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Master of Science / Department of Agricultural Economics / Vincent R. Amanor-Boadu / Maize is a staple food to many Zambians. It is for this reason that it has received a lot of support from government as a way of maintaining food security in the nation. No other crop in Zambia currently receives such level of support from government. Factors influencing its availability can thus seriously affect food security. In recent years, Zambia has not been spared by adverse climatic changes that have continued to affect the entire globe. In the early 1980s the southern “maize-belt” part of the country that was devastated by continuous drought that caused villagers to go hungry and lose a lot of livestock that was their main livelihood. The trend of decreasing rainfall in consecutive seasons has continued in many parts of the country. Because most smallholder farmers, who are the major contributors to the nation’s food supply, depend on rain for crop production, there has been a deliberate policy by government through the Ministry of Agriculture and Co-operatives to encourage the farmers to diversify their on- and off-farm activities to improve food security at household and national level. To this end, the government has continued to encourage the growing of cassava. Several studies have suggested that cassava is a nutritious food crop (Chitundu, Droppelman and Haggblade, 2006). Cassava has a number of industrial uses too. Good attributes of cassava lie not only in the nutrition content of the tuber and leaves but also in the fact that as a field crop it does not require expensive inputs like fertilizer and is better able to withstand drought compared to the maize crop. This study attempts to understand the economic factors that influence consumption of cassava to shed light on its potential to avert potential crisis associated with prolonged droughts. Based on the survey conducted in 2007 in Lusaka, the study found that price and quality of cassava meal are the principal determinants of cassava meal demand in Lusaka. Direct price elasticity of demand for cassava is -1.32, suggesting that cassava meal is price elastic. The study also found that the cross price elasticity between maize meal price and cassava meal demand is 0.04 suggesting that cassava meal is a substitute to maize meal, but inelastic. The income price elasticity of demand for cassava meal is -0.12. However, income was found to be statistically insignificant in determining the demand for cassava meal. As such these economic factors are keys to the consumption of cassava. Therefore, the study suggests that the demand for cassava meal in Zambia may be improved through deliberate promotion.

ABSTRACT Cassava is a known source of linamarin, but difficulties associated with its isolation have prevented it from being exploited as a source. A batch adsorption process using activated carbon at the appropriate contact time proved successful in its isolation with ultrafiltration playing a pivotal role in the purification process. Result revealed that optimum purification was obtained with increasing amount of crude cassava extract (CCE) purified. 60g of CCE took 32 mins, 80 g, 34 mins while 100 g took 36 mins of contact time, where 1.7 g, 2.0 g and 2.5 g of purified product were obtained, respectively. The purification process in batch mode was also carried out at different temperatures ranging from 25 to 65oC. Results showed that purification increases with increase in temperature. In a bid to ascertain the moles of linamarin adsorbed per pore volume of activated carbon used, the composite isotherm was found to represent the measured adsorption data quite well. The adsorption of linamarin was used to study the goodness of fit criteria (R2) for the entire process. Results showed that R2 value was best with decreasing amount of CCE purified (R2=1 for 60 g) at the temperature of 45oC. Compound elucidation of purified product by Picrate paper test, IR and 1HNMR confirmed the structure of linamarin. Cytotoxic effects of linamarin on MCF-7, HT-29, and HL-60 cells were determined using the 3 - (4, 5 – dimethylthiazol-2-yl) – 2, 5 – diphenyltetrazolium bromide (MTT) assay. Cytotoxic effects were significantly increased in the presence of linamarase, which catalysed the hydrolysis of linamarin to hydrogen cyanide. A 10–fold decrease in the IC50 values obtained for linamarin or crude extract in the presence of linamarase was determined for HL-60 cells. This study thus describes a method for the isolation and purification of linamarin from cassava, as well as the potential of this compound as an anticancer agent.

Cassava (Manihot esculenta Crantz) is an important tropical crop which provides a large portion of daily calories intake to hundreds of millions of people in Africa, Latin America, and tropical Asia. Cassava is grown for its starchy storage roots as staple food, as animal feed, and as industrial raw material. The utilisation of cassava is hindered by its characteristic physiological response, the post-harvest physiological deterioration (PPD). The inevitable wounding caused during harvesting and handling will trigger a series of physiological responses within 24 to 48 hours, which causes a blue-black discoloration in the storage roots, rendering these roots unmarketable and unpalatable in a few days. During the PPD response large amount of phenylpropanoid compounds, especially scopoletin and its glycoside, accumulate in the roots. Scopoletin may play an important role in PPD development but little work has been done on the possible relationship. Here we aim to examine the effects of altering scopoletin synthesis in cassava roots on the PPD response. In Arabidopsis thaliana, gene F6’H1 (feruloul CoA 6’-hydroxylase 1) is indispensable in the biosynthesis of scopoletin. Cassava F6’H1 candidate gene family involved in scopoletin synthesis were identified by their ability to functionally complement F6’H1 T-DNA insertion mutation in Arabidopsis thaliana that prevented synthesis of scopoletin. RNAi constructs targeting the identified cassava F6’H1 candidate gene family were designed, under the control of either constitutive CaMV 35S or root-specific StPAT promoters. These were used to transform wild-type cassava to down-regulate the expression of these scopoletin synthetic genes in F6’H1 gene family. The inhibition of cassava F6’H1 candidate gene expression and thus the scopoletin synthesis in transgenic cassava roots were confirmed by qRT-PCR and LC-MS, respectively. The RNAi transgenic cassava lines show less scopoletin accumulation and inhibited F6’H1 candidate genes expression during the PPD response. A reduced PPD discoloration development compared to that of the wild-type was also observed in the RNAi transgenic cassava lines.

Cassava ranks seventh in terms of worldwide crop production, providing a staple for over half a billion people. The production of cassava is limited by several factors, with post-harvest physiological deterioration (PPD) of storage roots a major constraint. PPD is a process initiated on harvesting and mediated by reactive oxygen species (ROS) that ultimately renders storage roots unpalatable and unmarketable. It is similar to a conventional plant wound response, but crucially lacks efficient wound repair and down-regulation of stress signalling. Therefore, the strategy utilised here to modulate PPD focussed on increasing the ROS scavenging ability of storage root tissue through a biotechnological approach. Three expression plasmids were produced, harbouring cassava genes encoding the antioxidant enzymes APX, CAT and SOD under the control of the storage rootspecific StPAT promoter. In addition, a reporter expression plasmid was created, with StPAT driving the expression of GusP. Transgenic Arabidopsis plants containing the StPAT::GusP cassette demonstrated root-specific GusP staining. Non-root tissue also showed wound-inducible GusP activity conferred by the StPAT promoter. This novel activity was detected almost immediately after wounding and occurred independently of ethylene, MeJa and ROS. The 3’ 261 bp of the StPAT promoter was sufficient to confer wound-inducible expression and contained putative wound responsive cis regulatory motifs. Analysis of PATATIN function indicated a role during early responses to wounding in the liberation of free fatty acids from cell membranes. Over-expression of the target genes in the model plant Arabidopsis increased the antioxidant enzyme activity in the roots of selected lines. Transgenic plants generally exhibited similar levels of oxidative stress resistance to wild-type plants, a result due in part to the efficient nature of the oxidative stress response of Arabidopsis – the APX activity of wild-type plants increased to transgenic levels under H2O2 stress. However, PPD in cassava is at least partially the result of a poor antioxidant response to harvesting, and so transformation of cassava with the expression plasmids remained a viable strategy. Transgenic cassava plants harbouring the expression cassettes are being generated and will soon be assessed for PPD resistance.

Participation of farmers in plant breeding programmes has been reported to increase breeding efficiency. Farmers’ participation bridges the gap between variety development and dissemination and provides an opportunity for farmers to select varieties they prefer. The breeders on the others hand learn more about the farmers’ preferences and the environment in which the new varieties will be grown. However, the advantages of participatory breeding can best be realized when farmers’ indigenous technical knowledge (ITK) and experience complement the breeder’s scientific knowledge and skills. Cassava (Manihot esculenta Crantz) is a clonally propagated crop grown in diverse environments by small scale farmers for subsistence. Information on the roles of farmers and breeders at various stages of breeding and their ability to effectively participate in breeding programmes is limited. The objectives of this study were to determine: (1) cassava farmers’ preferences, production constraints and systems; (2) farmers’ selection criteria of cassava varieties; (3) genetic inheritance of farmer preferred traits; (4) how farmers and breeders complement each other at all stages and activities of cassava breeding. Participatory rural appraisal was conducted in three purposefully sampled districts of western Kenya based on ethnicity and agro-ecology. The results reveal that cassava is predominantly grown by small scale farmers with mean land size of 1.6 ha mainly under mixed cropping system for subsistence. The storage roots are eaten either after boiling or processing to flour. The majority of farmers (over 60%) are aware of the improved varieties but adoption rate is low (18% in some districts). The effects of pests and diseases, and the lack of high yielding varieties, capital, land, and disease free planting material are the most important constraints to cassava production. Farmers prefer tall, high yielding varieties that are resistant to diseases and pests, early maturing and long underground storability of harvestable storage roots. The districts surveyed significantly differed in popularity of utilization methods, traits preferences and relative ranking of the production constraints indicative of differences in ethnicity and agro-ecology. Three farmer groups from the three districts selected in western Kenya were used to study farmers’ variety selection criteria based on their own indigenous technical knowledge (ITK). The groups evaluated 15 (10 landraces and five improved) popular cassava varieties with concealed identities on their farms. The results revealed that farmers have effective methods of selecting varieties for most of their preferred traits. However, ITK alone cannot be used to evaluate all the important traits, such as cyanide content. The genetic inheritance of farmer preferred traits was determined through a genetic study. Six landraces and four improved varieties popular in western Kenya were crossed using the North Carolina mating design II to generate 24 full-sib families. The 24 families, represented by 40 siblings each, were evaluated at two sites, Kakamega and Alupe research station farms, in a 24 x 40 a-lattice design. General combining ability (GCA) and specific combining ability (SCA) mean squares were significant (P<0.05) for all traits evaluated except dry matter content and cyanide content. However, non-additive gene action predominated over additive gene for cassava mosaic disease (CMD) resistance, height to first branching, total number of storage roots per plant and fresh storage root yield in all environments. The best crosses were not necessarily obtained from parents with high general combining ability confirming the presence of non-additive gene action. The best performing parents per se did not necessarily have high GCA effects implying that selection based on the per se performance of parents may not always lead to development of superior hybrids. The clonal evaluation trial (CET) was established at Alupe research station and evaluated by the breeder and farmers from two districts independently. Three selection criteria were tested to determine the most appropriate approach to selection of varieties that meet both farmers’ and breeder’s preferences. The selection criteria were; farmers’ independent selection index (SI) derived from farmers’ selection criteria from each district, breeder’s negative selection and independent SI, and a participatory SI which combines farmers’ and breeder’s selection criteria. There was 14% overlap among the top 100 varieties selected by farmers from all districts and the breeder when independent SI were used. However, there was 49% overlap among the top 100 varieties selected by farmers using participatory SI and the breeder’s SI. The farmers and the breeder have a role to play in the variety development process. Varieties with traits preferred by both the farmers and the breeder are likely to enhance breeding efficiency and effectiveness. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.

Cassava (Manihot esculenta Crantz), is the world’s most widely grown starch storage root crop. It is a principal food staple in sub-Saharan Africa where it accounts for approximately one-third of the total production of staple food crops. It plays a key role as a food security and an income-generating crop for millions of smallholder farmers. In Uganda, cassava ranks second to bananas (Musa spp.) in terms of area occupied, total production and per capita consumption; however, nearly 5% of the total population experiences hunger with the prevalence of food energy deficiency at the country level standing at 48%. Cassava is a crop with high potential to alleviate food shortages and energy deficiencies, owing to its unique advantages of producing acceptable yields and starch on infertile soils amidst erratic rainfall, when most other crops would fail. Hoewever, its yield potential has not been fully realised since most of the cassava cultivars grown are susceptible to pests and diseases, low yielding and late bulking. The main objective of the research was to develop high yielding, early bulking cassava genotypes that combine resistance to cassava brown streak disease (CBSD) and cassava mosaic disease (CMD) with farmer preferred traits for cultivation in Uganda. The specific objectives were to: (i) evaluate farmers’ attitudes to and/or perceptions of cassava early bulking, production constraints and cultivar preferences; (ii) determine the extent of genetic variability in storage root bulking and other important traits of selected cassava genotypes; (iii) assess the effects of genotype x environment interaction on early bulking and related traits of selected cassava genotypes; (iv) develop and evaluate cassava F1 families for early bulking in terms of the attainment of early, high fresh storage root yield (FSRY) and resistance to CBSD and CMD; and (v) determine the combining ability and gene action controlling early bulking and yield-related traits, as well as resistance to CBSD and CMD. Through the farmer participatory survey, a number of cassava production constraints were identified, key of which were: diseases, especially CBSD and CMD; lack of early bulking cultivars; rodents and insect pests. Farmers rated early bulking as the second most important preferred trait after FSRY, but suggested that early bulking should be complemented with high dry mass content (DMC), sweetness, high FSRY and resistance to pests and diseases. The analysis of variance of 12 cassava genotypes selected for evaluation in three diverse locations and at five different harvest times indicated significant variation among genotypes, harvest times, locations and their interactions for FSRY and most of the other traits evaluated. Fresh storage root yield and the other traits evaluated were predominantly under the control of genetic variation, indicating that genetic advance would be achieved through hybridisation of the test genotypes. Additive main effects and multiplicative interaction (AMMI) analysis of the data collected at nine months after planting (MAP) indicated a non-significant GEI for early FSRY, but significant GEI for other traits assessed. Eight of the 12 genotypes analysed had relatively low interaction with locations for early FSRY, signifying that these genotypes were relatively stable for early FSRY. Thirty-six F1 families were generated from a 9 x 9 diallel and exhibited a high degree of variation between and within families for all the traits assessed at the seedling evaluation stage. Diallel analysis at the seedling evaluation stage at 10 MAP indicated that additive gene effects were predominant in the expression of early FSRY and most of the other traits analysed. At the clonal evaluation stage, the 36 families were assessed for early FSRY at 8 MAP and this trait together with most of the other traits assessed were found to be predominantly under the control of non-additive gene effects. High mid- and better-parent heterosis for early FSRY was recorded in most families at the clonal evaluation stage with NASE3 x Nyara, Nyara x B11 and NASE3 x B11 recording the highest. Selection from the 36 families at the clonal evaluation stage based on farmers’ top two preferred traits, viz. early bulking for FSRY and DMC, plus resistance to CBSD and CMD identified 50 genotypes that had early FSRY of ≥25 t ha-1 at 8 MAP compared to the best parent, CT1 that had 15.9 t ha-1 at 8 MAP. The selected genotypes also had high DMC and dual resistance to CMD and CBSD. Advancement of the selected genotypes should go a long way towards increasing cassava yield per unit time, reducing food shortages and increasing the income of smallholder farmers in Uganda. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.

Thesis (Ph. D. in Economics)--Vanderbilt. / Includes bibliographical references (leaves 205-208).

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