Unit V
Commercial Plant Breeding & Seed Industry
Contents
Principles and techniques of seed production, types of seeds, quality testing in self and cross pollinated crops.
Principles of Seed Production
Seed production is a crucial aspect of agriculture that ensures the availability of high-quality and genetically pure seeds for planting. The following are the key principles of seed production:
- Genetic Purity: The foundation of seed production is maintaining genetic purity. This involves preventing cross-pollination between different varieties or species to ensure that seeds produced are true to type and possess the desired characteristics of the parent plants.
- Isolation Distance: To avoid cross-pollination, seed fields of different varieties or species must be adequately separated by specific isolation distances. The distance varies depending on the crop's mode of pollination (self-pollinated, cross-pollinated, or wind-pollinated) to prevent unintended hybridization.
- Roguing: Roguing involves the removal of off-type or diseased plants from the seed field during the growing season. This practice helps maintain genetic purity and ensures that only desirable traits are passed on to the seed.
- Field Selection: The selection of suitable seed fields is critical for seed production. Fields with good soil fertility, proper drainage, and adequate sunlight are preferred to promote healthy plant growth and seed development.
- Time of Planting: Timely planting is essential to synchronize flowering and seed development among plants. This helps minimize the risk of cross-pollination from nearby fields and ensures uniform seed maturation.
- Seed Certification: Seed certification is a formal process where seeds are inspected and certified by authorized agencies to meet specific quality standards. Certified seeds guarantee high quality and genetic purity, providing confidence to farmers.
- Seed Treatment: Seed treatment involves applying fungicides or insecticides to protect seeds from soil-borne diseases and pests during germination and early growth stages.
- Harvesting at Optimal Maturity: Seeds should be harvested at the optimum stage of maturity to ensure high germination rates and good storage characteristics.
- Seed Processing: After harvest, seeds are processed to remove impurities, weed seeds, and other foreign matter. Proper processing ensures that only clean and viable seeds are packaged and sold to farmers.
- Storage: Proper storage conditions are critical to maintaining seed viability and quality. Seeds should be stored in a cool, dry, and well-ventilated place to minimize deterioration.
- Seed Testing: Seed samples are subjected to various quality tests to determine germination rates, genetic purity, and other seed quality attributes. Seed testing helps assess the viability and overall quality of the seed lot.
- Seed Packaging and Labeling: Seeds should be packaged and labeled accurately to provide essential information to farmers, such as crop variety, germination percentage, and sowing instructions.
The principles of seed production encompass a series of practices aimed at ensuring the production of high-quality, genetically pure, and viable seeds. By adhering to these principles, seed producers can contribute to enhancing agricultural productivity and supporting sustainable farming practices.
Techniques of Seed Production
Seed production techniques vary based on the type of crop, its reproductive characteristics, and the desired seed quality. Here are the techniques commonly used in seed production:
1. Self-Pollinated Crops:
- Roguing: Removing off-type and diseased plants from the field during the growing season to maintain genetic purity.
- Isolation: Isolating different varieties or species to prevent cross-pollination.
- Emasculation: Removing the male reproductive organs (anthers) from flowers to prevent self-pollination and encourage controlled cross-pollination.
- Bagging: Covering emasculated flowers with bags to protect them from unwanted pollination.
- Hand Pollination: Transferring pollen from one selected plant to the stigma of another to ensure controlled cross-pollination.
- Selfing: In self-pollinated crops, allowing plants to self-pollinate naturally ensures genetic stability. Plants are grown under conditions that encourage natural self-pollination, minimizing the chances of cross-pollination.
- Time of Flowering: Ensuring that flowering periods of different varieties do not overlap helps prevent cross-pollination. This is especially important in crops with extended flowering periods.
2. Cross-Pollinated Crops:
- Isolation: Isolating different varieties or species by sufficient distance or time to prevent unintended cross-pollination.
- Roguing: Removing off-type and diseased plants to maintain genetic purity.
- Cytoplasmic Male Sterility (CMS): Some crops are bred to have a trait called cytoplasmic male sterility (CMS), where the plant's male reproductive organs are non-functional. This eliminates self-pollination and encourages cross-pollination.
- Restoring Fertility: In crops with CMS, breeders develop lines with a fertility-restoring gene (Rf) that counteracts the male sterility. These lines are used as pollen donors to ensure successful cross-pollination.
- Mass Selection: Selecting desirable plants from the entire population for seed production.
- Pedigree Breeding: Recording the pedigree (parentage) of plants to ensure genetic purity and traceability.
- Male Sterility and Hybrid Seed Production: Inducing male sterility in one parent and crossing it with a fertile line to produce hybrid seeds.
3. Vegetatively Propagated Crops:
- Cuttings: Propagating new plants from stem cuttings.
- Grafting: Joining a scion (a shoot with desired characteristics) to a rootstock to produce a new plant.
- Layering: Encouraging a stem to produce roots while it is still attached to the parent plant, and then separating it to create a new plant.
4. Greenhouse and Protected Cultivation:
- Controlled Environment: Providing optimal growing conditions, such as temperature, humidity, and light, to enhance seed production.
- Pollination Management: Hand pollination or introducing pollinators for cross-pollination in controlled environments.
5. Seed Treatment and Processing:
- Seed Treatment: Treating seeds with fungicides, insecticides, or other treatments to protect against pests and diseases.
- Seed Cleaning: Removing impurities, weed seeds, and other foreign matter from seeds to ensure purity.
6. Seed Storage:
- Drying: Reducing seed moisture content to prevent deterioration during storage.
- Cool Storage: Storing seeds in cool and dry conditions to maintain viability.
Seed production techniques involve a range of practices tailored to the reproductive characteristics of different crops. Whether for self-pollinated, cross-pollinated, or vegetatively propagated crops, these techniques aim to ensure genetic purity, high seed quality, and optimal conditions for seed development and storage.
Types of seeds
Seeds are essential for plant propagation and are classified based on various factors such as origin, use, and genetic makeup. Seeds can be categorized based on various criteria.
Classes of seed
Nuclear seed : This is the hundred percent genetically pure seed with physical purity and produced by the original breeder/Institute /State Agriculture University (SAU) from basic nucleus seed stock. A pedigree certificate is issued by the producing breeder.
Breeder seed : The progeny of nucleus seed multiplied in large area as per indent of Department of Agriculture and Cooperation (DOAC), Ministry of Agriculture, Government of India, under supervision of plant breeder / institute / SAUs and monitored by a committee consisting of the representatives of state seed certification agency, national / state seed corporations, ICAR nominee and concerned breeder. This is also hundred percent physical and genetic pure seed for production of foundation seed. A golden yellow colour certificate is issued for this category of seed by the producing breeder.
Foundation seed : The progeny of breeder seed produced by recognized seed producing agencies in public and private sector, under supervision of seed certification agencies in such a way that its quality is maintained according to prescribed field and seed standards. A white colour certificate is issued for foundation seed by seed certification agencies.
Registered seed : Registered seed shall be the progeny of foundation seed that is so handled as to maintain its genetic identity and purity according to standard specified for the particular crop being certified. A purple colour certificate is issued for this category of seed.
Certified seed : The progeny of foundation seed produced by registered seed growers under supervision of seed certification agencies to maintain the seed quality as per minimum seed certification standards. A blue colour certificate is issued by seed certification agency for this category of seed.
Here's a comprehensive breakdown of different types of seeds categorized by various characteristics:
1. Based on Cotyledon Number:
a. Monocotyledonous Seeds: Monocot seeds have a single cotyledon, which is the first leaf structure to emerge during germination. Monocots are known for certain features, including parallel leaf venation and scattered vascular bundles in the stem.
Examples of monocot plants include grasses (wheat, corn), lilies, orchids, and palms.
b. Dicotyledonous Seeds: Dicot seeds have two cotyledons, which usually emerge above the soil surface during germination. Dicots are characterized by reticulate (net-like) leaf venation and vascular bundles arranged in a circular pattern in the stem.
Examples of dicot plants include beans, peas, sunflowers, roses, and most trees.
2. Based on Germination Requirements:
a. Epigeal Germination: In epigeal germination, the cotyledons are pushed above the soil surface as the young seedling emerges. The cotyledons often become photosynthetic and green, aiding in the early growth of the plant. Examples of plants with epigeal germination include beans, sunflowers, etc.
b. Hypogeal Germination: In hypogeal germination, the cotyledons remain below the soil surface as the seedling emerges. The cotyledons might not be exposed to light and remain non-photosynthetic. The first true leaves develop above the cotyledons. Examples of plants with hypogeal germination include peas, peanuts, and many tree species.
3. Based on Economic Importance:
- Cereal Seeds: Cereal crops are staple foods that provide a significant portion of the world's caloric intake. These seeds are rich in carbohydrates and are consumed as grains. Examples include: Wheat, Rice Corn etc.
- Oilseed Seeds: Oilseed crops produce seeds that are rich in oil, which is extracted and used for cooking, industrial purposes, and biodiesel production. Examples include: Soybeans, sunflower seed, rapeseed etc.
- Pulse Seeds: Pulses are leguminous crops that produce protein-rich seeds. They are important sources of protein for human and animal consumption. Examples include: Lentils, Chickpeas, Peas etc.
- Fruit Seeds: Fruits provide essential vitamins, minerals, and antioxidants. Examples include: Tomato, Grape seeds, pepper seeds etc.
- Timber and Nut Seeds: Seeds from trees are essential for timber production and can also have economic value as nuts. Examples include: oak acorns, coconut seeds etc.
- Forage and Fodder Seeds: Certain seeds are grown as forage for livestock, providing animal feed and supporting the meat and dairy industry. For example- Alfalfa seeds, Timothy grass seeds etc.
4. Based on Seed Covering:
- Naked Seeds (Gymnosperms): Seeds not enclosed within a fruit. Examples: pine cones, ginkgo.
- Enclosed Seeds (Angiosperms): Seeds enclosed within a fruit. Examples: apples, berries.
5. Based on Storage Tissue:
- Endospermic Seeds: Have well-developed endosperm for nourishing the embryo. Examples: corn, castor beans.
- Non-Endospermic Seeds: Endosperm is absorbed during maturation. Most dicotyledonous seeds fall into this category.
6. Based on Seed Dispersal Mechanism:
- Wind-Dispersed Seeds: Adapted for wind dispersal, often lightweight with structures like wings or hairs. Examples: dandelions, maple seeds.
- Animal-Dispersed Seeds: Adapted for dispersal by animals. Can have hooks, barbs, or tasty fruit to entice animals. Examples: blueberries, acorns.
- Water-Dispersed Seeds: Designed to float and be carried by water currents. Examples: coconut seeds.
Quality testing in self and cross pollinated crops
Quality testing of seeds is crucial to ensure that farmers receive high-quality and genetically pure seeds for planting. The testing process involves various parameters to assess seed quality. Here are the key aspects of quality testing for self and cross-pollinated crops:
1. Genetic Purity Testing: Genetic purity testing is essential for both self and cross-pollinated crops. It involves the evaluation of seed samples to check for the presence of impurities or off-types.
Methods of Genetic Purity Testing:
- Morphological Evaluation: Seeds, seedlings, or plants are visually inspected to check if they exhibit the expected traits and characteristics of the variety.
- Molecular Markers: DNA-based techniques are used to analyze the genetic profile of seeds and plants to confirm their identity.
- Biochemical Markers: Biochemical markers can indicate the presence of specific traits or genes in the seed lot.
2. Germination Testing: Germination testing assesses the viability of seeds by determining their ability to sprout and develop into healthy seedlings. The percentage of seeds that successfully germinate under controlled conditions indicates seed quality and viability.
3. Vigor Testing: Vigor testing evaluates the overall health and robustness of seeds. It includes tests like accelerated aging and cold tests to simulate stressful conditions. Seeds with high vigor are more likely to establish and grow well under adverse conditions.
4. Purity and Inert Matter: Purity testing checks for the presence of foreign matter, weed seeds, or inert materials in the seed lot. High levels of impurities can negatively impact crop performance.
5. Moisture Content: Measuring the moisture content of seeds is vital to prevent deterioration during storage. Seeds with excessive moisture are prone to fungal growth and reduced viability.
6. Physical Characteristics: Physical characteristics, such as seed size, shape, and color, are assessed to ensure uniformity in the seed lot. Uniform seeds promote even germination and plant growth.
7. Disease Testing: Disease testing involves the detection of seed-borne pathogens that can negatively affect crop health. This is particularly important for cross-pollinated crops, where the transmission of diseases can occur through pollination.
8. Seed Health Testing: Seed health testing determines the presence of pathogens or pests on the seed surface or within the seed. Seed treatments and cleaning methods are used to reduce seed-borne pathogens.
9. Seed Weight: Seed weight is an essential factor in determining planting rates and seed distribution. It varies among different seed lots and can influence crop establishment and yield.
10. Seed Viability and Longevity: Assessing seed viability and longevity helps determine the potential storage life of seeds. Seeds with good viability and longevity can be stored for extended periods without significant reduction in germination rates.
Quality testing is a crucial step in ensuring that farmers receive high-quality and genetically pure seeds for planting. The various testing parameters mentioned above are tailored to specific characteristics of self and cross-pollinated crops. By conducting thorough quality testing, seed producers can provide farmers with seeds that have the best chances of successful germination, establishment, and robust growth, contributing to increased agricultural productivity and sustainability.
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