Authors: SANDEEP KUMAR BANGARWA
- Germplasm:- The sum total of hereditary material or genes present in a species is known as the germplasm of that species.
- Germplasm conservation: - It is defined as the maintenance of germplasm of a species by insitu conservation, field collection, seed banks, slow growth cultures, cryopreservation and DNA banks.
- Genetic erosion:- The gradual loss of variability in the cultivated forms and in their wild relatives is referred to as genetic erosion.
- Cryopreservation i.e. non-lethal storage of plant tissue at ultra-low temperature usually that of liquid nitrogen (-196°C) is the only available method for long-term conservation of germplasm of problem species. The major advantage of storage of biological material at such a low temperature is that both metabolic processes and biological deterioration are considerably slowed or even halted .
- The very objective of germplasm conservation is to preserve the genetic diversity of a particular plant or genetic stock for its use at an time in future.
- Organizations associated with germplasm
A. International level
IPGRI – International Plant Genetic Resources Institute.
B. National level
1. NBPGR – National Bureau of Plant Genetic Resources:- It deals with quarantine inspection of Agri. And Horti. Crops.
2. FRI – Forest Research Institute :- It deals with quarantine inspection of forest trees.
3. BSI – Botanical Survey of India:- It deals with quarantine inspection of medicinal and other plant species.
- Methods of germplasm conservation
2. Ex situ conservation
1. In situ conservation
- On site conservation.
- Conservation of germplasm under natural habitat is referred to as in situ conservation.
- This is achieved by protecting this area from human interference.
- Ex. Natural park, Biosphere reserve and Gene sanctuary etc.
- It is considered as a high priority germplasm preservation programmes.
- A gene sanctuary not only conserves the existing genetic diversity present in the population, it also allows evolution to continue. As a result, new alleles and new gene combinations would appear with time.
- A gene sanctuary is best located within the centre of origin of crop species concerned, preferably covering the microcenter with in the centre of origin.
- Gene sanctuary is a very good method of in situ conservation.
- This is a costly method of germplasm conservation.
- In situ conservation has practical limitations associated with shrinking of natural habitats, urbanization, industrialization and changing government policies.
- Off site conservation.
- Conservation of germplasm away from the area of its natural habitat.
- Ex. Seed gene banks, Plants or Field bank, Cell or Organ bank, DNA gene bank, herbal gardens, in vitro repositories etc.
- All gene banks are DNA banks.
- Cheap method of germplasm conservation.
- Handling of germplasm is easy.
- It is possible to preserve entire genetic diversity of a crop species at one place.
- Preservation in the form of seed is the most common and easy method, relatively safe, requires minimum space and easy to maintain.
- Seeds on the basis of their storability into two major groups-
1. Orthodox seeds
2. Recalcitrant seeds
- Seeds of this type can be dried to low moisture content of 5% and stored at a low temperature without losing their viability are known as orthodox seeds.
- Most of the crop seeds belong to this category.
- Ex. Sunflower , Wheat, Rice, Chickpea, Cotton etc.
- The viability of this group of seeds drops drastically if their moisture content is reduced below 12-30%.
- Ex. Seeds of many forest and fruit trees, and of several tropically crops like Cocoa, coffee, rubber, mango, jackfruit, etc. belong to this group.
- Such seeds present considerable difficulties in storage. They require in situ conservation.
1. Base collection / Principal collection:-
- These collections are used only when the germplasm of other sources is not available for use in crop improvement.
- It stored:-
- Temp = -18 to 20o c
- Moisture = 5%
- Time period= up to 100 years.(long storage)
- This category of germplasm is actively utilized in breeding programmers.
- It stored:-
- Temp = 0o c
- Moisture = 8%
- Time period= 8-10 years.(Medium term storage)
- This collection of frequently is actively utilized by breeder in crop improvement programmes.
- It stored:-
- Temp = 5-10o c
- Moisture = 8-10%
- Time period= 3 to 5 years.(Short term storage)
- In vitro conservation strategies can be divided into two categories – 1. In vitro conservation under slow growth (IVAG- in vitro active gene bank) 2. Cryopreservation (IVBG- in vitro base gene bank).
- In vitro slow growth has been used at various national and international research centers (CIP-International Potato Center, IITA-International Institute of Tropical Agriculture, NBPGR- National Bureau of Plant Genetic Resources) for conservation of vegetatively propagated germplasm.
- This method can satisfy only short to medium term conservation strategy but management of large collections through this method is problematic.
- Moreover, collections maintained under in vitro slow growth are prone to losses due to contamination and genetic instability.
- Cryopreservation is the storage of viable biological material at ultra-low temperatures, which provides a means for the long-term stable storage of plant germplasm.
- Cryopreservation is a safe and cost-effective technique for preservation of germplasm and management of in vitro produced material for biotechnological application .
- Cryopreservation is an alternative choice for a long-term conservation of germplasm.
- Cryopreservation at -196ºC in liquid nitrogen (LN) has been considered to be an ideal tool which offers long-term storage capability, maximal stability of phenotypic and genotypic behaviour of stored germplasm, and minimal storage space and maintenance requirements.
- Majority of crops that were worked out for cryopreservation belong to the temperate region, which has inherent capacity to tolerate low temperature.
- Cryopreservation methods are relatively less investigated with tropical species, though rich diversity of crop germplasm is predominant in this region.
- Pretreatments were crucial for the survival and regeneration of plant tissues after cryopreservation.
- Since at present, cryoprotectants alone cannot provide enough protection to untreated cells or tissues for high rates of survival, pretreatment techniques are needed to condition the cells to withstand the stresses imposed by freezing at ultralow temperatures.
- The genetic stability of cryopreserved plants can be assessed by analyzing them at phenotypic and molecular level analysis with a range of techniques.
- DNA-based markers have been routinely used for monitoring genetic stability of these species on cryopreservation.
- Glycerol and DMSO have been widely used and observed to be the most effective cryopreservative, on optimization with species.
- The optimum concentration of these cryopreservative agents depend upon the species and cell type and the highest concentration the plant can tolerate.
About Author / Additional Info:
I am currently pursuing Ph.D. in Plant Breeding and Genetics from MPUAT-Udaipur (Raj.)