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The effect of various environmental factors on flowering of gladiolus. III. Temperature and moisture
Scientia Horticulturae, 4(1976)147--155 Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
147
T H E E F F E C T OF VARIOUS E N V I R O N M E N T A L FA CT O RS ON F L O W E R I N G OF GLADIOLUS. III. T E M P E R A T U R E AND MOISTURE
R. SHILLO and A.H. HALEVY The Hebrew University of Jerusalem, Department of Ornamental Horticulture, Rehovot (Israel)
(Received 17 March 1975)
ABSTRACT Shillo, R. and Halevy, A.H., 1976. The effect of various environmental factors on flowering of gladiolus. III. Temperature and moisture. Scientia Hort., 4: 147--155. Under conditions of low light intensity in winter, low temperatures (1--4 °~C)increase the occurrence of flower blasting. This chilling damage was observed at two developmental stages -- immediately after plan£ing and at the 7th leaf stage when spike emergence starts. Gladioli are extremely tolerant to high temperatures (up to 50 °C) as long as air humidity and soil moisture are at an optimum. The damaging effect of high temperature is generally indirect via its effect on plant water balance. Plants were directly damaged by high temperature during the period from planting to the first leaf stage. Decrease in soil moisture reduced flowering at most stages of development. The stages immediately after planting and just before spike emergence were the most sensitive. INTRODUCTION Flower initiation in Gladiolus occurs after the corms are planted (Pfeiffer, 1931). The effect on flowering, of temperatures prevailing during c o r m storage, is t h e r e f o r e fairly limited and this aspect has been recently studied (Magie, 1968; Shillo and Simchon, 1973}. The present study deals only with the effect o f t e m p e r a t u r e during the period o f growth. The main effect o f t e m p e r a t u r e r e p o r t e d in the literature is on rate of growth and development. S u m mer grown gladioli flower 60--80 days after planting, whereas in winter 1 2 0 - 1 4 0 days are required (see e.g. Post, 1952). Apte (1960) and Post (1952) also m e n t i o n the specific effect which temperature has on winter flowering and t h e y state t h a t flower failure in glasshousegrown gladioli in winter is due t o a c o m b i n a t i o n of low light intensities, short days and high temperature. Flower p r o d u c t i o n in winter is mainly restricted to southern regions such as Florida and Israel (Magie and Cowperthwaite , 1954) where plants are grown in the open. Light intensities at these locations are high and temperatures are moderate. In Israel, winter flower failure has even been f o u n d in desert regions. Cloudy days are very few here and the average m i n i m u m tern-
148
perature is 7 °C. Frost is very rare indeed, but minimum night temperatures of 2--4 °C are not uncommon. In a previous study (Shillo and Halevy, 1963) we found that night temperatures of 2 °C during winter caused blasting of whole inflorescences and reduced the number of florets per spike in inflorescences which did flower. Plants at the 2-leaf and the 5-leaf stage were particularly sensitive to this temperature. Chilling plants to the same temperatures during daytime inhibited stalk elongation, but did not cause blasting. Blasting is generally a problem in gladioli flowering in mid winter. Occasionally however, this phenomenon is also encountered at the beginning of winter in plants which were planted at the end of summer. In this case blasting might be caused by high temperatures during early stages of growth or by water deficit which generally accompanies high temperatures. Halevy (1960, 1962) and Shillo and Halevy (1964) found that soil water potential affected gladiolus flowers even at fairly high values, whereas corm development was impaired only at lower values. The effects which air water deficit or soil water potential have on various plant developmental stages have not been studied. The objectives of the present study were to investigate in detail the effects of suband supra-optimal temperatures and moisture, which may occur at different stages of development, on the flowering of Gladiolus. MATERIALS AND METHODS
Experiments were conducted with cultivar 'Sans Souci' grown from 14 cm corms. Plants were grown individually in 3 1 plastic pots in a sandy loam, peat and vermiculite (1:1:1) mixture. Corms were planted at 7--10 day intervals to obtain plants at different developmental stages at any one time. They were grown in "good" but not controlled conditions as far as light and temperature were concerned. Before the start of treatments, uniform groups of plants at each of the different developmental stages were chosen. Experimental conditions generally lasted from 19 to 28 days. Experiments which included several developmental stages were conducted with 5 plants (replicates) each, whereas in experiments conducted with only one stage, 40 plants were treated (experiments 1 and ~L). Flowering data were recorded when 3 florets were open. In low temperature experiments, plants were transferred from outdoors to a refrigerated chamber every night. Short days were achieved by covering plants with black polyethylene sheets which were coated with a reflective metal layer to prevent excessive heating. Further details of the various experiments are given, together with the results. EXPERIMENTAL AND RESULTS
Low Temperatures. -- Experiment
1. L o w n i g h t t e m p e r a t u r e in s u m m e r . - -
Plants at the 2-leaf stage were chilled every night for 12 h at 1 + 0.5 °C. Treatment lasted 19 nights (between April 10 and May 5). At the end of the treatment period, plants had reached the 3-leaf stage. Control plants were grown
149 outside under natural conditions. Results of flowering are presented in Table 1. Cooling plants at night during summer slightly reduced the flowering percentage. This reduction, however, was much smaller than the 50 % reduction TABLE 1 Effect of 19 cold nights (1 °C for 12 h) on flowering of 'Sans Souci' gladioli. Treatments applied at the 2--3 leaf stage during summer Treatment
Flowering (%)
Stalk length (cm)
No. of florets /spike
Days to flowering
Control Cold night
100 91
85 83
7.4 7.3
92 99
N.S.
**(18.22)
Significance (and F values) N.S.
in flowering obtained in winter experiments (Shillo and Halevy, 1963). The number of florets per spike and the flower stalk length were not affected by the cold treatments. The flowering date was delayed by one week as a result of the cold. Summer day conditions, i.e. high solar irradiance and/or high temperature, may be the reason for the reduced deleterious effect of low night temperature. This possibility was examined in the following experiments. Experiment 2. L o w night temperature under short-day conditions in summer. -- Plants at different developmental stages were cold treated for 23 nights at 1 + 0.5 °C for 16 h. Flowering-data are presented in Table 2. Cold night treatment during summer affected flowering, unlike the effects obtained during winter (Shillo and Halevy, 1963). Cold treatment damaged only in two instances: a) when given immediately after planting in which case the whole inflorescence was blasted and consequently a low flowering percentage was obtained, and b) when cold was applied at the 7-leaf stage which resulted in the abortion of individual rioters. Flowering was normal following treatment at any of the other stages. It seems therefore that summer day conditions (light intensity and/or temperature) annul or greatly reduce the effect of low night temperatures. Experiment 3. Light intensity and day temperature in combination with low night temperature. ~ Plants were grown in a greenhouse (20 °C night temperature) during winter. On January 22, uniform: plants at each developmental stage were chosen and transferred to growth chambers for 28 days. Night (12 h) temperature was 4 °C in all treatments, whereas day temperatures were 10 or 20 °C, combined with light intensities of 13 or 25 Klux. After treatment, plants were returned to the greenhouse in which the night temperature was main-
150
TABLE 2 E f f e c t o f c o l d n i g h t s (1 °C f o r 1 6 h ) o n f l o w e r i n g o f ' S a n s S o u c i ' gladioli. T r e a t m e n t w a s applied for 23 nights at various stages of development during the summer.* Development stage during treatment
Flowering (%)
Stalk length (cm)
Spike length (cm)
No. of florets /spike
Days to flowering
P1 Sh-- 2 1 -- 3 2 -- 4 3 -- 5 4 --6 5 -- 7 6 --S.E. 7 -- An
25 100 100 100 100 100 100 100 80
-1 3 1 . 6 -+ 3 . 5 133.6-+ 3.7 134.4-+ 2 . 6 128.6-+ 3 . 8 127.6-+3.3 128.0-+ 2 . 0 115.6-+1.6 9 0 . 6 - + 6.7
-4 2 . 8 -+ 2.2 48.4+_ 1 . 2 48.4-+ 1 . 6 45.6-+ 1 . 5 47.4-+0.8 52.2-+ 2 . 2 49.4-+2.2 27.2+ 5.3
-11.6-+ 0 . 5 13.6-+ 0 . 2 13.2_+ 0.7 12.4_+ 0 . 5 14.0-+0.8 13.6 + - 1.0 12.2-+0.9 5.5-+ 1 . 8
92.0 92.4-+ 2 . 2 86.6-+ 2 . 0 87.4-+ 2.1 9 0 . 0 -+ 0 . 9 98.8-+0.5 1 0 1 . 0 -+ 1 . 2 99.2-+0.9 94.0-+ 1 . 6
96
111.0-+ 6 . 0
39.0-+ 3.7
11.6-+ 1.1
85.0-+ 1 . 2
Control
*Values are with Standard errors. Pl - - p l a n t i n g ; S h - - s h e a t h l e a v e s ; 1 - - 7 - - n u m b e r o f f o l i a g e l e a v e s ; S.E. - - s p i k e e m e r g e n c e ; An -- anthesis.
TABLE 3 The effect o f 2 day t e m p e r a t u r e s a n d 2 light intensities in c o m b i n a t i o n with low night t e m p e r a t u r e (4°C, 12 h daily) o n flowering o f 'Sans Souci' gladioli. T r e a t m e n t s were applied for 28 days, at different stages o f development. For stages o f d e v e l o p m e n t see Table 2. D e v e l o p m e n t stage during treatment
Day Temp. °C
Flowering (%)
Stalk length (cm)
13 Klux
13 Klux
25 Klux
No. o f florets /slaike
25 Klux 13 Klux
25 Klux
Pl - 1 P1 -- 1
10 20
71 0
100 75
131
S h - - 1--2 Sh -- 1 -- 2
10 20
33 0
0 0
144
1 - - 2--3 Sh-- 3
10 20
0 0
14 11
134 133
6.0 7.0
3 -- 4 3 -- 4 " 5
10 20
0 0
66 50
136 135
8.5 8.7
4 "--5
I0
0
0
4
20
0
0
-- 5
S.E. for all 10 ° C t r e a t m e n t s S.E. for all 20 ° C t r e a t m e n t s
6.7
135 131
8.2
8.0 8.2
10.0
4.1 2.8
1.1
0.7 0.7
151 tained at 15 °C. Results of flowering are presented in Table 3. It seems that light intensity is the dominant factor affecting flowering. At an intensity of 13 Klux there was no flowering at all if the treatment was applied after the 1st leaf stage. Intensity of 25 Klux resulted in partial flowering. Developmental stages sensitive to low night temperature were the 1--3 and the 4--5 leaf stages. Low day-temperature had no deleterious effect on flowering. The combination of high day temperatures and low light intensity was very damaging to flowering. High temperatures. -- The following experiments were set up to clarify whether
high temperature damages flowers directly or whether the effect is due to interference with the plant's water balance. E x p e r i m e n t 4. E f f e c t o f t r e a t m e n t at the 2--3 leaf stage. ~ Plants at the 2-leaf stage were given the following treatments: (1) heat and dry air; (2) heat and moist air; (3) control -- natural outdoor conditions. Plants of treatments 1 and 2 were placed in double-wailed polyethylene chambers in a greenhouse. Each chamber was equipped with thermostatically controlled heating elements and a fan which worked for 12 h per day. Humidity was raised in the "humid" chamber by wetting the floor and by hanging blotting-papers which were dipping in water. Light intensity at noon was 20 Klux. Temperature and humidity in the 2 chambers varied at different times of the day as recorded in Table 4. Heat treatments lasted 15 days (April 17 to May 2). The plants grew outdoors before and after treatment. At the end of the 15-day treatments, plants growing at low humidity reached the 3--4 leaf stage, whereas plants at high humidity had 4--5 leaves. Plants in both treatments were etiolated and leaf edges were scorched. The range of maximum temperatures was 5--6 °C higher in the dry air chamber than in the moist air one. The difference in relative humidity between the 2 chambers was 15--28 %. The flowering percentage and the number of florets per spike (Table 4) were low under conditions of dry air and high temperature. Blasted flower stalks, under these conditions, elongated up to the spike emergence stage. Surprisingly, plants grown in the moist air chamber under very high temperatures (36--40 °C) and light intensities which are lower than outdoors, produced flowers of better quality than plants growing outdoors throughout their development. This point was further verified in the following experiment. E x p e r i m e n t 5. -- Plants at different developmental stages were transferred for 23 days (June 21 to July 14) from outdoor conditions to high-temperature conditions at 2 different relative humidities. Light intensities, temperature and relative humidity in the dry and field control treatments were the same as in experiment 4. Hot humid conditions were obtained by placing plants in a completely closed whitewashed glasshouse in which a humidifier
152
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153
raised relative humidity to almost 100 % throughout the day. Temperatures reached values up to 50 °C at noon. Data of Table 5 show that plants subjected to a period of dry air heat produced shorter flower stalks and fewer florets per spike than those subjected to moist air heat, in spite of the fact that temperatures in the moist air chamber were approximately 5 °C higher than those prevailing in the ary air chamber. Heat in combination with moist air, given at any time between sprouting and spike emergence, enhanced growth and improved flowering. Flower stalks were longer and there were more florets per spike in this treatment than in plants growing outdoors continuously. Two stages in plant development were found to be sensitive to high temperatures. High temperatures occurring soon after planting caused a reduction in the flowering percentage. Damage was especially severe when high temperatures were accompanied by dry air, in which case even those plants which did flower, were adversely affected. The second sensitive stage is from the appearance of the 5th leaf onward. In this case all high temperature treatments caused a reduction in the number of florets per spike. -- Experiment 6. - - Irrigation of plants at various developmental stages was interrupted on June 19 for 22 days. Flowering-data are summarized in Table 6. The first stage of growth, immediately after sprouting, was most sensitive to low soil moisture. Although plants treated at this stage remained alive, none of them flowered. Plants were resistant to dryness at the stage lasting from sheath leaf emergence to the appearance of the second foliage leaf. Sensitivity increased with development and elongation Of the inflorescence and was most severe at the 4 - 6 leaf stage. Water deficit at this stage causes the death of all inflorescences. Sensitivity decreased again close to flowering-time.
Soil moisture.
TABLE 6
The e f f e c t o f l o w soil m o i s t u r e o n flowering o f ' S a n s Souci' gladioli. Irrigation was interr u p t e d f o r 22 days at various d e v e l o p m e n t a l stages. F o r developmental stage see Table 2. D e v e l o p m e n t a l stage during t r e a t m e n t
Flowering (%)
Stalk length (cm)
No. o f f l o r e t s / s p i k e
P1 - Sh-1 -2 --
Sh 2.5 2.5 3.5
0 100 60 20
-105 115 80
-11.2 13.0 6.0
3
--4.5
25
80
5.0
4
--4.5
0
--
--
0
--
-5.0 6.0 ± 0.9
5 --5.5 6 --7 7 -- S.E.--An S.E. f o r all stages Control (irrigated regularly)
20 40
100
93 93 +- 3.1
110 + - 6.0
11.2-+ 1.1
154 DISCUSSION The results reported above, concerning the effect of low night temperature (Table 1), are at variance with data previously published (Shillo and Halevy, 1963). Although night temperatures were comparable in the two experiments, conditions during day time differed since they were uncontrolled. In contrast to the earlier reported great reduction in flowering obtained following low night temperatures in winter, the present effect was only slight during summer. The strong effect obtained during winter cannot be ascribed to daylength since most plants in the present set of experiments flowered when subjected to a daylength of 8 h (Table 2) which is shorter than the shortest day in Israel. It seems probable that the factor causing flowering in summer, in spite of low night temperatures, is the daily high solar energy flux, which in summer is double that prevailing in winter (Stanhill, 1962). It is probably more correct to state the converse, i.e. that in winter, when total irradiation is marginal, low night temperatures increase the incidence of flower blasting. Similar re sults have been reported for roses (Moe and Kristoffersen, 1969). Sensitivity to low temperature was observed particularly at two stages, the first soon after planting and the second at the 7-leaf stage. Low temperature treatments at this first stage of development inhibited growth. Plants which failed to flower produced 3--4 small leaves which remained alive to the end of the experiment. Similar retardation of growth and flowering was observed when non-dormant corms were cooled prior to planting at 5 °C following storage at 30 °C (Shillo and Simchon, 1973). A reduction in the number of florets per spike was also found when plants at the 7th leaf stage were subjected to low temperature. The inflorescence has emerged from the axils of the leaves at this stage, and is very sensitive to low temperature. McCalla et ai. (1939), who studied the effect of temperature on the rate of elongation of gladiolus, state that at no high point, up to 25 °C, did temperature depress growth. The results of our experiments indicate that gladioli are very tolerant to extremely high temperatures (up to 50 °C) at most stages of development as long as relative humidity is very high (Tables 4 and 5). This implies that the main damaging effect of the high temperatures is not a direct effect but via their influence on the plant's water balance. The most sensitive stage to both low soil moisture (Halevy, 1962, and Table 6) and dry air (= vapour pressure deficit) was at the 4--7 leaf stage when flower stalk elongation is at the highest rate. The deleterious effect of high temperature was observed also at the very early stage just after planting (Table 5). At this stage the plant is still in the soil and is not exposed to air, and since the soil was well irrigated, the damage may be accredited to the direct effect of high temperature. At this stage plants were also very sensitive to low soil moisture (Table 6). A comprehensive evaluation of the effect of these and other environmental factors at the various developmental stages on flowering of gladiolus plants will be presented in the concluding paper of this series.
155
REFERENCES Apte, S.S., 1960. New approach to an old problem - - early flowering of gladiolus. The Gladiolus, New Eng. Glad. Soc. Y.B. 35: 123--130. Halevy, A.H., 1960. The influence of progressive increase in soil moisture tension on growth and water balance of gladiolus leaves and the development of physiological indicators for irrigation. Proc. Amer. Soc. Hort. Sci. 76: 6 2 0 - 6 3 0 . Halevy, A.H., 1962. Irrigation experiments with gladioli. In: Advances in Horticultural Science and their Applications. Pergamon, Oxford, 2: 279--287. Magie, R.O. and Cowperthwaite, W.B., 1954. Commercial gladiolus production in Florida. Contrib. Gulf Coast Exp. Sta. Bull., 535: 1---67. Magie, R.O., 1968. Disease control relative to new methods of harvesting, curing and storing of gladiolus corms. N. Amer. Gladiolus Counc. Bull., 95: 83--87. McCalla, A.C., Weir, J.R. and Neatby, K.W., 1939. Effects of temperature and sunlight on the rate of elongation of stems of maize and gladiolus. Can. J. Res., Sect. C, 17 (11): 388--409. Moe, R. and Kristoffersen, T., 1969. The effect of temperature and light on growth and flowering of rosa 'Baccara' in greenhouses. Acta Hort. 14: 157--163. Pfeiffer, E.N., 1931. A morphological study of gladiolus. Contrib. Boyce Thompson Inst., 3: 173--196. Post, K., 1952. Florist Crop Production and Marketing. Orange Judd. Pub. Co. New York. Shillo, R. and Halevy, A.H., 1963. The effect of low temperature on the flowering of gladioli. Isr. J. Agr. Res., 13: 141--145. Shillo, R. and Halevy, A.H., 1964. Experiments in the irrigation of gladioli according to absorption of viscous fluid through stomata. Isr. J. Agr. Res., 14: 89--95. Shillo, R. and Simchon, S., 1973. Effect of water content and storage temperature of gladiolus corms o n flowe~ing. Scientia Hort., 1: 57--62. Stanhill, G., 1962. Solar radiation in Israel. Bull. Res. Counc. Isr., Sect. G, 11: 34--41.
147
T H E E F F E C T OF VARIOUS E N V I R O N M E N T A L FA CT O RS ON F L O W E R I N G OF GLADIOLUS. III. T E M P E R A T U R E AND MOISTURE
R. SHILLO and A.H. HALEVY The Hebrew University of Jerusalem, Department of Ornamental Horticulture, Rehovot (Israel)
(Received 17 March 1975)
ABSTRACT Shillo, R. and Halevy, A.H., 1976. The effect of various environmental factors on flowering of gladiolus. III. Temperature and moisture. Scientia Hort., 4: 147--155. Under conditions of low light intensity in winter, low temperatures (1--4 °~C)increase the occurrence of flower blasting. This chilling damage was observed at two developmental stages -- immediately after plan£ing and at the 7th leaf stage when spike emergence starts. Gladioli are extremely tolerant to high temperatures (up to 50 °C) as long as air humidity and soil moisture are at an optimum. The damaging effect of high temperature is generally indirect via its effect on plant water balance. Plants were directly damaged by high temperature during the period from planting to the first leaf stage. Decrease in soil moisture reduced flowering at most stages of development. The stages immediately after planting and just before spike emergence were the most sensitive. INTRODUCTION Flower initiation in Gladiolus occurs after the corms are planted (Pfeiffer, 1931). The effect on flowering, of temperatures prevailing during c o r m storage, is t h e r e f o r e fairly limited and this aspect has been recently studied (Magie, 1968; Shillo and Simchon, 1973}. The present study deals only with the effect o f t e m p e r a t u r e during the period o f growth. The main effect o f t e m p e r a t u r e r e p o r t e d in the literature is on rate of growth and development. S u m mer grown gladioli flower 60--80 days after planting, whereas in winter 1 2 0 - 1 4 0 days are required (see e.g. Post, 1952). Apte (1960) and Post (1952) also m e n t i o n the specific effect which temperature has on winter flowering and t h e y state t h a t flower failure in glasshousegrown gladioli in winter is due t o a c o m b i n a t i o n of low light intensities, short days and high temperature. Flower p r o d u c t i o n in winter is mainly restricted to southern regions such as Florida and Israel (Magie and Cowperthwaite , 1954) where plants are grown in the open. Light intensities at these locations are high and temperatures are moderate. In Israel, winter flower failure has even been f o u n d in desert regions. Cloudy days are very few here and the average m i n i m u m tern-
148
perature is 7 °C. Frost is very rare indeed, but minimum night temperatures of 2--4 °C are not uncommon. In a previous study (Shillo and Halevy, 1963) we found that night temperatures of 2 °C during winter caused blasting of whole inflorescences and reduced the number of florets per spike in inflorescences which did flower. Plants at the 2-leaf and the 5-leaf stage were particularly sensitive to this temperature. Chilling plants to the same temperatures during daytime inhibited stalk elongation, but did not cause blasting. Blasting is generally a problem in gladioli flowering in mid winter. Occasionally however, this phenomenon is also encountered at the beginning of winter in plants which were planted at the end of summer. In this case blasting might be caused by high temperatures during early stages of growth or by water deficit which generally accompanies high temperatures. Halevy (1960, 1962) and Shillo and Halevy (1964) found that soil water potential affected gladiolus flowers even at fairly high values, whereas corm development was impaired only at lower values. The effects which air water deficit or soil water potential have on various plant developmental stages have not been studied. The objectives of the present study were to investigate in detail the effects of suband supra-optimal temperatures and moisture, which may occur at different stages of development, on the flowering of Gladiolus. MATERIALS AND METHODS
Experiments were conducted with cultivar 'Sans Souci' grown from 14 cm corms. Plants were grown individually in 3 1 plastic pots in a sandy loam, peat and vermiculite (1:1:1) mixture. Corms were planted at 7--10 day intervals to obtain plants at different developmental stages at any one time. They were grown in "good" but not controlled conditions as far as light and temperature were concerned. Before the start of treatments, uniform groups of plants at each of the different developmental stages were chosen. Experimental conditions generally lasted from 19 to 28 days. Experiments which included several developmental stages were conducted with 5 plants (replicates) each, whereas in experiments conducted with only one stage, 40 plants were treated (experiments 1 and ~L). Flowering data were recorded when 3 florets were open. In low temperature experiments, plants were transferred from outdoors to a refrigerated chamber every night. Short days were achieved by covering plants with black polyethylene sheets which were coated with a reflective metal layer to prevent excessive heating. Further details of the various experiments are given, together with the results. EXPERIMENTAL AND RESULTS
Low Temperatures. -- Experiment
1. L o w n i g h t t e m p e r a t u r e in s u m m e r . - -
Plants at the 2-leaf stage were chilled every night for 12 h at 1 + 0.5 °C. Treatment lasted 19 nights (between April 10 and May 5). At the end of the treatment period, plants had reached the 3-leaf stage. Control plants were grown
149 outside under natural conditions. Results of flowering are presented in Table 1. Cooling plants at night during summer slightly reduced the flowering percentage. This reduction, however, was much smaller than the 50 % reduction TABLE 1 Effect of 19 cold nights (1 °C for 12 h) on flowering of 'Sans Souci' gladioli. Treatments applied at the 2--3 leaf stage during summer Treatment
Flowering (%)
Stalk length (cm)
No. of florets /spike
Days to flowering
Control Cold night
100 91
85 83
7.4 7.3
92 99
N.S.
**(18.22)
Significance (and F values) N.S.
in flowering obtained in winter experiments (Shillo and Halevy, 1963). The number of florets per spike and the flower stalk length were not affected by the cold treatments. The flowering date was delayed by one week as a result of the cold. Summer day conditions, i.e. high solar irradiance and/or high temperature, may be the reason for the reduced deleterious effect of low night temperature. This possibility was examined in the following experiments. Experiment 2. L o w night temperature under short-day conditions in summer. -- Plants at different developmental stages were cold treated for 23 nights at 1 + 0.5 °C for 16 h. Flowering-data are presented in Table 2. Cold night treatment during summer affected flowering, unlike the effects obtained during winter (Shillo and Halevy, 1963). Cold treatment damaged only in two instances: a) when given immediately after planting in which case the whole inflorescence was blasted and consequently a low flowering percentage was obtained, and b) when cold was applied at the 7-leaf stage which resulted in the abortion of individual rioters. Flowering was normal following treatment at any of the other stages. It seems therefore that summer day conditions (light intensity and/or temperature) annul or greatly reduce the effect of low night temperatures. Experiment 3. Light intensity and day temperature in combination with low night temperature. ~ Plants were grown in a greenhouse (20 °C night temperature) during winter. On January 22, uniform: plants at each developmental stage were chosen and transferred to growth chambers for 28 days. Night (12 h) temperature was 4 °C in all treatments, whereas day temperatures were 10 or 20 °C, combined with light intensities of 13 or 25 Klux. After treatment, plants were returned to the greenhouse in which the night temperature was main-
150
TABLE 2 E f f e c t o f c o l d n i g h t s (1 °C f o r 1 6 h ) o n f l o w e r i n g o f ' S a n s S o u c i ' gladioli. T r e a t m e n t w a s applied for 23 nights at various stages of development during the summer.* Development stage during treatment
Flowering (%)
Stalk length (cm)
Spike length (cm)
No. of florets /spike
Days to flowering
P1 Sh-- 2 1 -- 3 2 -- 4 3 -- 5 4 --6 5 -- 7 6 --S.E. 7 -- An
25 100 100 100 100 100 100 100 80
-1 3 1 . 6 -+ 3 . 5 133.6-+ 3.7 134.4-+ 2 . 6 128.6-+ 3 . 8 127.6-+3.3 128.0-+ 2 . 0 115.6-+1.6 9 0 . 6 - + 6.7
-4 2 . 8 -+ 2.2 48.4+_ 1 . 2 48.4-+ 1 . 6 45.6-+ 1 . 5 47.4-+0.8 52.2-+ 2 . 2 49.4-+2.2 27.2+ 5.3
-11.6-+ 0 . 5 13.6-+ 0 . 2 13.2_+ 0.7 12.4_+ 0 . 5 14.0-+0.8 13.6 + - 1.0 12.2-+0.9 5.5-+ 1 . 8
92.0 92.4-+ 2 . 2 86.6-+ 2 . 0 87.4-+ 2.1 9 0 . 0 -+ 0 . 9 98.8-+0.5 1 0 1 . 0 -+ 1 . 2 99.2-+0.9 94.0-+ 1 . 6
96
111.0-+ 6 . 0
39.0-+ 3.7
11.6-+ 1.1
85.0-+ 1 . 2
Control
*Values are with Standard errors. Pl - - p l a n t i n g ; S h - - s h e a t h l e a v e s ; 1 - - 7 - - n u m b e r o f f o l i a g e l e a v e s ; S.E. - - s p i k e e m e r g e n c e ; An -- anthesis.
TABLE 3 The effect o f 2 day t e m p e r a t u r e s a n d 2 light intensities in c o m b i n a t i o n with low night t e m p e r a t u r e (4°C, 12 h daily) o n flowering o f 'Sans Souci' gladioli. T r e a t m e n t s were applied for 28 days, at different stages o f development. For stages o f d e v e l o p m e n t see Table 2. D e v e l o p m e n t stage during treatment
Day Temp. °C
Flowering (%)
Stalk length (cm)
13 Klux
13 Klux
25 Klux
No. o f florets /slaike
25 Klux 13 Klux
25 Klux
Pl - 1 P1 -- 1
10 20
71 0
100 75
131
S h - - 1--2 Sh -- 1 -- 2
10 20
33 0
0 0
144
1 - - 2--3 Sh-- 3
10 20
0 0
14 11
134 133
6.0 7.0
3 -- 4 3 -- 4 " 5
10 20
0 0
66 50
136 135
8.5 8.7
4 "--5
I0
0
0
4
20
0
0
-- 5
S.E. for all 10 ° C t r e a t m e n t s S.E. for all 20 ° C t r e a t m e n t s
6.7
135 131
8.2
8.0 8.2
10.0
4.1 2.8
1.1
0.7 0.7
151 tained at 15 °C. Results of flowering are presented in Table 3. It seems that light intensity is the dominant factor affecting flowering. At an intensity of 13 Klux there was no flowering at all if the treatment was applied after the 1st leaf stage. Intensity of 25 Klux resulted in partial flowering. Developmental stages sensitive to low night temperature were the 1--3 and the 4--5 leaf stages. Low day-temperature had no deleterious effect on flowering. The combination of high day temperatures and low light intensity was very damaging to flowering. High temperatures. -- The following experiments were set up to clarify whether
high temperature damages flowers directly or whether the effect is due to interference with the plant's water balance. E x p e r i m e n t 4. E f f e c t o f t r e a t m e n t at the 2--3 leaf stage. ~ Plants at the 2-leaf stage were given the following treatments: (1) heat and dry air; (2) heat and moist air; (3) control -- natural outdoor conditions. Plants of treatments 1 and 2 were placed in double-wailed polyethylene chambers in a greenhouse. Each chamber was equipped with thermostatically controlled heating elements and a fan which worked for 12 h per day. Humidity was raised in the "humid" chamber by wetting the floor and by hanging blotting-papers which were dipping in water. Light intensity at noon was 20 Klux. Temperature and humidity in the 2 chambers varied at different times of the day as recorded in Table 4. Heat treatments lasted 15 days (April 17 to May 2). The plants grew outdoors before and after treatment. At the end of the 15-day treatments, plants growing at low humidity reached the 3--4 leaf stage, whereas plants at high humidity had 4--5 leaves. Plants in both treatments were etiolated and leaf edges were scorched. The range of maximum temperatures was 5--6 °C higher in the dry air chamber than in the moist air one. The difference in relative humidity between the 2 chambers was 15--28 %. The flowering percentage and the number of florets per spike (Table 4) were low under conditions of dry air and high temperature. Blasted flower stalks, under these conditions, elongated up to the spike emergence stage. Surprisingly, plants grown in the moist air chamber under very high temperatures (36--40 °C) and light intensities which are lower than outdoors, produced flowers of better quality than plants growing outdoors throughout their development. This point was further verified in the following experiment. E x p e r i m e n t 5. -- Plants at different developmental stages were transferred for 23 days (June 21 to July 14) from outdoor conditions to high-temperature conditions at 2 different relative humidities. Light intensities, temperature and relative humidity in the dry and field control treatments were the same as in experiment 4. Hot humid conditions were obtained by placing plants in a completely closed whitewashed glasshouse in which a humidifier
152
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153
raised relative humidity to almost 100 % throughout the day. Temperatures reached values up to 50 °C at noon. Data of Table 5 show that plants subjected to a period of dry air heat produced shorter flower stalks and fewer florets per spike than those subjected to moist air heat, in spite of the fact that temperatures in the moist air chamber were approximately 5 °C higher than those prevailing in the ary air chamber. Heat in combination with moist air, given at any time between sprouting and spike emergence, enhanced growth and improved flowering. Flower stalks were longer and there were more florets per spike in this treatment than in plants growing outdoors continuously. Two stages in plant development were found to be sensitive to high temperatures. High temperatures occurring soon after planting caused a reduction in the flowering percentage. Damage was especially severe when high temperatures were accompanied by dry air, in which case even those plants which did flower, were adversely affected. The second sensitive stage is from the appearance of the 5th leaf onward. In this case all high temperature treatments caused a reduction in the number of florets per spike. -- Experiment 6. - - Irrigation of plants at various developmental stages was interrupted on June 19 for 22 days. Flowering-data are summarized in Table 6. The first stage of growth, immediately after sprouting, was most sensitive to low soil moisture. Although plants treated at this stage remained alive, none of them flowered. Plants were resistant to dryness at the stage lasting from sheath leaf emergence to the appearance of the second foliage leaf. Sensitivity increased with development and elongation Of the inflorescence and was most severe at the 4 - 6 leaf stage. Water deficit at this stage causes the death of all inflorescences. Sensitivity decreased again close to flowering-time.
Soil moisture.
TABLE 6
The e f f e c t o f l o w soil m o i s t u r e o n flowering o f ' S a n s Souci' gladioli. Irrigation was interr u p t e d f o r 22 days at various d e v e l o p m e n t a l stages. F o r developmental stage see Table 2. D e v e l o p m e n t a l stage during t r e a t m e n t
Flowering (%)
Stalk length (cm)
No. o f f l o r e t s / s p i k e
P1 - Sh-1 -2 --
Sh 2.5 2.5 3.5
0 100 60 20
-105 115 80
-11.2 13.0 6.0
3
--4.5
25
80
5.0
4
--4.5
0
--
--
0
--
-5.0 6.0 ± 0.9
5 --5.5 6 --7 7 -- S.E.--An S.E. f o r all stages Control (irrigated regularly)
20 40
100
93 93 +- 3.1
110 + - 6.0
11.2-+ 1.1
154 DISCUSSION The results reported above, concerning the effect of low night temperature (Table 1), are at variance with data previously published (Shillo and Halevy, 1963). Although night temperatures were comparable in the two experiments, conditions during day time differed since they were uncontrolled. In contrast to the earlier reported great reduction in flowering obtained following low night temperatures in winter, the present effect was only slight during summer. The strong effect obtained during winter cannot be ascribed to daylength since most plants in the present set of experiments flowered when subjected to a daylength of 8 h (Table 2) which is shorter than the shortest day in Israel. It seems probable that the factor causing flowering in summer, in spite of low night temperatures, is the daily high solar energy flux, which in summer is double that prevailing in winter (Stanhill, 1962). It is probably more correct to state the converse, i.e. that in winter, when total irradiation is marginal, low night temperatures increase the incidence of flower blasting. Similar re sults have been reported for roses (Moe and Kristoffersen, 1969). Sensitivity to low temperature was observed particularly at two stages, the first soon after planting and the second at the 7-leaf stage. Low temperature treatments at this first stage of development inhibited growth. Plants which failed to flower produced 3--4 small leaves which remained alive to the end of the experiment. Similar retardation of growth and flowering was observed when non-dormant corms were cooled prior to planting at 5 °C following storage at 30 °C (Shillo and Simchon, 1973). A reduction in the number of florets per spike was also found when plants at the 7th leaf stage were subjected to low temperature. The inflorescence has emerged from the axils of the leaves at this stage, and is very sensitive to low temperature. McCalla et ai. (1939), who studied the effect of temperature on the rate of elongation of gladiolus, state that at no high point, up to 25 °C, did temperature depress growth. The results of our experiments indicate that gladioli are very tolerant to extremely high temperatures (up to 50 °C) at most stages of development as long as relative humidity is very high (Tables 4 and 5). This implies that the main damaging effect of the high temperatures is not a direct effect but via their influence on the plant's water balance. The most sensitive stage to both low soil moisture (Halevy, 1962, and Table 6) and dry air (= vapour pressure deficit) was at the 4--7 leaf stage when flower stalk elongation is at the highest rate. The deleterious effect of high temperature was observed also at the very early stage just after planting (Table 5). At this stage the plant is still in the soil and is not exposed to air, and since the soil was well irrigated, the damage may be accredited to the direct effect of high temperature. At this stage plants were also very sensitive to low soil moisture (Table 6). A comprehensive evaluation of the effect of these and other environmental factors at the various developmental stages on flowering of gladiolus plants will be presented in the concluding paper of this series.
155
REFERENCES Apte, S.S., 1960. New approach to an old problem - - early flowering of gladiolus. The Gladiolus, New Eng. Glad. Soc. Y.B. 35: 123--130. Halevy, A.H., 1960. The influence of progressive increase in soil moisture tension on growth and water balance of gladiolus leaves and the development of physiological indicators for irrigation. Proc. Amer. Soc. Hort. Sci. 76: 6 2 0 - 6 3 0 . Halevy, A.H., 1962. Irrigation experiments with gladioli. In: Advances in Horticultural Science and their Applications. Pergamon, Oxford, 2: 279--287. Magie, R.O. and Cowperthwaite, W.B., 1954. Commercial gladiolus production in Florida. Contrib. Gulf Coast Exp. Sta. Bull., 535: 1---67. Magie, R.O., 1968. Disease control relative to new methods of harvesting, curing and storing of gladiolus corms. N. Amer. Gladiolus Counc. Bull., 95: 83--87. McCalla, A.C., Weir, J.R. and Neatby, K.W., 1939. Effects of temperature and sunlight on the rate of elongation of stems of maize and gladiolus. Can. J. Res., Sect. C, 17 (11): 388--409. Moe, R. and Kristoffersen, T., 1969. The effect of temperature and light on growth and flowering of rosa 'Baccara' in greenhouses. Acta Hort. 14: 157--163. Pfeiffer, E.N., 1931. A morphological study of gladiolus. Contrib. Boyce Thompson Inst., 3: 173--196. Post, K., 1952. Florist Crop Production and Marketing. Orange Judd. Pub. Co. New York. Shillo, R. and Halevy, A.H., 1963. The effect of low temperature on the flowering of gladioli. Isr. J. Agr. Res., 13: 141--145. Shillo, R. and Halevy, A.H., 1964. Experiments in the irrigation of gladioli according to absorption of viscous fluid through stomata. Isr. J. Agr. Res., 14: 89--95. Shillo, R. and Simchon, S., 1973. Effect of water content and storage temperature of gladiolus corms o n flowe~ing. Scientia Hort., 1: 57--62. Stanhill, G., 1962. Solar radiation in Israel. Bull. Res. Counc. Isr., Sect. G, 11: 34--41.