Regeneration is the renewal of a seed sample by taking a random sample of seeds, sowing and growing the resulting plants under conditions so that the seeds harvested will possess the same characteristics as the original population.
Regeneration of seeds is required when the germination percentage has fallen below acceptable levels or shortage of seed occurs. As a rule, the germination percentage should be above 80%. Exceptions are made for accessions that are very difficult to regenerate (like some wild species). For these accessions percentages between 60 and 80 % can be accepted.
When regenerating germplasm a number of points must be taken into consideration (van Soest, 1990):
- Selection within the original population as a result of regeneration procedures should be minimized.
- No contamination with other samples, both during regeneration and seed handling should be allowed.
- The breeding system of the crop in question is important. Cross pollinating crops need additional measures to assure proper isolation.
- The population size of the original sample should be sufficiently large to avoid genetic drift. Compared to self pollinating species, cross pollinating species usually require a higher number of plants for regenerations to maintain the genetic variation that exists within the population.
To minimize the impact that regenerations can have on the genetic identity of a seed sample, the frequency of regeneration should be kept as low as possible.
Plants that during regeneration clearly seem contaminants and do not belong to the total population are removed.
The reproduction rate should also be considered in order to produce sufficient seeds. So far only in the case of faba beans the reproduction rate is a limiting factor and a relatively high number of plants is used.
A very important aspect of regeneration is the production of healthy, viable seeds. In general, regenerations under glass yield better quality seeds compared to regenerations in the field.
Germplasm that is distributed by genebanks, must be carefully checked for the presence of seed-borne pathogens and pests to prevent contribution to the spreading of diseases and pests. It should provide an uncontaminated basic stock for breeding programmes. CGN maintains a high standard of disease and pest control, including pathogens with no official quarantine status, such as Lactuca Mosaic Virus.
During regeneration at CGN, the Plant Protection Service inspects all crops, particularly on seed born viruses.
Pollination of cross-pollinating species using blowflies
Research has been performed to study the use of honey bees and blowflies for pollination of cross pollinating crops such as cabbages (Boukema et al., 1988). Blowflies are used to cross pollinate crops in isolation cages. These flies are purchased, as larvae, from a commercial producer of larvae used as live bait for fishing, or as insect pollinators.
The firm produces mixtures of different types of larvae, of which the flies are either active under warm conditions (up to 35°C), or under colder conditions.
Depending on demand, 10-20 litre of larvae (in sawdust) are purchased per week. After 3-4 days in a dry room at 25°C, pupae develop. These can be kept for ± 1 month at 2°C. The pupae for immediate use are put in containers with a gauze lid and are kept at 25-30°C and 60-70% RH, to produce adults in ± 8 days. The flies inside these containers are fed a mixture of sugar and water. Three times a week, upon demand some 200 flies are released in the isolation rooms (±4x4x2 m).
Sometimes bumblebees are used for the pollination of cross pollinating crops.