DIFFERENTIAL TEMPERATURE (DIF) EFFECTS ON THE GROWTH, MORPHOLOGY AND FLOWERING OF ANTIRRHINUM MAJUS L. (SNAPDRAGON) CULTIVARS

Controlling stem height and the balance between vegetative and reproductive growth in the cut-flower snapdragon is a long-time problem in greenhouse production. DIF, a non-chemical method for controlling plant height is now used extensively in both Europe and the United States. We examined the responses of eight Antirrhinum majus L. cultivars in a series of growth chamber experiments. DIF treatments were imposed by increasing the air temperature from 18°C to 24(±0.3)°C (+DIF) and by decreasing the air temperature from 18°C to 12(±0.3)°C (-DIF), from 4am to 9am each day for group 3/4. By measuring differences in plant growth and development, we found that negative DIF significantly decreased stem height in group 3/4 (summer/fall) cultivars at vegetative and pre-anthesis stages, but the effect was not consistent in group 1/2 (winter/spring) cultivars. Negative DIF treatments reduced shoot and stem dry mass (DM), but had no effect on stem diameter or final harvest leaf number in group 3/4 cultivars, resulting in shorter, sturdier plants. Increasing the red/far-red (R/FR) ratios had different effects in cultivars that we tested. Negative DIF treatments appeared to slightly increase the vase-life and the total percentage of open flowers.

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