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Other specialized structures

• tubers
• tuberous roots
• rhizomes
• pseudobulbs

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Propagation of Irish potato (Solanum tuberosum)
tubers

• conventional method tuber is cut into sections,
  with an eye or node included tubers used for
  propagation are called seed potatoes
• micropropagation veg. buds are excised, grown,
  multiplied in culture, handled to produce
  microtubers for virus-indexed seed stock
• potato tubers are modified stems

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Fig. 15-15 and 15-16. Propagation of Irish
potatoes by tuber pieces.
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Propagation by tuberous roots

• Sweet potato (Ipomoea batatas)
• adventitious shoots develop on the fleshy root
• new slips are covered with soil, develop
  adventitious roots
• Dahlia
• plants are dug in the fall, divided
• ea. divided section contains a tuberous root and
  a piece of the crown with a shoot bud

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Fig. 15-18. Propagation of sweetpotato by
adventitious shoots from tuberous roots.
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Fig. 15-19. Propagation of dahlia by tuberous
roots.
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Figure of dahlia tuberous root division, showing
the right way and the wrong way (Free 1957)
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Rhizomes

• Defn specialized stem with the main axis of the
  plant growing horizontally at or below the ground
  surface
• Types
• Pachymorph a short, thick, fleshy clump,
  determinate (terminating in a flowering shoot),
  e.g., German iris
• Leptomorph a slender stem with long internodes,
  indeterminate (growing continuously from the
  terminal apex) e.g., lily-of-the-valley)

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Fig. 15-20 and 15-22. Photo and figure showing
pachymorph and leptomorph rhizomes
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Division of rhizomes

• pachymorphs rhizome sections are cut off,
  transplanted
• leptomorphs - lateral offshoots (1st or 2nd yr)
  or pips (3rd-yr shoots) removed and transplanted
• culm cuttings - culm (aerial flowering shoot) is
  laid horizontally, branches arise at the nodes
  (e.g., bamboo)

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Pseudobulbs

• Defn specialized storage structure of epiphytic
  orchids
• Propagation methods
• offshoots develop at the nodes of a long, jointed
  pseudobulb (e.g., Dendrobium)
• rhizome division (Cattleya), cut back from the
  terminal end to include 4-5 pseudobulbs in each
  section
• micropropagation

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Fig. 15-24. Cattleya orchid rhizome with several
attached pseudobulbs.
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Micropropagation of orchids

• disinfestation and plating of a shoot tip
• formation of a protocorm
• multiple shoots develop from protocorms
• shoots are separated, rooted, transplanted to soil

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Fig. 18-11 and figure from Bhojwani (1983).
Steps in the micropropagation of orchids.
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Recap

• Tubers and tuberous roots
• Rhizomes - types and propagation methods
• Pseudobulbs and protocorms - propagation methods
  for orchids
• And, from the text (Ch. 15) Who discovered that
  orchids could be vegetatively propagated by
  protocorms?