Foundations for a long term Dracaena breeding program : flower induction, irradiation, and polyploidization

Abstract

Dracaenas are important foliage plants not only in the United States, but also worldwide, and new varieties are needed to maintain consumer demand. Flower induction, mutation induction with gamma rays, and polyploidization using oryza1in were attempted on various dracaenas to lay down the foundations for a long-term breeding program to create new varieties for the foliage industry. Using traditional breeding methods for breeding requires the availability of flowers on plants intended for breeding. Two methods were employed to attempt flower induction - Gibberellic acid (GA3) applications and cold temperature treatments. GA3 solutions ranging in concentration from 0 to 6000 ppm were applied to nine different varieties of Dracaena to attempt out of season flower induction. Dracaena fragrans 'Massangeana' flowered at the rate of 8% in the 0, 500, and 1000 ppm treatments and 16% in the 2000 ppm treatment. Dracaena xmasseffiana flowered at rates of 0%, 41.67%,58.33% and 62.5% in the 0,500,1000, and 2000 ppm treatments, respectively. None of the other treated plants flowered during the experiments. Three cold temperature experiments using temperatures ranging from 8 to 20°C and treatment durations from 3 to 40 days were performed on seven different Dracaena varieties. D. xmasseffiana plants chilled for 0, 3, 6, or 9 days at 12°C flowered at the rate of 0%, 16.9%, 39.2%, and 86.7% of stems, respectively. None of the other plants treated had significant flowering percentages. Mutation induction using irradiation is a useful method for creating new varieties of ornamental plants that are vegetatively propagated. Unrooted cuttings of four Dracaena varieties were irradiated using Cesium-137 gamma rays at dosages ranging from 0 to 500 Grays (Gy) in the first round and 0 to 50 Gy in the second round in order to estimate the LD50 dosages for root and shoot formation. A general trend of decreased root and shot formation with increased radiation dosage was observed. For root formation, the LD50 dosages were estimated as 14.6,13.8,5.7, and 17.7 Gy and for shoot formation, the dosages were estimated as 19.4,16.6,22.1, and 10.9 Gy for D. deremensis 'Santa Rosa', D. fragrans 'Massangeana', D.fragrans 'Victoriae', and D. xmasseffiana, respectively. Visually detectable mutations for each treatment were observed at rates of 0% to 93.3% with chlorophyll mutations being the most common. Polyploid forms of plants often have horticulturally desirable characteristics such as more compact growth habit, thicker and more robust leaves, and a deeper green color. Two methods of polyploidization on Dracaena were attempted. Both methods employed six treatments consisting of three concentrations of oryzalin ranging (0%, 0.05% and 0.01 %) and two durations of treatment (24 and 48 h). The first method treated developing axillary buds of D. deremensis 'Santa Rosa' in vivo by placing oryzalin soaked cotton on the meristem and covering the meristem in plastic. The second method treated call us tissue of D. deremensis 'Lisa' in vitro by soaking the calli in oryzalin solution. The developed shoots from the axillary buds and the regenerated shoots from the callus tissue were tested for conversion to polyploidy using flow cytometry with leaf tissue nuclei. In vivo treatments resulted in only one mixoploid. In vitro treatments resulted in one mixoploid and one tetraploid plant. The tetraploid has shorter internodes and shorter leaves than its diploid counterpart and is being further evaluated for suitability as a new variety or for use in hybridizing efforts.