MAJOR CHROMOSOMAL LENGTH POLYMORPHISMS ARE EVIDENT AFTER MEIOSIS IN THE PHYTOPATHOGENIC FUNGUS LEPTOSPHAERIA-MACULANS

Chromosomal DNA of Australian field-isolates of the phytopathogenic as comycete Leptosphaeria maculans was resolved by pulsed-field gel elect rophoresis. All isolates examined had highly variable karyotypes. Asco spores (sexual spores) derived from single pseudothecia (sexual fruiti ng bodies) isolated from Brassica napus (oilseed rape) stubble were an alyzed. In two tetrads four distinct karyotypes were observed, with on ly one chromosomal DNA band in common to all the members of each tetra d. Although isolates had highly variable karyotypes, two overall patte rns were present. In one pattern there were at least 12 chromosomal DN A bands, the largest being greater than 2.2 Mb in size; in the other t here were more than 15 chromosomal DNA bands, the largest being about 2.0 Mb. The chromosomal DNA preparations included mitochondrial DNA wh ich migrated as a diffuse band between 0.10 and 0.15 Mb in size, and D NA molecules of 8 and 9 kb in size.