zure regen - forestry - forest decline - viability - synecology - environment - pollutants - pollution - adverse effects - desiccation - drying - precipitation - chemical properties - acidity - acid rain
    Weerstandsverhogende maatregelen in bossen
    Bouwma, I.M. ; Olsthoorn, A.F.M. - \ 1997
    Wageningen : IBN-DLO - 67
    bosbouw - geïntegreerde bestrijding - biologische bestrijding - bosplagen - ziekten - houtteelt - ziektebestrijdende teeltmaatregelen - achteruitgang, bossen - levensvatbaarheid - nederland - forestry - integrated control - biological control - forest pests - diseases - silviculture - cultural control - forest decline - viability - netherlands
    Non-homologous chromosome synapsis during mouse meiosis : consequences for male fertility and survival of progeny
    Peters, A.H.F.M. - \ 1997
    Agricultural University. Promotor(en): C. Heyting; P. de Boer. - S.l. : Peters - ISBN 9789054857761 - 182
    muridae - muizen - meiose - geslachtelijke voortplanting - parthenogenese - polyembryologie - vruchtbaarheid - overleving - levensvatbaarheid - interacties - milieu - uitsterven - stofverplaatsing - chromosoomtranslocatie - chromosomen - cytologie - histologie - muridae - mice - meiosis - sexual reproduction - parthenogenesis - polyembryony - fertility - survival - viability - interactions - environment - extinction - translocation - chromosome translocation - chromosomes - cytology - histology
    In the mouse, heterozygosity for several reciprocal and Robertsonian translocations is associated with impairment of chromosome synapsis and suppression of crossover formation in segments near the points of exchange during prophase of meiosis. This thesis describes the analysis of the consequences of the occurrence of non-homologous synapsis and/or suppression of meiotic crossover formation over many successive generations for male fertility and viability of the progeny.

    For studying chromosome synapsis, we modified a drying down technique which results in high yields of nuclei of all first meiotic prophase stages in both male and female from only small amounts of tissue (chapter 2). Preparations are suitable for synaptonemal complex (SC) analysis by normal light and electron microscopy (chapters 2, 3 and 7), for fluorescence immunocytochemistry and in situ hybridization (chapters 2, 8).

    In the study presented in chapter 3, we analysed the variation in male fertility of mice double heterozygous for two near identical reciprocal translocations T(1;13)70H and T(1;13)1Wa in relation to the synaptic behaviour of two differently sized heteromorphic bivalents during meiotic prophase. Male fertility rises when non-homologous synapsis in the small 1 13heteromorphic bivalent, leading to a "symmetrical" SC, is more frequent at the initial prophase stages. Based on the data presented, we favour the "unsaturated pairing site" model as the primary cause for male sterility.

    In T70H/T1Wa females not all heterologous synapsis within the small heteromorphic bivalent is effectuated during the early stages of meiosis; some is achieved lateron by the mechanism of "synaptic adjustment" (chapter 3). Each heteromorphic bivalent contains a copy of the chromosome 1 region between the T70H and T1Wa breakpoints which is about 10 cM in size (Δ1 segment). Although axial elements representing these Δ1 segments are seen to approach each other during early meiotic prophase stages, they never successfully constitute a synaptonemal complex in either sex (chapter 3). This agrees with the fact that in earlier cytogenetic studies quadrivalents were never seen at both male and female diakinesismetaphase 1.

    In chapter 7, we demonstrate that male fertility of the T70H/T1Wa mice is not only determined by the chromosomal constitution of the carrier but is additionally influenced by the pairing or synaptic history in previous meioses of especially the T70H and T1Wa short translocation chromosomes. Fertility of T70H/T1Wa males is more impaired after one or more successive transmissions of the T1Wa translocation chromosomes through a heteromorphic bivalent configuration, irrespective of the sex of the transmitting parent.

    Furthermore, we show that the introduction of the Robertsonian translocation Rb(l1.13)4Bnr into the T70H/T1Wa karyotype restores fertility of double heterozygous males by stimulating non-homologous synapsis of the small heteromorphic bivalent. We speculate that this Rb4Bnr effect is mediated by a prolongation of the early stages of meiotic prophase I.

    Successive female transmissions of the T1Wa translocation chromosomes in the presence of Rb4Bnr inititially resulted in an increase of the capacity for early meiotic nonhomologous synapsis within the small heteromorphic bivalent, leading to a restoration of fertility for the majority of carriers. Subsequently, a decrease of the capacity of the small heteromorphic bivalent to fully synapse was noticed, although a higher than original (F1) background level of male fertility remained.

    These variations in male fertility are most likely based on epigenetic variance, reflected as the capacity to engage into non-homologous synapsis early in male meiosis leading to a "symmetrical" SC, despite the different amounts of chromatin to accommodate.

    In chapter 4, the localization of several microsatellite markers and single copy genes relative to the T70H and T1Wa breakpoints, using quantitative PCR, quantitative Southern blotting and in situ hybridization, is described.

    In chapter 5, we investigated the level of suppression of meiotic recombination and impairment of chromosome synapsis in T70H heterozygotes in relation to the viability of the progeny. For T70H/+ females, the introgression of the D1Mit4, D1Mit20 and D1Mit122 microsatellite marker alleles positioned distal of the T70H breakpoint on the normal chromosome 1 into the 13 1T70H long translocation chromosome was suppressed in a distance dependent manner. This effect was more pronounced in T70H/+ females, additionally homozygous for Rb4Bnr. The delay in introgression was paralleled by a reduction of the frequency and extent of non-homologous synapsis in segments near the T70H breakpoints of the pachytene translocation multivalents in T70H/+ and Rb4BnT70H/Rb4Bnr+ males. The extend of non-homologous synapsis around the centre of the synaptic cross configuration in these males correlated with fluctuations in prenatal viability of segregating translocation homozygotes in crosses between (Rb4Bnr)T70H homozygous males and heterozygous females when meiotic drive at the female second meiotic division is excluded. The reduction in viability is explained by the gain of mutations resulting from incorrect processing of recombination intermediates which is due to non-homologous synapsis around the translocation breakpoints.

    In chapter 6, we analysed the consequences of the absence of crossing over for regions between the T70H and T1Wa breakpoints (Δ1 and Δ13 segments) of the Rb4BnrT1Wa translocation chromosomes, which have been transmitted for over 20 generations via heteromorphic bivalents in Rb4BnrT70H/Rb4BnrT1Wa females. Survival of heterozygous and homozygous carriers for these segments was taken as the phenotypic endpoint. The viability of progeny of crosses between Rb4BnrT70H homozygous males and Rb4BnrT70H/Rb4BnrT1Wa females, of which the latter principally produce 4 types of gametes, was estimated using a haplotype analysis of microsatellites in the Δ1 segment for genotyping (see chapter 4). We observed no differences in the pre- and postnatal survival rates of the double heterozygous and 13 1H, 13 1H, 1 13Wa 1 13H "duplication" progeny in which the Δ1 and Δ13 segments of the T1Wa translocation chromosomes had either no, an onegeneration or a multi-generation history of non-homologous synapsis in heteromorphic bivalents during previous female meioses. In addition, intercrossing of Rb4BnrT70H/Rb4BnrT1Wa double heterozygotes after genetic isolation of these Δ1 and Δ13 segments for 20 to 22 generations, showed that the viability of the Rb4BnrT1Wa homozygotes was not different from the Rb4BnrT70H homozygous and Rb4BnrT70H/Rb4BnrT1Wa karyotypes generated by this cross. Thus, exclusion of the Δ1 and Δ13 segments from meiotic crossing over within non-homologous synapsed heteromorphic bivalents during 20 to 25 successive generations does not result in an accumulation of recessive lethal mutations or an increased susceptibility for gaining dominant lethal mutations.

    For the D1Mit122 microsatellite used in offspring haplotyping a higher mutation frequency was observed after transmission through a double heterozygous than after transmission through a T70H homozygous karyotype (chapter 6). On the basis of the identity of the mutations, the ectopic pairing of the St2 gene copies (containing D1Mit122) during meiosis of T70H/T1Wa males (chapter 8) and the observation of ectopic homologous contacts of the Δ1 segments during the zygotene stage without SC formation (chapter 3), we speculate that these mutations are the result of ectopic homologous gene conversion events most likely occurring in the absence of a synaptonemal complex.

    The crossover suppressive influence of the Rb translocation on the Δ1 segment (chapter 5) enabled us to analyze the effects of introgression of genetic material from the Swiss +/+ stock into the translocation karyotypes. Introgression of "new" genetic material correlated with an increase in littersize of Rb4BnrT70H homozygotes (chapter 5), an improvement of the life expectancy of Δ1 duplication offspring from double heterozygous mothers (chapter 6) and a clear improvement of male fertility in double heterozygous and T70H homozygous males also carrying Rb4Bnr (chapter 7). These pleiotrophic findings are discussed in chapter 8 in terms of genetic versus epigenetic mechanisms of inheritance.

    Finally, when T1Wa was backcrossed for many generations to the Rb4BnrT70H/Rb4BnrT70H karyotype, essentially precluding genetic recombination in the Δ1 and Δ13 segments, or when T1Wa was combined with Rb4Bnr after many successive transmissions via alternating T1Wa heterozygotes and homozygotes, stable Rb4BnrT1Wa homozygous lines could not be bred (chapter 8). Especially female reproductive performance decreases after repeated male and female homologous meiosis. As non-homologous synapsis in the centre of the synaptic cross configuration in T1Wa/+ males is common too (unpublished results), more work into the genetic stability of chromosome segments, that have a history of hindered homologous interaction, is indicated (chapter 8).

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