Cybridization in Potato

Abstract

Due to the economical importance of potato and the relative ease of potato protoplast manipulations, these as well as other Solanum protoplasts were among the first to serve in studies aimed at regenerating plants from either non- fused or fused protoplasts (e.g., Melchers et al. 1978; and see reviews of Shepard et al. 1983; Miller and Lipschutz 1984; Bajaj 1987; Carlberg et al. 1987; Grun et al. 1987, as well as other chapters in this volume). In this chapter, studies of cybridization in which at least one of the fusion partners were protoplasts of potato or of another Solanum species are described, and included are intrageneric protoplast fusions in Solanum as well as fusions between protoplasts of Solanum with protoplasts of Lycopersicon. The term cybrid in our discussions requires definition. In a strict sense, a cybrid contains the nuclear genome of one species and organelle genomes (i.e., the plastome of chloroplasts and the chondriome of mitochondria) of another species. Such alloplasmic plants were rarely produced by protoplast fusion. They were produced by plant breeders in species that have a strict maternal inheritance of chloroplasts and mitochondria: the organelle donor served as seed parent and was pollinated with the nuclear donor; then the progenies were backcrossed many times with pollen of the nuclear donor. The breeder’s purpose was commonly to obtain cytoplasmic male sterility (CMS). CMS is very useful for the production of commercial F1 hybrid varieties because it negates the need for manual emasculation of the seed parent. Such CMS lines became desirable also in potato when, several years ago, True Potato Seed (TPS), rather than Seed Tubers, were found to be a favorable propagation material in certain areas. TPS do not transmit viral diseases and can be supplied annually at relatively low cost to the farmers. Hybrid TPS were found to yield good potato crops, especially in countries with long potato-cultivation seasons. Following the availability of protoplast-to-plant systems, the production of cybrids could be facilitated. Instead of many sexual generations, a single fusion procedure could result in cybrids (e.g., Zelcer et al. 1978; Aviv et al. 1980). Moreover, by sexual hybridization of species with maternal transmission of organelles (common in crop plants) the whole plasmone (both the plastome and the chondriome) was transferred together, while after protoplast fusion sorting- out of organelles takes place and either or both the chloroplasts and the mitochondria of an alien species could be combined with a given nuclear genome. In addition, when fused protoplast contain mitochondria of two species, the chondriomes may exchange DNA fragments, resulting in fusion derivatives having “novel” chondriomes.KeywordsCytoplasmic Male SterilityNuclear GenomeSomatic HybridProtoplast FusionFusion PartnerThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.