Staff Publications

Staff Publications

  • external user (warningwarning)
  • Log in as
  • language uk
  • About

    '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.

    We have a manual that explains all the features 

    Current refinement(s):

    Records 1 - 20 / 85

    • help
    • print

      Print search results

    • export

      Export search results

    Check title to add to marked list
    Understanding the productivity of cassava in West Africa
    Ezui, Kodjovi Senam - \ 2017
    Wageningen University. Promotor(en): Ken Giller, co-promotor(en): Linus Franke; A. Mando. - Wageningen : Wageningen University - ISBN 9789463430470 - 183
    manihot esculenta - cassava - crop production - rainfed agriculture - drought - crop yield - water use efficiency - radiation use efficiency - fertilizers - togo - ghana - west africa - manihot esculenta - cassave - gewasproductie - regenafhankelijke landbouw - droogte - gewasopbrengst - watergebruiksrendement - stralingsbenuttigingsefficiëntie - kunstmeststoffen - togo - ghana - west-afrika

    Drought stress and sub-optimal soil fertility management are major constraints to crop production in general and to cassava (Manihot esculenta Crantz) in particular in the rain-fed cropping systems in West Africa. Cassava is an important source of calories for millions of smallholder households in sub-Sahara Africa. The prime aim of this research was to understand cassava productivity in order to contribute to improving yields, food security and farm incomes in rain-fed cassava production systems in West Africa. A long-term goal was to contribute to a decision support tool for site-specific crop and nutrient management recommendations. Firstly, we studied farmers’ perception of cassava production constraints, assessed drivers of diversity among households and analysed the suitability of farmers’ resource endowment groups to the intensification of cassava production. The results indicate that farmers perceived erratic rainfall and poor soil fertility to be prime constraints to cassava production. The agricultural potential of the area and the proximity to regional markets were major drivers for the adoption of crop intensification options including the use of mineral and organic fertilizers. While the use of mineral and organic fertilizers was common in the Maritime zone that had a low agricultural potential, storage roots yields were below the national average of 2.2 Mg dry matter per hectare, and average incomes of 0.62, 0.46 and 0.46 US$ per capita per day for the high, medium and low farmer resource groups (REGs – HRE, MRE and LRE, respectively) were below the poverty line requirement of 1.25 US$. In the high agricultural potential Plateaux zone, HRE and MRE households passed this poverty line by earning 2.58 and 2.59 US$ per capita per day, respectively, unlike the LRE households with 0.89 US$ per capita per day. Secondly, we investigated the effects of mineral fertilizer on nutrient uptake, nutrient physiological use efficiency and storage roots yields of cassava since soil fertility was a major issue across the zones. We used an approach based on the model for the Quantitative Evaluation of the Fertility of Tropical Soils (QUEFTS). This model was successfully adapted for cassava and it appropriately assessed the response of cassava to N, P and K applications, especially in years with good rainfall. Under high drought stress, the model overestimated cassava yields. Thirdly, we investigated the impact of balanced nutrition on nutrient use efficiency, yield and return on investment compared to blanket fertilizer use as commonly practiced in cassava production systems in Southern Togo, and in Southern and Northern Ghana. The balanced nutrition approach of the QUEFTS model aimed to maximize simultaneously nutrient use efficiency of N, P and K in accordance with the plant’s needs. Larger nutrient use efficiencies of 20.5 to 23.9 kg storage root dry matter (DM) per kilo crop nutrient equivalent (1kCNE of a nutrient is the quantity of that nutrient that has the same effect on yield as 1 kg of N under balanced nutrition conditions) were achieved at balanced nutrition at harvest index (HI) of 0.50 compared to 20.0 to 20.5 kg storage root DM per kilo CNE for the blanket rates recommended by national research services for cassava production. Lower benefit:cost ratios of 2.4±0.9 were obtained for the blanket fertilizer rates versus 3.8±1.1 for the balanced fertilizer rates. Our study revealed that potassium (K) was a major yield limiting factor for cassava production, especially on the Ferralsols in Southern Togo. Hence, we fourthly studied the effect of K and its interaction with nitrogen (N), phosphorus (P), and the timing of harvest on the productivity of cassava in relation to the effects of K on radiation use efficiency (RUE), light interception, water use efficiency (WUE) and water transpiration. The results suggest that K plays a leading role in RUE and WUE, while N is the leading nutrient for light interception and water transpiration. Potassium effects on RUE and WUE depended on the availability of N and harvest time. Values of RUE and WUE declined with harvest at 4, 8 and 11 months after planting. Thus, enhanced K management with sufficient supply of N during the early stage of development of cassava is needed to maximize RUE and WUE, and consequently attain larger storage root yields. Given that erratic rainfall was another major constraint to cassava production according to the results of the farm survey, and due to the inability of QUEFTS modelling to assess drought effects on cassava yield successfully, another modelling approach based on light interception and utilization (LINTUL) was used. We quantified drought impacts on yields and explored strategies to improve yields through evaluation of planting dates in Southern Togo. The evaluation of the model indicated good agreement between simulated and observed leaf area index (Normalised Root Mean Square Error - NRMSE - 17% of the average observed LAI), storage roots yields (NRMSE 5.8% of the average observed yield) and total biomass yield (NRMSE 5.8% of the average observed). Simulated yield losses due to drought ranged from 9-60% of the water-limited yields. The evaluation of planting dates from mid-January to mid-July indicated that the best planting window is around mid-February. Higher amount of cropping season rainfall was also achieved with early planting. These results contradict current practices of starting planting around mid-March to mid-April. However, the results indicate the possibility to increase cassava yields with early planting, which led to less yield losses due to drought. By contrast, late planting around June-July gave larger potential yields, and suggested these periods to be the best planting window for cassava under irrigated conditions in Southern Togo. This shows that appropriate water control and planting periods can contribute to attaining larger yields in Southern Togo. Further improvement of the LINTUL model is required towards using it to assess water-limited yield, which can be used as boundary constraint in QUEFTS to derive site-specific fertilizer requirements for enhanced cassava yield and returns on investments in West Africa.

    People, soil and manioc interactions in the upper Amazon region
    Peña Venegas, C.P. - \ 2015
    Wageningen University. Promotor(en): Paul Struik, co-promotor(en): Tjeerd-Jan Stomph; Gerard Verschoor. - Wageningen : Wageningen University - ISBN 9789462573222 - 210
    bodem - landbouw - inheemse kennis - bodemtypen (antropogeen) - inheemse volkeren - ecosystemen - cassave - manihot - diversiteit - menselijke invloed - amazonia - soil - agriculture - indigenous knowledge - soil types (anthropogenic) - indigenous people - ecosystems - cassava - manihot - diversity - human impact - amazonia


    Clara Patricia Peña Venegas (2015). People, soil and manioc interactions in the upper Amazon region. PhD thesis, Wageningen University, The Netherlands, with summaries in English and Dutch, 210 pp.

    The presence of anthropogenic soils, or Amazonian Dark Earths (ADE), fuels the debate about how pristine the Amazon ecosystem actually is, and about the degree to which humans affected Amazonian diversity in the past. Most upland soils of the Amazon region are very acid, highly weathered, and have a limited nutrient holding capacity; together, these characteristics limit permanent or intensive agriculture. Várzeas or floodplains that are periodically enriched with Andean sediments carried and deposited by rivers that cross the Amazon Basin, are moderately fertile but experience periodic floods that limit agriculture to crops able to produce in a short time. ADE patches in uplands usually are more fertile than non-anthropogenic uplands, providing a better environment for agriculture. Most studies about how people manage a broad portfolio of natural and anthropogenic soils come from non-indigenous farmers of Brazil. There is limited information about how indigenous people use a broad soil portfolio, and how this affects the diversity of their staple crop, manioc. With the aim to contribute to the understanding of the role of ADE in indigenous food production, as compared with other soils, and in order to provide information about how indigenous people use and create diversity in Amazonia, research was carried out among five different ethnic groups living in two locations of the Colombian Amazon.

    Several social and natural science methods were used during the study. These included ethnography, participant observation, structured and un-structured interviews, sampling of soil and manioc landraces, standardized protocols for the quantification of soil physical and chemical variables, and molecular techniques to assess genetic diversity of manioc and arbuscular mycorrhizal fungi.

    Results indicate that ADE patches from the Middle Caquetá region of Colombia are not contrastingly more fertile than surrounding, non-anthropogenic upland soils, except for higher levels of available phosphorus in ADE. Indigenous farmers from the Middle Caquetá region do not use ADE more frequently or more intensively than non-ADE uplands. The swidden agriculture practiced on ADE and on non-ADE uplands is similar. Although ADE patches were not specifically important for swiddens and therefore relatively unimportant for the production of manioc. They were important as sites for indigenous settlements and for maintaining agroforestry systems with native and exotic species that do not grow in soils with low available phosphorus. Várzeas were also used for agriculture, whether farmers had access to ADE or not. Differences occurred between locations in the type of floodplains selected and the way they were cultivated. Those differences were not related to differences in soil conditions but were associated with the cultural traditions of the different ethnic groups who cultivate low floodplains, as well as labor availability when organizing collective work (mingas) to harvest floodplains.

    Manioc diversity among indigenous communities was not predominantly related with differences in soil types. Complete manioc stocks were cultivated equally on ADE, non-ADE uplands or várzeas. One issue that could be related with this non-specificity in manioc-soil combinations was the similar arbuscular mycorrhizal fungi diversity of soils and the high number of arbuscular mycorrhizal symbionts associated to manioc roots; these were shown to be independent from the physicochemical composition of the soil or the manioc landrace. Differences in the diversity of manioc stocks among ethnic groups were predominantly related to cultural values attached to different manioc landraces.

    This study of indigenous agriculture in environments with natural and anthropogenic soils indicates that people have had an important role in transforming the Amazonian ecosystem through agriculture, with consequences on forest composition and forest dynamics. Pre-Columbian people contributed to this by creating an additional soil- the Amazonian Dark Earths. Although ADE are not presently considered to play a major role in indigenous food production, indigenous people believe that ADE have had an important role in the management of the first maniocs cultivated by their ancestors. The domestication of manioc and the creation and maintenance of hundreds of different landraces by indigenous people contributed, and still contributes, to the region’s plant diversity.

    Yellow cassava: efficacy of provitamin A rich cassava on improvement of vitamin A status in Kenyan schoolchildren
    Talsma, E.F. - \ 2014
    Wageningen University. Promotor(en): Michael Zimmermann; Frans Kok, co-promotor(en): Inge Brouwer; Alida Melse-Boonstra. - Wageningen : Wageningen University - ISBN 9789461738554 - 143
    cassave - provitaminen - retinol - vitamine a tekort - voedingstoestand - schoolkinderen - kenya - fortificatie - cassava - provitamins - retinol - vitamin a deficiency - nutritional state - school children - kenya - fortification

    Background: Biofortified yellow cassava has great potential to alleviate vitamin A deficiency in sub-Saharan Africa and can be used as a complementary approach to other interventions. However, direct evidence whether yellow cassava can significantly contribute to the vitamin A intake and status of populations is required. The overall aim of this thesis is to provide proof of principle whether biofortified yellow cassava can improve the vitamin A status of schoolchildren in Kenya.

    Methods: The research was conducted in Kibwezi district, Eastern Kenya. First the effect of daily consumption of yellow cassava was assessed in 342 primary school children in Kenya in a randomized controlled feeding trial with serum retinol concentration as primary outcome. Furthermore we investigated the sensory and cultural acceptability of yellow cassava in a cross-sectional study (n=140) in three primary schools for children as well as their caretakers. Next we studied the diagnostic performance of several proxy markers to assess vitamin A deficiency in comparison with serum retinol concentration as a field based method to assess vitamin A deficiency (n=375). And last we used the dietary intake data of children in the randomized controlled trial to model the potential contribution of yellow cassava to the nutrient adequacy of micronutrient intake using linear programming.

    Results: The randomized controlled feeding trial collected complete data for 337 children with a compliance of 100%. Primary analyses (per protocol) showed that serum retinol concentrations in the yellow cassava group, increased with 0.04 μmol/L (95%CI: 0.00‒0.07 μmol/L) compared to the white cassava group and secondary analyses showed that serum β-carotene concentration increased with 524% (448%‒608%). No evidence of effect modification by initial vitamin A status, zinc status, or polymorphisms in the β-carotene monooxygenase gene was found. In the acceptability study 72% of caretakers and children were able to detect a significant difference in taste between white and yellow cassava and indicated to prefer yellow cassava because of its soft texture, sweet taste and attractive color. Serum concentrations of retinol binding protein, transthyretin and C-reactive protein combined showed excellent diagnostic performance in estimating vitamin A deficiency in primary school children, with an area under the curve of 0.98. Adding yellow cassava to the diet as a school lunch improved the nutrient adequacy of the diet of schoolchildren, however, even with the addition of nutrient dense foods such as fish and oil, nutrient adequacy could not be ensured for fat, riboflavin, niacin, folate and vitamin A.

    Conclusions: Consumption of yellow cassava is acceptable and improves the serum retinol concentrations of primary school children in Kenya. The combination of three proxy markers is a promising approach to measure vitamin A deficiency in a low resource setting. Yellow cassava contributes to a better nutrient adequacy but should be accompanied by additional dietary guidelines and interventions to fill the remaining nutrient gaps.

    Evaluation of local protein resources for growing pigs in Central Vietnam
    Nguyen Thi Hoa Ly, Ly - \ 2012
    Wageningen University. Promotor(en): Martin Verstegen; W.H. Hendriks, co-promotor(en): L.D. Ngoan. - S.l. : s.n. - ISBN 9789461732835 - 145
    diervoeding - varkens - eiwitten - groei - cassave - diëten - zoete aardappelen - vietnam - animal nutrition - pigs - proteins - growth - cassava - diets - sweet potatoes - vietnam

     The general objectives of the work presented here were to evaluate processing methods for the preservations of cassava leaves (CL) and sweet potato vines (SPV) for later feeding during feed shortages in Vietnam. In addition, the nutritional value (including hydrogen cyanide (HCN) contents) of stored and processed CL and SPV as ingredients in diets for pigs were studied to determine their optimal use.

    The impact of different levels of various carbohydrates added to CL on ensiling and chemical properties was investigated (study 1). Inclusion of rice bran or cassava root meal at 5 or 10% (fresh basis),produced good quality silage that can be stored for up to three months. Ensiling reduced the HCN content up to 80% compared to the content in fresh CL. Using ensiled or dry CL and SPV to replace 70%of the crude protein in a practical fish meal based diet commonly used in Vietnam, gave similar performance results and carcass traits of Large White×Mong Caipigs (study 2). However, increasing ensiled CL from variety KM94 from 0 to 20% (in DM) in diets caused a significant decrease in the average daily gain of pigs but resulted in a 9-18% reduction in feed cost (study 3). Studies into the ileal and total tract apparent digestibility of amino acids and crude protein of ensiled and dried CL and SPV showed that these feed ingredients have the potential to improve the supply of amino acids and protein to growing pigs when fed practical diets (study 4). The chemical analyses indicated CL to have a higher crude protein content than SPV and that ensiling slightly decreases the crude protein as well as the amino acids content. Ensiling however, resulted in a higher digestibility of dietary nutrients compared to drying. Thefirst and second limiting amino acids for ensiled and dried CL and SPV for growing pigs were methionine+cysteine and lysine. Mixing ensiled CL and SPV vines may provide additional benefits in terms of amino acid digestibility over feeding these ingredients alone to pigs. Supplementation of diets containing ensiled CL with methionine and lysine showed that the performance of growing pigs can be increased, as well as the economic benefits for farmers (study 5).

    The work presented shows that CL and SPV are economical alternatives for more traditionally protein source (e.g. fish meal, soybean meal) for pigs in Vietnam. Ensiling appears to be a practical solution to conserve sweet potato vines and cassava leaves and provide a solution for the rainy season when preservation by sun-drying is difficult.


    Dangerous assumptions : the agroecology and ethnobiology of traditional polyculture cassava systems in rural Cameroon and implications of green revolution technologies for sustainability, food security, and rural welfare
    Nchang Ntumngia, R. - \ 2010
    Wageningen University. Promotor(en): Patricia Howard, co-promotor(en): Lisa Price. - [S.l : S.n. - ISBN 9789085858423 - 392
    ontwikkelingsstudies - plattelandsontwikkeling - plattelandsvrouwen - bedrijfssystemen - teeltsystemen - meervoudige teelt - cassave - groene revolutie - duurzaamheid (sustainability) - voedselzekerheid - rurale welzijnszorg - kameroen - franssprekend afrika - ontwikkelingslanden - centraal-afrika - acs-landen - hoogopbrengende rassen - etnobotanie - agro-ecologie - middelen van bestaan - development studies - rural development - rural women - farming systems - cropping systems - multiple cropping - cassava - green revolution - sustainability - food security - rural welfare - cameroon - francophone africa - developing countries - central africa - acp countries - high yielding varieties - ethnobotany - agroecology - livelihoods
    The Alliance for a New Green Revolution in Africa and African government and
    CGIAR programmes oriented toward improving cassava production through intensification
    and the use of external inputs have the ultimate goals to improve food production, promote
    market integration, and increase incomes of small farm households. Essentially, AGRA’s
    arguments, which are either implicit or explicit in the policies and programmes of the Government
    of Cameroon and of several CGIAR institutes that the Government collaborates
    with, are that traditional farming systems and practices suffer from low productivity and are
    unsustainable. African soils are naturally poor, farmers use little or no fertiliser, and the
    fallow periods that, in the past, provided for nutrient recycling, are declining due to population
    pressure, leading farmers to mine the soil, which results in declining crop yields. Further,
    farmers’ local varieties are low yielding and are highly susceptible to pests and diseases
    compared to improved, high-yielding varieties (HYVs). Across Africa, per capita food
    production is declining, and families live in poverty and hunger. Population pressure is increasing,
    farmers are poor and thus in need of additional income and, if given the opportunity,
    they will seek to maximise their income from crops sales, which they in turn will
    reinvest in agriculture, given the right incentives. Farm households are food insecure and,
    by increasing their output and sales, they will become food secure.
    This dissertation challenges these underlying assumptions and questions the underlying
    parameters individually and as a whole by examining traditional and more commercial
    smallholder cassava agroecological systems and households in two study sites in rural
    Cameroon (where conditions are theoretically quite positive for the acceptance of such
    technologies) from agroecological, ethnobiological, economic, and cultural perspectives.
    The objective is to understand the implications of policies and programmes that promote
    Green Revolution-type technologies and market integration for the productivity and sustainability
    of such agroecological systems, for the conservation of crop genetic resources,
    and for the livelihoods, income, and food and nutritional security of smallholder farm
    households. The intention is to critically examine the assumptions and underlying parameters
    posited by AGRA, and to reformulate these on the basis of the findings to provide a
    more adequate framework for approaching and assessing agricultural innovations in the
    African context.
    The following questions orient the research: Are African farming systems, and
    farmers, characterised by attributes that AGRA ascribes to them? Are such farmers likely to
    accept the technologies that AGRA is promoting? Are AGRA technologies and strategies
    likely to lead to more sustainable, higher yielding farming systems? Are they likely to
    translate into greater market integration, higher incomes, greater food security, and renewed
    investment in agricultural intensification for small farm households? Are there trade-offs
    that farmers and their households and communities have to confront in adopting such technologies
    and, if so, how might these influence their strategies and responses to programmes
    that promote Green Revolution-type intensification of the ‘old’ or ‘new’ varieties?
    Findings presented in this dissertation show that Koudandeng and Malende farmers
    have barely accepted Green Revolution technologies and modern farming strategies and
    systems (including monoculture). The analysis of the findings proposes reasons for this,
    and attempts to explain farmers’ and households’ production systems and strategies from an
    emic (farmers’) perspective. It is argued that, if African farmers do not accept the Green

    Revolution-type technologies, or accept them only on their own terms and in accordance
    with the outcomes that they themselves desire that differ significantly from what governments
    and researchers and donors anticipate, then this may be attributable at least in part to
    the fact that the strategies and technologies that are promoted are based on erroneous assumptions,
    not least about the key parameters that define the performance of real African
    farming systems and real African farming households. These parameters are grouped under
    two main categories - agroecological and socio-economic – which, in AGRA’s discourse,
    are treated as if they were unrelated. There is thus an absence of attention to the relations
    between the agroecological (or what can be termed environmental, or ‘nature’), and the
    socioeconomic (or what can be termed ‘culture’), which in turn leads to an inattention to
    the diversity of cultures and agroecologies across Africa – its biocultural diversity – that
    permits blanket recommendations to be made on the basis of over-generalised and oversimplified
    When emphasising the need to give greater consideration to the relations between
    culture and nature – that is, to the diversity of African cultures, agroecologies, and socioeconomic
    systems and relations, and to the relations between culture, agroecology, and socioeconomics
    - this dissertation proposes three different interacting sets of analytical parameters
    that must be considered if insights into real African agriculture and real African farm
    households are to emerge. Two of these sets of parameters emerge from a critique of
    AGRA’s parameters and a third arises out of a framework for assessing the acceptability of
    crop varieties that has its foundations in ethnobiology.
    This comparative research, which was carried out between 2002 and 2008, involved
    a total of 206 farmers in two different villages in two regions in the South of Cameroon.
    The methods for collecting and analysing data were both quantitative and qualitative, and
    were drawn from sociology, anthropology, and ethnobiology (cognitive anthropology).
    Qualitative data collection methods included a review of grey and published literature, as
    well as ethnographic interviewing and participant observation. Quantitative methods included
    four closed question surveys and cognitive ethnobiological elicitation (freelisting
    and triads testing). Qualitative interview data were coded and analysed narratively (description,
    explanation, interpretation, quotations) using Microsoft Word. The small household
    sample size that was used did not permit the use of sophisticated statistical analyses according
    to population sub-samples, which limited the analysis of survey data to that which
    would be done using descriptive statistics, such as proportions, percentages, and frequencies.
    Regression analysis was done sparingly. Cultural consensus analysis, proximities
    analysis, multidimensional scaling, quadratic assessment product, cluster analysis, and
    property fitting regression were used to analyse the ethnobiological data that was collected.
    The general conclusions of this dissertation assert that traditional African polyculture
    systems and their genetic diversity (crop species and varieties) are often environmentally
    sustainable, able to meet income and food needs of rural households and communities,
    and fulfil multiple cultural needs relating to identity, foodways, spirituality, and social reciprocity.
    The assumptions behind the promotion of AGRA-type technologies are reductionist;
    they do not take into consideration the complexities of African agriculture and livelihoods,
    or the interrelation between farmers’ social and cultural norms, resource access, and
    livelihood strategies, and how they carry out agriculture (e.g. spatial and temporal configurations,
    cropping patterns, crop and varietal choices, cultural practices). Across most of
    Africa, smallholders and their agroecosystems are firmly embedded in ethnic and tribal
    communities that adhere more or less strongly to cultural norms, beliefs, and kinship or

    lineage-based social relations. Their agricultural knowledge and practices are often based
    largely on local knowledge and resources. Such ‘traditional’ agricultural systems generally
    represent a long-term adaptation between culture and nature, where both have co-evolved
    over time. Farmers’ knowledge and practices are embedded in social relations where many
    modes of subsistence are characterised by forms of communalism that are relatively egalitarian,
    which tends to ensure that resources are distributed in such a way that people have
    sufficient means to meet socially defined, as well as biological needs. Unsustainable practices
    and inegalitarian social relations that may accompany the adoption of Green Revolution
    technologies and greater market integration are likely to be mal-adaptive over the long
    The assumptions underlying the ‘New Green Revolution for Africa’ drastically
    over-simplify traditional African farming systems and ignore their diversity and thus do not
    hold everywhere in Africa which, it is argued, may represent yet another threat to the integrity
    of traditional African cultures, agroecological systems, and biological diversity. Eight
    major critiques of this over-simplification and the resultant dangerous consequences for
    African farm households include: i) the inappropriateness (technical and practical limitations)
    of the recommendations for integrated soil fertility management practices and fertiliser
    use for most African contexts; ii) the lack of consideration for farm households’ social
    constraints: differential access to income, land, and labour, and investments in other livelihood
    activities that compete with investments in agricultural inputs, which consequently
    may have implications for soil fertility management; iii) the lack of attention to the pests
    and diseases of most significance to farmers; iv) the relative inattention to the need to develop
    varieties that conform with local foodways and food processing and storage conditions;
    v) the implications of mass production of the reduction of crop diversity and varietal
    diversity for food security and nutrition and the consequences for human health; vi) the
    lack of serious consideration of farmers’ knowledge and practices in crop breeding strategies
    and the lack of precise methodologies for effectively and systematically accessing and
    document farmers’ varietal knowledge, perceptions, and preferences and relating these to
    farmer behaviour when accepting crop varieties; vii) the improbability that prices for mass
    produced HYVs will increase income and investments in inputs; and viii) the consequences
    of conversion to monoculture for livelihood and food security that are entailed in widescale
    acceptance of AGRA-type recommendations.
    Based on these critiques, the major policy recommendation emphasised in this dissertation
    is to give greater consideration to real African farming systems and real African
    farmers and how and why they function as they do, which, it is argued, must serve as the
    point of departure for agricultural policies and programmes across the region if these are to
    succeed in supporting such farmers, their communities, and their nations. Farmers’ culture,
    social relations, knowledge, practices, and experiences that remain, in the ‘New’ Green
    Revolution, as in the ‘Old’, a black box, should be newly considered in policies and research
    and development as positive points of departure for increasing food security in Africa.

    Oranje boven
    Kleis, R. ; Sikkema, A. ; Wolkers, H. - \ 2010
    Resource: weekblad voor Wageningen UR 4 (2010)21. - ISSN 1874-3625 - p. 12 - 13.
    planten - penen - algen - cassave - schimmels - kleur - plants - carrots - algae - cassava - fungi - colour
    Diverse Wageningse wetenschappers over oranje planten, voedingsmiddelen, algen en schimmels.
    Livelihoods of cassava farmers in the context of HIV/AIDS in northern Malawi
    Yajima, M. - \ 2010
    Wageningen University. Promotor(en): Arnold van Huis; J.L.S. Jiggins. - [S.l. : S.n. - ISBN 9789085855446 - 202
    cassave - boeren - acquired immune deficiency syndrome - sociale gevolgen - plantenziekten - insectenplagen - houding van boeren - malawi - middelen van bestaan - farmer field schools - cassava - farmers - acquired immune deficiency syndrome - social impact - plant diseases - insect pests - farmers' attitudes - malawi - livelihoods - farmer field schools
    Malawi is one of the poorest countries in Africa with a high population density and HIV prevalence. Most smallholder farmers grow maize as a staple, which is highly dependent on the uni-modal rainfall and off-farm inputs. The ‘New Variant Famine’ hypothesis argues that AIDS has aggravated food insecurity and stimulated cassava production because of lower labour demand in cultivation. The Farmer Field School (FFS) was introduced to support small-scale farmers, but its relevance to the Malawian context has been challenged. This study examined the ‘New Variant Famine’ hypothesis and the FFSs on cassava in northern Malawi. Participants and non-participants of cassava FFSs were interviewed on their crop management. The survey showed that although farmers recognised visible pest and diseases, they did not take action. Cultural controls are hardly used. Their participation in FFSs did not have a major impact. Curriculum design was found crucial in gaining farmers’ interest. Individual life history data and analysis of genealogical information indicated that AIDS is perceived as only one in the continuum of risks facing subsistence cassava growers. Perception of AIDS is changing, under the influence of social organisations that have emerged to offer community-level support. This suggests that increased programming effort would help small-scale farmers develop stronger ‘social immunity’ in coping with threats to their food security.

    Cassava and soil fertility in intensifying smallholder farming systems of East Africa
    Fermont, A.M. van - \ 2009
    Wageningen University. Promotor(en): Ken Giller, co-promotor(en): Mark van Wijk; Pablo Tittonell. - [S.l. : S.n. - ISBN 9789085853992 - 196
    manihot esculenta - cassave - bodemvruchtbaarheid - agronomie - bedrijfssystemen - systeemanalyse - voedselzekerheid - kunstmeststoffen - kenya - uganda - manihot esculenta - cassava - soil fertility - agronomy - farming systems - systems analysis - food security - fertilizers - kenya - uganda
    Keywords: Cost-benefits, Crop management, Farming systems, Fertilizer, Food security, Generalizations, Income, Labour, Land pressure, Niche, Rainfall, Sub-Saharan Africa, System analysis, Yield gap.
    Cassava is an important crop in Africa. This thesis focuses on cassava production in the mid altitude zone of East Africa, an area characterized by high population densities, bimodal rainfall patterns and relatively poor soils. The overall aim was to better understand the roles and production constraints of cassava in order to explore opportunities to improve the productivity and sustainability of intensifying cassava-based smallholder farming systems in East Africa. Increasing land pressure has changed agricultural landscapes from traditional millet-, cotton-, sugarcane- or banana-based systems with an important fallow component to continuously, cultivated cassava-based systems. Cassava cultivation on cropped fields increased from 1-11 to 16-55% in three to four decades as farmers believe that cassava improves soil fertility for the subsequent crop and increasingly target cassava to low fertility soils when land pressure increases. The substantial increase in cassava cultivation has allowed farmers to postpone intensification of crop management, but it seems that the elasticity of the traditionally low-input systems is coming to an end as production of the two most important crops (cassava and maize) is limited by nutrients. Farmers in areas of high land pressure have started to adopt fertilizer and manure and to improve crop management.
    Contrary to existing generalizations, cassava is not a food security crop for poorer farmers in East Africa, but an important food and cash crop for farmers from all wealth classes. Average farm income was not less than in other farming systems in the region, while average food security was higher (>10 months year-1) than in maize-based systems. Cassava is also not predominantly grown as an intercrop, as is often thought, nor is it grown without inputs, because farmers commonly use hired labour and improved genotypes. In addition, its labour requirements are higher than commonly assumed (287 man days ha-1), due to large requirements for weed control. Existing generalizations concerning cassava are therefore either false or half truths and a continued belief in them will hamper the effectiveness of policy and development efforts aimed at improving cassava production. Efforts to increase cassava production in cassava-based farming systems will, for example, improve its scope for commercialization, but will not significantly enhance food security.
    Average farmer yields for cassava (7-12 t ha-1) are far below attainable yields on farm (30-50 t ha-1). Still, on-farm yields are highly variable. Largest yields were obtained on farms with high labour availability, fertile soils, good weed management and timely (not too early) harvesting. An improved technology package more than doubled
    average yields in farmer fields, whereby the largest yield increase for a single technology was observed with 100-22-83 kg ha-1 N-P-K fertilizer. Multivariate analysis identified soil fertility, rainfall and weed management as the most important production constraints, while biotic factors were less important. Many fields were affected by multiple and interacting production constraints. Fertilizer responses were governed by the same, interacting factors influencing unfertilized cassava production. Genotype and biotic factors did not influence fertilizer response. Closing the considerable yield gap between actual and attainable cassava yields at farm level, can not be achieved by integrated pest management and breeding alone. Instead, research and development organizations should focus on addressing the whole range of interacting production constraints through the development and evaluation of integrated management packages. Improving cassava production will be more difficult for poorer than for wealthier farmers, as the first have less social and financial capital and less fertile soils and are therefore more likely to face multiple production constraints.
    The positive impact of cassava on soil fertility perceived by farmers is supported by model simulations and nutrient balances that indicate that cassava may improve SOC contents of low fertility soils compared with maize and contribute to higher N recycling through crop residues. Adoption of higher yielding genotypes and improved production practices will improve yields and increase nutrient removal rates, but may simultaneously have a positive effect on SOC contents and nutrient recycling rates. Improving cassava stem management after harvesting seems an interesting option to improve sustainability of the system.
    This thesis concludes that there is an urgent need to invest in agronomy and ISFM research and to reform existing research for developments programmes with a strong emphasis on breeding and IPM into integrated programmes that are able to address the multiple production constraints of cassava and thereby significantly contribute to improving the livelihoods of smallholder cassava farmers.

    Oranje cassave tegen ondervoeding
    Brouwer, I.D. - \ 2008
    Kennis Online 5 (2008)dec. - p. 11 - 11.
    ondervoeding - voedingsstoffenopname (mens en dier) - vitaminetekorten - cassave - undernutrition - nutrient intake - vitamin deficiencies - cassava
    De halve wereldbevolking krijgt te weinig vitaminen en mineralen binnen. Internationaal proberen wetenschappers in basisgewassen als rijst, maïs en cassave het niveau van vitamine A, zink en ijzer te verhogen. Wageningse onderzoekers kijken naar de opname van de stofjes
    Feeding activity of the East African millipede Omopyge sudanica Kraus on different crop products in laboratory experiments
    Ebregt, E. ; Struik, P.C. ; Abidin, P.E. ; Odongo, B. - \ 2007
    NJAS Wageningen Journal of Life Sciences 54 (2007)3. - ISSN 1573-5214 - p. 313 - 323.
    diplopoda - zoete aardappelen - waardplanten - cassave - zaden - voedselgranen (hele korrel) - experimenten - laboratoriumproeven - uganda - diplopoda - sweet potatoes - host plants - cassava - seeds - whole grains - experiments - laboratory tests - uganda - sweet-potato production - farmers information - infestation
    Millipedes can cause considerable damage in the production of sweet potato and some other crops in East Africa. Quantitative information on intake of crop diets by and body weight gain of millipedes was collected in short-term no-choice feeding activity laboratory experiments conducted in north-eastern Uganda using female millipedes of the species Omopyge sudanica. Diets consisted of sweet potato and cassava storage root material, groundnut seeds, or maize grains. Differences in intake and body weight gain between diets were not statistically different. The consumption index, i.e., the ratio between intake and body weight gain, was significantly higher for sweet potato than for most other diets. The efficiency of conversion of ingested food, i.e., 100 × the ratio between body weight gain and intake, was significantly lower for the root crops ? especially sweet potato ? than for the grain crops. The research showed how difficult it is to obtain reliable, quantitative data on the feeding habits of millipedes, but also illustrated that O. sudanica can cause harm to crops in north-eastern Uganda and elsewhere in East Africa
    Analysing and governing environmental flows: the case of Tra Co tapioca village, Vietnam
    Mol, A.P.J. ; Tran Thi My Dieu, - \ 2006
    NJAS Wageningen Journal of Life Sciences 53 (2006)3-4. - ISSN 1573-5214 - p. 301 - 317.
    landbouwindustrie - duurzaamheid (sustainability) - milieueffect - tapioca - cassave - technologie - gesloten systemen - vietnam - agribusiness - sustainability - environmental impact - tapioca - cassava - technology - closed systems - vietnam
    Environmental flows are of crucial importance for questions of sustainability. But analysing only the material side of environmental flows brings us half way understanding questions of sustainability. This article reports on the development of a more integrative approach in studying environmental impacts of agro-industrial systems in Asia, taking tapioca (cassava starch) processing in Vietnam as an example. The analysis of material flows and technological options to close material cycles is combined with an actor-network analysis from three angles: a policy, an economic and a social perspective, respectively. The paper finally assesses the additional value of the developed methodology and points out ways for further investigation and development of a more integrative approach to industrial transformations
    Cassave friet : een verkenning om gefrituurde cassaveproducten in Nederland op de markt te brengen
    Essers, A.J.A. - \ 2005
    Wageningen : Wetenschapswinkel Wageningen UR (Rapport / Wetenschapswinkel Wageningen UR 219) - ISBN 9789067549608 - 22
    cassave - gebakken voedsel - marketing van voedingsmiddelen - haalbaarheidsstudies - productontwikkeling - nederland - cassava - fried foods - food marketing - feasibility studies - product development - netherlands
    Infochemical use by predatory mites of the cassava green mite in a multitrophic context
    Gnanvossou, D. - \ 2002
    Wageningen University. Promotor(en): M. Dicke; R. Hanna. - S.l. : S.n. - ISBN 9789058085689 - 152
    cassave - mijten - predatoren - lokstoffen - manihot esculenta - mononychellus tanajoa - gastheer parasiet relaties - voedselketens - vluchtige verbindingen - phytoseiidae - cassava - mites - phytoseiidae - predators - attractants - volatile compounds - manihot esculenta - mononychellus tanajoa - host parasite relationships - food chains
    This thesis describes research on multitrophic interactions in a system consisting of (1) cassava plants ( Manihot esculenta ), (2) three herbivorous mites, i.e. the cassava green mite Mononychellus tanajoa, the red spider mite Oligonychus gossypii and the two-spotted spider mite Tetranychus urticae and (3) two exotic predatory mites Typhlodromalus manihoti and T. aripo , in Africa. The objectives are to understand how the two exotic predators (i) exploit chemical information to locate the target prey in pure and mixed odors conditions with the alternative prey mites, (ii) perform when feeding on different prey mite species and (iii) interact with each other.

    The predatory mites, T. manihoti and T. aripo were attracted to cassava leaves infested by M. tanajoa compared with non-infested leaves, when the predators were starved for 2, 6 or 10 hours. They were not attracted to 400 female M. tanajoa removed from infested plants nor to mechanically wounded leaves. In a choice situation, T. manihoti and T. aripo preferred odors from leaves infested by M. tanajoa to odors from leaves infested by O. gossypii regardless of the ratio M. tanajoa : O. gossypii . When M. tanajoa -infested leaves and T. urticae -infested leaves were offered in a choice situation, the response of the two predator species depended on the density of T. urticae . Typhlodromalus manihoti and T. aripo were attracted to odors from cassava leaves infested with both M. tanajoa and O. gossypii or to a mixture of odors from leaves infested with M. tanajoa and odors from leaves infested with O. gossypii, when compared to odors from non-infested leaves. In contrast, mixed odors from M. tanajoa -infested leaves and T. urticae -infested leaves did not yield a preference over odors from non-infested leaves.

    Typhlodromalus manihoti and T. aripo had a higher intrinsic rate of population increase (rm) and net reproduction (Ro), and a shorter generation time and doubling time on when they were feeding on M. tanajoa than on O. gossypii or T. urticae . Prey-related odor preference matched predator performance if the key prey is compared to the two inferior prey mite species.

    Typhlodromalus aripo displayed a marked preference for odors emitted from either infested cassava apices or infested young cassava leaves over infested old cassava leaves but showed equal preference for odors from apices and young leaves both infested with M. tanajoa . Typhlodromalus manihoti did not discriminate between volatiles from the three infested cassava plant parts. This mirrors the differential distribution of the two predators on cassava plant foliage.

    Carnivorous arthropods when searching for adequate food and habitat for themselves and their progeny should in the meantime avoid becoming food for other organisms. Intraguild interactions have been investigated for the predatory mite species T. manihoti , T. aripo and the native species Euseius fustis . Typhlodromalus manihoti is able to discriminate between odors from patches with con- and heterospecific competitors and prefers to visit patches with heterospecifics. Typhlodromalus aripo preferred to move away from patches with heterospecifics or conspecifics. Euseius fustis avoided odors from patches with conspecifics as well as odors from patches with the heterospecifics T. manihoti and T. aripo .

    In conclusion, this thesis shows that the distribution and diversity of prey species, intraguild predation and competition are likely to play an important role in infochemical use by T. manihoti and T. aripo . In addition to predator-prey interactions, interactions between predators can also be considered as important factors affecting population dynamics of both prey and predators.

    Analysis of post-harvest deterioration in tuberous roots of cassava (Manihot esculenta Grantz)
    Huang, J. - \ 2001
    Wageningen University. Promotor(en): R.G.F. Visser; E. Jacobsen. - S.l. : S.n. - ISBN 9789058085481 - 103
    manihot esculenta - cassave - bederf na de oogst - bewaarfysiologie - biochemie - enzymen - genetische merkers - genetische transformatie - moleculaire genetica - transgene planten - manihot esculenta - cassava - postharvest decay - postharvest physiology - biochemistry - enzymes - genetic markers - genetic transformation - molecular genetics - transgenic plants

    This thesis deals with the analysis of postharvest physiological deterioration (PPD) in cassava tuberous roots at the physiological, biochemical and molecular level. By setting up a uniform visual system to monitor the onset and maintenance of PPD under the experimental conditions, amongst others physico-chemical properties of starch were characterized. Furthermore using this system, around 6,000 TDFs (transcript derived fragments) were screened via 100 primer combinations using cDNA-AFLP. 70 TDFs showing an up-regulated, a down regulated or a transiently expression pattern were isolated following the first 72 hours of PPD. Based on the sequence information, a functional catalogue of these TDFs was established. By concentrating on enzymes possibly involved in oxidative stress, biochemical results indicated that PPD may be a peroxidase-mediated process. Using a reverse genetics approach, the putative cassava dad1 (defender against cell death gene 1) homologue was transformed into cassava FEC (friable embryogenic callus) lines. Transgenic plants were produced and characterized.

    New standard method for the assessment of the frying colour of French fries (in Dutch)
    Meinders, M.B.J. ; Timmermans, A.J.M. ; Eijck, P.C.M. van - \ 1997
    Aardappelwereld (1997)1. - ISSN 0169-653X - p. 15 - 17.
    cassave - karakteristieken - patates frites - kleur - voedselbewaring - voedingsmiddelen - lengte - meting - prestatieniveau - aardappelproducten - aardappelen - kwaliteit - wortelgewassen als groente - vorm - Solanum tuberosum - gewicht - optica - cassava - characteristics - chips (French fries) - colour - food preservation - foods - length - measurement - performance - potato products - potatoes - quality - root vegetables - shape - weight - optics
    Isolation and characterisation of starch biosynthesis genes from cassava (Manihot esculenta Crantz)
    Munyikwa, T.R.I. - \ 1997
    Agricultural University. Promotor(en): E. Jacobsen; R.G.F. Visser. - S.l. : Munyikwa - ISBN 9789054858416 - 128
    koolhydraten - polysacchariden - biosynthese - genen - genomen - manihot esculenta - cassave - carbohydrates - polysaccharides - biosynthesis - genes - genomes - manihot esculenta - cassava

    Cassava (Manihot esculenta Crantz) is a tropical crop grown for its starchy thickened roots, mainly by peasant farmers, in the tropics, for whom it is a staple food. There is an increasing demand for the use of cassava in processed food and feed products, and in the paper and textile industries amongst others. This thesis describes research on the cloning of the genes encoding ADP-glucose pyrophosphorylase small and large subunits (AGPase B and S, respectively) and granule bound starch synthase II (GBSSII). These genes and their products were extensively characterised to determine their role in starch biosynthesis in cassava. Functional verification of the genes was carried out by transforming potato and cassava followed by analysis of the starch produced by the transgenic plants.

    In Chapter 1 cassava production in the world in general and in Zimbabwe in particular is examined against the backdrop of new cloning and transformation strategies to improve starch quality and quantity. The development of cassava cultivars whose starches have novel physico-chemical properties by genetic modification of the process of starch biosynthesis is examined therein. The main criteria for these new cultivars to emerge are set forth as being: the availability of cloned and characterised starch biosynthesis genes, a universally applicable transformation and regeneration procedure for cassava, transfer to appropriate cassava cultivars, and biosafety analysis of transgenic cassava plants before disbursement to farmers.

    The cloning of the cassava starch biosynthesis genes encoding granule bound starch synthase II (GBSSII) and the large and small subunits of ADP-glucose pyrophosphorylase (AGPase) is described in Chapters 2 and 3. The cloning of GBSSII reveals that there is indeed a second isoform of this enzyme in cassava as in other plants species. While sharing very little amino acid sequence homology with cassava GBSSI the GBSSII isophorm shares high amino acid sequence homology to other GBSSII genes from pea and potato. Cassava GBSSII seems to be more important in leaf tissue where it is more highly expressed than in tuber tissue where GBSSI predominates. Mapping of GBSSII revealed that this is a single copy gene located on the male derived linkage group T of the cassava mapping population.

    Cloning of the cassava genes coding for the small (B) and large subunit (S) of AGPase revealed interesting aspects about the cassava enzyme. The cassava AGPase is likely to be heterotetrameric in constitution as had been found in other plant species. Comparison of the cassava AGPase sequences with those of already cloned AGPases revealed that AGPase B is more similar to small subunit genes from other plants than to cassava AGPase S coding for the large subunit (Chapter 3). Segregation analysis of a cassava mapping population revealed that AGPase S is a single copy gene that is localised on the female derived linkage group E of the cassava genetic map. Both genes are expressed in all cassava tissues but AGPase B was shown to have a higher steady state mRNA level than AGPase S especially in leaf and tuber tissue. Post-transcriptional control of small subunit polypeptide levels could be inferred from the discrepancy between AGPase B mRNA and polypeptide levels. The AGPase enzyme activity was much higher in young cassava leaves than older leaves and tubers. Cassava leaf AGPase activity was increased 3 fold by the addition of 3-PGA (3-phospho-glycerate) and inhibited by up to 90% in the presence of inorganic phosphate (Pi). The tuber enzyme was relatively unaffected by 3PGA, but was highly inhibited by Pi.

    In order to verify the biological role of the AGPase B gene antisense constructs were made of the cassava AGPase B behind a CaMV35S promoter (chapter 3). This was transferred into potato plants by Agrobacterium tumefaciens. While the 224 transgenic antisense AGPase B potato plants did not differ in appearance from normal potato plants, 45 transgenic plants, however, had more numerous and smaller tubers than control plants. Antisense plants with reduced AGPase B mRNA levels had 1.5 to 3 times less starch than tubers from the control plants. The levels of the soluble sugars in the antisense plants increased significantly (up to 10 times more glucose, 6 times the amount of fructose, and 5 times the amount of sucrose) when compared to those found in control plants. These results show that a heterologous gene from cassava can have an antisense effect in potato, but that the number of plants required to find plants exhibiting maximum antisense effect has to be very large. This is probably due to sequence homology differences between the cassava AGPase B and potato AGPase B genes which share only 68% amino acid sequence homology.

    Chapter 5 describes the further development of an efficient, time and labour saving protocol for transforming cassava based on stringent selection of the luciferase (firefly) marker gene. In addition the first reported transformation of cassava with a gene (AGPase B) other than a marker gene is described. An antisense construct was made for transforming cassava. This consisted of the cassava AGPase B gene which was placed in antisense orientation behind the CaMV35S promoter. This was then coupled to the luciferase gene driven by another CaMV35S promoter. After particle bombardment of cassava FEC transgenic tissue was selected using three different selection regimes: non stringent luciferase selection, stringent luciferase selection and combined chemical (phosphinothrycin) and luciferase selection. Stringent luciferase selection whereby luciferase positive FEC units were precisely pinpointed, isolated and cultured was found to be the most effective and time saving method. It was possible to generate cultures having more than 90% luciferase positive FEC tissue after 12 weeks of stringent LUC selection, compared to 45% and <1 % for combined selection and non stringent selection respectively. The number of luciferase positive mature embryos generated was directly proportional to the percentage of luciferase positive tissue in the original FEC culture. Stringent luciferase selection enabled the time taken for production of transgenic cassava plants to be reduced to 28-36 weeks as compared to 8 months to a year with no stringent selection or LUC/PPT selection.

    Cassava plants carrying the AGPase B antisense gene had extremely low levels of starch, compared to control plants, as shown by iodine staining of in vitro induced thick stems. In plants exhibiting the highest AGPase B antisense effect, starch formation was limited only to the epidermal layer. These results functionally confirm the identity of cassava AGPase B as well as emphasising the critical role of AGPase in starch formation in cassava.

    A discussion about the significance and implications of cloning cassava genes and producing transgenic cassava for culture in developing countries is carried out in Chapter 6. While there are clearly many economic and nutritional benefits to producing transgenic cassava, for resource poor farmers, many people in the South are not aware of the biosafety implications of growing transgenic crops. It is further emphasised that discussions and debate should be initiated to make local communities aware of the issues surrounding transgenic crops and their products. In addition it is recommended that some form of international legal framework be set up to ensure that resource poor farmers are not disadvantaged by the patenting of material originating from their communities by individuals and companies in the North. This thesis clearly demonstrates how it will be possible in the near future to produce new cassava cultivars carrying the appropriate genes to affect pronounced changes on tuber productivity and starch quality.

    Regeneration and transformation of cassava (Manihot esculenta Crantz.)
    Sofiari, E. - \ 1996
    Agricultural University. Promotor(en): E. Jacobsen; R.G.F. Visser. - S.l. : Sofiari - ISBN 9789054855361 - 136
    cassave - manihot esculenta - genetische transformatie - weefselkweek - somatische embryogenese - plantenveredeling - cassava - manihot esculenta - genetic transformation - tissue culture - somatic embryogenesis - plant breeding
    This thesis describes different regeneration systems of cassava. In the first system the embryos were highly organized. The use of the auxins NAA and 2,4-D to induce this organized system of somatic embryogenesis were compared in several genotypes. Bombardment of organized tissues did not result in transformed plants and culture of protoplasts isolated from organized cultures did not result in plant regeneration. In the second system, so called friable embryogenic callus, the embryos are less organized. Protoplasts isolated from friable embryogenic callus regenerated into plants. Bombardment of this friable embryogenic callus with DNA of constructs containing the luciferase gene resulted in transformed tissue. Transgenic tissue was selected using luciferase activity. Transformed mature embryos were multiplied by the organized system of embryogenesis before they were allowed to develop into plants. The transformed nature of the plant was confirmed by PCR and Southern Blot Analysis.
    Removal of cyanogens from cassava roots : studies on domestic sun-drying and solid-substrate fermentation in rural Africa
    Essers, A.J.A. - \ 1995
    Agricultural University. Promotor(en): A.G.J. Voragen; H. Rosling. - S.l. : Essers - ISBN 9789054853787 - 131
    opslag - manihot esculenta - cassave - afrika - derivaten - cyanen - storage - manihot esculenta - cassava - africa - derivatives - cyanogens

    Cassava is an important staple crop, but its potential toxicity has led to some health problems in Africa. The potential toxicity comes from endogenous cyanogenic glucosides, mainly linamarin, which may degrade by linamarase to cyanohydrins and subsequently to hydrocyanic acid (HCN). A study into a small outbreak of paralysis and poisoning in a cassava-dominated rural area of Mozambique revealed that the walking disability was konzo, a recently identified disease, and suggested that insufficient processing of the bitter cassava roots was a factor in its causation. The usual processing stages to turn roots into flour, sun-drying and heapfermentation, were studied in Uganda and The Netherlands. For evaluation of initial and resulting levels of the cyanogenic compounds, an analytical assay was tested and improved. Mechanisms of cyanogen removal from cassava by sun- drying and heap-fermentation were elucidated, to allow for its optimization.

    Sun-drying removed cyanogens insufficiently from roots with high initial levels. Dynamics of cyanogen levels are described. Continuing drying below moisture levels of 15% did not diminish linamarin levels further, but it was useful for further removal of the cyanohydrins formed. The dehydration rate influenced linamarin breakdown negatively. Reducing the size of the pieces to speed up drying, as done during the konzo outbreak, therefore resulted in higher residual linamarin levels. Linamarin breakdown can be enhanced by reducing the initial dehydration rate. Microbial contamination may need to be controlled to prevent the formation of microbial toxins.

    In Uganda and Mozambique certain communities promote fungal growth by heaping and covering the peeled roots. Their aim is to improve the palatability and reduce the toxicity. Cyanogen removal by this solid-substrate fermentation appeared more effective than by sun-drying alone, but several samples of this flour from rural households still had undesirably high levels of cyanogens. Screening of 30 flour samples for mycotoxins was negative, but the formation of mycotoxins cannot be excluded. The humid incubation of cassava extends the time of physiological cell-wall degradation, which allows for linamarase-linamarin interaction. The microflora had an additional positive effect on cyanogen removal by enhancing the cell-wall degradation. The linamarase activity shown by several microorganisms was of lesser importance. The food grade fungi Neurospora sitophila and Rhizopus oryzae were the most effective in cyanogen removal. Optimization of processing conditions, including the use of starter cultures, is recommended for ensuring safe products.

    Primary and cyclic somatic embryogenesis in cassava (Manihot esculenta Crantz)
    Raemakers, C.J.J.M. - \ 1993
    Agricultural University. Promotor(en): E. Jacobsen; R.G.F. Visser. - S.l. : Raemakers - ISBN 9789054851936 - 119
    planten - embryologie - manihot esculenta - cassave - somatische embryogenese - plants - embryology - manihot esculenta - cassava - somatic embryogenesis

    Cassava is one of the major food crops in the tropics. Several of the major problems in cassava can probably only be solved by breeding with cellular and molecular techniques, e.g., the introduction of specific genes (virus resistance, protein content, quality aspects and so on). These genes can be directly applied in existing varieties of vegetatively propagated crops like cassava. Genetic modification requires efficient, genotype-independent regeneration methods. Plant regeneration can be accomplished by two different pathways: organogenesis and somatic embryogenesis. In both organogenesis and embryogenesis, the regenerated structures either originate directly from the explant or indirectly from callus induced from the explant. In most species transformed plants are obtained by indirect regeneration, either by organogenesis or somatic embryogenesis. The callus phase is used to select and multiply transformed cells. Because organogenesis for cassava appeared to be not repeatable, somatic embryogenesis was further investigated. Somatic embryogenesis is defined as the process in which a bipolar embryo is formed which has no vascular connection with the parental tissue. It has been described in more than 200 species [Chapter 11. It was shown by others that in cassava (primary) embryos originated directly from young leaves or zygotic embryos. Direct embryogenesis has been used successfully in a some species for plant transformation. In these species primary somatic embryos themselves were an excellent source to start a new cycle of (secondary) embryogenesis. Repeated subculture of somatic embryos allowed the development of continuously proliferating embryogenic cultures (cyclic embryogenesis). The phase of embryo proliferation was used to select and multiply transformed cells. An overview of culture regimes which allows continuous proliferation of somatic embryos is given in Chapter 2.

    In initial experiments first cycle or primary embryos were formed from young cassava leaf explants derived from greenhouse grown plants. After 10 days of culture nodular or globular embryos were visible. Globular embryos developed into torpedo shaped embryos which germinated after tranfer to the a medium without auxins. Germinated embryos (GE) are defined as structures with a distinct hypocotyl and large green cotyledons. Five of the six tested South American and Indonesian clones formed germinated embryos. The number of germinated embryos produced, was strongly influenced by the genotype and by hardly controlled growing conditions of the donor plants in the greenhouse. The production of the Colombian clone M.Col22 varied between 0 and 22.1 GE per initial leaf explant (GE/IE). The other clones were considerably lower in their response [Chapter 3]. Therefore, M.Col22 was chosen as a model plant.

    To create uniform growing conditions in vitro grown donor plants were used as source for leaf explants. Using the same culture conditions as applied for greenhouse derived leaf explants, this approach gave less variation in germinated embryos but also a much lower production (< 1 GE/IE). Doubling of the 2,4-D concentration in the embryo induction medium increased the production to a maximum of 3.5 GE/IE. The embryogenic capacity of M.Col 22 could be further increased to 6.6 GE/IE by growing donor plants at reduced irradiance. The highest production (9.9 GE/IE) was obtained by a pretreatment of donor plants with 2,4-D, a few days before the isolation of leaf explants.

    Another advantage of the 2,4-D pretreatment of donor plants was studied in Nigerian clones. Only 5 out of 11 invitro grown clones formed globular embryos and only in 2 some of the globular embryos developed into germinated embryos. After 2,4-D pretreatment of the donor plants, 10 out of the 11 clones formed globular embryos and in 8 of them germinated embryos were formed [Chapter 6].

    Only torpedo shaped and germinated embryos initiate a new cycle of embryogenesis after reculture on induction medium. Germinated embryos were the best starting material to initiate cyclic cultures [Chapter 4]. Independent of the genotype, germinated embryos formed new germinated embryos at a high rate and the embryogenicity seemed not to be changed after one year of culture [Chapters 4 and 6]. The production of cyclic germinated embryos for M.Col22 varied between 6.8 and 9.9 GE/IE. The production of germinated embryos in liquid medium was significantly higher than on solid medium. Also fragmentation of the initial germinated embryos, before starting a new cycle of embryogenesis, enhanced the production. With both improvements, the production of M.Co122 increased to about 30 GE/IE [Chapter 5].

    Culture of torpedo shaped and germinated embryos on BA supplemented medium allowed their development into shoots.-As for the induction of new embryos, germinated embryos were also the best material to be cultured for shoot development [Chapter 4]. The frequency of shoot development appeared to be genotype dependent [Chapters 3 and 6]. In the clone M.Co122 more than 50 percent and in the clone Tjurug only 10 percent of the germinated embryos developed into shoots. All shoots, independent of the genotype, formed roots on growth regulator- free medium [Chapters 3, 4 and 5].

    Cyclic embryos originated directly from the cotyledons of the somatic embryo by a budding process. The origin appeared to be multicellular. The first embryogenic divisions started with cells in or near the vascular strands. These initial divisions led either directly to a somatic embryo or to meristematic tissue, of which later embryos were formed [Chapter 7].

    Almost 500 regenerants of up to the seventeenth cycle embryos were evaluated in vitro for somaclonal variation. Only one regenerant had a visible deviation from control plants (variegated leaves) which was assumed to be of genetic origin [Chapter 8]. About 110 regenerants were transferred to the greenhouse and evaluated for more than 1 year. Plants of the regenerants showed fewer virus-like symptoms than control plants. The root tubers of control plants were more uniform than that of regenerated plants. Some plants of the regenerants had irregularly shaped roots which were not observed in control plants. Not all plants of a particular regenerant had a abnormal root tuber phenotype and this is a clear indication that the cause of this variation is most probably epigenetic (physiological) and, therefore, is expected to disappear with prolonged multiplications.

    Cassava has proven to be amenable for Agrobacterium -mediated transformation and the transformed cells are able to divide. Unfortunately, the majority of them developed into callus cells and only a few into embryogenic competent cells. Culture procedures which increase the recovery of embryogenic competent cells from transformed cells together with an efficient non-destructive selection procedure should allow the development of an efficient, genotype-independent transformation procedure. This is of importance for breeding of this vegetatively propagated crop, cassava.

    Methodische vergelijking van het vaststellen van de P-verteerbaarheid van tapioca en mais en het effect van de hoeveelheid en herkomst van fytinezuur op de werking van microbieel fytase van Aspergillus niger = Methodological comparison of the assessment of P digestibility of tapioca and maize and the influence of amount and origin of phytic acid on the efficacy of microbial phytase of ...
    Dekker, R.A. ; Kemme, P.A. ; Jongbloed, A.W. - \ 1992
    Lelystad : IVVO-DLO (Rapport / IVVO-DLO no. 244) - 20
    dieren - cassave - verteerbaarheid - enzymen - experimenten - voer - voedergewassen - maïs - manihot esculenta - fosfor - planten - zea mays - in vivo experimenten - animals - cassava - digestibility - enzymes - experiments - feeds - fodder crops - maize - phosphorus - plants - in vivo experimentation
    Check title to add to marked list
    << previous | next >>

    Show 20 50 100 records per page

    Please log in to use this service. Login as Wageningen University & Research user or guest user in upper right hand corner of this page.