Overcoming hybrid lethality in a cross between Japanese pear and apple using gamma irradiation and confirmation of hybrid status using flow cytometry and SSR markers

Although there have been some attempts to obtain intergeneric hybrids between Japanese pear (Pyrus pyrifolia Nakai) and apple (Malus × domestica Borkh.) mature hybrids have not been generated due to hybrid lethality. Shoots from immature hybrid embryos were gamma irradiated and cultured at normal temperature conditions to obtain viable intergeneric plants. Gamma irradiation doses of 50 and 100 Gy cultured at 25 °C killed all shoots but there was one survivor at 150 Gy and 25 °C. Hybrid status of the shoot was confirmed by using morphology, flow cytometry and SSR markers. The intergeneric plant had similar leaf serrations to apple and similar petioles to Japanese pear. Flow cytometric analysis revealed that the intergeneric shoot had a DNA content intermediate between the parents. SSR analysis showed one allele from each parent for all 16 SSR loci investigated. These data strongly suggest that the obtained shoot is a true hybrid between Japanese pear and apple.