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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 to control crop height. A negative DIF exists when greenhouse night temperature is greater than the day temperature. Large negative differences in day and night temperatures strongly suppress stem elongation in many crops. We have explored the effects of negative DIF temperature regimes on leaf, flower, and stem carbohydrate levels in Lilium longiflorum Thunb. `Nellie White'. During two growing seasons, `Nellie White' plants were grown under positive or negative DIF regimes (±5 or 8C) under prevailing daylengths, with temperatures adjusted so that daily temperature averages were equal between regimes. Plants were harvested ≈10 days after visible bud stage and at anthesis. Carbohydrates in stems, leaves, and flowers were analyzed by high-performance liquid chromatography. Compared to plants grown under positive DIF, negative DIF plants showed significantly reduced stem length and leaf and stem dry weights. Negative DIF regimes reduced leaf and stem total soluble carbohydrate (TSC) content by 39% to 46% at visible bud and anthesis, while flower TSC content was reduced by 10% to 13%.

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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).

Open Access

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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The interactions of ancymidol drenches, postgreenhouse cold storage, and hormone sprays on postharvest leaf chlorosis and flower longevity of `Nellie White' Easter lilies (Lilium longiflorum Thunb.) were investigated. Ancymidol drenches (0.5 mg/plant twice) during early growth resulted in leaf chlorosis in the greenhouse which intensified further during postharvest. Cold storage (4 °C) of puffy bud stage plants for 2 weeks also accelerated leaf chlorosis. The combination of ancymidol treatment with cold storage resulted in the most severe leaf chlorosis. Promalin (GA4+7 and BA each at 100 mg·L-1) sprays completely prevented postharvest leaf chlorosis, whereas ProGibb (GA3 at 1000 mg·L-1) was ineffective. Cold storage reduced flower longevity and increased bud abortion, however, the degree of bud abortion varied among experiments in different years. Both ProGibb and Promalin sprays increased flower longevity. Compared to positive DIF (difference between day and night temperature) grown plants, forcing under negative DIF (-8 °C) increased the severity of postharvest leaf chlorosis. Leaves were sampled from basal, middle, and upper sections of the stem after 4 and 12 days in a postharvest evaluation room, and analyzed for soluble carbohydrates and N. Total leaf soluble carbohydrates and N concentrations were less in basal and middle sections of negative DIF-grown plants than in positive DIF-grown plants. Leaf chlorosis was associated with depletion of soluble carbohydrates and N in the leaves. Chemical names used: α-cyclopropyl-α-(p-methoxyphenyl)-5-pyrimidinemethanol (ancymidol); gibberellic acid (GA3); gibberellins A4A7 (GA4+7); N-(phenylmethyl)-1H-purine 6-amine (benzyladenine).

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