Browsing by Author "Van der Merwe, Elizabeth"

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    Evaluation of new postharvest fungicides for the control of Phytophthora brown rot
    (Stellenbosch : Stellenbosch University, 2020-03) Van der Merwe, Elizabeth; Van Niekerk, Jan; Lennox, Cheryl L.; Stellenbosch University. Faculty of AgriSciences. Dept. of Plant Pathology.
    ENGLISH ABSTRACT: Brown rot is a citrus postharvest disease caused by Phytophthora spp. during continuous wet conditions. Fruit closest to the soil surface in the orchard are usually infected when the infecting propagules present are splashed upward during irrigation or rain. When infections on fruit are still in early development, it may go unnoticed when fruit are harvested. Infections develop further after harvest and can infect other fruit while in storage or transit. In the current study, the efficacy of actives azoxystrobin, fludioxonil and potassium phosphite was tested for the control of postharvest Phytophthora brown rot on citrus, as there is currently nothing registered for the management of this disease in South Africa. The fungicide sensitivities of 121 Phytophthora nicotianae isolates belonging to either a previously unexposed population or previously possibly exposed population, were tested for against the strobilurin azoxystrobin, based on the growth of mycelium. The mycelial growth on corn meal agar (CMA) amended with azoxystrobin at 0-, 0.25-, 0.5-, 1-, 10-, 100-, and 2000 µg/ml with the addition of 100 µg/ml salicylhydroxamic acid (SHAM), to inhibit the alternative respiration route, was measured after 7 days. The addition of SHAM did not have a significant effect on the growth of mycelia. CMA was also amended with the phenylpyrrole fludioxonil at 0-, 1-, 100-, 1000-, and 10 000 µg/ml. The effective concentration for 50% reduction of mycelial growth (EC50) for azoxystrobin ranged from 0.01 to 0.46 µg/ml for both populations and the EC90 ranged from 4.28 to 84.85 µg/ml for both populations. Fludioxonil sensitivity had a much wider range and higher EC values. The EC50 for both populations ranged from 3.10 to 1613.52 µg/ml and the EC90 values were 1090.50 to 9929 µg/ml. Subsequently, curative and protective actions of aqueous postharvest dip treatments, were carried out with the use of azoxystrobin at 1125 µg/ml and fludioxonil at 598 µg/ml. With the in vivo trials, potassium phosphite was added as an additional treatment at 1500 µg/ml. These trials were repeated on three fruit types namely lemons, oranges and mandarins and at four time intervals. The data clearly showed that with all three fungicides, the curative efficacy is excellent when treatments occurred up to 12 hrs after inoculation. Azoxystrobin and potassium phosphite exhibited excellent protective activity up to 48 hrs between treatment and inoculation. An overall trend that was seen with all three fruit types, was that the longer the fungicide was present on the fruit, the better the protective activity. The nesting data clearly demonstrated that only azoxystrobin amended wax significantly reduced brown rot from spreading to the healthy fruit, when compared to the control. With this study, it could be seen that all three fungicides, with their different actives, have the potential to effectively manage postharvest brown rot. Considering that azoxystrobin and fludioxonil are already registered on citrus for the postharvest use of Penicillium management, and potassium phosphite that are registered as a preharvest Phytophthora treatment, this study indicate that they will also provide added protection against Phytophthora brown rot.
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    Die rol en persoon van die fasiliteerder van 'n christelike tienergespreksgroep
    (Stellenbosch : Stellenbosch University, 2001) Van der Merwe, Elizabeth; Van der Merwe, Lize; Ackermann, C. J.; Stellenbosch University. Faculty of Education. Dept. of Educational Psychology.
    ENGLISH ABSTRACT: This study addresses the role and person of the facilitator of a Christian teen discussion group. From the literature study it is evident that there are specific requirements concerning the role and person of the facilitator of a teen discussion group. These requirements and definitions should only serve as guidelines for the success of a teen discussion group The empirical study investigated the role and person of the facilitator of a teen discussion group. According to the results it seems that the most important characteristics of a facilitator, according to the teen discussion groups, are that of warmth as a person, caring and insight and that he must be a role model. The study also showed that the role and person of a facilitator of a teen discussion group to a great extent contributes to the success of these groups.