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 ba sed on RAPD analysis and cytological observation, In order to identify their cytoplasmic genome constitution, RPLP analysis of chloroplast a nd 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 segreg ated randomly, In addition, two regenerated plants derived from the sa me callus had different chloroplast genomes, indicating that the segre gation of the chloroplast genome occurred before shoot formation from callus, Concerning the mitochondrial genome constitution, 13 hybrids h arbored the genome of S, tuberosum type and the others the S, acaule t ype genome, This mode of segregation is obviously in favor of S, tuber osum 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 h ybrid 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 t hat the resistance to PVX is incorporated by fusion with S, acaule.