Crop Improvement – I (Kharif)
UNIT-III
Important concepts of breeding self-pollinated
Breeding of self-pollinated crops involves the development of new cultivars with desirable traits through controlled pollination and selection. Here are some important concepts of breeding self-pollinated crops:
Self-pollinated crops tend to be more homozygous than cross-pollinated crops. Homozygosity refers to the condition of having identical alleles for a particular gene. In self-pollinated crops, homozygosity can be achieved through repeated self-pollination and selection.
Pure lines are populations of self-pollinated plants that are genetically uniform. Pure lines are typically created through a process called inbreeding, which means they are created by selecting and propagating individual plants that have desirable traits through several generations of self-pollination. Pure lines are important in the development of new cultivars as they provide a genetically stable base for further breeding.
Once a pure line has been established, it can be used as the basis for further breeding efforts to develop new varieties with even better traits. For example, plant breeders may cross two different pure lines to create a hybrid variety that combines the desirable traits of both parents. Alternatively, they may use genetic engineering techniques to introduce specific genes or traits into a pure line.
- Initial selection: The plant breeder selects individual plants from a population that exhibit desirable traits, such as high yield or disease resistance. These plants become the starting population for the breeding program.
- Selfing: The selected plants are self-pollinated, either by removing the male reproductive structures (stamens) or by bagging the flowers to prevent cross-pollination. This produces offspring that are genetically identical to the parent plant.
- Second selection: The offspring are screened again for the desired traits, and the best individuals are selected for further breeding.
- Continued selfing: The selected plants are self-pollinated again, and this process is repeated for several generations. As the generations progress, the plants become increasingly homozygous for all genes, meaning that each individual has two copies of the same allele for every gene.
- Line selection: After several generations of selfing, the breeder selects individual plants that are genetically uniform and exhibit the desired traits. These plants are considered to be pure lines and can be used as the basis for further breeding efforts.
- Cross-breeding or genetic engineering: Once a pure line has been established, it can be used as a parent in a cross-breeding program to create new hybrid varieties with desired traits. Alternatively, genetic engineering techniques can be used to introduce specific genes or traits into the pure line.
Overall, the breeding of self-pollinated crops requires careful selection and maintenance of pure lines, as well as the use of techniques such as recurrent selection, outcrossing, and hybridization to introduce new genetic variation and improve traits. Understanding these concepts is important for the development of new cultivars with improved yield, quality, and disease resistance.
Important concepts of breeding Cross-pollinated
Breeding of cross-pollinated crops involves the development of new cultivars with desirable traits through controlled pollination and selection. Here are some important concepts of breeding cross-pollinated crops:
Heterozygosity:
Cross-pollinated crops tend to be more heterozygous than self-pollinated crops. Heterozygosity refers to the condition of having different alleles for a particular gene. In cross-pollinated crops, heterozygosity can be achieved through natural or artificial cross-pollination.
Genetic diversity:
Genetic diversity is important in breeding cross-pollinated crops because it provides the raw material for selection and the potential for improvement. Maintaining genetic diversity in cross-pollinated crops can be challenging due to the tendency for genetic drift and the loss of alleles over time.
Population improvement: Population improvement is a breeding technique used to improve quantitative traits such as yield and disease resistance in cross-pollinated crops. It involves selecting and propagating individuals with desirable traits from a genetically diverse population, followed by the recombination of their genes through natural or artificial cross-pollination. This process is repeated over several generations to improve the overall genetic makeup of the population.
Hybridization:
Hybridization is the process of crossing two genetically distinct parents to produce offspring with desirable traits. In cross-pollinated crops, hybridization can be used to introduce new genetic variation and improve traits such as yield and disease resistance. However, the development of hybrid cultivars in cross-pollinated crops can be challenging due to the need to maintain the genetic purity of the parents and to overcome outbreeding depression.
Phenotypic selection: Phenotypic selection is a breeding technique used to improve qualitative traits such as flower colour, seed size, and disease resistance in cross-pollinated crops. It involves selecting individuals with desirable traits based on their phenotype (observable physical characteristics), rather than their genotype (genetic makeup). Phenotypic selection can be effective in improving qualitative traits, but it can also be influenced by environmental factors and may result in the loss of genetic diversity.
Overall, the breeding of cross-pollinated crops requires the maintenance of genetic diversity, the use of techniques such as population improvement and hybridization to introduce new genetic variation, and the careful selection of individuals with desirable traits. Understanding these concepts is important for the development of new cultivars with improved yield, quality, and disease resistance.
Important concepts of breeding Vegetatively propagated crops
Breeding of vegetatively propagated crops involves the development of new cultivars with desirable traits through controlled propagation and selection. Here are some important concepts of breeding vegetatively propagated crops:
Clonal propagation: Vegetatively propagated crops are propagated by cloning, which involves the asexual reproduction of plants from vegetative tissues such as cuttings or bulbs. Clonal propagation ensures that the offspring are genetically identical to the parent plant, which can be advantageous in maintaining desirable traits.
Somaclonal variation: Somaclonal variation refers to genetic variation that arises during the tissue culture process, which is commonly used for the clonal propagation of vegetatively propagated crops. Somaclonal variation can lead to the development of new traits, but it can also result in the loss of desirable traits. Breeding programs for vegetatively propagated crops must carefully manage somaclonal variation to maintain genetic stability and improve desirable traits.
Mutation breeding: Mutation breeding is a technique used to induce genetic mutations in plants through the application of mutagens such as radiation or chemicals. Mutation breeding can be effective in generating new traits in vegetatively propagated crops, but it requires careful selection and screening to identify desirable mutations.
Heterozygosity: Vegetatively propagated crops can exhibit both heterozygosity and homozygosity, depending on the reproductive behaviour of the parent plant. Heterozygosity refers to the condition of having different alleles for a particular gene, and it can lead to the development of new traits through the recombination of genes.
In vitro selection: In vitro selection is a technique used to select plants with desirable traits in vegetatively propagated crops. It involves growing plant tissues in culture and subjecting them to selective pressure, such as exposure to toxins or herbicides, to identify plants with desirable traits.
Overall, the breeding of vegetatively propagated crops requires careful management of clonal propagation and the potential for somaclonal variation, the use of techniques such as mutation breeding and in vitro selection to generate and identify desirable traits, and the consideration of both heterozygosity and homozygosity in the breeding process. Understanding these concepts is important for the development of new cultivars with improved yield, quality, and disease resistance in vegetatively propagated crops..