Sweetpotato, Ipomoea batatas (L.) Lamarck was introduced into Lesotho in 1992 in the hope that it would help alleviate poverty levels. Efforts are being made to learn the potential constraints to optimal production of this crop. Insect pests especially the sweetpotato weevils, Cylas species are a major production constraint worldwide. Hence the main objective of the study was to predict if these pests have potential to establish themselves in Lesotho. Two Cylas species, C. formicarius and C. puncticollis are present in South Africa and the latter is found in the northern Free State and the Eastern Cape both of which border the central and southern lowlands of Lesotho respectively. Cylas puncticollis was chosen as the subject of this study because of its potential spread into Lesotho. Thermal requirements (lower development threshold and degree-days) of this pest were calculated in the laboratory by studying the effects of temperature on its development and survival at six constant temperatures (16°C, 19°C, 24°C, 26°C, 31°C and 36°C). The photoperiod was maintained at 12L:12D for all temperatures, but RH was not controlled. Thermal requirements (r and k) of this pest species were estimated for all the immature stages and for the total life-cycle using the linear regression method. The estimated lower temperature threshold (r) of the total development of the pest lies between 8°C and 12°C and the thermal constant (k) between 360°D and 380°D. The thermal needs of this pest obtained from the laboratory work were used to predict the potential for its establishment in Lesotho as well as determining the possible areas of distribution if it invades Lesotho. Actual soil temperatures to which the pest would be exposed to in Lesotho were recorded for a year. Both the calculated thermal needs of the pest and the field-recorded temperatures were used in the degree-day model to predict potential establishment of this pest. The second approach, climate matching in Geographical Information System (GIS) used the bio-climatic profile of C. puncticollis calculated from the known areas of its distribution in both South Africa and Swaziland. The bio-climatic profiles of the two countries were matched to the climatic conditions of Lesotho to predict the potential for its establishment. The two approaches, linear degree-day model and climate matching approach revealed that Cylas puncticollis is a potential pest in Lesotho. The former predicted the occurrence of this pest throughout the whole country with a maximum of eight generations per year being possible in the lowlands. Fewer generations (two to three) were predicted for the highlands and foothills agro-ecological zones, which are colder than the lowlands. The climate matching approach also confirmed the prediction although according to this method a patchy distribution of the pest was predicted. A survey was then carried out in Lesotho, first to determine if Cylas species were already present in Lesotho, secondly to identify any other pests of sweetpotato and lastly to determine other possible production constraints other than insect pests. The survey was conducted in the form of questionnaire and field sampling. Cylas species were neither documented by the farmers who were interviewed nor by the field sampling. Numerous common pests of sweetpotato were recorded during the sampling survey. These included the following leaf-feeding pests: Bedellia somnulentella Zeller, Acraea acerata Hewitson, Agrius convolvuli Linnaeus and locusts and grasshoppers. The root pests that were recorded were mole-rats, Blosyrus sp. and millipedes (Narceus sp.). According to the sampling carried out in Lesotho there were no insect pests that could be rated as major pests as yet. Sweetpotato farmers did not consider insect pests as an important production constraint for optimal yield of the crop. The major constraint was found to be lack of planting material, which contributed towards a slow adoption of the crop throughout the country. / Dissertation (MSc (Entomology))--University of Pretoria, 2007. / Zoology and Entomology / unrestricted

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

Spatial shifts and structural changes continue to occur in the United States agricultural industry. Researchers have documented that the potato industry has changed in response to demands of consumers, expectations of producers and improvements in research and development. The aim of this study was to provide empirical evidence that both institutional and infrastructural factors are important to potato production in North Dakota. Using secondary county-level potato production data for North Dakota, an empirical model was designed to estimate the direction and impact of growers' expectations of prices, yields and costs on their decision to produce potatoes. The results confirmed that institutional relationships established between growers and processors, as well as the infrastructure that growers have in place from one growing season to the next, are statistically significant in determining the total number of potato acres planted.

The potato (Solanum tuberosum L.) crop serves as a staple food worldwide and is capable of reducing the world’s food shortages because unlike cereals and other agricultural crops, it is less affected by prices in the international markets. Research on alleviation of food crises suggested root and tuber crops such as potatoes to be the solution to the problem of food shortage. The crop is widely cultivated but is difficult to produce due to susceptibility to numerous pests and pathogenic organisms, as well as abiotic stresses. To control these pests and diseases, strategies to limit susceptibility to factors that interfere with the growth and development of plants, or breeding new varieties that are able to withstand stresses are being researched. Recent studies have shown that non essential nutrients such as Silicon (Si) are beneficial to plants in terms of yield, protection from fungal diseases and improved uptake of phosphorus. Since very little research has focused on the role of Si in improving potato production, three glasshouse pot trials were conducted at the Hatfield Experimental farm and Department of Plant Pathology glasshouses of the University of Pretoria to evaluate the effect of various soil amendments on potato yield and quality. The effect of these soil amendments on pH was also investigated as P-uptake and development of common scab in potatoes are pH dependent. The soil amendments consisted of different silicon sources and an agricultural lime. The Si sources were Calmasil slag (Middleburg) (30% Si- containing liming material), fly ash (50% Si nonliming material), and Si fume/ash (99% Si non-liming material). Agricultural lime (CaCO3) was included as a control. The purpose of the first two trials was to identify the most promising silicon-containing source for potato production, while the third trial evaluated the effect of this silicon source on soil pH and potato tuber yield. In all three trials, agricultural lime was used as a control. Due to the high demand for nutrients by the potato crop, other nutrient elements were added to the soil through fertigation every 7 to 14 days, depending on the growth stage of the plants. Plants were irrigated with distilled water when necessary to maintain an adequate moisture level i.e. moist but not too wet. Weekly observations on growth parameters were made. To select the most promising soil amendment, parameters such as leaf chlorophyll content, plant height, tuber number and mass (Fwt), fresh and dry weight (top growth) and change in soil pH were analyzed. Slag treated plants tended to produce tubers with higher mass and better appearance. In this study the highest increase in soil pH was observed in soil mixed with slag, compared to all the other silicon sources. Although there was no significant difference observed among treatments there was a distinct difference in plant growth between trials when soil was amended with lime and slag. Plants treated with slag tended to produce tubers that weigh more, whilst plants treated with lime grew taller and had the highest tuber number. There was a significant rise in soil pH from both lime and slag, which might have in turn influenced vegetative and tuber growth. / Dissertation (MInst(Agrar)--University of Pretoria, 2013. / gm2014 / Plant Production and Soil Science / unrestricted

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