PowerPoint Presentation

Chapter 5. Principle of Breeding self-pollinated crops.

Selection- The process of permitting certain plants to reproduce in the next generation while preventing others from reproduction.

Natural selection: it is due to natural forces like climate, soil, biological factors and other factor of environment..

Selection Methods in Self- Pollinated Crops. Breeding self-pollinated species usually involves: identifying one or a few superior genotype & multiplying it Specific breeding methods commonly used for self-pollinated species are:.

plant height yield components seed color,. Mass selection is one of the oldest methods of plant improvement In mass selection: a large number of plants of similar phenotype are selected and their seeds are mixed together to constitute a new variety.

The improvement is limited to the genetic variability that existed in the original populations (i.e., new variability is not generated during the breeding Process).

[image] seedling1. [image] seedling1. [image] seedling1.

[image] seedling1. [image] seedling1. [image] seedling1.

Procedures of mass selection: First year. Large numbers of phenotypically similar plants are selected for their vigor, plant height, disease resistance and other desirable agronomic traits and seeds are composited to rise the next generation. Second year. Composite seeds are planted in a preliminary yield trial. Third to fifth year. The new line is evaluated in coordinated yield trial Seventh year. The new line may be released as a new variety.

Merits of mass selection Improvement of local varieties Purification of existing pure line varieties. they are more widely adapted than pure lines..

5.3.2. Pure line selection. The concept of pureline was proposed by Johannsen in 1903 on the basis of his studies with princess variety of beans (Phaseolus vulgaris). From a commercial seed lot he selected seeds of different sizes and grew them separately. The progenies differed in seed size. Progenies from larger seeds produced larger seeds than those obtained from smaller seeds. This clearly showed that the variation in seed size in the commercial seed lot of princess variety had a genetic base. As a result selection for seed size was effective..

pure line is a progeny of a single homozygous self-pollinated plant All the individual plants within a pureline variety are expected to be: genetically similar and homozygous any variation within a pure-line is solely due to environment and non-heritable.

Origins of genetic variation in pure-lines mechanical mixture natural hybridization mutation.

Pure line selection has several applications in improvement of self pollinated crops It is used to improve: Local varieties Old pure line varieties Introduced varieties.

General scheme of pure line selection. Select large number (up to 2000-3000) of individual plants on the basis of their phenotypic appearance and harvest each plant separately (ii) Grow progenies of each plant in a plant-to-row basis in a proper spacing Select best rows or plants within a row bulk the seed at harvest with critical evaluation of the seed.

(iii) Test the bulked seed from each individual selected-row in a preliminary yield trial and make further selections best entries (iv) Evaluate the progenies of selected entries in replicated variety trial for successive years and release outstanding ones as new varieties.

5.2.4. Merits and Demerits of Pure line Selection.

New genotypes are not created by pure line selection 2. Pure lines have limited adaptability hence can be recommended for cultivation in limited area only 3. Selection of pure lines requires great skill and familiarity with the crop 4. The breeder has to devote more time 5. No more improvement is possible after isolation of the best available genotype in the population.

8.3. Pedigree selection. In this method of selection individual plants are selected F2 generation and progenies of each selected plants are reselected in succeeding generation until genetic purity is obtained a detail record of relationships between the selected plants and their progenies is maintained, each progeny in every generations can be traced back to the F2 plant from which it originated. Such a record of parent offspring relationships is called pedigree..

A key difference between pedigree selection and mass selection or pure-line selection is that hybridization is used to generate variability. The method was first described by H. H. Lowe in 1927..

8.3.3. Procedures for pedigree method. 1st year: cross is made between the parents possessing desirable chxs 2nd year: Raise as many F1 plants as possible to produce large number of F2 seeds. Harvest in bulk. 3rd year: Grow 2000-10,000 plants of F2& The selected plants are harvested separately and given serial numbers and description entered in pedigree registers 4th year: From superior progeny rows, individual plants with desirable chxs are selected (about 50-100 families and about 5 plants in each family and harvested separately) 5th year: F4 plants raised again as head to row. Desirable plants are selected from desirable rows and harvested separately 6th year: F5 plants raised in 3 row plots i.e. seeds of each selected plant sown in 3 rows.

Procedures for pedigree method…Conti’d. 7th year: F6 individual plant progenies are grown in multi-row plots and evaluated inferior ones are rejected Superior plants from superior progenies are selected Plants from each progeny are bulked 8th year: F7 preliminary yield trials with 3 or more replications are conducted to identify superior lines 9th, 10th & 11th year: selected lines are tested in several localities for 2 or 3 years for adaptation tests 12th year: Selected superior lines is named, multiplied and released as a new variety Number of year can be reduced if generations are advanced during off seasons either: in green house or under irrigated conditions..

Merits & demerits of pedigree method. It gives maximum opportunity for the breeder to use his skill and judgement in selection of plants Inferior plants and progenies are eliminated in early generations It takes less time than bulk method to develop new variety.

Valuable genotypes may be lost in early generations if sufficient skill and knowledge are lacking in the breeder, at the time of selection ii. No opportunity for natural selection iii. Difficult to handle many crosses iv. Maintenance of records, selections, growing progeny rows etc are time consuming and laborious.

8.4. Bulk method. The bulk-population method of breeding differs from the pedigree method primarily in the handling of generations following hybridization. The F2 generation is sown at normal commercial planting rates in a large plot. At maturity the crop is harvested in mass, and the seeds are used to establish the next generation in a similar plot. No record of ancestry is kept. During the period of bulk propagation natural selection tends to eliminate plants having poor survival value. Two types of artificial selection also are often applied: destruction of plants that carry undesirable major genes and mass techniques such as harvesting when only part of the seeds are mature to select for early maturing plants or the use of screens to select for increased seed size. Single plant selections are then made and evaluated in the same way as in the pedigree method of breeding. The chief advantage of the bulk population method is that it allows the breeder to handle very large numbers of individuals inexpensively..

In the bulk method, F2 and subsequent generations are harvested in mass or as bulks to raise the next generation. At the end of the bulking period (F4 or F5), individual plants are selected and evaluated (in a similar manner as in the pedigree method).

Procedure of Bulk method. 1. F2 populations are grown and their F3 progenies are harvested in bulk without any artificial selection by the breeder 2. Grow sufficient samples of the F3 seeds and harvest the F4 seeds in bulk and repeat this if necessary for the next generation as well until sufficient level of homozygosity is attained 3. Then select individual superior plants and thresh them separately 4. Grow the progenies of the selected plants in rows and select best rows. 5. Test the progenies for yield and then under varietal evaluation trials..

Demerits of bulk selection It takes a much longer time to develop a new variety. It provides little opportunity for the breeder to exercise his skill or judgment in selection Less efficient than pedigree method on highly heritable traits (because can purge non-selections in early generations).