Spatial and Temporal Variation of Genetic Marker Patterns in Setosphaeria turcica Populations from Kenya

Setosphaeria turcica is an important fungal pathogen of maize in the humid mid-altitude and highland environments of East Africa, causing tiorthem corn leaf blight. To conduct a population genetic analysis, a total of 172 S. turcica isolates from four locations in western (Kakamega, Kitale) and central (Embu, Kikuyu) Kenya, collected in 1994 and 1995, were exatnined with 43 randotn amplified polymorphic DNA (RAPD) markers. Mating types were also determined. Of the total genetic variation, the greatest portion (70%) was attributed to differences between haplotypes in local populations. Only 26% of the variation was due to differences between regions and A°/a to locations within regions. Populations from the two regions clearly differed in their haplotype similarities and had different levels of gene and genotypic diversity. Isolation by distance and divergent selection are likely to be major causes of the differentiation between western and central Kenya. Migration between the two regions was weak. Within regions, population samples from different locations were very similar indicating intense migration. Samples collected early and late in the vegetation period or in consecutive years always showed the same population structure, i.e. little fluctuation occurred during the season. Clones were shown to be conserved over long distances and over years despite sexual recombination and an extremely high genotypic diversity