Characterization of somatic hybrids between tetraploid Solanum tuberosum L. and dihaploid S-acaule

Electrofusion was performed to produce somatic hybrids between Solanum tuberosum (2n=4x=48) and dihaploid S, acaule (2n=2x=24), Among the 18 regenerated plants obtained, 14 were found to be hexaploid hybrids based on RAPD analysis and cytological observation, In order to identify their cytoplasmic genome constitution, RPLP analysis of chloroplast and mitochondrial DNA was carried out, Six and eight hybrids were found to have S, tuberosum and S, acaule chloroplast genomes, respectively, suggesting that the chloroplast genomes of the somatic hybrids segregated randomly, In addition, two regenerated plants derived from the same callus had different chloroplast genomes, indicating that the segregation of the chloroplast genome occurred before shoot formation from callus, Concerning the mitochondrial genome constitution, 13 hybrids harbored the genome of S, tuberosum type and the others the S, acaule type genome, This mode of segregation is obviously in favor of S, tuberosum mitochondrial genome, Regarding cytoplasmic genome segregation in somatic hybrids, the mitochondrial genome was not associated with the chloroplast genome, For the cytoplasmic genomes of both species, no hybrid was observed with recombinant or heterogeneous genome from both parents, In most of the somatic hybrids, some characters such as plant habit, shape of foliage and shape of tuber, were generally similar to those of S, tuberosum. The high level of resistance to potato virus X (PVX) detected in dihaploid S. acaule and somatic hybrids, suggests that the resistance to PVX is incorporated by fusion with S, acaule.