PRODUCTION OF SOMATIC HYBRIDS BETWEEN FROST TOLERANT SOLANUM-COMMERSONII AND SOLANUM-TUBEROSUM - PROTOPLAST FUSION, REGENERATION AND ISOZYME ANALYSIS

Mesophyll protoplasts of Solanum commersonii, a frost tolerant wild species not crossable with the cultivated potato, were fused with either dihaploid or tetraploid S. tuberosum Protoplasts were aggregated by means of alternating current (AC) or polyethylene glycol (PEG), and electrofused with three direct current (DC) pulses. The treatments with PEG/DC generally resulted in very low heterofusion frequency and protoplast viability. On the other hand, AC/DC fusion conditions were optimized by increasing the fusion density of protoplasts and adding CaCl2 to fusion medium. When a density of 4.8 x 10(5) protoplasts ml-1 was used in the fusion medium containing 0.2 mM Ca++, AC/DC treated protoplasts showed heterofusion frequencies and plating efficiencies of about 10 and 3%, respectively. Fast growing calli from AC/DC fusion experiments were further cultured for regeneration. Fifty-seven plants were regenerated and cloned in vitro as shoot cultures. Compared to parents they showed heterotic vigor and could be identified as hybrids, based on isozyme analysis.