Lesson Notes By Weeks and Term v3 - Senior Secondary 3
Crop Improvement
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Crop Improvement
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Subject: Agricultural Science
Class: Senior Secondary 3
Term: 1st Term
Week: 1
Theme: Crop Production
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enumerate the aims of crop improvement. Explain the methods of crop improvement State Mendel’s 1st law of segregation of genes. State Mendel’s 2nd law of in dependent as sortment of genes. List the advantages and disadvantages of crop improvement.
Crop Production organism (plant, animal, or microorganism) can be isolated and transferred into the DNA of another plant to introduce a specific desired trait. These are known as Genetically Modified Organisms (GMOs).
Example: Transferring a gene for insect resistance from a bacterium (Bacillus thuringiensis - Bt) into maize or cotton to make them resistant to specific insect pests (e.g., Bt maize in Nigeria resistant to stem borers), thereby reducing pesticide use. Another example is developing vitamin A enriched cassava. 2.3 Mendel’s Laws of Inheritance Gregor Mendel (1822-1884), an Austrian monk, conducted experiments with pea plants and established the fundamental principles of heredity. His work, though initially overlooked, formed the basis of modern genetics.
Key Terms in Genetics: Gene: A unit of heredity that is transferred from a parent to offspring and determines some characteristic of the offspring.
Allele: One of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome. (e.g., T for tall, t for dwarf).
Dominant Allele: An allele that expresses its phenotypic effect even when heterozygous with a recessive allele.
Recessive Allele: An allele whose phenotypic effect is expressed only when homozygous; it is masked by a dominant allele.
Homozygous: Having two identical alleles for a particular gene (e.g., TT or tt).
Heterozygous: Having two different alleles for a particular gene (e.g., Tt).
Genotype: The genetic makeup of an organism (e.g., TT, Tt, tt).
Phenotype: The observable physical or biochemical characteristics of an organism, as determined by both genetic makeup and environmental influences (e.g., Tall, Dwarf).
P Generation: Parental generation, the first set of parents crossed in a genetic experiment.
F1 Generation: First filial generation, the offspring resulting from a cross between the P generation.
F2 Generation: Second filial generation, the offspring resulting from a cross between the F1 generation. 2.3.1 Mendel’s First Law of Segregation of Genes (Law of Segregation): Statement: "Alleles for each gene segregate (separate) from each other during gamete formation such that each gamete receives only one allele." Explanation: This law states that during the formation of gametes (sperm and egg cells), the two alleles for a heritable character (trait) separate from each other, so that each gamete carries only one allele for that character. When fertilization occurs, the zygote gets one allele from each parent.
Worked Example (Monohybrid Cross): Consider a hypothetical Nigerian crop, "Okro," where the allele for Tall stem (T) is dominant over the allele for Dwarf stem (t). If a homozygous tall Okro plant (TT) is crossed with a homozygous dwarf Okro plant (tt): P Generation: Phenotype: Tall Okro x Dwarf Okro Genotype: TT x tt Gametes: TT produces only 'T' gametes. tt produces only 't' gametes.
F1 Generation: All offspring will receive 'T' from the tall parent and 't' from the dwarf parent.
Genotype: All Tt Phenotype: All Tall Okro (due to the dominance of 'T') Now, if the F1 generation (Tt) is allowed to self-pollinate or cross with another F1 (Tt) plant: F1 x F1 Cross: Phenotype: Tall Okro x Tall Okro Genotype: Tt x Tt Gametes: Each Tt parent produces two types of gametes in equal proportion: 'T' and 't'.
F2 Generation (using Punnett Square): | Gametes | T | t | | :------ | :-- | :-- | | T | TT | Tt | | t | Tt | tt | F2 Genotypic Ratio: 1 TT : 2 Tt : 1 tt F2 Phenotypic Ratio: 3 Tall : 1 Dwarf This example demonstrates that alleles (T and t) separated during gamete formation in the F1 generation, allowing the recessive dwarf trait (tt) to reappear in the F2 generation. 2.3.2 Mendel’s Second Law of Independent Assortment of Genes (Law of Independent Assortment): Statement: "Alleles for different genes assort independently of one another during gamete formation." * Explanation: This law states that the alleles of two or more different genes get sorted into gametes independently of one another. In other words, the allele a gamete receives for one gene does not influence the allele received for another gene. This applies to genes Crop Improvement Term: 1st Term Week: 1 ---
1. Overview and Learning Objectives This topic introduces students to the fundamental principles and practices of enhancing crop varieties for increased productivity and resilience. Crop improvement is crucial for ensuring food security, boosting farmers' incomes, and adapting agricultural practices to environmental challenges prevalent in Nigeria. Understanding these concepts is vital for future agriculturists to develop and utilize superior crop varieties that can meet the demands of a growing population and a changing climate. Upon completion of this topic, students will be able to: Identify and list the various goals of improving crop plants for better performance and yield. Describe and explain the different scientific techniques used to develop improved crop varieties. State and comprehend Mendel's First Law, which explains how genetic traits separate during reproduction. State and comprehend Mendel's Second Law, which describes how different genetic traits are inherited independently of each other. Enumerate the benefits and drawbacks associated with the implementation of crop improvement techniques in agriculture.
Real-World Application in Nigeria: Aims of Crop Improvement: Students will understand why researchers in Nigeria focus on developing cassava varieties resistant to Cassava Mosaic Disease or maize varieties that yield more per hectare to feed the nation.
Methods of Crop Improvement: Students will appreciate how techniques like cross-breeding are used to develop hybrid maize varieties that perform better in Nigerian soils, or how selection helps farmers pick the best local yam tubers for planting.
Mendel's Laws: These laws provide the foundational genetic principles that agricultural scientists in Nigeria use when planning breeding programs for crops like cowpea or rice to combine desirable traits.
Advantages and Disadvantages: Students will be able to critically evaluate the pros (e.g., increased food availability, farmer income) and cons (e.g., cost of improved seeds, loss of local varieties) of agricultural policies promoting improved crops in Nigerian communities.
2. Key Concepts and Explanations Definition of Crop Improvement: Crop improvement refers to the process of developing new and improved crop varieties with desirable characteristics such as higher yield, better quality, resistance to pests and diseases, and tolerance to environmental stresses. This involves applying principles of genetics, breeding, and biotechnology. 2.1 Aims of Crop Improvement: Crop improvement programmes are initiated to achieve several objectives critical for sustainable agriculture and food security.
1. Increased Yield: The primary aim is to develop varieties that produce more harvestable biomass or grains per unit area. For example, breeding new maize varieties that yield 5-6 tonnes per hectare compared to local varieties yielding 1-2 tonnes.
2. Resistance to Pests and Diseases: Developing crops that can naturally withstand common pests (e.g., stem borers in maize) and diseases (e.g., Cassava Mosaic Disease, Rice Blast) reduces crop losses and reliance on chemical pesticides.
3. Early Maturity: Cultivating varieties that mature faster allows for multiple cropping cycles within a year, increasing overall productivity and enabling farmers to harvest before adverse weather conditions (e.g., short-duration millet varieties in arid regions).
4. Tolerance to Abiotic Stresses: Breeding crops that can tolerate harsh environmental conditions such as drought, salinity, flooding, extreme temperatures, and poor soil fertility (e.g., drought-tolerant sorghum, flood-tolerant rice).
5. Improved Nutritional Quality: Enhancing the nutritional content of crops, such as increasing protein content in maize, vitamin A in cassava (biofortification), or iron in beans, to combat malnutrition.
6. Better Quality of Produce: Improving characteristics like taste, shelf-life, processing quality (e.g., higher oil content in oil palm, better milling quality in rice, uniform size and appearance for market appeal).
7. Adaptability to Different Environments: Developing varieties that can perform well across a wide range of ecological zones, thus broadening their cultivation area.
8. Uniformity of Maturity: Achieving synchronous ripening of crops for easier and more efficient harvesting, especially for mechanized farming. 2.2 Methods of Crop Improvement: Several methods are employed to achieve the aims of crop improvement.
1. Selection: This is the oldest and simplest method. It involves identifying individual plants with desirable traits from a population and using their seeds or vegetative parts for propagation.
Mass Selection: Involves selecting a large number of phenotypically similar plants from a mixed population, harvesting their seeds together, of ecological zones, thus broadening their cultivation area.
8. Uniformity of Maturity: Achieving synchronous ripening of crops for easier and more efficient harvesting, especially for mechanized farming. 2.2 Methods of Crop Improvement: Several methods are employed to achieve the aims of crop improvement.
1. Selection: This is the oldest and simplest method. It involves identifying individual plants with desirable traits from a population and using their seeds or vegetative parts for propagation.
Mass Selection: Involves selecting a large number of phenotypically similar plants from a mixed population, harvesting their seeds together, and sowing them to produce the next generation. This is effective for improving heterogeneous populations.
Example: A farmer observes their yam field and consistently selects the largest, healthiest, and disease-free yam tubers each season for planting in the next season. Over time, the overall quality and size of yams in the field may improve.
Pure Line Selection: Applies to self-pollinated crops (e.g., rice, wheat, cowpea). It involves selecting a single superior plant, harvesting its seeds, and growing them to form a pure line (genetically uniform progeny). If successful, this pure line is multiplied and released as a new variety.
Example: From a field of self-pollinating cowpea, a plant showing exceptional pod length, high number of seeds per pod, and no signs of disease is identified. Its seeds are harvested separately, planted, and the resulting uniform progeny are evaluated. If superior, this becomes a new variety.
Clonal Selection: Applicable to vegetatively propagated crops (e.g., cassava, yam, sweet potato, sugarcane). It involves selecting a superior single plant from a mixed population and propagating it vegetatively (e.g., stem cuttings, tubers) to form a clone. All individuals in a clone are genetically identical.
Example: A particular cassava plant is noticed to have high yield, large tubers, and strong resistance to Cassava Mosaic Disease. Cuttings are taken from this plant and multiplied to establish a new disease-resistant, high-yielding clone.
2. Hybridization (Cross-breeding): This involves crossing two genetically dissimilar parents to combine desirable traits from both into a single progeny (hybrid). The F1 generation (first filial generation) often exhibits hybrid vigour (heterosis), leading to superior performance compared to either parent.
Process: Pollen from one parent (male) is transferred to the stigma of another parent (female) whose anthers have been removed (emasculation) to prevent self-pollination. The resulting seeds are hybrids.
Example: To combine the high yield of a local maize variety with the disease resistance of another, a breeder crosses them. The resulting hybrid maize (e.g., Oba Super-1) may yield significantly more and be more robust than its parents. This is common in maize, rice, and oil palm breeding in Nigeria.
3. Mutation Breeding: Involves inducing genetic changes (mutations) in the DNA of plants using physical mutagens (e.g., X-rays, gamma rays) or chemical mutagens (e.g., ethyl methanesulfonate). These induced mutations can create new desirable traits not present in the original population.
Example: Irradiating groundnut seeds with gamma rays might produce a mutant with increased oil content or improved disease resistance that can then be selected and developed into a new variety.
4. Polyploidy: This involves altering the number of chromosome sets in a plant. Polyploid plants have more than two sets of chromosomes (e.g., triploids, tetraploids). Often results in larger cell size, increased vigour, larger fruits, and sometimes sterility (e.g., seedless watermelons). Colchicine is a common chemical used to induce polyploidy.
Example: Developing tetraploid groundnuts that have larger seeds and greater vigour than diploid varieties.
5. Biotechnology / Genetic Engineering: Involves the direct manipulation of an organism's genes using molecular biology techniques. Specific genes from one organism (plant, animal, or microorganism) can be isolated and transferred into the DNA of another plant to introduce a specific desired trait. These are known as Genetically Modified Organisms (GMOs).
Example:* Transferring a gene for insect resistance from a bacterium (Bacillus thuringiensis - Bt) into maize or cotton to make them resistant to specific insect pests (e.g., Bt maize in Nigeria resistant to stem borers), thereby reducing pesticide use. Another example is developing vitamin A enriched cassava. 2.3 Mendel’s Laws of Inheritance Gregor Mendel (1822-1884), an Austrian monk, conducted experiments with