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Plant tissue culture as a novel tool.
i. Anther Culture:
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In vitro gametic embryogenesis has become an efficient means of producing haploids in a growing number of species since the success of Guha and Maheswari (1964) with cultured anthers of Datura.
Success in anther culture and more recently in isolated microspore culture has stimulated interest in this technology for plant breeding and applications in both monocots and dicot species of plants.
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The utility of haploid production in the rapid production of homozygous breeding lines from highly heterozygous parents is well recognized including reduced time requirements per cycle of plant breeding due to immediate phenotypic expression of the recessive traits in haploid derived homozygous plants.
Anther culture undoubtedly offers a unique tool for obtaining haploid plants. Already, a number of economically important crop plants have yielded encouraging results: Aegilops, rice, Brassica hybrid, B. napus, Capsicum annuum, Coffea arabica, Hordeum vulgare, Lycopersicon esculentum, Secale cereale, Solanum melongena, S. tuberosum, Triticum aestivum and Vitis vinifera.
In China the programme of large scale production of haploid plants through anther culture is reported to be progressing well and almost every crop is reported to be under test for obtaining haploids through anther culture.
ii. Somatic Hybridization and Genetic Modifications:
Hybridization, involving both sexual fertilization and a variety of protoplast-protoplast and cytoplast-protoplast fusion have been successfully demonstrated in vitro in a few crop species. Plant protoplasts cultures offer a potential system to achieve somatic hybridization and to create genotypically and cytoplasmically novel hybrids (hybrids and cybrids; see Chapter 30). Plant protoplasts also offer a system for genetic modification to attain the objective of crop improvement.
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This could be possible due to the remarkable property of plant protoplasts for the uptake of macromolecules such as proteins, DNA, ferritin, latex, polystrene, virus, bacteria and even isolated chloroplasts and whole nuclei.
Several investigators have reported interspecific and intergeneric protoplasts fusion in Petunia, Atropa belladonna, Vicia, Glycine, Bromus, carrot, lily, oat x maize, carrot x tobacco, Torenia fournieri x T. flava and Brassica chinensis X B. oleracea. Melchers et al. (1978) reported regeneration of somatic hybrid plants of potato and tomato from fused protoplasts.
iii. Propagation Through Tissue Culture:
Clonal propagation by vegetative methods is a practice followed since man started cultivating plants. The main objective of clonal propagation has been to reproduce plants of selected, desirable qualities uniformly and in bulk. The traditional propagation methods, requires long duration, whereas tissue culture helps in rapid plant multiplication.
A selected examples of clonal multiplication of trees and horticultural plants are as follows: Aegle marmelos, Tecomella undulata, Musa sp., citrus, peach, prunus, Malus, Prunica granatum etc. Improved cultivars developed by biotechnological methods are then clonally multiplied to replace inferior cultivated varieties, e.g. As in Mentha arvensis, m. Piperata, m. Spicata and several other aromatic plants.
iv. Production of Disease Free Plants:
A majority of the commercial crop plants propagated vegetatively through tubers, bulbs, cuttings and grafting which may contain systemic bacteria, fungi and viruses. Such infections affect the yield and quality of the crop, unless it is readily detected and the plants made free from infection.
The traditional method of eliminating viruses by heat treatment is applicable only to a few varieties. Generally, the apical meristem of a virus diseased plant contains very little virus, or is altogether free. Hence, plants obtained from apical meristem are usually free of viruses.
There are a number of instances where meristem and/or floral bud culture has resulted in elimination of the virus and restoration of healthy plants, e.g., Solanum tuberosum, Saccharum officinarum, Petunia spp Allium sativum, Ananas comosus, Brassica oleracea, Musa sp and Pisum sativum.
