|Author: ||K.W. Richards|
The mandate for any plant genebank is to conserve and provide quality germplasm with relevant information for use in crop variety development and plant genetic studies.
Even under optimal ex situ storage conditions, viability declines and genetic diversity is lost.
Thus, the monitoring of viability and timely regeneration of seeds must be a priority activity of all genebanks.
Two factors have a major impact on regeneration needs and capacity.
These are storage conditions and the capacity to handle cross-pollinated species.
Poor seed storage conditions result in the rapid loss of seed viability and the need for frequent regeneration.
Repeated regeneration can result in genetic change away from the genotypic composition of the originally collected sample, especially if selection pressure is inadvertently imposed during the process.
Inadequate facilities for handling cross-pollinated species can cause delays in or undermine the regeneration process so that the genetic integrity of the sample cannot be guaranteed.
Ideally, regeneration is conducted under neutral selection conditions, to reduce competition thereby minimizing genetic change through selection.
However, this is not always possible.
A certain degree of genetic change is inevitable, especially when regeneration takes place under conditions markedly different from those at the original collection site.
The danger of genetic change during regeneration applies more to heterogeneous populations/accessions than to homogenous ones.
This is because the probability of losing an allele (particularly a low frequency allele) increases, especially with smaller population sizes and under more stressful growing conditions.
The complexity and cost of maintaining the genetic integrity of accessions of a crop during regeneration depends on the reproductive biology of the species.
For instance, it is more difficult and costly to maintain the genetic integrity of cross-pollinated species than self-pollinated crops.
The complexity and expense are higher for species which are insect pollinated.
Reasons for regeneration problems also include: lack of resources (staff, funding, facilities, equipment); insufficient knowledge on the reproductive biology for a large number of crops; lack of pollinator availability; choice, or management technique; lack of adequate isolation distance; the need to use isolation cages; and insufficient information on the optimum number of plants required to maintain genetic integrity.
Solutions to some of these problems are suggested.
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