Fertile somatic hybrids of Solanum etuberosum (+) dihaploid Solanum tuberosum and their backcrossing progenies: relationships of genome dosage with tuber development and resistance to potato virus Y

The wild non-tuberous species Solanum etuberosum is resistant to biotic and abiotic stresses, but is very difficult to cross with cultivated potato. Therefore, interspecific somatic hybrids between a dihaploid clone of potato S. tuberosum (2n=2x=24, AA genome) and the diploid species S. etuberosum (2n=2x=24, EE genome) were produced by protoplast fusion. Among the 7 fertile fusion hybrids analysed by genomic in situ hybridisation (GISH), three groups of plants were found with the genomic constitution of AAEE, AAEEEE and AAAAEE. Four fusion hybrids had exactly the expected chromosome composition, while each of the three aneuploid hybrids had lost two chromosomes of S. etuberosum. Two backcross progenies were developed, and GISH analysis was applied to analyse transmission of the parental chromosomes into the sexual generations. BC1 hybrids derived from the crosses of the hexaploid somatic hybrids with tetraploid potato were pentaploid with the theoretically expected genomic composition or with slight deviation from this expectation. In the three BC2 hybrids analysed by GISH seven to 12 chromosomes of S. etuberosum were detected in the predominant S. tuberosum background. No recombinant chromosomes in the hybrids were detected. Genome dosage affects tuber formation in hybrids and their progenies, but has less effect on resistance to potato virus Y (PVY) in fusion hybrids. Several genotypes of the fusion hybrids and BC1 progeny did not show viral infection even in the grafting experiments.