PRODUCTION OF SOMATIC HYBRIDS BETWEEN FROST-TOLERANT SOLANUM-COMMERSONII AND SOLANUM-TUBEROSUM - CHARACTERIZATION OF HYBRID PLANTS

Somatic fusion of mesophyll protoplasts was used to produce hybrids be tween the frost-tolerant species Solanum commersonii (2n = 2x = 24) an d dihaploid S. tuberosum (2n = 2x = 24). This is a sexually incompatib le combination due to the difference in EBN (Endosperm Balance Number, Johnston et al. 1980). Species with different EBNs as a rule are sexu ally incompatible. Fifty-seven hybrids were analysed for variation in chromosome number, morphological traits, fertility and frost tolerance . About 70% of the hybrids were tetraploid, and 30% hexaploid. Chlorop last counts in stomatal guard cells revealed a low frequency of cytoch imeras. The frequency of aneuploids was relatively higher at the hexap loid level (hypohexaploids) than at the tetraploid level (hypotetraplo ids). The somatic hybrids were much more vigorous than the parents, an d showed an intermediate phenotype for several morphological traits an d moderate to profuse flowering. Hexaploid hybrid clones were less vig orous and had a lower degree of flowering than the tetraploid hybrid c lones. All of the hybrids were female fertile but male sterile except for one, which was fully fertile and self-compatible. Many seeds were produced on the latter clone by selfing and on the male-sterile clones by crossing. The somatic hybrid plants showed an introgression of gen es for frost tolerance and an adaptability to cold from S. commersonii . Therefore, the use of these somatic hybrids in breeding for and in g enetic research on frost tolerance and cold-hardening is suggested.