Selection
Selection in the oldest, simplest and most common method of plant breeding. This method is being practiced since ancient times. 'Selection' means, choosing plant of one's choice. Selection is basis of all crop improvement program.
At broader level, selction is of two types; natural selction and artificial selection.
As the name suggests, natural selection is a natural process. It happens in the nature without the any human interferance. According to the Darwin’s principle of “Survival of the fittest”, "plants which survive through the adversities of nature are preferred and the weaker ones are wiped out". Thus, nature itself is plant breeder and selects the fittest crop under prevailing circumstances. This selection pressure upon the crops gave rise to different 'subspecies' and 'ecotypes'.
In artificial selection, Man itself is the selecting agent, where he/she select the few of individual plants with desired characteristics form the mixed population varying in characteristics.
Artificial selection is of following types
At broader level, selction is of two types; natural selction and artificial selection.
As the name suggests, natural selection is a natural process. It happens in the nature without the any human interferance. According to the Darwin’s principle of “Survival of the fittest”, "plants which survive through the adversities of nature are preferred and the weaker ones are wiped out". Thus, nature itself is plant breeder and selects the fittest crop under prevailing circumstances. This selection pressure upon the crops gave rise to different 'subspecies' and 'ecotypes'.
In artificial selection, Man itself is the selecting agent, where he/she select the few of individual plants with desired characteristics form the mixed population varying in characteristics.
Artificial selection is of following types
- Mass selection
- Pure-line selection
- Progeny selection
- Clonal selection
Mass selection
Mass selection is defined as the selection of a number of phenotypically superior plants heads or seeds from the field population, harvesting and bulking their produce together for sowing the next year’s crop. This process is repeated several times till desired characters are achieved.
Mass selection is the simplest and oldest method of crop improvement practiced by farmers. This method is based on phenotype (external characters) only and the harvested seeds are composited without progeny testing.
This method can not introduce new genotype. This method is applicable to both, self-pollinated and cross-pollinated crops. In self-pollinating plants, this method maintain the purity of a variety, whereas, in cross-pollinated crops, it imroves the population.
Mass selection is the simplest and oldest method of crop improvement practiced by farmers. This method is based on phenotype (external characters) only and the harvested seeds are composited without progeny testing.
This method can not introduce new genotype. This method is applicable to both, self-pollinated and cross-pollinated crops. In self-pollinating plants, this method maintain the purity of a variety, whereas, in cross-pollinated crops, it imroves the population.
Procedure
| Step-1 | Seeds (500 to 1000) of the plants with desired characteristics are selected, harvested, thrashed together | Year 1 |
| Step-2 | The selected seeds are bulked and raised in isolated compartment of the plot with a standrd variety to for the camparision. Plant with best performance are selected and rest are discarded | Year-2 |
| Step 3 | Main yield trails are conducted to see the performance by repeating the step 1 and 2 | Year 3-5 |
| Step 4 | Trails are conducted in the experimental farms of different research station to see the adaptability under different agroclimatic conditions. After succefull trials, the new variety is released, named and distributed during 8th year. | Year 6-8 |
Merits
- No scietific knowledge is needed.
- This is easiest, simplest and quick method.
- There is no need to controll the pollination.
- This is only method of improving the local or wild varities.
Demerits
- There is no improvement in genotype, as only phenotype is focused.
- Pollination is not under controll, which leads to the heterozygousity. This causes gradual loss in the quality of desired characters.
- In cross-pollinated crops, variety produced as heterozygous.
Achievments
A number of varities are produced in maize, sugarbeet, alfalfa, red clover in different countires of the world. In India following crop varities developed by mass selection
- Maize:Tinpakhia, Jaunpur local, Basri
- Pearl Millet: Pusa moti, Bajra-207, Bajri-28-15, Bichpuri local
- Sorghum: RSI, T22
- Cotton: Dharwar American, Combodian cotton, Dodahatti local
- Mustard: Gurgaon brown sarson
- Peanut: TMV-1, TMV-2
Pure line selection
Pure line is group of plants, all descendent of a single, homozygous, self-fertilized plant. Pure-lines are therfore, unifrom genetically as well as phenotypically.
Selection of a homozygous (self-fertilized individual with desired trais from the mixed pupulation, and multiplying the same without contamination (cross-pollination) to release as a new variety is known as pure-line selection.
This method is applicable to the self-pollinated crops only.
Selection of a homozygous (self-fertilized individual with desired trais from the mixed pupulation, and multiplying the same without contamination (cross-pollination) to release as a new variety is known as pure-line selection.
This method is applicable to the self-pollinated crops only.
Procedure
| Step-1 | Individual plants (200-3000) with desired superior traits are selected from the mixed population of local variety and their seeds are harvested separtely. | Year 1 |
| Step-2 | The selected seed are sown separately with proper spacing to avoid mixing and cross-pollination. The plant with desired traits are selected, rest are discarded. Thus the number of progeny is highly reduced. | Year-2 |
| Step 3 | Preliminary yield trails are conducted by sowing all the seed separately. Plants with superior traits are retianed and inferior ones are rejected. | Year 3 |
| Multilocation trails are conducted to check the disease resistance and other qualities against a suitable varity. | Year 4-6 | |
| Step 4 | Progeny superior to the check variety is sle ted, multiplied and releases as new variety. | Year 7-8 |
Merits
- Maxiumum possible improvement can be achieved in variety, because finally selected variety consists of all self-fertilized homozygous individuals.
- The variety produced is extremely uniform and attractive, due to lack of genetic variation.
Demerits
- This method can not be applied in cross-pollinated crops.
- Maintainance of pure line requires more time, labor and space.
- Maximum improvement can not go beyond the original local variety.
- As the variety produced is homozygous, the adaptibilty to the diverse agroclimatic condition is less.
Achievments
Pure line selection is most extensively used method of plant breeding, because of presence of a number of local varities. Some of the varieties developled in India is listed here.
- Rice: M-351, Vidisa 60-1, Patni 6, Aispuri, BP 53
- Wheat: NP4, NP6, NP12, Pb-8, CI3, K46
- Barley: C-251, C-50, K-12
- Cotton: Coimbatore 2, Gadag 1, MCU
- Tobacco: NP28, NP63, NP70
Progeny selection
"Progeny" are offsprings or new individual organisms produced by the sexual or asexual reproduction. "Progeny test" is the evaluation of genotypic characters of an individual based on the performance of its progeny.
"Progeny selection" is the selection of progenies with superior phenotypic traits raised from the open-pollinated individuals. In progeny selection, plants are selected from open-pollinated heterogenous population on the basis of performance of progeny.
This method is also known as "Vilmorin principle", because he had utilized this method for the first time 1856 for improving the sugar content in wild sugar beet. This method is applicable to the cross-pollinated crops only.
"Progeny selection" is the selection of progenies with superior phenotypic traits raised from the open-pollinated individuals. In progeny selection, plants are selected from open-pollinated heterogenous population on the basis of performance of progeny.
This method is also known as "Vilmorin principle", because he had utilized this method for the first time 1856 for improving the sugar content in wild sugar beet. This method is applicable to the cross-pollinated crops only.
Procedure
Hopkins developed simplest method of pregeny selection, so called ear-to-raw method in 1908. This method was extensively used in maize.
| Step-1 | Plants with superior phenotypic traits (50-100 in number) are selected and allowed to open-pollinate. Seeds from each plant are harvested separately. | Year 1 |
| Step-2 | From each selected plant, 10-50 seeds are grown in a seprate progeny rows. Plant are allowed to open-pollinate. Superior progeny rows are identified and harvested separately. | Year-2 |
| Step 3 | Step-2 is repeated several times and preliminary yield trials are conducted at various sub-stations againat local and commercial cultivar. Finaly seeds are composited and released as new variety. | Year 3-7 |
Merits
- This method is relatively easy and simple.
- Selection is quick and easy as it is based on the progeny row rather than individuals (as in mass selection).
- Self pollination can easily avoided, if the number of individuals are large and diverse.
Demerits
- There is no control over pollination, hence maternal characters are taken into consideration.
- If progenies are to be tested in isolation, it would be more complicated.
Clonal selection
Clones are progeny or indiviual of single parents, all are obtained vegetatively. Clones are identical and heterozygous. Due to the absence of sexual reporduction, no segregation of allels occurs, hence traits of colnes are stable.
Clonal selection is the method of selecting the individuals with desired traits in such crops, which are propageted vegetatively, e.g., sugarcane, banana, potato, grapes, apple, etc. Method of clonal selection involves isolating best clones from the mixed population.
Clonal selection is the method of selecting the individuals with desired traits in such crops, which are propageted vegetatively, e.g., sugarcane, banana, potato, grapes, apple, etc. Method of clonal selection involves isolating best clones from the mixed population.
Merits
- Varities are stable and easy to maintain.
- This is the only method of vegetatively propagated crops.
Demerits
- As there is no crossing over occurs, new traits can not be developed.
- This method is applicable to the vegetatively propagted crops.
Achievments
Pure line selection is most extensively used method of plant breeding, because of presence of a number of local varities. Some of the varieties developled in India is listed here.
- Modern varieties of banana.
- "Kufri safed" and "Kufri red" of potato.
First published on 13-04-2021
Last updated on 06-05-2021
Last updated on 06-05-2021
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