DYNAMICS OF Cercospora zeina POPULATIONS IN MAIZE-BASED AGRO-ECOLOGIES OF UGANDA

Stability of pathogen populations characterised by slow temporal variation is important for durability of disease management systems in any agroecology. Temporal variation in population structure is attributed to factors related to ecology, biology and life history, and varies among organisms and ecosystems. The objective of this study was to investigate genetic variability of Cercospora zeina (previously called Cercospora zeae-maydis Type II) populations in maize (Zea mays) producing areas under Uganda conditions. Populations of the fungus were analysed for genetic variability using a fluorescent amplified fragment length polymorphism (AFLP) technique. Little or no genetic differentiation (fFST 0.05) was detected for populations sampled within the same year, within an agroecology. However, a weak to moderate population structure was detected between populations from different locations, within the same (fFST = 0.08) or different agroecologies (fFST = 0.09). Pair-wise comparisons using fFST gene diversity and genetic distance, showed a reduction in genetic diversity in younger populations, suggestive of minor effects of selection and genetic drift. Overall, the data suggest that during the 3 years of study the impact of selection and genetic drift on C. zeina populations in the two Ugandan agroecologies is slow, but progressive leading to homogenetity with agroecologies and differences between agroecologies.