Angel-Wing Begonia Growth and Water Requirements Affected by Paclobutrazol

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C.A. Conover, Ph.D.*

University of Florida/IFAS
Central Florida Research and Education Center
CFREC-Apopka Research Report RH-94-4

Paclobutrazol, a plant growth regulator, has been shown to be effective in producing foliage plants with attractive compact growth habits and in controlling the size of plants maintained in interiorscapes (Cox and Whittington, 1988; Davis et al, 1985; LeCain et al, 1984; Wang and Blessington, 1990). In earlier tests, paclobutrazol treated foliage plants growing in a greenhouse or maintained under interiorscape conditions used less water and fertilizer than untreated plants, even when plant growth was not noticeably affected (Poole and Conover 1992a; Poole and Conover 1992b). Reducing water and fertilizer needs during production as well as in interiors would save on labor and material costs and reduce risk of environmental pollution.

Angel-Wing begonias are attractive fibrous-rooted plants grown by the foliage plant industry in a variety of pot and basket sizes. Plants have cane-like stems which sometimes develop leggy, stretched growth. This experiment compared growth, quality and water requirements of Angel-Wing begonia not treated with growth regulators to that of plants treated with paclobutrazol.

On September 2, 1992, Begonia coccinea 'Pink' (Angel-Wing begonia) cuttings rooted in 7.6-cm pots were transplanted into 15-cm standard pots using Fafard #4 growing medium. The plants were grown in a greenhouse where light intensity was approximately 1600 ft-c and air temperatures ranged from 70 to 90°F. Plants were fertilized with 5 g/15-cm pot 19-6-12 Osmocote (Grace/Sierra Co., Milpitas, CA).

On September 3, 1992, the growing medium of plants was drenched with 100 ml water or 100 ml solutions containing 0.12, 0.25, 0.38 or 0.50 ml Bonzi™ [Bonzi™ flowable emulsion, 0.4% active ingredient paclobutrazol, (ICI Americas, Inc., Goldsboro NC)]. Six replications were provided for each drench treatment tested, with one plant as an experimental unit. Plants were watered one to three times per week as needed to maintain proper medium moisture levels.

Total water used by plants throughout the course of the experiment was determined by the following method: 1) at every watering, a 2000 ml beaker was placed under each pot in order to catch the leachate; 2) water was slowly applied to growing medium surface of each pot in measured increments until leaching was observed; and 3) after one hour, the volume of leachate in beakers was determined. Total water used by plants was defined as total water applied to pots minus total leachate collected. (This method does not account for water evaporation from medium surface between watering times).

Plants were graded on December 21, 1992, using a scale of 1 = dead, 2 = poor quality, unsalable, 3 = fair quality, salable, 4 = good quality and 5 = excellent quality. On December 30, 1992, plant height and width (cm) were measured. Plant size was defined as the average of plant height and width. Electrical conductivity (ymhos/cm) and pH of leachate were determined initially on September 9, 1992 and again when research was concluded on January 8, 1993.

Results

Only Bonzi™ treated plants were flowering when research was terminated. Plant height and size were also affected by drench treatments (Table 1). Although plants were smaller as Bonzi™ rate increased, more difference was observed in size of plants that did not receive Bonzi™ and size of plants treated with the low Bonzi™ rate compared to the size differences in plants getting 0.12 ml/15-cm pot Bonzi™ and plants drenched with 0.50 ml/15-cm pot.

Best quality plants received the lowest Bonzi™ rate tested, 0.12 ml/15-cm pot (Table 1). As Bonzi™ rate increased, plant height and size decreased resulting in lower plant grades. Quality of plants not treated with growth regulators was comparable to plants getting 0.25 ml/15cm pot Bonzi™. However, Angel-Wing begonia plants drenched with Bonzi™ solutions required less water during production than untreated plants. Differences in water use by plants receiving growth regulators showed a trend toward decreasing water use as Bonzi™ application rates increased. Height and size differences between treated and untreated plants probably accounted for some but not all of the differences in water use.

Leachate pH was unaffected by treatments and dropped slightly over time (Table 2). Leachate initial µmhos/cm showed a linear increase with treatment number but final µmhos/cm were over twice as high for Bonzi™ drenched plants compared to plants drenched with water. This would indicate fertilizer uptake decreased as growth regulator rate increased.

Conclusions

Angel-Wing begonias drenched with Bonzi™ used less than half the amount of water used by plants not receiving growth regulators and water use generally decreased as Bonzi™ application rate increased. However, benefits from reduced water and fertilizer needs would be meaningless if crop quality were not equal to or higher than quality of untreated plants. In this test, best quality Angel-Wing begonias received 0.12 ml/15-cm pot Bonzi™, the lowest rate tested. Although plants drenched with 0.25 ml/15-cm pot Bonzi™ were of comparable quality to untreated plants, untreated plants needed more water and fertilizer during production compared to treated plants and were not flowering when research was terminated.

*professor of Environmental Horticulture and Center Director (retired 7/96), Central Florida research and Education Center, 2807 Binion Road, Apopka, FL 32703-8504.

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References

1. Cox, C.A. and F.F. Whittington. 1988. Effects of paclobutrazol on height and performance of aluminum plant in a simulated interior environment. HortScience 23:222.
2. Davis, T.D., K. Emino, W.Shurtieff and N. Sankhla. 1985. The promise of paclobutrazol. Interior Landscape Industry 2 (11):36-41.
3. LeCain, D.R., K.A. Schekel and R.L. Wample. 1984. The effect of paclobutrazol on acclimatization of Ficus benjamina. HortScience 19:587 (abstract).
4. Poole, R.T. and C.A. Conover. 1992a. Paclobutrazol and indoor light intensity influence water use of some foliage plants. Proc. Fla. State Hort. Soc. 105: 178-180.
5. Poole, R.T. and C.A. Conover. 1992b. Water use and growth of eight foliage plants influenced by paclobutrazol. Foliage Digest (15)12:1-3.
6. Wang, Y.T. and T.M. Blessington. 1990. Growth of four tropical foliage species treated with paclobutrazol or uniconazole. HortScience 25:202-204.

Table 1. Growth, quality and water consumption of Angel-Wing begonia affected by Bonsi™.

^zPlants were drenched with 100 ml water or 100 ml solutions containing 0.12, 0.25, 0.38 or 0.50 ml Bonzi™ on September 3, 1992.
^yFinal height (cm) was measured on December 30, 1992.
^xPlant size was determined as the average of final height and final width (cm), both measured on December 30, 1992.
^wPlants were graded based on a scale of 1 = dead, 2 = poor quality, unsalable, 3 = fair quality, salable, 4 = good quality and 5 = excellent quality.
^vWater used = Total water applied - total leachate collected.
^uns, **; Results nonsignificant or significant at P = 0.01, respectively.

Table 2. Initial and final pH and electrical conductivity of leachate collected from containers of Angel-Wing begonia drenched with 100 ml water or a 100 ml solution containing 0.12, 0.25, 0.38 or 0.50 ml Bonzi™ on September 3, 1992.

^zPlants were drenched with 100 ml water or 100 ml solutions containing 0.12, 0.25, 0.38 or 0.50 ml Bonzi™ on September 3, 1992.
^yInitial pH and µmhos/cm were measured from leachate collected after Bonzi™ was applied on September 3, 1992. Final pH and µmhos/cm were measured from leachate collected on January 8, 1993.
^xns, *, **; Results nonsignificant, significant at P = 0.05 and significant at P = 0.01.respectively.