Nuclear DNA content as an index character discriminating taxa in the genusPetunia sensu Jussieu (Solanaceae)

Nuclear DNA contents over the total range of the genus Petunia sensu Jussie u comprising 20 laxa of Petunia sensu Wijsman (2n = 2x = 14) and 32 taxa of Calibrachoa (2n = 2x = 18) were estimated by flow cytometry after staining the nuclei with propidium iodide (PI) or 4',6-diamidino-2-phenylindole (DA PI). With respect to nuclear DNA content, taxa of Petunia sensu Wijsman see med to be homogeneous (2C = 2.60 to 3.41 pg), but Calibrachoa taxa were cle arly separated into two groups: (1) C. parviflora and C. pygmnea (1.56 to 1 .91 pg); and (2) remaining members of Calibrachoa (2.84 to 3.26 pg). Taxa o f Petunia sensu Wijsman exhibited larger PI/DAPI ratios (relative fluoresce nce intensity with PI staining to that with DAPI staining) than Calibrachoa species except C. parviflora and C. pygmaea. This suggests that Petunia se nsu Wijsman has nuclear DNA with more adenine-thymine rich regions than Cal ibrachoa. (C) 2000 Annals of Botany Company.