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The interaction of a dormancy-breaking cold treatment, ancymidol, and ethephon in relation to stem elongation and flower production of Lilium cultivars
Scientia Horticulturae, 8(1978) 57--64
57
Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
THE INTERACTION OF A DORMANCY-BREAKING COLD TREATMENT, ANCYMIDOL, AND ETHEPHON IN RELATION TO STEM ELONGATION AND FLOWER PRODUCTION OF LILIUM CULTIVARS
JOHN A. SIMMONDS and BRUCE G. CUMMING
Department of Biology, University of New Brunswick, Fredericton (Canada) (Received 4 May 1977)
ABSTRACT Simmonds, J.A. and Cumming, B.G., 1978. The interaction of a dormancy-breaking cold treatment, ancymidol, and ethephon in relation to stem elongation and flower production of Lilium cultivars. Scientia Hortic., 8: 57--64. Stem elongation of Lilium cultivars 'Black Beauty', 'Jamboree' and 'Nutmegger' was lessened by treating the bulbs with ancymidol (10 p.p.m. ) or ethephon (500 p.p.m.). Ancymidol was the more effective inhibitor of stem elongation, although applied at a much lower concentration. Application of the growth regulators prior to a dormancybreaking cold treatment provided more effective control of stem elongation than post cold-treatment application. The total number of flowers and the number of secondary flowers per stem of 'Black Beauty' and 'Nutmegger' were increased by treating the bulbs with ancymidol. However, unlike the optimal time for lessening stem elongation, enhancement of flower production was greatest when ancymidol was applied after completion of the cold treatment. Ethephon was unsatisfactory, since it inhibited flower production by 'Black Beauty' and 'Nutmegger', while 'Jamboree' was relatively insensitive to it, as indicated by a lack of inhibition of flower production and a small degree of inhibition of stem elongation. INTRODUCTION
The growth regulators ancymidol and ethephon are effective inhibitors of stem elongation of Lilium cultivars (Hasek et al., 1971; Dicks and Rees, 1973). Ancymidol has also been reported to promote the initiation and survival of secondary flowers (originating in the axils of the primary bracts) in Lilium cultivar 'Enchantment' (Dicks and Rees, 1973), but ethephon suppresses flower production (Dicks and Rees, 1973; Simmonds and Cumming, 1977). Further studies, carried out to verify the possible effect of ancymidol on secondary flower production, showed no significant treatment effects (Dicks et al., 1974). We previously reported that ancymidol and ethephon were more effective inhibitors of shoot elongation when applied directly to the bulb at the termination of the cold-requiring period, than when they were applied as postemergent soil drenches (Simmonds and Cumming, 1977). Because the chilling-
58
treatment of bulbs can lead to the production of growth-promoting substances that are gibberellin-like (Aung and De Hertogh, 1968; Halevy et al., 1971) and auxin-like (Tsukamoto, 1971), the action of ancymidol, an antagonist of gibberellin (Leopold, 1971), and ethephon, which releases ethylene (Edgerton and Blanpied, 1968), may be more effective if they are applied to the bulbs during the cold treatment. Using the bulb-dip method of application, we have investigated the interaction of these two growth regulators with the processes occurring during the dormancy-breaking cold treatment, as they relate to stem elongation and flower production. Three L i l i u m cultivars, which are potentially useful for forcing as cut flowers and for modification for landscaping, were selected for this study: L i l i u m cultivars 'Black Beauty' and 'Nutmegger' produce large numbers of secondary flowers when grown under field conditions and L i l i u m cultivar 'Jamboree' behaves similarly b u t to a lesser degree. However, under our greenhouse conditions secondary flower production is normally absent in all 3 cultivars. MATERIALS AND METHODS
Bulbs (22--25 cm circumference) of L i l i u m cv. 'Black Beauty', L. cv. 'Jamboree' (oriental hybrids) and L. cv. 'Nutmegger' {asiatic hybrid) were purchased from Oregon Bulb Farms, Gresham, Oregon, U.S.A. The bulbs were harvested in September and immediately transported to us. Care was taken to ensure that the bulbs were not exposed to chilling temperatures, and experimental procedures were initiated on their arrival.
Plant material. --
G r o w t h r e g u l a t o r s . - - Ancymidol (~-cyclopropyl -~- (4-methoxyphenyl)-5 pyrimidinemethanol) was kindly donated by Eli Lilly and Co., and ethephon (2-chloroethylphosphonic acid) by Amchem Products Inc. T r e a t m e n t p r o c e d u r e . - - Bulbs of uniform dimension were selected from each cultivar, placed in a cold room (5°C) and randomly assigned to the different experimental treatments. Equivalent groups of bulbs were treated with a growth regulator at one of the fortnightly intervals of the overall 6-week cold treatment period. The first samples of bulbs were treated at the onset of the cold period (Time 0). The bulbs were submerged in aqueous solutions of ancymidol (10 p.p.m.) or ethephon (500 p.p.m.) for 12 h at 5°C. Assuming complete uptake of the regulators, this would represent a maximum of 1 mg a.i./bulb of ancymidol and 50 mg a.i./bulb of ethephon, but the amount actually taken up was less than this. The bulbs were then potted, 3 per 28 cm-diameter pot using a standard U.N.B. soil mix (Simmonds and Cumming, 1976); each treatment involved 5 pots. Further samples of bulbs were treated with growth regulators after 2, 4 and 6 weeks of cold treatment, and all were held at 5°C until the termination of the cold treatment. The control samples received no growth regulators and were p o t t e d at the end of the 6week cold treatment. At this time all the pots were transferred to a green-
59
house and maintained in a 16-h photoperiod at 22°C daytime and 13°C nighttime temperatures. Natural daylength was extended with mercury vapour and incandescent, filament lamps, providing a minimum intensity of 400 foot-candles. The pots were periodically irrigated with a solution of 15 p.p.m. N: P205 : K20 (20:20:20) fertilizer. Primary and secondary flowers per plant were recorded at anthesis. Total stem height from the soil level was recorded when the plants had started to senesce. RESULTS elongation. - - Ancymidol (10 p.p.m.) was an effective inhibitor of shoot elongation of each cultivar at all the application times. The much higher concentration of ethephon (500 p.p.m.) was comparatively less inhibitory than ancymidol (Table 1). Stem
TABLE1 S t e m e l o n g a t i o n ( c m ) o f Lilium cultivars a f t e r a p p l i c a t i o n o f a n c y m i d o l ( 1 0 p.p.m.) o r e t h e p h o n ( 5 0 0 p . p . m . ) t o b u l b s at various t i m e s d u r i n g t h e d o r m a n c y - b r e a k i n g cold t r e a t m e n t . Values s c o r e d b y the same letter, w i t h i n each cultivar, are n o t significantly d i f f e r e n t (p - 0.05) b y D u n c a n ' s m u l t i p l e range test. Cultivar
Growth regulator
Time o f a p p l i c a t i o n (weeks) d u r i n g cold t r e a t m e n t None (control)
'Nutmegger' 'Black B e a u t y ' 'Jamboree'
Ancymidol Ethephon Ancymidol Ethephon Ancymidol Ethephon
198.1 a 149.2 a 110.4 abc
0
2
49.6 117.5 78.0 98.3
c a e cd
57.8 e 89.6 c
53.3 108.5 91.9 99.3
4
c b d cd
63.2 e 100.6 c
45.3 110.0 98.1 101.5
6
c b cd c
58.8 e 113.8 a b
46.8 110.6 99.5 113.4
c b cd b
57.8 e 117.2 a
To gain a clearer idea of the relative degree of inhibition obtained, the results of the growth-regulating treatments are listed as percentage inhibition of stem elongation as compared with the controls, and the treatments are ranked accordingly, in Table 2. Values are provided for results at the start (week 0) and at the end (week 6) of the cold treatment. Stem elongation of 'Nutmegger' was inhibited to a considerably greater extent than that of the other 2 cultivars. Even so, the inhibition by ancymidol was statistically significant for all cultivars at all treatment times (see Table 1). It was only in 'Black Beauty' that the effectiveness of the ancymidol treatment depended on the timing of its application: the inhibition obtained from an application immediately preceding the cold treatment (week 0) was significantly greater than any application made during the cold treatment (see Table 1).
60
Although stem elongation of all 3 cultivars was also inhibited by ethephon, the effects depended much more upon the specific cultivar and the time of treatment. 'Nutmegger' was inhibited to a greater degree than the other 2 cultivars, but the inhibition was not dependent on the time of treatment. With 'Jamboree', only the application of ethephon made just before the start of the cold treatment significantly inhibited stem elongation. With 'Black Beauty', ethephon application at week 0, 2 or 4 was more effective than that at week 6. TABLE 2 Stem elongation of Lilium cultivars treated with ancymidol (10 p.p.m. ) or ethephon (500 p.p.m.) before or after a dormancy-breaking cold treatment. Values represent inhibition as a percentage of the control growth. Treatment
Pre-coldtreatment application (Time 0)
Post coldtreatment application (Time 6)
Additional inhibition Time 0 versus Time 6
Ancymidol on 'Nutmegger' Ancymidol on 'Jamboree' Ethephon on 'Nutmegger' Ancymidol on 'Black Beauty' Ethephon on 'Black Beauty' Ethephon on 'Jamboree'
75 48 41 48 34 19
76 48 44 33 24 --6
0 0 0 15 I0 25
- - The total number of flowers produced per plant was increased by treating the lily bulb with ancymidol (Table 3), but this clearly depended on the time of treatment with respect to the cold period, and the cultivar. 'Nutmegger' flower production was significantly increased by ancymidol treatment at all application times, but the effect was greatest when the growth regulator was applied at the end of the cold treatment. The increase in the total number of flowers present at maturity was associated with the production of significantly more secondary flowers, regardless of time of treatment. No secondary flowers were produced on 'Nutmegger' control plants (although they were produced on plants growing in the field rather than in the greenhouse). There was also increased flower production on 'Black Beauty', including secondaries, but only when the amycidol was aptiied at the end of the cold period (week 6). Of the control plants, only 'Black Beauty' produced secondary flowers under the greenhouse and pottingconditions used in these experiments. 'Jamboree' did not respond to ancymidol treatment. Ethephon inhibited flower production on 'Nutmegger' and 'Black Beauty' at all application times. Flower production by 'Jamboree' was not affected by Ethrel (Table 3). Flower production.
61
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~
~
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62
DISCUSSION
Application of ancymidol or ethephon to Lilium bulbs can give more effective control of stem elongation when applied before rather than after a cold treatment (Tables 1 and 2). Under these conditions a further 10--25% inhibition of stem elongation could be obtained in some specific treatment combinations if a growth regulator was present during the cold treatment (Table 2). This effect could be demonstrated when post cold-treatment applications of inhibitors resulted in less than 44% inhibition of growth (Table 2). Pre-cold-treatment application of ancymidol was only more effective on 'Black Beauty'. However, the concentration of ancymidol (10 p.p.m.), used as a post cold-treatment bulb dip, caused very strong inhibition of 'Nutmegger' and 'Jamboree' stem growth (Tables 1 and 2), which would mask any interaction of ancymidol during the cold treatment. Lower concentrations of ancymidol should be used for these cultivars. By applying growth regulators to the bulbs prior to the cold treatment, it may therefore be possible to obtain acceptable levels of inhibition of stem elongation from lower concentrations of chemicals than was previously possible and thereby reduce any negative side-effects of these substances. Flower production by the 3 cultivars, when grown as potted plants in the greenhouse, was considerably below that which occurs under field conditions. For example, 'Black Beauty' can produce up to 50 flowers per stem in the field (Feldmaier, 1970, p. 188). One factor which may reduce flower formation in the greenhouse may be the production of gibberellins under these conditions. Flower production of lilies can be inhibited by gibberellic acid. Treatment of L. longiflorum with GA3 or GA4+ 7, as a soil drench prior to flower initiation, completely inhibited the initiation of secondary flowers, and GA4+ 7 enhanced abortion of primary flowers (De Hertogh and Blakely, 1972). Ancymidol has been shown to act against a number of growth functions of gibberellic acid (Leopold, 1971; Dicks et al., 1974). However, it was not possible to determine the effect of soil drench applications of ancymidol on floral initiation of Lilium cv. 'Enchantment', because the root system was not sufficiently well developed to allow meaningful uptake of the regulator at this stage (Dicks et al., 1974). Using bulb-dip applications, it was possible to demonstrate that ancymidol could increase flower production of 'Black Beauty' and 'Nutmegger' (Table 3). The time of application which was most effective in increasing flower production occurred after the cold treatment had been completed (Table 3). It has also been demonstrated that gibberellic acid is most effective at inhibiting flower production of L. longiflorum when it is applied at the end of a cold treatment (Laiche, 1973). This coincidence of timing of gibberellic acid and ancymidol actions supports the suggestion, made by Dicks and Rees (1973), that secondary flower production in Lilium may be enhanced by ancymidol antagonism of endogenous gibberellins. Although ancymidol treatment did substantially increase flower production in 'Black Beauty' and 'Nutmegger', it was still not pos-
63
sible to obtain the levels of production that occur under ideal field conditions. It should be noted that ancymidol increased flower production only in the more vigorous cultivars which have a strong tendency to produce secondary flowers. Ancymidol was without effect on flower production of 'Jamboree' (Table 3), 'Enchantment' or 'Harmony' (Simmonds and Cumming, 1977). Although Dicks et al. (1974) were unable to show any effect of ancymidol on flower production of 'Enchantment', because soil drench applications did not allow meaningful uptake of the regulator prior to floral initiation, their failure to demonstrate ancymidol-enhanced flower production may not be solely related to the timing of its application, since there are other limiting factors under greenhouse conditions. The inhibition of flower production in 'Black Beauty' and 'Nutmegger' by ethephon (Table 2) is in agreement with the previous report on the action of this regulator on Lilium cvs. 'Enchantment' and 'Harmony' (Simmonds and Cumming, 1977). However, 'Jamboree' was more resistant to, or tolerant of, ethephon, since its production of flowers was not inhibited (Table 3) and there was a relatively small degree of inhibition of stem elongation (Table 1). In conclusion, this investigation has demonstrated that ancymidol and ethephon can be more effective inhibitors of stem elongation if they are made available to the bulb during the cold treatment, than when they are applied after the cold treatment has been completed. Ancymidol also has good potential for use in the potted-plant industry to ensure increased flower production under greenhouse conditions, although its effects in this ~'egard are most pronounced when it is applied after a dormancy-breaking cold period. ACKNOWLEDGEMENT
This work was supported by a grant-in-aid of research to B.G. Cumming by the National Research Council of Canada. REFERENCES Aung, L.H. and De Hertogh, A.A., 1968. Gibberellin-like substances in non-cold and cold treated tulip bulbs (Tulipa sp.). In: F. Wightman and G. Setterfield (Editors), Biochemistry and Physiology of Plant Growth Substances. Runge, Ottawa, pp. 943--956. De Hertogh, A.A. and Blakely, N., 1972. Influences of gibberelllins A 3 and A,+ 7 on development of forced Lilium longiflorum Thumb. cv. Ace. J. Am. Soc. Hortic. Sci., 97: 320--323. Dicks, J.W. and Rees, A.R., 1973. Effects of growth-regulating chemicals on two cultivars of Mid-Century Hybrid lily. Scientia Hortic., 1: 133--142. Dicks, J.W., Gilford, J. McD. and Rees, A.R., 1974. The influence of timing of application and gibberellic acid on the effects of ancymidol on growth and flowering of MidCentury Hybrid lily cv. Enchantment. Scientia Hortic., 2: 153--163. Edgerton, L.J. and Blanpied, G.D., 1968. Regulation of growth and fruit maturation with 2-chloroethanephosphonic acid. Nature (London), 219: 1064--1065.
64
Feldmaier, C., 1970. In: Lilies. Arco, New York, p. 188. Halevy, A.H., Mor, J. and Valershtein, J., 1971. Endogenous gibberellin level in Ornithogalum arabicum and its relationship to storage temperatures of bulbs and to flower development. First Int. Syrup. Flower Bulbs, Acta Hortic., 23, I: 82--89. Hasek, R.F., Sciaroni, R.H. and Farnham, D.S., 1971, 1970--71. Japanese Georgia lily height control trials. Florists' Rev., 148 : 22--24; 62--64. Laiche, A.J., 1973. Response of lilies to gibberellic acid. Miss. Agric. For. Stn. Information Sheet, 1221. Leopold, A.C., 1971. Antagonism of some gibberellin actions by a substituted pyrimidine. Plant Physiol., 48: 537--540. Simmonds, J.A. and Cumming, B.G., 1976. Propagation of Lilium hybrids. I. Dependence of bulblet production on time of scale removal and growth substances. Scientia Hortic., 5: 77--83. Simmonds, J.A. and Cumming, B.G., 1977. Bulb-dip application of growth-regulating chemical for inhibiting stem elongation of 'Enchantment' and ' H a r m o n y ' lilies. Scientia Hortic., 6: 71~81. Tsukamoto, Y., 1971. Changes in endogenous growth substances in Easter lily as affected by cooling. First Int. Syrup. Flower Bulbs, Acta Hortic., 23, I: 75--81.
57
Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
THE INTERACTION OF A DORMANCY-BREAKING COLD TREATMENT, ANCYMIDOL, AND ETHEPHON IN RELATION TO STEM ELONGATION AND FLOWER PRODUCTION OF LILIUM CULTIVARS
JOHN A. SIMMONDS and BRUCE G. CUMMING
Department of Biology, University of New Brunswick, Fredericton (Canada) (Received 4 May 1977)
ABSTRACT Simmonds, J.A. and Cumming, B.G., 1978. The interaction of a dormancy-breaking cold treatment, ancymidol, and ethephon in relation to stem elongation and flower production of Lilium cultivars. Scientia Hortic., 8: 57--64. Stem elongation of Lilium cultivars 'Black Beauty', 'Jamboree' and 'Nutmegger' was lessened by treating the bulbs with ancymidol (10 p.p.m. ) or ethephon (500 p.p.m.). Ancymidol was the more effective inhibitor of stem elongation, although applied at a much lower concentration. Application of the growth regulators prior to a dormancybreaking cold treatment provided more effective control of stem elongation than post cold-treatment application. The total number of flowers and the number of secondary flowers per stem of 'Black Beauty' and 'Nutmegger' were increased by treating the bulbs with ancymidol. However, unlike the optimal time for lessening stem elongation, enhancement of flower production was greatest when ancymidol was applied after completion of the cold treatment. Ethephon was unsatisfactory, since it inhibited flower production by 'Black Beauty' and 'Nutmegger', while 'Jamboree' was relatively insensitive to it, as indicated by a lack of inhibition of flower production and a small degree of inhibition of stem elongation. INTRODUCTION
The growth regulators ancymidol and ethephon are effective inhibitors of stem elongation of Lilium cultivars (Hasek et al., 1971; Dicks and Rees, 1973). Ancymidol has also been reported to promote the initiation and survival of secondary flowers (originating in the axils of the primary bracts) in Lilium cultivar 'Enchantment' (Dicks and Rees, 1973), but ethephon suppresses flower production (Dicks and Rees, 1973; Simmonds and Cumming, 1977). Further studies, carried out to verify the possible effect of ancymidol on secondary flower production, showed no significant treatment effects (Dicks et al., 1974). We previously reported that ancymidol and ethephon were more effective inhibitors of shoot elongation when applied directly to the bulb at the termination of the cold-requiring period, than when they were applied as postemergent soil drenches (Simmonds and Cumming, 1977). Because the chilling-
58
treatment of bulbs can lead to the production of growth-promoting substances that are gibberellin-like (Aung and De Hertogh, 1968; Halevy et al., 1971) and auxin-like (Tsukamoto, 1971), the action of ancymidol, an antagonist of gibberellin (Leopold, 1971), and ethephon, which releases ethylene (Edgerton and Blanpied, 1968), may be more effective if they are applied to the bulbs during the cold treatment. Using the bulb-dip method of application, we have investigated the interaction of these two growth regulators with the processes occurring during the dormancy-breaking cold treatment, as they relate to stem elongation and flower production. Three L i l i u m cultivars, which are potentially useful for forcing as cut flowers and for modification for landscaping, were selected for this study: L i l i u m cultivars 'Black Beauty' and 'Nutmegger' produce large numbers of secondary flowers when grown under field conditions and L i l i u m cultivar 'Jamboree' behaves similarly b u t to a lesser degree. However, under our greenhouse conditions secondary flower production is normally absent in all 3 cultivars. MATERIALS AND METHODS
Bulbs (22--25 cm circumference) of L i l i u m cv. 'Black Beauty', L. cv. 'Jamboree' (oriental hybrids) and L. cv. 'Nutmegger' {asiatic hybrid) were purchased from Oregon Bulb Farms, Gresham, Oregon, U.S.A. The bulbs were harvested in September and immediately transported to us. Care was taken to ensure that the bulbs were not exposed to chilling temperatures, and experimental procedures were initiated on their arrival.
Plant material. --
G r o w t h r e g u l a t o r s . - - Ancymidol (~-cyclopropyl -~- (4-methoxyphenyl)-5 pyrimidinemethanol) was kindly donated by Eli Lilly and Co., and ethephon (2-chloroethylphosphonic acid) by Amchem Products Inc. T r e a t m e n t p r o c e d u r e . - - Bulbs of uniform dimension were selected from each cultivar, placed in a cold room (5°C) and randomly assigned to the different experimental treatments. Equivalent groups of bulbs were treated with a growth regulator at one of the fortnightly intervals of the overall 6-week cold treatment period. The first samples of bulbs were treated at the onset of the cold period (Time 0). The bulbs were submerged in aqueous solutions of ancymidol (10 p.p.m.) or ethephon (500 p.p.m.) for 12 h at 5°C. Assuming complete uptake of the regulators, this would represent a maximum of 1 mg a.i./bulb of ancymidol and 50 mg a.i./bulb of ethephon, but the amount actually taken up was less than this. The bulbs were then potted, 3 per 28 cm-diameter pot using a standard U.N.B. soil mix (Simmonds and Cumming, 1976); each treatment involved 5 pots. Further samples of bulbs were treated with growth regulators after 2, 4 and 6 weeks of cold treatment, and all were held at 5°C until the termination of the cold treatment. The control samples received no growth regulators and were p o t t e d at the end of the 6week cold treatment. At this time all the pots were transferred to a green-
59
house and maintained in a 16-h photoperiod at 22°C daytime and 13°C nighttime temperatures. Natural daylength was extended with mercury vapour and incandescent, filament lamps, providing a minimum intensity of 400 foot-candles. The pots were periodically irrigated with a solution of 15 p.p.m. N: P205 : K20 (20:20:20) fertilizer. Primary and secondary flowers per plant were recorded at anthesis. Total stem height from the soil level was recorded when the plants had started to senesce. RESULTS elongation. - - Ancymidol (10 p.p.m.) was an effective inhibitor of shoot elongation of each cultivar at all the application times. The much higher concentration of ethephon (500 p.p.m.) was comparatively less inhibitory than ancymidol (Table 1). Stem
TABLE1 S t e m e l o n g a t i o n ( c m ) o f Lilium cultivars a f t e r a p p l i c a t i o n o f a n c y m i d o l ( 1 0 p.p.m.) o r e t h e p h o n ( 5 0 0 p . p . m . ) t o b u l b s at various t i m e s d u r i n g t h e d o r m a n c y - b r e a k i n g cold t r e a t m e n t . Values s c o r e d b y the same letter, w i t h i n each cultivar, are n o t significantly d i f f e r e n t (p - 0.05) b y D u n c a n ' s m u l t i p l e range test. Cultivar
Growth regulator
Time o f a p p l i c a t i o n (weeks) d u r i n g cold t r e a t m e n t None (control)
'Nutmegger' 'Black B e a u t y ' 'Jamboree'
Ancymidol Ethephon Ancymidol Ethephon Ancymidol Ethephon
198.1 a 149.2 a 110.4 abc
0
2
49.6 117.5 78.0 98.3
c a e cd
57.8 e 89.6 c
53.3 108.5 91.9 99.3
4
c b d cd
63.2 e 100.6 c
45.3 110.0 98.1 101.5
6
c b cd c
58.8 e 113.8 a b
46.8 110.6 99.5 113.4
c b cd b
57.8 e 117.2 a
To gain a clearer idea of the relative degree of inhibition obtained, the results of the growth-regulating treatments are listed as percentage inhibition of stem elongation as compared with the controls, and the treatments are ranked accordingly, in Table 2. Values are provided for results at the start (week 0) and at the end (week 6) of the cold treatment. Stem elongation of 'Nutmegger' was inhibited to a considerably greater extent than that of the other 2 cultivars. Even so, the inhibition by ancymidol was statistically significant for all cultivars at all treatment times (see Table 1). It was only in 'Black Beauty' that the effectiveness of the ancymidol treatment depended on the timing of its application: the inhibition obtained from an application immediately preceding the cold treatment (week 0) was significantly greater than any application made during the cold treatment (see Table 1).
60
Although stem elongation of all 3 cultivars was also inhibited by ethephon, the effects depended much more upon the specific cultivar and the time of treatment. 'Nutmegger' was inhibited to a greater degree than the other 2 cultivars, but the inhibition was not dependent on the time of treatment. With 'Jamboree', only the application of ethephon made just before the start of the cold treatment significantly inhibited stem elongation. With 'Black Beauty', ethephon application at week 0, 2 or 4 was more effective than that at week 6. TABLE 2 Stem elongation of Lilium cultivars treated with ancymidol (10 p.p.m. ) or ethephon (500 p.p.m.) before or after a dormancy-breaking cold treatment. Values represent inhibition as a percentage of the control growth. Treatment
Pre-coldtreatment application (Time 0)
Post coldtreatment application (Time 6)
Additional inhibition Time 0 versus Time 6
Ancymidol on 'Nutmegger' Ancymidol on 'Jamboree' Ethephon on 'Nutmegger' Ancymidol on 'Black Beauty' Ethephon on 'Black Beauty' Ethephon on 'Jamboree'
75 48 41 48 34 19
76 48 44 33 24 --6
0 0 0 15 I0 25
- - The total number of flowers produced per plant was increased by treating the lily bulb with ancymidol (Table 3), but this clearly depended on the time of treatment with respect to the cold period, and the cultivar. 'Nutmegger' flower production was significantly increased by ancymidol treatment at all application times, but the effect was greatest when the growth regulator was applied at the end of the cold treatment. The increase in the total number of flowers present at maturity was associated with the production of significantly more secondary flowers, regardless of time of treatment. No secondary flowers were produced on 'Nutmegger' control plants (although they were produced on plants growing in the field rather than in the greenhouse). There was also increased flower production on 'Black Beauty', including secondaries, but only when the amycidol was aptiied at the end of the cold period (week 6). Of the control plants, only 'Black Beauty' produced secondary flowers under the greenhouse and pottingconditions used in these experiments. 'Jamboree' did not respond to ancymidol treatment. Ethephon inhibited flower production on 'Nutmegger' and 'Black Beauty' at all application times. Flower production by 'Jamboree' was not affected by Ethrel (Table 3). Flower production.
61
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62
DISCUSSION
Application of ancymidol or ethephon to Lilium bulbs can give more effective control of stem elongation when applied before rather than after a cold treatment (Tables 1 and 2). Under these conditions a further 10--25% inhibition of stem elongation could be obtained in some specific treatment combinations if a growth regulator was present during the cold treatment (Table 2). This effect could be demonstrated when post cold-treatment applications of inhibitors resulted in less than 44% inhibition of growth (Table 2). Pre-cold-treatment application of ancymidol was only more effective on 'Black Beauty'. However, the concentration of ancymidol (10 p.p.m.), used as a post cold-treatment bulb dip, caused very strong inhibition of 'Nutmegger' and 'Jamboree' stem growth (Tables 1 and 2), which would mask any interaction of ancymidol during the cold treatment. Lower concentrations of ancymidol should be used for these cultivars. By applying growth regulators to the bulbs prior to the cold treatment, it may therefore be possible to obtain acceptable levels of inhibition of stem elongation from lower concentrations of chemicals than was previously possible and thereby reduce any negative side-effects of these substances. Flower production by the 3 cultivars, when grown as potted plants in the greenhouse, was considerably below that which occurs under field conditions. For example, 'Black Beauty' can produce up to 50 flowers per stem in the field (Feldmaier, 1970, p. 188). One factor which may reduce flower formation in the greenhouse may be the production of gibberellins under these conditions. Flower production of lilies can be inhibited by gibberellic acid. Treatment of L. longiflorum with GA3 or GA4+ 7, as a soil drench prior to flower initiation, completely inhibited the initiation of secondary flowers, and GA4+ 7 enhanced abortion of primary flowers (De Hertogh and Blakely, 1972). Ancymidol has been shown to act against a number of growth functions of gibberellic acid (Leopold, 1971; Dicks et al., 1974). However, it was not possible to determine the effect of soil drench applications of ancymidol on floral initiation of Lilium cv. 'Enchantment', because the root system was not sufficiently well developed to allow meaningful uptake of the regulator at this stage (Dicks et al., 1974). Using bulb-dip applications, it was possible to demonstrate that ancymidol could increase flower production of 'Black Beauty' and 'Nutmegger' (Table 3). The time of application which was most effective in increasing flower production occurred after the cold treatment had been completed (Table 3). It has also been demonstrated that gibberellic acid is most effective at inhibiting flower production of L. longiflorum when it is applied at the end of a cold treatment (Laiche, 1973). This coincidence of timing of gibberellic acid and ancymidol actions supports the suggestion, made by Dicks and Rees (1973), that secondary flower production in Lilium may be enhanced by ancymidol antagonism of endogenous gibberellins. Although ancymidol treatment did substantially increase flower production in 'Black Beauty' and 'Nutmegger', it was still not pos-
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sible to obtain the levels of production that occur under ideal field conditions. It should be noted that ancymidol increased flower production only in the more vigorous cultivars which have a strong tendency to produce secondary flowers. Ancymidol was without effect on flower production of 'Jamboree' (Table 3), 'Enchantment' or 'Harmony' (Simmonds and Cumming, 1977). Although Dicks et al. (1974) were unable to show any effect of ancymidol on flower production of 'Enchantment', because soil drench applications did not allow meaningful uptake of the regulator prior to floral initiation, their failure to demonstrate ancymidol-enhanced flower production may not be solely related to the timing of its application, since there are other limiting factors under greenhouse conditions. The inhibition of flower production in 'Black Beauty' and 'Nutmegger' by ethephon (Table 2) is in agreement with the previous report on the action of this regulator on Lilium cvs. 'Enchantment' and 'Harmony' (Simmonds and Cumming, 1977). However, 'Jamboree' was more resistant to, or tolerant of, ethephon, since its production of flowers was not inhibited (Table 3) and there was a relatively small degree of inhibition of stem elongation (Table 1). In conclusion, this investigation has demonstrated that ancymidol and ethephon can be more effective inhibitors of stem elongation if they are made available to the bulb during the cold treatment, than when they are applied after the cold treatment has been completed. Ancymidol also has good potential for use in the potted-plant industry to ensure increased flower production under greenhouse conditions, although its effects in this ~'egard are most pronounced when it is applied after a dormancy-breaking cold period. ACKNOWLEDGEMENT
This work was supported by a grant-in-aid of research to B.G. Cumming by the National Research Council of Canada. REFERENCES Aung, L.H. and De Hertogh, A.A., 1968. Gibberellin-like substances in non-cold and cold treated tulip bulbs (Tulipa sp.). In: F. Wightman and G. Setterfield (Editors), Biochemistry and Physiology of Plant Growth Substances. Runge, Ottawa, pp. 943--956. De Hertogh, A.A. and Blakely, N., 1972. Influences of gibberelllins A 3 and A,+ 7 on development of forced Lilium longiflorum Thumb. cv. Ace. J. Am. Soc. Hortic. Sci., 97: 320--323. Dicks, J.W. and Rees, A.R., 1973. Effects of growth-regulating chemicals on two cultivars of Mid-Century Hybrid lily. Scientia Hortic., 1: 133--142. Dicks, J.W., Gilford, J. McD. and Rees, A.R., 1974. The influence of timing of application and gibberellic acid on the effects of ancymidol on growth and flowering of MidCentury Hybrid lily cv. Enchantment. Scientia Hortic., 2: 153--163. Edgerton, L.J. and Blanpied, G.D., 1968. Regulation of growth and fruit maturation with 2-chloroethanephosphonic acid. Nature (London), 219: 1064--1065.
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Feldmaier, C., 1970. In: Lilies. Arco, New York, p. 188. Halevy, A.H., Mor, J. and Valershtein, J., 1971. Endogenous gibberellin level in Ornithogalum arabicum and its relationship to storage temperatures of bulbs and to flower development. First Int. Syrup. Flower Bulbs, Acta Hortic., 23, I: 82--89. Hasek, R.F., Sciaroni, R.H. and Farnham, D.S., 1971, 1970--71. Japanese Georgia lily height control trials. Florists' Rev., 148 : 22--24; 62--64. Laiche, A.J., 1973. Response of lilies to gibberellic acid. Miss. Agric. For. Stn. Information Sheet, 1221. Leopold, A.C., 1971. Antagonism of some gibberellin actions by a substituted pyrimidine. Plant Physiol., 48: 537--540. Simmonds, J.A. and Cumming, B.G., 1976. Propagation of Lilium hybrids. I. Dependence of bulblet production on time of scale removal and growth substances. Scientia Hortic., 5: 77--83. Simmonds, J.A. and Cumming, B.G., 1977. Bulb-dip application of growth-regulating chemical for inhibiting stem elongation of 'Enchantment' and ' H a r m o n y ' lilies. Scientia Hortic., 6: 71~81. Tsukamoto, Y., 1971. Changes in endogenous growth substances in Easter lily as affected by cooling. First Int. Syrup. Flower Bulbs, Acta Hortic., 23, I: 75--81.