Somatic Hybridization and Somaclonal Variation

Tissue culture also makes possible two further routes to genetically novel plants that classical, seed-based cross-hybridization (described earlier in this chapter) cannot achieve on its own.

Somatic hybridization (protoplast fusion)

Ordinary sexual hybridization requires the two parent plants to be close enough relatives that their pollen and egg cells can fuse and produce viable, fertile seed -- a requirement that rules out combining useful traits from more distantly related species altogether. Somatic hybridization gets around this barrier by working with body (somatic) cells instead of sex cells. The rigid cellulose cell wall is first digested away enzymatically from cells of each parent plant, leaving behind a naked protoplast (a plant cell bounded only by its cell membrane); protoplasts from the two different parent plants -- which may belong to different species, or even different genera, that could never be crossed sexually -- are then brought together and induced to fuse, most simply using polyethylene glycol or a brief electric pulse, producing a single hybrid cell carrying the combined genetic material of both parents. This hybrid cell is cultured under tissue-culture conditions, first regenerating a new cell wall and dividing into a callus, and eventually regenerating into a complete somatic hybrid plant -- a genuinely new plant type combining traits from two species that ordinary breeding could never have crossed.

Somaclonal variation …