Gibberellin-Induced Flowering in Cordyline (Agavaceae)

Normal, terminal inflorescences of Corayline terminalis, a woody monocotyledon, appeared 4-6 weeks after apical buds were treated with gibberellin A3 (GA3) or GA4+7. There was no response to GA13. Large plants, newly rooted cuttings, and seedlings all responded, although there were clonal differences. Flowering was induced under natural day lengths throughout the year. Untreated control plants in all experiments remained vegetative. Dracaena spp. did not respond to the three gibberellins. INTRODUCTION Gibberellins are known to induce flowering in many temperate plants (Jones, 1973). Recently, gibberellin A3 (GA3) was also shown to induce precocious flowering in several tropical aroids (Alamu and McDavid, 1978; Harbaugh and Wilfret, 1979). This result offers a new and useful research tool for studying the reproductive and vegetative development of other tropical monocotyledonous crops and ornamentals. The control of flowering should also be of practical use in the breeding of these species. The use of auxin and ethylene for the induction of flowering in the tropical Bromeliaceae (including pineapple) is now widely used (Zeevaart, 1976). During an investigation into factors that regulate the production of rhizomes and leafy shoots in Cordyline terminalis (L.) Kunth (Fisher, 1972), a woody perennial member of the Agavaceae, I found that GA3 caused precocious flowering in young plants. The control of flowering in this species will allow a time course study of the developmental changes that occur in the shoot apex during the transition from vegetative to reproductive growth (Stevenson and Fisher, in press). Several anatomical features make Cordyline a significant plant for understanding the regulation of internode extension and the relationship between primary and secondary growth in monocotyledons. The vegetative axis of Cordyline, Dacaena, and other Agavaceae has true secondary growth while the adjacent inflorescence axis has only primary growth (Fisher and Tomlinson, 1972). The relatively short internodes of the vegetative axis develop from uninterrupted meristems while the long, first internode of the inflorescence develops from an intercalary meristem (Fisher and French, 1976, 1978). This content downloaded from 157.55.39.162 on Thu, 11 Aug 2016 04:23:00 UTC All use subject to http://about.jstor.org/terms 732 Fisher—Flowering in Cordyline Flower induction in this plant and a preliminary survey of the sensitivity to gibberellins by other members of this family are described. MATERIALS AND METHODS Seedlings and cuttings of several clones of Cordyline were grown in a glasshouse in Miami (latitude 25° 40' N). Unnamed c lones were selected from seedlings which showed a range in leaf shape and variations in red coloration. Seeds were collected originally from a tree that resembled cv. Madame Eugene Andre. Large, field-grown plants of Cordyline and Dracaena thalioides Hort. Makoy ex E. Morr. and well rooted cuttings of D. deremensis Engl., D. marginata Lam., and D. reflexa Lam. were also used. The following gibberellin analogues were used: GA3 (Eastman Kodak Co.), GAU (Imperial Chemical Industries Ltd.), GA4+7 (Imperial Chemical Industries Ltd.), and a commercial solution of GA4+7 (Pro-Gibb 47 from Abbott Laboratories). Solutions (see Tables 1 and 2) were made with 70% (v/v) ethanol except for Pro-Gibb 47 which was diluted with water. Control solutions were 70% ethanol or 70% iscpropanol (only when Pro-Gibb 47 was used). Three drops of solution were applied to the spear (unrolled) leaf and the next younger leaf on each of three consecutive days, i.e. a total of 0-12-0-15 ml was applied to each apical bud. Some larger Dracaena spp. received a total of 0-16-0-20 ml during the 3 d treatment period. Plants, grown under local day length conditions, were treated at various times throughout the year and observed regularly until 5 months after treatment.