GENETIC-VARIATION AMONG FIELD ISOLATES OF PYRENOPEZIZA-BRASSICAE

Amplified fragment length polymorphism (AFLP) markers were used to det ermine genetic diversity and population structure of Pyrenopeziza bras sicae, the causal agent of light leaf spot of Brassica sp. Fungal isol ates were sampled from six regions in the UK, one region in Germany an d one region in France. A high level of genetic diversity was found (H -T=58%), with most variation attributed to within regions (H-S=43%), w hich suggests that sexual reproduction is frequent. F-ST values sugges ted significant population differentiation between England and the con tinent, but not between Scotland and England and Scotland and the cont inent. Overall, a moderate but significant level of regional different iation was found (F-ST = 16 +/- 4.0) There was no correlation between F-ST values and distance, indicating that long-distance dispersal by n atural factors does not occur at high frequencies. However, the lack o f differentiation among populations from Aberdeen, Winchester and Camb ridge suggests that seed transmission or other artificial methods of d ispersal may be important.