Horticulture Digest #106
METHOD OF APPLICATION AFFECTS EFFECTIVENESS OF
CYTOKININ IN INDUCING BUD BREAK ON HELICONIA RHIZOMES

Heliconias are readily propagated by rhizome pieces. New roots must be developed if the old ones have been trimmed off for shipping. The normal practice is to leave about 8-10 inches of old pseudostem base on the cleaned, trimmed swollen rhizome base. The rhizome base is planted in a clean medium such as sand, perlite, cinders, or coarse vermiculite until roots develop. It can then be transplanted to a large container or into the field with good assurance of success.

The rhizome pieces can also be direct-planted into the field, and while not every piece will "take", this method is also practiced as a means of avoiding the extra work of transplanting rooted plants.

In most cases, a new bud emerges from the old rhizome base to develop as a new shoot. This shoot, in turn, produces roots and basal shoots establishing a clump over a period of time.

A group of plant hormones called cytokinins (CK) is known to induce bud break on many kinds of plants on both aerial and below-ground parts. Several synthetic cytokinins are available, albeit with limited registrations for uses. These include materials su ch as thiadiazuron (TDZ), benzylaminopurine (BA), and Accel (tm) (also known as PBA).

Results:
Injection of the cytokinins into the pseudostem was not particularly easy as excess solution squirted out of the cut end. A concentration of 200 ppm CK was used which means that 0.2 milligrams of cytokinins was actually injected. The BA and PBA treatments were only slightly more successful in stimulating bud break when compared to non-injected controls (2.3, 2.0, and 1.8 new basal shoots, respectively), whereas the TDZ treatment stimulated only I basal shoot per rhizome (these appeared somewhat deformed). Mortality was 60% for the TDZ shoots and 40, 25, and 16% for the PBA, BA, and non-injected controls, respectively.

For the rhizome and pseudostem soak treatments, 400 ppm BA was used. All of the nontreated controls survived, but there was 40% mortality for the rhizome soak and 20% for the pseudostem soak treatments. The rhizome soak did not stimulate more basal bud br eak than on the controls, but the inverted pseudostem soak stimulated 2.8 breaks per piece compared to 1.8 for the controls.

In brief, it is practical to soak inverted pseudostems in a CK solution, and uptake appears to be sufficient to stimulate basal bud break. The rhizome soaks may have prevented root development as this is a known effect of cytokinins. The injection method was too cumbersome to use on a large scale and rhizome mortality was high, although surviving pieces were slightly superior to non-injected controls in terms of basal bud break.

Experiment:
Because of an interest in stimulating greater bud break on heliconia rhizome pieces, some trials were conducted with these cytokinins in the fall of 1994 on several different heliconia species. The methods of application were soaking the rhizome in a CK s olution for 10 to 30 minutes, injecting one milliliter of CK solution into the pseudostem, and inverting the pseudostem into a CK solution.

Richard A. Criley, criley@hawaii.edu
Horticulturist

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