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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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    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.

    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.

    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.

    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
    An atlas of cassava in Africa : historical, agroecological and demographic aspects of crop distribution
    Carter, S. ; Fresco, L.O. ; Jones, P. - \ 1992
    Cali : CIAT (CIAT publication 206) - ISBN 9789589183380 - 85
    manihot esculenta - cassave - geografie - regio's - reizen - beschrijvingen - afrika - kaarten - illustraties - grafische documenten - agro-ecologie - manihot esculenta - cassava - geography - regions - travel - descriptions - africa - maps - illustrations - graphic documents - agroecology
    This book contains 6 chapters covering: the dynamics of cassava in Africa; the introduction and diffusion of cassava in Africa; current distribution of cassava in Africa; the relationship of cassava distribution to environment and population; distribution and change in cassava production in Nigeria, Tanzania and Zaire; and conclusions. The book includes 8 coloured maps (58 × 40 cm, 1:15 000 000) of Africa south of about 20°N., dated February 1992 (except map 1, dated August 1990) covering: cassava distribution in 1980; climatic classification for cassava; soil restrictions for cassava; population density (persons/km²) in 1980; dry season length and generalized soil constraints; percentage of land area in cassava (1980 fitted values); residuals from the cassava distribution model; and percentage of land area in cassava (2000 fitted values). There are 3 appendices describing the sources of data for the map of cassava distribution, the techniques used for environmental and demographic mapping and the population data used.
    The identification of agro-ecological zones for cassava in Africa with particular emphasis on soils.
    Stoorvogel, J. ; Fresco, L.O. - \ 1991
    Ibadan : IITA/COSCA (COSCA working pape 5) - 7
    manihot esculenta - cassave - ecologie - gewassen - landbouw - fenologie - acclimatisatie - afrika - agro-ecologie - cassava - ecology - crops - agriculture - phenology - acclimatization - africa - agroecology
    Report of a panel of experts on the safe and efficient international movement of germplasm of sweet potato, yam, and edible aroids, Wageningen, The Netherlands, November 14 -18, 1988
    Anonymous, - \ 1989
    Wageningen : IPO - 12
    cassave - dioscorea - export - genenbanken - genetische bronnen - germplasm - import - manihot esculenta - genetische bronnen van plantensoorten - planten - quarantaine - hulpbronnenbehoud - wortelgewassen - knollen - yams - cassava - exports - gene banks - genetic resources - imports - plant genetic resources - plants - quarantine - resource conservation - root crops - tubers
    The importance of cassava in world food production
    Bruijn, G.H. de; Fresco, L.O. - \ 1989
    Netherlands Journal of Agricultural Science 37 (1989)1. - ISSN 0028-2928 - p. 21 - 34.
    cassave - manihot esculenta - wereldvoedselproblemen - cassava - manihot esculenta - world food problems
    De belangrijkheid van cassave in de wereldvoedselproduktie wordt voor een periode van 22 jaar nagegaan
    Cassava in shifting cultivation : a systems approach to agricultural technology development in Africa
    Fresco, L.O. - \ 1986
    Landbouwhogeschool Wageningen. Promotor(en): M. Flach; N.G. Röling. - Wageningen : Fresco - ISBN 9789068320138 - 245
    zwerflandbouw - manihot esculenta - cassave - bedrijfssystemen - economische sectoren - economische situatie - agrarische bedrijfsvoering - afrika - economische productie - shifting cultivation - manihot esculenta - cassava - farming systems - economic sectors - economic situation - farm management - africa - economic production - cum laude

    The background of this study forms the debate about the nature and causes of the 'African crisis', the declining food availability per head of the African population. Generalized statements on African agriculture, based on aggregated production figures, however, do not adequately reflect the diversity in performances between crops and regions and do not allow the formulation of solutions adapted to local situations. In order to gain a better understanding of the African crisis, changes in cassava production in the Kwango-Kwilu region in central Zaire are analysed in detail. This analysis involves factors of different natures and rates of change. For that reason, a framework is developed that allows the integration of technical and socio-economic aspects of crop production. This framework draws upon ecological system analysis and, to a lesser extent, on farming systems research.

    Market impact on cassava's development potential in the Atlantic Coast region of Colombia
    Janssen, W.G. - \ 1986
    Landbouwhogeschool Wageningen. Promotor(en): F.P. Jansen; M.T.G. Meulenberg. - Wageningen : Janssen - 357
    cassave - colombia - economische situatie - agrarische bedrijfsvoering - manihot esculenta - handel - economische productie - cassava - colombia - economic situation - farm management - manihot esculenta - trade - economic production

    The impact of markets on agricultural development was analyzed by means of a case study on cassava in the Atlantic Coast region of Colombia. In the development process, the demand for agricultural products changes considerably. Traditional food products, such as roots and tubers, face a decreasing demand in the course of urbanization and income growth. Feed grains and animal products face a growing demand. The agricultural sector is often not able to adapt to these demand changes and imports result. In case the structure of agriculture is dualistic, small farmers might be harmed and large farmers benefitted by these changes. This leads to unbalanced agricultural development. Market improvement strategies directed to small farm products might correct part of the unbalanced development.

    Cassava in the Atlantic Coast region is a small farm crop which faces severe market(ing) problems in the development process. Fresh cassava consumption, the traditional utilization, decreases because it has a high marketing margin, because it has to be bought on the day of consumption and because other products become more widely available.

    Two market improvement strategies for cassava are evaluated: improvement of the traditional fresh cassava market by means of improved storage; opening the market for dried cassava as an animal feed in order to replace sorghum. To study the impact of these strategies the role of cassava in the Atlantic Coast region is analyzed within a systems framework. The interactions that are found between production, marketing and consumption are strong. Cassava production will be stimulated by the price stabilization that the establishment of a cassava drying industry will cause. The improvement of cassava's storage characteristics will decrease marketing costs, increase consumer convenience and, therefore, stimulate cassava consumption.

    Because of the interactions encountered, the impact of cassava market improvements cannot be measured in the market alone. An analysis of the cassava system that integrates production, marketing and consumption is needed. The integrated analysis is made by means of a multi-market, multi-farm type simulation model. The model forecasts the impact of market improvement strategies given different assumptions on the development of the Atlantic Coast economy and on the cassava systems behavior. Cassava drying for animal feed is a strategy, which explicitly benefits cassava producers. Additionally Colombia could save on sorghum imports. Improvement of the fresh market would most benefit urban consumers. Considering the rural-urban migration problems of Latin America, cassava drying appears the most attractive strategy.

    Both market improvement strategies have very favorable rates of return. Market improvement projects might serve additionally as a diving board for further rural development efforts. Increased attention to the role of markets could contribute to fulfilling the goals of agricultural development and to balancing overall economic growth.

    Simulatie van de droge stof-produktie en de Leaf area index van cassave
    Gijzen, H. - \ 1985
    Wageningen : Gijzen (Verslag / Vakgroep Tropische Plantenteelt, Landbouwhogeschool ) - 67
    cassave - computersimulatie - bladoppervlakte-index - manihot esculenta - simulatie - simulatiemodellen - oogsttoename - oogstverliezen - opbrengsten - cassava - computer simulation - leaf area index - simulation - simulation models - yield increases - yield losses - yields
    Physiological causes of yield variation in cassava (Manihot esculenta Crantz)
    Veltkamp, H.J. - \ 1985
    Landbouwhogeschool Wageningen. Promotor(en): M. Flach, co-promotor(en): G.H. de Bruijn. - Wageningen : Veltkamp - 132
    oogsttoename - oogstverliezen - opbrengsten - manihot esculenta - cassave - plantenfysiologie - yield increases - yield losses - yields - manihot esculenta - cassava - plant physiology
    Cassava (Manihot esculenta Crantz) is an important crop in many parts of the tropics, being mainly cultivated for its storage roots. Farmers' yields are low and one of the constraints to higher yields is the lack of adequate clones. At the beginning of the 1970s an extensive cassava research programme was started at CIAT (Colombia). One of its aims was to develop high-yielding clones by genetic modification of the plant habitus.

    This thesis begins with a literature review in which the available information on the physiological determinants of the yield of cassava storage roots is described.

    Next, a series of experiments carried out to deepen and to broaden this knowledge on physiological causes of yield variation in cassava is described. MCol 1684 (the best cultivar of the CIAT cassava germ plasm bank) and MPtr 26 were used as the reference cultivars in the experiments, both in the field and in the greenhouse.

    Rate of leaf photosynthesis was measured by infrared gas analysis. Measurements of the photosynthetic rate were carried out using the youngest fully expanded leaf from plants growing outdoors that were 35 - 45 days old. Maximum photosynthetic rates varied from 0.74 x 10 -6to 0.81 x 10 -6kg CO 2 .m -2leaf.s -1. MCol 22 had the highest leaf photosynthetic rate. A relatively low photonflux density level was required for light saturation of the photosynthetic rate. This is characteristic for a plant species with a C 3 cycle. Photosynthesis increased only slightly from 1000 to 1500 μE .m -2.s -1PAR (photosynthetically active radiation). Light efficiency at low light intensities (α) varied from 9.0 x 10 -9to 12.4 x 10 -9kg CO 2 .J -1. The CO 2 concentration remained at an approximately constant level in the intercellular spaces, independent of the light level, being 212 vppm (0.387 x 10 -3kg.m -2). At a photonflux density of 1500 μE.m -2.s -1mesophyl resistance was higher than leaf resistance to CO 2 (335 s.m -1compared with 185 s.m -1). Transpiration rates did not differ between clones, but increased with light intensity. water use efficiency (WUE)
    varied from 15.1 to 17.1 mg CO 2 uptake per g H 2 O, and was most efficient for MCol 22.

    Linear relationships were found between total dry matter yield and the amount of intercepted PAR. Photosynthetic efficiency varied from 1.9% to 2.5%, based on PAR during the first six months of the growth period, and decreased markedly in older plants. The fraction of incoming intercepted PAR varied from 43% to 69% during the first six months. Cultivars had an extinction coefficient (K) of 0.72 to 0.88 and their leaves were dominantly planophile.

    A leaf area index (LAI) of 1.0 (about 50% light interception) was attained at 60 to 90 days from planting. An LAI = 3, which coincides with a light interception by the leaf canopy of approximately 90% was reached 120 to 150 days after planting, so about 40% of a growth period of one year had elapsed before complete ground cover was achieved. Genotypes with very different canopy characteristics reached an LAI of 3 in approximately the same time.

    Cassava has an indeterminate habit with sympodial branching. The length of the period until first branching depended on genotype and planting date. Large genetic differences were found in leaf life, leaf size, plant age at which maximum leaf size was reached and leaf formation rate per apex. Small variations in environmental conditions caused significant differences in canopy characteristics.

    During the growth period of cassava two periods with constant dry matter partitioning could be distinguished, with the apparent initiation of the filling of storage roots (AISS) being the crucial point. A constant proportion of the dry matter formed is distributed to the storage roots: this is the efficiency of storage root production (ESRP). Genetic differences were found for ESRP and AISS.

    The influence of daylength on growth and yield was studied. Daylength was increased by light bulbs, while the other growth conditions remained similar. Daylength had only a very slight influence on AISS value. ESRP was negatively influenced by long days. Differences in ESRP were the main cause of differences in yield of storage roots for plants grown at different daylengths. For MCol 22, the ESRP value was also considerably lower under long-day conditions, but the yield of storage roots was nevertheless only slightly reduced, because of the higher total dry matter yield. MCol 22 is the first detected cassava clone whose yield of storage roots is nearly dayneutral and thus it is suitable for cultivation at higher latitudes. Long-day conditions caused a large increase in LAI. The higher LAI values were caused by a higher leaf formation rate per apex and a larger number of apices per m 2. Photosynthetic efficiency was not influenced by daylength.

    The implications of the findings are discussed. Plant properties that could be useful for improving storage root yield are: a high ESRP value, a low AISS value, a high growth vigour (short period until 50% light interception), a light interception of about 90% as long as possible, and a good sink potential.

    Present knowledge of cassava cultivation techniques is such that high yields are possible. Potential yield of storage roots is about 30 t.ha -1.year -1on dry weight basis and about 90 t.ha -1.year -1on fresh weight basis. The highest recorded yield of fresh storage roots at the CIAT experimental farm is of that order (namely 82 t.ha -1), and was achieved after a growth period of one year.

    Selection of technology for food processing in developing countries
    Bruinsma, D.H. ; Witsenburg, W.W. ; Wurdemann, W. - \ 1983
    Wageningen : Pudoc - ISBN 9789022008379 - 199
    voedselindustrie - voedseltechnologie - maïs - verwerking - rietsuiker - manihot esculenta - cassave - aangepaste technologie - ontwikkelingslanden - food industry - food technology - maize - processing - cane sugar - manihot esculenta - cassava - appropriate technology - developing countries
    De mogelijkheden van hefbomen bij de mechanisatie van de cassave - oogst
    Vermaat, P. - \ 1978
    (Paramaribo) : C.E.L.O.S. (CELOS rapporten no. 126) - 21
    cassave - manihot esculenta - suriname - cassava - manihot esculenta - suriname
    Fabricage van tapioca - zetmeel
    Anonymous, - \ 1976
    Wageningen : Pudoc (Literatuurlijst / Centrum voor landbouwpublikaties en landbouwdocumentatie no. 3966)
    bibliografieën - cassave - manihot esculenta - tapioca - bibliographies - cassava
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