Development of an effective protoplast fusion system for production of new potatoes with disease and insect resistance using Mexican wild potato species as gene pools

Somatic hybridization through protoplast fusion is an important alternative approach for overcoming sexual incompatibility between diploid Solanum species and cultivated potatoes. However, compared with other potato species, methods for protoplast isolation and plant generation for several Mexican wild diploid potato species are not well established. In this study, a systematic procedure was designed for the isolation of a large number of high-quality protoplasts from various Mexican wild species that carry high levels of disease (late blight) and insect [Colorado potato beetle (CPB)] resistance. Using this procedure, an effective potato protoplast fusion system was developed to produce new somatic hybrids between two Mexican, one Argentina wild species, and cultivated potato clones. Regenerated plants and somatic hybrids were obtained at a high frequency from the protoplasts of the diploid wild species and their fused cells with S. tuberosum. Morphological, cytological and molecular marker analyses demonstrated that somatic hybrids were successfully obtained from the cell fusion of S. tuberosum and the diploid species S. pinnatisectum, S. cardiophyllum, and S. chacoense. Assessment of disease and insect reactions demonstrated that several of the protoplast-derived clones and somatic hybrids showed a higher level of resistance to both late blight and CPB than was found in S. tuberosum, confirming that the protoplast system is a powerful tool in potato breeding programs for the development of disease and insect resistance. This new fusion system provides breeders with opportunities to transfer disease and insect resistance genes from Mexican wild species into cultivated potato. Key words: Somatic hybrid, protoplast, fusion, potato, Solanum, late blight, disease resistance, Colorado potato beetle insect resistance