Genetic variation among field isolates of Pyrenopeziza brassicae

Amplified fragment length polymorphism (AFLP) markers were used to determine genetic diversity and population structure of Pyrenopeziza brassicae, the causal agent of light leaf spot of Brassica sp. Fungal isolates were sampled from six regions in the UK, one region in Germany and 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%), which suggests that sexual reproduction is frequent. F-ST values suggested significant population differentiation between England and the continent, but not between Scotland and England and Scotland and the continent. Overall, a moderate but significant level of regional differentiation was found (F-ST = 16 +/- 4.0) There was no correlation between F-ST values and distance, indicating that long-distance dispersal by natural factors does not occur at high frequencies. However, the lack of differentiation among populations from Aberdeen, Winchester and Cambridge suggests that seed transmission or other artificial methods of dispersal may be important.