|Authors: ||C.T. Miller, C.M. Filios, W.B. Miller|
|Keywords: ||geophyte, plant growth regulators, floriculture, anti-gibberellin|
Amaryllis (Hippeastrum) is a popular potted bulb grown and marketed for major holidays, including Christmas and Mother’s Day, for their large stately flowers.
However, flowering amaryllis often become too tall and unstable, due to the large flowers and tall stems.
A series of plant growth regulator (PGR) bulb soaks and media drench experiments were conducted using anti-gibberellins; flurprimidol, paclobutrazol and uniconazole.
Sixty-minute pre-plant bulb soaks (100 and 200 ppm) of flurprimidol and paclobutrazol were effective on amaryllis ‘Pamela’. Similar results were obtained between the PGRs for reducing flower stem height.
A negative dose response was observed for flower stem and leaf length reduction, with 200 ppm PGR treatments having the greatest response for both PGRs.
Leaf length also decreased with increasing PGR concentrations.
Flurprimidol PGR treatments had a greater effect in leaf length reduction, producing leaves 40% shorter than that of the control.
The number of days to flower was not affected by either PGR or concentration.
Media PGR drenches of flurprimidol and paclobutrazol on amaryllis ‘Pamela’ had no effect on flower height.
Leaf length was reduced with paclobutrazol and uniconazole by 9 and 14% respectively, while flurprimidol actually increased leaf length by 9%. None of the PGRs affected the number of days to flower.
Amaryllis bulb cultivars ‘Black Pearl’ and ‘Pamela’ were pre-plant soaked in flurprimidol (100 ppm), paclobutrazol (100 ppm) solutions for 60, 120, or 180 min or 60 or 120 min soaks in uniconazole (25 ppm). ‘Black Pearl’ was more responsive to PGR treatments than ‘Pamela’. Results showed inconsistent differences between duration of bulb soaks; that is, bulbs soaked for 180 min did not develop significantly reduced flower stem and leaf lengths than bulbs soaked for 60 min.
When soak length data for ‘Black Pearl’ of all treatment durations of individual PGRs were pooled, paclobutrazol treatments had reduced flower stem and leaf lengths compared to the control.
In ‘Pamela’, no differences between PGRs were observed for reducing leaf length.
A 180-min flurprimodol application significantly reduced flower stem length by 38%.
The results obtained from these experiments demonstrate that pre-plant bulb soaks for at least an hour, are effective in controlling plant height.
However, further investigations on PGRs and application on Hippeastrum will be beneficial.
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