A pure line is the progeny of a single, homozygous, self-pollinated plant. In pure line selection, a large number of plants are selected from a self-pollinated crop and are harvested individually; individual plant progenies from than are evaluated, and the best progeny is released as pure line variety. Therefore, pure line selection is also known as individual plant selection. A pure line variety is a variety obtained from a single homozygous plant of a self-pollinated crop.
CHARACTERISTIC OF PURE LINES
1. All the plants within a pure line have the same genotype as the plant from which the pureline was derived.
2. The variation within a pure line is environment and non-heritable.
3. Pure lines become genetically variable with time. The genetic variation is produced by mechanical mixtures, natural hybridization or mutation.
Merits of pure line selection
1. Pure line selection achieves the maximum possible improvement over the original variety. This is because the variety is the best pure line present in the population.
2. Pure line varieties are extremely uniform since all the plants in the variety have the same genotype. Such a uniform variety is more liked by the farmers and the consumers than a less uniform variety developed through mass selection.
3. Due to its extreme uniformity the variety is easily identified in seed certification programmes.
Demerits of pure line selection
1. The varieties developed through pure line selection generally do not have wide adaptation and stability in production possessed by the local varieties from which they are developed.
2. The procedure of pure line selection requires more line space and more expensive yield trials than mass selection.
3. The upper limit on improvement is set by the genetic variation present in the original population.
4. The breeder has to devote more time to pure line selection than o mass selection. This leaves less time for other breeding programmes.