Pure line Selection - Plant Breeding

Pure line Selection

Pureline – Definition:

    Pureline is the progeny of a single, homozygous, self pollinated plant.

Pure line Selection – Definition:

          Pure line selection is a method in which new variety is developed by selection of single best plant progeny among traditional varieties or land races.

Genetic basis for Pureline Selection:

v Pureline varieties are homozygous and homogeneous as they are genetically similar and true breeding.

v  Such varieties possess narrow genetic base so they are more susceptible to diseases, and have poor adaptability.

v A pure line breeding method is normally used for self-pollinated crops, but has importance in breeding of inbred lines that are used to make hybrids in self or cross pollinated crops.

 Examples of Pureline

Crop	Variety	Features
Cowpea	-Suvita-2-	Striga resistant line
Wheat-	Kanred-	Better in winter hardiness, rust resistance, earliness in maturity
Oat-	Columbia-	Matures early, grain with high test weight.

Pure-line Selection-Steps

 cant be shown

Ø Select desirable plants

•         Number depends on variation of original population, space and resources for following year progeny tests

•         Selecting too few plants may risk losing superior genetic variation

•         A genotype missed early is lost forever

Ø Seed from each selection is harvested individually

Ø Single plant progeny rows grown out

•         Evaluate for desirable traits and uniformity

•         Should use severe selection criteria (rogue out all poor, unpromising and variable progenies)

Ø Selected progenies are harvested individually

Ø In subsequent years, run replicated yield trials with selection of highest yielding plants

Ø After 4-6 rounds, highest yielding plant is put forward as a new cultivar

Applications of Pureline Selection:

v As pure line selection gives out uniformity in maturity, height etc. suitable for cultivars in which machines are used for the various production processes like harvesting.

v Because of the same reason as above it can be used for varieties grown for processing market, as uniformity in texture, canning qualities is important in here.

v It is practiced after hybridization within segregating populations.

v Though it can serve above purposes this method has limited practical use in the breeding of major cultivated species.

v  However, the method is still widely used while breeding less important species that have not yet been heavily selected.

v Logically it was first step in the development of a uniform variety for the newly domesticated crops, with some amount of variability

Advantages of Pureline Selection:

v Merits of pureline selection are listed below.

v Easy and cheap method of crop improvement.

v Rapid method, lines are usually genetically fixed and yield trials can be immediately conducted.

Plants in such variety react in similar fashion to environmental conditions, means they are uniform in performance and at the same time in appearance too

Disadvantages of Pureline Selection:

v Pure lines have poor adaptability due to narrow genetic base, just opposite to mass selected variety.

v Superior genotypes can only be isolated from the mixed population. This selection is powerless to bring changes in hereditary factors i.e. to develop new genotype.

v Mostly popular or in fact limited to self pollinated spp. Only.

v Time and space consuming.

v More expensive yield trials have to be conducted than in mass selection.