Masters Degrees (Agronomy)

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Browsing Masters Degrees (Agronomy) by browse.metadata.advisor "Combrink, Nicolaas J. J."

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    Identifying and using tuber characteristics to predict potato keeping quality
    (Stellenbosch : Stellenbosch University, 2018-03) Gericke, Rian; Le Roux, Marcellous; Combrink, Nicolaas J. J.; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.
    ENGLISH ABSTRACT: Potato production in South Africa occurs in all nine provinces of South Africa and it is further divided into 16 production areas. The trial was undertaken in the Sandveld and Ceres production areas, which are characterised by dry and warm weather in summer, which presents obvious challenges to produce high-volume quality potatoes. A macronutrient that is very important for cell wall strength of potato tubers is calcium (Ca). In a previous study, no correlation between keeping quality and tuber Ca content was found (Bester, 1993). The reaction of Ca with organic acids might be part of the reason no correlation between keeping quality and tuber Ca could be found (Venter, 1989). Calcium oxalate forms when Ca reacts with organic acids and the cells it forms in are referred to as idioblasts. Calcium and magnesium (Mg) are strongly competitive and it seems that the plasma membrane binding site at the root has higher affinity for Ca2+ than for the highly hydrated Mg2+ (Marschner, 1995). Calcium has the ability to form a insoluble complex with pectin due to the free carboxyl groups on the pectin chain (Walter, 2012). Pectin methylesterase (PME) is an enzyme responsible for removing the methoxyl groups and enabling divalent cations Ca2+ and Mg2+ to react with pectin, creating rigid structures with an increase in firmness (Tajner-Czopek, 2003). Due to the high immobility of Ca in plants it is sometimes hard to increase the Ca content in tubers. On the other hand, Mg is mobile in the plant and increasing tuber concentrations is not as difficult as Ca, although Mg deficiencies caused by cation competition is a global phenomenon (Marschner, 2012). A study done in South Africa on several cultivars showed that of all the cultivars tested, Sifra had the lowest Mg content and that Fianna had the highest (Van Niekerk, 2015). Potato is highly susceptible to Mg deficiency, which has been shown to particularly affect the carbon assimilation and the transformation of energy (Hochmuth, 2007; Barker and Pilbeam, 2015). Considerable fewer studies have been done on Mg to the extent that it is often dubbed the “orphan nutrient” compared to Ca (Rosanoff, 2010). When producers export or sell their seed- or ware potatoes it is important for the buyer to know in advance the quality of the product. If the keeping quality can be predicted it will help both the producer and buyer to know the quality of the product and compensation can then be arranged more accurately, since good keeping quality potatoes should have higher value than poor keeping quality potatoes. To predict the keeping quality of seed- and ware potatoes, various quality characteristics must be identified and used. The main objective for this study was to develop a measuring tool that can be used to routinely predict the keeping quality of a tuber. Tubers were sampled throughout 2016 season and partially through the 2017 season. Inspection for IBS and hollow heart were assessed to see if any of the quality characteristics could correlate with these disorders. Tubers were stored at 25℃ and 5℃ respectively, while mass loss was determined as percentage (%) loss throughout the storage period. Different quality characteristics were measured to use in a prediction model.