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

English: 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.