Some examples signifying contribution of somatic hybridization in genetic improvement are given below:
Example # 1. Cereals:
Rice:
Plants have been regenerated from isolated protoplasts of Japonica and Indica types of rice, thereby eliminating one of the major barriers to in vitro genetic manipulation of this cereal crop.
Attempts have been made to multiply the conventional breeding barrier by interspecific fusion of rice with four different species including Oryza brachyantha, O. eichingeri, O. officinalis and O. perrieri. The productions of fertile interspecific diploid rice hybrid plants have been possible through somatic hybridization.
Example # 2. Oil Seeds:
(i) Brassica Sp:
Moricandia arvensis resistant to Albugo Candida, Alternaria brassicae and Plasmodiophora brassicae was crossed with Brassica napus using somatic hybridization technology to make B. napus disease resistant. The methodology used to enhance the level of industrially useful fatty acid in Brassica napus was based on exploitation of somatic hybridization using wild crucifer germplasm as fusion partner.
(ii) Helianthus Annuus:
The technique of somatic hybridization has been tried to overcome the sexual incompatibility barriers.
Example # 3. Vegetables:
(i) Lycopersicon Esculentum:
The first somatic hybridization produced with tomato was the tomato + potato hybrid. The wild species have served as important source of agronomic traits via sexual process. Many sexual crosses between tomato and wild species that were troublesome to perform due to bilateral and unilateral incompatibility were overcome by somatic hybridization.
(ii) Solarium Melangena:
Sexual crossing barriers in egg plants have limit the transfer of agronomically important traits such as insect resistance and disease resistance, from related wild species. Using somatic hybridization desired properties have been incorporated. Symmetric somatic hybridization between S. melangena and S. khasianum, S. aethiopicum etc., has been produced.
(iii) Solanum Tuberosum:
Potato protoclones resistant to several pathogens like Altemaria, Phytophthora, Fusarium have been reported. S. brevidens is used as a fusion partner and hybrids expressing late blight and potato leaf roll virus resistance gene are reported. Frost tolerance and cold hardening traits have been transferred from S. commersonii to S. tuberosum by somatic hybridization. Both interspecific (S. tuberosum + S. brevidens) and intergeneric (S. tuberosum + Nicotiana tobaccum) somatic hybrids have been obtained.
Example # 4. Fruit:
(i) Citrus Sp.:
Somatic hybridization aids in citrus breeding programmes providing an opportunity to overcome sexual incompatibility and to increase the variability of cytoplasmic genome which is maternally, transmitted in sexual cross. It has resulted in production of intergeneric somatic hybrid plants between citrus and related genera. Functional mature fruit bearing citrus trees have been regenerated from protoplast fusion.
(ii) Cucumis Melo:
Cucurbits suffer economic loss due to different diseases. Resistance could not be transferred to melon by sexual crossing due to crossing barriers. Hence, asymmetric protoplast fusion using a melon and cucumber presents a way to transfer genes.
(iii) Prunus Sp.:
Somatic hybrids of Prunus spinosa and Prunus cerasifera, and hexaploid somatic hybrid have been produced.
Example # 5. Ornamentals:
(i) Rosa Hybrida:
The sexual barriers hampering the production of new cultivars have been overcome by somatic cell technologies through genetic recombination involving sexually incompatible genotype.
(ii) Gentiana Sp.:
Gentiana is an important ornamental plant in Japan. Its breeding is possible by intra- and interspecific crosses using only two species – G. triflora and G. scabra. The genetic base of common Gentiana cultivars, therefore, is rather restricted. Somatic hybridization can help improve the genetic base of ornamental plants.
Example # 6. Others:
(i) Nicotiana Sp.:
In order to overcome sterility of sexual and somatic hybrid, asymmetric hybridization helps produce two asymmetric somatic hybrids with TMV resistance and female fertility properties. This enabled them to be back crossed to tobacco.
(ii) Medicago Sativa:
Flowering somatic hybrids are produced between sexually compatible species, M. sativa and M. falcata. There are at least 20 reports on plant regeneration from protoplasts of 9 Medicago species, involving 14 reports on M. sativa cultivars (lucerne, alfalfa). A large number of lucerne cultivars, breeding lines and clones have been identified capable of regeneration from callus tissue. Regeneration of plants was possible through protoplasts isolated from leaves, cotyledons, roots and suspension cells.
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