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Seed Technology - II

 Unit – II : Seed processing and storage

 

2.1 Seed processing

 

Seed processing is a critical step in ensuring high-quality seed for planting. It involves a series of operations aimed at removing impurities, reducing moisture content, and improving seed viability. By understanding and applying the principles of pre-cleaning, precuring, and drying, seed processors can significantly improve seed quality, enhance storability, and ultimately contribute to successful crop production.

 

1. Pre-Cleaning

Pre-cleaning is the initial step in seed processing, where large-sized impurities are removed from the seed lot. The primary goal is to reduce the bulk and improve the efficiency of subsequent processing steps.

 

Principles of Pre-Cleaning:

·         Separation based on size and density: Impurities like sticks, stones, and large weed seeds are removed using screens, sieves, or wind separators.

·         Removal of foreign matter: Heavy impurities are separated from the seed lot using gravity or specific gravity separators.

·         Reduction of processing load: By removing large impurities, the subsequent cleaning processes become more efficient and effective.

 

2. Precuring:

Precuring is primarily applied to forest seeds and involves controlled drying of fruits or cones to facilitate seed extraction and improve seed quality.

 

Principles of Precuring:

·         Moisture reduction: The moisture content of the fruits or cones is reduced to a suitable level for efficient seed extraction.

·         Seed maturation: Precuring helps in completing the seed maturation process, improving seed viability and germination.

·         Facilitates seed extraction: By drying the fruits or cones, the process of seed extraction becomes easier and less damaging to the seeds.

3. Drying

Drying is a crucial step in seed processing to reduce moisture content to safe levels for storage and transportation. It helps in preventing seed deterioration and maintaining seed viability.

 

Principles of Drying:

·         Moisture reduction: The moisture content of the seed is lowered to a safe level based on the seed type and storage conditions.

·         Temperature control: Drying temperature is critical to avoid seed damage and maintain seed quality.

·         Airflow: Proper airflow is essential for efficient moisture removal.

·         Timely drying: Quick and uniform drying is necessary to prevent mold growth and deterioration.

 

Common Drying Methods:

         i.            Sun drying: A low-cost method suitable for small quantities of seed, but susceptible to weather conditions.

       ii.            Artificial drying: Using dryers with controlled temperature and airflow for efficient and consistent drying.

 

 

2.2 Seed Extraction

Seed extraction is the process of removing seeds from their surrounding plant matter. This can vary significantly depending on the type of plant.

 

Common methods include:

         i.            Hand extraction: This is often used for small quantities or delicate seeds.

       ii.            Mechanical extraction: Machines are used for large-scale extraction of seeds from fruits, vegetables, and grains.

      iii.            Chemical extraction: This method involves using chemicals to break down the plant matter and release the seeds.

 

Seed Cleaning

Seed cleaning is essential to remove impurities and unwanted materials from the extracted seeds. This improves seed quality and germination rates.

 

Common cleaning methods:

         i.            Air cleaning: Uses airflow to separate light impurities from heavier seeds.

       ii.            Screening: Separates seeds based on size using different mesh sizes.

      iii.            Gravity separation: Separates seeds based on density differences.

      iv.            Magnetic separation: Removes metallic contaminants.

       v.            Colour sorting: Uses optical sensors to remove seeds with undesirable colors.

 

Seed Grading

Seed grading involves sorting seeds based on size, shape, weight, and other quality parameters. This ensures uniformity and consistency in the seed lot.

 

Common grading methods:

         i.            Size grading: Uses screens or sieves to separate seeds based on size.

       ii.            Shape grading: Uses optical sensors or mechanical separators to sort seeds based on shape.

      iii.            Weight grading: Uses specific gravity separators or electronic sorters to separate seeds based on weight.

 

Benefits of Seed Cleaning and Grading:

                                              i.            Improved seed quality and germination rates

                                             ii.            Increased crop yield and uniformity

                                           iii.            Reduced disease and pest problems

                                           iv.            Enhanced seed marketability

 

2.3 Cleaning and Grading of Seeds in Seed Technology

 

Cleaning and grading are crucial steps in seed technology to ensure high-quality seed products. These processes involve removing impurities and sorting seeds based on size, weight, and other characteristics.

Importance of Cleaning and Grading

• Improved Seed Quality: Removes impurities, weed seeds, and damaged seeds.
• Enhanced Germination: Clean seeds have better germination rates.
• Standardized Seed Lots: Grading ensures uniform seed size and weight.
• Disease Prevention: Reduces the spread of seed-borne diseases.
• Accurate Seed Counting: Proper grading facilitates precise seed counting.

Cleaning Processes

Several methods and machines are used for seed cleaning:

Physical Cleaning

• Screening: Separates seeds based on size using sieves with different mesh sizes.
• Aspiration: Removes light impurities like chaff and dust using airflow.
• Gravity Separation: Separates seeds based on density differences.
• Indentation Separation: Removes seeds with specific shapes or imperfections.

Other Methods

• Magnetic Separation: Removes iron contaminants.
• Color Sorting: Uses electronic sensors to separate seeds based on color.
• Hand Picking: Manual removal of impurities for high-value seeds.

Grading Processes

Seeds are graded based on size, weight, and other parameters:

• Size Grading: Uses screens or sieves to separate seeds into different size categories.
• Weight Grading: Employing specific gravity separators to classify seeds based on weight.
• Shape Grading: Separating seeds based on their shape, such as round, oval, or elongated.

Common Seed Cleaning and Grading Equipment

• Air screen cleaners
• Gravity separators
• Seed graders
• Magnetic separators
• Color sorters

Challenges and Considerations

• Efficient removal of similar-sized impurities.
• Maintaining seed viability during cleaning and grading.
• Cost-effective cleaning and grading processes.
• Seed-specific cleaning and grading requirements.

 

2.4 Pre-Storage Treatments in Seed Technology

 

Pre-storage treatments are crucial steps in seed technology aimed at preserving seed quality and longevity. These treatments help protect seeds from deterioration, insect and pathogen attacks, and improve their overall viability.

Objectives of Pre-Storage Treatments:

• Protection: Shield seeds from physical damage, insects, diseases, and environmental factors.
• Quality Preservation: Maintain seed vigor, germination potential, and genetic purity.
• Longevity Enhancement: Extend seed life and storage duration.

Types of Pre-Storage Treatments:

1. Seed Disinfection:

• Removal of fungal and bacterial spores from the seed coat or deeper tissues.
• Involves chemical treatments (fungicides, bactericides) applied as dips, soaks, or dusts.

2. Seed Disinfectation:

• Destruction of surface-borne organisms contaminating the seed surface.
• Similar methods as seed disinfection, focusing on surface decontamination.

3. Seed Protection:

• Application of insecticides, fungicides, or other chemicals to protect seeds during storage.
• Helps prevent insect and disease attacks.

4. Moisture Adjustment:

• Reducing seed moisture content to safe levels for storage.
• Drying is a common method to achieve this.

5. Seed Cleaning:

• Removal of impurities, chaff, and foreign matter from the seed lot.
• Improves seed purity and uniformity.

6. Seed Grading:

• Sorting seeds based on size, weight, or other physical characteristics.
• Ensures uniform seed lots and better planting performance.

7. Seed Pelleting:

• Coating seeds with inert materials to improve handling, sowing precision, and germination.
• Commonly used for small seeds.

8. Seed Inoculation:

• Introducing beneficial microorganisms (e.g., Rhizobium) to the seed coat.
• Promotes symbiotic relationships for nutrient uptake.

Common Pre-Storage Treatment Methods:

• Drying: Reducing seed moisture content to safe levels.
• Heat Treatment: Applying heat to kill certain pathogens or insects.
• Chemical Treatments: Using fungicides, insecticides, or other chemicals for protection.
• Pelleting: Coating seeds with inert materials.

2.5 Bagging and labeling in seed technology

Bagging

• Purpose: Packaging seeds into convenient units for handling, storage, and distribution.  
• Materials:
• Plastic bags (various types for different seed sizes and moisture levels)
• Paper bags (for breathable storage)
• Other specialized containers (pouches, bottles, etc.)
• Process:
• Filling: Seeds are filled into bags using manual or automated machines.  
• Sealing: Bags are sealed to prevent moisture, pests, and contamination.
• Weight verification: Bags are weighed to ensure they meet the specified weight.

Labeling

• Purpose: Providing essential information about the seed to farmers and consumers.  
• Information:
• Crop variety
• Seed class (certified, registered, etc.)
• Net weight
• Germination percentage
• Purity level
• Production date
• Lot number
• Seed treatment information (if any)
• Other relevant details as per regulations
• Types of labels:
• Paper labels (attached to the bag)
• Printed directly on the bag
• Tags (for larger containers)
• Regulations: Labeling requirements vary by country and seed type.

Importance of Bagging and Labeling

• Preservation: Proper bagging protects seeds from damage and degradation.  
• Identification: Clear labeling ensures traceability and prevents seed mix-ups.  
• Quality assurance: Information on the label guarantees seed quality and performance.
• Regulatory compliance: Adhering to labeling standards is essential for legal seed sales.

2.6. Safety Precautions During Seed Processing

 

Seed processing involves handling various machinery, chemicals, and biological materials, making it essential to prioritize safety. Here are some crucial precautions:

Personal Protective Equipment (PPE)

• Eye protection: Goggles or safety glasses to shield from dust and chemicals.
• Respiratory protection: Dust masks or respirators, especially when handling treated seed or working in dusty environments.
• Hand protection: Gloves to prevent skin contact with chemicals and irritants.
• Skin protection: Long sleeves and pants to minimize skin exposure.
• Foot protection: Safety shoes to protect feet from heavy objects or machinery accidents.

Machinery Safety

• Regular maintenance: Ensure all machinery is in good working condition.
• Operator training: Provide comprehensive training to operators on safe operation procedures.
• Emergency stops: Ensure easy access to emergency stop buttons.
• Guards and enclosures: Use safety guards and enclosures to protect operators from moving parts.  
• Lockout/tagout procedures: Implement proper lockout/tagout procedures during maintenance or repairs.

Chemical Safety

• Proper storage: Store chemicals in a secure, well-ventilated area, away from heat and ignition sources.
• Labeling: Clearly label all chemical containers.  

 

• Handling: Use appropriate handling techniques, avoiding direct contact with skin and eyes.
• Ventilation: Ensure adequate ventilation when handling chemicals.  
• Emergency procedures: Develop and implement emergency procedures for chemical spills or accidents.

Seed Handling Safety

• Dust control: Use dust extraction systems to minimize dust exposure.
• Hygiene: Maintain good hygiene practices, including handwashing before and after handling seeds.
• Ergonomics: Design workstations and tasks to minimize physical strain.
• Seed treatment: Handle treated seed with care, avoiding contact with skin and eyes.  

Fire Safety

• Fire extinguishers: Provide appropriate fire extinguishers in accessible locations.
• Fire exits: Ensure clear and accessible fire exits.
• Fire drills: Conduct regular fire drills to prepare employees.
• No smoking: Implement a no-smoking policy in processing areas.

General Safety

• First aid: Have a well-stocked first aid kit available.
• Emergency contacts: Post emergency contact information prominently.
• Housekeeping: Maintain a clean and organized work environment.
• Regular inspections: Conduct regular safety inspections to identify and address hazards.
• Employee training: Provide ongoing safety training to all employees.

 

2.7. Seed Storage Process and Methods

 

Seed storage is a critical aspect of seed technology, ensuring the preservation of genetic resources and maintaining seed viability for future planting. The process involves various stages and methods, depending on the type of seed and storage duration.  

 

Stages of Seed Storage

1. Physiological Maturity to Harvest: This initial stage involves seed development in the field. Proper harvesting practices are crucial to maintain seed quality.  
2. Harvest to Packaging: Seeds are dried to safe moisture levels and cleaned before packaging.  
3. Packaging to Distribution: Seeds are stored in appropriate containers and conditions until distribution.  
4. Distribution to Retailer: Seeds are transported and stored at the retailer level until purchased by farmers.

Types of Seed Storage

Seed storage can be categorized based on various factors such as storage duration, purpose, and environmental conditions.

1.      Based on Storage Duration

·         Short-term storage:

o    Typically for commercial seeds stored for a few months.

o    Often involves ambient temperature and humidity conditions.  

o    Seeds are usually dried to safe moisture levels and stored in well-ventilated areas, protected from pests and moisture.

·         Medium-term storage:

o    For seeds stored for several months to a few years.

o    Requires controlled moisture and temperature conditions.

o    Seeds are typically dried to lower moisture content and stored in sealed containers in a cool, dry environment.

·         Long-term storage:

o    For genetic conservation and preservation of seed viability for decades or even centuries.

o    Involves extremely low temperatures and moisture levels.

o    Methods include cryopreservation and hermetic storage.

2.      Based on Purpose

·         Commercial seed storage:

o    For storing large quantities of seeds for sale to farmers.

o    Emphasizes efficient handling, bulk storage, and pest control.

·         Carry-over seed storage:

o    For storing surplus seeds from the previous harvest for future planting.  

o    Focuses on maintaining seed quality for the next planting season.

·         Foundation/stock seed storage:

o    For preserving high-quality seed for breeding and multiplication purposes.

o    Requires strict control of environmental conditions and regular testing.

·         Germplasm seed storage:

o    For long-term preservation of genetic diversity.

o    Involves cryopreservation or hermetic storage for maximum seed longevity.

3.      Based on Storage Methods

a)      Dry storage:

·         Most common method.

·         Seeds are dried to low moisture content and stored in airtight containers at low temperatures.  

b)      Cryopreservation:

·         Seeds are stored at extremely low temperatures (-196°C) in liquid nitrogen for long-term preservation.  

c)      Hermetic storage:

·         Seeds are stored in airtight containers with controlled atmosphere to reduce oxygen levels.

Methods of Seed Storage

a)       Dry Storage: Seeds are dried to low moisture content and stored in airtight containers at low temperatures.  

b)       Cryopreservation: Seeds are stored at extremely low temperatures (-196°C) in liquid nitrogen for long-term preservation.  

c)       Hermetic Storage: Seeds are stored in airtight containers with controlled atmosphere to reduce oxygen levels.

Factors Affecting Seed Storage

• Seed Type: Different seed species have varying storage requirements.  
• Moisture Content: Lower moisture content prolongs seed life.  
• Temperature: Low temperatures slow down seed deterioration.  
• Oxygen Levels: Reduced oxygen levels can improve seed longevity.  
• Pests and Pathogens: Infestations can reduce seed quality.

 

2.8 Orthodox and Recalcitrant Seeds

Seeds can be broadly classified into two main categories based on their storage behavior: orthodox and recalcitrant.

These classifications determine the methods used for their conservation and preservation.  

Orthodox Seeds:

·         Tolerant to drying and freezing: These seeds can withstand low moisture content and freezing temperatures without losing viability.  

·         Long lifespan: They can be stored for extended periods under appropriate conditions.  

·         Examples: Most crop plants like wheat, rice, maize, legumes, and many forest tree species.

Recalcitrant Seeds:

·         Sensitive to drying and freezing: These seeds cannot tolerate low moisture content or freezing temperatures. Drying or freezing causes irreversible damage to the embryo.  

·         Short lifespan: They have a limited storage life and need special handling.  

·         Examples: Many tropical tree species like mango, avocado, rubber, coconut, and some aquatic plants.  

 

Feature	Orthodox Seeds	Recalcitrant Seeds
Moisture content	Low (10% or less)	High (25-45%)
Temperature tolerance	Low temperatures (-20°C or below)	Cannot tolerate freezing
Storage duration	Long (years or decades)	Short (months or a few years)
Conservation methods	Drying, freezing, cryopreservation	Controlled humidity, refrigerated storage, tissue culture

 

Challenges and Conservation:

Orthodox seeds are relatively easy to conserve using traditional methods like drying and freezing.

Recalcitrant seeds pose a significant challenge for conservation due to their sensitivity to drying and freezing. Researchers are exploring methods like:

·         Controlled humidity storage: Maintaining high humidity levels to prevent desiccation.

·         Refrigerated storage: Storing seeds at low, non-freezing temperatures.

·         Tissue culture: Propagating plants from seed tissues to bypass seed storage.

·         Cryopreservation of embryos: Storing embryos isolated from seeds at ultra-low temperatures.

 

2.9 Natural Longevity of Seeds

 

The natural longevity of seeds varies widely depending on the species. Factors such as seed coat thickness, moisture content, and storage conditions significantly influence how long a seed can remain viable.  

 

Factors Affecting Seed Longevity:

         i.            Seed Coat: A thick, impermeable seed coat provides better protection against moisture, oxygen, and pests, extending longevity.

       ii.            Moisture Content: Lower moisture content generally increases seed longevity.  

      iii.            Storage Conditions: Cool, dry conditions slow down metabolic processes, prolonging seed life.  

      iv.            Oxygen Levels: Reduced oxygen levels can inhibit seed deterioration.

 

Classification of Seed Longevity:

To categorize seed longevity, seeds are often classified into three groups:

         i.            Microbiotic: Seeds with a lifespan of less than three years.

       ii.            Mesobiotic: Seeds with a lifespan of 3 to 15 years.

      iii.            Macrobiotic: Seeds with a lifespan of more than 15 years.

 

While most seeds have a relatively short lifespan, some remarkable exceptions have been documented. Lotus seeds found in ancient lakebeds have germinated after thousands of years! These extraordinary cases highlight the incredible potential for seed longevity under specific conditions.  

 

Importance of Seed Longevity

Understanding seed longevity is crucial for:

·         Crop production: Ensuring seed viability for planting.

·         Plant conservation: Preserving genetic diversity through seed banks.  

·         Scientific research: Studying seed biology and aging processes.

 

2.10 Factors affecting longevity in storage; storage conditions, methods and containers.

 

The longevity of seeds in storage is influenced by a combination of factors. Optimal storage conditions, methods, and containers are crucial for preserving seed viability.  

 

Factors Affecting Seed Longevity

 

         i.            Seed Moisture Content: Lower moisture content is directly linked to increased longevity. Seeds should be dried to a safe moisture level before storage.  

       ii.            Temperature: Low temperatures slow down metabolic processes, extending seed life. Cooler storage conditions are generally better.  

      iii.            Oxygen Levels: Reduced oxygen levels inhibit seed deterioration. Hermetic storage or vacuum packaging can help.  

      iv.            Light: Exposure to light can accelerate seed aging. Storing seeds in dark conditions is recommended.  

       v.            Relative Humidity: High humidity can lead to increased seed moisture content, promoting mold growth and reducing longevity.

      vi.            Seed Viability at Harvest: The initial quality of the seed significantly impacts its storage potential. High-quality seeds have a better chance of long-term viability.  

    vii.            Seed Species: Different seed species have varying storage requirements. Some seeds are more tolerant of adverse conditions than others.  

   viii.            Seed Pests and Diseases: Insect infestations and fungal infections can damage seeds during storage. Proper sanitation and pest control are essential.  

Storage Conditions

         i.            Temperature: Ideally, seeds should be stored at temperatures close to freezing, but above the freezing point to prevent ice formation.

       ii.            Relative Humidity: The storage environment should have low relative humidity to prevent moisture absorption by the seeds.

      iii.            Oxygen Levels: Reduced oxygen levels can improve seed longevity. Consider using airtight containers or modified atmosphere storage.

      iv.            Light: Seeds should be stored in dark conditions to minimize light exposure.  

 

Storage Methods

         i.            Dry Storage: The most common method, involving drying seeds to low moisture content and storing them in airtight containers at low temperatures.

       ii.            Hermetic Storage: Seeds are stored in airtight containers with controlled atmospheres to reduce oxygen levels.

      iii.            Cryopreservation: Seeds are stored at extremely low temperatures (-196°C) in liquid nitrogen for long-term preservation.

      iv.            Controlled Atmosphere Storage: The composition of the atmosphere within the storage container is modified to optimize seed longevity.

 

Storage Containers

The choice of container depends on the seed type, quantity, and desired storage duration.

         i.            Metal Cans: Provide excellent protection against moisture, light, and pests.

       ii.            Glass Jars: Transparent for inspection but less protective against light.  

      iii.            Plastic Bags: Convenient but may not offer optimal protection against moisture and pests.

      iv.            Mylar Bags: Offer good protection against moisture, light, and oxygen.  

       v.            Vacuum-Sealed Bags: Can significantly reduce oxygen levels, extending seed life.