Incidence of Fusarium spp. and levels of fumonisin B-1 in maize in westernKenya

Maize kernel samples were collected in 1996 from smallholder farm storages in the districts of Bomet, Bungoma, Kakamega, Kericho, Kisii, Nandi, Siaya, Trans Nzoia, and Vihiga in the tropical highlands of western Kenya, Two-th irds of the samples were good-quality maize, and one-third were poor-qualit y maize with a high incidence of visibly diseased kernels. One hundred fift y-three maize samples were assessed for Fusarium infection by culturing ker nels on a selective medium. The isolates obtained were identified to the sp ecies level based on morphology and on formation of the sexual stage in Gib berella fujikuroi mating population tests. Fusarium moniliforme (G. fujikur oi mating population A) was isolated most frequently, but F. subglutinans ( G. fujikuroi mating population E), F. graminearum, F. oxysporum, F, solani, and other Fusarium species were also isolated. The high incidence of kerne l infection with the fumonisin-producing species F. moniliforme indicated a potential for fumonisin contamination of Kenyan maize. However, analysis o f 197 maize kernel samples by high-performance liquid chromatography found little fumonisin B-1 in most of the samples. Forty-seven percent of the sam ples contained fumonisin B-1 at levels above the detection limit (100 ng/g) , but only 5% were above 1,000 ng/g, a proposed level of concern for human consumption. The four most-contaminated samples,,vith fumonisin B-1 levels ranging from 3,600 to 11,600 ng/g, were from poor-quality maize collected i n the Kisii district. Many samples with a high incidence of visibly disease d kernels contained little or no fumonisin B-1, despite the presence off. m oniliforme. This result may be attributable to the inability of F. monilifo rme isolates present in Kenyan maize to produce fumonisins, to the presence of other ear rot fungi, and/or to environmental conditions unfavorable for fumonisin production.