Micropropagation: Definition, Stages, Techniques, Applications and Advantages

Table of Contents

• Introduction to Micropropagation
• Stages of Micropropagation
• Types of Micropropagation Techniques
• Applications of Micropropagation
• Advantages of Micropropagation
• Limitation of Micropropagation
• References

Introduction to Micropropagation

• Micropropagation is a technique for the rapid vegetative propagation of plants under in vitro conditions.
• It involves growing and multiplying plant tissues under controlled environmental conditions, including:
• High light intensity
• Controlled temperature
• A defined nutrient medium
• Micropropagation has been successfully applied to a large number of commercially important vegetatively propagated plant species.
• Plants can be propagated through two major methods:
• Sexual reproduction: Propagation through the formation and germination of seeds.
• Asexual reproduction: Propagation through the multiplication of vegetative plant parts rather than through seeds.
• Asexual propagation is the only practical in vivo method for certain plant species that do not produce viable seeds.
• Examples of plants commonly propagated vegetatively because of the absence or lack of viable seeds include banana, grape, fig, and chrysanthemum.
• Micropropagation provides a controlled in vitro approach to rapidly multiply plants, making it particularly valuable for the commercial propagation of vegetatively reproduced crops.

Stages of Micropropagation

• Micropropagation is a complex, multistep process that is traditionally divided into three main stages: Stage I, Stage II, and Stage III.
• For a more comprehensive description, some protocols and authors include an additional Stage 0 before culture initiation and Stage IV after plant development.

Stage 0: Selection and Preparation of Stock Plants

• Stage 0 is the preparatory phase of micropropagation and involves the selection and growth of healthy stock plants.
• Stock plants are maintained under controlled environmental conditions, generally for approximately 3 months, before explants are collected.
• Proper preparation of stock plants helps provide suitable, healthy explants for culture initiation.

Stage I: Culture Initiation and Establishment

• Stage I involves the initiation and establishment of plant tissue culture on a suitable nutrient medium.
• Selection of an appropriate explant is an important factor for successful culture establishment.
• Commonly used explants include:
• Plant organs
• Shoot tips
• Axillary buds
• The selected explant is surface sterilized and thoroughly washed before being introduced into the culture medium.
• The objective of this stage is to establish a clean, viable, and actively growing culture.

Stage II: Shoot Multiplication

• Stage II is the major multiplication phase of micropropagation, during which explants are cultured on a defined nutrient medium to produce multiple plant structures.
• It primarily involves:
• Rapid multiplication of shoots, or
• Rapid formation of embryos from the explant, depending on the plant species and culture system.
• Cultures are generally maintained in a controlled growth chamber at approximately 20–24°C.
• A light intensity of about 2,000–4,000 lux is commonly used.
• The cultures are typically exposed to a photoperiod of approximately 16 hours of light per day.

Stage III: Root Development

• Stage III involves the development of roots from the multiplied shoots.
• Shoots are transferred to a suitable medium that promotes rapid root formation and development.
• In some cases, shoots may be transferred directly to soil or another rooting substrate for root development.
• In vitro rooting is generally preferred when handling a large number of plant species because it allows rooting to occur under controlled conditions.

Stage IV: Establishment of Plantlets

• Stage IV involves transferring rooted plantlets from laboratory conditions to soil or another suitable growing substrate.
• Plantlets produced during Stage III are gradually established under greenhouse or other controlled environmental conditions.
• This stage is important for successful acclimatization and establishment of in vitro-derived plants in the external environment.
• For some plant species, Stage III may be omitted. In such cases, unrooted shoots produced during Stage II are directly transferred to pots containing a suitable compost or growing mixture, where rooting and further development occur.

Types of Micropropagation Techniques

Micropropagation techniques can be classified into three major types according to the method by which new plants or plant structures are produced:

1. Propagation from Shoots

• This method involves the multiplication of existing shoots, typically using a culture medium supplemented with cytokinins.
• Commonly used cytokinins include:
• Benzyladenine (BA)
• Kinetin
• The cytokinin promotes the development and multiplication of shoots from suitable explants.
• The resulting shoots generally require a separate rooting phase before they can be established as complete plants.
• Indole-3-acetic acid (IAA) and naphthaleneacetic acid (NAA) are among the auxins that may be used to promote root development.

2. Multiple Shoot Differentiation from Callus

• In this approach, plant tissues first undergo dedifferentiation, resulting in the formation of callus tissue.
• The callus is subsequently induced to differentiate and produce multiple shoots.
• Auxins, such as indole-3-acetic acid (IAA), can be used to regulate differentiation and development.
• The regenerated shoots require a rooting phase, which may involve the use of auxins such as IAA or NAA.

3. Embryo Differentiation from Callus

• In this method, embryos are differentiated from callus tissue under suitable in vitro culture conditions.
• These embryos can subsequently develop into complete plants.
• Because the process involves a dedifferentiated callus phase, there is a possibility of genetic variation among regenerated plants.

Preferred Micropropagation Method

• Shoot propagation is currently the most widely preferred approach among these methods.
• The main reason is that propagation through pre-existing shoots generally avoids the prolonged dedifferentiated callus phase.
• In contrast, methods involving callus formation can increase the possibility of genetic variation (somaclonal variation) because of the dedifferentiated state of the tissue.
• Therefore, direct shoot multiplication is often preferred when genetic uniformity of the propagated plants is important.

Applications of Micropropagation

• Commercial plant propagation: Micropropagation is widely used for the large-scale production of fruit, ornamental, forestry, and other commercially important plants.
• Mass production of elite varieties: Selected plants with desirable characteristics can be rapidly multiplied to produce large quantities of uniform planting material.
• Production of disease-free planting material: Meristem culture is applied to produce pathogen-free or disease-free stocks, particularly for vegetatively propagated crops.
• Horticulture and floriculture: The technique is extensively applied for the rapid multiplication of ornamental and floricultural plants, including the production of vigorous and uniform plants.
• Fruit crop propagation: Micropropagation allows the rapid, year-round multiplication of important fruit crops and selected cultivars.
• Forestry: It can be used for the rapid multiplication of economically valuable tree species and selected superior plants.
• Conservation of endangered and rare plants: Micropropagation serves as a tool for ex situ conservation, multiplication, and maintenance of threatened plant species.
• Germplasm conservation: In vitro culture systems can be used to maintain valuable plant genetic resources and support long-term conservation programs.
• International exchange of plant material: Micropropagated plant material can be used for the exchange and distribution of germplasm between countries, while appropriate quarantine and phytosanitary procedures are followed.
• Seed production: Micropropagation can support the production of planting material for certain crops where high genetic uniformity and conservation of desirable genetic characteristics are important.
• Production of phytopharmaceuticals: In vitro plant culture and micropropagation can support the production of plant-derived pharmaceutical compounds and phytopharmaceuticals.
• Production of valuable biochemicals: Controlled plant tissue culture systems can provide an alternative approach for producing specific plant-derived biochemical compounds in controlled quantities.
• Plant biotechnology and research: Micropropagation is an important component of plant tissue culture and biotechnology research, providing material for studies involving plant regeneration, genetic conservation, and the production of valuable plant metabolites.

Advantages of Micropropagation

• Rapid mass propagation: A small amount of plant tissue can be used to produce millions of clones within a year, whereas conventional propagation would require considerably more time to produce an equivalent number of plants.
• Efficient use of space: Large numbers of plants can be maintained in relatively small spaces, making micropropagation highly efficient for plant production and conservation.
• Rapid multiplication of selected varieties: A desirable plant variety can be multiplied in large quantities within a short period, and the time required for developing new varieties may be reduced by approximately 50%.
• Propagation of difficult-to-propagate species: Micropropagation provides an alternative for plant species that are difficult or resistant to conventional bulk propagation methods.
• Production of disease-free plants: Meristem tip culture can be used to produce planting material free from many systemic diseases and pathogens.
• Year-round propagation: In vitro cultures can be maintained and multiplied throughout the year, independent of seasonal limitations.
• Conservation of endangered species: The technique allows valuable, rare, or endangered plants to be multiplied and maintained in controlled conditions.
• Germplasm conservation: Micropropagation can support the storage and conservation of plant genetic resources in relatively small areas.
• Improved plant vigor and yield: Micropropagated plants can contribute to increased yield and improved vigor, particularly in commercially important floriculture species.
• Facilitated movement of plant material: In vitro plant material can facilitate the rapid international exchange of plant germplasm while reducing the risk of introducing diseases, subject to applicable phytosanitary and quarantine requirements.
• High multiplication rate: A large number of genetically similar plants can be generated from a relatively small amount of starting material, making the technique particularly useful for commercial plant production.

Limitation of Micropropagation

• High labor requirements: Micropropagation is a labor-intensive technique because several steps, including explant preparation, sterilization, culture transfer, subculturing, rooting, and acclimatization, often require careful manual handling.
• Limited commercial scalability: The high labor requirement can increase production costs and limit the commercial application of micropropagation, particularly when large numbers of plants need to be produced.
• Need for automation: Automation of tissue culture procedures can reduce manual labor, improve production efficiency, and help make large-scale commercial micropropagation more economically feasible.

References

• https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/micropropagation
• http://www.biologydiscussion.com/biotechnology/clonal-propagation/micro-propagation-technique-factors-applications-and-disadvantages/10732
• https://link.springer.com/chapter/10.1007/978-81-322-2283-5_16
• http://irrecenvhort.ifas.ufl.edu/plant-prop-glossary/09-tissue-culture/01-types/04-tctypes-micropropagation.html
• https://www.researchgate.net/publication/268494390_Plant_Micropropagation