Towards enhancement of B-carotene content of high dry mass sweetpotato genotypes in Zambia.

Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.The enrichment of B-carotene, a precursor to vitamin A, in the local sweetpotato (Ipomoea batatas L.) cultivars is an attractive option in order to improve vitamin A intake in Zambia. The study was conducted to: 1) identify sweetpotato genotypes high in B-carotene content and high root dry mass (RDM) and to determine their combining ability, as measured through their progeny performance; and 2) screen progeny for root characteristics, yield, B-carotene content, and RDM. Firstly, a participatory rural appraisal (PRA) was conducted to determine the consumer preferences for sweetpotato. These preferences would form the basis for selecting desirable genotypes. Secondly, five selected parents were crossed in a full diallel for genetic variance studies. A selected subset of the diallel progeny were evaluated in three environments. Thirdly, 15 polycross progeny were evaluated for stability in five environments using additive main effect and multiplicative interaction (AMMI). The PRA revealed that consumers preferred high RDM combined with high fresh root yield. The diallel crosses recorded significant general combining ability (GCA) and specific combining ability (SCA) effects for B-carotene, RDM, harvest index (HI) and root fresh yield (RFY). The ratios of GCA to SCA variances were large (0.68-0.92). Two high B-carotene parents exhibited positive high GCA effects, indicating that additive gene effects were predominant in the inheritance of B-carotene. Reciprocal mean squares were not significant for RDM but they were significant (p=0.01) for B-carotene content. The estimate of narrow sense heritability of RDM (76.3%) was high; but heritability of B-carotene (20.9%), HI (29.1%) and RFY (34.9%) were much lower. These results suggest that rapid genetic gains should be possible with mass selection breeding techniques based on the phenotype of the parent for RDM but progress will be slow for B-carotene content HI, and RFY. The AMMI analysis identified progeny G2 (B-carotene content = 5.0 mg 100 g-1 and RDM = 37%), G6 (B-carotene content = 4.7 mg 100 g-1 and RDM = 37%), and G8 (B-carotene content = 4.7 mg 100 g-1, RDM = 35%) from the polycross as stable across environments for both B-carotene content and RDM. Genotype G3 was best suited to one of the test environments and had the highest B-carotene content (9.421 mg 100 g-1) and a high RDM (35.47%)

Physiological and Morphological Responses of Cassava Genotypes to Fertilization Regimes in Chromi-Haplic Acrisols Soils

The objective of this study was to evaluate the performances of three cassava genotypes on yield, physiology and morphological traits under different fertilization regimes. A field experiment was conducted in a split-plot design for two consecutive seasons in the Mansa district of the Luapula Province of Northern Zambia in the highly weathered Chromi-haplic Acrisol soils. Four fertilization regimes, control-M3, lime-M1, NPK fertilizer-M4 and NPK fertilizer + lime-M2 were the main plots, while three varieties (Mweru-V1, Bangweulu-V2 and Katobamputa (local)-V3) were subplots. Periodic measurements of leaf area index, light interception, yield and yield components from 75 days after planting (DAP) up to 410 DAP and daily weather measurements of data were recorded. Fertilization significantly increased the radiation use efficiency (RUE) and light extinction coefficient (K) in two seasons compared to the control. Significant fertilization regimes and varietal effects were observed for seasonal LAI, stem yield, root yield, biomass, harvest index (HI), tuber number, root diameter, plant height and SPAD (chlorophyll index). A significant year’s effects on root yield, yield components and physiological performances were observed while significant fertilization × variety interaction was observed on seasonal LAI, tuber number, root diameter, plant height and SPAD. Significant fertilization × year interaction effects were observed on root yield, yield components and physiological performances. Variety × year interaction was significant for seasonal LAI, stem yield, harvest index and plant height and no three-way interactions were observed on all the traits. NPK fertilizer + lime and NPK fertilizer treatments may be adopted to increase the response of cassava varietal yield, physiology and morphological traits in low soil nutrient conditions under high rain-fed conditions

Cropping Practices and Effects on Soil Nutrient Adequacy Levels and Cassava Yield of Smallholder Farmers in Northern Zambia

Cassava is a staple food and a major source of income for many smallholder farmers. However, its yields are less than 6 t ha-1 compared to a potential yield of 20-25 t ha-1 in Zambia. Understanding cropping practices and constraints in cassava production systems is imperative for sustainable intensification. Therefore, a survey of 40 households each with three fields of cassava at 12, 24, and 36 months after planting (MAP) was conducted. Analyzed soil data, leaf area index (LAI), intercepted photosynthetically active radiation, and management practices from 120 fields were collected and subjected to descriptive statistics. To explain yield differences within the same cassava growth stage group, the data were grouped into low- and high-yield categories using the median, before applying a nonparametric test for one independent sample. Stepwise regressions were performed on each growth stage and the whole dataset to determine factors affecting tuber yield. Cassava intercropping and monocropping systems were the main cropping systems for the 12 and 24-36 MAP, respectively. Cassava yields declined by 209 and 633 kg ha-1 at 12 and 36 MAP due to soil nutrient depletion for each year of cultivation until field abandonment at 8-9 years. Fresh cassava yields ranged from 3.51-8.51, 13.52-25.84, and 16.92-30.98 t ha-1 at 12, 24, and 36 MAP, respectively. For every one unit increment in exchangeable K (cmol (+)/kg soil), cassava yield increased by 435, 268, and 406 kg ha-1 at 12, 24, and 36 MAP, respectively. One unit increment of magnesium (cmol (+)/kg soil) gave the highest yield increase of 525 kg ha-1 at 24 MAP. The low levels of soil organic carbon explained the deficient nitrogen in cassava fields, which limits the LAI growth and consequently reduced intercepted radiation and low yields. The effect of exchangeable K on growth was limited by the moderate availability of Mg and low N, thus the need for balanced fertilizer regimes. © 2021 Peter Kaluba et al

Physiological and Morphological Responses of Cassava Genotypes to Fertilization Regimes in Chromi-Haplic Acrisols Soils

The objective of this study was to evaluate the performances of three cassava genotypes on yield, physiology and morphological traits under different fertilization regimes. A field experiment was conducted in a split-plot design for two consecutive seasons in the Mansa district of the Luapula Province of Northern Zambia in the highly weathered Chromi-haplic Acrisol soils. Four fertilization regimes, control-M3, lime-M1, NPK fertilizer-M4 and NPK fertilizer + lime-M2 were the main plots, while three varieties (Mweru-V1, Bangweulu-V2 and Katobamputa (local)-V3) were subplots. Periodic measurements of leaf area index, light interception, yield and yield components from 75 days after planting (DAP) up to 410 DAP and daily weather measurements of data were recorded. Fertilization significantly increased the radiation use efficiency (RUE) and light extinction coefficient (K) in two seasons compared to the control. Significant fertilization regimes and varietal effects were observed for seasonal LAI, stem yield, root yield, biomass, harvest index (HI), tuber number, root diameter, plant height and SPAD (chlorophyll index). A significant year’s effects on root yield, yield components and physiological performances were observed while significant fertilization × variety interaction was observed on seasonal LAI, tuber number, root diameter, plant height and SPAD. Significant fertilization × year interaction effects were observed on root yield, yield components and physiological performances. Variety × year interaction was significant for seasonal LAI, stem yield, harvest index and plant height and no three-way interactions were observed on all the traits. NPK fertilizer + lime and NPK fertilizer treatments may be adopted to increase the response of cassava varietal yield, physiology and morphological traits in low soil nutrient conditions under high rain-fed conditions

Cassava commercialization in Southeastern Africa

Purpose – Cassava production surged noticeably in Southeastern Africa beginning in the 1990s. The purpose of this paper is to examine the commercial responses and food security consequences of cassava production growth in the region. Design/methodology/approach – The paper incorporates a mix of quantitative analysis, based primarily on original analysis of national farm household survey data, together with key informant interviews with value chain participants in the three neighboring countries of Malawi, Mozambique and Zambia. Findings – In the cassava production zones, cassava's high productivity translates into per kilogram carbohydrate costs 60 per cent to 70 per cent of the cost of cereals such as maize and wheat, thereby opening up a range of profitable opportunities for commercialization of cassava-based foods, feeds and industrial products. Despite this potential, cassava commercialization in Southeastern Africa remains in its formative stages, with only 10 per cent to 30 per cent of production currently marketed. Unlike West Africa, where cassava commercialization has centered on marketing prepared cassava-based convenience foods, the emerging cassava markets in Southeastern Africa have centered on fresh cassava, low value-added cassava flour, and experiments in industrial processing of cassava-based starches, biofuels and feeds. Strategic investment in a set of key public goods (breeding, training in food sciences and food safety, and research on in-ground cassava storage) can help to shape this transition in ways that benefit both commercial interests and the food security of vulnerable households. Originality/value – The paper compares cassava commercialization across differing agro-climatic zones, policy environments and food staple zones