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Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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    Seed quality in informal seed systems
    Biemond, P.C. - \ 2013
    Wageningen University. Promotor(en): Paul Struik, co-promotor(en): Tjeerd-Jan Stomph. - S.l. : s.n. - ISBN 9789461736420 - 120
    zaadkwaliteit - zaadfysiologie - vigna unguiculata - vignabonen - zaadkieming - zaadpathologie - mycotoxinen - zea mays - nigeria - seed quality - seed physiology - vigna unguiculata - cowpeas - seed germination - seed pathology - mycotoxins - zea mays - nigeria

    Keywords: informal seed systems, seed recycling, seed quality, germination, seed pathology, seed health, seed-borne diseases, mycotoxigenic fungi, Fusarium verticillioides, mycotoxins, Vigna unguiculata, Zea mays, Nigeria.

    Seed is a crucial input for agricultural production. Approximately 80% of the smallholder farmers in Africa depend for their seed on the informal seed system, consisting of farmers involved in selection, production and dissemination of seed. The lack of overhead, distribution and seed testing costs enables seed-producing farmers to offer seed for low prices, but seed quality is not always good. Seed-producing farmers multiply their seed on-farm without frequent seed renewal, referred to as seed recycling, which may lead to low seed quality. This research analysed the effect of seed recycling on physiological quality and seed health of cowpea and maize, and compared seed quality of the formal and informal seed system.

    We tested the physical and physiological quality of cowpea seeds produced by the formal and informal seed system. Five out of six foundation seed samples, 79 out of 81 samples of farmers’ seed, and six out of six seed company samples failed to meet standards for foundation and certified seeds of the National Agriculture Seed Council (NASC), the seed industry regulatory agency in Nigeria. No evidence was found for a negative effect of seed recycling on physiological quality of cowpea seeds. We analysed 45,500 cowpea seeds for seed-borne bacteria and fungi to compare the performance of formal and informal seed systems. All samples were heavily infected with seed-borne pathogens, including Fusarium oxysporum (69% of the samples) and Macrophomina phaseolina (76%). No evidence was found that seed recycling in the informal seed system did lead to increased levels of seed-borne pathogens. We also analysed seed quality of farmer-produced maize seed to compare it with the formal seed system. The seed company samples had significantly higher germination (99.3%) than farmer-produced seed (97.7%), but not a single sample passed the requirements for certified seed of the NASC. Twelve seed-borne pathogens were identified including Bipolaris maydis (found in 45% of the farmer-produced samples), Botryodiplodia theobromae (97%) and Fusarium verticillioides (100%). Seed recycling had no negative effect on the physiological quality or seed health of maize seed. We analysed formal and informal seed systems to assess the opportunities to prevent mycotoxigenic fungi infection in maize seeds. A range of control methods to avoid fungal infection and mycotoxin production is discussed in relation to three criteria for sustainable implementation in developing countries. An integrated approach is recommended, with special attention towards the local seed system. As an overall conclusion of the work it can be stated that the informal seed system did not underperform compared to the formal seed system for cowpea, but did underperform in relation to seed company samples of maize. There was no evidence that seed recycling reduces seed quality of cowpea and maize seed samples, so frequent seed renewal will not improve seed quality of the informal seed system. We recommend a new quality assurance system for the informal seed system based on seed quality testing by farmers themselves, without interference by government or external laboratories. Farmers publish their seed testing results on the bag, while buyers can retest the seed to verify the quality. Further research is required to develop and implement this system in different countries, agro-ecologies and crops, and to develop methods that enable farmers to test seed health quality themselves.

    Keeping local foods on the menu: a study on the small-scale processing of cowpea
    Madodé, Y.E.E. - \ 2012
    Wageningen University. Promotor(en): Tiny van Boekel; D.J. Hounhouigan, co-promotor(en): Anita Linnemann; Rob Nout. - S.l. : s.n. - ISBN 9789461734358 - 176
    vignabonen - voedselverwerking - landrassen - antinutritionele factoren - verteerbaarheid - west-afrika - benin - cowpeas - food processing - landraces - antinutritional factors - digestibility - west africa - benin

    Agriculture plays a significant role in the economy of most African countries. Yet malnutrition and micronutrient deficiencies occur regularly. Concomitantly, many carbohydrate rich staple foods and meat products are dumped on the African market and compet strongly with local products. The present thesis studied the potential of indigenous resources and locally developed practices to supply culturally acceptable and nutritious foods to African resource-poor people, using cowpea as model crop. This research is implemented using an interdisciplinary approach, which comprised plant breeding, food science and technology, human nutrition and social sciences. This thesis reports the findings of the research on food science and technology.

    This study aimed to (i) characterise cowpea landraces in use in Benin with regard to nutritional, anti-nutritional and functional properties; (ii) determine present cowpea processing methods and eating habits with special reference to the content of cowpea dishes in available iron, zinc and calcium; (iii) assess the effect of the use of alkaline cooking aids on amino acids of cooked cowpea, and (iv) assess the impact of processing techniques on the flatulence generated by the intake of cowpea foods.

    The genetic, nutritional and technological characterisation of cowpea landraces in use in Benin showed that a high level of similarity among unpigmented landraces as opposed to pigmented landraces. The cluster of unpigmented landraces significantely differed from the pigmented landraces for their fibre (24 vs. 56 g/kg, d.w.) and phenolics (3 vs. 8 g/kg, d.w.) contents as well as their seed size (200 vs. 139 g/1000 seeds, d.w.) and water absorption capacity (1049 vs. 1184 g/kg, d.w.).

    An inventory of 18 cowpea dishes was obtained, which are produced by the combination of the following main unit operations: cooking, dehulling, deep-fat frying, steaming, roasting and soaking. Fermentation and germination are unusual technological practices in West-Africa. Consumers mainly consume Ata, Atassi and Abobo. These dishes contain little available iron because their [phytate] : [iron] molar ratio is above the required thresholds for a good iron uptake by the human body. The incorporation of cowpea leaves in certain dishes resulted in appropriate available iron and calcium potentials.

    The constraints to cowpea processing were identified as: their long cooking time, the tediousness of the dehulling process and the perishability of beans and dishes. The local answer to the long cooking time is the use of alkaline cooking aids. These alkaline salts and the applied cooking conditions did not induce any significant change in the amino acid composition of pigmented landraces. Moreover, the toxicity potentially associated with this practice was not confirmed as no lysinoalanine could be quantified while using up to 0.5 % (w/v) of alkaline cooking aids.

    Flatulence was indicated as the main constraint to cowpea consumption. Cowpea hulls are usually pointed as the main responsible for flatulence. In this research, galactose-oligosaccharides that are indigestible for humans and cause flatulence formation were not found in cowpea hulls. Fermentation wih Rhizopus or Bacillus bacteria reduced significantly the fermentability of cowpea in vitro and in vivo as compared with traditional processes.

    The present study demonstrates the opportunities to improve the quality of cowpea dishes by the incorporation of the leaves and the possibilities to sustain the consumption of cowpea by focusing on soaking and/or fermentation processes.

    Technology development and market access: from a food sovereignty perspective
    Quaye, W. - \ 2012
    Wageningen University. Promotor(en): Tiny van Boekel; Guido Ruivenkamp, co-promotor(en): Joost Jongerden. - S.l. : s.n. - ISBN 9789461734952 - 169
    vignabonen - markten - kleine landbouwbedrijven - ghana - technologieoverdracht - gewasproductie - voedselsoevereiniteit - cowpeas - markets - small farms - ghana - technology transfer - crop production - food sovereignty

    The concepts of ‘relevant social groups’ and ‘technical code’ are used to investigate the social relations in cowpea variety development (technology studies) and also the relationship of small-scale farmers to the Ghana School Feeding Program (market access) against the background of food sovereignty. For the technology studies, empirical findings reveal the wider socio-cultural context within which cowpea production, processing and consumption are organized and the differences in social meanings constructed for cowpea varieties among relevant social groups (RSGs) in the local cowpea network. Farmers attach social meanings to variety choices in relation to the purpose of cultivation, either primarily for household food provision or for commercial purposes, and select varieties on the basis of these social meanings alongside other, technical considerations, such as yield and tolerance to diseases and pests. There is another, sharper contrast between social meanings ascribed to cowpea variety choice by (small-scale) processors and consumers from that of the farmers. Processor and consumer cowpea variety preferences are tied to bean characteristics, such as white seed colour, short cooking time and taste, which aremore attuned to the social relevance of consumption than technical functionality for cultivation.

    There are different desires for different traits and thus different varieties of cowpea among the various RSGs, yet empirical findings show that the technical codes in variety designs do not reflect these. In particular, the social meanings constructed for preferred cowpea varieties among the RSGS in the user (processor/consumer, as opposed to producer) category go unrecognised in the variety designs produced in Ghana. Basically, empirical findings confirm a mismatch between what farmers grow and what consumers want. Thereis thus a demand on the Ghanaian cowpea market that local farmers fail to take advantage of, an opportunity that has been taken instead by foreign producers. To understand why the variety preferences of some RSGs have been neglected in Ghanaian cowpea variety development, we unearth the structural and asymmetric power relations among the RSGs in constructing the technical codes of variety designs.

    Research reveals three major phases in the social organisation of cowpea variety development in Ghana: the upstream breeding, downstream breeding and validation and release. A core element in the upstream breeding is the development of technical codes in variety designs or exotic lines using local germplasm as raw material at the international breeding centres. These codes have both technical specifications and in-built socio-cultural assumptions that become explicit through critical reflection on the variety development process. In the downstream breeding phase, the core element of the variety development process becomes the adaptability of the exotic lines to the local environment, basically involving evaluation of and selection from the variety designs developed upstream. At the validation and release phase, interpretative differences and design flexibility come to a closure as the National Variety Release Committee (NVRC) determines a proposed improved variety to be an improvement over already existing varieties.

    There is a strong influence of international researchers in the development of exotic lines upstream, largely due to power imbalances between this and other RSGs, such as in technical know-how, research infrastructure and funding resources. This asymmetric relationship means that downstream breeding activities are centrally controlled through the functioning of standardized breeding procedures developed by international breeding institutions at the upstream breeding phase working with the basic intention of a universal applicability of (cowpea) variety design. This research thus points especially to the need for institutional rearrangements that encourage a greater engagement of local researchers in upstream breeding and the inclusion of other RSGs in the user category in the breeding process. And in order to enhance flexibility in attuning exotic lines developed at international organisations to locality specific contexts in downstream breeding, this study recommends the establishment of localized (rather than global) breeding frameworks, with clear (sets of) RSG defined breeding objectives that consider the differences in variety preferences at production and consumption levels, for both market and household consumption. Indeed, small-scale farmers can enhance their access to the domestic market and their food sovereignty if demand driven varieties are produced.

    The market access study using the Ghana School Feeding Program (GSFP) typifies a food re-localisation strategy which elaborates on the relationship of market access for smallholder farmers to their food sovereignty situations. Similarly to the empirical findings from the technology studies, the code analysis of the market access study shows structural limitations and unequal power relations among GSFP RSGs. Despite the good intentions of decentralizing decisions pertaining to the GSFP, this research reveals a top-down bureaucratic approach to program conceptualization and implementation that has effectively negated some RSGs. The GSFP was implemented with little involvement by small-holder farmers who are supposed to represent one of the beneficiaries of the programme (by supplying the market it creates) The local (district and school) level bodies supposed to be responsible for mobilizing community support and linking smallholders to the GSFP market were not empowered to perform. They were given little support or direction as to their roles and responsibilities and there were funding shortages for food purchases. This situation gave traders and other food suppliers the power to use their money to take advantage of the market opportunities created.

    The asymmetry of power influence among the RSGs in the GSFP network is reflected in the choice of food procurement model. A code analysis of the market access study shows three procurement models to be operative in the GSFP: i) theSupplier Model, which employs the use of contractors or suppliers to supply food items to the schools, ii) the School-Based Model,which involves thecommunity mobilization of resources and purchase of raw foodstuffs from local farmers, and iii) theCaterer Model, which involves the handling of food purchases and food preparations by contracted qualified caterers. In practice, the caterer model is found to be mostly used largely due to convenience and power imbalances, even though it is the school-based model that best fits the programme objectives. This is shown to be a significant cause of the failure of smallholders to access the GSGP market and their ‘replacement’ by traders and other food suppliers.

    Nevertheless, assessment of the socio-economic impact on the group of farmers (less than 30% of 100 farmers interviewed in GSFP participating communities) who have been able to access the GSFP market shows a very positive relationship between market access and household food sovereignty. In the space of a year, production of the crop sold (rice) went up 30%, food stocks rose by a half (from six to nine months) and farmers’ incomes increased by 80%. Notably, these farmers were organised, by a development agency, which also provided various inputs (including credit and technical assistance) and, acting as the link to the GSFP, guaranteed the market.

    Several factors are found to have limited and continue to restrict effective implementation of the GSFP, but from the code analysis it is clear that the GSFP can be socially reconstructed to seek specific goals. Despite the constraints limiting smallholder farmer access to the GSFP market, critical investigations into the procurement models open-up possibilities for reconstructing the GSFP market and making it an endogenous structure that can facilitate smallholder access. Identification also of the factors enabling access on the part of some farmers also suggests ways in which interventions in social relations can enable localised producer-consumer linkages through the GSFP that promote food sovereignty.

    Since resource constraints favour the use of supplier and caterer procurement models, it is recommended that contract agreements specify food purchases from local farmers. Concrete proposals for endogenizing the GSFP to facilitate the linkage between local food production and school feeding (local consumption) include i) strengthening collaboration efforts with strategic partners working with farmer groups, ii) developing social relations between farmers and caterers or school kitchen centres, and iii) affirming the roles and responsibilities of actors who have the capacity to develop farmer-GSFP linkages through performance contract agreements and regular monitoring. The Ministry of Food and Agriculture and FONG, an apex organisation of farmers’ groups, were identified as actors that could be developed for important, nationwide roles at the local level.

    This research shows a link betweenendogenous development andhousehold food sovereignty. Empirical findings from the GSFP analysis provide a test case of what actually happens to the food sovereignty situation of small-scale farmers who have good access to a domestic market. Using a range of measures at the household level as proxy for food sovereignty, this study shows a positive linkage between domestic market access for smallholder farmers and food sovereignty. However, it is realised that farmers in marginalized areas, especially those in hunger hotspots, cannot just produce for the GSFP market unless it is organised in a way that reflects endogenous capacities and improves small-scale farmers’ access to production resources.

    The technological studies and market access parts of this research both reveal the importance ofparticipation by RSGs – the former especially through genuinely participatory plant breeding programmes and the latter through the need for communities and farmers’ groups to be proactively introduced into and involved in the organisation of food procurement. Underscoring this, the linkage of fundamental failures, again in both programmes – both in breeding (at the upstream phrase) and school feeding (conceptualisation and implementation) – to asymmetric social power relations attest to the need to confront and restructure these in practical, creative ways.

    Biology and ecology of Apanteles taragamae, a larval parasitoid of the cowpea pod borer Maruca vitrata
    Dannon, A.E. - \ 2011
    Wageningen University. Promotor(en): Marcel Dicke; Arnold van Huis, co-promotor(en): M. Tamò. - [S.l.] : S.n. - ISBN 9789085859482 - 188
    vigna unguiculata - vignabonen - insectenplagen - maruca vitrata - boorders (insecten) - apanteles - sluipwespen - biologie - levensgeschiedenis - biologische bestrijding - vigna unguiculata - cowpeas - insect pests - maruca vitrata - boring insects - apanteles - parasitoid wasps - biology - life history - biological control

    Maruca vitrata Fabricius is a key insect pest of cowpea in West Africa. Larvae of this moth can cause up to 80% of yield losses. The first classical biological control programme against M. vitrata started in 2005 with the introduction of Apanteles taragamae Viereck from Taiwan into Benin by the International Institute of Tropical Agriculture (IITA), Benin station.Thorough knowledge on the bioecology of A. taragamae is a prerequisite for implementing such programme. The work described in the present thesis evaluated the biological potential of this larval parasitoid to fill to the gap of information on its biology and ecology. Special emphasis was put on the main factors that determine the effectiveness/suitablility of biological control candidates, such as reproductive capacity, functional response, climatic adaptability, host foraging capacity, and non-target effects. The results revealed that two-day-old larvae were the most suitable host age, giving the highest percentage parasitism, lifetime fecundity and proportion of females. Larvae older than three days were not successfully parasitized. The percentage parasitism of two-day-old larvae was positively correlated with host density, indicating a good functional response of A. taragamae. Between 20 and 30 °C, the curve that described the relationship between the intrinsic rate of natural increase and the temperature for A. taragamae was above that of M. vitrata, suggesting that the parasitoid can faster build up its population than its host. The parasitoid showed its ability to use volatiles produced by cowpea flowers and host caterpillars when foraging. A host plant odour experience enhanced the capacity of the parasitoid to find uninfested flowers. The growth of non-parasitized or A. taragamae-parasitized larvae was slower and with reduced proportion of female wasps on some host plants compared to those reared on artificial diet. With regard to the non-target effects, the physiological host range and competitive ability of A. taragamae were assessed. None of the following lepidopteran species, Eldana saccharinaWalker, Chilo partellus (Swinhoe), Mussidia nigrivenella Ragonot, Cryptophlebia leucotreta (Meyrick), Sylepta derogata FabriciusandCorcyra cephalonica Stainto,was successfully parasitized by A. taragamae, suggesting its specificity for M. vitrata in Benin. In no-choice competition with the egg-larval parasitoid Phanerotoma leucobasis, A. taragamae outcompeted the latter. All the above attributes suggest that A. taragamae should be a suitable biocontrol agent against M. vitrata. A cage release strategy involved the host plant Sesbania cannabina, which was artificially infested with M. vitrata, and inoculated with adults of A. taragamae. The parasitoid was released in seven selected locations in Benin but the first recovery studies did not yet yield any information on its establishment after the first generation.

    Genetic analysis of abiotic and biotic resistance in cowpea [Vigna unguiculata (L.) Walp.]
    Agbicodo, A.C.M.E. - \ 2009
    Wageningen University. Promotor(en): Richard Visser, co-promotor(en): Gerard van der Linden; C.A. Fatokun. - [S.l. : S.n. - ISBN 9789085854777 - 168
    vigna unguiculata - vignabonen - genetische analyse - droogteresistentie - plantenziekteverwekkende bacteriën - xanthomonas axonopodis pv. vignicola - ziekteresistentie - plantenveredeling - resistentieveredeling - vigna unguiculata - cowpeas - genetic analysis - drought resistance - plant pathogenic bacteria - xanthomonas axonopodis pv. vignicola - disease resistance - plant breeding - resistance breeding

    Cowpea [Vigna unguiculata (L.) Walp.] is a most versatile African crop, it feeds people, their livestock and because of its ability in nitrogen-fixation, it improves soil fertility, and consequently helps to increase the yields of cereal crops when grown in rotation and contributes to the sustainability of cropping systems. Because of its ability to tolerate some level of drought stress, cowpea is a crop of choice where > 10 million hectares are cultivated to cowpea in the semiarid Savanna and Sahelian zones of West and Central Africa. However due to the infrequent drought stress throughout cropping seasons over the last 3 decades, the crop suffers important yield reduction. Moreover, cowpea plants under water stress condition are more vulnerable to diseases, parasites and insect pests attacks. In this thesis we carried out genetic analyses of seedling and terminal drought tolerance and cowpea bacterial blight (CoBB) resistance. Two cowpea genotypes with contrasting reactions to drought and CoBB stresses, Danila (resistant) and TVu7778 (susceptible) were used to develop recombinant inbred lines (RILs) mapping population. The RILs and parents were phenotyped for CoBB resistance and for physiological drought tolerance traits and productivity traits under different water regimes in multiple environments at seedling and adult plant stages. A genetic linkage map of 282 single nucleotide polymorphism (SNP) loci covering a map distance of 633 cM distributed over 11 linkage groups (LG) from the same RILs was used for quantitative traits loci (QTL) analyses. Moisture stress significantly affected RILs performances with number of pods per plant as the yield component most adversely affected by water stress. Correlation and path analyses revealed that grain yield components (mainly number of pods per plant) and plant biomass had the largest direct effects on grain yield under moisture stress and irrigation. Stem greenness was an excellent predictor of seedling survival to drought (r2 = 0.91). Two QTLs were identified for each of the three traits scored under greenhouse, drought-induced trifoliate senescence (DTS), stem greenness (Stg) and survival (Sur) on LG3 and LG7. For all traits measured under field trials, a total of 42 QTLs were detected, 4 for stomatal conductance (Gs), 6 for delayed leaf senescence (DLS), 5 for flowering time and 16 for grain yield components (pod number/plant, seed number/pod, seed weight), 6 for grain yield and 5 for fodder yield. Three QTLs were detected for CoBB resistance, with two major ones (named CoBB-1 and CoBB-2 confirmed over two experiments) on LG3 and LG5 and one minor QTL (CoBB-3 only for experiment 1) on LG9. Although number of QTLs detected seems to be important, association between QTLs of different traits sharing a common genomic region was observed on LG3, LG5, LG7 and LG8 where QTLs for Gs, DLS, and flowering time co-localized with QTLs for yield parameters, DLS and DTS shared common chromosomal regions with CoBB resistance, on LG3 and LG5. These results suggest that common genes might mediate CoBB resistance and DLS. Two QTLs detected for DLS in the field, co-localized with QTLs under greenhouse for seedling drought tolerance traits DTS, Stg and Sur on LG7. This indicates the presence of potential loci controlling senescence in this genomic region. Moreover, this genomic region represents a syntenic genomic region between cowpea, soybean and Medicago. Our findings provide evidence for QTLs mediating seedling and terminal drought tolerance and CoBB resistance in cowpea. QTL and phenotypic analysis revealed that it should be possible to pyramid CoBB resistance with seedling and terminal drought tolerance. The fact that the genetic map of Danila x TVu7778 is integrated in a consensus map of cowpea of 6 RIL populations will permit comparative genomic studies which will enhance the discovery of functional markers for MAS of seedling and terminal drought tolerance and CoBB resistance in cowpea.

    Socio-cultural factors influencing and maintaining yam and cowpea diversity in Benin
    Zannou, A. ; Tossou, R.C. ; Vodouhè, S. ; Richards, P. ; Struik, P.C. ; Zoundjihékpon, J. ; Ahanchédé, A. ; Agbo, V. - \ 2007
    International Journal of Agricultural Sustainability 5 (2007)2-3. - ISSN 1473-5903 - p. 140 - 160.
    vignabonen - pachyrhizus erosus - diversiteit - benin - geslacht (gender) - rituelen - cowpeas - pachyrhizus erosus - diversity - benin - gender - rituals
    Yam and cowpea are important elements in the food culture of local communities in the Transitional Guinea-Sudan Zone of Benin. Yam and cowpea serve to satisfy vital needs in households and in communities, but also play an essential role in the rituals and ceremonies of the agrarian civilizations of Benin. The diversity of rituals, food habits, technological traits and food security strategies for the two crops contributes to the maintenance of varietal diversity. It is not possible for one or even a few varieties to meet all needs. The more a variety is culturally and socially embedded, the greater the chance that it will meet acceptance on the local and regional market. Farmers' ambition to meet market demands in order to satisfy socio-economic needs also sustains and increases varietal diversity. Especially female farmers growing cowpea showed positive diversity maintenance behaviour. Overall, the study shows that the management of on-farm genetic resources is a socially and culturally constructed system. Any external strategy to improve management of on-farm diversity should take into account these social and cultural aims.
    Ecology and management of charcoal rot (Macrophomina phaseolina) on cowpea in the Sahel
    Ndiaye, M. - \ 2007
    Wageningen University. Promotor(en): Ariena van Bruggen, co-promotor(en): Aad Termorshuizen. - [S.l.] : S.n. - ISBN 9789085046646 - 114
    macrophomina phaseolina - vigna unguiculata - vignabonen - plantenziekten - plantenziekteverwekkende schimmels - geïntegreerde plagenbestrijding - teeltsystemen - compost - biologische bestrijding - sahel - niger - macrophomina phaseolina - vigna unguiculata - cowpeas - plant diseases - plant pathogenic fungi - integrated pest management - cropping systems - composts - biological control - sahel - niger
    Keywords: Senegal/Niger/rotation/millet/isolate characterization/fonio/compost amendment / bioagent/ Clonostachysrosea /solarization

    Cowpea ( Vignaunguiculata Walp.) is the most important pulse crop in theSahelwith nearly 12.5 million hectares per year and is a valuable source of protein for human and animal nutrition. The most limiting factors for crop growth in the Sahelian zone of West Africa are water and nutrient stress. The average cowpea yields in farmers' fields are low (0.2-0.5 ton/ha) and charcoal rot causes on average a yield loss of 10%, which is equivalent to 30.000 tons cowpea - an estimated value of $146 million for Niger and Senegal alone.Disease resistant or tolerant cultivars of cowpea against M . phaseolina are the most efficient control measures but such cultivars are not yet available. Solarization, addition of organic matter, maintenance of high soil moisture, fumigation and use of biocontrol agents have shown to be potential methods for control of soilborne pathogens.The objectives of the thesis is: 1)to characterize cowpea isolates of Macrophomina phaseolina prevalent in the different cowpea cropping systems in Niger and Senegal with respect to culture characteristics and host range; 2) to determine effects of rotation of cowpea with fonio and millet on M. phaseolina disease of cowpea, and production and survival of microsclerotia in soil; 3) to study the effects of compost and a biocontrol agent on M. phaseolina and charcoal rot on cowpea; 4) to study the effects of solarization alone or in combination with organic residues on M. phaseolina and charcoal rot on cowpea.

    Macrophominaphaseolina causes heavy yield loss to cowpea ( Vignaunguiculata ) grown in different cropping systems in the Sahel region ofAfrica. It was not known if cropping systems could influence physiological, genetic and pathogenic characteristics of M. phaseolina isolates. This study therefore aimed to analyze the population structure of M . phaseolina associated with three cropping systems in theSahel. Isolates were collected from soil and infected tissues of different cropping systems in Senegal and Niger and their growth potential at different temperatures, their morphology on PDA medium, their virulence on three cowpea cultivars and sequence analysis of the ITS (internal transcribed spacer) region of the nuclear ribosomal DNA gene studied.Isolates of M. phaseolina differed to a limited extent in temperature optimum, genetic make-up, and pathogenicity to cereal crops. The grouping according to physiological and genetic traits did not coincide with that based on pathogenicity. However, for the first time, we showed some specialization in pathogenicity to cereal crops except fonio ( Digitaria exilis )) for isolates obtained from fields grown to millet next to cowpea.

    Field observations and invitro studies indicated that fonio is a non-host to M. phaseolina , and millet a poor host, respectively. The influence of continuous cropping of these crops on soil inoculum density of M.phaseolinawas studied under field conditions. The data showed thatfonio was not infected by M. phaseolina , while the root systems of millet had low densities of microsclerotia. Cowpea yielded significantly more hay and pods after 3 years of fonio than after 3 years of millet. We conclude that rotation of cowpea with a gramineous crop may lead to a relatively fast decline of inoculum density. In the case of a high inoculum density, fonio can be grown for three years to reduce M . phaseolina densities in soil.

    A field experiment was conducted on the effect of compost on soil inoculum and symptom severity of charcoal rot. The experiment was carried out in naturally infested farmers' fields. The effect of 3 or 6 tons of compost and of 6 tons of compost supplemented with 50 kg NPK fertilizer ha -1 , applied in planting holes, on charcoal rot was assessed for three consecutive years. Besides, the combined effects of 3 tons of compost ha -1 and the biocontrol agent Clonostachysrosea (10 8 CFU's per g compost) on charcoal rot development and cowpea production were investigated. Our results indicated that in Sahelian sandy soil good control and substantial increase of cowpea yield can be achieved by soil amendment with 6 tons of compost ha -1 . An even greater yield increase is achieved by soil amendment with 6 tons of compost and 50 kg NPK ha -1 or 3 tons ha -1 of compost augmented by C.rosea .

    The combined effects of soil solarization and amendment with millet residues and paunch contents on the survival of M . phaseolina and development of charcoal rot of cowpea were assessed in a naturally infested soil.In amended plots, solarization increased the soil temperature to 50°C for at least 4 h day -1 during June, leading to a significant reduction of soil inoculum of M . phaseolina by 44%. Paunch amendment (3 tons ha -1 ) caused 66% reduction of initial inoculum in the solar-heated plots while millet amendment did not enhance microsclerotia reduction in solarized plots. These observations demonstrated that under conditions where solarization alone does not provide sufficient control, the combination with organic amendments improves yields and reduces infection by M . phaseolina . High-N containing amendments may be most effective, such as the paunch used in this study. Solarization as well as application and incorporation of millet residues or paunch content in moistened soil can double cowpea production in poor, naturally infested soil of the Sahelian zone and contribute to the management of paunch waste from slaughter houses in big cities.

    In conclusion the study indicated that M . phaseolinaisolates from different cropping systems in theSahelvary with respect to virulence and ability to cause infection on crop species and cultivars.For the first time we found isolates of C . rosea in theSahelthat are efficient at controlling M . phaseolina . In addition we showed that including fonio in the rotation scheme of cowpea and millet, adding millet residues or paunch contents with or without solar heating and application of 3 tons ha -1 of compost augmented with C . rosea reduced charcoal rot disease and increased cowpea yield. These methods can be integrated intodifferent combinations according to local conditions for managing charcoal rot.
    Socio-economic, agronomic and molecular analysis of yam and cowpea diversity in the Guinea-Sudan transition zone of Benin
    Zannou, A. - \ 2006
    Wageningen : Wageningen University and Research Centre (Tropical resource management papers no. 80) - ISBN 9789085850991 - 236
    boeren - kennis - inheemse kennis - communicatie - genetische bronnen van plantensoorten - pachyrhizus erosus - vignabonen - rassen (planten) - innovaties - bedrijfsvoering - benin - vigna unguiculata - yams - dioscorea - farmers - knowledge - indigenous knowledge - communication - plant genetic resources - pachyrhizus erosus - cowpeas - varieties - innovations - management - benin - vigna unguiculata - yams - dioscorea
    Socio-economic, agronomic and molecular analysis of yam and cowpea diversity in the Guinea-Sudan transition zone of Benin
    Zannou, A. - \ 2006
    Wageningen University. Promotor(en): Paul Richards; Paul Struik, co-promotor(en): V. Agbo; J. Zoundjihékpon. - Wageningen : WUR - ISBN 9789085044352 - 236
    farmers - knowledge - indigenous knowledge - communication - plant genetic resources - pachyrhizus erosus - cowpeas - varieties - innovations - management - benin - vigna unguiculata - yams - dioscorea - boeren - kennis - inheemse kennis - communicatie - genetische bronnen van plantensoorten - pachyrhizus erosus - vignabonen - rassen (planten) - bedrijfsvoering - benin - innovaties - vigna unguiculata - yams - dioscorea
    Keywords: Cowpea (Vigna unguiculata(L.) Walp.),yam ( Dioscorea spp. ), agro-biodiversity, farmer perception, market and consumer preferences, socio-cultural preferences, human and social capitals, genotype by environment interaction, socio-technical knowledge, domestication, inter-(trans)disciplinarity / Beta-gamma science.

    Management and use of yam and cowpea genetic resources analysed in this thesis are important to realize agricultural development inBenin, both on the short and long run. In this thesis the diversity of local varieties of yam and cowpea, often ignored by classical research, is analysed. Different meth­odological approaches, including technography, diagnostic study at village level, and joint farmer-researcher managed experimentation, have been combined with socio-cultural, market and consumer studies. Molecular tools have been used to assess the level of genetic diversity in these two crops.

    Socio-cultural determinants, market and consumers' preferences, and the morphological and agronomic characteristics of different varieties of these two crops are all relevant for social acceptability and adaptability, and for the adoption of new varieties by local subsistence farmers. Different yam and cowpea varieties are used for rituals each year. The yield performance varied from one variety to another, and within one variety, from one year to another (or one place to another) depending on variability in agro-climatic conditions. While any successful variety of yam or cowpea should be adapted to stressful agro-climatic or poor soil conditions, it should be also adapted to the often specific needs of the farmer and to his/her socio-cultural environment. Moreover, varieties need to satisfy consumer preferences and market demands. Often, one single variety of yam or cowpea cannot meet all these criteria. Given these multiple purposes and multiple objectives, adequate management of diversity of varieties is essential to farmers, as a strategy to cope with food security and income generation all year round.

    Prices of different varieties of yam and cowpea on the market reflect the food technological or taste characteristics perceived or recognized by consumers in these varieties. The market provides important information on diversity of varieties and on their characteristics.

    Based on the morphogenetic and physiological characteristics recognized by farmers as limitations, or as natural constraints in the proper use of seed tubers of different yam varieties, this thesis undertook a participatory technology development programme with farmers to improve the knowledge of both the researcher and the farmers of seed tuber propagation through induced sprouting, and through use of different parts of the tuber as planting materials. The thesis also pays attention to farmers' own experimentation in developing new yam varieties by domesticating wild yams, and shows that this activity - probably of ancient provenance inBenin- remains effective for farmers excluded by poverty from market participation. The improvement of the performance of these local
    varieties remains a major future task for researchers and policy-makers inBenin.

    Two major conclusions can be drawn from this thesis. The first is that both social and natural sciences are necessary contributors to the understanding of diversity in yam and cowpea varieties as managed and maintained by farmers. This diversity is expressed at the molecular level and at farm level, but is also highly relevant on the market and in the socio-cultural life of the farmers. The second conclusion relates to findings concerning the possibility of engaging farmers and researchers in joint study of yam and cowpea diversity, with beneficial practical consequences. Joint experimentation focused on varietal characterization, and the joint participatory technology development, indicated that more effective research results can be obtained when farmers' perceptions and depth of experience is fully incorporated in research design. In this regard, technography and diagnosis remain continuously reviewed, allowing the incorporation of new ideas or innovations and new stakeholders in the experimentation process. The results assessment with and by farmers remains an essential aspect of judging work in farmer conditions to improve local livelihoods. In particular, the thesis emphasizes that - through domestication of yam - the poor show that they can contribute actively to development of scientific perspectives. These aspects of the Convergence of Sciences as focused upon yam and cowpea varietal management embrace both an inter-disciplinary and trans-disciplinary research perspective. Cooperation and co-knowledge generation with farmers needs follow-up, and a scaling-up to reach other farmers. Specifically, it needs to be incorporated in the curricula of national research training systems.
    Input levels and intercropping productivity: exploration by simulation
    Wubs, A.M. ; Bastiaans, L. ; Bindraban, P.S. - \ 2005
    Wageningen : Plant Research International (Nota note 369) - 100
    sorghum bicolor - sorghum - vigna unguiculata - vignabonen - teeltsystemen - tussenteelt - simulatiemodellen - input van landbouwbedrijf - watergebruiksrendement - afrika - sorghum bicolor - sorghum - vigna unguiculata - cowpeas - cropping systems - intercropping - simulation models - farm inputs - water use efficiency - africa
    Voorstudie van het effect van verschillende niveaus van waterinput op een sorghum-cowpea intercrop
    Biocontrol in store: spatial and behavioural aspects of foraging by Uscana lariophaga, egg parasitoid of Callosobruchus maculatus, in stored cowpea
    Stolk, C. - \ 2002
    Wageningen University. Promotor(en): J.C. van Lenteren; A. van Huis; W. van der Werf. - S.l. : S.n. - ISBN 9789058087416 - 160
    vignabonen - callosobruchus maculatus - voorraadplagen - biologische bestrijding - vigna unguiculata - trichogrammatidae - parasitoïden - voedingsgedrag - gedrag bij zoeken van een gastheer - cowpeas - vigna unguiculata - callosobruchus maculatus - stored products pests - trichogrammatidae - parasitoids - feeding behaviour - host-seeking behaviour - biological control

    Cowpea ( Vigna unguiculata Walpers), an important crop for West African subsistence farmers, is often infested in storage by the bruchid beetle Callosobruchus maculatus Fabricius. The indigenous egg parasitoid Uscana lariophaga Steffan (Hym.: Trichogrammatidae) is responsible for substantial mortality of C. maculatus eggs and might therefore be used in a conservation strategy of biological control. This thesis focuses on foraging behaviour of U. lariophaga females in a spatial context. In stored cowpea, the bruchid oviposits in clusters. Uscana lariophaga is well adapted to such clusters, since it shows a strong arrestment response after an encounter with an unparasitized host. Previous investigations had already shown attraction of the parasitoid to host-related odours; it is now shown that directed search probably occurs at a short distance (4-6 beans) from the host patch. The probability that a host patch in stored cowpea is found decreases rapidly with increasing distance between the host patch and the site of release of the parasitoid. The 'critical distance' within which the host patch is quickly found by the parasitoid increases if more searching time is allowed. If an experienced parasitoid arrives in a host patch and encounters parasitized hosts, it is likely to superparasitize, but it will stop superparasitizing as soon as an unparasitized host has been encountered in the same patch. Superparasitism by experienced females is not due to failure in host discrimination, as appears from the fact that females adapt the sex ratio of their offspring during superparasitism. If no or few hosts are available, the parasitoid lives shorter than when many hosts are available. This reduced longevity at low host densities may be due to an increased walking activity at low host densities. Finally, the potential of a simulation model of U. lariophaga behaviour is shown, and consequences of behaviour for the prospects of biological control are discussed.

    Traditional African plant products to protect stored cowpeas against insect damage : the battle against the beetle
    Boeke, S.J. - \ 2002
    Wageningen University. Promotor(en): M. Dicke; J.J.A. van Loon; A. van Huis. - S.l. : S.n. - ISBN 9789058087362 - 151
    vigna unguiculata - vignabonen - callosobruchus maculatus - voorraadplagen - plantaardige insecticiden - insecticiden bevattende planten - vigna unguiculata - cowpeas - callosobruchus maculatus - stored products pests - botanical insecticides - insecticidal plants

    Seeds of the cowpea plant, Vigna unguiculata , a tropical crop, are very susceptible to attack by the cowpea beetle. This specialist beetle needs only the beans to reproduce rapidly.

    Most farmers in West Africa have few possibilities to treat the beans and they face their stored supply, on which they are dependent for their daily nourishment, be destroyed within a few months. From lack of other measures, these farmers traditionally used plants, stored together with the beans for protection. In the laboratory, such plants have been tested as powders and as extract for their effect against the beetle. Side effects on natural enemies of the beetle have also been tested for and in a review of the literature, effects on humans have been investigated. Together with the results from a field test in Africa, this gives a picture of the potency of local means to protect stored seeds against insects.

    Origin of the membrane compartment for cowpea mosaic virus RNA replication
    Carette, J.E. - \ 2002
    Wageningen University. Promotor(en): A. van Kammen; J. Wellink. - S.l. : S.n. - ISBN 9789058085573 - 120
    koebonenmozaïekvirus - dna-replicatie - membranen - vigna unguiculata - vignabonen - blaasjes - virusreplicatie - plantenziekten - cowpea mosaic virus - dna replication - membranes - vigna unguiculata - cowpeas - vesicles - viral replication - plant diseases

    Replication of many positive-stranded RNA viruses takes place in association with intracellular membranes. Often these membranes are induced upon infection by vesiculation or rearrangement of membranes from different organelles including the early and late endomembrane system. Upon infection of cowpea cells with cowpea mosaic virus (CPMV) typical cytopathological structures are formed, which consist of an amorphous matrix of electron-dense material traversed by rays of small membranous vesicles. This thesis describes the studies that were undertaken to define the cellular components involved in the establishment of the site of viral RNA replication consisting of vesiculated membranes and electron-dense material. Furthermore, the role of individual viral proteins as well as host proteins in this process was investigated.

    The helper component-proteinase of cowpea aphid-borne mosaic virus
    Mlotshwa, S. - \ 2000
    Agricultural University. Promotor(en): A. van Kammen; J. Wellink; I. Sithole-Niang. - S.l. : S.n. - ISBN 9789058083401 - 111
    vigna unguiculata - vignabonen - potyvirus - kousenbandrolmozaïekvirus - pathogeniteit - weerstand - dna-sequencing - dna - genoomanalyse - genetische modificatie - genetische transformatie - ziekteresistentie - vigna unguiculata - cowpeas - potyvirus - blackeye cowpea mosaic virus - pathogenicity - resistance - dna sequencing - dna - genome analysis - genetic engineering - genetic transformation - disease resistance

    Cowpea aphid-borne mosaic potyvirus causes severe yield losses in cowpea, an important legume crop in semi-arid regions of Africa. We have elucidated the genomic sequence of the virus and subsequently focused our attention on the so-called helper component-proteinase (HC-Pro), a virus-encoded multifunctional protein with roles in different steps of the virus life cycle. Our study has shed more insight into some of the molecular properties of this protein. We have shown that HC-Pro is able to shut down host defense responses, and this puts HC-Pro at the core of the success of CABMV as a pathogen. The phenomenon also seems to benefit other viruses as they accumulate to higher levels and elicit enhanced symptoms in the presence of HC-Pro. On the other hand, we have found that the host does manifest an ability to counter the deleterious effects of HC-Pro. A full understanding of the molecular basis of this contest would enable the design of effective new strategies to protect plants from virus infections.

    Molecular characterisation of the cowpea mosaic virus movement protein
    Bertens, P. - \ 2000
    Agricultural University. Promotor(en): A. van Kammen; J. Wellink. - S.l. : S.n. - ISBN 9789058083104 - 144
    virologie - koebonenmozaïekvirus - vignabonen - vigna unguiculata - comovirus - transport - eiwitten - plasmodesmata - virology - cowpea mosaic virus - cowpeas - vigna unguiculata - comovirus - transport - proteins - plasmodesmata

    Virussen zijn subcellulaire parasieten die niet zelfstandig kunnen bestaan, maar cellen binnendringen en cellulaire mechanismen van hun gastheer gebruiken voor vermenigvuldiging. Virussen zijn verantwoordelijk voor vele ernstige ziektes bij mensen en dieren (zoals bijvoorbeeld griep, verkoudheid of AIDS), maar ook bij planten, waar virussen verantwoordelijk kunnen zijn voor de vernietiging van hele oogsten. Virussen zijn vrij eenvouding van structuur en bevatten een kleine hoeveelheid genetisch materiaal, dat uit DNA of RNA kan bestaan. Dit genoom is omgeven door een beschermende eiwitlaag, de mantel.

    Terwijl dierlijke virussen normaal cellen binnenkomen via chemische interacties met specifieke herkenningsmoleculen (receptoren) in de celmembraan, zijn celmembranen van plantencellen omhuld door een pantserbekleding van cellulose die een ondoordringbare hindernis vormt voor plantenvirussen. De meeste virussen kunnen een plant pas binnendringen na mechanische beschadiging of met behulp van een biologische vector (b.v. een bladluis of een ander insect) die de virussen tijdens het voeden rechtstreeks in een gastheercel binnenbrengen. In zo een initiëel geïnfecteerde cel wordt het virale genoom, dat uit één of meerdere DNA of RNA moleculen kan bestaan, vertaald in virale eiwitten die zorg dragen voor de replicatie van het virale genoom en de bemanteling van het virale RNA. Na deze vermenigvuldigingsstap verspreidt het virus zich verder door de plant en zal in eerste instantie de naburige cellen infecteren (via het zogeheten lokaal transport of cel-cel transport). Nadat een infectie de vaatbundels bereikt heeft, zullen virusdeeltjes zich via de vaatbundels door de rest van de plant verspreiden (het lange-afstands transport). In de hoger gelegen bladeren treedt het virus de vaatbundels weer uit, en verspreidt het zich opnieuw via cel-cel transport naar andere cellen van dat blad.

    Als een virus zich vanuit een initiëel geïnfecteerde cel naar naburige cellen wil verspreiden, stuit het opnieuw op de ondoordringbare celwand. Deze hindernis wordt met behulp van een speciaal mechanisme omzeilt. In de celwand zitten nauwe kanaaltjes, de plasmodesmata, die naburige cellen met elkaar verbinden. Deze kanaaltjes spelen een rol bij de verspreiding van (voedings)stoffen en worden door de plant gebruikt voor intercellulaire communicatie. Virussen zouden deze plasmodesmata kunnen gebruiken voor lokaal transport, ware het niet dat ze te groot zijn om door de kanaaltjes heen te kunnen gaan. De oplossing die virussen hebben ontwikkeld om dit probleem te omzeilen is even elegant als simpel: ze coderen voor een specifiek eiwit (het transporteiwit, afgekort MP voor het Engelse "movement protein"), die de diameter van plasmodesmata kan vergroten, waardoor transport van virusdeeltjes of complexen van viraal RNA en MP mogelijk wordt. In hoofdstuk 1 wordt een overzicht gegeven van virale MPs en de verschillende mechanismen die plantenvirussen hebben ontwikkeld om zich van cel naar cel te verspreiden.

    Dit proefschrift beschrijft een onderzoek waarin het MP van het koebonenmozaïekvirus (op z'n Engels "cowpea mosaic virus" (CPMV) geheten) centraal staat. Dit virus infecteert voornamelijk tropische planten, waaronder kouseband ( Vigna unguiculata ), een plant waarvan de peulen vooral in Afrika en Zuid-Amerika een belangrijke voedingsmiddel zijn (kouseband is ook in Nederland op veel plaatsen te koop; voor een tip hoe deze te bereiden, kan de auteur van dit proefschrift benaderd worden). Een infectie van kouseband door CPMV wordt gekenmerkt door de vorming van milde tot hevige mozaïek-symptomen op geïnfecteerde bladeren, die tot afsterven van het blad kan leiden. Het genoom van CPMV bestaat uit een tweetal enkelstrengs RNA moleculen met een positieve polariteit. Deze RNA moleculen worden in een geïnfecteerde cel vertaald in een drietal polyeiwitten, die door een viraal enzym in stukken worden geknipt tot kleinere producten. De door het RNA1 gecodeerde eiwitten zijn betrokken bij de virale replicatie. De eiwitten die gecodeerd worden door RNA2, spelen een rol bij het cel-cel en het lange-afstands transport van CPMV. Dit zijn de twee manteleiwitten LCP en SCP, een 58K eiwit, dat nodig is voor replicatie van RNA2 en het MP.

    Met behulp van electronen-microscopische analyse zijn in CPMV-geïnfecteerd weefsel buisvormige structuren aangetroffen, die gevuld zijn met virusdeeltjes. Deze buizen steken door een gemodificeerde plasmodesma van een geïnfecteerde cel in het cytoplasma van een naburige cel. Soortelijke structuren zijn aangetroffen in protoplasten (geïsoleerde plantencellen) die geïnfecteerd zijn met CPMV en in protoplasten of insectencellijnen waarin alleen het MP specifiek tot expressie is gebracht. Deze experimenten laten zien dat voor de vorming van de buizen geen plasmodesmata nodig zijn. Biochemische analyse van de buizen heeft laten ziendat de buizen grotendeels of zelfs helemaal zijn opgebouwd uit het MP.

    Het proces van buisvorming gebeurd waarschijnlijk in een aantal stappen. Nadat het MP aangemaakt is in virale replicatie complexen moet het naar de celmembraan getransporteerd worden, waar het zich bij plasmodesmata zal ophopen en een buis zal vormen. Tijdens deze buisvorming worden de virusdeeltjes in de buis ingebouwd. De plasmodesma waarin de buis wordt gevormd, wordt drastisch gemodificeerd. Verschillende gebieden (domeinen) van het MP zullen een specifieke rol hebben en betrokken zijn bij een of meerdere van de hierboven beschreven stappen. In hoofdstuk 2 hebben we getracht zulke domeinen te vinden door met behulp van moleculair-biologische technieken mutaties aan te brengen binnen het MP en het effect hiervan op onder andere de buisvorming te onderzoeken. Uit de resultaten blijkt dat het resultaat van een subtiele mutatie heel drastisch kan zijn. Sommige mutaties hebben tot gevolg dat het MP geen buizen meer kan vormen. Virussen die dit mutant MP bezitten zijn niet meer in staat om zich te verspreiden in planten. Mutaties aangebracht op andere plaatsen in het MP lijken nauwelijks effect te hebben op de eigenschappen van het transporteiwit. We hebben ontdekt dat het N-terminale en het centrale deel van het MP nodig zijn voor het transport naar de plasmodesmata en voor de vorming van de buizen.

    Het volgen van een virusinfectie in levende planten is erg moelijk. Virussen zijn alleen maar te zien onder een electronenmicroscoop waarvoor men echter de delen van de plant die men wil onderzoeken moet fixeren. Door deze behandeling sterven de plantcellen en kunnen er allerlei ongewilde veranderingen (artefacten) optreden in het weefsel. Een paar jaar terug is er een nieuwe methode ontwikkeld om een virusinfectie in levende planten te volgen. Men maakt hiervoor gebruik van een fluorescent eiwit, het "green fluorescent protein" (GFP). Dit eiwit komt van nature voor in kwallen en heeft de bijzondere eigenschap om groen op te lichten (te fluoresceren) indien het wordt beschenen met UV-licht. Met behulp van moleculair-biologische technieken is dit GFP ingebouwd in CPMV. Als we planten hiermee infecteren, kunnen we de infectie in de tijd volgen door de planten onder een UV-lamp of onder een fluorescentie-microscoop te onderzoeken, zoals staat beschreven in de hoofdstukken 3 en 4.

    In hoofdstuk 3 hebben we ons geconcentreerd op het C-terminale deel van het MP. Door de analyse van deletie-mutanten en hybride MPs (bestaande uit delen van het MP van het rode-klavervlekkenvirus en dat van CPMV) was het mogelijk om bijna op het aminozuur nauwkeurig de grens aan te geven van het domein dat betrokken is bij de vorming van buizen. De buizen gevormd door een MP mutant, waarin de laatste 10 aminozuren waren vervangen door GFP, bleken geen virusdeeltjes te bevatten. Blijkbaar blokkeert GFP het functioneren van een MP domein dat betrokken is bij de inbouw van virusdeeltjes in buizen. Indien een virus naast wild-type (normaal) MP ook een mutant MP (die geen functionele C-terminus heeft) bezit, verspreidt het virus zich toch door de plant. De buizen, die waarschijnlijk zowel uit het wild-type alsook het mutant MP bestaan, zijn niet helemaal netjes gevuld met virusdeeltjes. Af en toe lijkt er wat ruimte tussen de verschillende deeltjes te zitten. Deze resultaten geven aan dat alle C-termini nodig zijn voor het virale transport.

    Een van de bijzondere eigenschappen van GFP is, dat na fusie van GFP aan een ander eiwit (b.v. het MP), de intracellulaire localisatie van dat eiwit kan worden bekeken in levend materiaal. In hoofdstuk 4 hebben we de intracellulaire locatie van een aantal fusieproducten tussen GFP en het CPMV MP nader onderzocht. In eerste instantie hebben we een fusie gemaakt tussen het wild-type MP en GFP. Een virus coderend voor dit MP:GFP fusieproduct was in staat (fluorescente) buizen te maken in protoplasten. In planten hoopt het MP:GFP zich op als opvallende punten (spots) in de celwand. Deze plaatsen zijn waarschijnlijk de eerder aangehaalde gemodificeerde plasmodesmata, waar cel-cel verspreiding van het virus plaatsvindt. In sommige gevallen werden zelfs fluorescente buizen in de celwand aangetroffen. De infectie van dit genetisch gemodificeerde virus bleek echter beperkt tot enkele cellen. Vervolgens zijn een aantal van de in hoofdstuk 2 gekarakteriseerde MP mutanten gefuseerd aan GFP en is de localisatie van deze mutant MP:GFP eiwitten bekeken in protoplasten en planten. MPs die een mutatie bevatten in hun centrale deel bleken verstoord te zijn in het intracellulaire transport naar de celmembraan en hoopten zich op in het cytoplasma. Een van de mutant MP:GFPs hoopte zich tevens op in structuren die in de buurt van de celkern in het cytoplasma liggen. Waarschijnlijk zijn dit virale replicatie-complexen en is dit mutant MP:GFP niet in staat zich hieruit los te maken. Mutante MP:GFPs met veranderingen in het C-terminale deel van het MP werden wel naar de celmembraan getransporteerd, maar waren verstoord in de initiatie of elongatie van de buizen.

    We kunnen concluderen dat het in dit proefschrift beschreven onderzoek heeft geleid tot een beter inzicht in het mechanisme dat CPMV gebruikt voor zijn cel-cel verspreiding. Middels mutatie-analyse en door gebruik te maken van GFP hebben we een aantal functionele domeinen van het CPMV MP geïdentificeerd. We kunnen het MP grofweg in twee functionele domeinen verdelen. Een groot deel van de N-terminale en centrale gebieden van het eiwit zijn betrokken bij de vorming van buisvormige structuren in protoplasten en planten. Dit domein is onder te verdelen in gebieden die betrokken zijn bij het intracellulaire transport naar de plasmodesmata toe en in gebieden die een rol spelen bij de initiatie van buisvorming. Het C-terminale deel is niet betrokken bij buisvorming, maar speelt een rol bij de inbouw van virusdeeltjes in de buizen. De in dit proefschrift beschreven resultaten zullen worden gebruikt voor vervolgstudies, die onder andere gericht zullen zijn op de identificatie van gastheer-eiwitten die een interactie aangaan met het CPMV MP en op het ophelderen van het intracellulaire transport van het MP.

    Expression and silencing of cowpea mosaic virus transgenes
    Sijen, T. - \ 1997
    Agricultural University. Promotor(en): A. van Kammen; J. Wellink. - S.l. : Sijen - ISBN 9789054857235 - 133
    koebonenmozaïekvirus - genexpressie - pleiotropie - genetische modificatie - recombinant dna - vigna - vignabonen - cowpea mosaic virus - gene expression - pleiotropy - genetic engineering - recombinant dna - vigna - cowpeas

    Plant viruses are interesting pathogens because they can not exist without their hosts and exploit the plant machinery for their multiplication. Fundamental knowledge on viral processes is of great importance to understand, prevent and control virus infections which can cause drastic losses in crops. In this thesis, cowpea mosaic virus (CPMV) was studied. This virus consists of two, icosahedral particles that each carry a distinct single stranded RNA molecule of positive polarity. Several years of research have revealed much information on the genomic organisation, the strategy of gene expression and the multiplication processes of CPMV, which are described in Chapter 1, but also many aspects remain to be elucidated.

    To study individual viral processes, like replication, encapsidation or cell to cell movement, transgenic plants can be generated that express individual viral genes like the replicase, coat protein or movement protein gene. A prerequisite in this approach is the presence of an efficient and reliable plant regeneration and transformation system. (CPMV) 5 natural host is the tropical grain legume cowpea, Vigna unguiculata, a plant species that is recalcitrant at regeneration. Although in experiments described in Chapter 2 fertile plants could be regenerated from nodal thin cell layer segments, the explants were not competent for Agrobacterium-mediated transformation. Possibly in further studies, these nodal explants could prove suited for another transformation method.

    Therefore, tobacco, which is also a host for CPMV and highly competent for regeneration and transformation, was preferred as the species to generate transgenic plants carrying CPMV specific genes. Especially the CPMV movement proteins (MP) genes appealed to us for overexpression studies. CPMV cell to cell movement is enabled by the CPMV MPs that act to modify plasmodesmata. They are assumed to channel plasmodesmata with MP-containing tubular structures and through or with these tubules virus particles are transported to adjacent cells. To obtain more information on the plasmodesmatal modifications brought about by the MPs, transgenic tobacco plants were generated that carried the MP gene under the control of either a constitutive or an inducible 35S promoter. However, in none of these plants the MPs were expressed to detectable levels (Chapter 3). Using the potato virus X (PVX)-based expression vector, accumulation of CPMV MPs was observed in the form of tubular structures extending from the surface of infected protoplasts into the medium. These PVX-derivatives look promising for providing effective tools in future studies on the effects of the CPMV MPs in plants.

    Studies on MP functioning could involve complementation experiments with a CPMV mutant that is defective in cell to cell movement. In experiments described in Chapter 4 is was analysed by a molecular approach whether the CPMV mutant N123, that was first described in 1976, could be used to this effect. As the basis of the N123 specific phenotype was found not only to rest in the movement protein gene but also in one of the two coat protein genes, this mutant seemed not very suitable for complementation studies. Presumably a recently developed CPMV mutant in which the MP gene has been replaced by the fluorescent marker protein GFP (green fluorescent protein), will be a more appropriate tool.

    Transgenic Nicotiana benthamiana plants that were expressing either the CPMV MP or the replicase gene under the control of a constitutive promoter, were found to exhibit a resistant phenotype when inoculated with CPMV (Chapter 5). Protoplast studies revealed that the resistance occurred as full immunity and was maintained in the cell. Resistance was specific to viruses highly homologous to CPMV, and in addition it was found to be specifically directed against the replication of the CPMV segment of which the transgene was derived (Chapter 5). Pathogen derived resistance can be mediated either by the protein encoded by the transgene or by the transcribed mRNA. Protein -mediated resistance generally offers moderate protection against a broad range of viruses, while RNA-mediated resistance results in immunity at the cellular level. Resistance obtained in transgenic plants transformed with defective genes confirmed that an RNA-based mechanism was underlying the highly specific transgenic resistance against CPMV (Chapter 6).

    Specifically in the resistant lines, the transgene mRNA steady state levels were low compared to the relative transgene nuclear transcription rates (Chapter 6). This indicated that resistance occurs from a specific, cytoplasmic RNA turnover mechanism. This process can be regarded as a post- transcriptional gene-silencing process, that is primarily induced on the transgene mRNAs but to which also incoming, homologous CPMV genomes fall victim. In addition, heterologous RNA molecules, like PVX genomes, that contain the sequences corresponding to the transgene, are eliminated (Chapter 6). By inserting sequences homologous to only parts of the transgene in the genome of PVX and studying the fate of these recombinant genomes, it was shown that the degradation process is primarily targeted to a defined region of the transgene mRNA, the 3' region. Further analyses revealed that degradation can occur at various sites within this 3' region and that not a specific sequence or structure is of predominant importance. We observed that small inserts, like of only 60 nucleotides, can tag recombinant PVX molecules for the elimination process, albeit with reduced efficiency, which suggested that the RNA turnover process carries quantitative features.

    On the intruiging question why post-transcriptional gene-silencing is induced in only some of the transgenic lines, we revealed (Chapter 6) that the organisation of integrated transgene sequences has an important role. Transformation with a transgene containing a directly repeated MP gene, increased the frequency at which resistant lines arise to 60%, compared to 20% of resistant lines that occur upon transformation with a transgene with a single MP gene. Thus, the resistance process seems influenced by qualitative features of the integrated transgenes. Also, it was observed that resistance concurred with extensive methylation at the transcribed transgene sequences (Chapter 6), which could indicate an essential role of methylation at transcribed sequences in obtaining RNA-mediated pathogen derived resistance.

    From these observations and from data described in literature, a model for RNA-mediated virus resistance was made and presented in Chapter 6. In Chapter 7, the post-transcriptional gene-silencing phenomenon is discussed in more details and in addition an approach is presented by which the process could be exploited to efficiently engineer virus resistance or study plant gene expression.

    Foraging behaviour of the egg parasitoid Uscana lariophaga : towards biological control of bruchid pests in stored cowpea in West Africa
    Alebeek, F. van - \ 1996
    Agricultural University. Promotor(en): J.C. van Lenteren; A. van Huis. - S.l. : Van Alebeek - ISBN 9789054856139 - 176
    Chalcididae - Eulophidae - Trichogrammatidae - diergedrag - Vigna - vignabonen - insecten - plantenplagen - Bruchidae - biologische bestrijding - nuttige insecten - Chalcididae - Eulophidae - Trichogrammatidae - animal behaviour - Vigna - cowpeas - insects - plant pests - Bruchidae - biological control - beneficial insects

    Seed beetles cause considerable losses in traditionally stored cowpea ( Vigna unguiculata Walp.) under subsistence farming conditions in West Africa. The indigenous egg parasitoid Uscana lariophaga Steffan (Hymenoptera; Trichogrammatidae) is evaluated as a candidate for a conservation strategy of biological control against the major pest Callosobruchus maculatus Fab. (Coleoptera; Bruchidae). Different aspects of U. lariophaga 's searching efficiency, such as host habitat location, host cluster location, the functional response, egg laying capacity and egg load, host handling time, arrestment response, photo- and geotaxis, dispersal and walking behaviour, have been investigated and results are reported in this thesis. Uscana lariophaga uses odour of uninfested cowpea seeds and of C. maculatus eggs to locate host habitats and host clusters therein. Host clusters with many eggs are more frequently located than clusters with few eggs, probably through olfaction. The parasitoid demonstrates a Holling Type II functional response, and the maximum number of hosts parasitized is determined by her ovarial egg load. Due to a strong arrestment response within host clusters, and area restricted searching behaviour after an oviposition, U. lariophaga parasitizes more eggs in host clusters with an even or clumped distribution than in clusters with a low density random distribution. Uscana lariophaga is positive phototactic and negative geotactic, and can move through cowpea stock over several meters a day. Under optimal conditions, U. lariophaga can significantly reduce losses in stored cowpea by C. maculatus . Further progress towards biological control of cowpea storage pests is discussed.
    Photothermal regulation of phenological development and growth in bambara groundnut (Vigna subterranea (L.) Verdc.)
    Linnemann, A.R. - \ 1994
    Agricultural University. Promotor(en): M. Wessel, co-promotor(en): R. Rabbinge; E. Westphal. - S.l. : Linnemann - ISBN 9789054853350 - 123
    vigna - vignabonen - licht - fotoperiodiciteit - vigna - cowpeas - light - photoperiodism

    The photothermal regulation of phenological development and growth in bambara groundnut ( Vigna subterranea ) wa s studied to elucidate the crop's potential and limitations in current or future cropping systems. Eight accessions from the germplasm collection of the International Institute of Tropical Agriculture (IITA) were used for a preliminary assessment of sensitivity to photoperiod. In some accessions, photoperiods of 14 h or longer delayed or inhibited the onset of two developmental stages, flowering and podding, in comparison with photoperiods of 11 h or less. Within an accession, podding was always affected more than flowering. Microscopic studies in the laboratory enabled the cause of the delay or absence of the onset of podding under long photoperiods (14 h or more) to be identified as a check in the growth of fertilized ovaries. The minimal inductive period for the onset of podding was determined for two accessions differing in sensitivity to photoperiod. In the comparatively photoperiod-sensitive accession, the time of pod induction in relation to pod position on the plant was studied too. Three accessions were used to test whether the rate of progress towards flowering and the rate of progress towards podding could be described as functions of mean diurnal temperature and/or photoperiod. Finally, earlier indications that photoperiod influences growth as well as development were verified. The results of the experiments demonstrate the flexibility in the development of bambara groundnut, particularly in relation to changes in photoperiod. This flexibility largely explains why the crop can produce itself under marginal conditions in rain-fed areas.

    Cultivation of bambara groundnut (Vigna subterranea (L.) Verdc.) in Western Province, Zambia : report of a field study
    Linnemann, A.R. - \ 1990
    Wageningen : Agricultural University (Tropical crops communication / Wageningen Agricultural University, Department of Tropical Crop Science no. 16) - 34
    vignabonen - teelt - cultuurmethoden - peulvruchten - vigna - zambia - cowpeas - cultivation - cultural methods - grain legumes
    Early stages in cowpea chlorotic mottle virus infection
    Roenhorst, J.W. - \ 1989
    Agricultural University. Promotor(en): R.W. Goldbach; B.J.M. Verduin. - S.l. : Roenhorst - 99
    plantenziekten - plantenvirussen - vigna - vignabonen - virussen - cellen - relaties - plant diseases - plant viruses - vigna - cowpeas - viruses - cells - relationships

    Virussen zijn infectieuze eenheden, bestaande uit nucleïnezuren welke omgeven zijn door een eiwitmantel en eventueel een membraan. Voor wat betreft hun vermenigvuldiging zijn virussen afhankelijk van een levende gastheercel, waarbij ze over het vermogen moeten beschikken deze binnen te dringen, zich erin te vermenigvuldigen en zich vervolgens naar andere cellen te verspreiden.

    Gedurende de laatste decennia is onze kennis over virussen en hun vermogen tot infectie enorm toegenomen. De opkomst van de moleculair- en celbiologische technieken heeft bijgedragen tot een gedetailleerde kennis van zowel de organisatie van het virale genoom, als de mechanismen die aan de expressie en replicatie ervan ten grondslag liggen. Daarnaast hebben biofysische studies informatie verschaft over de structuur en assemblage van het virale deeltje. De kennis over de initiële stadia van het infectieproces, het binnendringen in de gastheercel en de ontmanteling van het virale genoom bleef echter zeer schaars. Het feit dat in veel gevallen slechts enkele virusdeeltjes verantwoordelijk zijn voor infectie heeft vooral bestudering van de initiële interacties tussen virus en gastheercel aanzienlijk bemoeilijkt.

    Dit proefschrift beschrijft het onderzoek verricht aan deze initiële stadia van virusinfecties bij planten. Twee vragen stonden hierbij centraal: (1) hoe en in welke vorm dringt een plantevirus een te infecteren cel binnen en (2) welk mechanisme is verantwoordelijk voor de ontmanteling van het virale genoom? Als model voor dit onderzoek is gekozen voor cowpea chlorotic mottle virus (CCMV) en geïsoleerde cowpea ( Vigna unguiculata ) mesophyl protoplasten. Een aantal eigenschappen van dit modelsysteem zijn weergegeven in de inleiding (Hoofdstuk l).

    Met betrekking tot de initiële interacties tussen virus en gastheercel is voor zowel dierals plantevirussen een beknopt literatuuroverzicht gegeven van de tot nu toe bekende mechanismen (Hoofdstuk 2). Zowel op het niveau van de binding aan het celoppervlak, het binnendringen in de gastheercel, als ook op het niveau van de ontmanteling van het virale genoom, zijn verschillen en overeenkomsten tussen dier- en plantevirussen belicht. De meest opmerkelijke verschillen werden aangetroffen bij de binding en binnendringing van de gastheercel. Is voor de meeste diervirussen binding aan specifieke componenten van de plasmamembraan (receptoren) noodzakelijk voor penetratie, voor plantevirussen lijkt alleen een beschadiging van de plasmamembraan voldoende.

    Om na te gaan in hoeverre ook voor plantevirussen (specifieke) interacties met membraancomponenten van belang zijn voor infectie van de cel, is de binding van CCMV aan cowpea protoplasten -bestudeerd in relatie tot binnendringing en infectie (Hoofdstuk 3). Uit de resultaten van dit onderzoek bleek dat de binding van CCMV aan geïsoleerde protoplasten gebaseerd is op (aspecifieke) elektrostatische interacties, terwijl penetratie afhankelijk is van mechanische beschadiging van de plasmamembraan. Tevens zijn aanwijzingen verkregen dat virusdeeltjes, welke middels endocytose worden opgenomen, niet betrokken zijn bij infectie van de cel. Uit deze gegevens werd geconcludeerd dat alleen die virusdeeltjes, die via membraanbeschadigingen direct in het cytoplasma van de gastheercel terecht komen, verantwoordelijk zijn voor infectie. Ten gevolge hiervan moet worden verondersteld dat ontmanteling van het virale genoom intracellulair plaatsvindt.

    Aangezien voor het tabaksmozaïekvirus (TMV) inmiddels sterke aanwijzingen waren verkregen dat cytoplasmatische ribosomen een rol spelen bij ontmanteling van het genoom middels "cotranslational disassembly", werd nagegaan in hoeverre dit mechanisme ook van toepassing zou kunnen zijn op CCMV. "Cotranslational disassembly" veronderstelt dat ontmanteling plaatsvindt gelijk-tijdig met translatie van het virale genoom, waarbij in het geval van TMV het virusdeeltje vooraf zodanig behandeld moet worden dat het 5'-uiteinde van het RNA beschikbaar is voor initiatie van translatie.

    Door in eerste instantie gebruik te maken van celvrije translatiesystemen werden aanwijzingen verkregen dat ook voor CCMV "cotranslational disassembly" een rol zou kunnen spelen bij de ontmanteling (Hoofdstuk 4). Na toevoeging van intacte virusdeeltjes aan dergelijke systemen werd synthese van virus specifieke eiwitten waargenomen. Bovendien kon de aanwezigheid van translationeel actieve virus-ribosoom complexen worden aangetoond.

    De interactie tussen CCMV en ribosomen werd vervolgens nader geanalyseerd op eiwitniveau (Hoofdstuk 5). Hiertoe werden electroblots van ribosomale eiwitten, gescheiden onder denaturerende omstandigheden, geïncubeerd met virus, en werd het gebonden virus met behulp van immunologische methoden zichtbaar gemaakt. Ongeveer twintig eiwitten, behorend tot zowel de grote als kleine ribosomale subeenheden, bleken virus en/of viraal mantel-eiwit te binden. Dezelfde ribosomale eiwitten bleken eveneens betrokken te zijn bij binding van een aantal andere plantevirussen. Hoewel de beschreven experimenten hierover onvoldoende uitsluitsel geven, zou de waargenomen binding van virus aan deze ribosomale eiwitten op een functionele rol kunnen duiden.

    Naast deze analyse op eiwitniveau is tevens gekeken naar de rol van "cotranslational disassembly" in de ontmanteling van CCMV in vivo (Hoofdstuk 6). Op verschillende tijdstippen na inoculatie werden met CCMV geïnoculeerde cowpea protoplasten gelyseerd en vervolgens geanalyseerd op de aanwezigheid van virus-ribosoom complexen. Inderdaad werden virus-ribosoom complexen aangetroffen, echter in tegenstelling tot in vitro, kon hun translationele activiteit in vivo niet worden aangetoond. Hiervoor wordt een aantal mogelijke verklaringen gegeven. Anderzijds benadrukten ook deze resultaten nogmaals de sterke affiniteit tussen CCMV en ribosomen, en werden aanwijzingen verkregen dat de vorming van virus-ribosoom complexen vooraf zou kunnen gaan aan een eventuele initiatie van "cotranslational disassembly".

    Tenslotte zijn de in de diverse experimentele systemen verkregen gegevens samengevat in een model (Hoofdstuk 7, Figuur l). Dit model beoogt een beeld te geven van die gebeurtenissen die van toepassing zijn op de wellicht minder dan 0,01 % van de virusdeeltjes die verantwoordelijk zijn voor infectie van de cel. Met name daar waar het de interactie tussen virusdeeltje en ribosoom betreft, voorafgaand aan de initiatie van "cotranslational disassembly", bestaan nog veel vraagtekens. Een verdere ontrafeling van deze complexe interacties, alsmede het aantonen van "cotranslational disassembly" van CCMV in vivo. kunnen bijdragen tot een beter begrip van de initiële stadia van virusinfecties bij planten.

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