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Flowering control of recently introduced F1-hybrid cultivars of Godetia
Scientia Horticulturae, 46 ( 1991 ) 2 9 5 - 2 9 9
295
Elsevier Science Publishers B.V., A m s t e r d a m
Flowering control of recently introduced F1hybrid cultivars of Godetia Abraham H. Halevy and David Weiss The Hebrew University of Jerusalem, Faculty of Agriculture, Department of Horticulture, P.O. Box 12, Rehovot 76100 (Israel) (Accepted for publication 15 August 1990)
ABSTRACT Halevy, A.H. and Weiss, D., 1991. Flowering control of recently introduced F~-hybrid cultivars of Godetia. Scientia Hortic., 46: 295-299.
Clarkia amoena, commonly known as Godetia, is a well-known garden plant. The recent introduction of F r h y b r i d cultivars of this plant have greatly increased its value as a source of cut flowers. The plant was found to be sensitive to high temperatures. At 24°C and higher the plants died after a few weeks of growth, before flower bud formation. At 20-24°C Godetia behaved as a neutral-day plant, initiating flowers under both long-day (LD) and short-day (SD) conditions. At lower temperatures, however, it behaved as an absolute LD plant. Both flower initiation and development were enhanced under LD conditions. Plants grown under LD conditions (natural winter SD plus supplementact photoperiodic !ight) produced flowering stems of superior quality: the stems were much longer and the flowers were concentrated at the top of the stems, not along the shoot as in SD plants. Keywords: Clarkia amoena; flowering; Godetia; photoperiod; temperature. Abbreviations: L D = l o n g day; N D = natural day; S D = s h o r t day.
INTRODUCTION
The: plant commonly known as godetia (Godetia g r a n d i f l o r a = G. a m o e n a , Onagraceae ), a native of California, is a popular garden plant that in the past was used only to a small extent as a cut flower. Newly introduced Fl-hybrid cultiwars have greatly increased the value of this plant as a potentially important source of cut flowers, Botanists now include the species formerly named Godetia in the genus Clarkia, and the species used for cut flowers is Clarkia amoena (Bailey, 1976; Everett, 1981 ). The gardening literature (Everett, 1981 ) emphasizes the sensitivity of the plant ~Lohot, humid weather. Full exposure to sunlight, good ventilation and fairly low temperatures are absolute necessities. As to photoperiod, there is some controversy in the literature. According to 0304-4238/91/$03.50
© 1991 - - Elsevier Science Publishers B.V.
296
A,H. HALEVY AND D. WEISS
Post (1952) godetia does not require a specific photoperiod for flower formation, while other authors (Allard and Garner, 1940; Lewis and Went, 1945 ) consider it to be an LD plant. The meagre information available on the flowering physiology of godetia was all obtained using wild plants or old garden varieties, and even for these plants the data are not clear-cut. There is as yet no information on the responses of the new F~-hybrid cultivars of godetia to photoperiod or temperature. As our preliminary experiments indicated that the new cultivars have great potential as cut flowers, we studied their responses to different combinations of photoperiod and temperature. MATERIALS AND METHODS
The godetia Fl-hybrid cultivars 'Grace Rose' and 'Grace Salmon', from Sakata (Yokahama, Japan), were used in all the experiments. Two sets of experimental conditions were established: controlled conditions in the phytotron and ambient temperature conditions in a net-house. Phytotron experiments. - Two successive experiments were conducted, one
with cv. 'Grace Rose' and the other with 'Grace Salmon'. Six-week-old seedlings were planted individually in 15-cm pots containing 50% volcanic scoria and 50% peat. Ten clays later the plants were moved from the greenhouse to the phytotron, where they were divided into eight lots of five plants each. Four day/night temperature regimes were selected: 32/27, 27/22, 22/17 and 17/12 ° C. For each temperature regime there were two photoperiodic treatments: SD, i.e. 8 h of natural daylight, and LD, i.e. 8 h of daylight plus 8 h of incandescent light at 5/~mol m -2 s-1. Net-house e x p e r i m e n t s . , Experiments with the two cultivars were carried out
during two winter seasons (1988/1989 and 1989/1990). Seedlings were planted in early October in ground beds in a saran net-house giving 15% shade, under ambient temperature conditions. All plants grew in natural day (ND) light until the end of December, when they were divided into two photoperiodic treatments: ND (9½-10½ h), and LD (natural daylight plus incandescent light throughout the night at 5-10/~mol m - z s- ~). RESULTS
The results summarized in Table l clearly show that godetia plants cannot withstand high temperatures. At the highest temperature regime (32/27 °C) all plants died within one m o n t h of planting. At 27/22 °C they survived a few
FLOWERING CONTROL OF F~-HYBRID CULTIVARS OF GODETIA
297
weeks longer, but died before anthesis. Only plants raised under the two lowtemperature regimes (22 / 17 and 17 / 12 ° C ) reached full anthesis. The plants exposed to the highest temperature regime died before any flower buds appeared, and we could therefore not assess the effect of photoperiod on flower initiation at this temperature. At temperatures 5 °C lower (27/22 °C) flower buds were initiated under both LD and SD conditions in both cultivars, but the plants died before anthesis. At 22/17°C, flower buds were initiated during both photoperiodic treatments in 'Grace Rose' (Table 1 ), but in 'Grace Salmon' only under LD (data not shown). At the low-temperature regime ( 17/12 °C) flowers were formed only under LD conditions in both cultivars. In plants grown at ambient winter temperatures (7-22 °C) in the net-house, all plants bloomed under both N D and LD conditions, but anthesis was advanced by about 3 weeks in the LD plants (Table 2 ). Supplementary lighting greatly improved the quality of the flowers. Stems were longer by 20-50 cm in plants grown under LD conditions (Tables 1 and TABLE 1 Effects of photoperiod and temperature on flowering of godetia cultivar ' G r a c e Rose'. Plants were grown in controlled greenhouse chambers. Values are means of five replicates -+ SE
Treatment
Days from planting to anthesis
(day/night °C)
Days from planting to Photoperiod flower bud appearance
32/27 32/27 27/22 27/22 22/17 22/17 17/12 17/12
LD SD LD SD LD SD LD SD
77 _+ 3 78_+2 98_+4 -
Temperature
56 56 56 56 56 -
Length of Remarks flowering stems (cm)
All plants died All plants died Plants died before anthesis Plants died before anthesis 94+8 74+4 97+4
No flower buds formed
TABLE 2 Effect 0 f photoperiod on flowering of godetia cultivar 'Grace Rose' grown under ambient winter t e m p e r a t u r e s . Plants were grown under natural day ( N D ) conditions or in N D plus supplementary incandescent lighting throughout the n i g h t ( L D )
Treatment
ND LD
Days from planting to flower bud appearance
Days from planting to anthesis
Length of flowering
88 +__5 88 + 6
172 + 10 153 + 9
82 _+ 9 140 _+ 12
Remarks
stem (cm)
Prostrate growth Erect growth
298
A.H. HALEVY A N D D. WEISS
Fig. 1. Godetia plants grownin a saran net-houseat ambient temperatures. Left: under natural day (ND) photoperiod in the winter (9½-10½ h). Right: under long day (LD) photoperiod (ND, plus incandescentilluminationthroughoutthe night). 2). These plants were erect and their flowers were concentrated at the top of the stem, rather than on the lower lateral branches (Fig. 1 ). DISCUSSION The results of this study throw some light on the controversy in the literature concerning the effect ofphotoperiod on flowering in godetia (Allard and Garner, 1940; Lewis and Went, 1945; Post, 1952). A clear interaction between photoperiod and temperature was observed. At relatively warm temperatures (average 20-24 °C), godetia is a neutral-day plant, with flower initiation occurring under both SD and LD conditions. At lower temperatures ( 17/12 °C ) it is an absolute LD plant, with not even one flower bud initiated under SD conditions (8 h of daylight); these plants showed retarded growth and remained completely vegetative until the end of the experiment (5 months after planting). Under ND conditions (about 10 h of daylight) all plants grown at winter temperatures formed flowers (Table 2), thus indicating that the critical day length is between 8 and 10 h. In the net-house experiment (Table 2 ), supplementary lighting in the LD
FLOWERING CONTROL OF F~-HYBRID CULTIVARS OF GODETIA
299
treatment was started only at the beginning o f January and therefore did not affect flower initiation. However, under LD conditions flower development was enhanced, and anthesis was advanced by 19 days. Our findings thus confirm the c o m m e n t s in the gardening literature on the sensilLivity o f g o d e t i a to hot weather (Everett, 1981 ). In the phytotron experiments all plants grown at mean temperatures o f 24 °C and higher died. Observations in commercial plots bear out this conclusion: plants grown in unheated greenhouses with poor ventilation, where day temperatures reach over 3 5 °C at midday, collapsed and died before anthesis. ACKNOWLEDGEMENT This work was supported by the Pearlstein F u n d for Research in Ornamental Horticulture at the Hebrew University of Jerusalem. We are grateful to the donors for their support.
REFERENCES Allard~ H.A. and Garner, W.W., 1940. Further observations on the response of various species ofl:,lants to length of day. U.S. Dept. Agric. Tech. Bull., 727: 1-64. Bailey, L.H. Staff of Hortorium, 1976. Hortus Third. Macmillan,New York. Everett, T.N., 1981. The New York Botanical Garden Encyclopediaof Horticulture. Vol. 3. Garland, New York, pp. 780-783. Lewis, H. and Went, F.W., 1945. Plant growth under controlled conditions. IV. Responses of California annuals to photoperiod and temperature. Am. J. Bot., 32: 1-12. Post, I~L,1952. Florist Crop Production and Marketing. Orange Judd, New York.
295
Elsevier Science Publishers B.V., A m s t e r d a m
Flowering control of recently introduced F1hybrid cultivars of Godetia Abraham H. Halevy and David Weiss The Hebrew University of Jerusalem, Faculty of Agriculture, Department of Horticulture, P.O. Box 12, Rehovot 76100 (Israel) (Accepted for publication 15 August 1990)
ABSTRACT Halevy, A.H. and Weiss, D., 1991. Flowering control of recently introduced F~-hybrid cultivars of Godetia. Scientia Hortic., 46: 295-299.
Clarkia amoena, commonly known as Godetia, is a well-known garden plant. The recent introduction of F r h y b r i d cultivars of this plant have greatly increased its value as a source of cut flowers. The plant was found to be sensitive to high temperatures. At 24°C and higher the plants died after a few weeks of growth, before flower bud formation. At 20-24°C Godetia behaved as a neutral-day plant, initiating flowers under both long-day (LD) and short-day (SD) conditions. At lower temperatures, however, it behaved as an absolute LD plant. Both flower initiation and development were enhanced under LD conditions. Plants grown under LD conditions (natural winter SD plus supplementact photoperiodic !ight) produced flowering stems of superior quality: the stems were much longer and the flowers were concentrated at the top of the stems, not along the shoot as in SD plants. Keywords: Clarkia amoena; flowering; Godetia; photoperiod; temperature. Abbreviations: L D = l o n g day; N D = natural day; S D = s h o r t day.
INTRODUCTION
The: plant commonly known as godetia (Godetia g r a n d i f l o r a = G. a m o e n a , Onagraceae ), a native of California, is a popular garden plant that in the past was used only to a small extent as a cut flower. Newly introduced Fl-hybrid cultiwars have greatly increased the value of this plant as a potentially important source of cut flowers, Botanists now include the species formerly named Godetia in the genus Clarkia, and the species used for cut flowers is Clarkia amoena (Bailey, 1976; Everett, 1981 ). The gardening literature (Everett, 1981 ) emphasizes the sensitivity of the plant ~Lohot, humid weather. Full exposure to sunlight, good ventilation and fairly low temperatures are absolute necessities. As to photoperiod, there is some controversy in the literature. According to 0304-4238/91/$03.50
© 1991 - - Elsevier Science Publishers B.V.
296
A,H. HALEVY AND D. WEISS
Post (1952) godetia does not require a specific photoperiod for flower formation, while other authors (Allard and Garner, 1940; Lewis and Went, 1945 ) consider it to be an LD plant. The meagre information available on the flowering physiology of godetia was all obtained using wild plants or old garden varieties, and even for these plants the data are not clear-cut. There is as yet no information on the responses of the new F~-hybrid cultivars of godetia to photoperiod or temperature. As our preliminary experiments indicated that the new cultivars have great potential as cut flowers, we studied their responses to different combinations of photoperiod and temperature. MATERIALS AND METHODS
The godetia Fl-hybrid cultivars 'Grace Rose' and 'Grace Salmon', from Sakata (Yokahama, Japan), were used in all the experiments. Two sets of experimental conditions were established: controlled conditions in the phytotron and ambient temperature conditions in a net-house. Phytotron experiments. - Two successive experiments were conducted, one
with cv. 'Grace Rose' and the other with 'Grace Salmon'. Six-week-old seedlings were planted individually in 15-cm pots containing 50% volcanic scoria and 50% peat. Ten clays later the plants were moved from the greenhouse to the phytotron, where they were divided into eight lots of five plants each. Four day/night temperature regimes were selected: 32/27, 27/22, 22/17 and 17/12 ° C. For each temperature regime there were two photoperiodic treatments: SD, i.e. 8 h of natural daylight, and LD, i.e. 8 h of daylight plus 8 h of incandescent light at 5/~mol m -2 s-1. Net-house e x p e r i m e n t s . , Experiments with the two cultivars were carried out
during two winter seasons (1988/1989 and 1989/1990). Seedlings were planted in early October in ground beds in a saran net-house giving 15% shade, under ambient temperature conditions. All plants grew in natural day (ND) light until the end of December, when they were divided into two photoperiodic treatments: ND (9½-10½ h), and LD (natural daylight plus incandescent light throughout the night at 5-10/~mol m - z s- ~). RESULTS
The results summarized in Table l clearly show that godetia plants cannot withstand high temperatures. At the highest temperature regime (32/27 °C) all plants died within one m o n t h of planting. At 27/22 °C they survived a few
FLOWERING CONTROL OF F~-HYBRID CULTIVARS OF GODETIA
297
weeks longer, but died before anthesis. Only plants raised under the two lowtemperature regimes (22 / 17 and 17 / 12 ° C ) reached full anthesis. The plants exposed to the highest temperature regime died before any flower buds appeared, and we could therefore not assess the effect of photoperiod on flower initiation at this temperature. At temperatures 5 °C lower (27/22 °C) flower buds were initiated under both LD and SD conditions in both cultivars, but the plants died before anthesis. At 22/17°C, flower buds were initiated during both photoperiodic treatments in 'Grace Rose' (Table 1 ), but in 'Grace Salmon' only under LD (data not shown). At the low-temperature regime ( 17/12 °C) flowers were formed only under LD conditions in both cultivars. In plants grown at ambient winter temperatures (7-22 °C) in the net-house, all plants bloomed under both N D and LD conditions, but anthesis was advanced by about 3 weeks in the LD plants (Table 2 ). Supplementary lighting greatly improved the quality of the flowers. Stems were longer by 20-50 cm in plants grown under LD conditions (Tables 1 and TABLE 1 Effects of photoperiod and temperature on flowering of godetia cultivar ' G r a c e Rose'. Plants were grown in controlled greenhouse chambers. Values are means of five replicates -+ SE
Treatment
Days from planting to anthesis
(day/night °C)
Days from planting to Photoperiod flower bud appearance
32/27 32/27 27/22 27/22 22/17 22/17 17/12 17/12
LD SD LD SD LD SD LD SD
77 _+ 3 78_+2 98_+4 -
Temperature
56 56 56 56 56 -
Length of Remarks flowering stems (cm)
All plants died All plants died Plants died before anthesis Plants died before anthesis 94+8 74+4 97+4
No flower buds formed
TABLE 2 Effect 0 f photoperiod on flowering of godetia cultivar 'Grace Rose' grown under ambient winter t e m p e r a t u r e s . Plants were grown under natural day ( N D ) conditions or in N D plus supplementary incandescent lighting throughout the n i g h t ( L D )
Treatment
ND LD
Days from planting to flower bud appearance
Days from planting to anthesis
Length of flowering
88 +__5 88 + 6
172 + 10 153 + 9
82 _+ 9 140 _+ 12
Remarks
stem (cm)
Prostrate growth Erect growth
298
A.H. HALEVY A N D D. WEISS
Fig. 1. Godetia plants grownin a saran net-houseat ambient temperatures. Left: under natural day (ND) photoperiod in the winter (9½-10½ h). Right: under long day (LD) photoperiod (ND, plus incandescentilluminationthroughoutthe night). 2). These plants were erect and their flowers were concentrated at the top of the stem, rather than on the lower lateral branches (Fig. 1 ). DISCUSSION The results of this study throw some light on the controversy in the literature concerning the effect ofphotoperiod on flowering in godetia (Allard and Garner, 1940; Lewis and Went, 1945; Post, 1952). A clear interaction between photoperiod and temperature was observed. At relatively warm temperatures (average 20-24 °C), godetia is a neutral-day plant, with flower initiation occurring under both SD and LD conditions. At lower temperatures ( 17/12 °C ) it is an absolute LD plant, with not even one flower bud initiated under SD conditions (8 h of daylight); these plants showed retarded growth and remained completely vegetative until the end of the experiment (5 months after planting). Under ND conditions (about 10 h of daylight) all plants grown at winter temperatures formed flowers (Table 2), thus indicating that the critical day length is between 8 and 10 h. In the net-house experiment (Table 2 ), supplementary lighting in the LD
FLOWERING CONTROL OF F~-HYBRID CULTIVARS OF GODETIA
299
treatment was started only at the beginning o f January and therefore did not affect flower initiation. However, under LD conditions flower development was enhanced, and anthesis was advanced by 19 days. Our findings thus confirm the c o m m e n t s in the gardening literature on the sensilLivity o f g o d e t i a to hot weather (Everett, 1981 ). In the phytotron experiments all plants grown at mean temperatures o f 24 °C and higher died. Observations in commercial plots bear out this conclusion: plants grown in unheated greenhouses with poor ventilation, where day temperatures reach over 3 5 °C at midday, collapsed and died before anthesis. ACKNOWLEDGEMENT This work was supported by the Pearlstein F u n d for Research in Ornamental Horticulture at the Hebrew University of Jerusalem. We are grateful to the donors for their support.
REFERENCES Allard~ H.A. and Garner, W.W., 1940. Further observations on the response of various species ofl:,lants to length of day. U.S. Dept. Agric. Tech. Bull., 727: 1-64. Bailey, L.H. Staff of Hortorium, 1976. Hortus Third. Macmillan,New York. Everett, T.N., 1981. The New York Botanical Garden Encyclopediaof Horticulture. Vol. 3. Garland, New York, pp. 780-783. Lewis, H. and Went, F.W., 1945. Plant growth under controlled conditions. IV. Responses of California annuals to photoperiod and temperature. Am. J. Bot., 32: 1-12. Post, I~L,1952. Florist Crop Production and Marketing. Orange Judd, New York.