PowerPoint Presentation

[Virtual Presenter] In this presentation, we will discuss the fundamental principles and methods employed in plant breeding to create high-yielding and disease-resistant crop varieties. We will start by analyzing the process of selecting and evaluating crop populations..

[Audio] Selection is the process of isolating desirable plant types from the population. This is done by permitting certain plants to reproduce in the next generation while preventing others from doing so. There are two fundamental requirements for selection to operate effectively. Firstly, there must be variation present within the population. Secondly, this variation must be heritable, meaning that it can be passed down from parent to offspring..

[Audio] There are two main types of selection. Natural selection occurs when plants are exposed to environmental pressures such as climate, soil, and biological factors. This type of selection can lead to changes in the population over time. Artificial selection, on the other hand, is a process where humans actively select for certain traits in a population. For instance, the progeny test is the foundation of modern plant breeding methods..

[Audio] Breeding self-pollinated species typically involves identifying one or a few superior genotypes and multiplying them. Mass selection, pure-line selection, pedigree breeding, backcross breeding, and bulk populations are several specific breeding methods commonly used for self-pollinated species. These methods enable breeders to select and multiply desirable traits while maintaining the integrity of the original genetic material..

[Audio] Mass selection is one of the oldest methods of plant improvement. A large number of plants with similar phenotypes are selected and their seeds are mixed together to form a new variety. These plants are chosen based on their physical characteristics, such as seed size, disease resistance, plant height, yield components, and seed color..

[Audio] The improvement in self-pollinated crops is limited to the genetic variability that already exists within the original population. This means that no new variability can be introduced through the breeding process. However, this existing variability can still be utilized through the process of selection. Selection can take two forms - positive or negative. Negative selection involves identifying and eliminating the least desirable plants, whereas positive selection involves identifying and preserving the most desirable plants. By doing so, we can obtain a population that is more uniform than the original one..

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[Audio] In this stage of mass selection, we select large numbers of phenotypically similar plants based on their vigor, plant height, disease resistance, and other desirable agronomic traits. We then composite these seeds to raise the next generation. This process helps to concentrate the desired genes within the population..

[Audio] Mass selection has several merits. One of its advantages is that it can improve local varieties. Additionally, it can purify existing pure-line varieties, making them more widely adaptable. However, there are also some demerits associated with this method. For instance, it's difficult to determine whether a selected phenotype is superior because of genetic factors or environmental influences. Furthermore, mass selection does not create new variability; instead, it relies on the existing variation within a population..

[Audio] The concept of pureline was proposed by Johannsen in 1903 based on his studies with the princess variety of beans. He selected seeds of different sizes from a commercial seed lot and grew them separately. The progenies differed in seed size, with those from larger seeds producing larger seeds than those from smaller seeds. This demonstrated that the variation in seed size in the commercial seed lot of princess variety had a genetic basis, making selection for seed size effective..

[Audio] All the individual plants within a pure-line variety are genetically similar and homozygous. Any variation within a pure-line is solely due to environmental factors and is non-heritable. A pure-line is a progeny of a single homozygous self-pollinated plant..

[Audio] Genetic variation in pure lines originates from three primary mechanisms: mechanical mixture, natural hybridization, and mutation. All plants within a pure line possess the same genotype, and any observed variation is attributed to environmental factors, which are non-heritable..

[Audio] Pure line selection has several applications in improving self-pollinated crops. It is used to improve local varieties, old pure-line varieties, and introduced varieties. The process involves selecting the best individuals within each category and breeding them to produce improved offspring. This method allows breeders to enhance the desired traits and characteristics of the crops, making them more suitable for specific environments or markets. However, it is essential to note that pure line selection has limitations, as it relies on the existing genetic variation within the population and does not create new variability. Furthermore, the breeder must possess great skill and familiarity with the crop to successfully apply this method..

[Audio] In this step, we select a large number of individual plants based on their phenotypic appearance. These plants are chosen because self-pollinated crops do not exhibit significant variation among individuals, so we rely on visual selection to identify those with desirable traits. Each plant is harvested separately to obtain its seeds. Next, the progenies of each plant are grown in a plant-to-row basis, with proper spacing between them. Within these rows, the best rows or individual plants exhibiting the desired characteristics are selected. Finally, the seed is bulked at harvest, with careful evaluation of the quality of the seed produced by each plant. This process enables us to identify the most promising lines and advance our breeding program..

[Audio] The next step in breeding self-pollinated crops involves testing the bulked seed from each individual selected row in a preliminary yield trial. This allows us to identify the best entries and make further selections based on their performance. We then evaluate the progenies of these selected entries in replicated variety trials over several years. Finally, we release the outstanding ones as new varieties.

[Audio] The pure lines are extremely uniform because all the plants in the variety have the same genotype. This uniformity makes them attractive to farmers and consumers. Additionally, pure lines are stable and can withstand testing for many years. Furthermore, their extreme uniformity allows them to be easily identified during seed certification programs..

[Audio] Pure line selection does not create new genotypes as it does not introduce genetic variation into the population. Instead, it selects existing variations within the population. Once the best available genotype has been isolated, no further improvement is possible. Moreover, pure lines have limited adaptability and can only be cultivated in a specific area. Breeders must devote considerable time and effort to select the most suitable genotype, requiring great skill and familiarity with the crop..

[Audio] Individual plants are chosen from the F2 generation in this method of selection. Then, the progenies of each selected plant are reselected in subsequent generations until genetic purity is achieved. A detailed record of the relationships between the selected plants and their progenies is kept, allowing each progeny in every generation to be traced back to its original F2 parent. This record of parent-offspring relationships is known as a pedigree..

[Audio] In pedigree selection, hybridization is a key difference compared to other breeding methods, generating variability for desirable trait selection. This method was first described by H. H. Lowe in 1927. Breeders can rely on moderate to high heritability when selecting traits like seed color, presence of awns, or disease resistance. However, selecting for vigor is less effective due to factors such as heterozygosity, genetic-environmental interactions, and environmental conditions. Careful consideration is necessary when selecting plants in the F2 generation using the pedigree method..

[Audio] In the fifth generation, we raise F4 plants as heads-to-row. This means that the seeds of each selected plant are sown in separate rows. We then select desirable plants from these rows and harvest them separately. This process helps us to identify and isolate the most promising individuals within our breeding program..

[Audio] The principle of breeding self-pollinated crops involves selecting individual plants with desirable traits, growing them in multi-row plots, evaluating their performance, and rejecting any inferior plants. The selected superior plants are then grown in preliminary yield trials with multiple replications to identify the most promising lines. These lines are then tested in various locations over several years to ensure they adapt well to different environments. After completing these rigorous tests, the selected superior line is named, multiplied, and released as a new variety. This process typically takes around 12 years, but it can be accelerated using techniques like greenhouses or irrigation during off-seasons..