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Flowering of Centradenia inaequilateralis ‘Cascade’ as influenced by temperature and photoperiod
Scientia Horticulturae, 41 (1989) 125-130 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
125
F l o w e r i n g of Centradenia Inaequilateralis 'Cascade' as Influenced by T e m p e r a t u r e and Photoperiod K I R S T E N FRIIS* and OLE VOIGT C H R I S T E N S E N
Institute of Glasshouse Crops, Research Centre for Horticulture, Kirstinebjergvej 10, DK~5792 Aarslev (Denmark) (Accepted for publication 1 May 1989)
ABSTRACT Friis, K. and Christensen, O.V., 1989. Flowering of Centradenia inaequilateralis 'Cascade' as influenced by temperature and photoperiod. Scientia Hortic., 41: 125-130. The effects of temperature and photoperiod on the flowering of Centradenia inaequilateralis cultivar 'Cascade' were investigated. The percentage of shoots with visible flower buds increased and flowering was more prolific at 12 or 15 °C than at 9 or 18°C. No flower buds were observed at 21 or 24°C. The percentage of shoots with visible flower buds increased with increasing duration of temperature treatment (from 1 to 6 weeks). Plants treated for 1 week only produced very few flower buds, regardless of temperature. Photoperiod did not influence flowering and the number of days to flowering was on average 57-58 days. Keywords: Centradenia inaequilateralis; flowering; photoperiod; temperature.
INTRODUCTION
Centradenia inaequilateralis (Schlechtd. & Cham.) G. Don belongs to the Melastomataceae family. The small ( ~ 1 cm in diameter) pink flowers are borne on a subfasciculate cluster or short raceme. The inflorescences are borne terminally, but usually on lateral shoots (Almeda, 1977). C. inaequilateralis flowers profusely and, with its graceful habit, appears to have potential as a potted plant. In pot plant production, it is important to know whether it is possible to increase and to regulate the time of flowering. A survey of the literature did not reveal which factors control the flowering of Centradenia. According to Almeda (1977), flowering occurs all year in the distribution area, which is *Present address: Funen's Family Farmers Association, Rugaardsvej 197, DK-5210 Odense, Denmark.
0304-4238/89/$03.50
© 1989 Elsevier Science Publishers B.V.
126
K. FRIIS AND O.V. CHRISTENSEN
widespread, but localized at elevations of 200-1900 m from southeastern Mexico to north central Guatemala, east to western and central Honduras, and south through central and western Nicaragua, to Costa Rica and Panama. Encke (1960) describes Centradenia as a winter flowering plant, which is in accordance with observations made at the Institute of Glasshouse Crops (latitude 55 ° 18' N), where flowering has been recorded from January to April, when plants were grown at 20/18 °C (day/night) and under natural day length. A preliminary experiment had shown that temperature affects the initiation of flower buds and the time of flowering. Plants grown at 8-h photoperiods flowered earlier when treated for 4, 6 or 8 weeks at 18/15 °C (day/night) than plants treated at 21/18°C (day/night). It was also observed that the development of initiated flower buds took place at both 8- and 16-h photoperiods. Plants grown at 24°C remained in the vegetative stage regardless of photoperiod. On the basis of these preliminary results, an experiment was undertaken to determine the effects of temperature and photoperiod on flowering of
Centradenia. MATERIALSAND METHODS Plants of C. inaequilateralis cultivar 'Cascade' were obtained from the Botanical Garden of the University of Copenhagen. Cuttings were planted on 21 December 1983 and transplanted into l l - c m pots 6 weeks later. Until the start of treatments, plants were grown at 24 ° C and a photoperiod of 16 h to ensure vegetative growth. Plants were potted in a fertilized peat medium (VAPO B2) and nutrients were added during every irrigation in a combination of N: 168, P : 31, K: 208 (mg l-1) in concentrations of 0.84 g 1-1. The C02 level was kept at 900 zl l-1 in the greenhouse compartments. A factorial arrangement of six temperatures (minimum 9, 12, 15, 18, 21 or 24°C, ventilation at + 3 ° C above minimum), three photoperiods (8, 12 or 16 h ) and five durations of treatment (1, 2, 3, 4 or 6 weeks) was used. Treatments were started on 20 March 1984 with eight plants in each of the 90 treatments. During the treatments, plants were placed in the greenhouse compartments of the phytotron from 07.45 to 15.45 h and then automatically transferred to the connected dark chambers where supplementary light from incandescent lamps (photon flux density of 3.5 + 1.9 #mol s - 1 m - 2) was supplied in 4 or 8 h to ensure 12- and 16-h photoperiods. After the treatments, the plants were transferred to two greenhouse compartments, where they remained until flowering. The temperature was maintained at a minimum of 24 ° C (ventilation at + 3 ° C above minimum). In this period, the plants were grown at natural photoperiod (14-19.40 h). Data were collected on the number of days to flowering (from the start of
FLOWERING OF CENTRADENIA INAEQUILATERALIS
127
treatments) and the percentage of shoots with visible flower buds was calculated when the first flower had opened. Collection of data was terminated on 13 June 1984, 85 days after the treatments were started. RESULTS
During the experimental period, no visible flower buds were observed in plants treated at 21 or 24°C, thus these treatments have not been included in the statistical analysis of the recorded data.
Percentage of shoots with visible flower buds Temperature and duration of the temperature treatment did affect the percentage of shoots with visible flower buds to flower (Fig. 1). The percentage of shoots with visible flower buds increased as the duration increased. The highest percentage (almost 100% ) was achieved at 12 and 15 °C after 6 weeks at either temperature. Lower (9 ° C) and higher (18 ° C) temperatures caused a decrease in the percentage of reproductive shoots. Photoperiod did not influence the percentage of reproductive shoots at 9, 12 or 15°C, but the percentage at 18°C was higher at an 8-h photoperiod compared with 12 or 16 h (Fig. 2). Regardless ofphotoperiod and duration of treat-
100 90
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2 3 4 DURATION(WEEKS)
I
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Fig. 1. Figure to show the influence of temperature and temperature duration on the percentage of shoots with visible flower buds.
128
K. FRIIS AND O.V. CHRISTENSEN
100 90
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Fig. 2. Figure to show theinfluenee ofphotoperiodon the percentage ofshootswith visible flower buds. 70
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Fig. 3. Figure to show the influence ofduration oftreatments and temperature on the number of days to flowering.
FLOWERING OF CENTRADENIA INAEQUILATERALIS
129
ment, no visible flower buds were observed at 21 and 24 °C during the experimental period. N u m b e r of days to flowering Photoperiod. - The time to flowering was on average 8, 12 and 16 h, 57.3, 57.8 and 58.4 days, respectively (LSDo.o5 0.6 days). Temperature and duration of treatments. - The numbers of days to flowering showed a general increase with increasing duration of treatments at temperatures ~<18 ° C (Fig. 3). T h e earliest flowering was obtained in plants treated at 12 or 15 °C compared with 9 and 18 ° C. W h e n the duration of t r e a t m e n t was 4 or 6 weeks, the numbers of days to flowering were significantly higher at 12 ° C than at 15 ° C.
DISCUSSION Flower formation in Centradenia is strongly affected by temperature, whereas photoperiod has no importance. T h e increase in the percentage of shoots with visible flower buds at an 8-h photoperiod at 18°C can be as a result of the circumstance that the incandescent light extending the day length to 12 and 16 h m a y have raised the leaf temperature and therefore decreased the amount of flowering. During this experiment, no visible flower buds were recorded at 21 °C, perhaps on account of an insufficient inductive period. At 24 ° C, no visible flower buds were recorded, either in the experiment or during cultivation, indicating that the m a x i m u m temperature for flower formation of Centradenia is between 21 and 24°C. The earliest flowering was obtained at 15 ° C, which was also the optimum temperature for flower formation. After a t r e a t m e n t of 4 or 6 weeks, plants at 15 °C flowered earlier than at 12 ° C, indicating that 15 °C is better, although percentages of flowering shoots were the same at b o t h temperatures. Riinger (1971) stated that flower b u d initiation will be increasingly delayed as the deviation from the optimum temperature is increased. This also means that the interactions between temperature and duration of treatment, both on rate of visible flower buds and n u m b e r of days to flowering, could be expected. Temperature treatments caused noticeable differences in plant quality. Our work suggests that a temperature t r e a t m e n t of 15 °C for 4 weeks followed by a higher temperature ( 2 1 - 2 4 ° C ) is best for production of C. inaequilateralis 'Cascade' as a flowering p o t plant. A t r e a t m e n t at lower temperatures or one of > 4 weeks duration will lead to plants of poorer quality.
130
K. FRIISANDO.V.CHRISTENSEN
CONCLUSIONS
Flowering of C. inaequilateralis is affected by temperature treatment with an optimum at 15 °C for 4-6 weeks, while 21 °C for 6 weeks is not sufficient to ensure flowering and at 24 oC flower formation is inhibited. C. inaequilateralis appeared to be a day-neutral plant. To ensure the best plant quality, it is recommended to treat the plants at 15 ° C for 4 weeks followed by 21-24 oC to flowering, The plants will then flower 57-58 days after the start of the temperature treatment. ACKNOWLEDGEMENTS
The authors wish to thank Mr. K.O. Dideriksen and Mr. L.L. Rasmussen for their valuable technical assistance. The statistical analyses were made by Dr. Kristian Kristensen, Biometric Section, Lyngby, Denmark.
REFERENCES Almeda, F., Jr., 1977. Systematics of the neotropical genus Centradenia (Melastomataceae). J. Arnold Arbor., 58: 73-108. Encke, F., 1960. Parey's Blumeng~tnerei. Paul Parey, Berlin, 2, Auflage, Band II, 840 pp. R~inger, W., 1971. Bliitenbildungund Blfitenentwicklung.Paul Parey, Berlin, 207 pp.
125
F l o w e r i n g of Centradenia Inaequilateralis 'Cascade' as Influenced by T e m p e r a t u r e and Photoperiod K I R S T E N FRIIS* and OLE VOIGT C H R I S T E N S E N
Institute of Glasshouse Crops, Research Centre for Horticulture, Kirstinebjergvej 10, DK~5792 Aarslev (Denmark) (Accepted for publication 1 May 1989)
ABSTRACT Friis, K. and Christensen, O.V., 1989. Flowering of Centradenia inaequilateralis 'Cascade' as influenced by temperature and photoperiod. Scientia Hortic., 41: 125-130. The effects of temperature and photoperiod on the flowering of Centradenia inaequilateralis cultivar 'Cascade' were investigated. The percentage of shoots with visible flower buds increased and flowering was more prolific at 12 or 15 °C than at 9 or 18°C. No flower buds were observed at 21 or 24°C. The percentage of shoots with visible flower buds increased with increasing duration of temperature treatment (from 1 to 6 weeks). Plants treated for 1 week only produced very few flower buds, regardless of temperature. Photoperiod did not influence flowering and the number of days to flowering was on average 57-58 days. Keywords: Centradenia inaequilateralis; flowering; photoperiod; temperature.
INTRODUCTION
Centradenia inaequilateralis (Schlechtd. & Cham.) G. Don belongs to the Melastomataceae family. The small ( ~ 1 cm in diameter) pink flowers are borne on a subfasciculate cluster or short raceme. The inflorescences are borne terminally, but usually on lateral shoots (Almeda, 1977). C. inaequilateralis flowers profusely and, with its graceful habit, appears to have potential as a potted plant. In pot plant production, it is important to know whether it is possible to increase and to regulate the time of flowering. A survey of the literature did not reveal which factors control the flowering of Centradenia. According to Almeda (1977), flowering occurs all year in the distribution area, which is *Present address: Funen's Family Farmers Association, Rugaardsvej 197, DK-5210 Odense, Denmark.
0304-4238/89/$03.50
© 1989 Elsevier Science Publishers B.V.
126
K. FRIIS AND O.V. CHRISTENSEN
widespread, but localized at elevations of 200-1900 m from southeastern Mexico to north central Guatemala, east to western and central Honduras, and south through central and western Nicaragua, to Costa Rica and Panama. Encke (1960) describes Centradenia as a winter flowering plant, which is in accordance with observations made at the Institute of Glasshouse Crops (latitude 55 ° 18' N), where flowering has been recorded from January to April, when plants were grown at 20/18 °C (day/night) and under natural day length. A preliminary experiment had shown that temperature affects the initiation of flower buds and the time of flowering. Plants grown at 8-h photoperiods flowered earlier when treated for 4, 6 or 8 weeks at 18/15 °C (day/night) than plants treated at 21/18°C (day/night). It was also observed that the development of initiated flower buds took place at both 8- and 16-h photoperiods. Plants grown at 24°C remained in the vegetative stage regardless of photoperiod. On the basis of these preliminary results, an experiment was undertaken to determine the effects of temperature and photoperiod on flowering of
Centradenia. MATERIALSAND METHODS Plants of C. inaequilateralis cultivar 'Cascade' were obtained from the Botanical Garden of the University of Copenhagen. Cuttings were planted on 21 December 1983 and transplanted into l l - c m pots 6 weeks later. Until the start of treatments, plants were grown at 24 ° C and a photoperiod of 16 h to ensure vegetative growth. Plants were potted in a fertilized peat medium (VAPO B2) and nutrients were added during every irrigation in a combination of N: 168, P : 31, K: 208 (mg l-1) in concentrations of 0.84 g 1-1. The C02 level was kept at 900 zl l-1 in the greenhouse compartments. A factorial arrangement of six temperatures (minimum 9, 12, 15, 18, 21 or 24°C, ventilation at + 3 ° C above minimum), three photoperiods (8, 12 or 16 h ) and five durations of treatment (1, 2, 3, 4 or 6 weeks) was used. Treatments were started on 20 March 1984 with eight plants in each of the 90 treatments. During the treatments, plants were placed in the greenhouse compartments of the phytotron from 07.45 to 15.45 h and then automatically transferred to the connected dark chambers where supplementary light from incandescent lamps (photon flux density of 3.5 + 1.9 #mol s - 1 m - 2) was supplied in 4 or 8 h to ensure 12- and 16-h photoperiods. After the treatments, the plants were transferred to two greenhouse compartments, where they remained until flowering. The temperature was maintained at a minimum of 24 ° C (ventilation at + 3 ° C above minimum). In this period, the plants were grown at natural photoperiod (14-19.40 h). Data were collected on the number of days to flowering (from the start of
FLOWERING OF CENTRADENIA INAEQUILATERALIS
127
treatments) and the percentage of shoots with visible flower buds was calculated when the first flower had opened. Collection of data was terminated on 13 June 1984, 85 days after the treatments were started. RESULTS
During the experimental period, no visible flower buds were observed in plants treated at 21 or 24°C, thus these treatments have not been included in the statistical analysis of the recorded data.
Percentage of shoots with visible flower buds Temperature and duration of the temperature treatment did affect the percentage of shoots with visible flower buds to flower (Fig. 1). The percentage of shoots with visible flower buds increased as the duration increased. The highest percentage (almost 100% ) was achieved at 12 and 15 °C after 6 weeks at either temperature. Lower (9 ° C) and higher (18 ° C) temperatures caused a decrease in the percentage of reproductive shoots. Photoperiod did not influence the percentage of reproductive shoots at 9, 12 or 15°C, but the percentage at 18°C was higher at an 8-h photoperiod compared with 12 or 16 h (Fig. 2). Regardless ofphotoperiod and duration of treat-
100 90
I LSDo.o~5
8O 70 ~
60
~
50
la_
~
3O
20 10 0 l
I
~
¢
i
i
21 and 24°C ~ |
2 3 4 DURATION(WEEKS)
I
6
Fig. 1. Figure to show the influence of temperature and temperature duration on the percentage of shoots with visible flower buds.
128
K. FRIIS AND O.V. CHRISTENSEN
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15
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TEMPERATURE (°C)
Fig. 2. Figure to show theinfluenee ofphotoperiodon the percentage ofshootswith visible flower buds. 70
'~" LLI
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65
o=
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~
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~
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o
>>_
60
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~
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~
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50 I
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TEMPERATURE (°C)
Fig. 3. Figure to show the influence ofduration oftreatments and temperature on the number of days to flowering.
FLOWERING OF CENTRADENIA INAEQUILATERALIS
129
ment, no visible flower buds were observed at 21 and 24 °C during the experimental period. N u m b e r of days to flowering Photoperiod. - The time to flowering was on average 8, 12 and 16 h, 57.3, 57.8 and 58.4 days, respectively (LSDo.o5 0.6 days). Temperature and duration of treatments. - The numbers of days to flowering showed a general increase with increasing duration of treatments at temperatures ~<18 ° C (Fig. 3). T h e earliest flowering was obtained in plants treated at 12 or 15 °C compared with 9 and 18 ° C. W h e n the duration of t r e a t m e n t was 4 or 6 weeks, the numbers of days to flowering were significantly higher at 12 ° C than at 15 ° C.
DISCUSSION Flower formation in Centradenia is strongly affected by temperature, whereas photoperiod has no importance. T h e increase in the percentage of shoots with visible flower buds at an 8-h photoperiod at 18°C can be as a result of the circumstance that the incandescent light extending the day length to 12 and 16 h m a y have raised the leaf temperature and therefore decreased the amount of flowering. During this experiment, no visible flower buds were recorded at 21 °C, perhaps on account of an insufficient inductive period. At 24 ° C, no visible flower buds were recorded, either in the experiment or during cultivation, indicating that the m a x i m u m temperature for flower formation of Centradenia is between 21 and 24°C. The earliest flowering was obtained at 15 ° C, which was also the optimum temperature for flower formation. After a t r e a t m e n t of 4 or 6 weeks, plants at 15 °C flowered earlier than at 12 ° C, indicating that 15 °C is better, although percentages of flowering shoots were the same at b o t h temperatures. Riinger (1971) stated that flower b u d initiation will be increasingly delayed as the deviation from the optimum temperature is increased. This also means that the interactions between temperature and duration of treatment, both on rate of visible flower buds and n u m b e r of days to flowering, could be expected. Temperature treatments caused noticeable differences in plant quality. Our work suggests that a temperature t r e a t m e n t of 15 °C for 4 weeks followed by a higher temperature ( 2 1 - 2 4 ° C ) is best for production of C. inaequilateralis 'Cascade' as a flowering p o t plant. A t r e a t m e n t at lower temperatures or one of > 4 weeks duration will lead to plants of poorer quality.
130
K. FRIISANDO.V.CHRISTENSEN
CONCLUSIONS
Flowering of C. inaequilateralis is affected by temperature treatment with an optimum at 15 °C for 4-6 weeks, while 21 °C for 6 weeks is not sufficient to ensure flowering and at 24 oC flower formation is inhibited. C. inaequilateralis appeared to be a day-neutral plant. To ensure the best plant quality, it is recommended to treat the plants at 15 ° C for 4 weeks followed by 21-24 oC to flowering, The plants will then flower 57-58 days after the start of the temperature treatment. ACKNOWLEDGEMENTS
The authors wish to thank Mr. K.O. Dideriksen and Mr. L.L. Rasmussen for their valuable technical assistance. The statistical analyses were made by Dr. Kristian Kristensen, Biometric Section, Lyngby, Denmark.
REFERENCES Almeda, F., Jr., 1977. Systematics of the neotropical genus Centradenia (Melastomataceae). J. Arnold Arbor., 58: 73-108. Encke, F., 1960. Parey's Blumeng~tnerei. Paul Parey, Berlin, 2, Auflage, Band II, 840 pp. R~inger, W., 1971. Bliitenbildungund Blfitenentwicklung.Paul Parey, Berlin, 207 pp.