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  • Author or Editor: Terri I. Kirk x
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Commercial greenhouse operators are increasingly using “negative DIF” temperature regimes for crop height control. A negative DIF exists where the night temperature (NT) is greater than day temperature (DT). Large differences in DT-NT strongly suppress stem elongation in many crops, and have been used to reduce labor and material costs for chemical growth regulator applications on Easter lily. We have explored some of the biochemical effects of negative DIF temperature regimes. 'Nellie White Easter lilies were grown (1989 and 1991) at Purdue under a +10 or -10 DIF regime with temperatures adjusted so that daily averages were equal. Plants were harvested at visible bud (VB) and anthesis. Carbohydrates in stems, leaves and flowers were analyzed by HPLC With both temperature regimes, timing data indicated equal daily temperature averages were achieved. Negative DIF severely reduced stem length, and leaf and stem dry weight. Negative DIF reduced leaf and stem total soluble carbohydrate (TSC) content 39-46% at VB and anthesis, while flower TSC was reduced 10-13%. These results indicate negative DIFs have potentially detrimental biochemical effects on Easter lilies. Other techniques, such as early morning temperature drops, were not a part of this study, and their physiological effects should be evaluated as well.

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Abstract

Ancymidol and paclobutrazol (13 weekly foliar spray applications of 100 mg/liter AI) stimulated inflorescence initiation of Hydrangea macrophylla Ser. ‘Merritt's Supreme’ plants under a noninductive continuous photoperiod at 24°C minimum daily temperature. Inflorescence primordia were present on plants having 12-14 subtending leaf pairs. Four expanded leaf pairs prior to initiation of treatments were sufficient to sustain inflorescence development. Plant height was controlled effectively with 10,000 mg/liter daminozide, 50 and 100 mg/liter ancymidol, and 100 mg/liter paclobutrazol treatments. Chlormequat at 3000 mg/liter did not suppress internodal elongation. Number of expanded leaf pairs per plant was significantly less than on control plants for all treatments except chlormequat at 3000 mg/liter. Chemical names used: α-cyclopropyl-α-(4-methoxyphenyl)-5-pyrimidinemethanol (ancymidol); β[(4-chlorophenyl)methyl]-α-(l,l-dimethylethyl)-1H-l,2,4-triazole-l-ethanol (paclobutrazol); butanedioic acid mono (2,2-dimethylhydrazide) (daminozide); [2-chloro-N,N,N-trimethylethanaminium chloride (chlormequat chloride); 1H-indole-3-butanoic acid (IBA).

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