Indian Administrative Service IAS Agriculture Optional Paper 2- Section A- 1,2

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1.(a) What is polyploidy? Give a brief account of the classification of polyploids.

Answer: Polyploidy is a condition in which an organism has more than two complete sets of chromosomes in its cells. This can occur naturally, such as in plants, or as a result of human intervention, such as in the creation of some seedless fruits. Polyploids are often classified based on the number of chromosomes sets they possess. The classifications are as follows:

Autopolyploids: These are polyploids that have multiple sets of chromosomes that are derived from the same species. This can occur due to errors in cell division or crossing over during meiosis.

Allopolyploids: These are polyploids that have multiple sets of chromosomes that are derived from different species. This can occur when two different species hybridize and their chromosomes combine.

Segmental Polyploids: These are polyploids that have duplicated only part of their genome, often resulting in a more complex karyotype.

Paleopolyploids: These are ancient polyploids that occurred in the distant past, often resulting in an entire genome doubling, that is, where all chromosomes were duplicated.

Polyploids can have significant genetic and morphological differences from their diploid counterparts, which can lead to changes in the organism's phenotype and adaptation to new environments. Polyploidy is common in plants and has been hypothesized to have played an important role in plant evolution.

(b) What are the applications of mass selection in self-pollinated crops? Describe its merits and demerits.

Answer: Mass selection is a method of plant breeding that involves selecting and propagating the best-performing plants from a population based on their observable traits, without considering the genetic makeup of the plants. This method is commonly used in self-pollinated crops such as wheat, rice, and beans.

Applications of mass selection in self-pollinated crops:

Improvement of quantitative traits: Mass selection is particularly useful for improving quantitative traits such as yield, which are controlled by many genes and are difficult to select for using other methods.

Maintenance of genetic diversity: Since mass selection is based on the selection of plants with desirable phenotypic traits, it allows for the maintenance of genetic diversity within a population, which can help in the adaptation of crops to changing environments.

Easy to implement: Mass selection is a simple and inexpensive method of plant breeding, which makes it particularly useful for small-scale farmers and breeders.

Merits of mass selection in self-pollinated crops:

It is simple and easy to implement, requiring no special equipment or expertise.

It can be used to improve a wide range of traits, particularly quantitative traits such as yield.

It allows for the maintenance of genetic diversity within a population.

Demerits of mass selection in self-pollinated crops:

It can lead to the loss of desirable genes if they are not linked to the phenotypic trait being selected for.

It can lead to the accumulation of deleterious genes in the population over time, which can reduce the overall fitness of the population.

It is not as effective as other methods of plant breeding such as hybridization and molecular breeding for improving complex traits or introducing new traits into the population.

In conclusion, the mass selection is a useful method of plant breeding in self-pollinated crops, particularly for improving quantitative traits and maintaining genetic diversity. However, it has some limitations, and its effectiveness depends on the specific context and objectives of the breeding program.

(c) What do you understand by the vertical and horizontal disease resistance in crop plants?

Answer: Vertical and horizontal disease resistance are two types of resistance mechanisms that crop plants use to protect themselves from pathogens.

Vertical resistance, also known as race-specific resistance, is a type of resistance that is effective against a specific pathogen strain or race. This resistance is controlled by a single gene or a small number of genes, and plants with this type of resistance can completely resist the pathogen strain or race to which they are resistant. However, the pathogen can evolve to overcome this resistance if the gene(s) that control vertical resistance is not present in the plant population.

Horizontal resistance, also known as non-race-specific resistance, is a type of resistance that is effective against multiple pathogen strains or races. This resistance is controlled by multiple genes and is based on the plant's ability to recognize and respond to common pathogen features rather than specific pathogen strains or races. Plants with horizontal resistance can slow down or limit the growth of the pathogen, but they may not be able to completely resist it. Unlike vertical resistance, horizontal resistance is durable and can provide long-term protection against a broad range of pathogens.

In conclusion, vertical resistance is effective against specific pathogen strains or races, while horizontal resistance is effective against multiple pathogen strains or races. Both types of resistance are important in crop plants, and a combination of the two can provide the most effective protection against pathogens.

(d) Define seed quality. Describe the characteristics of a seed that decide its quality.

Answer: Seed quality refers to the degree of excellence of a seed in terms of its ability to germinate, establish and produce a healthy, vigorous, and high-yielding crop. Seed quality is determined by a combination of physical, physiological, and genetic characteristics.

The following are some of the characteristics that decide the quality of a seed:

Genetic purity: The seed should be genetically pure and true to the variety, with no admixture of other varieties or species.

Germination percentage: The percentage of seeds that germinate under ideal conditions is an important factor in seed quality. High-quality seeds should have a high germination percentage.

Vigor: Vigor refers to the ability of the seed to germinate and establish quickly under adverse conditions. Seeds with high vigor will produce more uniform and vigorous seedlings, leading to better crop establishment and yield.

Seed size and weight: Seeds that are uniform in size and weight are generally considered to be of higher quality as they ensure more consistent sowing and emergence.

Physical purity: The seed should be free from foreign matter, such as weed seeds, plant debris, and other crop seeds.

Moisture content: The seed should have a moisture content within the acceptable range to prevent deterioration and ensure optimal germination.

Freedom from diseases and pests: The seed should be free from diseases and pests that can reduce germination and crop yield.

Seedling vigor: The seedlings produced by high-quality seeds should be strong, healthy, and capable of withstanding environmental stresses.

In conclusion, seed quality is essential for the success of crop production. The characteristics that define seed quality include genetic purity, germination percentage, vigor, seed size and weight, physical purity, moisture content, freedom from diseases and pests, and seedling vigor. Farmers should always aim to purchase seeds of high quality to achieve optimal yields and profitability.

(e) Define matric potential, osmotic potential, and turgor potential, and explain their interrelationships with water potential.

Answer: Matric potential, osmotic potential, and turgor potential are three components of water potential, which is the total potential energy that water has in a system. Water moves from areas of high water potential to areas of low water potential. Understanding the interrelationships between these components is important for understanding how water moves through plants and other systems.

Matric potential is the energy required to remove water from the soil or other porous material. It is affected by the size and distribution of soil particles, as well as the amount of water already present in the soil. When soil is very dry, the matric potential is very negative, indicating that a lot of energy would be required to remove water from the soil.

Osmotic potential is the energy required to move water across a membrane due to differences in solute concentration. When a solution has a high concentration of solutes, such as salts or sugars, water tends to move from areas of low solute concentration to areas of high solute concentration. This movement of water is driven by the osmotic potential, which is negative for solutions with high solute concentrations.

Turgor potential is the pressure exerted by the cell wall against the protoplast in plant cells. This pressure is due to the influx of water into the cell, which creates a positive pressure that pushes against the cell wall. Turgor pressure helps maintain the shape of the cell and is important for plant growth and development.

The relationship between these components of water potential can be expressed by the following equation:

Water potential = matric potential + osmotic potential + turgor potential

In this equation, water potential represents the total potential energy of the water in the system. The individual components of water potential can be positive or negative, depending on the conditions of the system. For example, a plant cell with high turgor pressure will have a positive turgor potential, while a solution with a high concentration of solutes will have a negative osmotic potential. By understanding the interrelationships between these components of water potential, we can better understand how water moves through different systems and how it affects plant growth and other processes.

2. (a) Discuss the structure of a plant chromosome and its role in genetic diversity.

Answer: Plant chromosomes are the structures within the nucleus of a plant cell that carries genetic information in the form of DNA. They play a crucial role in genetic diversity by serving as the carriers of the genetic material that is passed from one generation to the next.

Plant chromosomes vary in number and size depending on the species. For example, a diploid plant species have two sets of chromosomes, while a tetraploid plant species has four sets of chromosomes. The chromosomes themselves are made up of DNA molecules, which are wrapped around histone proteins to form a compact structure called chromatin.

Plant chromosomes can be visualized using specialized techniques such as staining, which reveals characteristic banding patterns that can be used to identify individual chromosomes. The banding patterns are created by differences in the DNA sequence and can be used to study chromosomal rearrangements that can lead to genetic diversity.

One mechanism by which plant chromosomes can generate genetic diversity is through the process of recombination. Recombination occurs during meiosis when homologous chromosomes exchange genetic material. This can result in the formation of new combinations of alleles, which can lead to genetic diversity within a population.

Another mechanism by which plant chromosomes can generate genetic diversity is through mutations. Mutations are changes in the DNA sequence that can occur spontaneously or as a result of exposure to environmental factors such as radiation or chemicals. Mutations can alter the function of genes or regulatory regions, leading to new phenotypic traits that can be passed on to the next generation.

In summary, the structure of plant chromosomes is critical to genetic diversity, as it allows for the exchange of genetic material between homologous chromosomes during meiosis, as well as the generation of new mutations. These mechanisms contribute to the genetic variation within plant populations, which is essential for adaptation to changing environmental conditions and the survival of the species.

(b) Discuss the concept of the center of origin of crops and its role in plant breeding. Describe the role of N. I. Vavilov in identifying the center of origin of various crops with appropriate examples.

Answer: The concept of the center of origin of crops refers to the geographic regions where the domestication and evolution of crops occurred. These regions are characterized by the highest genetic diversity of a particular crop species and are considered to be the primary sources of genetic variation for that crop. Understanding the center of origin is crucial for plant breeding, as it allows for the identification and utilization of the genetic resources necessary for developing new and improved crop varieties.

Nikolai Ivanovich Vavilov was a Russian botanist who made significant contributions to the study of plant genetics and the identification of the centers of origin of various crops. Vavilov believed that the genetic diversity of crop plants was influenced by their geographic origins, and he led expeditions to collect plant specimens from all over the world in order to study their genetics and origins.

Vavilov identified several centers of origin of crops, including:

The Andes Mountains in South America, which is the center of origin for potatoes, tomatoes, and quinoa.

The Fertile Crescent region in the Middle East is the center of origin for wheat, barley, and other cereal crops.

Central Asia, is the center of origin for apples, apricots, and many other fruit and nut crops.

Vavilov's work on identifying the centers of origin of crops has been critical in plant breeding. It has allowed plant breeders to identify the genetic resources necessary for developing new crop varieties with improved yields, disease resistance, and other desirable traits. For example, the identification of the center of origin of wheat allowed for the discovery of wild wheat species with genes that confer resistance to various pests and diseases. These genes have been used to develop new wheat varieties with improved resistance to biotic and abiotic stresses.

In conclusion, the concept of the center of origin of crops is crucial in plant breeding, and the work of scientists like Vavilov in identifying these centers has played a vital role in developing new crop varieties. Understanding the origins and genetic diversity of crop plants allows for the identification and utilization of genetic resources necessary for developing crops that can meet the needs of a growing population and changing climate.

(c) What are the factors that affect the longevity of seeds during storage in warehouses? Describe.

Answer: The longevity of seeds during storage in warehouses is influenced by a variety of factors, including:

Seed moisture content: Seeds that are too moist are at risk of developing mold, which can lead to degradation and reduced viability. Conversely, seeds that are too dry may become desiccated and lose their viability. Optimal moisture content varies by seed type but generally ranges between 5-10%.

Temperature: Seeds that are stored at higher temperatures tend to degrade more rapidly than those stored at lower temperatures. For example, every 10-degree Celsius increase in temperature can result in a two-fold reduction in seed viability.

Relative humidity: Humidity levels can impact seed moisture content and, therefore, seed viability. High humidity levels can lead to increased seed moisture content and increased risk of fungal growth, while low humidity levels can cause seed desiccation.

Seed age: The age of the seed can impact its viability during storage. As seeds age, their genetic material may degrade, leading to reduced germination rates and lower viability.

Seed quality: Seed quality at the time of storage can impact its longevity. Seeds that are damaged or diseased before storage are more likely to degrade and lose viability over time.

Storage conditions: The type of storage containers used, as well as the conditions of the storage environment, can affect seed longevity. For example, seeds stored in poorly ventilated containers may experience increased moisture levels, while those stored in damp environments may be at higher risk of fungal growth.

In order to maximize seed longevity during storage, it is essential to maintain optimal seed moisture content, temperature, and humidity levels. Seed storage containers should be well-ventilated and protected from dampness and direct sunlight. Regular monitoring of seed quality and storage conditions can help ensure optimal seed viability over time. Additionally, seeds can be treated with fungicides and other chemicals to help protect against fungal growth and other pests that can damage seeds during storage.

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