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Let us learn about Micropropagation. After reading this article you will learn about: 1. Meaning of Micropropagation 2. Application of Micropropagation 3. Advantages.
Meaning of Micropropagation:
Tissue culture serves as an alternative to vegetative propagation by conventional methods, such as by rooting of cuttings. This is particularly valuable in the case of difficult-to-root species and those species like the palms which can neither be rooted by cuttings nor grafted because they lack a cambium. Recently, genetically uniform oil palms (Elaeis guineensis) have been produced by tissue culture.
Attempts are being made in the same direction with the coconut palm also. Vegetative propagation through tissue culture is called micro-propagation, because it uses very small quantities of starter material, say, a single cutting or even a few grams of tissue to regenerate hundreds of plants.
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However, seedlings from tissue cultures are relatively more expensive than those produced by other means of vegetative propagation such as cuttings. Therefore, it is applied only to high value species like oil palm where, moreover, other alternative vegetative propagation methods do not exist. For low value species such as Eucalyptus rooted coppice shoot cuttings are still used commercially.
Plants raised from tissue cultures require a longer hardening period before they become fit for transplanting, especially in harsh forest environments. Genetic instability of callus cultures is another drawback. Thus chromosome abnormalities are common in tissue cultures of Gymnosperms which, constitute important components of temperate and arboreal forests.
In recent years, the application of micro-propagation techniques as an alternative means of asexual propagation of important plants has increased the interest of workers in various fields.
The micro-propagation techniques are preferred over the conventional asexual propagation methods due to following reasons:
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(i) In this method only a small amount of tissue is needed as the initial explant for regeneration of millions of clonal plants in a year.
(ii) This method provides a possible alternative method for developing resistance in many species.
(iii) It provides a mean for international exchange of plant materials, hence the problem for introduction of disease can be solved in quarantine.
(iv) Stock can be quickly proliferated in vitro as it is not season dependent.
(v) Valuable germplasm can be stored for a long time.
Application of Micropropagation:
In Horticulture and Forestry:
Regeneration of plantlets in cultured plant cells and tissues has been achieved in many trees of high economic value. Many of the studies are aimed at large scale micro-propagation of important trees yielding fuel, pulp, timber, oil or fruits.
Hence, clonal forestry and horticulture are gaining an increasing recognition as an alternative for tree improvement. However, strategies for transferring cultured plants in vitro to field conditions are based on relatively higher priced horticultural species rather than agricultural and forestry species.
Regeneration of plantlets in cultured tissue has been described by Murashige (1974) into three under-mentioned stages:
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(i) Establishment of explant aseptically.
(ii) Multiplication of propagules by repeated subcultures on a specific nutrient medium.
(iii) Rooting and hardening of plantlets and planting into soil.
Later on Fossard (1987) has described the following four stages of micro-propagation:
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(i) Selection of a suitable explant and inoculation into nutrient medium.
(ii) Multiplication and growth of culture which takes about two months, followed by repeated subcultures.
(iii) Cultures are obtained by changing the medium to planting out.
(iv) This is ‘planting out’ stage where plantlets are aseptically removed from test tube environment to natural and harsh environment. At this stage, roots should be fully functional in potting mix, the soil where plantlets are transplanted.
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However, at planting out stage, the plantlets fail to survive due to sudden change in the environment and invasion by soil microbes. Scientists have suggested that the ‘regenerates’ should be transferred first to green house and then to field.
The humidity should be controlled by covering the plants with transparent polyethylene sheets. This acclimatization requires several weeks which should be followed by potting into sterile peat or soil.
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In recent years, the interest has created in commercialising the in vitro propagation of forest trees. For betterment and improvement of tree plants of high economic value, a breakthrough in forestry research has come with production of artificial seeds in Eucalyptus, and genetic transformation and in vitro regeneration in conifers. Moreover, micro-propagation has been successfully done in many trees.
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Advantages of Micropropagation:
Micro-propagation, an essential component of plant biotechnology, has been proved to be means of producing millions of identical plants by culturing plant tissues or organs under aseptic conditions.
The advantages of micro-propagation over conventional methods, of a sexual reproduction are as follows:
(i) Greater output,
(ii) Economy of time and space,
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(iii) Freedom from seasonal constraints,
(iv) Multiplication under disease-free conditions.
Hence, this technique is ideal for the species where:
(i) Traditional methods of propagation are inadequate to meet the demand for planting material.
(ii) Marked variability exists in the natural population and productivity can be significantly increased by cloning of superior individuals.
(iii) Virus can be eliminated by culturing the shoot meristem, thus pathogen-free stock can be maintained by routine micro-propagation.
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In the modern days, tissue culture has been successfully employed for the multiplication of orchids and many other ornamental plants. In the developed countries, tissue culture is a routine method of multiplication while in developing countries; the techniques are largely used for producing plants for export markets.
The Department of Biotechnology (DBT), Government of India, set up two pilot-scale national facilities for large scale production of elite planting material of forest trees through tissue culture, one at the Tata Energy Research Institute (TERI), New Delhi, and the other at the National Chemical Laboratory (NCL), Pune.
