Nuclei isolated from young leaves were stained with propidium iodide (PI) and their fluorescence intensities were measured by flow cytometry. The ratio of fluorescence intensities of four calibration standards and 34 roses to an internal standard, parsley ( Petroselinum crispum ), provided a basis for estimating the DNA amounts of P. crispum and rose. The 2C DNA amount of P. crispum (2 n  = 22) was estimated as 4.46 pg (s.d. ± 0.08 pg). The 2C DNA amounts of diploid roses (2 n  = 14) varied between subgenera, sections and cultivars, and ranged from 0.78 pg (s.d. ± 0.08 pg) in Rosa xanthina and R. sericea (section Pimpinellifoliae) to 1.29 pg (s.d. ± 0.08 pg) in ‘Félicité et Perpétue’ (Hybrid Sempervirens). Within each section, the DNA amounts of diploid species were similar. In the sections Carolinae and Cinnamomeae, DNA amounts were proportional to ploidy numbers. In the Pimpinellifoliae, DNA amounts of tetraploids were disproportionately larger than those of diploids which suggests that they originated as hybrids with species of sections with larger DNA amounts. Ratios of the fluorescence intensities of nuclei of roses to P. crispum (internal standard) were also measured using 4′,6-diamidino-2-phenylindole (DAPI) which binds preferentially to AT base pairs. These DAPI ratios were lower than, but closely correlated ( r2  = 0.997) with PI ratios. Fluorescence intensities of either PI or DAPI-stained nuclei of roses can be used as rapid indicators of ploidy if variation in the DNA amounts between different taxonomic groups is taken into account. Copyright 2000 Annals of Botany Company

Received: 23 November 1999 ; Accepted: 16 December 1999


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