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%.

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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