Germplasm Activity – Conservation
Conservation refers to protection of genetic diversity of crop plants from genetic erosion. There are two important methods of germplasm conservation or preservation viz. 1) In situ conservation, and 2) Ex situ conservation. These are described below:
1) In – situ Conservation:
Conservation of germplasm under natural habitat is referred to as in situ conservation. It requires establishment of natural or biosphere reserved national parks or protection of endangered areas or species. In this method of conservation, the wild species and the complete natural or semi natural ecosystem are preserved together. This method of preservation has following main disadvantages.
1. Each protected are will cover only very small portion of total diversity of a crop species, hence several areas will have to be conserved for a single species.
2. The management of such areas also poses several problems.
3. This is a costly method of germplasm conservation.
2) Ex-Situ Conservation:
It refers to preservation of germplasm in gene bombs. This is the most practical method of germplasm conservation. This method has following three advantages:
1. It is possible to preserve entire genetic diversity of a crop species at one place.
2. Handling of germplasm is also easy.
3. This is a cheap method of germplasm conservation.
The germplasm is conserved either 1) In the form of seed. Or 2) In the form of meristem cultures. Preservation in the form of seed is most common and easy method. Seed conservation is relatively safe, requires minimum space (except coconut, etc) and easy to maintain .Glass, tin or plastic containers are used for preservation and storage of seeds. The seeds can be conserved under long term (50 to 100 years), medium term (10-15 years) and short term ( 3-5 years) storage condition. Roberts (1973) has classified seeds into two groups for storage purpose, viz. 1) orthodox and 2) Recalcitrant.
1. Orthodox:
Seeds which can be dried to low moisture content and stored at low temperature without losing their viability are known as orthodox seeds. This group includes seeds of corn, wheat, rice, carrot, beets, papaya, pepper, chickpea, lentil, soybean, cotton, sunflower, various beans, egg plant and all the Brassicas. These seeds can be dried and stored at low temperatures for long periods of time.
2. Recalcitrant:
Seeds which show very drastic loss in viability with a degree in moisture content below 12 to 13% are known as recalcitrant seeds. This group includes cocoa, coconut, mango, tea, coffee, and rubber, jackfruit, and oil palm seeds. Such seeds cannot be conserved in seed banks and therefore, require in situ conservation. Crop species with recalcitrant seeds are conserved in field gene banks which are simply areas of land in which collections of growing plants are assembled.
For conservation of meristem cultures, meristem cultures, meristem or shoot tip banks are established. Conservation of genetic stocks by meristem cultures has several advantages as given below:
1. Exact genotype can be conserved indefinitely free from virus or other pathogens and without loss of genetic integrity.
2. It is advantages for vegetatively propagated crops like potato, sweet potato, cassava, etc, because seed production in these crops is poor.
3. Vegetatively propagated material can be saved from natural disasters or pathogen attack.
4. Long regeneration cycle can be envisaged from meristem cultures.
5. Perennial plants which take 10-20 years to produce seeds can be preserved any time by meristem cultures.
6. Regeneration of meristem is extremely easy.
7. Plant species having recalcitrant seeds can be easily conserved by meristem cultures.