Swart, W. J.Pretorius, J. C.Tesfaendrias, Michael Tecle2018-09-042018-09-042002http://hdl.handle.net/11660/9205English: Kenaf is propagated by seed and thus its cultivation depends on good quality seed and uniform emergence of seedlings. The aim of chapter two of this study was to investigate factors that are related to the establishment of kenaf from seed. Consequently, a total of nine fungal genera were identified from surface disinfested kenaf seeds of ten cultivars. In all cases Alternaria spp. was the most common followed by Chaetomium spp. The cultivar, Whitten had the highest incidence with 60% of seeds contaminated. Of the fungal species isolated from nine genera, Fusarium subglutinans was considered to be the most potentially pathogenic. In the glasshouse trials, kenaf cultivars artificially inoculated with F. subglutinans produced disease symptoms which resulted in damping-off of seedlings. This suggests that the pathogen can be expected to influence kenaf production in South Africa. Kenaf seed treatment with ComCat® and thiram did not improve seed germination.A stimulatory effect of ComCat® on seedling emergence, fresh and dry root weight as well as fresh foliage of kenaf seedlings was not observed. ComCat® was nevertheless involved in the increase of dry weight of the above ground parts. The latter suggests that it has a potential role in improving dry matter production of kenaf. In the field trials, kenaf plants inoculated with Botrytis cinerea displayed brown necrotic lesions and girdling of the stem which resulted ill loding. There was variation in susceptibility between cultivars. Everglades 41 and SF 459 had the largest and smallest lesion lengths respectively. Surface wetness and temperature are important factors in epidemics of il. cinerea. It was found that optimum temperature for mycel ial growth of B. cinerea isolated from kenaf plants occurred between 15 and 20°C. Studies on the effect of irrigation on the incidence of grey mould, found no significant difference in grey mould incidence between three moisture regimes. Trials were conducted in vitro to determine possible fungicides thatwould be employed for the control of B. cinerea. Benemyl displayed the highest inhibition. Variation in sensitivity to benornyl was observed between B. cinerea isolates. The objectives of the fourth chapter were to characterize Pyhtium group G on kenaf in terms of its pathogenicity to kenaf cultivars, optimum temperature requirements and its sensitivity to selected fungicides. In pathogenicity trials, the artificially inoculated fungus colonized the cambial tissue of all ten kenaf cultivars. Reisolation of Pythium group G from artificially inoculated tissue confirmed its pathogenicity to kenaf plants. Seedl ing damping-off studies were conducted by artificially inoculating kenaf seedlings grown in pots in the glasshouse. Mortality of kenaf seedlings occurred rapidly but no significant difference in susceptibility was observed between cultivars. Growth studies conducted in vitro found that the optimum temperature for mycelial growth for Pythium group G ranged between 20-30°C. Screening of six fungicides was conducted in vitro to determine their inhibitory effect on radial colony growth of Pythium group G isolate. Dichlorophen and mancozeb/metalaxyl were found to be the most effective fungicides. Results of this study established that B. cinerea and Pythium group G are virulent to kenaf and could hamper its establishment as a new crop in South Africa. Satisfactory control of the pathogens could be achieved by the integration of cultural practices and chemical control. Effecti ve programs to monitor the distri bution of the pathogens and control strategies should be implemented to prevent serious losses to kenaf.Afrikaans:Kenaf word deur middel van saad gepropageer en die verbouing daarvan is dus van hoë kwalitiet saad en die gelymatige opkoms van saailinge afhanklik. Die doel van hoofstuk twee van die huidige studie was om faktore wat verband hou met die vestiging van kenaf vanaf saad te ondersoek. Nege swam-genera is vanaf oppervlakkig-gedisinfesteerde saad van tien kenaf kultivars geïdentifiseer. In alle gevalle was Alternaria spp. die mees algemene swamspesie gevolg deur Chaetomium spp. Die kultivar, Whitten het die hoogste voorkoms van swarnme getoon, met 60% van saad wat besmet was. Van al die swamspesies wat geïsoleer is, was F. subglutinans potensieel, die mees patogeniese spesie. In glashuisproewe, het kenaf kultivars wat kunsmatig met F. subglutinans geïnokuleer is, siektesimptome getoon wat tot omval-siekte aanleiding gegee het. Dit impliseer dat hierdie patogeen 'n negatiewe impak op kenaf verbouing in Suid-Afrika kan meebring. Die behandeling van kenaf saad met ComCat® en thiram het nie saadontkieming verbeter nie. 'n Stimulerende effek van ComCat® op saadopkorns, vars- en droëgewig van wortels asook die varsgewig van blare was nie te bespeur nie. ComCat® het desnieteenstaande 'n toename in die bogrondse droëgewig van saailinge veroorsaak wat impliseer dat die produk 'n potensieeie rol in die verbouing van kenaf het. In veldproewe, het kenaf plante wat met Botrytis cinerea geïnokuleer is, bruin nekrotiese letsels op die stam getoon wat tot knak van die stam gelei het. Variasie in vatbaarheid tussen kenaf kultivars was duidelik waarneembaar. Everglades 41 en SF 459 het onderskeidelik die grootste en kleinste stamletsels getoon. Vog en temperatuur is belangrike faktore in die infeksie van B. cinerea. Daar was gevind dat die optimum temperatuur vir die groei van B. cinerea miselium tussen 15 en 20°C plaasgevind het. Studies op die effek van besproeing op die voorkoms van B. cinerea het geen noemenswaardige verskil tussen drie verskillende vogvlakke getoon nie. Proewe was in vitro uitgevoer om moontlike fungisiedes vir die beheer van B. cinerea te toets. Benomyl het die meeste inhibisie van miseliumgroei getoon. Variasie tussen isolate in terme van hul sensitiwiteit teenoor benomyl was ook waargeneem. The doelwitte van die vierde hoofstuk was om Pythium groep G op kenaf te karaktiseer in terme van patogenisiteit teenoor kultivars, optimum temperatuur en sensitiwiteit teenoor geselekteerde fungisiedes. In patogenisiteitsproewe, het die inokulasie van volwasse plante met die swam duidelike simptome In die cambium veroorsaak. Vooropkomsafsterwing van saailinge was ook ondersoek deur om plante in potte in die glashuis te inokuleer. Afsterwing van saailinge het vinnig plaasgevind maar geen beduidende verskil in vatbaarheid tussen kultivars was waargeneem nie. Studies wat in vitro uitgevoer is het gevind dat die optimum groei-temperatuur vir Pythium groep G tussen 20 en 30° C is. Proewe was in vitro uitgevoer om ses moontlike fungisiedes virdie beheer van 'n Pythium groep G isolaat te toets. Dichlorophen en mancozeb/metalaxyl was die mees inhiberende fungisiedes. Resultate van die huidige studie bewys dat B. cinerea en Pythium groep G potensieel die verbouing van kenaf as 'n nuwe gewas in Suid-Afrika grootliks kan belemmer. 'n Redelike mate van beheer van hierdie twee patogene kan wel deur middel van geïntegreerde siektebeheermaatreëls bewerkstellig word. Effektiewe programme om die verspreiding van die patogene te monitor asook beheer strategieë behoort dus geïmplementeer te word om emstige oesverliese te vermy.enKenaf (Hibiscus cannabinus L.)Kenaf -- Diseases and pests -- South AfricaCotton -- Diseases and pests -- Control -- South AfricaDissertation (M.Sc.Agric. (Plant Sciences))--University of the Free State, 2002DissertationUniversity of the Free State