PowerPoint Presentation

Chapter 5. Principle of Breeding self-pollinated crops.

[Audio] Selection is a crucial step in the breeding process of self-pollinated crops. There are two fundamental requirements that need to be met for this process to operate effectively. Firstly, there must be variation present within the population. This variation can arise from various sources such as genetic mutations, gene flow, or environmental influences. Secondly, the variation must be heritable, meaning it needs to be passed down from one generation to the next through the transmission of genes..

[Audio] There are two main types of selection. Natural selection occurs due to natural forces such as climate, soil, and biological factors in the environment. This type of selection can lead to changes in the population over time. Artificial selection, on the other hand, is carried out by humans. For instance, the progeny test is an example of artificial selection, which is the foundation of modern plant breeding methods..

[Audio] Breeding self-pollinated species typically requires identifying one or a few superior genotypes and multiplying them. There are several specific breeding methods commonly used for self-pollinated species, including mass selection, pure-line selection, pedigree breeding, backcross breeding, and bulk populations. These methods allow breeders to identify and multiply desirable traits while eliminating unwanted characteristics. By using these methods, breeders can develop high-yielding and disease-resistant varieties that meet the needs of farmers and consumers..

[Audio] Mass selection is one of the oldest methods of plant improvement. This technique involves selecting a large number of plants with similar phenotypes and mixing their seeds together to create a new variety. The selection process is based on the physical characteristics of the plants, including seed size, disease resistance, plant height, yield components, and seed color. These easily observable traits are used to identify desirable plants and exclude those with undesirable features. By combining the seeds of these selected plants, breeders can develop new varieties with improved performance and quality..

[Audio] The improvement of self-pollinated crops is limited to the genetic variability that already exists in the original populations, meaning that new variability is not generated during the breeding process. The selection process for self-pollinated crops can be either positive or negative. Negative selection involves identifying and eliminating the least desirable plants, whereas positive selection involves identifying and preserving the most desirable plants. Both negative and positive selection play a crucial role in the breeding of self-pollinated crops, helping to narrow down the gene pool and focus on desirable traits. This process ultimately leads to the development of new and improved varieties..

[Audio] 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 plants..

[Audio] The principle of breeding self-pollinated crops is essential for preserving desirable traits within a plant species. To achieve successful breeding, careful selection and cross-pollination of plants with desirable traits are necessary. However, self-pollination can also result in a lack of genetic diversity, which may lead to inbreeding depression and reduced plant health..

[Audio] In the first year of mass selection, large numbers of plants with desirable characteristics such as vigor, plant height, disease resistance, and other agronomic traits are identified. These plants are selected based on their phenotype, and their seeds are combined to form a composite seed lot. This process helps to concentrate the desired traits in the next generation..

[Audio] Mass selection is a method of breeding that offers several advantages. It allows us to improve local varieties, which are often well-suited to specific environments. Purification of existing pure-line varieties is also possible through this method. Moreover, mass-selected varieties tend to be more widely adapted than pure lines. However, there are some limitations to consider. We cannot determine whether a selected phenotype is superior because of its genetic makeup or environmental influences. Furthermore, mass selection does not create new variation; instead, it relies on the existing variation within a population..

[Audio] Pure line selection was first proposed by Johannsen in 1903 based on his research with the princess variety of beans. He selected seeds of varying sizes from a commercial seed lot and grew them separately. The resulting offspring exhibited differences in seed size, with those derived from larger seeds producing even larger seeds. This demonstrated that the variation in seed size within the commercial seed lot had a genetic basis, making it possible to effectively select for this trait..

[Audio] Pure line selection is a common method of improving especially the landraces. A pure line is a progeny of a single homozygous self-pollinated plant. All the individual plants within a pure line variety are genetically similar and homozygous. Any variation within a pure line is solely due to environment and non-heritable..

[Audio] Pure-line selection is a common method of improving especially the landraces. A pure line is a progeny of a single homozygous self-pollinated plant. All the individual plants within a pure-line variety are expected to be genetically similar and homozygous. Any variation within a pure-line is solely due to environment and non-heritable. New genotypes are not created by pure-line selection. Pure lines have limited adaptability, hence can be recommended for cultivation in limited areas only. Selection of pure lines requires great skill and familiarity with the crop. The breeder has to devote more time. No more improvement is possible after isolation of the best available genotype in the population..

[Audio] Pure line selection is a valuable tool in improving self-pollinated crops. It is used to enhance local varieties, old pure line varieties, and even introduced varieties. This technique allows breeders to identify and select the most desirable traits within these populations, leading to improved cultivars. By applying this method, farmers can expect better yields, disease resistance, and overall performance from their crops..

[Audio] The principle of breeding self-pollinated crops involves selecting individual plants based on their phenotypic appearance, harvesting them separately, growing their progenies in a plant-to-row basis, critically evaluating each plant's traits, and selecting the best rows or plants within a row for breeding. Critical evaluation is essential in determining which rows or plants are the best for breeding. After harvesting, the seed must be bulked with critical evaluation of its quality before storage..

[Audio] The principle of breeding self-pollinated crops involves two important steps: testing and evaluation. The third step is to test the bulked seed from each individual selected-row in a preliminary yield trial, allowing us to evaluate the potential of each selected entry and make further selections based on their performance. Once the best entries are identified, they are evaluated in replicated variety trials for successive years, helping us identify the most outstanding entries and release them as new and improved varieties..

[Audio] Pure line selection has several merits in improving self-pollinated crops. One of these merits is that pure lines are extremely uniform, as all the plants in the variety will have the same genotype. This uniformity makes it easier for farmers to predict the yield and quality of their crops, resulting in higher satisfaction for both farmers and consumers. Another merit is that pure lines are highly attractive and liked by both farmers and consumers, due to their uniformity and consistency in appearance. Furthermore, pure lines are stable and can last for many years, making them a reliable choice for farmers and ensuring a consistent supply of the variety for consumers. Additionally, pure lines have an advantage in seed certification programmes, as they can be easily identified due to their extreme uniformity..

[Audio] Pure line selection does not create new genotypes because it does not introduce genetic variation into the population. Instead, it selects existing variations within the population. This limitation means that pure lines may not be suitable for cultivation in areas with diverse environmental conditions, as they may not perform well outside their adapted range. Moreover, selecting pure lines requires significant expertise and knowledge about the crop, as well as a substantial amount of time. Once the best available genotype has been isolated, no further improvements can be made, as there is no opportunity to introduce new genetic material into the population..

[Audio] In pedigree selection, individual plants are chosen from the F2 generation and then reselected in subsequent generations until genetic purity is achieved. A detailed record of the relationships between these selected plants and their progenies is kept, enabling each progeny to be tracked back to its original F2 origin. This record of parent-offspring connections is referred to as a pedigree..

[Audio] Hybridization is a crucial step in generating variability, which sets pedigree selection apart from other methods like mass selection or pure-line selection. This technique was first introduced by H H Lowe in 1927. When selecting for desirable traits, we focus on those with moderate to high heritability, such as seed color, presence of awns, or disease resistance. However, selecting for vigor can be challenging because it's influenced by factors like heterozygosity, genotype-environment interactions, and environmental conditions. As breeders, we need to consider these complexities when making selections in the F2 generation during pedigree methods..

[Audio] The pedigree method of breeding involves crossing parents with desirable characteristics in the first year, resulting in F1 plants. In the second year, the goal is to raise as many F1 plants as possible to produce a large number of F2 seeds, which are harvested in bulk. In the third year, 2000 to 10000 F2 plants are grown, selected based on desirable traits, and harvested separately with serial numbers and descriptions entered into pedigree registers. The fourth year involves selecting individual plants with desirable characteristics from superior progeny rows, resulting in 50 to 100 families with 5 plants each being harvested separately. The fifth year sees the selected F4 plants raised again as head to row, with desirable plants selected and harvested separately. Finally, in the sixth year, F5 plants are raised in 3 row plots, with seeds of each selected plant sown in 3 rows..

[Audio] The process of breeding self-pollinated crops involves evaluating the F6 individual plant progenies in multi-row plots and selecting the superior plants from superior progenies. In the subsequent years, the selected lines are tested in preliminary yield trials with multiple replications to identify the best candidates for further testing and development. The lines are then tested in several localities for two or three years to assess their adaptability. After twelve years, the selected superior lines are named, multiplied, and released as a new variety..

[Audio] 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 plants. In the bulk method, the test of selected entries is done by evaluating the progenies of selected entries in replicated variety trials for successive years and releasing outstanding ones as new varieties..

[Audio] New genotypes are not created by pure line selection. Pure lines have limited adaptability, hence they can be recommended for cultivation in limited areas only. Selection of pure lines requires great skill and familiarity with the crop. The breeder has to devote more time, and no more improvement is possible after isolation of the best available genotype in the population. 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. The population obtained from the selected plants would be more uniform than the original population. The bulk 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 plants..

[Audio] In the bulk-population method of breeding, the F2 generation is grown at normal commercial planting rates in a large plot. At maturity, the entire crop is harvested and used to establish the next generation in a similar plot. This approach eliminates the need to keep records of ancestry, allowing breeders to focus on selecting for desirable traits through natural and artificial means. During this process, natural selection tends to eliminate plants with poor survival value, while artificial selection can be applied through methods such as destroying plants carrying undesirable genes or using screens to select for specific characteristics. Ultimately, single plant selections are made and evaluated in the same way as in the pedigree method, but the bulk-population method offers the advantage of being able to handle large numbers of individuals inexpensively..

[Audio] In the bulk method of breeding, we harvest F2 and subsequent generations in mass or as bulks to raise the next generation. This process continues until the end of the bulking period, typically around F4 or F5. At this point, individual plants are selected and evaluated in a similar manner as in the pedigree method. The key difference between the two methods lies in how generations are handled following hybridization..

[Audio] In self-pollinated crops, we grow F2 populations and harvest their F3 progenies without any artificial selection by the breeder. We then grow sufficient samples of the F3 seeds and harvest the F4 seeds in bulk, repeating this process until a sufficient level of homozygosity is attained. Once homozygosity is achieved, we select individual superior plants and thresh them separately. The best rows are chosen, and the progenies of the selected plants are tested for yield and conducted in varietal evaluation trials to determine the best-performing varieties..

[Audio] Bulk selection is a principle of breeding self-pollinated crops that has both merits and demerits. On the one hand, it is considered simple, convenient, and inexpensive because it does not require the breeder to keep extensive pedigree records, which can save a lot of time and labor. Moreover, bulk selection makes it easier to isolate desirable types, and less work and attention is needed in F2 and subsequent generations. On the other hand, one of the major drawbacks of bulk selection is that it takes a much longer time to develop a new variety compared to other methods. Additionally, this method provides little opportunity for the breeder to exercise their skill or judgment in selection. It is also less efficient than the pedigree method when it comes to highly heritable traits, as it cannot purge non-selections in the early generations..