Abstract
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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