Pretorius, J. C.Hüster, ThomasSwart, W. J.2015-08-202015-08-202011-12http://hdl.handle.net/11660/986English: A recently commercialized natural bio-stimulant, ComCat®, that contains three active brassinosteroids (BRs) of which two were identified previously, was scrutinized in this study for its potential to be applied in the agricultural industry. Concerning objective (1), seven biotests were employed to quantify the bio-stimulatory activity of ComCat® under laboratory and glasshouse conditions. The product was tested at different concentration levels and the 0.5 mg ℓ-1 application repeatedly emerged as the optimum concentration in terms of contributing towards increases in all of the parameters measured. Treatment with ComCat® had little or no effect on seed germination, but especially root growth of seedlings from different crops was significantly and consistently induced. Concerning objective (2), two cultivars for each of five test crops were treated with ComCat® over two growing seasons under field conditions in order to ascertain their yield response. Some of the test crops, but not all, showed cultivar sensitivity to treatment with ComCat®. However, overall the significant yield increases measured in one or both cultivars of the five different test crops and in one or both seasons confirmed the potential of ComCat® to be applied in agriculture and to contribute to economic prosperity for a farmer. Concerning objective (3), gas chromatographic analyses of a crude extract of the product as well as semi-purified fractions thereof by, using internal BR standards, were employed to identify an unknown BR contained in ComCat®. This was confirmed to be 24-epi-brassinolide. The latter as well as the previously identified 24- epi-castasterone and 24-epi-secasterone are known to be active BRs of the brassinosteroid group. In conclusion, the bio-stimulatory characteristic of ComCat® was confirmed both in vitro and in vivo under laboratory, glasshouse and field conditions in this study. Significant yield increases in all of the test crops over two seasons in some instances, confirmed the potential of ComCat® to be applied sustainably in the agricultural practice. Based on the results obtained in this study, three possible application methods of ComCat® are suggested. These include 1) seed treatment, 2) foliar application or 3) soil application.Afrikaans: n Onlangs gekommersialiseerde natuurlike biostimulant, ComCat®, wat drie aktiewe brassinosteroïede (BRs) waarvan twee voorheen geïdentifiseer is bevat, is in hierdie studie t.o.v. die potensiaal om in die landboupraktyk toegepas te word ondersoek. M.b.t. doelwit (1) is sewe biotoetse ingespan om die biostimulerende aktiwiteit van ComCat® onder laboratorium- en glashuistoestande te kwantifiseer. Die produk is teen verskillende konsentrasies getoets en 0.5 mg ℓ-1 is herhalend as die optimum konsentrasie, in terme van bydra tot verhoging in al die gemete parameters, geïdentifiseer. Behandeling met ComCat® het weinig of geen effek op saadkieming gehad nie, maar veral wortelgroei in saailinge van verskillende gewasse is betekenisvol en konsekwent geïnduseer. Ten opsigte van doelwit (2) is twee cultivars vir elk van vyf toetsgewasse oor twee seisoene met ComCat® behandel en die oesopbrengs onder veldtoestande gemeet. Sommige van die toetsgewasse, maar nie almal nie, was cultivar sensitief t.o.v. behandeling met ComCat®. Maar, oorkoepelend het die betekenisvolle oesopbrengsverhogings wat in een of beide cultivars van die vyf verskillende toetsgewasse en oor een of beide groeiseisoene gemeet is, die potensiaal vir ComCat® om in die landbou toegepas te word en tot ekonomiese welvaart vir die boer by te dra, bevestig. Met betrekking tot doelwit (3) is ‘n ru-ekstrak van die produk asook semigesuiwerde fraksies daarvan gaschromatografies geanaliseer, deur van interne BRstandaarde gebruik te maak, ten einde die onbekende BR in ComCat® te identifiseer. Laasgenoemde is bevestig om 24-epi-brassinolied te wees wat, tesame met die voorheen geïdentifiseerde 24-epi-castasteroon en 24-epi-secasteroon, bekend is as aktiewe BRs van die brassinosteroïed groep. Ten slotte is beide die in vitro en in vivo bio-stimulerende eienskappe van ComCat® onder laboratorium-, glashuis- en veldtoestande in hierdie studie bevestig. Betekenisvolle oesopbrengsverhoging wat in al die toetsgewasse, in sommige gevalle oor twee seisoene verkry is, het die potensiaal vir ComCat® om volhoubaar in die landboupraktyk toegepas te word, bevestig. Gebaseer op die resultate wat in hierdie studie bekom is, word drie moontlike aanwensdingsmetodes vir ComCat® voorgestel. Dit sluit 1) ‘n saadbehandeling, 2) ‘n blaarbespuiting of 3) ‘n grondbehandeling in.enThesis (Ph.D. (Soil, Crop and Climate Sciences))--University of the Free State, 2011BrassinosteroidsChromatographic analysisCrop yieldsPlant regulators -- AnalysisThesisUniversity of the Free State