Plant Selection PDF

# Selection ## Mass Selection **Definition:** Several plants are selected from the field populations on the basis of their phenotypic characters like plant height, grain colour, grain size, disease resistance, tillering ability, lodging resistance, shattering resistance etc. **Applications of Mass...

# Selection ## Mass Selection **Definition:** Several plants are selected from the field populations on the basis of their phenotypic characters like plant height, grain colour, grain size, disease resistance, tillering ability, lodging resistance, shattering resistance etc. **Applications of Mass Selection:** - Improvement of local varieties - Purification of the existing pureline varieties. **Procedure of mass selection:** - **First Year:** - From a variable population, 200-2,000 plants with similar but desirable traits are selected. - The seeds from selected plants are composited. - **Second Year:** - The composited seed is planted in a preliminary yield trial along with standard checks. - Phenotype of the selected population is critically evaluated. - **Third to Fifth Years:** - Promising selections are evaluated in coordinated yield trials at several locations. - If outstanding, released as a new variety. - **Sixth Year:** Seed multiplication for distribution. **Demerits of Mass Selection:** 1. The varieties developed through mass selection show variation and are not as uniform as pure-line varieties. 2. The improvement through mass selection is generally less than that could be achieved through pure-line. 3. Due to the popularity of the pure-line varieties, mass selection is not commonly used in the improvement of self pollinated crops. 4. Varieties developed by mass selection are more difficult to identify than pure-lines in seed certification programmes. 5. Only those varieties / populations that show genetic variation can be improved through mass selection. **Merits of Mass Selection:** 1. Varieties developed through mass selection are likely to be more widely adapted than purelines. 2. Often extensive and prolonged yield trials are not necessary. This reduces the time and cost needed for developing the new variety. 3. Mass selection retains considerable genetic variability in the new variety. 4. It is a less demanding method. Therefore the breeder can devote more time to other breeding programmes. ## Pureline selection **Definition:** A pureline is the progeny of a single, homozygous, self pollinated plant. As a result, all the individual within a pure-line have identical genotype, and any variation present within a pureline is solely due to the environment. **Procedure:** A large number of plants are selected from a self pollinated crop and are harvested individually; individual plant progenies from them are evaluated, and the best progeny is released as a pure-line variety. **Characteristics of Purelines:** 1. All the plants within a pureline have the same genotype. 2. The variation present within a pureline is environmental and nonheritable. 3. Purelines become genetically variable with time due to mechanical mixture, natural hybridization and mutation. **Uses of purelines:** 1. Purelines may be used as a commercial variety. 2. Used as parents in a hybridization programmes. 3. Used in studies on mutation. 4. Used in many biological investigations, such as those in medicine, immunology, physiology, biochemistry, nutrition etc., This is done to avoid genetic variation in the experimental material. **Applications of pureline selection:** 1. It is used to improve Local varieties. 2. It is used to improve old pureline varieties. 3. It is used to improve introduced varieties. **Merits of pureline selection:** 1. Pureline selection achieves the maximum possible improvement over the original variety. 2. Pureline varieties are extremely uniform since all the plants in the variety have the same genotype. 3. Due to its extreme uniformity, the variety is easily identified in seed certification programmes. **Demerits of pureline selection:** 1. The varieties developed through pureline selection generally do not have wide adaptation. 2. The procedure of pureline selection requires more time, space and more expensive yield trials than mass selection. 3. The breeder has to devote more time to pureline selection than to mass selection. **A general scheme for pureline selection:** - **First Year:** 200-3,000 plants are selected on the basis of their phenotype. - **Second Year:** - Individual plant progenies are grown. - Undesirable progenies are rejected. - **Third Year:** - Remaining progenies are planted in a preliminary yield trial. - Inferior progenies are rejected. - **Fourth to Sixth Years:** - Replicated yield trials are conducted at several locations. - Inferior progenies are rejected. - Disease resistance and quality tests are done. - **Seventh Year:** - Best progeny is released as new variety. - Seed multiplication begins for distribution. ## Clonal Selection **Definition:** A clone is a group of plants produced from a single plant through asexual reproduction. All the members of a clone have the same genotype as the parent plant. It does not involve sexual reproduction - clonal selection. **Selection procedure:** - **First Year:** Few to several hundred superior plants selected. - **Second Year:** - Clones from the selected plants grown separately. - Desirable clones selected. - **Third Year:** - Preliminary yield trial with standard checks. - Selection for quality, disease resistance, etc. - Disease nurseries may be planted. - Few outstanding clones selected. - **Fourth-Sixth Years:** - Multilocation yield trials with standard checks. - Best clone identified for release as a new variety. - **Seventh Year:** - The best clone released as a new variety. - Seed multiplication for distribution begins. **Merits of clonal selection:** 1. It is the only method of selection applicable to clonal crops. It avoids inbreeding depression, and preserves the gene combinations present in the clones. 2. Clonal selection, without any substantial modification, can be combined with hybridization to generate the variability necessary for selection. 3. The selection scheme is useful in maintaining the purity of clones. **Demerits of Clonal Selection:** 1. This selection method utilizes the natural variability already present in the population; it has not been devised to generate variability. 2. Sexual reproduction is a prerequisite for the creation of variability through hybridization.