Variability between silver thiosulfate and
1-naphthaleneacetic acid applications in prolonging
bract longevity of potted bougainvillea
Y.-S. Chang
*, H.-C. Chen
Department of Horticulture, National Taiwan University, No. 1, Section 4, Roosevelt Road, Taipei, 10617 Taiwan, ROC
Accepted 6 May 2000
Abstract
Potted bougainvillea `Purple Flower' and `Taipei Red' in four different stages of bract development were sprayed with STS (0.1, 0.5 mM) or NAA (25, 50 ppm) and were moved to low-light indoor conditions after treatment. The experiment was conducted twice, and the results showed that 0.5 mM STS and NAA (25, 50 ppm) could signi®cantly prolong the longevity of bracts at certain stages in both cultivars. Treatment with 0.1 mM STS, however, had no effect on bract longevity of `Taipei Red' at any stage. The prolonging effect of STS was more obvious in early bract stages and decreased as the bract stage increased, whereas NAA applications at later bract stages produced better results on prolonging bract longevity. The ethylene production rates of bracts in these two cultivars were higher in early stages and gradually decreased with bract growth. We propose that this phenomenon is related to the variability between STS and NAA in prolonging bract longevity of bougainvillea.#2001 Elsevier Science B.V. All rights reserved.
Keywords: Bract longevity; Bract stage; Bougainvillea; Ethylene production; 1-Naphthaleneacetic acid; Silver thiosulfate
1. Introduction
The shelf life and commercial value of many potted plants are seriously affected when subjected to dark transport or low-light indoor conditions, which often induces ¯ower and leaf abscission (Halevy and Kofranek, 1976; Tjosvold
*
Corresponding author. Tel.:886-2-23630231; fax:886-2-23635849.
E-mail address: [email protected] (Y.-S. Chang).
et al., 1994). The same is also true of bougainvillea when exposed to long periods of cloudy or rainy weather or dim indoor lighting. Wein and Turner (1989) pointed out that dim lighting induces ethylene evolution of bell pepper, thereby causing ¯ower bud abscission. Ethylene also induces ¯ower and bud abscission in some ¯ower crops, such asSchlumbergera truncata (Cameron and Reid, 1981),
Hibiscus rosa-sinensis (Thaxton et al., 1988), and Impatienshawkeri (Dostal et al., 1991).
Some cut ¯owers are generally treated with silver thiosulfate (STS) to prevent ¯ower senescence (Borochov and Woodson, 1989). Cameron and Reid (1981, 1983) reported that STS could reduce the ¯ower abscission of zygocactus, slipperwort, and bougainvillea when those potted plants are subjected to environmental stress. Serek (1993), Cushman and Pemberton (1994), and Tjosvold et al. (1994) showed that spraying STS on miniature roses before transportation could prolong ¯ower longevity. Experiments on Christmas begonia (Fjeld, 1991) and Easter cactus (Han and Boyle, 1996) showed that STS was more effective when applied during early ¯ower development.
The auxin, 1-naphthaleneacetic acid (NAA), has been shown to prevent ¯ower bud abscission in roses (Halevy and Kofranek, 1976) and peppers (Wein and Turner, 1989; Wein and Zhang, 1991). For bougainvillea, Hackett et al. (1972) indicated that the drop of mature ¯ower-bracts can be delayed 2±3 weeks by applying NAA at the time of bract opening. They concluded that the NAA effects were almost always due to differences in ¯ower-bract maturity. This study investigates the effects of different concentrations of STS and NAA on bract longevity when applied during different bract development stages of potted bougainvillea `Purple Flower' and `Taipei Red'.
2. Materials and Methods
2.1. Chemical application
illumination from ``cool-white'' ¯uorescent lamps providing 400±700 lx. During the experiment, bract senescence, bud abscission, leaf chlorosis, and leaf abscission were recorded daily. ``Bract longevity'' was de®ned as the number of days from treatment to bract abscission. Experimental data were subjected to 2-factor nested analysis of variance (stage nested within treatment) using the general linear model procedure within SAS (SAS, 1985). The experiment was conducted twice: the ®rst experiment (Experiment 1) began on 29 November 1997 and ended on 4 January 1998; the second experiment (Experiment 2) began on 23 November 1998 and ended on 3 January 1999.
2.2. Measurement of ethylene production rate
For each sample, three units (one unit is bracts of three ¯owers) at the same stage were placed in a 40 ml sealed plastic jar at a temperature of 2028C under continuous illumination from ``cool-white'' ¯uorescent lamps providing 400± 700 lx. Each bract stage had three samples (replicates) in both cultivars. A 1.0 ml gas sample was injected into a Shimadzu GC-14A gas chromatograph with a ¯ame ionization detector and activated alumina column (15 m in length and 60/ 80 mesh). Column, detector, and injector temperature were 70, 110, and 1108C, respectively. The carrier gas was nitrogen and the standard gas was 1 ppm ethylene.
3. Results
Experiment 1. For `Purple Flower', applying 0.1 or 0.5 mM STS prolonged bract longevity at stages 1 and 2, and the bract longevity decreased as stage increased (Table 1). However, bract longevity of all stages was prolonged by
Table 1
Effects of STS and NAA on bract longevity in different bract stages of potted bougainvillea `Purple Flower' (Experiment 1)
Treatment Bract longevity (days)
Stage 1 Stage 2 Stage 3 Stage 4
Control 9.6cAa 8.0cAB 6.0cB 6.0cB
0.1 mM STS 20.3aA 17.0bA 12.3cB 7.6cC
0.5 mM STS 22.0aA 18.6bA 10.3cB 8.6cB
25 ppm NAA 15.3bC 20.3bB 25.0bA 25.6bA
50 ppm NAA 18.6abB 30.0aA 32.6aA 35.6aA
a
applying 25 or 50 ppm NAA and increased as bract stage increased. When the effects of NAA and STS at the same stage were compared, the prolonging effect of NAA was signi®cantly better than that of STS at later stages (stages 3 and 4) (Table 1). For `Taipei Red', bract longevity was not affected by 0.1 mM STS application but was prolonged by 0.5 mM STS at all stages (Table 2). Regardless of the concentration of STS applied, bract longevity decreased as the bract stage increased. Except for stage 1, the prolonging effects of NAA were better than those of STS at the other three stages (Table 2).
Experiment 2. For `Purple Flower', 0.1 mM STS prolonged bract longevity except at stage 3, and 0.5 mM STS prolonged the bract longevity of all stages (Table 3). Similar to Experiment 1, bract longevity of the STS treatment decreased when bract stage increased (Table 3). Applying 25 or 50 ppm NAA prolonged the bract longevity, which increased as bract stage increased, from stages 2 to 4. A comparison of the effects of these two chemicals on bract longevity at the same bract stage showed that the effect of NAA was signi®cantly better than that of STS at bract stages 3 and 4, but was worse at stage 1. However, Table 2
Effects of STS and NAA on bract longevity in different bract stages of potted bougainvillea `Taipei Red' (Experiment 1)
Treatment Bract longevity (days)
Stage 1 Stage 2 Stage 3 Stage 4
Control 7.2cAa 6.7cA 4.5cB 4.2cB
0.1 mM STS 9.5bcA 8.7bcA 6.7bcB 5.7bcB
0.5 mM STS 12.0abA 10.7bA 8.0bB 7.5bB
25 ppm NAA 11.0abC 17.2aB 19.2aAB 22.0aA
50 ppm NAA 14.0aD 19.0aC 21.0aB 22.7aA
a
Mean separation within columns (lowercase) and rows (uppercase) by analysis of Duncan's multiple range test.
Table 3
Effects of STS and NAA on bract longevity in different bract stages of potted bougainvillea `Purple Flower' (Experiment 2)
Treatment Bract longevity (days)
Stage 1 Stage 2 Stage 3 Stage 4
Control 14.7bAa 11.9cB 10.5cB 5.3dC
0.1 mM STS 22.1aA 18.2bB 12.8cC 11.0cC
0.5 mM STS 24.1aA 21.4abA 14.2cB 12.7cB
25 ppm NAA 17.0bC 24.1aB 26.5bAB 28.0bA
50 ppm NAA 17.5bC 23.7aB 30.5aA 32.0aA
a
for `Taipei Red', 0.1 mM STS had no effect on bract longevity, and application of 0.5 mM STS had only positive effects on stages 1 and 2 (Table 4). As with `Purple Flower', the bract longevity of STS treatment decreased as bract stage increased. The prolonging effect of NAA was signi®cantly better than that of STS at later bract stages (stages 3 and 4) (Table 4).
Ethylene production rate. Bracts of both `Purple Flower' and `Taipei Red' at stage 1 had the highest ethylene production rate, which decreased when bract stage increased (Fig. 1). Furthermore, the ethylene production rates of `Taipei Red' were higher than those of `Purple Flower' at stages 2±4.
Table 4
Effects of STS and NAA on bract longevity in different bract stages of potted bougainvillea `Taipei Red' (Experiment 2)
Treatment Bract longevity (days)
Stage 1 Stage 2 Stage 3 Stage 4
Control 14.0cAa 11.7cB 10.2cC 8.4cD
0.1 mM STS 17.5bcA 15.4bcAB 13.0cBC 9.9cC
0.5 mM STS 23.2abA 18.7bB 14.6cC 11.3cD
25 ppm NAA 19.8bB 22.0bB 27.8bA 30.8bA
50 ppm NAA 25.1aB 27.8aB 34.1aA 35.3aA
aMean separation within columns (lowercase) and rows (uppercase) by analysis of Duncan's
multiple range test.
4. Discussion
Cameron and Reid (1983) reported that 0.5 mM STS delayed bract abscission of bougainvillea. In our experiment, bract longevity was signi®cantly prolonged by treatment with 0.5 and 0.1 mM STS in `Purple Flower' (Tables 1 and 3) and treatment with 0.5 mM STS only in `Taipei Red' (Tables 2 and 4). However, the prolonging effects of STS in the two cultivars were more effective in the early stages of bract development, and the effects decreased as the bract stage increased. These results are in agreement with those using Christmas begonia (Fjeld, 1991) and Easter cactus (Han and Boyle, 1996).
In both cultivars, except bracts of `Purple Flower' at stage 1 in Experiment 2, bract longevity was extended by treatment with 25 or 50 ppm NAA (Tables 1±4), which is consistent with the results exhibited by potted roses (Halevy and Kofranek, 1976) and peppers (Wein and Turner, 1989). Our data also revealed that the effect of NAA treatment on bract longevity was more effective when it was applied during the later stages of bract development. These results are similar to those proposed by Hackett et al. (1972) that NAA prevents drop of mature ¯ower-bracts only. Therefore, the prolonging effect of NAA treatment was apparently better than that of STS during the later stages of bract development in both cultivars (Tables 1±4). Halevy and Kofranek (1976) reported that spraying potted roses with 15 and 30 ppm NAA caused serious leaf abscission or leaf chlorosis. In the two experiments, the plants treated with 50 ppm NAA had a longer bract longevity than those treated with 25 ppm NAA, but `Purple Flower' exhibited slight leaf abscission and `Taipei Red' exhibited slight leaf chlorosis.
abscission more effectively. That is, the variable effects of STS and NAA treatments at different bract stages could be due to differences in ethylene production and/or sensitivity at different bract maturities.
Because ethylene evolution of bracts was measured after the end of Experiments 1 and 2, it is regrettable that the ethylene evolution of treated bracts was not assessed, especially as such measurements might have reinforced our proposed mechanism. In order to con®rm the hypothesis above, further research is necessary.
To summarize, STS should be applied during the earlier stages of bract development and NAA should be applied during the later stages (i.e. marketable plant stage) to prolong bract longevity in potted bougainvillea. NAA is more effective than STS and is recommended for indoor applications and for use on potted bougainvilleas being transported.
Acknowledgements
This research was supported by Council of Agriculture, Executive Yuan, Taiwan, Republic of China. The statistical advice of Prof. Liang Li is greatly appreciated.
References
Abeles, F.B., Morgan, P.W., Saltveit Jr., M.E., 1992. Ethylene in Plant Biology, 2nd Edition. Academic Press, New York, 414 pp.
Borochov, A., Woodson, W.R., 1989. Physiology and biochemistry of ¯ower petal senescence. Hort. Rev. 11, 15±43.
Cameron, A.C., Reid, M.S., 1981. The use of silver thiosulfate anionic complex as a foliar spray to prevent ¯ower abscission of Zygocactus. HortScience 16, 761±762.
Cameron, A.C., Reid, M.S., 1983. Use of silver thiosulfate to prevent ¯ower abscission from potted plants. Sci. Hort. 19, 373±378.
Cushman, L.C., Pemberton, H.B., 1994. Cultivar, ¯ower stage, silver thiosulfate, and BA interactions affect performance of potted miniature roses. HortScience 29, 805±808.
Dostal, D.L., Agnew, N.H., Gladon, R.J., Weigle, J.L., 1991. Ethylene, simulated shipping, STS, and AOA affect corolla abscission of New Guinea Impatiens. HortScience 26, 47±49. Fjeld, T., 1991. Effects of silver thiosulfate, ethephon, temperature, and irradiance level on keeping
quality of Christmas Begonia (BegoniaCheimantha Everett). Gartenbauwissenschaft 56, 66± 70.
Hackett, W.P., Sachs, R.M., Debie, J., 1972. Growing bougainvillea as a ¯owering pot plant. Calif. Agric. 26 (8), 12±13.
Halevy, A.H., Kofranek, A.M., 1976. The prevention of ¯ower bud and leaf abscission in pot roses during simulated transport. J. Am. Soc. Hort. Sci. 101, 658±660.
Montgomery, D.C., 1991. Design and Analysis of Experiments, 3rd Edition. Wiley, New York, pp. 439±460.
SAS Institute, 1985. SAS/STAT Guide for Personal Computers, Version 6. SAS Institute, Cary, NC. Serek, M., 1993. Ethephon and silver thiosulfate affect postharvest characteristics ofRosa hybrida
`Victory Parade'. HortScience 28, 199±200.
Thaxton, D.R., Kelly, J.W., Frett, J.J., 1988. Control ofHibiscus rosa-sinensis L. bud abscission during shipping. Sci. Hort. 34, 131±137.
Tjosvold, S.A., Wu, M.J., Reid, M.S., 1994. Reduction of postproduction quality loss in potted miniature roses. HortScience 29, 293±294.
Wein, H.C., Turner, A.D., 1989. Hormonal basis for low light intensity-induced ¯ower bud abscission of pepper. J. Am. Soc. Hort. Sci. 114, 981±985.
