The purpose of this experiment was to determine the value of sulphur dioxide as a dehydrating agent for sweet potatoes.

The purpose of the present study is to determine the effect of cooking on the vitamin A value of "Vita-Yam" candy and cookies.

Thesis (MScAgric)--University of Stellenbosch, 2000 / ENGLISH ABSTRACT: Approximately 7000 ha of potatoes are cultivated under irrigation. The greatest part of the planting is entered under the South African Certification Scheme as seed potatoes, representing between 35 and 40 % of seed production in South Africa. The production of high-quality tubers is, therefore, in the interest of the entire country. Some production factors in the area, however, have a very negative influence on quality with a resultant increase in input costs. These factors include mainly low clay content of the soil «5 %), low organic matter content (% C = 0,2 to 0,4 %), a low pH value as well as a high level of chlorides (400 mg.kg") in the irrigation water. Nitrogen conversion as well as uptake can be influenced by these factors. There may also be negative influences on the environment if leaching of nitrates to subterranean water sources is involved, which can pose a threat to sensitive protected areas. Leaching of various nutritional elements occurs as a result of the low clay content of the soils. Over-irrigation or intense thundershowers could lead to the leaching of nearly all of the fertilisers from these soils. Various management aids are therefore needed to facilitate the decision-making process for corrective steps. Soil, leaf or total-plant analyses are possible, but it is a time-consuming process and the results could become available too late to be of any use. Consequently, the development of methods to determine the nutritional element status of plants on the land and the establishment of norms are both essential. A method which has been tried on a wide scale with varying results is the use of the nitrate content of the petiole, which is determined by means of a reflectoquant and nitrate strips. To evaluate the sensitivity of the method two sites in the Sandveld have been selected. A trial planting has been established at Wadrift and information was also obtained from a leaching trial at Sandberg. The cultivars Up-to-Date and Hertha were established in four nitrogen treatments (100, 200, 300 and 400 kg N.ha-1 ), and repeated over two seasons. At Sandberg irrigation was applied at three application levels and three fertigation divisions for one season. Drip irrigation was applied in both cases to enable the accurate distribution of water and fertilisers during the planting season. Petiole samples were taken weekly or every second week in all the trials. The first mature leaf was sampled (about 20 to 30 leaves per plot). During the initial planting at Wadrift nitrate N in petiole sap (measured by means of nitrate strips and a reflectoquant) was compared to nitrate N of dried petioles measured with an auto-analyser. In all test cases a good correlation was found. The readings from the auto-analyser were about 14.5 times higher than the readings from the petiole sap as a result of moisture loss during the drying process. A better correlation was obtained during the second season when the petiole sap was used for strips as well as the auto-analyser. The petiole nitrate content was increased by high N application rates and the 400 kg N.ha-1 treatment showed significant differences from the other N treatments. A substantially higher yield was obtained during the last season. Varying results were obtained regarding specific gravity for cultivars and nitrogen treatments. At Sandberg (1998) over-irrigation lowered the nitrate content of the petiole sap significantly. It was found that the optimum irrigation level and frequency, is two fertigations a week and kept at field water capacity. From the trial it was clear that the use of nitrogen strips in combination with the reflectoquant gave a good indication of the nitrate-N content of the petiole sap. It is, however, difficult to lay down a norm or critical range, as conditions during the growth period on sandy soil as well as the growth stage have a significant influence on the nitrate-No If yield is the only objective the 400 kg N.ha-1 curve can probably be used as an optimum nitrate-N norm for the particular cultivars. It is also not clear whether the nitrate N content of the petiole sap gives a good reflection of growth and yield potential. / AFRIKAANSE OPSOMMING: In die Sandveld word bykans 7000ha aartappels onder besproeiing verbou. Die grootste deel van die aanplanting word as saadaartappels onder die Suid-Afrikaanse sertifiseringskema ingeskryf en verteenwoordig tussen 35 en 40% van Suid Afrika se saadproduksie. Die produksie van hoë kwaliteit knolle is dus van landsbelang. Somminge produksiefaktore van die area het egter 'n uiters negatiewe invloed op kwaliteit en het 'n meegaande verhoging van insetkostes tot gevolg. Faktore wat veral hieronder tel is die grond se lae klei inhoud «5%), lae organiese materiaal inhoud (%C = 0.2 tot 0.4%), lae pH asook hoë chloriede (400mg.kg-1 ) in die besproeiingswater. Hierdie faktore kan 'n invloed op die omsetting van stikstof en die opname daarvan hê. Daarmee saam kan dit 'n negatiewe effek op die omgewing hê indien loging van nitrate na ondergrondse waterbronne plaasvind wat sensitiewe bewaarareas kan bedreig. Weens die lae klei-inhoud van die gronde vind loging van verskeie voedingselemente plaas. Oorbesproeiing of hewige reënbuie kan tot gevolg hê dat bykans alle bemestingstowwe uit hierdie grond geloog word. Bestuurshulpmiddels is dus nodig om die besluitnemingsproses vir korrektiewe stappe te vergemaklik. Grond-, blaar- of hele plantontledings is moontlik maar is tydrowend en resultate daarvan kan soms te laat beskikbaar wees. Die ontwikkeling van metodes om die voedingselement inhoud van plante op die land te bepaal en die daarstelling van normes is dus noodsaaklik. 'n Metode wat reeds wyd deur ander navorsers met wisselende resultate beproef is, is die gebruik van nitraat inhoud van die petiool wat met 'n reflektoquant en nitraat strokies bepaal is. Om die sensitiwiteit van die metode te evalueer is twee proefpersele in die Sandveld gebruik. 'n Proef is by Wadrift geplant terwyl data ook van 'n logingsproef te Sandberg verkry is. By Wadrift is die kultivars Up-to-Date en Hertha by 4 N-behandelings (100, 200,300 en 400 kg N.ha-1) en vier herhalings vir twee seisoene aangeplant. By Sandberg is besproeiings teen drie toedingspeile met 3 sproeibemestingsverdelings vir een seisoen gedoen. In alle gevalle is van drupbesproeiing gebruik gemaak om akkurate plasing van water en bemestingstowwe oor die plantseisoen moontlik te maak. Petiool monsters is weekliks of tweeweekliks van alle behandelings geneem. Die eerste volwasse blaar is gemonster en daar is tussen 20 en 30 blare per perseel geneem. Tydens die eerste planting te Wadrift is nitraat-N in petioolsap, gemeet met nitraatstrokies en reflektoquant, vergelyk met nitraat-N van gedroogde petiole, gemeet met In outo-analiseerder. Hierdie waardes was goed gekorreleerd vir alle gevalle wat getoets is. Die outo-analiseerder se lesing was ±14.5 keer hoër as die petioolsap lesings weens die vog wat tydens droging verwyder is. Tydens die tweede seisoen is In beter korrelasie verkry waar petioolsap vir strokies asook vir die outo-analiseerder gebruik is. Petiool nitraat is deur hoë Ntoedieningspeile verhoog en die 400 kg N.ha-I behandeling het betekenisvol van die ander N-behandelings verskil en die laaste seisoen ook In betekenisvol hoër opbrengs gelewer. Wisselende resultate is t.o.v. soortlike gewig vir kultivars en stikstofbehandelings verkry. By Sandberg (1998) is gevind dat oorbesproeiing In betekenisvolle verlagende effek op die nitraat-N inhoud in die petioolsap het. Daar is getoon dat die optimum besproeiingspeil en frekwensie, veldwaterkapasiteit met twee sproeibemestings per week is. Uit die ondersoek is dit duidelik dat die nitraatstrokies in kombinasie met die reflektoquant In uiters bruikbare aanduiding van die nitraat-N in die petioolsap gee. Dit is egter moeilik om In norm of kritiese nitraat-N grens aan te dui, aangesien toestande tydens die groeiperiode op sandgrond en die groeistadium In beduidende effek op die nitraat-N het. Indien opbrengs as enigste doelwit gestel word, mag die 400 kg N.ha-I kurwe moontlik as aanduiding van 'n optimum nitraat-N norm vir die betrokke kultivars dien. Daar bestaan ook onduidelikheid of nitraat-N in die petioolsap wel In goeie refleksie van groei en opbrengspotensiaal is.

Thesis (MScAgric)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The potato can be considered as one of the most important food crops in many African countries. The potential of this crop is reflected in the large increase in area of production where Africa showed the highest rate of growth within the developing world over the past twenty years. The multiplication rate of potatoes is very low compared to other crops. Therefore it is essential to investigate methods of increasing the number of minitubers produced from disease free in-vitro plantlets. There is a number of potato propagation procedures that are currently being used worldwide to multiply seed potatoes. As aeroponics is still a relatively new technique that has not been researched extensively for the production of minitubers, a study relating to the production practises including the nutritional requirements of potato minitubers produced in a aeroponic system were undertaken. Potato plantlets, cv BP1, were grown aeroponically at two different densities (20 and 30 plants/m2) and four harvest intervals (7, 10, 14 and 18 days). The interaction between harvesting intervals and plant densities did not influence plant growth, minituber quality or yield. Best results were realised when harvesting every 7 days with a higher total tuber number over the growing period. Harvest interval also influenced the phosphorus and copper concentration in minitubers. To study the effect of Calcium (Ca) application rate, potato plantlets of cultivars Up-to-date, Mnandi, Buffelspoort and BP1 were grown at four different Ca levels (8.40, 6.75, 5.10 and 3.45 meq/L). The interaction between Ca application levels and cultivars significantly influenced the percentage stolon branching. BP1 had more stolons at the lowest Ca application level and Buffelspoort had more stolons at the full Ca application levels. However, low Ca treatments produced the highest yield. The minituber number and weight harvested were three times more for Mnandi. An aeroponic study on the irrigation frequency (20, 30, 40 and 50 minutes interval) was conducted on four potato cultivars (Up-to-date, Mnandi, Buffelsoort and BP1). Significant differences were noted in the interaction between irrigation frequencies and cultivars for the percentage tuberised plants and stolon and tuber dry mass. When irrigated every 40 minutes, 48% of the Buffelspoort plants produced tubers. Plant height was also significantly affected by the interaction between irrigation frequencies and potato cultivars, with Mnandi producing taller plants when irrigated every 30 minutes. Total tuber number and tuber fresh and dry weight was higher at the irrigation frequency of 20 minutes. The interaction between irrigation frequencies and cultivars on the response to macro and trace elements was not significant for sodium and iron but was for phosphorus, potassium, calcium, zinc and aluminium. A field study was conducted in a greenhouse where potato seed of BP1 obtained from the first trial were graded into different sizes (Small: >20, medium: 20–40 and large: > 40 mm of diameter) and stored at 3 different temperatures (3, 16 and 25oC) for 2 supplementary months before being planted. Sprouting capacity was mostly influenced by temperature regardless of other factors applied to potato seed minitubers such as harvest intervals and sizes. The higher storage temperature of 25oC resulted in tubers with a higher number of sprouts, longer sprouts and with a higher sprouting capacity. / AFRIKAANSE OPSOMMING: Aartappels is een van die belangrikste voedselgewasse in baie lande in Afrika. Die potensiaal van die gewas word gereflekteer in die groot toename in produksie areas, met Afrika wat die vinnigste van al die ontwikkelende lande gegroei het die laaste 20. In vergelyking met ander gewasse is die tempo van planvermeerdering by aartappels baie stadig. Dit is dus essensieel om metodes te ondersoek wat sal help om die aantal miniknolle wat per in vitro plantjie verkry kan word te verhoog. Daar is heelparty plant vermeerderings prosedures wat tans wêreldwyd gebruik word om saad aartappels te vermeerder. Aangesien aeroponika nog steeds ʼn relatiewe nuwe tegniek is wat nog nie ekstensief ondersoek is vir die verbouing van miniknolle nie, is ‘n studie geloods om te kyk na die produksie praktyke, wat insluit die voedingsbehoeftes van aartappel miniknolle in ʼn aeroponika sisteem. Aartappel plantjies, kultivar, BP1, is aeroponies verbou by twee plant digthede (20 en 30 plante/m2) en vier oesintervalle (7, 10, 14 en 18 dae). Die interaksie tussen oesintervalle en plantdigtheid het geen effek gehad op plant groei, miniknol kwaliteit of opbrengs nie. Die beste resultate is verkry waar die knolle elke 7 dae geoes is met ‘n hoër totale aantal knolle oor die groeiseisoen. Die oesinterval het ook ‘n effek gehad op die fosfaat en koper konsentrasie van die miniknolle. Om die effek van die Kalsium (Ca) toedieningspeil te ondersoek is aartappel plantjies; kultivars Up-to-date, Mnandi, Buffelspoort en BP1 gekweek by vier verskillende Ca peile (8.40, 6.75, 5.10 en 3.45 meq/L). Die interaksie tussen Ca toedienings peile en kultivars het ‘n beduidende effek gehad op die persentasie stolon vertakking. BP1 het meer stolons gehad by die laagste Ca toedieningspeil en Buffelspoort het meer stolons gehad by die volle Ca toedieningspeil. Die hoogste opbrengste is egter waargeneem by die laagste Ca toedieningspeil. Die aantal miniknolle en oes massa was drie keer meer vir Mnandi. ‘n Aeroponiese studie op die besproeiingsfrekwensie (20, 30, 40 en 50 minuut intervalle) is gedoen met vier aartappel kultivars (Up-to-date, Mnandi, Buffelsoort en BP1). Beduidende verskille is opgemerk in die interaksie tussen besproeiings frekwensie en kultivars vir die persentasie plante met knolle en stolon en knol droë massa. Met besproeiings elke 40 minute het 48% van die Buffelspoort plante knolle produseer. Plant hoogte is ook beduidend beïnvloed deur die interaksie tussen besproeiingsfrekwensie en aartappel kultivar met Mnandi plante wat hoër was wanneer dit elke 30 minute besproei is. Die totale aantal knolle en knol vars- en droë massa was hoër wanneer daar elke 20 minute besproei is. Die interaksie tussen besproeiings frekwensie en kultivars op die makro- en mikro element inhoud van die knolle was nie beduidend vir natrium en yster nie, maar wel vir fosfaat, kalium, kalsium, sink en aluminium. ‘n Potproef is gedoen in ‘n kweekhuis waar aartappel saad van BP1 verkry vanaf die eerste proef nadat knolle verdeel is in verskillende grootte klasse (klein: < 20mm, medium: 20-40mm en groot: >40mm) en gestoor is by drie verskillende temperature (3, 16 en 25oC) vir 2 addisionele maande voor plant. Spruit ontwikkelings kapasiteit was meestal beïnvloed deur temperatuur ten spyte van ander behandelings soos oes intervalle en knol grootte. Die hoër bergings temperatuur 25oC het aanleiding gegee tot knolle met ‘n hoër aantal spruite, langer spruite en ‘n hoër spruit ontwikkelings kapasiteit.

Effect of a sudangrass green manure in two soil types on the activity, populations and community structure of soil microorganisms, populations of Verticillium dahliae in soil and on potato roots, and potato early dying, were evaluated in a field microplot experiment in the Columbia Basin. Potato cv. Russet Burbank was grown in identical green manure and fallow soil treatments transported from Idaho and Washington where sudangrass previously suppressed or enhanced early dying of potatoes, respectively. Incorporation of sudangrass increased total microbial activity (TMA) by 46.2 and 30.1% in the Idaho soil in 1996 and 1997, and by 43.0% in the Washington soil in 1996 only. Neither green manure or soil type, however, affected soil populations of Fusarium, total bacteria, or actinomycetes. Across soil type, fluorescent pseudomonad populations were unaffected or increased by 107% in 1996 and 1997, respectively. Although not repeated across years, Fusarium root populations were 19.7 and 28.3% higher in sudangrass treated soil from Washington in 1996 and Idaho in 1997, respectively, but the proportion of Fusarium species were similar across soil types. Bacterial rhizosphere communities, based on sole-carbon-source utilization patterns on Biolog GN microplates, did not differ among the soil types or green manure treatments. Across soil type, V. dahliae soil and root populations were unaffected in 1996, but were lower by 20.4 and 41.2% in Idaho sudangrass soil treatments in 1997. Apical stem populations of V. dahliae and disease severity, however, did not differ among the treatments. Although tuber yield in Washington soil was 31.5% higher than Idaho soil in 1996, yield was not affected by a sudangrass green manure. Because suppression of early dying of potato observed in Idaho was not replicated in transported soil in the Columbia Basin, the macroenvironment may interact with the sudangrass green manure to regulate the effect, or lack of effect on disease. TMA is not an indicator of disease suppressive ability of a soil following sudangrass as activity increased despite a lack of effect on disease. Based on this study, there is no evidence for differences in microbial populations or communities between the Idaho and Washington soils that could explain the suppression or enhancement of early dying of potato by a sudangrass green manure. / Graduation date: 1998

Graduation date: 1992

Thesis (M. Sc.) (Hons.) -- University of Western Sydney, Hawkesbury, 1997. / Thesis submitted for the degree of Master of Science (Honours), School of Horticulture, University of Western Sydney, Hawkesbury, 1997. In Chapter 1, figures 1.1 and 1.2 are not reproduced in the text. Bibliography : leaves 112-135.

In order for a medicinal product to produce a consistent and reliable therapeutic response, it is essential that the final composition of the product is invariable and that the active ingredient/s is/are present in appropriate, non-toxic amounts. However, due to the complexity involved in the standardization of natural products, quality control (QC) criteria and procedures for the registration and market approval of such products are conspicuously absent in most countries around the world. African Potato (AP) is of great medical interest and this particular plant has gained tremendous popularity following the endorsement by the South African Minister of Health as a remedy for HIV/ AIDS patients. Very little information has appeared in the literature to describe methods for the quantitative analysis of hypoxoside, an important component in AP. It has also been claimed that sterols and sterolins present in AP are responsible for its medicinal property but is yet to be proven scientifically. To-date, no QC methods have been reported for the simultaneous quantitative analysis of the combination, β- sitosterol (BSS)/ stigmasterol (STG)/ stigmastanol (STN), purported to be present in preparations containing AP. The effect of concomitant administration of AP and other herbal medicines on the safety and efficacy of conventional medicines has not yet been fully determined. Amongst the objectives of this study was to develop and validate quantitative analytical methods that are suitable for the assay and quality control of plant material, extracts and commercial formulations containing AP. Hypoxoside was isolated from AP and characterized for use as a reference standard for the quality control of AP products and a stability-indicating HPLC/ UV assay method for the quantitative determination of hypoxoside was developed. In addition, a quantitative capillary zone electrophoretic (CZE) method was developed to determine hypoxoside, specifically for its advantages over HPLC. A HPLC method was also developed and validated for the quantitative analysis of BSS, STG and STN in commercially available oral dosage forms containing AP material or extracts thereof. The antioxidant activity of an aqueous extract of lyophilized corms of AP along with hypoxoside and rooperol were investigated. In comparison with the AP extracts and also with hypoxoside, rooperol showed significant antioxidant activity. The capacity of AP, (extracts, formulations, hypoxoside and rooperol as well as sterols to inhibit in vitro metabolism of drug substrates by human cytochrome P450 (CYP) enzymes such as CYP 3A4, 3A5 and CYP19 were investigated. Samples were also assessed for their effect on drug transport proteins such as P-glycoprotein (P-gp). Various extracts of AP, AP formulations, stigmasterol and the norlignans, in particular the aglycone rooperol, exhibited inhibitory effects on CYP 3A4, 3A5 and CYP19 mediated metabolism.These results suggest that concurrent therapy with AP and other medicines, in particular antiretroviral drugs, can have important implications for safety and efficacy. Large discrepancies in marker content between AP products were found. Dissolution testing of AP products was investigated as a QC tool and the results also revealed inconsistencies between different AP products.

Please read the abstract in the section 00front of this document. Also note that an abstract is provided for each chapter as well / Thesis (DPhil (Entomology))--University of Pretoria, 2005. / Zoology and Entomology / unrestricted

The sequence of 3553 nucleotides corresponding to the 3'-terminal region of potato virus S (PVS) has been determined from cloned cDNA. The sequence obtained contains six open reading frames with the potential to encode proteins of Mr 10,734, Mr 32,515, Mr 7,222, Mr 11,802, Mr 25,092 and at least Mr 41,052. The amino acid sequence of the 33K ORF has been confirmed to be that of the viral coat protein gene. The nucleotide sequence of this ORF was obtained from expression plasmids which were isolated by binding with a specific monoclonal antibody to PVS, and the expression of coat protein fusion products was verified by Western blots of bacterial cell lysates. The deduced amino acid sequence of a 70 amino acid portion from the central region of the PVS coat protein was 59% identical to the analogous region of potato virus X. In addition, the 7K, 12K and 25K ORF's displayed significant sequence homology with similar sized ORF's from a number of potexviruses. The partial 41K ORF was homologous with the C-terminal portion of the viral replicase proteins of potato virus X and white clover mosaic virus. While the biological functions of the 12K and 25K non-structural proteins coded for by PVS and members of the potexvirus group remain unknown, the 12K protein displays a hydropathicity profile consistent with a membrane associated protein and the 25K protein contains a conserved sequence motif found in a number of nucleoside triphosphate binding proteins. Members of the carlavirus group are distinguished from the potexviruses by the presence of a small [11K (PVS, potato virus M) - 16K (lily symptomless virus)] 3' terminal ORF which appears to contain a sequence motif similar to the 'zinc-finger' domain found in many nucleic acid binding proteins. The coat protein gene from potato virus S (PVS) was introduced into Nicotiana debneyii tobacco as well as a commercial potato cultivar, 'Russet Burbank', by leaf disc transformation using Agrobacterium tumefaciens. Transgenic plants expressing the viral coat protein were highly resistant to subsequent infection following mechanical inoculation with the Andean or ME strains of PVS as indicated by a lack of accumulation of virus in the upper leaves. The coat protein mediated protection afforded by these transgenic plants was sufficient to prevent the accumulation of virus in the tissues of non-transformed 'Russet Burbank' shoots which had been grafted onto transgenic plants inoculated with PVS, and in reciprocal grafts, transgenic shoots accumulated less than 2% (6 weeks after grafting) of the concentration of PVS found in non-transformed shoots similarly grafted onto plants systemically infected with PVS. These transgenic plants also displayed a measure of resistance to inoculation with a related carlavirus from potato, potato virus M. In agreement with previous reports for plants expressing PVX coat protein, plants expressing PVS coat protein were also protected from inoculation with PVS RNA. These results provide further evidence that coat protein mediated protection for these two groups of viruses, which share similar genome organizations, may involve inhibition of some early event in infection, other than, or in addition to, virus uncoating. Specific monoclonal antibodies were prepared against a C-terminal derived 18 kDa portion of the 25K protein of PVS expressed as an in-frame chimeric fusion protein with the glutathione S-transferase gene. The in vivo expression of this non-structural protein in virus infected tissue, as well as tissue from transgenic tobacco (var Xanthi-nc) engineered to contain the entire 25K gene, was verified by Western immunoblot labelling. / Medicine, Faculty of / Biochemistry and Molecular Biology, Department of / Graduate