📦 Seed Storage and Packaging

This lesson builds core elective concepts in BSc Agriculture with practical applications and exam-oriented clarity.

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Seed Storage and Packaging

Importance of Seed Storage

Seeds are living organisms. From harvest to planting, seed quality must be maintained. Deterioration is irreversible — once germination declines, no treatment can fully restore it. The goal of seed storage is to:

• Maintain viability (germination capacity)
• Maintain vigour (performance under field stress)
• Prevent loss from pests (insects, rodents, fungi)
• Bridge the gap between harvest season and planting season (typically 3–12 months; up to decades for gene banks)

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Factors Affecting Seed Longevity

The primary factors are:

1. Seed Moisture Content

The single most important factor. As moisture content increases:

• Respiration rate of seed increases exponentially
• Fungal growth (storage moulds: Aspergillus, Penicillium) becomes active above 70% ERH (corresponding to ~14% MC in cereals)
• Insect activity increases
• Seed deterioration accelerates

2. Storage Temperature

Lower temperature slows all biological processes:

• Enzyme activity decreases
• Insect development and reproduction slows
• Fungal growth rate decreases

3. Seed Quality at Harvest

Seeds must have high initial quality to store well:

• Seeds with mechanical damage, disease infection, or low vigour at harvest will deteriorate faster
• "You cannot improve seed quality in storage — only maintain it"

4. Relative Humidity (RH) of Storage Environment

Seed moisture content equilibrates with ambient RH over time. High RH storage environments continuously add moisture to the seed.

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Harrington's Rules (Roberts' Rules)

Two empirical rules that quantify the relationship between storage conditions and seed longevity:

Rule 1: For each 1% decrease in seed moisture content, seed storage life is doubled.

Rule 2: For each 5°C decrease in storage temperature, seed storage life is doubled.

These rules apply in the range of: MC 5–14%, temperature 0–50°C.

Combined effect: Reducing both MC by 1% AND temperature by 5°C → 4× longer storage life.

This is the basis for the "10/50 rule" used in gene bank management: storing at 10°C and 50% RH (or equivalent MC) provides long-term storage.

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Safe Moisture Content for Storage

Crop Type	Safe Moisture (%)
Cereals (rice, wheat, maize)	≤ 12
Pulses (chickpea, pigeon pea)	≤ 8
Oilseeds (mustard, sunflower)	≤ 7
Groundnut (pods)	≤ 8
Vegetable seeds	≤ 6–8 (varies)

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Equilibrium Relative Humidity (ERH)

ERH is the relative humidity at which seed moisture content neither increases nor decreases with the surrounding air. Each crop has a characteristic moisture sorption isotherm.

• Storing seed in an environment with RH above the seed's ERH → seed absorbs moisture
• Hermetic storage traps the seed in equilibrium with a small enclosed atmosphere → prevents further moisture ingress after equilibrium is reached

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Seed Storage Structures

1. Conventional Warehouse Storage

• Description: Jute or HDPE bags stacked on pallets in covered warehouses
• Temperature/RH: Ambient (not controlled); depends on season and location
• Duration: 6–12 months (short term)
• Suitable for: Certified seed that will be distributed within a season
• Problems: Subject to seasonal RH fluctuations; insect and rodent infestation; requires fumigation

2. CAP Storage (Covered and Plinth)

• Description: Bulk grain stored under polythene cover on a raised concrete plinth; outdoors
• Duration: 45 days emergency storage only
• Use: Temporary overflow during peak procurement; not suitable for quality seed

3. Cold Storage

• Conditions: 10–15°C, 50–60% RH
• Duration: 2–5 years (foundation and certified seed)
• Use: Breeder seed storage at ICAR/SAU; foundation seed between multiplication generations
• Cost: High; requires electricity; suitable for high-value seed

4. Hermetic Storage

Hermetic storage uses airtight containers or structures to create a modified atmosphere:

• As seed and insects respire, O₂ is consumed and CO₂ builds up
• Near-zero oxygen stops insect respiration (insects die in 4–6 days)
• Low O₂ also reduces seed respiration → slower deterioration
• No fumigant chemicals needed

Types of hermetic storage:

Type	Capacity	Material	Notes
PICS bags (Purdue Improved Crop Storage)	50–100 kg	Triple-layer polyethylene	Developed for cowpea; widely used for all crops; low cost
Metal silos	100 kg – 3 t	Galvanized iron	Durable; rodent-proof; 3–5 year lifespan
GrainPro Cocoon	Up to 1,000 t	PVC fabric	Large-scale hermetic; suitable for cooperatives
Super grain bags	50–100 kg	Triple-layer HDPE	Similar to PICS

Key benefit: PICS bags extend storage life of cowpea from 3 months to 2+ years without insecticides.

5. Base Collection Storage (Gene Banks)

• Conditions: −18°C, 15–25% RH (sealed aluminium foil containers)
• Duration: 50–100 years
• Use: Long-term preservation of germplasm — national gene banks (ICAR-NBPGR, New Delhi)
• National Gene Bank (NGB), NBPGR: holds >4.6 lakh accessions

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Seed Storage Insects

Major insect pests of stored seed:

Insect	Crops Attacked	Type
Sitophilus oryzae (Rice weevil)	Rice, wheat, maize	Primary (attacks whole grain)
Sitophilus granarius (Grain weevil)	Wheat, barley	Primary
Tribolium castaneum (Red flour beetle)	Flour, broken grain	Secondary
Callosobruchus maculatus (Pulse beetle)	Cowpea, chickpea, mung bean	Primary (attacks field-to-store)
Rhyzopertha dominica (Lesser grain borer)	Wheat, maize	Primary

Control methods:

• Fumigation: Aluminium phosphide (3 g/t or 1 tablet/t); releases PH₃ (phosphine gas); lethal to all life stages
• Contact insecticides: Malathion, Pyrethrin dusts applied to bags/floor
• Hermetic storage: No chemicals needed (see above)
• Physical methods: Cleaning storage structure; maintaining cool conditions; double-bag storage

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Seed Packaging

Packaging Materials and Properties

Material	MVTR*	Use Case	Notes
Polythene bags (LDPE)	Low	Short-term storage, ≤12 months	Moisture-proof; prone to UV degradation
HDPE woven bags	Moderate	Large quantities, OPV seed	Strong; not fully moisture-proof
Cloth/jute bags	High	Breeder seed (short term)	Breathable; poor moisture protection
Metal/tin cans	Zero	Long-term; expensive seed	Ideal for gene bank accessions
Aluminium foil laminate pouches	Near zero	Vegetable seed; high-value hybrid	Best moisture barrier; long shelf life (3–5 years)

*MVTR = Moisture Vapour Transmission Rate (lower = better moisture protection)

Foil laminate pouches (aluminium foil + polyethylene inner layer) are the gold standard for vegetable and hybrid seed storage — they maintain seed quality for 3–5 years if properly sealed.

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Seed Labelling

Mandatory Label Information (under Seed Act, 1966)

Every seed bag sold in India must carry a label with:

1. Crop name and variety name
2. Seed class (Breeder / Foundation / Certified / TL)
3. Lot number (traceable back to seed plot and processing record)
4. Net weight (in kg/g)
5. Germination percentage (test result)
6. Physical purity percentage
7. Moisture content
8. Date of test (month and year)
9. Valid up to (expiry date — typically 6–12 months from test date)
10. Seed treatment chemical (if treated; active ingredient, concentration)
11. Name and address of producer/seller

Certification Tag

The certification tag (attached to the bag by SCA) additionally shows:

• Certification Agency name and state
• Tag serial number
• Crop, variety, seed class
• Lot number
• Date of certification
• Colour coding: Breeder = Golden Yellow, Foundation = White, Certified = Blue, TL = Opal Green

Language Requirements

• Label must be in English (mandatory) and the regional/vernacular language of the state
• Font size minimum as prescribed (legible at arm's length)

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Seed Storage Systems

Storage Type	Temperature	RH	Duration	Best For
Conventional warehouse	Ambient	Ambient	6–12 months	Certified seed (short season)
Hermetic bags (PICS)	Ambient	Sealed	1–3 years	Pulses, cereals (small farmer)
Cold storage	10–15°C	50–60%	2–5 years	Foundation/Breeder seed
Gene bank (NGB)	−18°C	15–25%	50–100 years	Germplasm accessions

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Summary Cheat Sheet

Topic	Key takeaway
Main focus	Seed longevity, Harrington's rules, storage structures including hermetic storage, seed packaging materials, labelling requirements under Seed Act.
Section context	Revise this lesson with the rest of Post-Harvest Seed Technology for stronger conceptual continuity.