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Home >> Protoplast Culture, Somatic Hybrdization and Somatic Cybridization >> Somatic Hybridization and Cybridization
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Somatic Hybridization and Cybridization - Conventional sexual crossing in higher plants is a highly regulated system of hybridization wherein sexual crosses are limited to phylogenetically related plant species. This is because of the incompatibility barrier which exists in higher plants that limits expansion of the gene pool.

Also, the classical methods of breeding employed for transfer of beneficial traits from wild species to cultivated varieties are time consuming and require extensive backcrossing with the cultivated variety in order to eliminate most of the genome of the wild species while retaining the useful genes.

Another process, other than the sexual cycle has recently become available for higher plants, which can lead to genetic recombination. This nonconventional genetic procedure involving fusion between isolated somatic protoplasts under in vitro conditions and subsequent development of their product (heterokaryon) to a hybrid plant is known as somatic hybridization.

Ever since the first report on protoplast fusion derived somatic hybrid plants of Nicotiana guauca +- N. langsdorffii by Carlson et al. (1972), somatic hybridization has opened up several possibilities for the parasexual manipulation of plants.

Protoplast technology, which includes the isolation, culture, and fusion of higher plant protoplasts leading to the production of whole plants, is considered one of the most exciting developments in experimental botany in recent years.

Protoplast culture provides excellent opportunities for research on plant improvement, first by exploring genetic variations among the existing crops and then by attempting to transfer the available genetic information from one species to another through fusion of protoplasts isolated from somatic tissues of these crops.

Somatic hybridization involves fusion of two distantly related, to closely related plant protoplasts at intraspecific, interspecific, intergeneric, and interfamily levels, with sub sequent regeneration of hybrid cells into hybrid plants. The term protoplast was first used by Manstein in 1880.

Plastids and mitochondrial genomes (cytoplasmically encoded traits) are inherited maternally in sexual crossings. Through the fusion process the nucleus and cytoplasm of both parents are mixed in the hybrid cell (heterokaryon). This results in various nucleocytoplasmic combinations. Sometimes interactions in the plastome and genome contribute to the formation of cybrids (cytoplasmid hybrids).

Cybrids, in contrast to conventional hybrids, possess a nuclear genome from only one parent but cytoplasmic genes from both parents. The process of protoplast fusion resulting in the development of cybrids is known as cybridization. In cybridization, heterozygosity of extrachromosomal material can be obtained, which has direct application in plant breeding.

Somatic hybridization involves four major steps:
1) isolation of protoplasts,
2) culture of protoplasts,
3) fusion of protoplasts, and
4) identification and selection of hybrid cells and their subsequent regeneration into whole plants.

 
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