Novel somatic hybrids (Solanum tuberosum L. + Solanum tarnii) and their fertile BC1 progenies express extreme resistance to potato virus Y and late blight

Solanum tarnii, a wild diploid, tuber-bearing Mexican species belonging to the series Pinnatisecta is highly resistant to Potato virus Y (PVY) and Colorado potato beetle and shows a strong hypersensitive reaction to Phytophthora infestans. Therefore, it could be a potential source of resistance to pathogens for potato breeders. S. tarnii (2n = 2x = 24) is reproductively isolated from tetraploid Solanum tuberosum and hence diYcult to include in potato breeding programmes. In this study, interspeciWc somatic hybrids were produced for the Wrst time by protoplast electrofusion of the cells of potato cv. Delikat (Solanum tuberosum L.) and Solanum tarnii. The hybrid nature of the regenerants was conWrmed by simple sequence repeat (SSR) and ampliWed fragment length polymorphism (AFLP) markers and by morphological analysis and Xow cytometry. Selected somatic hybrids were successfully backcrossed with cv. Delikat. Parental lines, primary somatic hybrids and BC1 progeny were assessed for resistance to PVY by mechanical inoculation, grafting and exposure to viruliferous aphid vectors in the Weld, and resistance to late blight (P. infestans) by detached leaXet and whole tuber tests. The somatic hybrids showed no symptoms of viral infection and most of them displayed high levels of resistance to foliage blight. The BC1 progenies were highly resistant to PVY and a few were resistant to foliage blight. Selected hybrids and BC1 clones were evaluated in the Weld for tuber quality and tuber yield. Some BC1 clones produced yields of good quality tubers. The results conWrm that both the resistance to PVY and to late blight of S. tarnii is expressed in somatic hybrids, and PVY resistance is transferred to BC1 progeny, whereas blight resistance is harder to transfer. Somatic hybridization again proved to be a valuable tool for producing pre-breeding material with increased genetic diversity.