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Influence of temperature prior to seed ripening and at germination on rosette formation and bolting of Eustoma grandiflorum
Scientia Horticulturae, 53 (1993) 225-230
225
Elsevier Science Publishers B.V., Amsterdam
Influence of temperature prior to seed ripening and at germination on rosette formation and bolting of Eustoma grandiflorum K.Ohkawa, M.Korenaga and T.Yoshizumi Department of Biological Science, Faculty of Agriculture, Shizuoka University, 836 Ohya, Shizuoka 422, Japan (Accepted 6 October 1992)
ABSTRACT Ohkawa, K., Korenaga, M. and Yoshizumi, T., 1993. Influence of temperature prior to seed ripening and at germination on rosette formation and bolting ofEustoma grandiflorum. Scientia Hortic., 53: 225-230. Rosette formation and subsequent bolting ofEustoma grandiflorum are influenced by temperature conditi,ans prior to seed ripening and after germination has commenced. Rosette formation was decreased if parent plants were matured at 23/18 °C (day/night) temperature and was increased at 33/ 28°C. IZurther low temperature seed treatment of hydrated seeds at 3°C or 10°C for 5 weeks decreased rosette formation and enhanced subsequent seedling bolting. Different cultivars responded differently to the various seed temperature treatments. Cultivars which formed rosettes easily, showed less of a response to low temperature after harvest. However, if seeds were ripened under a cooler environment, then germinated at low temperatures and seedlings grown in a coc~lenvironment, rosette formation of seedlings in E. grandiflorum was essentially eliminated. Keywords: Bolting; Eustoma grandiflorum; rosette; seed ripening; seedling development.
INTRODUCTION
Seedlings of Eustoma grandiflorum typically bolt after they develop three leaf pairs; however, no bolting occurs when seedlings are grown at or above 25°C. Seedlings are most sensitive to high temperatures during the first 2 weeks, after hydration and when the cotyledons are developing. Such sensitivity to high temperature gradually declines over time, and sensitivity is not apparent after two leaf pairs have developed. Rosette formation is intensified when seedlings are exposed to temperatures above 25°C. However, future Correspondence to: K. Ohkawa, Department of Biological Science, Faculty of Agriculture, Shizuoka University, 836 Ohya, Shizuoka 422, Japan.
© 1992 Elsevier Science Publishers B.V. All rights reserved 0304-4238/93/$06.00
226
K. OHKAWAET AL.
bolting is accelerated when plants are grown at temperatures lower than 20 ° C (Ohkawa et al., 1991 ). We developed a hypothesis suggesting that temperatures during seed ripening also influence rosette formation based on the observation that temperatures during seed hydration influence the low temperature treatment response. MATERIALS AND METHODS
Experiment 1. Effect of temperatures during seed development and ripening on rosetting and subsequent bolting of seedlings. - Seeds of E. grandiflorum cultivar 'Fukushihai' (Fukukaen Co. ) were germinated and grown until flower buds were visible in a 2 5 / 1 8 ° C (day/night) glass house. Upon appearance of buds, plants were transferred to natural-light phytotrons set at 33/28, 28/ 23 or 23/18 °C day/night temperature. Seeds were harvested and in turn sown and grown in natural-light phytotrons set at 33/28, 28/23 or 23 / 18 oC. There were 32 plants in four replications in each regime. A coated slow-release fertilizer (14N-12P-14K) was mixed into 31 of soil at a level of 6 g per 32 plants. Water was supplied by subirrigation for 5 weeks after sowing, followed by overhead irrigation. Eight weeks after seed hydration, the number of seedlings which had bolted were counted. When plants reached a height of 5 cm, the number of true leaves which had formed before bolting were counted. Natural day-length during the test period ranged from 10.8 to 12.6 h. This experiment was discontinued after 18 weeks. Temperatures in all experiments in the phytotron were controlled with errors of _+ 1 ° C. Experiment 2. Effect of low temperature seed treatments on the bolting rate of seedlings. - Seeds of 'Fukushihai' and 'Miyakomomo' were hydrated at 28/ 23°C for up to 3 days and then stored at 3 or 10°C for 5 weeks. These treatments were given under continuous irradiance (15.0-25.3/tmol m -z s -~ ). Upon completion of the 3 or 10°C temperature treatment, seedlings were transferred into a 33/28 or 2 8 / 2 3 ° C (day/night) phytotron. At that time, control seeds were sown and also maintained at 33/28 or 2 8 / 2 3 ° C (day/ night). There were 32 plants in four replications for all treatments. The experiment was discontinued after 16 weeks. RESULTS
Experiment 1. Effect of temperatures during seed development and ripening on the rosetting and subsequent bolting of seedlings. - Temperatures during seed
INFLUENCEOF TEMPERATUREON E. GRANDIFLORUM
227
pod development and ripening on the mother plant influenced the future stem elongation of seedlings developing from these seeds. Some 42% of the plants rosetted when seeds were matured at 2 3 / 1 8 ° C , even if seeds were subsequently germinated and grown at 3 3 / 2 8 ° C (Fig. 1 ). However, when a 33/ 28°C treatment was given both before seed maturation and at germination and early growth, almost 100 % rosetted. When seeds were matured at 2 8 / 2 3 ° C , but germinated and grown at 3 3 / 28 ° C, 89.1 °/0 of the seedlings rosetted. Similarly, when seeds were matured at 2 8 / 2 3 ° C, rosetting rate was 54% when seeds were subsequently grown at 2 8 / 23°C, but only 4.8% at 2 3 / 1 8 ° C (Fig. 1 ). The number of true leaves which developed before bolting was directly proportional to both temperature treatments; i.e. those applied during seed pod development and at the seedling stage. For example, when seeds were ma100
z~
n~--
,-, 80
=~ 60
~ 4o 20 0 23/18°C
28/23°C
33/28°C
Temperature prior to seed harvest Fig. 1 Influence on bolting rate when mother plants were grown, matured and their seed pods ripened at various temperatures, and the seeds were subsequently germinated and grown at temperatures of 33/28 ( O ) 28/23 ( [] ) or 23/18 °C ( & ) TABLE [ The number of true leaves developed prior to bolting as influenced by temperatures during seed development and ripening as well as during and after seed germination and seedling growth Temperature prior to seed har,est
Temperature during seedling germination and growth (°C)
(oc)
33/28
28/23
23/18
33/28 28/23 23/18
_1 6.7_+ 1.0 6.0_+0.0
8.9_+ 1.42 7.8_+ 1.1 6.5_+0.8
7.6_+0.9 7.0_+ 1.1 6.5+_0.8
JNo bolti ng occurred. 2Standard deviation.
228
K. OHKAWA
ET AL.
tured at 33/28°C, some 8.9 true leaves formed before bolting when seeds were subsequently grown at 28/23°C; when matured at 2 3 / 1 8 ° C only 6.0 leaves formed at 3 3 / 2 8 ° C (Table 1 ). Experiment 2. Effect of low temperature seed treatments on the bolting rate of seedlings. - When the seeds of the two cultivars used were subjected to 5 weeks of low temperatures, bolting was accelerated. With 'Fukushihai', a bolting rate of nearly 100% occurred when low temperature treatments ( 3 or 10 °C ) were given for 5 weeks regardless of whether pre-temperatures were or were not applied for 3 days at 2 8 / 2 3 °C during hydration of the seeds. However, in the control plants, which were not treated by 3 or 10°C low temperatures, the bolting rate was 19.5% at 3 3 / 2 8 ° C and 48.2% at 2 8 / 2 3 ° C (Fig. 2). With ' Miyakomomo ' 100
100
33/28°C
8O t.-r.~
~o
8O
6O
e-
"=" O
4O
60
40
2O 0
28/23°C
' Control
, 3°C
, 10°C
20
, Control
, 30C
, 10°C
' Fukushihai ' 100
100 ~-.
80
80 60
e-
60
c~
40
40
20
20
0
0
i
i
i
Control
3°C
10°C
0
i
i
i
Control
3°C
IO°C
Fig. 2 I n f l u e n c e o n b o l t i n g rate w h e n seeds w e r e l o w - t e m p e r a t u r e treated at 3 or 10 ° C for 5 w e e k s a n d t h e r e a f t e r g r o w n at 3 3 / 2 8 or 2 8 / 2 3 ° C . C o n t r o l seeds w e r e s o w n w i t h o u t l o w - t e m p e r a t u r e t r e a t m e n t a n d g r o w n at 3 3 / 2 8 o r 2 8 / 2 3 ° C. W i t h h a s t e n i n g o f g e r m i n a t i o n for 3 days at 2 8 / 2 3 °C b e f o r e l o w t e m p e r a t u r e t r e a t m e n t ( © ) , w i t h o u t h a s t e n i n g o f g e r m i n a t i o n at 2 8 / 23°C (e).
INFLUENCEOF TEMPERATUREON E. GRANDIFLORUM
229
TABLE 2 The effect of low temperature seed treatment on the number of true leaves developed prior to bolting
Seedling growth temperature (°C)
Pre-germination treatment ( 5 week stage) 3°C
10°C
Control 3
Yes I
No 2
Yes
No
6.2±0.74 6.1±0.5
6.4±1.0 6.1±0.5
6.8±1.3 6.0±0.4
6.1±0.6 5.9±0.4
6.8±1.0 7.4±1.6
7.5±1.4 6.5±0.9
7.8±1.5 6.9±1.0
8.3±1.4 6.2±0.7
7.7±1.4 6.5±1.0
8.0±0.0 6.8±1.2
'Fukuskihai" 33/28 28/23
'Miyakomomo" 33/28 28/23
Ipre-germination treatment for 3 days at 28/23 °C. 2No pre-germination treatment. 3Without pre-germination or low temperature treatment. 4Standard deviation.
"Miyakomomo', rosette formation was common and was little influenced by low temperature treatments when compared with 'Fukushihai' when both were grown at 33/28°C. When seedlings were grown at 33/28°C, bolting was 53.2%. However, when seedlings were grown at 28/23 ° C, bolting was greatly accelerated. There were no differences in bolting between 3 or 10°C treatments if seeds were pretreated at 28/23 °C for 3 days. The bolting ratio in the control plants was 5.4% for treatment at 33/28°C and 28.6% at 28/23°C (Fig. 2). The number of true leaves developed prior to bolting was less in plants grown~ from seeds which were treated with low temperatures when compared with plants grown from untreated seeds (Table 2 ). DISCUSSION
Gregory and Purvis (1936) reported that rye seeds could be vernalized during seed development. Using beet (Beta vulgaris ), O'Connor ( 1970 ) also reported that low temperatures during seed ripening influenced subsequent bolting and flowering of plants from these seeds. Suge and Yamada (1965 ) found that, in the case of low-temperature treatment of wheat during ripening, the effect of subsequent low temperature treatments increased in inverse proportion to the number of days of cold at germination for bolting. The life cycle of plants begins with fertilization; fully ripened seeds with their embryo are only temporarily dormant. Therefore, it is reasonable to assume that there are no great physiological differences between seeds prior to
230
K. OHKAWA ETAL.
ripening and seeds after germination, because seeds apparently respond to low temperatures before and after germination. Eustoma grandiflorum is also influenced by temperatures prior to ripening. Seeds harvested from different environments respond differently to the degree of rosette formation, and such a response is dependent upon past temperature histories. Cultivars with strong tendencies for rosette formation had reduced rosette characteristics if grown and harvested under low temperatures, or inversely, cultivars with weak rosette characteristics had increased rosette characteristics if grown and harvested under high temperature environments (Fig. 1 ). Kageyama et al. (1990) have reported that with E. grandiflorum, bolting of seedlings can be enhanced by low temperature treatments of seeds. Similar results have been obtained in the present study. Specifically, 'Fukushihai', which has weak rosette formation tendencies, bolted in nearly 100 % of cases when seeds were treated with low temperatures, regardless of germination temperature. However, with 'Miyakomomo', which has strong rosette formation tendencies, bolting rate was 53.2% when germination temperatures were high, but bolting reached 90.1% when temperatures were 28/23 oC. There were no differences in bolting of seedlings when pretreated at 28/23 °C prior to the 3 or 10 ° C, 5 week treatment. However, in the case of no pretreatment, 3°C had less of an effect than 10°C. Considering the above findings, if mature seeds are ripened at low temperatures and this treatment is combined with low temperature treatments during seed germination, it is feasible to entirely prevent rosette formation, regardless of cultivar.
REFERENCES Gregory, F.G. and Purvis, O.N., 1936. Vernalization. Nature 138:249. Kageyama, Y., Fukushima, Y. and Konishi, K., 1990. Effects of raising seedling at cool temperature and chilling treatment of seed on rosette formation of Eustoma. J. Jpn. Soc. Hort. Sci. 59 (suppl. 1 ):496-497 (in Japanese). O'Connor, L.T., 1970. Environmental influence during beet seed production on bolting and quality characteristics of the subsequent root crop. 1.1.R.B., 4:207-216. Ohkawa, K., Kano, A., Kanematsu, K. and Korenaga, M., 1991. Effects of air temperature and time on rosette formation in seedlings ofEustoma grandiflorum (Rat.) Shinn. Scientia Hottic., 48: 171- 176. Suge, H. and Yamada, N., 1965. Flower-promoting effect of gibberellin in winter wheat and barley. Plant Cell Physiol., 6: 147-160.
225
Elsevier Science Publishers B.V., Amsterdam
Influence of temperature prior to seed ripening and at germination on rosette formation and bolting of Eustoma grandiflorum K.Ohkawa, M.Korenaga and T.Yoshizumi Department of Biological Science, Faculty of Agriculture, Shizuoka University, 836 Ohya, Shizuoka 422, Japan (Accepted 6 October 1992)
ABSTRACT Ohkawa, K., Korenaga, M. and Yoshizumi, T., 1993. Influence of temperature prior to seed ripening and at germination on rosette formation and bolting ofEustoma grandiflorum. Scientia Hortic., 53: 225-230. Rosette formation and subsequent bolting ofEustoma grandiflorum are influenced by temperature conditi,ans prior to seed ripening and after germination has commenced. Rosette formation was decreased if parent plants were matured at 23/18 °C (day/night) temperature and was increased at 33/ 28°C. IZurther low temperature seed treatment of hydrated seeds at 3°C or 10°C for 5 weeks decreased rosette formation and enhanced subsequent seedling bolting. Different cultivars responded differently to the various seed temperature treatments. Cultivars which formed rosettes easily, showed less of a response to low temperature after harvest. However, if seeds were ripened under a cooler environment, then germinated at low temperatures and seedlings grown in a coc~lenvironment, rosette formation of seedlings in E. grandiflorum was essentially eliminated. Keywords: Bolting; Eustoma grandiflorum; rosette; seed ripening; seedling development.
INTRODUCTION
Seedlings of Eustoma grandiflorum typically bolt after they develop three leaf pairs; however, no bolting occurs when seedlings are grown at or above 25°C. Seedlings are most sensitive to high temperatures during the first 2 weeks, after hydration and when the cotyledons are developing. Such sensitivity to high temperature gradually declines over time, and sensitivity is not apparent after two leaf pairs have developed. Rosette formation is intensified when seedlings are exposed to temperatures above 25°C. However, future Correspondence to: K. Ohkawa, Department of Biological Science, Faculty of Agriculture, Shizuoka University, 836 Ohya, Shizuoka 422, Japan.
© 1992 Elsevier Science Publishers B.V. All rights reserved 0304-4238/93/$06.00
226
K. OHKAWAET AL.
bolting is accelerated when plants are grown at temperatures lower than 20 ° C (Ohkawa et al., 1991 ). We developed a hypothesis suggesting that temperatures during seed ripening also influence rosette formation based on the observation that temperatures during seed hydration influence the low temperature treatment response. MATERIALS AND METHODS
Experiment 1. Effect of temperatures during seed development and ripening on rosetting and subsequent bolting of seedlings. - Seeds of E. grandiflorum cultivar 'Fukushihai' (Fukukaen Co. ) were germinated and grown until flower buds were visible in a 2 5 / 1 8 ° C (day/night) glass house. Upon appearance of buds, plants were transferred to natural-light phytotrons set at 33/28, 28/ 23 or 23/18 °C day/night temperature. Seeds were harvested and in turn sown and grown in natural-light phytotrons set at 33/28, 28/23 or 23 / 18 oC. There were 32 plants in four replications in each regime. A coated slow-release fertilizer (14N-12P-14K) was mixed into 31 of soil at a level of 6 g per 32 plants. Water was supplied by subirrigation for 5 weeks after sowing, followed by overhead irrigation. Eight weeks after seed hydration, the number of seedlings which had bolted were counted. When plants reached a height of 5 cm, the number of true leaves which had formed before bolting were counted. Natural day-length during the test period ranged from 10.8 to 12.6 h. This experiment was discontinued after 18 weeks. Temperatures in all experiments in the phytotron were controlled with errors of _+ 1 ° C. Experiment 2. Effect of low temperature seed treatments on the bolting rate of seedlings. - Seeds of 'Fukushihai' and 'Miyakomomo' were hydrated at 28/ 23°C for up to 3 days and then stored at 3 or 10°C for 5 weeks. These treatments were given under continuous irradiance (15.0-25.3/tmol m -z s -~ ). Upon completion of the 3 or 10°C temperature treatment, seedlings were transferred into a 33/28 or 2 8 / 2 3 ° C (day/night) phytotron. At that time, control seeds were sown and also maintained at 33/28 or 2 8 / 2 3 ° C (day/ night). There were 32 plants in four replications for all treatments. The experiment was discontinued after 16 weeks. RESULTS
Experiment 1. Effect of temperatures during seed development and ripening on the rosetting and subsequent bolting of seedlings. - Temperatures during seed
INFLUENCEOF TEMPERATUREON E. GRANDIFLORUM
227
pod development and ripening on the mother plant influenced the future stem elongation of seedlings developing from these seeds. Some 42% of the plants rosetted when seeds were matured at 2 3 / 1 8 ° C , even if seeds were subsequently germinated and grown at 3 3 / 2 8 ° C (Fig. 1 ). However, when a 33/ 28°C treatment was given both before seed maturation and at germination and early growth, almost 100 % rosetted. When seeds were matured at 2 8 / 2 3 ° C , but germinated and grown at 3 3 / 28 ° C, 89.1 °/0 of the seedlings rosetted. Similarly, when seeds were matured at 2 8 / 2 3 ° C, rosetting rate was 54% when seeds were subsequently grown at 2 8 / 23°C, but only 4.8% at 2 3 / 1 8 ° C (Fig. 1 ). The number of true leaves which developed before bolting was directly proportional to both temperature treatments; i.e. those applied during seed pod development and at the seedling stage. For example, when seeds were ma100
z~
n~--
,-, 80
=~ 60
~ 4o 20 0 23/18°C
28/23°C
33/28°C
Temperature prior to seed harvest Fig. 1 Influence on bolting rate when mother plants were grown, matured and their seed pods ripened at various temperatures, and the seeds were subsequently germinated and grown at temperatures of 33/28 ( O ) 28/23 ( [] ) or 23/18 °C ( & ) TABLE [ The number of true leaves developed prior to bolting as influenced by temperatures during seed development and ripening as well as during and after seed germination and seedling growth Temperature prior to seed har,est
Temperature during seedling germination and growth (°C)
(oc)
33/28
28/23
23/18
33/28 28/23 23/18
_1 6.7_+ 1.0 6.0_+0.0
8.9_+ 1.42 7.8_+ 1.1 6.5_+0.8
7.6_+0.9 7.0_+ 1.1 6.5+_0.8
JNo bolti ng occurred. 2Standard deviation.
228
K. OHKAWA
ET AL.
tured at 33/28°C, some 8.9 true leaves formed before bolting when seeds were subsequently grown at 28/23°C; when matured at 2 3 / 1 8 ° C only 6.0 leaves formed at 3 3 / 2 8 ° C (Table 1 ). Experiment 2. Effect of low temperature seed treatments on the bolting rate of seedlings. - When the seeds of the two cultivars used were subjected to 5 weeks of low temperatures, bolting was accelerated. With 'Fukushihai', a bolting rate of nearly 100% occurred when low temperature treatments ( 3 or 10 °C ) were given for 5 weeks regardless of whether pre-temperatures were or were not applied for 3 days at 2 8 / 2 3 °C during hydration of the seeds. However, in the control plants, which were not treated by 3 or 10°C low temperatures, the bolting rate was 19.5% at 3 3 / 2 8 ° C and 48.2% at 2 8 / 2 3 ° C (Fig. 2). With ' Miyakomomo ' 100
100
33/28°C
8O t.-r.~
~o
8O
6O
e-
"=" O
4O
60
40
2O 0
28/23°C
' Control
, 3°C
, 10°C
20
, Control
, 30C
, 10°C
' Fukushihai ' 100
100 ~-.
80
80 60
e-
60
c~
40
40
20
20
0
0
i
i
i
Control
3°C
10°C
0
i
i
i
Control
3°C
IO°C
Fig. 2 I n f l u e n c e o n b o l t i n g rate w h e n seeds w e r e l o w - t e m p e r a t u r e treated at 3 or 10 ° C for 5 w e e k s a n d t h e r e a f t e r g r o w n at 3 3 / 2 8 or 2 8 / 2 3 ° C . C o n t r o l seeds w e r e s o w n w i t h o u t l o w - t e m p e r a t u r e t r e a t m e n t a n d g r o w n at 3 3 / 2 8 o r 2 8 / 2 3 ° C. W i t h h a s t e n i n g o f g e r m i n a t i o n for 3 days at 2 8 / 2 3 °C b e f o r e l o w t e m p e r a t u r e t r e a t m e n t ( © ) , w i t h o u t h a s t e n i n g o f g e r m i n a t i o n at 2 8 / 23°C (e).
INFLUENCEOF TEMPERATUREON E. GRANDIFLORUM
229
TABLE 2 The effect of low temperature seed treatment on the number of true leaves developed prior to bolting
Seedling growth temperature (°C)
Pre-germination treatment ( 5 week stage) 3°C
10°C
Control 3
Yes I
No 2
Yes
No
6.2±0.74 6.1±0.5
6.4±1.0 6.1±0.5
6.8±1.3 6.0±0.4
6.1±0.6 5.9±0.4
6.8±1.0 7.4±1.6
7.5±1.4 6.5±0.9
7.8±1.5 6.9±1.0
8.3±1.4 6.2±0.7
7.7±1.4 6.5±1.0
8.0±0.0 6.8±1.2
'Fukuskihai" 33/28 28/23
'Miyakomomo" 33/28 28/23
Ipre-germination treatment for 3 days at 28/23 °C. 2No pre-germination treatment. 3Without pre-germination or low temperature treatment. 4Standard deviation.
"Miyakomomo', rosette formation was common and was little influenced by low temperature treatments when compared with 'Fukushihai' when both were grown at 33/28°C. When seedlings were grown at 33/28°C, bolting was 53.2%. However, when seedlings were grown at 28/23 ° C, bolting was greatly accelerated. There were no differences in bolting between 3 or 10°C treatments if seeds were pretreated at 28/23 °C for 3 days. The bolting ratio in the control plants was 5.4% for treatment at 33/28°C and 28.6% at 28/23°C (Fig. 2). The number of true leaves developed prior to bolting was less in plants grown~ from seeds which were treated with low temperatures when compared with plants grown from untreated seeds (Table 2 ). DISCUSSION
Gregory and Purvis (1936) reported that rye seeds could be vernalized during seed development. Using beet (Beta vulgaris ), O'Connor ( 1970 ) also reported that low temperatures during seed ripening influenced subsequent bolting and flowering of plants from these seeds. Suge and Yamada (1965 ) found that, in the case of low-temperature treatment of wheat during ripening, the effect of subsequent low temperature treatments increased in inverse proportion to the number of days of cold at germination for bolting. The life cycle of plants begins with fertilization; fully ripened seeds with their embryo are only temporarily dormant. Therefore, it is reasonable to assume that there are no great physiological differences between seeds prior to
230
K. OHKAWA ETAL.
ripening and seeds after germination, because seeds apparently respond to low temperatures before and after germination. Eustoma grandiflorum is also influenced by temperatures prior to ripening. Seeds harvested from different environments respond differently to the degree of rosette formation, and such a response is dependent upon past temperature histories. Cultivars with strong tendencies for rosette formation had reduced rosette characteristics if grown and harvested under low temperatures, or inversely, cultivars with weak rosette characteristics had increased rosette characteristics if grown and harvested under high temperature environments (Fig. 1 ). Kageyama et al. (1990) have reported that with E. grandiflorum, bolting of seedlings can be enhanced by low temperature treatments of seeds. Similar results have been obtained in the present study. Specifically, 'Fukushihai', which has weak rosette formation tendencies, bolted in nearly 100 % of cases when seeds were treated with low temperatures, regardless of germination temperature. However, with 'Miyakomomo', which has strong rosette formation tendencies, bolting rate was 53.2% when germination temperatures were high, but bolting reached 90.1% when temperatures were 28/23 oC. There were no differences in bolting of seedlings when pretreated at 28/23 °C prior to the 3 or 10 ° C, 5 week treatment. However, in the case of no pretreatment, 3°C had less of an effect than 10°C. Considering the above findings, if mature seeds are ripened at low temperatures and this treatment is combined with low temperature treatments during seed germination, it is feasible to entirely prevent rosette formation, regardless of cultivar.
REFERENCES Gregory, F.G. and Purvis, O.N., 1936. Vernalization. Nature 138:249. Kageyama, Y., Fukushima, Y. and Konishi, K., 1990. Effects of raising seedling at cool temperature and chilling treatment of seed on rosette formation of Eustoma. J. Jpn. Soc. Hort. Sci. 59 (suppl. 1 ):496-497 (in Japanese). O'Connor, L.T., 1970. Environmental influence during beet seed production on bolting and quality characteristics of the subsequent root crop. 1.1.R.B., 4:207-216. Ohkawa, K., Kano, A., Kanematsu, K. and Korenaga, M., 1991. Effects of air temperature and time on rosette formation in seedlings ofEustoma grandiflorum (Rat.) Shinn. Scientia Hottic., 48: 171- 176. Suge, H. and Yamada, N., 1965. Flower-promoting effect of gibberellin in winter wheat and barley. Plant Cell Physiol., 6: 147-160.