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RHS Level 2 Certificate - week 12 overview
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RHS Level 2 Certificate - week 12 overview

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    RHS Level 2 Certificate - week 12 overview RHS Level 2 Certificate - week 12 overview Presentation Transcript

    • RHS Level 2 Certificate Week 12 – Plant Propagation introduction
    • Learning outcomes
      • 1. Plant propagation – introduction
      • 1.1 Define the terms: ‘seed propagation’ and ‘vegetative propagation’.
      • 1.2 Compare two characteristics of plants produced from seed as compared to those produced by vegetative methods.
      • 1.3 State the relative benefits and limitations of seed propagation and vegetative propagation.
      • 2. Propagation by seed (1)
      • 2.1 Define the terms: ‘physical’ and ‘physiological’ dormancy.
      • 2.2 Describe one method of overcoming a named physical and a named physiological dormancy.
      • 2.3 State the conditions for successful germination of viable seed.
      • 2.4 Describe the seed harvesting and collection of a range of different plants.
      • 2.5 Describe the effects of storage on seed.
    • Plant propagation - definitions
      • Meaning of ‘propagation’ – human-mediated production of plants; as opposed to ‘reproduction’ which is the plant’s natural processes without human intervention.
      • Seed propagation – producing plants in a human controlled manner from seeds
      • Vegetative propagation - producing plants in a human controlled manner from parts of a plant.
    • Seed propagation – advantages/disadvantages Guarantee only applies to vegetable seeds. Guaranteed germination rates and disease free Slower to maturity than vegetatively propagated plants. Storage – most seed can easily be stored for some time Seeds for single colour of some flower varieties may not be available. Choice – a huge range of seed available Takes time and space to grow from seed to plants ready to plant out. Large volumes of seed – cheap way to produce new plants Open pollinated plants may not come true from seed The ability to breed new varieties Disadvantage Advantage
    • Varieties normally propagated by seed
      • Hardy Annual – Centaurea cyanus (Cornflower)
      • Half Hardy Annual – Impatiens walleriana (Busy Lizzie)
      • Tender perennial – Heliotropium aborescens (Cherry Pie plant) usually grown as an annual
      • Hardy perennial – Liatris spicata (Gay Feather)
    • Vegetative propagation – advantages/disadvantages Smaller volumes in general – but NB - tissue culture. Ability to adapt plant to environment using rootstock choice e.g. Malus Gradual loss of juvenility unless care of parent plants is very skilled. Speed to maturity is much quicker. Time – each plant has to be individually propagated. The only way to reproduce sterile varieties such as Vitis vinifera ‘Thompson’s Seedless’ Cost – requires skilled labour and aftercare. Uniformity – each will be exactly the same. Little chance of a new variety arising. Monocultures are susceptible to disease. True to type – each is a clone of the parent. Only way for some varieties e.g. variegation. Disadvantages Advantages
    • Varieties normally propagated vegetatively
      • Wisteria sinensis – perennial climber; desirable flower form and colour not reliable from seed. Long juvenility.
      • Petunia ‘Surfina’ ( P. hybrida x P. pendula ) – will not reproduce from seed; PBR applies.
      • Mallus domestica ‘Bramley’s Seedling’ – all apple varieties are produced vegetatively by grafting. This enables reproduction of the variety characteristics and also the control of the size of the eventual tree by choice of rootstock.
    • Seed dormancy
      • Physical dormancy – thick or impervious seed coat prevents water from entering the seed.
      • Physiological dormancy – an inherent characteristic of the embryo that prevents germination. For example, the requirement for chilling.
    • Breaking physical dormancy
      • Scarification – deliberate controlled damage to the seed coat to allow water to enter. For example, nicking the seeds of Lathyrus odoratus with a sharp knife.
      • Another method for small seed – soaking in very hot water.
      • Also used commercially – soaking in sulphuric acid to carbonise the seed coat. High risk of damage to the embryo if not properly done. Used for Daphne sp.
    • Breaking physiological dormancy - stratification
      • Stratification – deliberate and controlled exposure of moistened seed to required period of chilling (or warm and then chilling)
      • Process breaks down chemicals that retard germination such as ethylene and also stimulates embryo development.
    • Conditions for germination
      • These are the limiting factors for respiration
      • Water – required for imbibition. Seeds that dry out after imbibition may die, or enter a deep dormancy (double dormancy).
      • Temperature – the ideal varies between species. Lycopersicon esculentum (Tomato) requires soil temperatures of 15 °C. Lactuca sativa (Lettuce) seed will become dormant at temperatures over 25°C.
      • Oxygen – required for respiration
      • Food – provided by the endosperm or cotyledons. If seeds are planted too deep or are only marginally viable they may use up their food supply before the shoot breaks the surface.
      • Light – may trigger or prevent germination dependent on species. Not all species are light sensitive.
      • Time – required for imbibition, breaking of dormancy etc.
    • Seed harvesting and storage
      • Why? Free seed; keep your favourites even if they fall out of fashion; share seed with friends or neighbours.
      • Harvesting – mature seed, dry (not after rain), clean to avoid rotting in storage or after sowing.
      • Storage – controlling respiration. Three types of seed – orthodox, intermediate, recalcitrant.
    • Effects of storage on seed
      • Viability – if respiration is not controlled then the percentage of seeds that will germinate is reduced.
      • Vitality – if respiration is not controlled then seeds may use up food required for strong germination.
      • Dormancy – some seeds may become dormant if stored. The seeds of Baptisia australis (Wild Indigo) develop seed coat dormancy when the seed coat dries.
    • Learning outcomes
      • 1. Plant propagation – introduction
      • 1.1 Define the terms: ‘seed propagation’ and ‘vegetative propagation’.
      • 1.2 Compare two characteristics of plants produced from seed as compared to those produced by vegetative methods.
      • 1.3 State the relative benefits and limitations of seed propagation and vegetative propagation.
      • 2. Propagation by seed (1)
      • 2.1 Define the terms: ‘physical’ and ‘physiological’ dormancy.
      • 2.2 Describe one method of overcoming a named physical and a named physiological dormancy.
      • 2.3 State the conditions for successful germination of viable seed.
      • 2.4 Describe the seed harvesting and collection of a range of different plants.
      • 2.5 Describe the effects of storage on seed.