❥ preservation for germplasm conservation. Cryopreservation of vegetative propagated and recalcitrant seed species.

preservation for germplasm conservation. Cryopreservation of vegetative propagated and recalcitrant seed species. 

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1. Introduction

Germplasm conservation is the systematic preservation of genetic resources for present and future use. Many economically important plants are vegetatively propagated (banana, potato, sugarcane, cassava) or produce recalcitrant seeds (cocoa, rubber, coconut), which cannot be conserved by conventional seed storage.

Cryopreservation offers a safe, long-term and genetically stable method for conserving such germplasm by storing living tissues at –196°C in liquid nitrogen (LN).

2. Need for Preservation of Germplasm

Prevention of genetic erosion

Conservation of elite, endangered and rare species

Backup of field and in-vitro collections

Support to crop improvement and breeding

Preservation of pathogen-free planting material

Conservation of plants with non-orthodox seeds

3. Limitations of Conventional Storage Methods

Seed Banks

Not suitable for vegetatively propagated crops

Ineffective for recalcitrant seeds (desiccation-sensitive)

Field Gene Banks

High cost and space requirement

Vulnerable to pests, diseases, climate change

Risk of genetic drift

In-vitro Slow Growth Storage

Limited duration

Genotype-specific responses

Risk of somaclonal variation

4. Cryopreservation – Concept and Principle

Definition

Cryopreservation is the storage of viable plant material at ultra-low temperature (–196°C) in liquid nitrogen, where all metabolic and biochemical activities are completely arrested.

Principle

Cellular dehydration

Prevention of ice crystal formation

Vitrification (glass-like state)

Use of cryoprotectants

5. Cryopreservation of Vegetatively Propagated Crops

Examples

Banana

Potato

Cassava

Sugarcane

Yam

Garlic

Suitable Explants

Shoot tips (apical meristems)

Axillary buds

Somatic embryos

In-vitro nodal segments

Reasons for Cryopreservation

No true seeds or sterile plants

High heterozygosity

Risk of disease accumulation

Need for clonal fidelity

Cryopreservation Methods Used

1. Vitrification

Treatment with plant vitrification solutions (PVS2, PVS3)

Rapid cooling in LN

No ice crystal formation

2. Droplet Vitrification

Explants placed in droplets on aluminum foil

Ultra-rapid cooling

High survival and regeneration rates

3. Encapsulation–Dehydration

Explants encapsulated in calcium alginate beads

Partial dehydration

Direct immersion in LN

Advantages

Maintains genetic stability

Long-term conservation

Minimal space requirement

Protection from contamination

6. Cryopreservation of Recalcitrant Seed Species

Recalcitrant Seeds – Definition

Seeds that lose viability when dried below a critical moisture content and cannot tolerate low temperature storage.

Examples

Cocoa (Theobroma cacao)

Rubber (Hevea brasiliensis)

Coconut

Mango

Jackfruit

Problems in Conservation

High moisture content

Desiccation sensitivity

Rapid loss of viability

Short storage life

Materials Used for Cryopreservation

Excised embryos

Embryonic axes

Plumules

Shoot apices from seedlings

Cryopreservation Techniques

1. Excised Embryo Cryopreservation

Removal of seed coat and endosperm

Partial dehydration

Freezing in LN

2. Vitrification of Embryonic Axes

Treatment with cryoprotectants

Rapid freezing and thawing

3. Encapsulation–Vitrification

Combines protection of alginate beads and vitrification

Advantages for Recalcitrant Seeds

Overcomes desiccation sensitivity

Enables long-term storage

Preserves rare and endangered species

7. Cryoprotectants in Germplasm

Cryopreservation

Penetrating Cryoprotectants

DMSO

Glycerol

Ethylene glycol

Non-penetrating Cryoprotectants

Sucrose

Mannitol

Sorbitol

PEG

Function:

Protect membranes

Reduce ice crystal formation

Stabilize cellular structures

8. Thawing and Recovery

Rapid thawing at 35–40°C

Removal of cryoprotectants

Culture on recovery medium

Gradual acclimatization

9. Advantages of Cryopreservation for Germplasm Conservation

Long-term and secure storage

High genetic fidelity

Minimal maintenance

Suitable for vegetatively propagated and recalcitrant seed species

Effective backup system

10. Limitations

High initial cost

Need for skilled personnel

Species-specific protocols

Post-thaw regeneration challenges

11. Applications

Conservation of endangered plant species

Preservation of elite clones

Germplasm exchange and quarantine safety

Conservation of transgenic plants

Support to biodiversity conservation programs

12. Conclusion

Cryopreservation plays a crucial role in germplasm conservation, especially for vegetatively propagated crops and recalcitrant seed species that cannot be stored by conventional methods. By arresting metabolic activity at ultra-low temperatures, cryopreservation ensures long-term genetic stability, safety and sustainability of plant genetic resources, making it an indispensable tool in modern plant biotechnology and conservation biology.

50 MCQs – Germplasm Conservation & Cryopreservation

1. Germplasm conservation mainly aims to

A. Increase fertilizer use

B. Preserve genetic diversity

C. Increase mutation rate

D. Eliminate wild species

✔ Answer: B

2. Vegetatively propagated crops are difficult to conserve because

A. They produce many seeds

B. Seeds show dormancy

C. Seeds do not breed true

D. They lack genetic variation

✔ Answer: C

3. Which crop is vegetatively propagated?

A. Wheat

B. Rice

C. Banana

D. Maize

✔ Answer: C

4. Recalcitrant seeds are characterized by

A. Low moisture content

B. High desiccation tolerance

C. Sensitivity to drying

D. Long storage life

✔ Answer: C

5. Which is a recalcitrant seed species?

A. Wheat

B. Rice

C. Cocoa

D. Barley

✔ Answer: C

6. The ideal method for long-term conservation of vegetative crops is

A. Field gene bank

B. Seed bank

C. Cryopreservation

D. Cold storage

✔ Answer: C

7. Cryopreservation temperature is

A. 0°C

B. –20°C

C. –80°C

D. –196°C

✔ Answer: D

8. Liquid nitrogen is used because it

A. Enhances growth

B. Prevents contamination

C. Arrests metabolic activity

D. Improves regeneration

✔ Answer: C

9. Suitable explant for cryopreservation of vegetative crops is

A. Mature leaf

B. Root hair

C. Shoot tip

D. Senescent tissue

✔ Answer: C

10. Major injury during freezing is due to

A. Cell elongation

B. Ice crystal formation

C. Chlorophyll loss

D. Protein synthesis

✔ Answer: B

11. Cryoprotectants are used to

A. Kill cells

B. Promote cell division

C. Prevent freezing damage

D. Increase temperature

✔ Answer: C

12. Which is a penetrating cryoprotectant?

A. Sucrose

B. Mannitol

C. PEG

D. DMSO

✔ Answer: D

13. A non-penetrating cryoprotectant is

A. Glycerol

B. Ethylene glycol

C. Sucrose

D. DMSO

✔ Answer: C

14. Vitrification results in

A. Ice crystal formation

B. Glassy state of cytoplasm

C. Cell rupture

D. Rapid cell division

✔ Answer: B

15. PVS2 solution is used in

A. Slow freezing

B. Seed storage

C. Vitrification

D. Cold storage

✔ Answer: C

16. Droplet vitrification involves

A. Slow cooling

B. Use of aluminum foil strips

C. High temperature storage

D. No cryoprotectant

✔ Answer: B

17. Encapsulation–dehydration uses

A. Agar

B. Alginate beads

C. Charcoal

D. Gelatin

✔ Answer: B

18. Best explant for recalcitrant seed cryopreservation is

A. Whole seed

B. Mature endosperm

C. Embryonic axis

D. Seed coat

✔ Answer: C

19. Recalcitrant seeds cannot be stored in seed banks because

A. They are dormant

B. They require light

C. They are desiccation-sensitive

D. They are too small

✔ Answer: C

20. Example of recalcitrant seed crop is

A. Sorghum

B. Maize

C. Rubber

D. Mustard

✔ Answer: C

21. Metabolic activity during cryostorage is

A. Increased

B. Reduced

C. Completely arrested

D. Irregular

✔ Answer: C

22. Thawing of cryopreserved samples should be

A. Slow

B. Very slow

C. Rapid

D. At room temperature

✔ Answer: C

23. Preferred thawing temperature is

A. 5–10°C

B. 20–25°C

C. 35–40°C

D. 60°C

✔ Answer: C

24. Cryopreservation ensures genetic stability because

A. Cells divide actively

B. DNA replication stops

C. Growth hormones are added

D. High temperature is used

✔ Answer: B

25. Major advantage of cryopreservation is

A. Frequent subculturing

B. Unlimited storage duration

C. High mutation rate

D. Large space requirement

✔ Answer: B

26. Field gene banks are risky due to

A. Genetic stability

B. Climate and pest hazards

C. Easy maintenance

D. Low cost

✔ Answer: B

27. Cryopreservation is most suitable for

A. Annual seed crops

B. Vegetatively propagated crops

C. Weed species

D. Fast-growing plants

✔ Answer: B

28. Coconut seeds are classified as

A. Orthodox

B. Recalcitrant

C. Intermediate

D. Dormant

✔ Answer: B

29. Cryopreservation overcomes problems of

A. Dormancy

B. Seed viability loss

C. Desiccation sensitivity

D. Germination failure

✔ Answer: C

30. Encapsulation–vitrification is

A. Seed drying

B. Field storage method

C. Combination of alginate beads and vitrification

D. Cold storage

✔ Answer: C

31. Example of vegetatively propagated crop conserved by cryopreservation

A. Wheat

B. Rice

C. Potato

D. Sorghum

✔ Answer: C

32. Which structure is ideal for clonal fidelity?

A. Callus

B. Leaf disc

C. Shoot meristem

D. Root tissue

✔ Answer: C

33. Cryopreservation minimizes somaclonal variation because

A. Cells are actively growing

B. Cells remain dormant

C. DNA mutates rapidly

D. Hormones are removed

✔ Answer: B

34. Which cryoprotectant stabilizes membranes?

A. Sucrose

B. Auxin

C. Cytokinin

D. Gibberellin

✔ Answer: A

35. Rubber (Hevea brasiliensis) seeds are

A. Orthodox

B. Recalcitrant

C. Dormant

D. Hard-coated

✔ Answer: B

36. Major limitation of cryopreservation is

A. Genetic instability

B. Need for skilled expertise

C. High contamination

D. Frequent transfer

✔ Answer: B

37. Cryopreserved materials are stored in

A. Deep freezers

B. Refrigerators

C. Liquid nitrogen tanks

D. Incubators

✔ Answer: C

38. Excised embryo technique is mainly used for

A. Orthodox seeds

B. Recalcitrant seeds

C. Vegetative propagation

D. Callus culture

✔ Answer: B

39. PEG acts as

A. Growth regulator

B. Nutrient

C. Cryoprotectant

D. Antibiotic

✔ Answer: C

40. Cryopreservation provides backup to

A. Seed banks only

B. Field gene banks

C. In-vitro cultures

D. All conservation systems

✔ Answer: D

41. Banana germplasm is conserved mainly through

A. Seed storage

B. Field banks only

C. Cryopreservation of shoot tips

D. Pollen storage

✔ Answer: C

42. High moisture content in recalcitrant seeds causes

A. Dormancy

B. Desiccation tolerance

C. Storage problems

D. Rapid germination

✔ Answer: C

43. Cryopreservation is a form of

A. Medium-term storage

B. Short-term storage

C. Long-term storage

D. Temporary storage

✔ Answer: C

44. Ideal cooling rate in vitrification is

A. Very slow

B. Slow

C. Ultra-rapid

D. Moderate

✔ Answer: C

45. Genetic erosion refers to

A. Increase in diversity

B. Loss of genetic diversity

C. Mutation induction

D. Hybridization

✔ Answer: B

46. Somatic embryos are useful in cryopreservation because

A. They are highly differentiated

B. They regenerate efficiently

C. They lack genetic material

D. They are non-viable

✔ Answer: B

47. Cryopreservation is essential for

A. Hybrid seed production

B. Conservation of endangered species

C. Fertilizer production

D. Weed control

✔ Answer: B

48. Which factor is most critical for success of cryopreservation?

A. High light intensity

B. Proper dehydration

C. High temperature

D. Rapid growth

✔ Answer: B

49. Mango seeds are classified as

A. Orthodox

B. Recalcitrant

C. Dormant

D. Intermediate

✔ Answer: B

50. Germplasm conservation ultimately supports

A. Genetic erosion

B. Sustainable agriculture

C. Monoculture

D. Habitat loss

✔ Answer: B

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