What is genetic diversity?

Original source of germplasm

The original source of conserved germplasm is from either a collecting/gathering event or from a breeding event. The collecting person assigns a collecting number to the original plant material collected during a gathering event. This number is an important descriptor and part of the accession passport descriptors (MCPD) developed and published from IPGRI/FAO. Most germplasm genebanks document this number as part of the accession unit level metadata records. In addition to the germplasm gathered from the wild in a natural habitat, many germplasm accessions originate from a breeding event. Plant material (way back original source gathered from the wild) cultivated by humans in a non-natural habitat is stressed to acquire traits and characters that are useful to humans. The breeding/cultivation process can be traditional in combination with farming and food production where the farmers themselves select the material for the next generation (landraces). Or the cultivation can be through modern plant breeding performed by designated plant breeding companies isolated from the farmer and the food production activity (commercial cultivars). In either case the cultivated germplasm acquire characters and genotypes it is hard to expect the material to acquire in a natural habitat. Germplasm from a breeding event is produced from germplasm originally gathered in the wild (often way back) and the contribution from this material could perhaps be calculated if a complete pedigree is given.

When is a germplasm accession created?

Is the germplasm accession created when the crop (wild relative) is collected in the wild and when the breeder is growing up a new cultivar...? For the landraces and the wild material one could come back and collect again after 10 years and find the same population or landrace, but with new properties acquired... It is assumed here that the collecting/gathering event and the breeding event are the two relevant original sources of germplasm.

Conserved germplasm

Germplasm can be conserved in situ or ex situ. In situ conservation means conservation in the natural habitat in the original location. In situ conservation is often understood to include the traditional farming environment of the landraces. Wild germplasm can also be conserved in the natural habitat in nature reserves and protected areas. This is the more widely understood definition of the term in situ conservation. Germplasm is also conserved ex situ, which means outside the natural habitat. Germplasm from commercial cultivars produced by modern breeding can often only be conserved ex situ, as there is no natural environment available. Ex situ conservation of orthodox seeds (that tolerate drying and freezing) is also more cost effective than in situ conservation. During ex situ conservation the germplasm is not exposed to natural stresses and is often described as freezing evolution. Ex situ conservation more often aim at storing the germplasm as similar to the received sample as possible. The most common methods for ex situ conservation of plant germplasm are seed storage, clonal archives and in vitro tissue culture.

Genebanks

The plant genetic resources community (PGR) is dominated by the genebanks with large collections of plant seeds from the economically valuable crops. Most of the seed collections are conserved as frozen seed samples with accession catalogue numbers unique within the institute. The seeds are regularly tested for viability and rejuvenated if necessary. One of the main activities of the genebanks is the distribution of germplasm to commercial and scientific purpose. If the amount of stored seeds falls below a defined threshold, more seeds are produced by multiplication. Rejuvenation and multiplication is achieved through growing plants in the field and harvesting the seeds of the mature plants (regeneration). Most genebanks maintain a well-documented database of metadata on the stored seed samples (accessions). The seeds samples are also classified to the relevant nomenclature and labeled by a taxonomic name. Most genebanks keep track of the metadata on the original gathering/collecting event and the breeding event. Some genebanks also maintain separate metadata on taxonomic nomenclature units, gathering event units and the breeding event units isolated from the germplasm accession metadata.