FISH Karyotype Comparison between Wild and Cultivated Perilla Species Using 5S and 45S rDNA Probes

Perilla species (Lamiaceae) have been used as a resource for oilseeds and vegetables, and medicinal purposes. Cytogenetic studies based on chromosomal composition are essential to understand the basic genome structure of a species and to provide vital information for crop improvements. However, only a few studies have assessed the cytogenetic aspects of Perilla species. Fluorescence in situ hybridization (FISH) karyotypes using 5S and 45S rDNA probes were analyzed for the wild and cultivated species of Perilla: P. citriodora and P. frutescens. Chromosome complements were diploid in P. citriodora and allotetraploid in P. frutescens. The chromosome length ranged from 3.07 to 4.92 m and 2.41 to 5.73 m in the diploid and allotetraploid variants, respectively. The karyotypic formula was 2n = 12m + 8sm (2 satellites) for P. citriodora and 2n = 20m + 20sm (2 satellites) for P. frutescens. A pair of 5S signals was detected in the telomeric region of chromosome pair 7, while a pair of 45S rDNA signals was detected in the telomeric region extending through the satellite region of chromosome 2 of P. citriodora. However, two pairs of 5S signals were detected from the interstitial to the telomeric regions of chromosome 7 and 17, and a pair of 45S rDNA signals was located on the satellite region of chromosome 20 of P. frutescens. This result will provide useful information to develop a breeding program and to construct the chromosomal backbone for the ongoing genome sequence assembly project.