Authors: SANDEEP KUMAR BANGARWA* and AMARDEEP KOUR
- Kitto and Janick (1982) first developed the synthetic seed of carrot.
- Many fruit crops are difficult to multiply by conventional propagation methods and improve traditional breeding programmes.
- Among the innovative techniques of micropropagation, the concept of somatic embryogenesis with synthetic seed production or artificial seed technology is very promising.
- Synthetic seeds are defined as artificially encapsulated somatic embryos, shoot buds, cell aggregates, or any other tissue that can be used for sowing as a seed and that possess the ability to convert into a plant under in vitro or ex vitro conditions, and that retain this potential also after storage
- Large scale production of somatic embryos and their encapsulation is referred to as Artificial or synthetic seed production.
- It is an alternative to traditional micro propagation for production and delivery of cloned plantlets.
- Implementation of synthetic seed technology requires manipulation of in vitro culture systems for large-scale production of viable materials, that are able to convert into plants, for encapsulation.
- The synthetic seed technology is designed to combine the advantages of clonal propagation with those of seed propagation and storage.
- The encapsulation technology has been applied to produce synthetic seeds of a number of plant species belonging to angiosperms and gymnosperms.
- The concept of synthetic seeds has been set free from its bonds to somatic embryogenesis, and links the term not only to its use (storage and sowing) and product (plantlet) but also to other techniques of micropropagation like organogenesis and enhanced axillary bud proliferation system.
- Artificial seeds may be produced by one of the two following ways (1) Dessicated (2) Hydrated systems
- The production of synthetic seeds for the first time by Kitto and Janick involved encapsulation of carrot somatic embryos followed by their desiccation.
- In the dessicated system the somatic embryos are first hardened to withstand dessication and then are encapsulated in a suitable coating material to yield desiccated artificial seeds.
- The desiccated synthetic seeds are produced from somatic embryos either naked or encapsulated in polyoxyethylene glycol (Polyox) followed by their desiccation.
- Polyoxyethylene is readily soluble in water and dries to form a thin film, does not support the growth of micro-organisms and is non-toxic to the embryo.
- Desiccation can be achieved either slowly over a period of one or two weeks sequentially using chambers of decreasing relative humidity, or rapidly by unsealing the petri dishes and leaving them on the bench overnight to dry.
- Somatic embryo may be hardened either by treating or coating mature somatic embryos with a suitable polymer followed by drying or treating them with ABA during their maturation phase ABA treatment also improves germination of somatic embryos
- Such types of synseeds are produced only in plant species whose somatic embryos are desiccation tolerant.
- In 1984 Redenbaugh et al. developed a technique for hydrogel encapsulation of individual somatic embryos of alfalfa.
- Since then encapsulation in hydrogel remains to be the most studied method of artificial seed production.
- Hydrated synthetic seeds are produced in those plant species where the somatic embryos are recalcitrant and sensitive to desiccation.
- Hydrated synthetic seeds are produced by encapsulating the somatic embryos in hydrogel capsules.
- Calcium alginate is the most suitable gel.
- Procedure for production of Artificial Seed
- Mixture of (Somatic embryo + 2% sodium alginate)
Somatic embryo + Calcium alginate = Artificial seed / Synthetic seed
- Calcium replace the sodium.
- The beads become hardened as calcium alginate is formed.
- Hydrated seeds (enclosed somatic embryo) are sticky and difficult to handle on a large scale and dry rapidly in the open air. These problems can be resolved by providing a waxy coating over the beads.
- Desiccated somatic embryo and synthetic seed can be stored at low (4 oC) or ultralow (-20 oC) temp. for prolonged periods.
- Encapsulation methods for synthetic seed
B. Automatic encapsulation process
A. Dropping procedure
- Drip 2-3 percent sodium alginate drops from at the tip of the funnel and the somatic embryos are inserted.
- Keep the encapsulated embryos complex in calcium salt for 20 minutes.
- Rinsed the capsules in water and then stored in a air tight container.
- This is the quick method of artificial seed production.
- Alginate solution with embryo is feed from supply tank.
- Alginate capsules were planted in speeding trays using a vaccum seeder.
- The capsules are planted in the field using stanhay planter.
- A hydrophobic coating is required for mechanical handling.
- Table:-Artificial seed production and plant conversion
| In vitro propagules for encapsulation | Crops |
| Somatic embryos | Carrot, Papaya, Alfalfa, Brassica, Mango, Lettuce etc. |
| Auxiliary buds / Adventitious buds | Citrus, Vitis, Pineapple etc. |
| Shoot tips | Apple, Banana, Cardamom etc. |
- Practical implementation of the technology is constrained due to the following main reasons:-
2. Large scale production of high quality somatic embryos is a costly affair.
3. Limited production of viable micropropagules useful in synthetic seed production.
4. Poor germination of synthetic seeds due to lack of supply of nutrients, sufficient oxygen, microbe invasion and mechanical damage of somatic embryos.
5. Lack of dormancy and stress tolerance in somatic embryos that limit the storage of synthetic seeds.
6. Occurrence of somaclonal variation.
7. Improper maturation of the somatic embryos that makes them inefficient for germination and conversion into normal plants.
8. Special skills are required to carry out the work.
- Advantages
2. High efficiency in multiplication.
3. Production of virus and disease free plants.
4. Elimination of the need of edible seeds or tubers for propagation.
5. Propagation of desirable genotypes with genetic uniformity.
6. Fixation of hybrid vigour, eleminate the need of inbred lines to produce F1 hybrids.
7. It can be produced throughout the year.
8. Direct delivery of tissue cultured plants to the field.
9. Preservation of germplasm and convenience in germplasm exchange.
10. Protection of seedlings by encorporating useful chemicals in the encapsulation material
About Author / Additional Info:
I am currently pursuing Ph.D. in Plant Breeding and Genetics from MPUAT-Udaipur (Raj.)