No description available.

In vitro culture techniques are widely used in potato for rapid production of specific pathogen tested plantlets and microtubers, which are essential for seed certification programs. The limited calcium (Ca) uptake in vitro promotes physiological disorders in many micropropagated species including potato. Factors that may affect Ca uptake by potato plantlets, including cations, osmotic potential, and boron (B) were examined. The possibility of improving microtuber yield by low pH shock or successive harvests, which stimulated greenhouse potato production, were also investigated. Ca uptake by cvs. Norland and Bintje potato plantlets grown on modified Murashige and Skoog (MS, 1962) media was enhanced by diluting the total macroelements in the nutrient medium, except Ca. Increasing Ca:specific cation ratios, by lowering either NH 4, Mg or K, had little effect on Ca uptake by Norland plantlets. At equivalent Ca:total cation, Ca uptake was promoted further when the total macroelement concentration was reduced by half than when the Ca level was doubled (from 3 to 6 mM). This suggested that the increase in the osmotic potential of the medium had a great impact on Ca uptake, probably by affecting the root pressure. B contamination from impurities in the nutrient chemical components always occurred. The addition of the recommended H3BO 3 level of 0.1 mM (1.08 ppm) or more (0.3 mM) to the medium decreased Ca content of leaves and shoots in Norland but not Bintje, while addition of only 25% of this level was sufficient to provide plantlets with adequate B tissue concentration without compromising normal growth. Macroelement dilution along with Ca addition, and lower B levels than commonly used in MS (0.1 mM) are recommended for optimal Ca uptake in potato and possibly other plant species. Microtuber yield was not improved by a low pH shock. Adjusting microtuberization medium pH to less than 5.7 (3.5, 4.3 or 5.2), prior to autoclaving, reduced microtuber number and/or weight

Various aspects of Ca2+ uptake into greenhouse-grown potato plants and micropropagated potato plantlets were examined, including the movement of Ca2+ into potato plants and tubers, identification of Ca-packing genotypes and assessment of the effect of improved medium Ca2+ level on different parameters such as plantlet growth, microtuber induction, yield and tissue Ca concentration. The effect of exogenous vitamin Ds and UV-elicited endogenous vitamin D synthesis on regulation of 45Ca 2+ uptake into plantlet shoots was also examined. Safranin dye was not as suitable as the tracer 45Ca2+ for monitoring translocation of Ca2+ into tubers. Uptake of Ca2+ into tubers occurred indirectly through the main basal roots and stolon roots and directly through tuber periderm. Liquid scintillation counting and flame atomic absorption spectrophotometry were used to screen six potato cultivars and two wild species for ability to take up Ca2+ from treatment solutions containing high or low Ca2+ levels. In vitro potato micropropagation, microtuberization, and tissue calcium concentration were compared for six cultivars when Murashige-Skoog basal medium Ca2+ level was increased from 3, to 5 or 15 mM. All aspects of growth including shoot dry weight, early microtuber induction, microtuber yield and tissue Ca concentration were improved when medium Ca2+ level was 15 mM. Cultivar Bintje was the most efficient genotype at accumulating Ca 2+ from treatment solutions or growth media containing high or low Ca2+ levels. Vitamin Ds improved 45Ca 2+ uptake into shoots of micropropagated potato plantlets and D 3 was more efficient in this regard than D2 or a combination of D3 and D2. Plantlets had increased 45Ca 2+ uptake when exposed to UV irradiation compared with the untreated control plantlets. Plantlets given a 24 hour interval in the dark after UV exposure had even greater 45Ca2+ uptake, suggesting that vitamin D, metabolites, specifically calcitriol (1, 25(OH)2-v

No description available.

Since sweet potatoes, which also furnish vitamin A, are a common food in the popular diets of Texas and are so generally grown over the state, the purpose of this study is (1) to ascertain the amount of vitamin C in eight of the varieties most commonly grown and (2) to determine the effect of the three most popular methods of cooking (boiling, baking, and candying) on the vitamin C content of these varieties of sweet potatoes.

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.

Text in English / Potato is an important source of energy to most micronutrient malnourished affected population in South Africa. Improvements through bio-fortification can therefore enhance access to essential micronutrients. The study was aimed at determining the level of variability of iron and zinc concentration among 20 potato genotypes as a preliminary step for future breeding program. The materials were evaluated using inductively coupled plasma optical emission spectrometry. Statistical analysis indicated significant (P<0.001) variation of Fe and Zn among the genotypes. The average concentration ranges from 34.67 to 76.67 mg kg-1 and 12.88 to 66.1 mg kg-1 for iron and zinc respectively. The best performing genotypes were cultivar Mnandi, Hertha, Buffelspoort and breeding lines-N105-1, 00-S100-33 and 03-627-50. Iron concentration was positively correlated with Zinc concentration. The study showed that enough variability of Fe and Zn concentration exist among the evaluated genotypes, which can be exploited for use in potato bio-fortification breeding programme. / Agriculture, Animal Health and Human Ecology / M.Sc. (Agriculture)

Potato is an important source of energy to most micronutrient malnourished affected population in South Africa. Improvements through bio-fortification can therefore enhance access to essential micronutrients. The study was aimed at determining the level of variability of iron and zinc concentration among 20 potato genotypes as a preliminary step for future breeding program. The materials were evaluated using inductively coupled plasma optical emission spectrometry. Statistical analysis indicated significant (P<0.001) variation of Fe and Zn among the genotypes. The average concentration ranges from 34.67 to 76.67 mg kg-1 and 12.88 to 66.1 mg kg-1 for iron and zinc respectively. The best performing genotypes were cultivar Mnandi, Hertha, Buffelspoort and breeding lines-N105-1, 00-S100-33 and 03-627-50. Iron concentration was positively correlated with Zinc concentration. The study showed that enough variability of Fe and Zn concentration exist among the evaluated genotypes, which can be exploited for use in potato bio-fortification breeding programme. / Agriculture, Animal Health and Human Ecology / M.Sc. (Agriculture)