Practical Applications of Somatic Hybridization and Cybridization
1. Means of Genetic Recombination in Asexual or Sterile Plants:
Somatic cell fusion appears to be the only approach through which two different parental genomes can be recombined among plants that cannot reproduce sexually. Similarly, protoplast of sexually sterile plants can be fused to produce fertile diploids and polyploids. There are several reports describing the amphidiploid and hexamploid plants produced from fusion of haploid protoplasts of tobacco. Protoplasts isolated from dihaploid potato clones have been fused with isolated protoplasts of Solanum brevidens to produce hybrids of practical breeding value. Haploid protoplasts from an anther- derived callus of rice cultivars upon fusion also produce fertile diploid and triploid hybrids.
2. Overcoming Barriers of Sexual Incompatibility:
In plant breeding programmes, sexual crossing at Interspecific and Intergeneric levels often fails to produce hybrids due to incompatibility barriers, which can be overcome by somatic cell fusion.
Schieder ( 1978) obtained amphidiploid Datura innoxia (+) D. discolor and D. innoxia (+) D. stramonium, by fusing their diploid mesophyll protoplast. These hybrids cannot be produced conventionally and they are industrially important because show heterosis and higher (20-25%) scopolamine content than in the parental forms.
Nicotiana repanda, N.nesophila and N.stockoni are resistant to number of disease but are not sexually crossable with N. tabacum (Tobacco). However, fertile hybrids have been reported in combination N. tabacum ( +) N nesophila and N. tabacum (+) N. Stockoni by protoplast fusion. Somatic hybridisation of dihaploid and tetraploid potato protoplast with isolated protoplasts of Solanum brevidens, S. phureja and S. penelliii resulted in the synthesis of fertile, partially amphidiploid plants possessing important agricultural traits, e.g. resistance to potato leaf virus V and Erwinia soft rot.
Similarly, somatic hybrids between Brassica napus and B. nigra have been produced which is resistant to Phoma Lingam.
3. Cytoplasm Transfer:
Power et.al. (1975) fused mesophyll protoplasts of Petunia with cultured cell protoplast of the crown gall of Parthenocissus and selected a line which contained the chromosomes of only Parthenocissus but exhibited some of the cytoplasmic properties of Petunia for some time. This was followed by direct application of cybridisation in agricultural biotechnology by transfer of cytoplasmic male sterility from Nicotiana techne to N. tabacum, N. tabacum to N.sylvestris and Petunia hybrida to P. axillaries. Besides cytoplasmic male sterility, the genophore of the cytoplasm codes for number of practially important traits, such as the rate of photosynthesis, low or high temperature tolerance, and resistance to disease or herbicides.
In genus Brassica, two desirable traits coded by cytoplasmic genes have been genetically manipulated through Interspecific cybridisation between different species of Brassica. These traits include cytoplasmic male sterility ( cms) and resistance herbicide. Similarly, cytoplasmic genes coding for Atrazine and cms have been transferred into cabbage, rice and potato.