Orientador : Cesar Francisco Ciacco / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos e Agricola / Made available in DSpace on 2018-07-15T18:25:15Z (GMT). No. of bitstreams: 1 SalcesRuiz_Franz_M.pdf: 5204043 bytes, checksum: c560e5f4711d26bd722e4936f7d60b23 (MD5) Previous issue date: 1984 / Resumo: A desidratação. da batata doce após a colheita ou determinado período de armazenamento tem sido preconizada como uma al tentativa tecnológica para o melhor aproveitamento deste tubérculo. Este trabalho teve como objetivo estudar o processo de desidratação de batata doce usando rolos secadores (Drum-Dryer). O efeito dos parâmetros operacionais nas propriedades tecnologia dos flocos foi investigado com auxilio da Metodologia de Resposta de Superfícies (Response Surface Methodology - RSM). As análises de variança mostraram um ajuste altamente significativo pa-ra a maioria dos modelos matemáticos que relacionaram o efeito dos parâmetros operacionais e as propriedades tecnológicas dos flocos. O teste indicou que os modelos para o rendimento, porcentagem de retenção de vitamina C, porcentagem de carotenóides, viscosidade inicial e o Índice de solubilidade em água foram altamente significativos, ao nível de 0,01%. Os modelos para cor, viscosidade máxima e viscosidade a 509C e o índice de absorção em água foram significantes ao nível de 0,14, 0,26, 0,90 e 15,00%, respectivamente. Estes resultados mostraram que o Índice de absorção em água não variou significativamente em função das variáveis experimentais. A representação gráfica dos modelos matemáticos, como respostas de superfície (curvas de nível), permitiu estudar como as variáveis independentes (parâmetros operacionais) afetaram as 1fespostas (características tecnológicas). O rendimento foi afetado principalmente pela abertura entre os rolos e a concentração de sólidos, sendo pouco afetado pela pressão. de vapor, O rendimento máximo foi obtido para concentrações entre 16 e 20% de sólidos e aberturas em to~no de 0.30mm, em uma grande faixa de pressão. de vapor. A porcentagem de retenção de vitamina C e carotenó1des foi afetada, principalmente, pela pressão de vapor e a concentra ção de sólidos no purê, A maior retenção de vitamina C (81%) e corotenóides '(98%), ocorreu para pressões de cerca de 80lb/po12, entre 15-17% de concentração de sólidos e aberturas entre 0,10 e O,20mm. As curvas de nível mostraram que a viscosidade inicial e a viscosidade máxima foram controladas, essencialmente, pela abertura entre os rolos. A pequena influência da pressão de vapor nestas duas variáveis indicou que mesmo as pressões mais baixas testadas (40 lb/pol ) foram suficientes para uma extensiva gelatinização do amido. O efeito das variáveis operacionais sobre a viscosidade a 509C foram semelhantes aos observados para a viscosidade máxima. A pressão e abertura entre os rolos foram as variáveis de maior influência no índice de absorção de água. As curvas de nível mostraram a existência de um efeito de compensação entre a temperatura dos rolos e a espessura do filme. Filmes finos provocaram uma gelatinização mais efetiva do amido que aquelas obtidas com filmes mais espessos. Conseqüentemente a absorção de água dos produtos obtidos co~ pequenas aberturas foi superior àquelas obtidas com aberturas maiores, nas mesmas condições de pressão de va-por. As curvas de nível do índice de solubilidade em água mostraram um comportamento oposto ao apresentado pelas curvas do índice de absorção em água. Os máximos valores do índice de solu-bilidade em água, foram obtidos a altas pressões entre 65-76 lb/po12l, concentrações intermediárias (entre 18 a 23%) e aberturas pequenas menores que O,20mm), Provavelmente, o aumento do índice de solubilidade em água foi devido à desintegração dos grânulos de amido, que solubilizando diminuíram o índice de absorção em água. O maior efeito no índice .de solubilidade em água foi devido a abertura entre os rolos. O maior efeito sobre a cor foi devido a variações na abertura. Aumentos na abertura até cerca de O,30rnrn, em uma ampla faixa de pressão de vapor e concentrações de sólidos, resultaram em alto DE. Estes resultados em conjunção com aqueles de retenção de carotenóides indicaram que não existe uma relação entre a cor observada e o conteúdo deste composto. Estudos com batata doce armazenadas a 209C e 90% de umidade relativa mostraram que o tempo de armazenamento, até 5 se-manas, teve uma influência positiva na cor e rendimento dos flocos. Estes resultados .foram provavelmente devido ao aumento na concentração de sólidos solúveis totais durante este período de armazenamento / Abstract: Dehydration of sweet potato after harverst or storage was recommended as a technoloical alternative for the better exploitition of this tuber. The objetive of this project was to study the dehydra-tion process of sweet potato with a double Drum-Dryer. The Res-ponse Surface Methodology was used to study the re1ation between.the process parameters (roll temperature, roll spacing and total solids content in the puree)and some technological properties of the flakes obtained. The analyses of variance indicated that the mathemat1ca1 models expressing the relation between the processing .parameters and the techno10gica1 propert1es were we adjusted. The F va1ue 1ndicated that the mathematica1 models for yie1d, as-corbic acid and caroten01d retentions, initlal v1scosity and water solubility index were s1gn1ficant at the 0.01% level. The models for color, maximum vlscosity, viscosity at S09C and water absorp- tion index were sign1ficant at the 0.14, 0.26, 0.90 and 15.00% 1eve1s, respective1y. These resu1ts showed that the model for water absorption index was not significant1y affected operational parameters. The effect of the operat10na1 parameters on the techno10- by the g1ca1 properties, of the f1akes was a1so studied by .contour plóts. The yie1d was ma1n1y affected by the spac1ng between the rolls and total sol1ds concentrat10n. The steam pressure d1d not have a significant effect on the yie1d. The maximum y1e1d was obtained at 16 to 20% of the total 801ids concentrat10n and around 0.30mm ro11 spacing. The ascorbic acid and carotenoid retentions were ma1n1y affected by the steam pressure and total so11ds concentrat10n of the puree, The maximum ascorbic actd (Bl%) and carotenoid (98%) retentions were obtained at about 80 psig, 15-17% solids concentra tion.and roll spacings between 0,10 and 0.2G mm. The contours plots showed that the inicial viscosity and maximum viscosity were affected essentially by the roll spacing. The small influence of steam pressure on the initial viscosity in dicated that even the low stearn pressure used led to extensive starch gelatinization. The effect of the processing pararneters on the viscosity at 509C was similar to that observed with the maximum viscosity, The pressure and the roll spacing were the variables that influenced the water absorption index. The contour plots showed a compensation effect between the surface temperature and film thickness. Thin films caused more effective starch gelatinization than thick ones, at the sarne roll surface temperature, Consequen-tly the water absorption of the products obtained with the smallest spacing was higher than that obtained with a larger roll spacing. On the other hand the maximum water solubility index values were obtainàd with a higher steam pressure (ranging from 60 tô 80 psig), total solids concentration from 17 to 23% and a rollcing below 0.20 mm, Flakes with high DE were obtained at 0.30 mm roll spacing spa- whith wide ranges of steam pressures and total solids concentra-tions, The storage of sweet potatoes at 209C and 90% relative humidity showed that storage up to 5 weeks had remarkable effects on the color and yield. These results were probably due to the increase in the soluble solids content .during the storage period / Mestrado / Mestre em Tecnologia de Alimentos

No description available.

The composition of the non-starch polysaccharides in sweet potato was determined and their flatulence-inducing potential evaluated. A preparative adaptation of the AOAC enzymatic method was used to isolate the insoluble and soluble non-starch polysaccharides. The insoluble non-starch fraction was mainly cellulose, but contained a substantial amount of hemicellulosic glucose, suggesting the presence of an independent glucan fraction. Relatively small amounts of xylose, galactose, arabinose, mannose, rhamnose and fucose were present. Galactose was the predominant sugar in the soluble non-starch polysaccharide fraction, although substantial quantities of arabinose and mannose were also present. Xylose, rhamnose, glucose and fucose were also present in small quantities. Uronic acids also made up a substantial portion of the soluble non-starch polysaccharides. Appreciable protein and ash were present in both the insoluble and soluble NSP fractions. The in vitro test for gas production using Clostridium perfringens as a test organism showed that both the insoluble and soluble non-starch polysaccharides are potential flatulence-inducers in sweet potato. However, the presence of the hemicellulosic glucans in the insoluble fraction make the latter a more likely candidate for flatus-inducer. / Master of Science

Sweet potato single-leaf cuttings of cultivars ‘Centennial,’ ‘Jewel,’ and ‘Nemagold’ were planted in plastic pots containing steam-sterilized sand. Fully opened leaves were counted from the terminal apex on stock plant stems, and leaf positions 1 to 3 and 7 to 9 were referred to as mean leaf positions 2 and 8 respectively. Dry weight and its partitioning among plant organs (leaf, stem, petiole, new shoot, fibrous roots, and stronger roots) differed among the three cultivars. ‘Centennial’ had the highest storage root dry weights in both the first (December-March) and second (April-June) experiments. The new shoots and storage root dry rates of ‘Centennial’ and ‘Jewel’ were 3 to 25 times greater at 79 days after planting (DAP) in the second experiment than at 70 DAp in the first experiment. The new shoot was the dominant sink in ‘Nemagold’ between 28 and 70 DAP in the first experiment but not in the second experiment, and the storage root never became a strong sink in either experiment. A shift from leaf dry weight increases to decrease was observed in the first experiment but not in the second experiment. Leaves in mean leaf position 2 showed higher original plant material (leaf, petiole, and stem) dry weight than mean leaf position 8, but there were no significant differences in final storage root dry weight between these two mean leaf positions in both experiments. Mean leaf positions 2 approximant net assimilation rate (NAR) values based on leaf and new shoot dry weight exceeded mean leaf positions 8 approximate NAR values in both experiments. Plants with stem attachment had higher new shoot and storage root dry weights than plants without stem attachment. Dry weight of the original leaf decreased in plants with steam attachment but not in plants without stem attachment. / M.S.

Yeast breads were prepared with three levels of mashed sweet potato pulp and of mung bean flour. Nine combinations of mashed sweet potato pulp (10, 20, 30 percent), and of mung bean flour (4, 8, 16 percent) substitutions for wheat flour were used to determine the acceptability of these enriched breads. Added liquid was adjusted for moisture in sweet potato pulp. Sensory evaluation data was analyzed by analysis of variance to determine the major effective factor on the acceptability of bread. Objective measurements were used to determine bread volume, percent crude nitrogen, percent ether extractable crude fat, and moisture content of the breads. The sensory evaluation results indicated that the bread quality decreased with increase in the amount of mung bean flour; mashed sweet potato pulp did not affect the bread quality except that the highest level (30 percent) has a slight adverse effect on bread texture. The characteristics of all breads made with mashed sweet potato pulp and mung bean flour varied with the amount of substitute ingredient. In general, mung bean flour affected the acceptability of bread and bread quality. Breads made with 20 percent mashed sweet potato pulp and 4 or 8 percent mung bean flour were judged to have more desirable eating quality. Volume of bread was decreased with increase in the amount of mung bean flour and of mashed sweet potato pulp. The percent crude nitrogen increased with the addition of mung bean flour and decreased with the addition of mashed sweet potato pulp. Bread enriched with 16 percent mung bean flour and 10 percent mashed sweet potato pulp increased in the amount of percent crude nitrogen approximately 16.7 percent compared with the control. Percent ether extractable crude fat content of all breads was low and was varied. Moisture content increased with addition of mung bean flour and mashed sweet potato pulp. / Master of Science

Sweet potato [Ipomoea batatas (L.) Lam] is technically a perennial plant, cultivated and explored as an annual crop. Thus, the identification of the cultivation cycle and sweet potato clones is important for a better utilization of this crop, in both, human and animal nutrition, as for ethanol production. The aim of this work was to evaluate the performance of sweet potato clones grown in different cultivation cycles. The experimental design was a randomized block design, in a split-plot scheme, with three replications. We tested in the plots three cultivation cycles (3, 5 and 7 months), and in the split plots, six sweet potato clones (accessions IBP-007, IBP-038, IBP-075, IBP-079 and IBP-149, and cultivar Brazlândia Rosada). The experiment was carried out at the Research Farm "Campus Rural da UFS", located in the municipality of São Cristovão-SE. The analyzed variables were: survival, damages caused by soil insects, fresh and dry weight of the aerial part, total root yield, content of root dry matter, starch and amylose, and yield of starch and ethanol. All variables were subjected to analysis of variance with the F test, and when significant, the means were compared by the Skott-Knott test at 5% probability. The lowest survival rates occurred in the seventh month of cultivation (51.11%), together with the greatest damage caused by soil insects (4.29), where the clones IPB-038 (2.84), IPB-075 (3.01) and IPB-149 (2.88) showed resistance at the seven month cultivation cycle. Clone IPB-007 presented high values of fresh (14.07 t.ha-1) and dry weight (2.81 t.ha-1) of the aerial part in all the cultivation cycles, presenting also high yield of roots (33.16 t.ha-1), starch (6.63 t.ha-1) and ethanol (4,379 L.ha-1). For content of root dry matter (38.32%) and starch (26.70%), and ethanol yield (176.26 L.t-1), the clone IPB-149 stood out. There was no significant difference in amylose content. The starch content (13.94%) and the yield of roots (7.53 t.ha-1), starch (1.64 t.ha-1) and ethanol (1,034 L.ha-1 and 92.04 L.t-1) were lower for most of the clones evaluated with three months of cultivation. We recommend the use of the cultivation cycle of five months. / A batata-doce [Ipomoea batatas (L.) Lam.] é tecnicamente uma planta perene, plantada e explorada como anual. Sendo assim, a identificação do ciclo de cultivo e de clones de batata-doce é importante para um melhor aproveitamento dessa cultura, tanto na alimentação humana e animal, como para produção de etanol. O objetivo do presente trabalho foi avaliar o desempenho de clones de batata-doce cultivados em diferentes ciclos de cultivo. O delineamento experimental foi o de blocos casualizados, em esquema de parcelas subdivididas, com três repetições. Foram testados nas parcelas três ciclos de cultivo (3, 5 e 7 meses), e nas subparcelas, seis clones de batata-doce (acessos IBP-007, IBP-038, IBP-075, IBP-079 e IBP-149, e a cultivar Brazlândia Rosada). O experimento foi implantado na Fazenda Experimental Campus Rural da UFS , localizada no Município de São Cristovão-SE. As variáveis analisadas foram: sobrevivência, danos causados por insetos de solos, massa fresca e seca de parte aérea, produtividade total de raízes, teor de matéria seca de raiz, amido e amilose e rendimento de amido e etanol. Todas as variáveis foram submetidas à análise de variância com teste F e, quando significativa, as médias foram comparadas pelo teste de Skott-Knott ao nível de 5% de probabilidade. Os menores índices de sobrevivência ocorreram no sétimo mês de cultivo (51,11%), juntamente com os maiores danos causados por insetos de solo (4,29), onde os clones IPB-038 (2,84), IPB-075 (3,01) e IPB-149 (2,88) apresentaram resistência no ciclo com sete meses. O clone IPB-007 apresentou elevados valores de massa fresca (14,07 t.ha-1) e seca (2,81 t.ha-1) de parte aérea, em todos os ciclos de cultivo, apresentando também, alta produtividade de raiz (33,16 t.ha-1), amido (6,63 t.ha-1) e etanol (4.379 L.ha-1). Já para teor de matéria seca de raiz (38,32%) e amido (26,70%) e rendimento de etanol (176,26 em L.t-1), o clone IPB-149 se destacou. Não houve diferença significativa para o teor de amilose. O teor de amido (13,94%) e o rendimento de raiz (7,53 t.ha-1), amido (1,64 t.ha-1), e etanol (1.034 L.ha-1 e 92,04 L.t-1) foram menores para a maioria dos clones avaliados no ciclo com três meses de cultivo. Recomenda-se usar o ciclo de cultivo de cinco meses.

Thesis. (M. A. Agriculture (Agricultural Economics)) -- University of Limpopo, 2022 / Food security, poverty and hunger issues, as well as methods of addressing remain a concern for many South Africans. Smallholder farmers' agricultural production is seen as the key to simultaneously alleviating poverty and ensuring food security, especially in rural areas. The sweet potato crop is commonly produced by smallholder farmers in rural areas as a staple in many South African households with the potential to reduce hunger and poverty. Nevertheless, just like other crops, the sweet potato is impaired by external factors such as extreme weather conditions, insects, pests and diseases, thus threatening food security. The most destructive pest to sweet potatoes acknowledged in the literature is the sweet potato weevil (SPW), which can cause between 5-100% in areas where it is not controlled. While there are many SPW control measures Entomopathogenic Nematodes (EPNs) are emerging as one of the Integrated Pest Management (IPM) bio-control techniques that have shown promise in controlling SPW infestations in South Africa and globally. This study conducts a socio-economic analysis of smallholder sweet potato production and analyses the acceptability of EPNs as bio-control measures against the SPW in the Gauteng, Limpopo and North West Provinces of South Africa. This was done through an assessment of farmers‘ knowledge, attitudes, perception and practices (KAPP analysis), exploration of the acceptability of EPNs by farmers, determination of and factors influencing profitability and technical efficiency. Primary data was collected from 119 respondents who were selected through non-probability sampling techniques; purposive, census, and snowball. The analytical tools used to analyse the data were descriptive statistics, Gross Margin Analysis, Multiple linear regression model, Data Envelopment Analysis (DEA) and the Tobit regression model. From the results, an average knowledge score of 2.30 based on a 3–point Likert scale revealed that sweet potato farmers are knowledgeable of the SPW, the impacts and the control measures. Despite this level of knowledge, the farmers were impartial about the attitudes and perceptions regarding the SPW and the control measures. This was based on the findings of a 5-point Likert scale, which yielded average scores of 2.53 and 2.74, respectively. The study also revealed that the majority of the farmers prefer the use of indigenous and physical practices to control SPW. With regards to acceptance of the EPNs bio-control innovation towards control of the SPW, a mean Composite Index of Acceptancy (CIA) of 0.77 revealed the willingness of farmers to accept the EPNs as a bio-control measure. A Gross margin of R9 552.37 indicates that sweet potato farming is generally profitable, and this is influenced by socio-economic factors such as marital status, employment status, sweet potato output per cycle and access to machinery. On the other hand, while sweet potato farming was found to be profitable, the DEA score of 0.09 reveals that these farmers are technically inefficient. Their technical inefficiency is influenced by sweet potato output per cycle, gross margins, farm size, and access to credit, employment status, and chemical use. Based on these findings, the study recommends farmers‘ support through capacity development initiatives for the sweet potato farmers with regards to general economics of sweet potato production and marketing to maximise and sustain their revenue generation, as well as their general efficiency. In addition, increased training and awareness of the EPNs and their benefits as bio-control measures towards SPW infestation will work towards changing farmers‘ mindset with regard to SPW control measures. / Department of Social Innovation (DSI) and United States Agency for International Development (USAID)

Thesis (M.Sc. (Horticulture)) --University of Limpopo, 2022 / Worldwide, water scarcity, land degradation and unavailability of agricultural lands have posed serious threats on food security and income generation. Hunger, micronutrient deficiencies and starvation are likely to go up in Africa due to increasing urbanisation and rise in global food prices. As a result, it is important to identify innovative vegetable growing-based strategies, which can increase access to food by utilising the limited space available in rural and urban areas. Therefore, sack gardening technology could be a solution to both the lack of arable land and water scarcity in urban and rural areas. The objective of the study was to determine whether axillary bud number will have an effect on agronomic parameters and yield of sweet potato cv. 'Blesbok' produced using the sack gardening technology. Treatments, namely, 1, 2, 3, 4, and 5 number of axillary buds per stem cutting, were arranged in randomised complete block design, with 10 replicates. One bud (1) was used as a control. Different stem cuttings measuring from 10 to 30 cm long with approximately one (1) to six (6) axillary buds were collected from mature sweet potato plantation at a certified nursery from cv. 'Blesbok'. A total of eight (8) stem cuttings were planted in sacks consisting of growing media mixture of steam pasteurised loam soil and compost (3:1 v/v), 4 on top side of the sack and the remaining four on the side-holes of the sack. Insect pests were scouted and monitored weekly, while diseases were managed using spraying programmes as in commercial sweet potato production systems. Two weeks after transplanting, each plant was fertilised with 5 g nitrogen (N), phosphorus (P), and potassium (K) 2:3:2 (26) + 0.5% Zinc (Zn) + 5% sulphur (S) and 5% calcium (Ca). Number of axillary buds had significant effects on vine length, fresh shoot mass, number of shoots and dry shoot mass contributing 59%, 58%, 45% and 58% in total treatment variation (TTV), respectively, whereas axillary bud numbers had no significant effects on fresh tuberous root mass, chlorophyll content, vine stem diameter, tuberous root diameter, tuberous root length, dry tuberous root mass and number of tuberous roots. Relative to control (one bud), two (2), three (3), four (4), five (5) number of axillary buds decreased vine length, fresh shoot mass and dry shoot mass by 8-37, 30-55 and 26-55%, respectively. However, relative to control (one bud), number of axillary buds increased number of shoots by 8-17%. The quadratic relationship models were explained by 95, 92, 96 and 98% of vine length (VL), number of shoots (NS), fresh shoot mass (FSM) and dry shoot mass (DSM), respectively. In conclusion, findings of the study demonstrated that a single (1) or two (2) axillary bud(s) on stem cuttings of sweet potato CV. „Blesbok‟ showed better results for both yield and growth parameters as compared to three (3), four (4) and five (5) buds. / AgriSETA

Sweet potato (Ipomoea batatas Lam.) is ranked as the seventh most important food crop in the world and its large biomass and nutrient production give it a unique role in famine relief. However, multiple virus infection is the main disease limiting factor in sweet potato production worldwide. The main objective of this research project was to develop a transgenic sweet potato cultivar with broad virus resistance in South Africa (SA). A review of current literature assembled background information pertaining to the origin, distribution and importance of the sweet potato crop; viruses and complexes infecting sweet potato; and the strategies used in sweet potato virus detection and control. A survey to determine the occurrence and distribution of viruses infecting sweet potato (Ipomoea batatas Lam.) was conducted in major sweet potato-growing areas in KwaZulu-Natal (KZN). A total of 84 symptomatic vine samples were collected and graft inoculated onto universal indicator plants, Ipomoea setosa Ker. and Ipomoea nil Lam. Six weeks post inoculation, typical sweet potato virus-like symptoms of chlorotic flecking, severe leaf deformation, stunting, chlorotic mosaic, and distinct interveinal chlorotic patterns were observed on indicator plants. Under the transmission electron microscope (TEM), negatively stained preparations of crude leaf sap and ultra-thin sections from symptomatic grafted I.setosa plants revealed the presence of elongated flexuous particles and pinwheel type inclusions bodies‟ that are characteristic to the cytopathology of Potyviruses. Symptomatic leaf samples from graft-inoculated I. setosa and I. nil were assayed for Sweet potato feathery mottle virus (SPFMV), Sweet potato mild mottle virus (SPMMV), Sweet potato chlorotic stunt virus (SPCSV), Sweet potato chlorotic fleck virus (SPCFV), Sweet potato virus G (SPVG), Sweet potato mild speckling virus (SPMSV), Sweet potato caulimo-like virus (SPCaLV), Sweet potato latent virus (SPLV), Cucumber mosaic virus (CMV), and Sweet potato C-6 virus (C-6) using the nitrocellulose membrane enzyme-linked immunosorbent assay (NCM-ELISA). The majority of leaf samples (52%) tested positive for virus disease and showed the occurrence of SPFMV, SPMMV, SPCSV, SPCFV, SPVG, SPMSV, and SPCaLV. Of these 7 viruses, the most frequently detected were SPFMV (39%), SPVG (30%), followed by SPCSV (13%) and SPMMV (12%). SPCaLV and SPCFV at 10% and SPMSV at 7% were found exclusively in samples collected from one area. SPFMV, SPVG, SPCSV, and SPMMV were identified as the most prevalent viruses infecting sweet potato in KZN. The genetic variability of the three major viruses infecting sweet potato (Ipomoea batatas Lam.) in KZN was determined in this study. A total of 16 virus isolates originating from three different locations (Umbumbulu, Umfume and Umphambanyomi River) in KZN were analyzed. These comprised of 10 isolates of Sweet potato feathery mottle virus (SPFMV), five isolates of Sweet potato virus G (SPVG) and one isolate of Sweet potato chlorotic stunt virus (SPCSV). The phylogenetic relationships of the SPFMV, SPVG and SPCSV isolates from KZN relative to isolates occurring in SA and different parts of the world were assessed. The division of SPFMV into four genetic groups (strains) according to the phylogenetic analysis of coat protein encoding sequences revealed mixed infections of the O (ordinary) and C (common) strains in sweet potato crops from KZN. All SPFMV isolates showed close lineage with isolates from South America, East Asia and Africa. The SPVG isolates showed high relatedness to each other and close lineage with other isolates, especially those from China and Egypt. Analysis of the partial sequence of the Heat shock protein 70 homologue (Hsp70h) gene indicated that the SPCSV isolate from KZN belongs to the West African (WA) strain group of SPCSV and showed close relatedness to an isolate from Argentina. The knowledge of specific viral diversity is essential in developing effective control measures against sweet potato viruses in KZN. Multiple virus infections of Sweet potato feathery mottle virus (SPFMV), Sweet potato chlorotic stunt virus (SPCSV), Sweet potato virus G (SPVG) and Sweet potato mild mottle virus (SPMMV) cause a devastating synergistic disease complex of sweet potato (Ipomoea batatas Lam.) in KZN. In order to address the problem of the multiplicity and synergism of sweet potato viruses in KZN, this study aimed to develop transgenic sweet potato cv. Blesbok with broad virus resistance. An efficient and reproducible plant regeneration protocol for sweet potato (Ipomoea batatas Lam.) cultivar Blesbok was also developed in this study. The effect of different hormone combinations and type of explants on shoot regeneration was evaluated in order to optimize the regeneration protocol. Coat protein (CP) gene segments of SPFMV, SPCSV, SPVG and SPMMV were fused to a silencer DNA, the middle half of the nucleocapsid (N) gene of Tomato spotted wilt virus (TSWV) and used as a chimeric transgene in a sense orientation to induce gene silencing in the transgenic sweet potato. Transformation of apical tips of sweet potato cv. Blesbok was achieved by using Agrobacterium tumefaciens strain LBA4404 harboring a modified binary vector pGA482G carrying the plant expressible neomycin phosphotransferase ll gene (nptll), the bacterial gentamycin-(3)-N-acetyl-transferase gene and the expression cassette. A total of 24 putative transgenic plants were produced from the transformed apical tips via de novo organogenesis and regeneration into plants under 50mg/L kanamycin and 200 mg/L carbenicillin selection. Polymerase chain reaction (PCR) and Southern blot analyses showed that six of the 24 putative transgenic plants were transgenic with two insertion loci and that all plants were derived from the same transgenic event. The six transgenic sweet potato plants were challenged by graft inoculation with SPFMV, SPCSV, SPVG and SPMMV- infected Ipomoea setosa Ker. Although virus presence was detected using NCM-ELISA, all transgenic plants displayed delayed and milder symptoms, of chlorosis and mottle of lower leaves when compared to the untransformed control plants. These results warrant further investigation under field conditions. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.

Sweetpotato (Ipomoea batatas) is a major staple food in Africa and the rest of the world where they are discovered to be a good source of carbohydrates, vitamin A, vitamin C and protein. The maximum production potential of the crop is being hampered by severe drought which ravages most parts of Africa. The main aim of this project therefore is to screen collected accessions of sweetpotatofor drought tolerance in a quick screening method with a view to identify cultivars that can perform well under water stress conditions. Fifty selected sweetpotato accessions consisting of cultivars and breeding lines collected from the ARC-VOPI gene bank were planted for drought screening in the glass house for 6 weeks during which water was withheld to induce stress. Observations were made on number of dead plants and days to wilting point, the results were analyzed and 12 best performing cultivars were selected for field trials. The field trial was carried out in Lwamondo, Thohoyandou for 6months under rain-fed conditions. The experiment was conducted in a complete randomized block design with 6 replicates.Yield data and growth parameters were collected every 8 weeks during the trial period and the data collected was analyzed using ANOVA. The best performing cultivars were Zapallo, Tacna, Ejumula, 2004-9-2 and Ndou. They were therefore recommended for further evaluation in other drought prone areas of the country. / Agriculture and  Animal Health / M. Sc. (Agriculture)