The stability properties of superior varieties may be susceptible to deterioration. Some factors affecting the deterioration of the genetic purity are: variations in the development, mechanical mixing, mutation, natural crossbreeding, minor variations in the genetic, effects of disease, and plant breeding techniques.
These factors, mechanical mixing, natural crossbreeding, and the influence of disease is the important reason of varieties deterioration for seed production; so if the seed production conducted in areas far from a natural adaptation, it will cause variations in its development and genetic changes in varieties.
Mixing varieties, the biggest cause of the deterioration varieties, often occurs when the same volunteer plants with plants that are planted in the same land or there are different varieties are planted close together. Natural crossbreeding is a source of deterioration in crop varieties. Deterioration occurs due to natural crossbreeding with the type of unwanted, infected plants or off-type disease. In the pollinating of plants himself, a natural crossbreeding was not a serious source of contamination except male sterile varieties and planted near other varieties. Isolation of plant is the most important factor in avoiding contamination.
To maintain genetic purity varieties in seed production, the following steps need to be done:
1. Sources of seeds for multiplication of seeds must come from a class on it. Seed class shall consist of:
- Breeder Seed
- Foundation Seed
- Stock Seed
- Extension Seed
2. Inspection of land before planting to avoid contamination because volunteer plants.
3. Isolation of plants from various sources of contamination through natural crossbreeding with other varieties and off-type with the help of wind and insects.
4. Certification of seed to maintain genetic purity and seed quality. Field inspection (by central institute for supervision and seed certification) in the critical phases of plants growth performed for verification of genetic purity, detection of mixing, harmful weeds, and seedborne diseases.
5. Roguing off-types that differ in the characteristics of the varieties planted. Off-types can be derived from the existence of recessive genes in heterozygous, arise because mutations. Heterozygous plants segregating for characters that are influenced by specific genes in the next production cycle to produce off-type. Volunteer plants from seed that is not intentionally planted or from seed produced previously, so resulting off-type.
6. Periodically test the genetic purity of seed by growing of plants to maintain quality.
7. Planting seeds in area of adaptation to avoid genetic changes.
8. Avoid contamination caused by mechanical mixing during planting, harvesting, threshing, processing, and handling, and seedborne disease.