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Selection method of crop improvement

 

Selection method of crop improvement

What is Plant breeding?

Please refer our article –

Plant breeding – objectives and Methods | Agristudent.com

What are the different methods of plant breeding?

Please refer our article –

Plant breeding – objectives and Methods | Agristudent.com

Which is the oldest and rapid method of crop improvement?

Please refer our article –

Introduction Method of Plant breeding – Instant Info

What is ‘Selection’ in crop improvement?

Isolation of desirable plant types from the population is known as selection

It is basic to any crop improvement project since the main aim of crop improvement is

1. Creation of Variation and

2. Selection of the desirable form this variation..!

It may be brought about by

1. Nature (known as natural selection)

2. Man (known as artificial selection)

In modern era of plant breeding, artifiicial selection is of great importance

The most important points to be remembered are

1. Selection utilises variation but does not create new variation

2. The variations should be heritable

How are selction methods classified?

Selection methods are classified as

1. Natural selection

2. Artificial selection –

(i) Mass selection

(ii) Progeny selection

(iii) Pure line selection

What is Mass selection?

It consists of selecting individuals on the basis of phenotypic superiority for using as planting material for next season

It is the earliest and most basic method

What is the procedure evolving a variety by Mass selection method?

Procedure for evolving variety

First year

Large number (few hundred to few thousand) of phenotypically similar plants having desirable characters are selected

The seeds from the selected plants are composited to raise the next generation

Second year

Composited seed planted in a preliminary field trial along with standard checks

The variety from which the selection was made should also be included as check

Phenotypic characterlistics of the variety are critically examined and evaluated

Third to sixth year

The variety is evaluated in coordinated yield trials at several locations

It is evaluated in an initial evaluation (IET) trial for one year

If found superior it is promoted to main yield trials for 2 or 3 years

Seventh year

if the variety is proved superior in main yield trials it is multiplied and released after giving a suitable name

Which popular varieties have been developed with mass selection?

 

Cotton: Dharwad American Cotton

Groundnut : TMV-1 & TMV-2

Bajra : pusa moti, Baja puri, Jamnagar gaint, AF3

Sorghum : R.S. 1

Rice : SLO 13, MTU-15

Potato : K122

What are the Merits and Demerits of Mass selection method?

Merits of Mass selection

1. Can be practiced both in self and cross pollinated crops

2. The varieties developed through mass selection are more widely adopted than pure lines.

3. It retains considerable variability and hence further improvement is possible in future by selection

4. Helps in preservation of land races

5. Improvement of characters governed by few genes with high heritability is possible

7. Less time consuming and less expensive

Demerits of mass selection

1. Varieties are not uniform

2. Since no progeny test is done, the genotype of the selected plant is not known

Which popular varieties have been released by Mass selection method?

Cotton : Dharwad American Cotton

Groundnut : TMV-1 & TMV-2

Bajra : pusa moti, Baja puri, Jamnagar gaint, AF3

Sorghum : R.S. 1

Rice : SLO 13, MTU-15

Potato : K122

What is progeney selection?

Progeny selection is commonly used in cross-pollinated and often cross-pollinated crops

Progeny is new individual organisms that results from the process of sexual or asexual reproduction.

Progeny selection is the selection procedure in which superior plants are selected from a heterogeneous population on the basis of performance of their progenies

The test of genotypic value of an individual based on the basis of performance of its progeny is called progeny test (first used by valmorin in 1856)

What are the steps in progeny selection?

The most used and simple method of progeny selection is ear-to-row method

This method was developed by Hopkins in 1908

This method is used on a large scale in maize crop

Step 1 (first year)

50 to 100 plants are selected on the basis of their superior phenotypes and allowed to open pollinate

The seeds from each plant are harvested seperately

Step 2 (Second year)

10 to 50 seeds from each plants are grown seperately in progeny rows

These rows are evaluated and superior ones are identified

Plants are allowed to open pollinate and seeds harvested seperately

Step 3 (Third year)

Same as done in second year and may be repeated one or more times. Then seeds are released for yield trials

What are the merits and demerits of progeny selection?

Merits:

(i) This method is very simple and convenient.

(ii) In the identification of superior genotypes, this method is more effective than mass selection because it is based on progeny test and not on the phenotypes of the individual plant.

(iii) Inbreeding may be avoided if sufficiently large number and diverse progenies are selected.

Demerits:

(i) There is no control over pollination. Plants are allowed to open pollinate.

(ii) Certain methods of progeny selection are complicated.

(iii) If the progeny of each plant is tested in isolation, it would require lot of area which is not practically possible

What is Pureline selection?

Progeny of a single individual obtained by selfing is called a pure line

A pure line is an inbred homogenic strain

The process of isolating a desirable homozygous individual from the mixed population and multiplying the same without contamination to release as a new variety is Pureline selection

The credit of development of  pure line selection goes to Danish scientist – W.L. Johanssen in 1903

What is the general procedure for evolving a variety by Pureline selection?

The pureline selection has three steps.

1. Selection of individual plants from a local variety or some other mixed population

2. Visual evaluation of individual plant progenies and

3. Yield trials

First year

A large number of plants (200-3000) which are superior than the rest are selected from a local variety or mixed population and harvested separately (in some cases individual heads or stems may be selected)

The number of plants to be selected depends upon the breeder’s discretion but should be as large as possible in view of the available time, land, funds, labour etc

It is advisable to select for easily observable characters such as flowering, maturity, disease resistance, plant height etc.

Second year

Progenies of individual plants selected in 1st year are grown separately with proper spacing (plant to row or head to row)

The progenies are evaluated by taking elaborate date on visual characters such as plant height, duration, grain type, ear characters besides yield

The number of progenies should be reduced as much as possible

Disease epiphytotics may be created to test the progenies for disease resistance, poor, weak, diseased, insect attacked and segregating progenies are rejected

The superior progenies are harvested separately

If necessary the process may be repeated for one or more years

Third year

The selected progenies, now called as cultures are grown in replicated trial for critical evaluation of yield etc

The best local variety is used as a check and should be grown at regular intervals, after every 15 or 20 cultures for comparision

This is known as preliminary yield trial

Superior cultures based on observable characters and yield are selected

The number is drastically reduced

Fourth & Fifth years

The superior cultures are tested against the local checks in yield trials

Observations are recorded on many characters like diseases resistance, days to flower, days to maturity, height of the plant ear characters, test weight and yield

The data is subjected to statistical analysis to identify really superior culture

If necessary the trials may be extended for one more year or season

Inferior culture are rejected and a few (4-5) promising cultures are selected

Sixth, Seventh and Eighth years

The promising cultures selected are evaluated at several locations along with strains or cultures of other breeders and local checks

One or two promising cultures are selected

Ninth year

The best progeny identified earlier is multiplied, named and released as a variety for official release of any variety (approval from the variety releasing committee of the state or central is necessary)

What are the achievements of Pure line selection?

Several varieties developed by pureline. Some examples are

Rice : Mtu-1, Mtu-3, Mtu-7, Bcp-1, Adt-1, 3, 5, and 10

Sorghum : G 1 & 2, M 1 & 2, OO 1, 4 & 5,

Groundnut : TMV 3, 4, 7, 8 and Kadiri 71-1

Redgram : TM-1, ST-1

Chillies : G1 & G2

Ragi : AKP 1 to 7

What are the merits and demerits of pureline selection?

Merits

1. The purelines are extremely uniform since all the plants in the variety will have the same genotype

2. Attractive and liked by the farmers and consumers

3. Purelines are stable and long test for many years

4. Due to its extreme uniformity the variety can be easily identified in seed certification programmes

Demerits

1. New genotypes are not created by pureline selection

2. Improvement is limited to the isolation of the best genotype present in population. No more improvement is possible after isolation of the best available genotype in the population

3. Selection of purelines require great skill and familiarity with the crop

4. Difficult to detect small differences that exist between cultures

5. The breeder has to devote more time

Further reading and references

Principles of plant breeding – BD Singh

http://wikipedia.com