A propensity to form polyploid hybrids is a peculiar feature of roses. Herklotz and Ritz investigate the population genetics of forty five mixed stands of dog roses across Central and South-Eastern Europe using microsatellite markers and flow cytometry.
They find that hybrids have originated independently at each locality with crossing barriers strongly biased towards the more abundant paternal parent. The majority of hybrids had a higher ploidy level than their parents because they emerged from unreduced egg cells. The authors conclude that the facilitation of unreduced egg cell formation in the maternal parent ensures correct chromosome pairing in hybrids.
This paper is part of the Annals of Botany Special Issue on Polyploidy in Ecology and Evolution. It will be free access until October 2017, then available only to subscribers until August 2018 when it will be free access again.