What is In Vitro Germplasm Conservation?

Due to rapidly growing human population, plant and agriculture scientists have produced many new varieties to feed the population. Because the traditional and wild varieties cannot meet the demand of increasing population.

But the traditional varieties need to be preserved because they are important for future breeding programmes. However, there is danger of erosion of genetic resources due to extensive use of newly introduced varieties.

In 1972, conservation of habitats rich in genetic diversity was recommended in the UN conference. Then an International Board for Plant Genetic Resource (IBPGR) was established.

This board has objectives to provide necessary support for collection, conservation and utilisation of plant genetic resources from anywhere in the world.

India has also established the National Bureau of Plant Genetic Resources (NBPGR), Pusa Campus, and New Delhi for similar objectives.

1. Modes of Conservation :

It has been estimated that about 9,000 wild plant species are threatened. Global climatic changes also affect the natural plant habitats, thereby contributing to rapid changes in agricultural strategies. There are two modes of conservation of plant species as given below:

(a) In situ Conservation:

Since 1980, in situ conservation has received high priority in the world conservation strategy. The method of conservation is to preserve land races with wild relatives in which genetic diversity exists.

(b) Ex situ Conservation:

It is the chief mode of conservation of genetic resources including both cultivated and wild ones. Under suitable conditions genetic resources are conserved for a long term as gene bank. Such gene bank is of two types:

(i) In vivo Gene Bank:

Generally plant seeds, vegetative propagules are used for storage for long time. The whole plants are preserved. This type of conservation strategy is called in vivo gene bank. In this approach, conservation method of storage is used for preservation of plant genetic resources,

There are several limitations in germplasm conservation done by conventional methods. These includes: seed dormancy, seed- borne disease, short-life of seeds, high inputs of cost and labour and non-applicability to vegetatively propagated crops (e.g. Dioscorea, Ipomoea, potato, etc.).

(ii) In vitro Gene Bank:

This approach includes the conservation of genetic resources by non-conventional methods. In this approach explants are grown on medium. The genetic resources are conserved in the form of in vitro maintained plant cells, tissues and organs. By doing so the germplasm is made available to breeders so that new and improved varieties could be developed.

2. Methods of Preservation :

There are several methods for preservation of plant materials. A few of them are briefly discussed herewith.

(a) Free Preservation or Cryopreservation:

Cryopreservation (Latin Kuos means frost) means storage of materials at very low temperature. Plant cells and tissue cultures are brought to zero state of metabolism by subjecting them to ultra-low temperature i.e. -I96°C.

It is done by using liquid nitrogen which provides approximately -496°C. Cryo-protectants (e.g. glycerol, proline, mannitol, dimethylsulfoxide, sorbitol) are also used to protect the viable cells from the damage during freezing and thawing (to become unfrozen or warm).

Cryo-protectants minimise the harmful action of electrolyte concentration that results after conservation of water into ice. Applying cryopreservation plant cell and tissues can be cultured for indefinite time.

(b) Cold Storage:

Germplasm of some plants (in the form of shoot tips, nodal or meristem explant culture) are stored at low and non-freezing temperature (1-9°C). At low temperature, growth of plant material is slow down but not completely stopped as in cryo-preservation. In cold storage there is no risk of cold injuries.

Cold storage is successful for in vitro derived shoots/plants of fruit species. About 800 cultivars of grape plants have been stored for over 15 years at 9°C by yearly transfer to fresh medium.

(c) Low-pressure and Low-oxygen Storage:

For conservation of cultured plant materials low-pressure storage (LPS) and low-oxygen storage (LOS) have been developed. There are alternative methods of cryopreservation and cold storage.

In LPS, the atmospheric pressure surrounding the tissue cultures is reduced, while in LOS inert gases (especially nitrogen) are combined with oxygen to create low oxygen pressure.