“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 and 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 Propagation of sweetpotato by adventitious shoots from tuberous roots.

Fig 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 and 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 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 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?