Doctoral Degrees (Agronomy)

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

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    Witloof chicory (Cichorium intybus L. var.foliosum) - evaluation of new forcing techniques
    (Stellenbosch : Stellenbosch University, 2002-03) Konig, Roman; Combrink, Nicolaas; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.
    ENGLISH ABSTRACT: South Africa is one of the worlds leading producers of chicory (Cichorium intybus L.). Most of the chicory produced is used locally for the production of instant coffee. Witloof chicory, or Belgian endive, however, is a vegetable crop grown from the root of Cichorium intybus L. var. foliosum. This is done by placing the mature taproot in a controlled, dark environment after vernalization and supplying it with water and nutrients by means of hydroponics. Witloof chicory is new to the South African market and is only produced on a limited scale. Nonetheless, seeing that chicory is successfully grown on a large scale for the coffee industry it seemed reasonable to investigate the cultivation of this essentially unknown vegetable locally. The focus of this study was on the evaluation of new witloof production techniques during the second stage of witloof (chicon) cultivation, also called 'forcing'. To this end, locally grown witloof chicory roots were used in all trials. In order to establish the effects of several irrigation methods on lateral root formation and chicon quality, witloof chicory roots were forced using the conventional means of hydroponic irrigation as well as ebb-and-flood and aeroponic irrigation. Lateral root formation was significantly increased when either ebb-and-flood or aeroponic irrigation was applied compared to that obtained with the conventional method. This increase in lateral root formation was, however, to the detriment of chicon quality (QI), possibly as a result of competition for limited carbohydrate reserves. In an attempt to optimize the aeroponic irrigation method, roots were forced in non-vertical positions. Placing roots horizontally during forcing resulted in a significantly lower marketable chicon yield than where roots were placed vertically. The loss in yield was probably brought about by an increased fallout percentage rather than by a decrease in chicon production. Considering the pivotal role that sucrose plays in the development of the chicory head, sucrose was applied exogenously to the root before and/or during forcing. Dry matter chicon yield was negatively effected by exogenously applied sucrose. This could have been due to an increased incidence of fungal or bacterial infections or causative of roots absorbing less water resulting in the inability of the plant to utilize the applied sucrose during chicon development. Fungal and bacterial infections are known to have a detrimental effect on witloof chicory production. An environmentally friendly product for disease control, 'Desogerme SP®', was used to contain or reduce infection. Irrigation of roots with 'Desogerme SP®' containing nutrient solution increased chicon yield by 31%. From this study it became clear that some new production techniques applied had the potential of improving lateral root formation or quality during growth. However, the conventional way of irrigation remains the most effective compared to the other techniques applied, but could possibly be improved to some extent by incorporating 'Desogerme SP®' either as a pretreatment or in the nutrient solution. A breakthrough was made with the development of the quality index (QI). The ongoing limitation of statistically analyzing quality data of chicons sorted according to quality-classes was overcome by making use of this tool. Despite the fact that the index was developed specifically for use on witloof, it is has the potential of being applied to quality data of a wide variety of crops.