Effects of GA3 on Poinsettia Over-retarded with Paclobutrazol

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  • 1 Weslaco ISD, Weslaco High School, Weslaco, TX 78596
  • 2 Texas A&M Univ., Horticultural Sciences, Weslaco, TX 78596

A study was initiated to determine the effect of GA3 as a counter measure to restore the growth of over-retarded poinsettia. Euphorbia pulcherrima `Sonora Red' plants were treated once foliarly with paclobutrazol at 40 or 80 mg·L-1 one week following pinching. Four weeks later, plants receiving the 80 mg·L-1 rate were treated once foliarly with GA3 at 0, 10, 20, 30 or 40 mg·L-1. The effect of GA3 was visible within 3 days of application. GA3 between 10 and 40 mg·L-1 caused long internodes, excessive stem elongation, as well as small leaves and bracts, resulting in unmarketable plants. Plants receiving 10 mg·L-1 GA3 were nearly twice the height of the over-retarded plants (31 vs. 17 cm), with increasingly taller plants at higher concentrations, up to 30 mg·L-1. In a second experiment, single-stemed plants were treated with one foliar spray of 50 or 150 mg·L-1 paclobutrazol two weeks following the beginning of short days. After another 3 weeks, the overdosed plants were then foliarly treated once with 0, 3, 5, 10, or 15 mg·L-1 GA3. GA3 at all rates promoted stem elongation and resulted in large bracts and much increased inflorescence diameter. The 15 mg·L-1 GA3 rate resulted in undesirable long internodes on the upper stem. Plants that received 3, 5, or 10 mg·L-1 GA3 were of excellent quality, with their heights and inflorescence sizes similar to those of plants receiving 50 mg·L-1 paclobutrazol (26 cm). Parallel experiments using `Burgundy Cortez' had similar results.

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