Cytological analyses of the karyotypes and chromosomes of three Colletotrichum species, C. orbiculare, C. graminicola and C. higginsianum

In contrast to the recent accomplishments of genome projects, cytological information on chromosomes and genomes of the genus Colletotrichum is very scarce. In this study, we performed mitotic cytological karyotyping for the three species, C. orbiculare, C. graminicola, and C. higginsianum by fluorescence microscopy and compared the results with those from genome projects. Chromosome number (CN) of C. orbiculare was determined for the first time to be n = 10 with no minichromosomes (MCs) in the genome, while CNs of C. graminicola and C. higginsianum were consistent with those from their genome project including the number of MCs. Regarding chromosome features, C. orbiculare was peculiar in that each chromosome was distinctly partitioned into a highly AT-rich pericentromeric region and the remaining highly GC-rich regions, and the pericentromeric region was judged to be constitutive heterochromatin. Integrating all the discernible morphological characteristics such as chromosome length, nucleolar organizing region, and DAPI-stained regions, idiograms were constructed for the three species. The overall cytological features of the chromosomes and genomes fit well with the data from the genome projects in terms of genome size, GC-content, and the occurrence of AT-rich regions. This study represents the most comprehensive and detailed mitotic cytological karyotyping of fungi ever reported.