Seed Maturity & Propagation Techniques: Lab Methods & Field Practices
Determining Seed Maturity: Lab Methods
1. Dry Weight
Maximum dry weight indicates maturity.
2. Moisture Content
Some fruits lose moisture during maturation.
3. Analysis and X-ray Method
Chemical analysis and X-ray imaging can assess maturity.
Determining Seed Maturity: Field Methods
1. Fruit Weight
Fruit weight generally decreases with maturity.
2. Seed Contents
Mature seeds have a firm, white endosperm and a well-developed embryo.
3. Fruit Color and Odor
Slight variations in color and odor can indicate maturity.
Fruit Extraction: Normal and forced methods, similar to natural processes.
Artificial Heating: Using a furnace (e.g., Klor). Pre-assessment is done, moisture and air are passed, but temperatures should not exceed 60°C for fir and cedar, and 30-35°C for others. Crucial step: separating the fruit. Dry mashing is done, then hot water is added to accelerate decomposition. Fruits are then dried and sieved.
Seed Storage:
Orthodox seeds can tolerate low moisture content (up to 5%) and low temperatures (4-6°C) for long-term storage.
Recalcitrant seeds require higher moisture content (20-50%) and near-freezing temperatures (0-2°C) for storage.
Seed Treatments
Three types of dormancy:
Exogenous Dormancy
Due to seed coat.
1. Physical
Seed coat impermeability. Scarification with hot water (70-100°C) followed by cooling, or acid treatment (H2SO4 for 15-60 minutes).
2. Chemical
Presence of inhibiting substances. Washing or leaching can remove them.
3. Mechanical
Embryo restriction. Moist heat or physical removal of the seed coat can help.
Endogenous Dormancy
Due to internal embryo conditions or reserve substances.
1. Morphological
Underdeveloped embryo requiring a period for further development.
2. Physiological
Mature embryo but presence of inhibiting substances. Stratification (moist chilling) can overcome this, using a mix of sand and seeds.
Double Dormancy
Requires treatments for both exogenous and endogenous dormancy.
Seed Viability
Biochemical Tetrazolium Test: A viability indicator. Live tissue stains red with tetrazolium salt.
Embryo Cutting and Analysis: Embryos are extracted and incubated to assess viability.
X-ray: Useful for identifying hollow, abnormal embryos, and seed damage.
Seedling Acclimatization
Seeds can be acclimatized in protected environments (tunnels, greenhouses). Substrate should have good drainage, be disinfected, and weed-free. Use fine-grain, porous materials. Seedbeds: Large-scale planting. Sandy soils are preferred.
Vegetative Propagation
Cuttings
1. Woody Cuttings
- Taken from previous year’s growth during winter (15-20 cm long).
- A knot is made below the basal cut, below the last bud.
2. Herbaceous Cuttings
- Taken during active growth, selecting shoots with preformed flowers.
- Spring cuttings: Taken from early sprouting branches before winter dormancy ends (March-April).
- Late spring/summer cuttings: Taken in May-June when buds are well-developed.
Objectives: Prevent desiccation. Use a hermetic box with a transparent lid. Disinfected substrate with good aeration and water retention. Mist systems provide periodic misting to maintain a water film on cuttings. Irrigation is reduced at night to minimize evaporation. Fog systems create high humidity. Plastic covers can also be used, with daily ventilation for conifers and semi-woody cuttings.
Final Step: In summer (September-October), plant the rooted cuttings. A piece of the main branch (heel) can be left at the base of the cutting.
Rooting Hormones: Substances (auxins) that promote root formation.
Objectives: Accelerate root initiation and improve rooting quality and percentage.
Types:
- IAA (Indole Acetic Acid): Natural, unstable, low activity.
- IBA (Indole Butyric Acid): More stable, localized action, lower effective dose.
- NAA (Naphthaleneacetic Acid): Similar to IBA but less sensitive.