Micro propagation – Techniques and Applications
Micropropagation is the practice of rapidly multiplying reserve plant material to produce a large number of progeny plants, using modern methods of plant tissue culture. Micropropagation is used to multiply noble plants, such as those that have been genetically modified or raised through conventional plant breeding methods. It is also used to provide a sufficient number of seedlings to plant from a common plant that does not produce seeds, or does not respond well to vegetative reproduction.
Micropropagation is a complicated process and comprises mainly 4 stages (I, II, III and IV).
This is the initial step in micro-propagation, and involves the selection and growth of common plants for about 3 months under controlled conditions.
Stage I – Establishment:
In this stage, the initiation and establishment of the culture is achieved in a suitable medium. The selection of appropriate explants is important. The most commonly used explants are organs, shoot tips and axillary shoots. The explant selected is surface sterilized and washed prior to use.
Stage II – Multiplication:
At this stage, the main activity of micro propagation occurs in a defined culture medium. Phase II mainly involves the multiplication of shoots or the rapid formation of explant embryos.
Stage III – Rooting:
This stage involves the transfer of shoots to a medium for rapid development in shoots. Sometimes sprouts are planted directly on the ground to develop roots. In vitro rooting of shoots is preferred while simultaneously handling a large number of species.
Stage IV – Acclimatization:
This stage involves the establishment of seedlings in the soil. This is done by transferring seedlings from stage III of the laboratory to the environment of the greenhouse. For some plant species, stage III is omitted, and nonrooted shoots of stage II are planted in pots or in a suitable compost mix.
Factors Affecting Micro-propagation:
For success in clonal propagation in vitro (micro-propagation), optimization of several factors is necessary.
- Genotype of the plant:
Selection of the correct genotype of plant species (by screening) is necessary to improve micropropagation. In general, plants with a vigorous germination and branching ability are more suitable for micro-propagation.
- Physiological status of explants:
The explants (plant materials) of the most recently produced parts of plants are more effective than those of the older regions. A good knowledge of the process of natural propagation of donor plants, with special reference to the stage of growth and seasonal influence, will be useful in the selection of explants.
- Culture media:
Conventional plant tissue culture media are suitable for micropropagation during stage I and stage II. However, for stage III, certain modifications are essential. The addition of growth regulators (auxins and cytokinins) and alterations in mineral composition is essential. This depends largely on the type of crop.Cultural environment:
The photosynthetic pigment in cultured tissues absorbs light and, therefore, influences micropropagation. Variations in daytime lighting also effect micropropagation. In general, a lighting of 16 hours of day and 8 hours of night is suitable for the proliferation of shoots.
The majority of micropropagation culture necessitates optimum temperature around 25 °C. However, there are some exceptions.
- Suitable alternative to traditional methods
- High prevalence of plants
- The production of disease-free plants
- Seed production in some crops
- Cost effective process
- Automated micro propagation
- Very small size explants can be used
- Only practical method of multiplying genetically modified cells or cells after protoplast fusion.
- Ease in keeping, packing and transport of material multiplied by micropropagation