Nuclear DNA Content as an Index Character Discriminating Taxa in the Genus Petunia sensu Jussieu (Solanaceae)

Nuclear DNA contents over the total range of the genus Petunia sensu Jussieu comprising 20 taxa of Petunia sensu Wijsman (2 n=2 x=14) and 32 taxa of Calibrachoa(2 n=2 x=18) were estimated by flow cytometry after staining the nuclei with propidium iodide (PI) or 4′,6-diamidino-2-phenylindole (DAPI). With respect to nuclear DNA content, taxa of Petunia sensu Wijsman seemed to be homogeneous (2C=2.60 to 3.41pg), but Calibrachoa taxa were clearly separated into two groups: (1)C. parviflora and C. pygmaea(1.56 to 1.91pg); and (2) remaining members of Calibrachoa(2.84 to 3.26pg). Taxa of Petunia sensu Wijsman exhibited larger PI/DAPI ratios (relative fluorescence intensity with PI staining to that with DAPI staining) than Calibrachoa species exceptC. parviflora and C. pygmaea. This suggests that Petunia sensu Wijsman has nuclear DNA with more adenine-thymine rich regions than Calibrachoa.