“Other” specialized structures

• tubers

• tuberous roots

• rhizomes

• pseudobulbs

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

Fig. 15-15 and 15-16. Propagation of “Irish” potatoes by tuber pieces.

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

Fig. 15-18. Propagation of sweetpotato by adventitious shoots from tuberous roots.

Fig. 15-19. Propagation of dahlia by tuberous roots.

Figure of dahlia tuberous root division, showing the “right” way and the “wrong” way (Free 1957)

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)

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

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)

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

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

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

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

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?