Hypervariable Mini-Chromosomes of Colletotrichum gloeosporidoides Infecting the Pasture Legume genus Stylosanthes

Coiletotrichum gloeosporioides causes anthracnose disease of the tropical pasture legumes Stylosanthes, Two pathotypes and multiple physiological races are present in Australia. The mechanisms producing genetic variation in this pathogen are not understood. Electrophoretic karyotyping has revealed considerable variation in the size and number of a group of small chromosomes (0.2-1.2 Mb in size) both between and within types. Molecular analysis of a selected mini-chromosome using chromosome-specific DNA probes suggests that it has originated by horizontal transfer from a genetically distinct strain. This mini-chromosome is unique to race 3 within the Type B pathogen and may determine race specificity. A functional analysis of its role in determining specificity has begun by the isolation of race-specific cDNA clones encoded on this chromosome.