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dc.contributor.advisorMarasas, W. F. O.
dc.contributor.advisorWingfield, M. J.
dc.contributor.advisorCardwell, K. F.
dc.contributor.authorNgoko, Zachee
dc.date.accessioned2017-05-22T06:55:53Z
dc.date.available2017-05-22T06:55:53Z
dc.date.issued1999-09
dc.identifier.urihttp://hdl.handle.net/11660/6260
dc.description.abstractEnglish: Maize (Zea mays L.), the staple food crop of the majority of the population of Cameroon, is damaged by insects and diseases from the fields to the stores. As a result, the quantity and the quality of harvested grain is reduced. This study was undertaken to identify constraints associated with the production and post-harvest losses of this commodity in two ecological zones ofCameroon from 1995 to 1997. Farmers' perceptions of diseases and pests play an important role in their acceptance of new pest management technologies. From the survey conducted to assess their perceptions, farmers reported that borers (Busseola fusca) were the main constraint to maize production in the Humid Forest and Western Highlands. Locusts (Zonecerus variegatus) and rodents were the second most important limiting factor in the Humid Forest. The storage weevil (Sitophilus zeamais) was the most damaging storage insect. Diseases were not generally known by farmers who could only recognize smuts and ear rots by the visible damage caused by them. While the period of the outbreaks of insect infestation was not reported with precision, most farmers reported that diseases occurred at the mid-season. Control practices were not well established. Disease surveys conducted from 1995 to 1997, revealed that lowland blight (Bipolaris maydis, Diplodia leaf spot (Stenocarpella macrospora) and sheath blight (Rhizoctonia solani) were the most important maize diseases in the Humid Forest, while highland blight (Exserohilum turcicum) and grey leaf spot (Cercospora zeae-maydis) prevailed in the Western Highlands. Phaeosphearia leaf spot (Phaeosphaeria maydis) was specific to the Western Highlands with a negative relationship with grey leaf spot. Busseola fusca infested maize plants at all stages of growth with high prevalence in the Humid Forest. The identification of factors -affecting maize yield demonstrated that diseases, insects and their interactions with soil infertility, soil texture, weeds, and maize varieties were responsible for the reduction of maize production. Yield reductions were 30% and 33.6% respectively, in the Humid Forest in 1995 and 1996 due to Stenocarpella macrospora, Puccinia polysora and Rhizoctonia solani. In the Western Highlands, Cercospora zeaemaydis, Busseola fusca, stem diseases, and physiological spot caused yield reductions of 51.2%, and 37.9% in 1996 and 1997, respectively. Mycological and chemical analyses of maize grain collected from 72 farmers' stores showed that several pathogens were associated with grain quality deterioration. Nigrospora spp. were the most frequently isolated fungi on kernels, followed by Fusarium moniliforme and Fusarium graminearum. Aspergillus spp. were rare in both zones. Fumonisin B1, deoxynivalenol and zearalenone were detected in maize samples at levels ranging from 300 to 26,000ng/g, 100 to 1300 ng/g, and 50 to 110 ng/g, respectively. This is the first report on the natural occurrence of these Fusarium mycotoxins in maize in Cameroon. Surveys conducted to identify the biological and physical factors that enhanced the infection of maize kernels by fungi and the contamination with fumonisin , identified several agricultural techniques related to grain quality in the Western Highlands. Harvesting in June (11.1 %) or July (23.6%), sorting right from the field (16.7%), drying over the fireplace with husk (19.4) or without husk (33.3%) and storing shelled grain in bags (19.4%) or boxes (9.7%) reduced fumonisin contamination. Continuous production of maize on the same field, harvesting in August, and the infestation by the weevil Sitophilus zeamais were factors that increased fumonisin contamination. Crop rotation, sorting maize during all the post-harvest processes and the treatment of maize grain with appropriate insecticides should decrease the risk of contamination by fumonisin. Continuing collaborative research should aim at understanding farmers' needs and priorities, investigating the epidemiology of maize diseases, screening for resistance to the most important maize diseases and improving harvesting, sorting, drying and storing methods in Cameroon.en_ZA
dc.description.abstractAfrikaans: Mielies (Zea mays L.), die stapelvoedsel van die meerderheid van die bevolking van Kameroen, word beskadig deur insekte en siektes, vanaf die land tot in opberging. Gevolglik word die hoeveelheid en die gehalte van die ge-oeste graan verlaag. Hierdie studie is onderneem om die beperkings op die produksie van mielies en na-oes verliese in twee ekologiese gebiede van Kameroen gedurende 1995 tot 1997, te identifiseer. Boere se persepsies omtrent siektes en plae speel 'n belangrike rol in hulle aanvaarding van nuwe plaagbeheer metodes. In die opname om hulle persepsies te evalueer, het boere aangemeld dat boorders (Busseola fusca) die belangrikste beperking op die produksie van mielies in die "Humid Forest" en die "Western Highlands" was. Sprinkane (Zonecerus variegatus) en knaagdiere was die tweede belangrikste beperkende faktor in die "Humid Forest". Die kalander (Sitophilus zeamais) was die insek wat die meeste skade in opberging veroorsaak het. Siektes was nie algemeen bekend aan boere nie en hulle kon slegs brande en kopvrotte herken aan die sigbare skade wat hierdie siektes veroorsaak. Alhoewel die tydperk wanneer insekplae uitbreek nie noukeurig gerapporteer kon word nie, het die meeste boere aangedui dat siektes in die middel van die seisoen voorkom. Beheermaatreels was nie goed gevestig nie. Siekte opnames wat vanaf 1995 tot 1997 uitgevoer is, het aangedui dat laeveld skroei (Bipolaris maydis), Diplodia blaarvlek (Stenocarpella macrospora) en blaarskede skroei (Rhizoctonia solani), die belangrikste mieliesiektes in die "Humid Forest" was, terwyl ho4veld skroei (Exserohilum turcicum) en grys blaarvlek (Cercospora zeae-maydis) oorheersend was in die "Western Highlands". Phaeosphaeria blaarvlek (Phaeosphaeria maydis) was beperk tot die "Western Highlands" en het 'n negatiewe verwantskap met grys blaarvlek vertoon. Busseola fusca het mielieplante in alle groeistadia aangeval met 'n ho4 voorkoms in die "Humid Forest". Die identifikasie van faktore wat die opbrengs van mielies be.nvloed, het aangedui dat siektes, insekte en hulle interaksies met grondvrugbaarheid, grondtekstuur, onkruide en mielie vari4teite, verantwoordelik was vir die verlaging in opbrengs. Oesverliese in die "Humid Forest" was 30% en 33.6%, respektiewelik, in 1995 en 1996 as gevolg van Stenocarpella macrospora, Puccinia po/ysora and Rhizoctonia so/ani. In die "Western Highlands" het Cercospora zeae-maydis, Busseo/a fusca, stamsiektes en fisiologiese vlek oesverliese van 51.2% en 37.9% in 1996 en 1997, respektiewelik, veroorsaak. Mikologiese en chemiese analises van mielies wat versamel is van 72 boere se opbergingsplekke het aangetoon dat verskeie patogene betrokke was by die verlaging van die gehalte van die graan. Nigrospora spp. Was die mees dikwels geesoleerde fungi vanaf mieliepitte gevolg deur Fusarium moniliforme en Fusarium graminearum. Aspergillus spp. was skaars in beide gebiede. Fumonisin B" deoxynivalenol en zearalenone is vasgestel in mieliemonsters teen vlakke vanaf 300 tot 26000 ng/g, 100 tot 1300 ng/g, en 50 tot 110 ng/g, respektiewelik. Hierdie is die eerste aanmelding van die natuurlike voorkoms van hierdie Fusarium toksiene in mielies in Kameroen. Opnames wat gedoen is om die biologiese en fisiese faktore te identifisser wat die infeksie van mieliepitte deur fungi en die kontaminasie met fumonisin bevorder, het verskeie. landboukundige tegnieke geedentifiseer wat die gehalte van graan in die "Western Highlands" beenvloed. Oes in Junie (11.1 %) of Julie (23.6%), sortering op die land (16.7%), droogmaak oor die vuurherd met die kopblare aan (19.4%) ofsonder die blare (33.3%) en die opberging van gedorste graan in sakke (19.4%) of in kiste (9.7%), het fumonisin kontaminasie verlaag. Aanhoudende produksie van mielies op dieselfde land, oes in Augustus en besmetting met die kalander, Sitophilus zeamais, was faktore wat fumonisin kontaminasie verhoog het. Wisselbou, sortering van mielies gedurende al die na-oes prosedures en die behandeling van mielies met geskikte insekdoders behoort die risiko van fumonisin kontaminasie te verminder. Voortgesette kollaboratiewe navorsing moet gerig wees daarop om boere se behoeftes en prioriteite te verstaan, om die epidemiologie van mieliesiektes te ondersoek, om te toets vir weerstandbiedendheid teen die belangrikste mieliesiektes, en om die metodes van oes, sortering en opberging van mielies in Kameroen te verbeter.af
dc.description.sponsorshipPROMEC in South Africaen_ZA
dc.language.isoenen_ZA
dc.publisherUniversity of the Free Stateen_ZA
dc.subjectPathogenic fungi -- Cameroonen_ZA
dc.subjectCorn -- Diseases and pests -- Cameroonen_ZA
dc.subjectThesis (Ph.D. (Microbiology and Biochemistry))--University of the Free State, 1999en_ZA
dc.titleMycotoxin contamination of maize in relation to insect infestation, agricultural practices and agroecology in the Republic of Cameroonen_ZA
dc.typeThesisen_ZA
dc.rights.holderUniversity of the Free Stateen_ZA


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