What is regeneration
Regeneration is the renewal of germplasm accessions by sowing seeds or planting vegetative materials and harvesting the seeds or plant materials which will posses the same characteristics as the original population.
Germplasm regeneration is the most critical operation in genebank management, because it involves risks to the genetic integrity of germplasm accessions due to selection pressures, out-crossing, mechanical mixtures and other factors. The risk of genetic integrity loss is usually high when regenerating genetically heterogeneous germplasm accessions. Germplasm regeneration is also very expensive.
Why should germplasm be regenerated
Germplasm is regenerated for the following purposes:
1. To increase the quantity of initial seeds or plant materials
In new collections or materials received as donations, the quantity of seeds or plant materials received by the genebank is often insufficient for direct conservation. Seeds or plant materials may also be of poor quality due to low viability or infection. All these materials require regeneration. Newly acquired germplasm of foreign origin may need to be initially regenerated under containment or in an isolation area under the supervision of the national plant quarantine authorities.
2. To replenish seed stocks or plant materials in active and base collections
Accessions that require regeneration are identified through monitoring viability and quantity during storage. Seed stocks or plant materials require regeneration for accessions that have:
- Low viability identified during periodic monitoring;
- Insufficient stocks for distribution or conservation.
Active collections should be regenerated from original seeds or plant materials from a base collection; this is particularly important for out-breeding species to maintain the requested seeds as close as possible to the original sample. Using seeds from an active collection (click here to view the video showing this genebank procedure) for up to three regeneration cycles before returning to the original seeds or plant materials (base collection) is also acceptable (FAO 2013).
Base collections also require regeneration at very frequent intervals and should normally be regenerated using the seed or plant materials from the same sample.
Regeneration is expensive and time consuming, especially for perennial tree species which may not flower until over 20 years after planting, and comes with risks to genetic integrity and loss of material attached. Therefore, it is usual to harvest sufficient seeds to return seeds to the base collection for long term storage and the active collection to meet anticipated distribution needs as well as prepare subsamples for safety duplication from the same regeneration cycle.
How is it done
Each crop is different and requires its own environment and agronomic management during planting, growth and harvesting. Information provided in this section is general but specific regeneration guidelines have been developed for a range of crops and can be accessed by clicking here.
The following are the main factors to consider when regenerating germplasm accessions:
- Suitability of environment (click here to view the video showing this genebank procedure) to minimize natural selection;
- Suitability of site with adequate water and suitable soil type to minimize risk of loss of plants;
- Distance from other fields of the same crop to reduce unintentional geneflow and sources of diseases or pests;
- Adequate numbers of plants to maintain genetic integrity and retain genes in low frequency;
- Special requirements, if any, to break dormancy (click here to view the video showing this genebank procedure) and stimulate germination or promote flowering;
- Correct spacing (click here to view the video showing this genebank procedure) for optimum seed set;
- Breeding system of the plant and need for controlled pollination or isolation during field management;
- Harvesting (click here to view the video showing this genebank procedure) and mixing equal numbers of seeds from all plants to obtain representative samples.
If possible, regenerate germplasm in the ecological region of its origin or one to which it is adapted and likely to flower and produce seeds. Daylength or vernalization are important for some crops and wild species to trigger flowering and seed set. Seek an environment that does not select some genotypes in preference to others in a population to maintain genetic integrity. Examine the biotic environment in the context of prior information about the plants and past experience – an inappropriate biotic environment can be detrimental to the quality of plants, seed or propagation materials and the genetic integrity of an accession.
If no suitable site is found, seek collaboration with an institute that can provide a suitable site or regenerate in a controlled environment such as a greenhouse or growth room. The latter is important to control seed dispersal for wild species and crop relatives that may be considered as arable weeds (click here to view the video showing this genebank procedure).
Meeting special requirements
There may be special requirements for regeneration of accessions with special traits that breeders and researchers use frequently—such as high-yielding, pest-and disease-resistant accessions and genetic stocks — or if there are insufficient seeds (click here to view the video showing this genebank procedure) for safety duplication and repatriation.
When should it be done
It should be done when either the quantity and/or the quality of a particular seed or plant material are not sufficient in a genebank.
The regeneration of accessions that have inadequate quality (low viability) should take priority over that of accessions with inadequate numbers of seeds or planting materials but with high viability.
The regeneration of accessions in base collections should take priority over regenerating those in active collections.
Regeneration guidelines for specific crops
Crop specific regeneration guidelines are available for the following crops:
- Introduction to regeneration guidelines
- Barley (included in guidelines for small-grained cereals)
- Finger millet
- Forage grasses
- Forage legumes
- Major aroids
- Oats (included in guidelines for small-grained cereals)
- Pearl millet
- Pigeon pea
- Sweet potato
- Wheat (included in guidelines for small-grained cereals)
- Wild potato
References and further reading
Crossa J. 1995. Sample size and effective population size in seed regeneration of monoecious plants. In: Engels JMM, Rao RR, editors. Regeneration of seed crops and their wild relatives. Proceedings of a consultation meeting, 4–7 December 1995, ICRISAT, Hyderabad, India. IPGRI, Rome, Italy. pp.140–143.
Crossa J. 1989. Methodologies for estimating the sample size required for genetic conservation of outbreeding crops. Theoretical and Applied Genetics 77: 153-161.
Crossa J, Hernandez CM, Bretting P, Eberhart SA, Taba S. 1993. Practical considerations for maintaining germplasm in maize. Theoretical and Applied Genetics 86: 673–678.
Crossa J, Vencovsky R. 1994. Implications of the variance effective population size on the genetic conservation of monoecious species. Theoretical and Applied Genetics 89:936–942.
Crossa J, Vencovsky R. 1997. Variance effective population size for two-stage sampling of monoecious species. Crop Science 37:14–26.Engels JMM, Visser L, editors. 2003. A guide to effective management of germplasm collections. IPGRI Handbooks for Genebanks No. 6. IPGRI, Rome, Italy. Available in English (1.4 MB) and Spanish (1.5 MB).
FAO. 2013. Genebank standards for plant genetic resources for food and agriculture. Food and Agriculture Organization of the United Nations, Rome. Available in English, Spanish, French, Arabic, Russian and Chinese here.
Rao NK, Hanson J, Dulloo ME, Ghosh K, Nowel D, Larinde M. 2006. Manual of seed handling in genebanks. Handbooks for Genebanks No. 8. Bioversity International, Rome, Italy. Available in English (1.5 MB), Spanish (1.4 MB) and French (1.9 MB).
Sackville Hamilton NR, Chorlton KH. 1997. Regeneration of accessions in seed collections: a decision guide. Handbooks for Genebanks No. 5. IPGRI, Rome, Italy. Available here.
Thormann I, Metz T, Engels JMM. 2004. The Species Compendium (release 1.0; December 2004). [online]. Available from URL: http://www.bioversityinternational.org/scientific_information/information_sources/species_databases/species_compendium.html. Date accessed 30 March 2010
Vencovsky R, Crossa J. 1999. Variance effective population size under mixed self and random mating with applications to genetic conservation of species. Crop Science 39:1282–1294.