Foundation of Biology

• Clones


  Groups of plants that are identical to their parent (or donor) plant
• Examples of plants that can only be propagated asexually

  • Bartlett pear
  • Red Delicious apple
• Major methods of asexual propagation of stems and leaves

  • Cuttings
  • Layering
  • Division
  • Grafting

  
• Specialized plant parts that allow for asexual propagation

  • Tubers
  • Bulbs
  • Rhizomes
  • Corms
  • Stolons

  
• Root tissue can also be used for plant propagation, although less frequent

  
• Advantages of vegetative reproduction


  • Higher levels of stored reserves are available throughout the year
  • The parent plant with its root system can absorb water from quite a wide area
  • Buds are produced in an environment where the parent is able to flourish, but many seeds dispersed from plants never reach a suitable situation for effective germination

  
• Vegetative reproduction does not usually result in rapid and widespread distribution of offspring in the same way as seed dispersal, but tends to produce a dense clump of plants with little room for competitors between them
• Species regarded as weeds are difficult to eradicate, since even a small piece of an asexual propagule bearing a bud can give rise to a new colony (clone)

  
• Separation


  1. Natural structures are simply removed from the parent plant and planted to grow on their own

  2. Crown division is one method and one of the best methods to propagate herbaceous perennial plants

  3. Individual growing points (shoots) that contain roots may then be used be used to form new plants

  4. Some woody perennials that branch or sucker (adventitious shoots) from the main plant can also be reproduced in this way

  
• Grafting and budding


  1. Plant parts from one plant are attached onto those of another so that the two plant types join together

  2. One plant is selected for its root characteristics and this is called the stock or rootstock

  3. The other plant is selected for its vegetative characteristics such as stem, leaf, flower or fruit and is called the scion

  
• Layering


  1. The potential cutting(s) is (are) attached to the plant until the adventitious roots form

  2. This is done by covering the developing rooting areas with some form of media such as soil, sand, or a potting mix

  3. A variation of this procedure is air layering where a stem is covered 1 - several nodes with a media until adventitious roots form, then the stem can be severed from the stock plant
• Cuttings


  1. A vegetative plant part which is severed from the parent plant in order to produce a plant that is genetically identical to the donor

  2. Cuttings may be taken at any time on herbaceous plants but may vary with perennial plants

  3. At least one node should be below the media surface since many plant types will produce roots with this plant part, but some plants can root at the internodes

  4. Variations include tip cuttings, cane cuttings, and leaf cuttings

  
• Vegetative plant structures that have the capacity to produce new plants

  • Stolons
  • Bulbs
  • Rhizomes
  • Tubers

  
• Stolon


  A horizontal stem that can root and produce new adventitious roots

  
• Plants that produce stolons or runners

  • Strawberry
  • Spider plant
  • Bermudagrass

  
• Bulb


  Consists of very short stems with closely packed leaves arranged in concentric circles round the stem, the leaves are swollen with stored food

  
• Rhizome


  Stems which grow horizontally under the ground, may be swollen with food reserves, the terminal bud turns upwards to produce the vegetative shoot and the lateral buds may grow out to form new rhizomes

  
• Plants that produce rhizomes


  • Sedge (Cyperus spp.)
  • Johnsongrass (Sorghum halepense)
  • Bermudagrass

  
• Tuber


  Thick, underground stems that develop at the end of rhizomes
• Rhizome


  • Produces adventitious roots
  • Produces lateral buds that can grow into new rhizomes
  • Tissue has stored reserves
  • Has nodes with axillary buds covered by leaf scales
  • Can produce shoots and adventitious roots
  • Can be cut into pieces with at least one node to produce a new plant

  
• Rhizome producing plants


  • Sedge (Cyperus spp.)
  • Johnsongrass (Sorghum halepense)

  
• Stolon


  • Horizontal stem that grows above the ground and produces roots and shoots at the nodes

  
• Tuber


  • Thick, underground stem that develops at the end of rhizomes
  • Has nodes and internodes
  • Has 'eyes' (nodes) arranged spirally
  • Contains stored reserves
  • Produced in one growing season for propagation
  • Example is potato (Solanum tuberosum)

  
• Corm


  • Shortened, swollen stem that stores food
  • Has circular leaves that form papery scales
  • Terminal bud grows into flowering shoot, lateral buds produce new plants
  • Differs from bulb in having solid internal structure rather than layered fleshy scales
  • Examples are taro (Colocasia esculenta) and crocus (Crocus spp.)

  
• Tuberous root


  • Modified lateral root that is enlarged and stores food for future growth
  • Has a proximal end attached to old plant and an apical end with crown tissue that produces buds
  • Biennial in duration, first year produces root tubers, next year produces new shoots
  • Example is sweet potato (Ipomoea batatas)

  
• Plants that reproduce through true root system

  • Horsenettle (Solanum carolinense)
  • Plants in Asteraceae family, especially thistles
• Asexual propagation by cuttings

  1. Take sharp blade dipped in alcohol/bleach to remove cutting from parent plant

  2. Remove flowers/buds to allow use of stored reserves

  3. Use rooting hormone to stimulate rooting

  4. Insert cuttings into rooting medium and keep moist

  5. Place in growth chamber with optimal temperature and light
• Cuttings will develop adventitious roots or shoot growth in 10-14 days

  
• Asexual propagation produces genetically identical plants (clones)
• Asexual propagation using modified stems or roots maintains genetic purity