Nuclear genome size variation in the allopolyploid Onosma arenaria – O. pseudoarenaria species group: methodological issues and revised data

We used flow cytometry (FCM) to investigate genome size variation in two polymorphic allopolyploids, Onosma arenaria and O. pseudoarenaria, in Central Europe and the Balkan Peninsula. An intercalating DNA stain, propidium iodide (PI), and internal standardization were used. Our data showed that cytosolic compounds may be present in FCM samples and could inhibit, or more frequently promote, PI intercalation. In the absence of PI intercalation interference, leaf-based genome size estimates were observed to be lower than seed-based ones in O. pseudoarenaria, whereas no difference was recorded in O. arenaria. In incubation tests genome size values frequently increase after a longer staining period. For final genome size measurements, we applied the FCM protocol based on seed material using a ~150-min incubation period, and provide evidence of mean genome size variation among populations of both species. Two and four natural genome size groups were revealed in O. arenaria and O. pseudoarenaria respectively. Gr...