Alteration of the genomic composition of Solanum nigrum (+) potato backcross derivatives by somatic hybridization: selection of fusion hybrids by DNAmeasurements and GISH

Fusion experiments were performed with a first (BC1-6738) and a second (BC2 -9017) generation backcross hybrid of 6x Solanum nigrum (+) 2x potato somat ic hybrids with potato cultivars. Because no progeny was obtained from the BC2 genotypes, alternative approaches were sought to overcome the sexual cr ossing barrier. Five potato genotypes, one of which contains the hygromycin resistance gene, were used in the fusion experiments. All vigorous regener ants were used for the estimation of nuclear DNA content using flow cytomet ry. Plants with a DNA content higher than that of the BC1-6738 or BC2 genot ypes were considered potential somatic hybrids. Forty-nine potential somati c hybrids resulted from fusion experiments with BC1-6738, from which 20 gre w vigorously in the greenhouse and flowered. After pollination with several 4x potato cultivars. eight genotypes produced seeded berries and five geno types gave seedless berries. In addition. Il of these 13 somatic hybrids we re selected for genomic in situ hybridization (GISH) analysis to determine their genomic composition. Nine had exactly or approximately the expected n umber of 36 S. nigrum and 60 potato chromosomes. In one genotype. only 22 i nstead of 36 S. nigrum chromosomes were found acid one potato chromosome wa s possibly missing. Only five potential somatic hybrids were detected among the 79 regenerants from BC2-9017 (+) 2x potato Fusion experiments that wer e analysed by flow cytometry. Two of these hybrids were rather vigorous and did flower, but pollinations with potato have not yet yet any berries.