Effectiveness of Plant Growth Regulators under Photoselective Greenhouse Covers

• Published in: Journal of the American Society for Horticultural Science Vol. 125; no. 6; pp. 673 - 678
• Main Authors: Tatineni, Anuradha, Rajapakse, Nihal C, Fernandez, R. Thomas, Rieck, James R
• Format: Journal Article
• Language: English
• Published: 01.11.2000
• ISSN: 0003-1062; 2327-9788
• DOI: 10.21273/jashs.125.6.673

Responses to selected chemical growth retardants (daminozide, paclobutrazol, and prohexadione-Ca) and GA 1 and GA 3 under photoselective greenhouse covers with various phytochrome photoequilibrium estimates (φ e ) were evaluated using `Bright Golden Anne' chrysanthemum [ Dendranthema × grandiflora Kitam. (syn. Chrysanthemum morifolium Ramat.)] as the model plant to better understand the height control mechanism by far red (FR) light depleted environments. Plant height linearly decreased as φ e increased from 0.72 to 0.83. The rate of height decrease of daminozide treated plants was less than that of water (control) or GA 3 -treated plants. The rate of height reduction was not different between control and GA 3 -treated plants among chambers with various φ e . Both paclobutrazol and prohexadione-Ca reduced plant height regardless of φ e , but the height reduction by paclobutrazol was more than that by prohexadioneCa. The combination of paclobutrazol and prohexadione-Ca reduced plant height more than either alone. GA 1 reversed the height reduction caused by paclobutrazol and prohexadione-Ca regardless of φ e , but the height increase by GA 1 was more when it was applied with prohexadione-Ca than when applied alone. Results show that photoselective covers with high φ e were effective in controlling height of chrysanthemums without chemical growth retardants. The linear relationship between plant height and φ e suggests that effectiveness of photoselective covers increased as φ e increased. The photosynthetic photon flux (PPF) transmission of photoselective covers decreased as the φ e increased because of the increasing dye concentration. Identifying photoselective covers that effectively filter out FR light from sunlight and reduce plant height while minimizing the PPF reduction is critical for commercial success of photoselective covers. Gibberellins are, at least partially, involved in height control by photoselective covers. Photoselective greenhouse covers did not reduce responsiveness to gibberellins, and it appears that the mechanism may be to suppress gibberellin biosynthesis. Results also suggest that increased metabolism of GA 1 to GA 8 was not the mechanism of height control by photoselective covers. Chemical names used: butanedioic acid mono (2,2-dimethylhydrazide) [daminozide]; (±)-(R * ,R * )-b-((4-chlorophenyl)methyl)-a-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol [paclobutrazol]; 3,5-dioxo-4-(1-oxopropyl)cyclohexanecarboxylic acid [prohexadione-Ca]; gibberellic acid [GA].