Genetic diversity of isolates of the Leptosphaeria maculans species complex from Australia, Europe and North America using amplified fragment length polymorphism analysis

Amplified Fragment Length Polymorphism (AFLP) analysis has been used to ana lyse 100 Australian, European and North American isolates of Leptosphaeria maculans;. All isolates had distinct AFLP profiles. They could be classifie d into five types, which had very few AFLP bands in common and corresponded to classifications made previously on the basis of ability to cause stem c ankers on Brassica napus (A group), or inability to do so (B group), and on host range. Four isolates had AFLP profiles completely dissimilar to these groups and to each other. Genetic diversity and geographic differentiation were analysed separately within AFLP types 1 and 2. UPGMA analysis of the 66 AFLP type 1 (A group) isolates using 50 polymorphic bands did not provid e evidence for clustering according to geographic origin. Non-metric multid imensional scaling (NMDS) analysis suggested that the Australian and Europe an populations were separate adjacent clusters, while the North American po pulation partially overlapped both the others. This geographic differentiat ion was supported by Wright's fixation index (F-st) analysis. Three measure s of genetic variability between isolates within regions (effective number of alleles, gene diversity, and Shannon index) showed that the North Americ an A group isolates were less diverse than those from Australia and Europe. The 21 AFLP type 2 (B group; NAI sub-group) isolates did not duster based on geographic region which was confirmed by NMDS and F-st analysis. There w as a similar degree of genetic diversity within A group and the NAI sub-gro up of B group isolates. Unlike other techniques, AFLP analysis can readily discriminate between group B isolates of the L. maculans complex that were previously difficult to classify and also provides individual fingerprints for isolates. Isolates of the A group and of the NAI sub-group of B group c ould be also distinguished readily by electrophoretic karyotyping, as the l atter isolates had more bands smaller than 1.4 Mb than the A group isolates .