The Handbook on Plumeria

 RESEARCH ON PLUMERIAS

Studies on Branching

A study on branching has been conducted under the direction of Dr. Richard Criley at the University of ^^^ i>. Criley has written us recently that the project will not be completed for several months more but so far it has been found that "... lanolin paste applications of N-6-benzyladenine (rates from 0.5 to 4 mg BA per gram of lanolin) to cut stumps/branches produced an increased number of breaks over the controls, but there were insufficient replications for good statistics."

In 1973 Dr.Criley published some valuable research in the Horticulture Digest, a publication of the Cooperative Extension Service, University of Hawaii, entitled "Investigations into Plumeria Flowering". He has kindly allowed me to include this research in our handbook. We quote in full:

Investigations into Plumeria Flowering

"by Richard A. Criley, Associate Horticulturist

Based on work ( on other flower crops showing regrowth and flowering following cut-back, we attempted to time plumeria ('Common Yellow') for winter flowering by cutting back during summer. Ten plants were cut back to leave 8- to 12-inch stubs on July 1, July 22, and August 15. Half of each treatment ^as placed in front of silver-painted boards to provide • more total light.

Regrowth was longest on the earliest cut-back, but no treatment showed early flower bud development, nor did the reflector appear to influence earlier flowering.

That year, however, on 72 breaks developing on the 15 plants in front of the reflector, (here were 21 inflorescences while on 70 breaks on the other group, only 15 inflorescences developed. During the next year, the plants in front of the reflector produced 29 inflorescences on the original breaks plus 12 more on the shoots produced below some of the 21 inflorescences of the year before, for a total of 41 inflorescences. The plants without the reflector had 19 inflorescences and none on breaks which subtended the previous year's inflorescences.

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The reflector apparently was responsible for doubling the number of inflorescences produced in two seasons following a severe cut-back. The actual amount of light could not be accurately measured but it was estimated that there was about 33 percent reflectance. Another research project Dr. Criley has shared with us is entitled "Flowering of Young Plumeria Cuttings". Since the research is too lengthy to quote in full we will abstract some of the most important data:

An alternative to outdoor flower production of plumerias during winter is to force the inflorescences of budded shoots in a heated greenhouse. The advantages would be more dense spacing, ease of harvest, and ability to harvest every flower produced. We do not know if the inflorescence can be induced to develop if the shoot is removed from the rest of the plant and not allowed to form roots, but it is possible to root these shoots as cuttings and force the inflorescence. In addition to the implications for winter production of plumeria flowers for leis, such a system would be happily embraced by producers of cuttings for sale to Hawaii's tourists.

This is a report on a preliminary study which demonstrates the concept of forcing rooted cuttings into bloom when a bud is already present in the terminal.

The following is a brief summary of the experiment: cuttings were rooted in one gallon pots in the fall of 1973. Rooted plants showing buds were then forced in a warm greenhouse in December. A teaspoon of Osmokote 14-14-14 was topdressed on each pot and irrigation was by hand, as needed. Greenhouse temperatures fluctuated between 64 and 93 degrees F. (N/D), averaging 74 to 79 degrees F. Although the infloresence size was smaller for the forced plants in containers than for field-grown plants, one group averaged 104 flowers per inflorescence, while the duration of flowering averaged from 5 weeks to 12 weeks for the same variety. During the peak of flowering at the 3rd and 4th weeks, the same cultivar produced an average of 16 flowers per plant per week. This should be a great encouragement to anyone who would like to grow plumerias under greenhouse conditions during the winter months.

For those who would like to experiment further, we quote the final paragraph of Dr. Criley's paper:

The results of this trial lend some optimism to the concept of developing a system for production of plumeria flowers during winter months, but many questions remain to be investigated. While we have demonstrated the ability to force flowers on rooted shoots of plumerias during the winter, this does not necessarily mean that budded, but unrooted, shoots would respond similarly although we have observed flower development to anthesis on branches which have been left lying in the field after pruning. A means to identify shoots in which the inflorescence has been initiated must be found so that a high proportion of productive plants can be assembled for winter forcing. While the temperatures encountered during this experimental period were sufficient to permit forcing, we do not know how cool temperatures would have to be to delay

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development. We would also like to know what must be done in order for an inflorescence to produce up to the potential observed on field-grown plants.

During the 1970's some research was conducted in India on the structure of cymes and a new hybrid named in honor of former prime minister Indira Gandhi was introduced.

In the ts4ay 1980 issue of The Planter, published in Kuala Lumpur, Malaysia, there is an article on the viablility of plumeria seeds (Mossel in Amsterdam successfully germinated seeds 16 months old), percentage of germination and studies on the insertion of cotyledons.

There have been several highly technical studies listed in the Horticultural Abstracts which we researched from 1968 through 1988, some concerning the reversion of embryos in Plumeria rubra, others detailing the finding of iridoids with algicidal properties in the roots of plumerias, an in-depth study of chromosome counts that should be of much importance in future breeding, and one study on the fragrance of one species of plumeria. Other than the studies quoted above and the important observations of dedicated plumeria growers, there is not much more to be found.

Locally, some important work has been accomplished by Elizabeth Thornton. In one experiment she sprayed gibberellic acid on new flower buds when they were just

^1/8 to ^1/4 inch high and found that this treatment increased seed set. She has also researched Nature's pollinators, and has related her observations on the hummingbird, the hummingbird hawk moth and the braconid in her 1985 revision of The Exotic Plumeria.

George Slusser of Woodinville, Washington, continues to send us detailed accounts of his experiments in germination and rooting plumeria cuttings in water, a fascinating study, which we have included in the chapter on Propagation.

Michael Pettit of Garland, Texas, is working on closed pollination in an attempt to develop hybrids that will flower easily in temperate climates and will be more compact.

Dr. Criley has recently sent me two progress reports on further research on plumerias undertaken through grants from the Plumeria Society of America. The first study is to determine the effect of growth retardants on stem elongation of P. 'Common Yellow'. Preliminary research indicates that all four of the retardants used seem o be effective, with marked effects at higher concentrations. The second study is on he effect of growth regulators on branching of P. 'Common Yellow'. A third study concerns the storage longevity of plumeria flowers and ethylene production by plumeria flowers. The best temperature to hold flowers was determined to be 10 degrees

C.  The longest lasting cultivars were 'Irma Bryan', 'Elena', 'Common Yellow', 'White Shell', 'Pauahi Alii' (formerly 'Angus Gold') and 'Peachglow Shell'. We quote from the final few sentences of Dr. Criley's preliminary report:

-Addition of ethylene to the holding environment did hasten the development of browning when compared to an ethylene-free system or a system to which air was flushed to remove accumulated ethylene.

The implication of this work is that ethylene is probably involved in reducing the keeping life of harvested (and old) plumeria flowers. If some

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way can be found to prevent the action of ethylene, it may be possible to extend the keeping life of plumerias used in leis or as cut flowers.

It is most gratifying to us to be able to receive reports from all parts of the world relating to current studies on plumerias and to share this information with interested plumeria growers. In this way we all benefit by a greater understanding of Nature"s extraordinary gifts. As the poet and sage, Sri Aurobindo, has written: "All's rniracle here and can by miracle change."

PLUMERIA SOURCES

Although many local nurseries now offer plumerias and other tropicals such as mandevilla, the best mail order source is:

Stokes Tropicals

P.O. Box 9868

New Iberia, LA 70562-9868

1-800-624-9706

email: gstokes@lstnet.com

Glenn and Yvonne Stokes offer an extraordinary selection of plumerias and oti'e1" colorful tropicals and semi-tropicals such as hibiscus, bougainvilleas, gingers, banai's5' heliconias, and bromeliads. They also have an excellent website with great color photos of the plants they offer: www.stokestropicals.com

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