Principles of Plant Breeding (2+1)

Origin of variation in purelines

1. Mechanical mixtures.
2. Natural hybridization.
3. Chromosomal aberrations.
4. Natural mutation.
5. Environmental factors.
A Pure line is the progeny of a single, self pollinated, homozygous plant. Development of new variety through identification and isolation of single best plant progeny is known as pure line selection.
All the individuals within a pure line have identical genotype any variation present within a pure line is solely due to environment. So Pure line is a large number of plants are selected from self pollinated crops and are harvested individually. Individual plant progenies from them are evaluated and the best progeny is released as a pure line variety.

Characters
All the plants within a pure line have the same genotype. Because the parent plant was homozygous and self-fertilized.
The variation present within a pure line is environmental andnon heritable. So selection within pure line is not effective.
Pure lines become genetically variable with time. The genetic variation is produced by mechanical mixture, Natural hybridization or mutation.
Narrow adaptation, due to narrow genetic base.