Somatic hybridization

 

What is somatic hybridization? How are the protoplast fusion and somatic hybridization advantageous over traditional sexual hybridization? Find the importance of protoplast fusion and somatic hybridization. 

Somatic hybridization:-

       Somatic hybridization is a technique of fusing protoplast from two contrasting genotypes for production of hybrid or cybrids which contain various mixtures of nuclear acid and/or cytoplasmic genomes, respectively.

Protoplast fusion and somatic hybridization advantageous over traditional sexual hybridization:-

       In protoplast technology, from any two genotypically different plant protoplasts are isolated from the somatic cell and are experimentally fused to obtain parasexual hybrid protoplast. Isolation of protoplast and in vitro fusion are two techniques developed in tissue culture.

Diagram

       These are advantageous over the traditional sexual hybridization. Traditional sexual hybridization is carried out by plant breeders to develop improved variety of present day crops. It may be intravarietal, intervarietal or intergeneric. The advantages of somatic hybridization are well established.

       Sexual hybridization is a time consuming process and includes various steps, such as selection of parent, their evaluation, heritability, emasculation, pollination, rising of F₁ plants and their multiplication. Very often sexual hybridization results in the production of inferior variety instead of hybrid vigor. More over F₁ plant raised through hybridization may be sterile. Improvement of crop plant through sexual hybridization requires at least 5-8 years.

       On the contrary such limitation can be overcome through protoplast fusion and somatic hybridization. In case of distant hybridization there is failure of the fusion between opposite nuclei. In case of somatic hybridization isolated protoplasts are fused in vitro using chemofusogen as for example PEG. The fused product may be either a hybrid or a cybrid. In both cases new cell wall may be regenerated and new plant may be developed.

Importance of protoplast fusion and somatic hybridization:-

       Protoplast fusion and somatic hybridization opened a new avenue in plant science. It is now a well known fact that the somatic hybridization in plant can be used in the improvement of medicinally and economically important plants. The importance of somatic hybridization and protoplast fusion are as follows-

(i) Distant hybrid production:-

       By this process, production novel interspecific and intergeneric crosses between plants that are difficult or impossible to hybridize conventionally. In other words it includes the formation of somatic hybrid between two species, which are sexually incompatible. Thus protoplast fusion provides a method of combining the defined genome of different genera and species, which have the potential of overcome sexual incompatibility barrier between plants. Several plants have been developed through protoplast fusion and somatic hybridization. Some of them are Nicotiana gloca, Solanum tuberosum, Lycopersicon esculentum etc.

(ii) Production of new genetic variation:-

       In recent years it has been emphasize that plant tissue culture appears to be a rich source of genetic variation. Such genetic variation can be enhanced by protoplast cloning. This undoubtly leads to the production of new genetic variation.

(iii) Gene transfer:-

       By protoplast fusion, it is possible to transfer some useful genes, such as disease resistant, N₂ fixation, protein quality, drought resistant etc. from one species to another.

(iv) Production of autotetraploid:-

       Somatic hybridization can be used as an alternative to obtain tetraploids and if this is unsuccessful, cholchicine treatment can be used.

(v) Hybrid vigor production:-

       Hybrid vigor is well known in sexual hybridization and it has been suggested that somatic hybridization may produce even great hybrid vigor.

(vi) Production of cybrid couple:-

       The cytoplasmic mix obtain from protoplast fusion is novel with the opportunity for the production of cybrid couple opportunity for the formation of mitochondrial recombinants. Mitochondria can regenerate or recombine their DNAs to form a new type of mitochondria.

(vii) Sterile protoplast become fertile:-

       Protoplast of sexual sterile,i.e. haploid, triploid, aneuploid etc. plants can be fused to produce fertile diploid and polyploidy during protoplast culture.

(viii) Hybrid production of juvenile plant:-

       Hybridization becomes possible between plants that are still in the juvenile phase by protoplast culture.

(ix) Production of heterozygous line:-

       It make possible to production of heterozygous line within a single species that normally could only be propagated by vegetative means, e.g. potato and other tuber and root crops.

(x) Chloroplast transplantation:-

       In this method non mutant chloroplast is incorporated in the cytoplasm of a plant during protoplast culture. Then the4 whole plant was regenerated. This may lead to improvement of plants for efficient photosynthesis.

(xi) Justification of newly synthesized cell:-

       Studies of fusion product can give information about compatibility or incompatibility of the nuclei or cytoplasm.

(xii) Improvement of crop:-

       In case of vegetatively reproducing plant the genetic variation can be induced through protoplast fusion of two species, variety or two different genera. In case of sugar cane, w2hich is vegetative. The production of somatic hybrid between different varieties which may be highly beneficial to the sugar cane industry.