Mycotoxin contamination of maize in relation to insect infestation, agricultural practices and agroecology in the Republic of Cameroon

[摘要] English: Maize (Zea mays L.), the staple food crop of the majority of the population of Cameroon, isdamaged by insects and diseases from the fields to the stores. As a result, the quantity and thequality of harvested grain is reduced. This study was undertaken to identify constraintsassociated with the production and post-harvest losses of this commodity in two ecologicalzones ofCameroon from 1995 to 1997.Farmers' perceptions of diseases and pests play an important role in their acceptance ofnew pest management technologies. From the survey conducted to assess their perceptions,farmers reported that borers (Busseola fusca) were the main constraint to maize production inthe Humid Forest and Western Highlands. Locusts (Zonecerus variegatus) and rodents werethe second most important limiting factor in the Humid Forest. The storage weevil (Sitophiluszeamais) was the most damaging storage insect. Diseases were not generally known byfarmers 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, mostfarmers reported that diseases occurred at the mid-season. Control practices were not wellestablished.Disease surveys conducted from 1995 to 1997, revealed that lowland blight (Bipolarismaydis, Diplodia leaf spot (Stenocarpella macrospora) and sheath blight (Rhizoctoniasolani) were the most important maize diseases in the Humid Forest, while highland blight(Exserohilum turcicum) and grey leaf spot (Cercospora zeae-maydis) prevailed in theWestern Highlands. Phaeosphearia leaf spot (Phaeosphaeria maydis) was specific to theWestern Highlands with a negative relationship with grey leaf spot. Busseola fusca infestedmaize plants at all stages of growth with high prevalence in the Humid Forest.The identification of factors -affecting maize yield demonstrated that diseases, insects andtheir interactions with soil infertility, soil texture, weeds, and maize varieties wereresponsible 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 of51.2%, and 37.9% in 1996 and 1997, respectively.Mycological and chemical analyses of maize grain collected from 72 farmers' storesshowed that several pathogens were associated with grain quality deterioration. Nigrosporaspp. were the most frequently isolated fungi on kernels, followed by Fusarium moniliformeand Fusarium graminearum. Aspergillus spp. were rare in both zones. Fumonisin B1,deoxynivalenol and zearalenone were detected in maize samples at levels ranging from 300to 26,000ng/g, 100 to 1300 ng/g, and 50 to 110 ng/g, respectively. This is the first report onthe natural occurrence of these Fusarium mycotoxins in maize in Cameroon.Surveys conducted to identify the biological and physical factors that enhanced theinfection of maize kernels by fungi and the contamination with fumonisin , identified severalagricultural 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 withhusk (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 thatincreased fumonisin contamination. Crop rotation, sorting maize during all the post-harvestprocesses and the treatment of maize grain with appropriate insecticides should decrease therisk of contamination by fumonisin.Continuing collaborative research should aim at understanding farmers' needs andpriorities, investigating the epidemiology of maize diseases, screening for resistance to themost important maize diseases and improving harvesting, sorting, drying and storing methodsin Cameroon.

[发布机构] University of the Free State