Nuclear DNA content and 1Cx-value variations in genus Rosa L.

In order to investigate the systematic relationship and to complete the karyological data of rose, for the purpose of exploring desirable traits for genetic improvement of modern cultivars, nuclear DNA content of 204 accessions representing almost all sections of genus Rosa were estimated by flow cytometry. The 1Cx-value of each taxon was calculated according to the estimated DNA content. The results were as follows: (1) nuclear DNA content of the studied taxa varied from 0.73 pg in diploid R. zhongdianensis (Section Pimpinellifoliae) to 5.07 pg in decaploid R. praelucens (Section Microphyllae), and nuclear DNA content of rose species generally increased with, but not simply proportional to, ploidy level; (2) 1Cx-value varied from 0.37 pg in R. zhongdianensis to 0.89 pg in R. brunonii (Section Synstylae), and the studied taxa were significantly different from each other in 1Cx-value; (3) there exist significant differences of 1Cx-values among sections, varying from 0.46 pg in Section Pimpinellifoliae to 0.77 pg in Section Synstylae; (4) ploidy level varied within most sections except in Section Banksianae, Section Bracteatae, Section Laevigatae and Section Synstylae, while the variation of 1Cx-value with ploidy level differed greatly among sections. The results suggested that taxonomic section should be taken into consideration when assigning ploidy of rose species from rapid estimates of DNA content by flow cytometry. Also, although it does not reflect the taxonomy and biosystematics sufficiently, nuclear DNA content and 1Cx-value can be used as reference points in the biogeographic, systematic and evolutionary study of genus Rosa.