5. Cybrids or cytoplasmic hybrids:

Sexual hybridization involves fusion of the nuclear genes of both the parents but somatic hybrids involves even cytoplasm from both the parental species in hybrid obtained by protoplast fusion. However, in another case somatic hybrids containing nuclear genome of one parent but cytoplasm from both the parents, are termed as cybrids. The approach is time consuming and require several years of crossing plants provides an opportunity to study interparental mitochondrial, chloroplast fusion giving rise to plants with novel genomes.

5.1. Methods to produce cybrids: They are produced in variable frequencies in normal protoplast fusion experiments due to one of the following methods:

1.  Fusion of normal protoplast with an enucleated protoplast. The enucleated protoplast can be produced by high speed centrifugation (20,000-40,000xg) for 60 min with 5-50% percoll.

2.  Fusion between a normal protoplast and another protoplast with a non-viable nucleus or suppressed nucleus.

3.  Elimination of one of the nuclei after heterokaryons formation.

4.  Selective elimination of chromosomes at a later stage.

5.  Irradiating (with X-rays or gamma rays) the protoplasts of one species prior to fusion in order to inactivate their nuclei.

6.  By preparing enucleate protoplasts (cytoplasts) of one species and fusing them with normal protoplasts of the other species.

Cybrids provide the following unique opportunities: (i) transfer of plasmogenes of one species into the nuclear background of another species in a single generation, and even in (ii) sexually incompatible combinations, (iii) recovery of recombinants between the parental mitochondrial or chloroplast DNAs (genomes), and (iv) production of a wide variety of combinations of the parental and recombinant chloroplasts with the parental or recombinant mitochondria.