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General Forestry for APPSC Forest Section Officer · Chapter 2

Seeds and Propagation: Dormancy, Pre-treatment, Nursery, Grafting and Layering

What to remember

  • A good seed lot is judged by purity, germination per cent and moisture. Dormant seeds need pre-treatment such as hot water, acid, scarification, soaking or stratification.
  • Nursery work moves from seed bed to polybag, then to hardening and field planting. Vegetative propagation by cuttings, layering, budding and grafting copies the parent exactly.
  • Seed storage is orthodox (can be dried and stored) or recalcitrant (cannot be dried and loses viability fast). Sal, mango and jackfruit seeds are recalcitrant.

1. Seed biology and quality

A seed is a ripened ovule containing an embryo, stored food and a seed coat. Seeds are formed by sexual reproduction, so each seedling differs slightly from the mother.

Seed source and collection

  • Seed should be collected from good, healthy, mature trees with straight stems and good form. These are plus trees. A seed production area and a seed orchard are used for superior seed.
  • Seed is collected when ripe. Signs are a change of colour of the fruit, natural dropping or opening of pods. Collection methods are picking from the ground, shaking, climbing and lopping.
  • Provenance is the geographic source of the seed. Using the right provenance gives better survival and growth.

Seed testing

TestMeaningFormula
Purity per centShare of pure seed in a sample(weight of pure seed ÷ total weight) × 100
Germination per centShare of seeds that sprout under test(number germinated ÷ number sown) × 100
1000-seed weightSeed size indicatorWeight of 1000 pure seeds
Moisture contentWater in seed(fresh weight − dry weight) ÷ fresh weight × 100
ViabilityLiving seeds, tested by tetrazolium or cut test–

Seed value (planting value) = (purity per cent × germination per cent) ÷ 100.

*Worked example:* purity 90 per cent and germination 80 per cent give seed value = 90 × 80 ÷ 100 = 72 per cent.

*Worked example:* seed to be sown to get 3,600 plants if the seed value is 72 per cent and no loss in the nursery: seeds needed = 3,600 ÷ 0.72 = 5,000.

2. Seed storage

  • Orthodox seeds tolerate drying to a low moisture level (5 to 10 per cent) and cold storage. Examples are teak, Acacia, Eucalyptus, Casuarina and most legumes.
  • Recalcitrant seeds cannot be dried and lose viability quickly. Examples are Sal, mango, jackfruit, Shorea and Dipterocarps. They need moist storage and quick sowing.
  • Cool and dry conditions extend life. Insects are controlled by fumigation. Containers should be airtight for orthodox seeds.

3. Seed dormancy and pre-treatment

Dormancy is a state in which a viable seed fails to germinate even with water, air and warmth.

Types and causes:

  • Hard (impermeable) seed coat: in legumes such as Acacia, Albizia and Cassia.
  • Physiological dormancy: immature embryo or chemical inhibitors in the seed.
  • Embryo dormancy: needs cold or after-ripening.

Pre-treatments:

Pre-treatmentMethodTypical use
Cold water soaking12 to 24 hoursBamboo, Teak (alternate wet and dry)
Hot water treatmentPour boiling water, let cool for a dayAcacia, Albizia, Prosopis
Mechanical scarificationNicking or rubbing the coatLarge hard seeds
Acid scarificationConcentrated sulphuric acid for a short time, then washHard-coated legumes
StratificationMoist, cool storageTemperate species
LeachingRunning waterSeeds with inhibitors
Growth regulatorsGibberellic acidSome physiologically dormant seeds

Teak seed has a thick hard fruit wall. Pre-treatment by alternate wetting and drying, or soaking, improves germination. Acacia nilotica and Albizia respond to hot water.

4. Nursery practices

A forest nursery raises planting stock. It may be temporary or permanent. A good site is level, near water, well drained, sheltered, and close to the planting area.

Nursery components: seed beds, transplant beds, polybag or container area, shade, hardening area, water source, compost pit and tool store.

Raising stock

  • Seed beds are raised beds of fine soil. Seeds are sown in lines, covered thinly, and watered with a rose can.
  • Pricking out (transplanting) is shifting germinated seedlings to polybags or transplant beds.
  • Polybags are filled with a mix of soil, sand and farmyard manure, often in a ratio like 3:1:1 (check local practice). Drainage holes are needed.
  • Root trainers guide roots and reduce root coiling.
  • Hardening is gradual reduction of watering and shade to prepare seedlings for field conditions.
  • Stumps are made by cutting the shoot and trimming the root. Teak is often planted as a stump. Striplings are older, thicker plants.
  • Shade is given to delicate seedlings and gradually removed. Weeding, watering and pest control are needed.

Damping off is a common fungal disease of seedlings. It is prevented by well-drained beds, thin sowing, and treating soil or seed with a fungicide.

5. Vegetative propagation

Advantages: the offspring is identical to the parent (a clone), flowering starts earlier, and difficult species can be multiplied. Its drawback is narrow genetic base.

Cuttings. A piece of stem, root or leaf is made to form roots. Types are hardwood, softwood and semi-hardwood cuttings. Auxins such as IBA improve rooting. Poplar, Eucalyptus clones and Casuarina can be raised by cuttings. A high humidity chamber (mist chamber) helps.

Layering. A branch is made to root while it is still attached to the parent plant.

  • Simple layering: a branch is bent and a portion covered with soil.
  • Air layering (gootee): a ring of bark is removed, wrapped in moist moss and covered with plastic. Used for guava and litchi.
  • Mound (stool) layering: shoots are earthed up at the base.

Budding. One bud on a small piece of bark is inserted into the stock. T-budding (shield budding) and patch budding are common.

Grafting. A scion (the shoot of the desired variety) is joined to a rootstock. The two must be closely related and the cambium layers must touch.

GraftFeature
Whip or tongue graftScion and stock of equal thickness
Cleft graftScion wedge fitted into a split in the stock
Side graftScion fitted at the side of the stock
Approach graftBoth plants remain rooted until the union forms
Veneer graftA thin slice fits to the stock

The graft union is the join. The rootstock provides the roots and the scion gives the shoot.

Micropropagation (tissue culture). Small pieces of tissue (explants) are grown on a sterile medium with auxin and cytokinin. Used for bamboo, teak, Eucalyptus and sandalwood.

6. Nursery calculations and field planting

  • Plants to raise = plants needed ÷ (1 − expected loss fraction). For 1,200 plants with 20 per cent loss, raise 1,200 ÷ 0.8 = 1,500.
  • Seeds per kg = 1,000 g ÷ weight of 1,000 seeds (in g) × 1,000. A species with 40 g per 1,000 seeds gives 25,000 seeds per kg.
  • Area of nursery depends on the number of plants and the spacing of polybags or beds. Extra area is kept for paths and compost.
  • Seedlings are planted out at the start of the rains, when the soil is wet. They should be sturdy, with a well-developed root system, a woody stem and no signs of disease.
  • Containerised plants (polybag or root trainer) suit dry sites because the root ball is intact. Bare-root plants and stumps are lifted from beds and planted soon after lifting.
  • For many species of Andhra Pradesh forests, such as teak, Eucalyptus, Casuarina, Pongamia, Neem and red sanders, forest nurseries of the Forest Department and community nurseries raise planting stock. Fast-growing clonal Eucalyptus and Casuarina are raised from rooted cuttings in mist chambers.

Sowing methods. Seeds are sown by broadcasting, in lines (drilling), by dibbling (a seed at each spot) or in seed pots. Fine seed such as Eucalyptus is mixed with sand and sown thinly. Depth of sowing is about two to three times the thickness of the seed.

Exam traps

  • 1. Seed value is purity × germination ÷ 100, not purity + germination.
  • 2. Orthodox seeds can be dried. Recalcitrant seeds cannot.
  • 3. Scarification breaks a hard coat. Stratification gives cold and moisture.
  • 4. Air layering is a layering method, not a grafting method.
  • 5. In grafting, the scion gives the shoot and the stock gives the roots.
  • 6. The cambium of the scion and stock must match for a graft to succeed.
  • 7. Pricking out is moving seedlings from seed bed to polybag, not final planting.
  • 8. Vegetative propagation gives clones. Seed propagation gives variable plants.

One-liners

  • 1. Provenance means the geographical source of seed.
  • 2. Seed value = purity per cent × germination per cent ÷ 100.
  • 3. Sal and jackfruit seeds are recalcitrant.
  • 4. Hot water treatment is used for hard-coated legume seeds.
  • 5. Acid scarification uses concentrated sulphuric acid.
  • 6. Damping off is a fungal disease of seedlings.
  • 7. Hardening prepares seedlings for field conditions.
  • 8. A plus tree is a superior tree chosen for seed.
  • 9. Cuttings are rooted better with IBA.
  • 10. Air layering is also called gootee.
  • 11. Scion is the shoot part in grafting.
  • 12. Tissue culture uses auxin and cytokinin in a sterile medium.

Practice questions

  1. Seed value (planting value) is calculated as:

    1. Germination / purity
    2. Purity + germination
    3. Purity x germination / 100
    4. Purity - germination
    Answer

    C. Purity x germination / 100

    Seed value = purity per cent x germination per cent / 100.

  2. A seed lot has purity 80 per cent and germination 75 per cent. Its seed value is:

    1. 78 per cent
    2. 55 per cent
    3. 65 per cent
    4. 60 per cent
    Answer

    D. 60 per cent

    80 x 75 / 100 = 60 per cent.

  3. A seed sample shows 450 seeds germinated out of 500 sown. Germination per cent is:

    1. 90
    2. 95
    3. 85
    4. 80
    Answer

    A. 90

    450/500 x 100 = 90 per cent.

  4. A 200 g sample contains 190 g of pure seed. Purity per cent is:

    1. 95
    2. 97
    3. 90
    4. 92
    Answer

    A. 95

    190/200 x 100 = 95 per cent.

  5. Seed value of a lot is 50 per cent. To get 2,000 plants with no nursery loss, seed needed is:

    1. 1,000
    2. 2,000
    3. 3,000
    4. 4,000
    Answer

    D. 4,000

    2,000 / 0.5 = 4,000 seeds.

  6. A seed lot has 10 g fresh weight and 9 g dry weight. Moisture content on fresh weight basis is:

    1. 5 per cent
    2. 10 per cent
    3. 20 per cent
    4. 11 per cent
    Answer

    B. 10 per cent

    (10 - 9)/10 x 100 = 10 per cent.

  7. If purity is 90 per cent and seed value is 72 per cent, the germination per cent is:

    1. 70
    2. 75
    3. 80
    4. 85
    Answer

    C. 80

    72 = 90 x G / 100, so G = 80 per cent.

  8. 1000-seed weight of a species is 40 g. Number of seeds in 1 kg is:

    1. 10,000
    2. 25,000
    3. 15,000
    4. 40,000
    Answer

    B. 25,000

    1000 g / 40 g x 1000 = 25,000 seeds.

  9. Seeds that cannot be dried and lose viability quickly are:

    1. Dormant seeds
    2. Orthodox seeds
    3. Hybrid seeds
    4. Recalcitrant seeds
    Answer

    D. Recalcitrant seeds

    Recalcitrant seeds are damaged by drying and chilling.

  10. Which of the following has recalcitrant seeds?

    1. Casuarina
    2. Teak
    3. Sal
    4. Acacia
    Answer

    C. Sal

    Sal (Shorea robusta) seeds lose viability within days.

  11. Dormancy is best defined as failure of a viable seed to germinate even when:

    1. Water, air and warmth are available
    2. Seed is dead
    3. Seed is crushed
    4. Soil is acidic
    Answer

    A. Water, air and warmth are available

    A dormant seed fails to germinate under favourable conditions.

  12. Hard impermeable seed coats are common in:

    1. Legumes
    2. Grasses only
    3. Ferns
    4. Mosses
    Answer

    A. Legumes

    Acacia, Albizia and Cassia seeds have hard coats.

  13. Which pre-treatment suits hard-coated Acacia seeds?

    1. Boiling water poured over seeds and left to cool
    2. Freezing
    3. Drying in the sun
    4. Rubbing with sand only for 1 minute
    Answer

    A. Boiling water poured over seeds and left to cool

    Hot water softens the hard seed coat of Acacia.

  14. Treating seed with concentrated sulphuric acid is called:

    1. Stratification
    2. Hardening
    3. Acid scarification
    4. Leaching
    Answer

    C. Acid scarification

    Acid scarification weakens the hard seed coat.

  15. Storage of seeds in moist, cool conditions to break dormancy is called:

    1. Fumigation
    2. Pricking out
    3. Scarification
    4. Stratification
    Answer

    D. Stratification

    Stratification gives cold and moisture.

  16. Shifting seedlings from seed bed to polybags is:

    1. Lopping
    2. Pricking out
    3. Stumping
    4. Hardening
    Answer

    B. Pricking out

    Pricking out is transplanting young seedlings.

  17. Gradual reduction of water and shade before planting out is:

    1. Grafting
    2. Hardening
    3. Layering
    4. Scarification
    Answer

    B. Hardening

    Hardening prepares seedlings for field conditions.

  18. Fungal disease causing collapse of seedlings at the soil line is:

    1. Rust
    2. Smut
    3. Damping off
    4. Wilt of mature trees
    Answer

    C. Damping off

    Damping off affects young seedlings in wet, crowded beds.

  19. Teak is commonly planted as a:

    1. Stump
    2. Bare cutting only
    3. Tissue-culture plant only
    4. Seed only
    Answer

    A. Stump

    Teak stumps (trimmed root and shoot) are widely used.

  20. Plants raised by cuttings are genetically:

    1. Variable
    2. Hybrids
    3. Mutants
    4. Identical to the parent
    Answer

    D. Identical to the parent

    Vegetative propagation produces clones.

  21. Air layering is also known as:

    1. Stooling
    2. Budding
    3. Cleft grafting
    4. Gootee
    Answer

    D. Gootee

    Air layering or gootee is common in guava and litchi.

  22. In grafting, the part that gives the roots is the:

    1. Bud
    2. Scion
    3. Rootstock
    4. Explant
    Answer

    C. Rootstock

    The rootstock provides the root system.

  23. For a successful graft, it is essential that the:

    1. Fruits are present
    2. Leaves of both are touching
    3. Roots of both are joined
    4. Cambium of scion and stock touch
    Answer

    D. Cambium of scion and stock touch

    Cambium contact lets the tissues unite.

  24. A graft in which both plants remain rooted until union forms is:

    1. Cleft graft
    2. Approach graft
    3. Veneer graft
    4. Whip graft
    Answer

    B. Approach graft

    In approach grafting both plants are on their own roots until the union forms.

  25. A scion wedge fitted into a split in the stock is a:

    1. Cleft graft
    2. Side graft
    3. Whip graft
    4. Approach graft
    Answer

    A. Cleft graft

    This is the cleft graft.

  26. Insertion of a single bud on a rootstock is:

    1. Stratification
    2. Pricking out
    3. Budding
    4. Layering
    Answer

    C. Budding

    Budding is a form of grafting using one bud.

  27. Which growth substance improves rooting of cuttings?

    1. Ethylene
    2. Indole butyric acid
    3. Colchicine
    4. Abscisic acid
    Answer

    B. Indole butyric acid

    IBA is a common rooting hormone.

  28. Micropropagation is propagation by:

    1. Seeds only
    2. Tissue culture of explants
    3. Grafting
    4. Layering
    Answer

    B. Tissue culture of explants

    Micropropagation grows explants on sterile medium.

  29. Consider these statements. 1. Orthodox seeds can be dried to low moisture. 2. Recalcitrant seeds can be stored for years in dry rooms. Which is correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    A. 1 only

    Recalcitrant seeds cannot be dried and soon lose viability.

  30. Consider these statements. 1. Scarification breaks a hard seed coat. 2. Stratification gives cold, moist conditions. Which is correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    C. Both 1 and 2

    Both describe these pre-treatments correctly.

  31. Consider these statements. 1. Vegetative propagation gives clones. 2. Seed propagation gives uniform copies of the mother. Which is correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    A. 1 only

    Seeds give variable offspring. Clones come only from vegetative parts.

  32. Consider these statements. 1. A scion forms the shoot. 2. A rootstock forms the root system. Which is correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    C. Both 1 and 2

    Both are correct.

  33. Consider these statements. 1. Hardening involves more water and shade. 2. Hardening prepares seedlings for the field. Which is correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    B. 2 only

    Hardening reduces water and shade gradually.

  34. Consider these statements. 1. Provenance is the geographic source of seed. 2. A plus tree is chosen for superior traits. Which is correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    C. Both 1 and 2

    Both definitions are standard.

  35. Consider these statements. 1. Air layering needs the branch to be cut from the parent first. 2. Air layering uses a girdled branch wrapped in moist moss. Which is correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    B. 2 only

    The branch is cut only after roots form. It is girdled and wrapped.

  36. Consider these statements. 1. Seed value combines purity and germination. 2. A seed lot with high purity always has high germination. Which is correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    A. 1 only

    Purity and germination are independent. A pure lot may have dead seeds.

  37. Match the pre-treatment to the seed type: hot water is best for:

    1. Thin-coated germinating seed
    2. Fresh Mango seed
    3. Recalcitrant Sal seed
    4. Hard-coated legume seed such as Albizia
    Answer

    D. Hard-coated legume seed such as Albizia

    Hot water softens hard coats in legumes.

  38. A good nursery site should be:

    1. Waterlogged
    2. Far from any water
    3. In a deep pit
    4. Level, near water and well drained
    Answer

    D. Level, near water and well drained

    A nursery needs water, drainage and shelter.

  39. Polybags used in nurseries must have:

    1. No holes
    2. Metal lining
    3. Sealed bottoms
    4. Drainage holes
    Answer

    D. Drainage holes

    Drainage holes prevent waterlogging.

  40. Root trainers in nurseries are used to:

    1. Guide roots and reduce coiling
    2. Store seeds
    3. Grow cuttings in water
    4. Increase stem height only
    Answer

    A. Guide roots and reduce coiling

    Root trainers reduce root coiling.

  41. Seed orchards are established to:

    1. Produce genetically superior seed
    2. Store seeds
    3. Raise fruit trees only
    4. Keep animals
    Answer

    A. Produce genetically superior seed

    A seed orchard is planted with selected superior clones or families.

  42. Which type of cutting is taken from current-season mature wood?

    1. Softwood
    2. Semi-hardwood or hardwood
    3. Leaf cutting only
    4. Root cutting only
    Answer

    B. Semi-hardwood or hardwood

    Hardwood and semi-hardwood cuttings come from mature wood.

  43. Mound or stool layering is done by:

    1. Wrapping with moss in air
    2. Joining two plants
    3. Cutting the root
    4. Earthing up shoots at the base
    Answer

    D. Earthing up shoots at the base

    Shoots are covered with soil at the base of the stool.

  44. A nursery needs 1,200 plants and expects 20 per cent loss. Number of plants to raise is:

    1. 1,600
    2. 1,440
    3. 1,500
    4. 1,800
    Answer

    C. 1,500

    1,200 / 0.8 = 1,500 plants.

  45. Seeds of a species number 20,000 per kg. Seeds in 250 g are:

    1. 50,000
    2. 5,000
    3. 2,500
    4. 10,000
    Answer

    B. 5,000

    20,000 x 0.25 = 5,000 seeds.

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