Interspecific somatic hybridization has been performed in potato breeding experiments to increase plant resistance to biotic and abiotic stress conditions. We analyzed the mitochondrial and plastid genomes as well as 45S ribosomal DNA (45S rDNA), Sc) and their somatic hybrid (StSc) of cultivated potato (S. tuberosum, St), wild potato (S. commersonii). Complex genomic components and structures were identified, such as hybrid forms of 45S rDNA in StSc, unique plastids and recombinant mitotic genomes in Sc. However, the mitogenome exhibits a dynamic multipart structure in both species as well as in somatic hybrid. In St, the mitotic genome is 756,058 bp and consists of 5 subgenomes ranging from 297,014 to 49,171 bp. In Sc, it is 552,103 bp long and consists of two subgenomes of 338,427 and 213,676 bp in length. StSc has a 447,645 bp long mitotic genome with two subgenomes of 398,439 and 49,206 bp in length, respectively. The mitogen structure exhibits dynamic recombination mediated by tandem repeats; however, it contains highly conserved genes across all three species. Of the 35 protein-coding genes in the StSc mitotic genome, 21 were identical for all three species, and 12 and 2 were unique among Sc and St, respectively. Recombinant mitotic genomes likely arise from homologous recombination between two species during somatic hybrid development.
Somatic Cell Hybridization Technology:
- Isolate single cells from selected plants.
- Removal of cell walls of fused cells with enzymes such as pentosidase and cellulose. These enzymes digest the cell wall to expose naked protoplasts.
- Fuse the isolated protoplasts of the selected parents on a special nutrient medium under sterile conditions to obtain hybrid protoplasts. This fusion is induced by the use of polyethylene glycol (PEG) or by brief high voltage currents.
- Hybrid protoplasts are grown on a suitable nutrient medium where they regenerate cell walls and begin to divide to form new plantlets. These plantlets are somatic hybrid.
Advantages of somatic cell hybridization:
Somatic hybridization can occur between species, but sexual hybridization is not possible. These hybrids can actually be used in breeding programs to transfer useful genes into crops, or they can be used as new species. It opens up possibilities for in vitro genetic manipulation of plants to improve crops. Some applications are mentioned below:
- Production of fertile diploids and polyploids from sexually sterile haploids, triploids and aneuploids.
- Recombinant genomes of organelles, such as mitochondria, in somatic hybridsand hybrids may have useful features.
- Somatic hybridization facilitates the successful transfer of some disease resistance genes from one species to another. For example, resistance to diseases such as tmv leaf blight virus and environmental tolerance of pests have been introduced in tomato.
- Some environmental factors such as cold; frost and salt also challenge crops. Genes responsible for tolerance to these factors have been successfully introduced by somatic hybridization, eg, cold tolerance genes in tomato.
- Quality characteristics: Somatic hybrid have also been developed for the production of high nicotine content and low uric acid
. Limitations of somatic cell hybridization:
Plants do not always produce fertile and visible seeds by somatic hybridization. Although protoplast fusion between different species or genera is easy, it is not possible in all cases to produce viable somatic hybrid.
Somatic hybridization between two diploids results in the formation of unfavorable double diploids. This is why haploid protoplasts are recommended in somatic hybridization.