DISTRIBUTION AND RELATIONSHIP OF CHROMOSOME-SPECIFIC DISPENSABLE DNA-SEQUENCES IN DIVERSE ISOLATES OF COLLETOTRICHUM-GLOEOSPORIOIDES

DNA hybridization probes specific to a dispensable 1 2 Mb chromosome i dentified in some isolates of biotype B of Colletotrichum gloeosporioi des pathogenic on the legume Stylosanthes guianensis were used to asse ss the distribution and chromosomal location of homologous sequences i n a diverse collection of other Colletotrichum isolates. Homologous se quences were not detected in isolates representing C. lindemuthianum, C. musae, C. crassipes, C. trifolii, C. dematium and C. truncatum but were in some C. gloeosporioides isolates. Thus these sequences were no t conserved in the genus and deleted in some C. gloeosporioides strain s. Partly homologous DNA sequences were detected in genetically distin ct biotypes of C. gloeosporioides pathogenic on hosts other than Stylo santhes, which suggests that these DNA sequences may have evolved with in the species C. gloeasporioides prior to host specialization. Highly homologous chromosomes were identified in some isolates of the fungus from Stylosanthes from outside Australia including one isolate from t he Philippines which appeared to have a 1.2 Mb chromosome almost ident ical to that of Australian biotype B strains. The DNA probes revealed a range of sizes of homologous chromosomes in other strains of C. gloe osporioides but in general the chromosome-specific DNA probes were lin ked, suggesting a common origin with subsequent gross chromosomal rear rangement or exchange. The possibility that the chromosome-specific ma rkers may be useful diagnostic probes for biotype B isolates virulent on S. guianensis cv. Graham was tested using 10 new isolates with this virulence phenotype and three of these isolates lacked both the chrom osome and the DNA sequence homology. This suggests that the 1.2 Mb min i-chromosome is not associated with race-specificity The significance of these results for the origin and function of dispensable chromosome s in C. gloeosporioides is discussed.