Plant genetic resources and gene banks
Plant genetic resources explained: gene pools, genetic erosion, ex situ and in situ conservation, seed storage, core collections, NBPGR and ITPGRFA.
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Every new variety starts from genetic variation. Disease resistance in wheat, submergence tolerance in rice, dwarfing genes and quality traits all came from older varieties, landraces or wild relatives that someone collected and kept. Plant genetic resources (PGR), also called germplasm, are the total genetic material of crops and their relatives that has actual or potential value for food and agriculture.
That diversity is being lost. When farmers switch to a few modern varieties, landraces disappear. Forests are cleared, grazing intensifies and the climate changes, and wild relatives go with them. This loss is called genetic erosion. FAO estimates that about 75% of crop genetic diversity was lost from farmers' fields during the twentieth century. Gene banks and conservation programmes exist to stop this loss and make the material available to breeders.
What counts as germplasm
- Landraces: traditional farmer varieties, which are variable, locally adapted and often stress-tolerant.
- Obsolete and modern varieties, including released cultivars that are no longer grown.
- Breeding lines, mutants and genetic stocks.
- Crop wild relatives: wild species related to crops, which are rich in resistance genes.
- Weedy forms that cross with crops.
Gene pools
Harlan and de Wet (1971) grouped a crop's relatives by how easily they can be crossed with it:
| Gene pool | Crossability | Example for wheat |
|---|---|---|
| Primary (GP1) | Crosses easily; hybrids are fertile | Other bread wheats and landraces, T. aestivum subspecies |
| Secondary (GP2) | Crosses with some difficulty; hybrids partly fertile | Aegilops tauschii and tetraploid wheats |
| Tertiary (GP3) | Crosses only with special techniques such as embryo rescue or bridging species | Rye, Thinopyrum and other wild grasses |
Genes from the tertiary pool can be valuable. The 1BL.1RS rye translocation, which gave many wheats rust resistance and higher yield, came from rye.
Ex situ conservation
Ex situ conservation keeps material outside its natural habitat.
Seed gene banks
Seed banks are the main method for most crops. Seeds are dried, sealed and stored:
- Base collections are kept for the long term at about −18 °C with seed moisture of 3–7%. Seeds can stay viable for decades, sometimes more than a century.
- Active collections are kept for the medium term at about 0–10 °C, and seed is distributed from them.
- Viability is tested periodically. A sample is regenerated when germination falls below about 85% of its initial value.
This works only for orthodox seeds, which tolerate drying and freezing: cereals, pulses and most vegetables. Recalcitrant seeds die when dried, so they cannot be stored this way. Examples are mango, jackfruit, cocoa, rubber, coconut and litchi.
Other ex situ methods
- Field gene banks keep living plant collections for recalcitrant and clonally propagated crops, such as mango, banana, tea, coconut and sugarcane. They are costly and exposed to pests, disease and weather.
- In vitro conservation keeps tissue cultures under slow-growth conditions. It is used for potato, banana and cassava.
- Cryopreservation stores embryos, shoot tips, pollen or seeds in liquid nitrogen at −196 °C. All metabolism stops, so storage can be indefinite.
- DNA and pollen banks store only genetic material.
Gene banks of note
- India's National Bureau of Plant Genetic Resources (NBPGR), New Delhi, set up in 1976, runs the National Gene Bank. It holds more than 450,000 accessions, one of the world's largest collections. NBPGR also handles plant quarantine for imported germplasm.
- The CGIAR centres hold international collections: IRRI for rice, CIMMYT for maize and wheat, and ICRISAT for sorghum, pearl millet, chickpea, pigeonpea and groundnut.
- The Svalbard Global Seed Vault in Norway, opened in 2008, is a "backup of backups". It holds over a million duplicate samples from gene banks worldwide.
In situ conservation
In situ conservation keeps populations in the places where they evolved, so they continue adapting to climate, pests and farmers' needs.
- Protected areas and gene sanctuaries protect wild relatives. India's first gene sanctuary, for wild Citrus, is in the Garo Hills of Meghalaya, within the Nokrek Biosphere Reserve.
- On-farm conservation supports farmers who keep growing landraces, through seed fairs, community seed banks, recognition and market incentives for traditional varieties.
Making collections usable
Large collections are hard to evaluate in full. Frankel and Brown (1984) proposed the core collection: a subset of about 10% of a collection that captures at least 70% of its genetic diversity.
A mini core for chickpea
ICRISAT's chickpea collection held about 17,000 accessions. A core collection of about 1,950 accessions was selected, and from it a mini core of 211 accessions, about 1% of the whole, was chosen to represent the diversity. Screening those 211 lines for drought, salinity and disease is quick enough to do in replicated trials, and promising sources can then be traced back into the full collection.
Germplasm is described by passport data (where and when it was collected), characterisation (stable traits such as plant type) and evaluation (traits such as yield and stress response).
Policy and access
- The Convention on Biological Diversity (1992) recognised national sovereignty over genetic resources. The Nagoya Protocol (2010) set rules for access and benefit sharing.
- The International Treaty on Plant Genetic Resources for Food and Agriculture (ITPGRFA, adopted 2001) set up a Multilateral System for 64 major crops and forages. Material is exchanged under a Standard Material Transfer Agreement (SMTA), and benefits go to a shared fund.
- In India, the Protection of Plant Varieties and Farmers' Rights Act, 2001 recognises farmers as conservers and breeders. The Biological Diversity Act, 2002 regulates access to biological resources.
Key points
- PGR includes landraces, varieties, breeding lines and wild relatives. Genetic erosion is the loss of this diversity.
- Gene pools: primary (crosses easily), secondary (with difficulty), tertiary (needs special techniques).
- Ex situ methods are seed banks (base collections at −18 °C, 3–7% moisture), field gene banks, in vitro banks and cryopreservation (−196 °C). In situ methods are protected areas, gene sanctuaries and on-farm conservation.
- Orthodox seeds can be dried and frozen; recalcitrant seeds (mango, cocoa, coconut) cannot.
- A core collection is about 10% of a collection and holds at least 70% of its diversity.
- NBPGR (1976) is India's national gene bank. Svalbard is the global backup. ITPGRFA's Multilateral System uses the SMTA.
What the exams ask
- Define genetic erosion and explain the gene pool concept.
- Compare ex situ and in situ conservation.
- Distinguish orthodox and recalcitrant seeds, with examples.
- Define core and mini core collections.
- Name India's gene sanctuary and the role of NBPGR, ITPGRFA and the PPV&FR Act.
Described in general terms: the kind of examination, not a past paper. Laisha never reproduces exam questions.
Questions people ask
Why not just store everything in Svalbard?
Svalbard holds safety duplicates only; it does not distribute seed or regenerate it. Working gene banks are still needed to test, multiply, characterise and supply material. Svalbard is insurance against loss, as when ICARDA retrieved its duplicates after the Syrian conflict forced it to leave Aleppo.
Can farmers get seed from the national gene bank?
Gene banks mainly supply researchers and breeders, usually in small quantities, under material transfer agreements. Community seed banks and farmer networks are better sources for farmers. Some gene banks now return landraces to the communities they came from.
Why are wild relatives so important now?
Climate change is creating heat, drought and new pest pressures that modern varieties have never met. Wild relatives evolved under harsh conditions and carry tolerance genes that are missing from the cultivated gene pool. A large global project has collected crop wild relatives specifically for climate adaptation.
Sources
- FAO. The Second Report on the State of the World's Plant Genetic Resources for Food and Agriculture. FAO, Rome, 2010.
- Harlan, J. R. and de Wet, J. M. J. "Toward a rational classification of cultivated plants." Taxon 20, 509–517 (1971).
- Frankel, O. H. and Brown, A. H. D. "Plant genetic resources today: a critical appraisal." In Holden, J. H. W. and Williams, J. T. (eds) Crop Genetic Resources: Conservation and Evaluation. Allen and Unwin, 1984.
- Upadhyaya, H. D. and Ortiz, R. "A mini core subset for capturing diversity and promoting utilization of chickpea genetic resources in crop improvement." Theoretical and Applied Genetics 102, 1292–1298 (2001).
- FAO. Genebank Standards for Plant Genetic Resources for Food and Agriculture. FAO, Rome, 2014.
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