. 2006. Somatic hybridization between Solanum tuberosum and S. cardiophyllum. Can. J. Plant Sci. 86: 539-545. The wild diploid Mexican species, Solanum cardiophyllum Lindl. (2n = 2x = 24), is resistant to important potato diseases. However, introgression of resistance to the tetraploid cultivated potato (S. tuberosum L.) (2n = 4x = 48) by conventional crossing is not feasible due to the difference in their endosperm balance number between these species. Somatic hybrids between S. cardiophyllum and S. tuberosum were produced for the first time by electrofusion of protoplasts isolated from young leaves of each parental line. The hybrid nature of the regenerated plants was confirmed based on morphology, chromosome number and DNA species-specific RAPD markers. All the somatic hybrids produced a violet pigmentation on their stems and petioles, which resembled the wild partner. Most of the hybrid plants had 2n = 72 chromosomes and exhibited a morphology intermediate between the two fusion parents, but with a tendency towards cultivated potato. These plants flowered and set fruit when backcrossed with their S. tuberosum fusion parent. Mots clés: Pomme de terre (Solanum tuberosum), S. cardiophyllum, fusion des protoplastes, marqueur RAPD Potatoes (Solanum tuberosum L.) are plagued by many kinds of diseases. Of these diseases, late blight, caused by Phytophthora infestans (Mont.) de Bary, is the most devastating one worldwide. Under cool wet conditions, the pathogen rapidly attacks the leaves, stems and tubers, causing significant reductions in yield and quality. All of the current commercial potato cultivars are highly susceptible to late blight. Surveys have shown that the disease costs potato growers $3 billion annually worldwide . Control of potato late blight is currently achieved through the extensive use of fungicides. Therefore, it is not surprising that seeking a genetic resource with resistant traits to the disease has long attracted potato breeders' attention. For example, the Mexican wild species Solanum demissum Lindl. was reported to be resistant to late blight (Reddick 1930). Unfortunately, the resistance was only effective against certain races of the pathogen (Black and Gallegly 1957). An accession of another Mexican wild species, S. cardiophyllum Lindl., was recently found to possess a high level of resistance to late blight . However, S. cardiophyllum and the cultivated potato, S. tuberosum are reproductively incompatible due to differences in their endosperm balance numbers although they can be crossed with several other diploid Mexican wild species (Chen et al. 2004). Thus, this prevents the exploitation of this valuable germplasm using conventional breeding methods.Protoplast fusion offers an alternative to conventional crossing as it provides a means of circumventing the sexual reproduction barriers and allows the incorporation of desirable traits from wild species into cultivated potatoes. Using somatic hybridization, several resistance genes have been introduced into cultivated potato from wild s...