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 sp ecies not crossable with the cultivated potato, were fused with either dihaploid or tetraploid S. tuberosum Protoplasts were aggregated by m eans of alternating current (AC) or polyethylene glycol (PEG), and ele ctrofused with three direct current (DC) pulses. The treatments with P EG/DC generally resulted in very low heterofusion frequency and protop last viability. On the other hand, AC/DC fusion conditions were optimi zed by increasing the fusion density of protoplasts and adding CaCl2 t o fusion medium. When a density of 4.8 x 10(5) protoplasts ml-1 was us ed in the fusion medium containing 0.2 mM Ca++, AC/DC treated protopla sts showed heterofusion frequencies and plating efficiencies of about 10 and 3%, respectively. Fast growing calli from AC/DC fusion experime nts were further cultured for regeneration. Fifty-seven plants were re generated and cloned in vitro as shoot cultures. Compared to parents t hey showed heterotic vigor and could be identified as hybrids, based o n isozyme analysis.