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Effects of photoperiod and temperature on tuberous root formation in winged bean (Psophocarpus tetragonolobus)
Scientia Horticulturae, 49 ( 1992 ) 1-8 Elsevier Science Publishers B.V., Amsterdam
Effects of photoperiod and temperature on tuberous root formation in winged bean
( Psophocarpus tetragonolobus ) Hiroshi Okubo, Teruyuki Masunaga~, Hirotsugi Yamashita 2 and Shunpei Uemoto 3 Laboratory of Horticuhural Science, Faculty of Agriculture, Kyushu University, Fukuoka 812, Japan (Accepted I 1 July 1991 )
ABSTRACT Okubo, H., Masunaga, T., Yamashita, H. and Uemoto, S., 1992. Effects of photoperiod and temperature on tuberous root formation in winged bean (Psophocarpus tetragonolobus). Scientia Hortic., 49: 1-8. Effects of photoperiod and temperature on tuberous root formation in some winged bean varieties were investigated. Tuberous root formation was induced by short days. Relatively low temperature (20°C) also caused formation of tuberous root even under long days, but both lower (15°C) and higher temperatures (25°C) did not. Plants must reach a ce~ain age for tuberous root induction by temperature. The daylength requirement for tuberous root formation in photo-sensitive and insensitive varieties seems to closely parallel that for flowering. Keywords: photoperiod; Psophocarpus tetragonolobus; temperature; tuberous root; winged bean.
INTRODUCTION
Winged bean (Psophocarpus tetragor.olobus) has recently been recognized as a nutritious crop because its immature pods, mature seeds and leave.; are rich in protein (Masefield, 1973; Claydon, 1975 ). The tuberous roots of the crop are also reported to contain a higher percentage of protein on a dry weight basis than any other ti'opical root crop known, such as taro, yam, cassav~ and sweet potato (Claydon, 1975). Tuberous roots of winged bean are a highly prized food in some parts of Papua New Guinea and Burma where they are peeled, baked or boiled and then eaten as a snack (Poulter, 1982 ). t Present address: Ukiha Agricultural Extension Office, Yoshiimachi 839-13, Fukuoka Prefecture, Japan. 2present address: Kumamoto Prefecture Office, Kumamoto 862, Japan. ~Present address: Oita Junior College, Oita 870, Japan.
© 1992 Elsevier Science Publishers B.V. All rights reserved 0304-4238/92/$05.00
2
H. OKUBO ET AL.
Having originated in the tropical regions, winged bean is essentially a typical short-day plant for flower initiation (Kahn, 1978; Herath and Ormrod, 1979 ). For the purpose of producing young pods as a new vegetable in Japan, many efforts have been made in our laboratory to select photoperiod-insensitive varieties for flower induction. Several completely photo-insensitive varieties for summer pod production in open fields (KUS (Kyushu University Selections) varieties) were also produced (S. Uemoto, unpublished data, 1983). It has been reported that tuberous root formation was affected more by daylength than by temperature, and that short days are necessary to initiate tuberous root formation almost irrespective of the temperature (Wong, 1981 ). Wong ( 1981 ) also showed that, unlike the flowering response to photoperiod, tuberous root development continued irrespective of daylength once the stimulus was received. Greater dry matter accumulation was found to occur at a daylength of 14 h than at I l h (Herath and Ormrod, 1979 ). Since winged bean has been traditionally cultivated only within tropical or subtropical zones where daylength is short, there is little informatio, on the response of tuberous root formation to photoperiod, temperature or combination treatments. The present paper is concerned with the effects of photoperiod and temperature on tuberous root formation in some winged bean varieties. MATERIALS AND METHODS 1. ~ Two varietie:; of winged bean, cultivars 'UPS-122' and 'UPS45' (UPS, University of Papua New Guinea Selections) were used. Seeds were sown on 2 November and germinated at 30°C. Young seedlings were potted in sand and grown until the third trifoliate leaf stage ( 18 November) in a glasshouse. They were subjected to 15, 20, 25 and 30°C with relative humidity of 80 +_5% in the phytotron of the Biotron Institute, Kyushu University under short and long days. Short days (8 h) were provided by covering the growing plants from 17:00 h to 09:00 h of the following day. Long days were achieved by extending the daylength to 16 h with white fluorescent lamps. On 8 February, they were transferred into the glasshouse at a minimum temperature of 15 °C and daylength treatments were continued until the measurement of tuberous root formation on 20 February.
Experiment
Effects of temperature under long days ( 16 h ) were examined. Seeds of 'LIPS-!22' were germinated on 4 November and. grown to the third trifoliate leaf stage (20 November) at 25°C. After this initial period, the plants were potted and subjected to experimental conditions in the phytotron for an additional I I weeks as follows: (A) 20°C for I I weeks; (B) 20°C for 8 weeks then 25°C for 3 weeks; (C) 20°C for 4 weeks then 25°C for 7 weeks; (D) 20°C for 2 weeks then 25°C for 9 weeks; (E) 25°C for I l weeks; (F) 25°C for 8 weeks then 20°C for 3 weeks; (G) 25°C for 4 weeks Experiment
2. - -
TUBEROUS ROOT FORMATION IN WINGFD BEAN
3
then 20°C for 7 weeks; (H) 25°C for 2 weeks then 20°C for 9 weeks. Measurements were made on 7 February. 3. m Tuberous root formation in photo-sensitive (cultivars 'UPS99' and "UPS- 121') and photo-insensitive varieties for flowering (cultivars 'KUS-5' and 'KUS-10'), was examined in response to photoperiod and temperature. Seeds were sown on 25 June and germinated at 30°C. After germination they were potted and grown in the phytotron at 20, 25 and 30°C under 8 and 16 h daylength until 30 September. In all the experiments, the plants were fed with rautrient solution containing N/P2Os/K20 ( 15:8:17 ) as required. All flowers ~ere removed. Tuberous root formation was defined as the formation of a localized region of visibly thickened adventitious roots.
Experiment
RESULTS
Growth of seedlings of both 'UPS-122' and 'UPS-45' was inhibited at a constant temperature of 15 °C. Shoot growth of both varieties was more vigorous under long than short days. Figure 1 shows the tuberous roots of'UPS-122' formed under short day at 20°C. One hundred percent tuberous root formation was observed in both varieties under short days at 20 and 25 °C, and at 30°C only 'UPS-45' formed tuberous roots at low percentage (Table 1 ). Tuberous root formation also occurred in both varieties under long days at 20°C, but not at 25 and 30°C. Experiment
1. ~
Fig. 1. Tuberous root development of'UPS-122' as affected by short days (right) and long days (left) at 20 ° C.
4
H. OKUBOET AL.
TABLE I Effect of photoperiod and temperature on tuberous root formation of~UPS - 122' and 'UPS-45' Temperature (°C)
15
Daylength (h)
16 8 16 8 16 8 16 8
20 25 30
'UPS-122'
'UPS-45"
% of plants with tuberous roots
No. of tuberous roots per plant
% of plants with tuberous roots
No. of tuberous roots per plant
0 0 37.5 100 0 100 0 0
0 0 3.0a 5.4a 0 4.8a 0 0
0 0 10 100 0 100 0 20
0 0 1.0a 1.6ab 0 2.3b 0 1.0a
Mean separation within columns by Duncan's multiple range test, 5% level. TABLE 2 Effect of temperature on tuberous root formation of'U PS-122' under long days Treatment
% of plants with tuberous roots
No. of tuberous roots per plant
20°C 20°C 20°C 20°C
for i ! weeks for 8 weeks and 25°C for 3 weeks for 4 weeks and 25°C for 7 weeks tbr 2 weeks and 25°C for 9 weeks
60 50 0 0
2.0abe i.6ab 0 0
25 ° C for I ! weeks 25'~C for 8 weeks and 20°C for 3 weeks 25°C for 4 weeks and 20°C for 7 weeks 25°C for 2 weeks and 20°C for 9 weeks
0 20 89 90
0 0.5a 2,9bc 4.1c
Mean separation by Duncan's multiple range test, 5% level.
The highest percentages of tuberous root formation were obtained when the plants were given the first 2 or 4 weeks at 25°C, and were then transferred to 20°C (Table 2). When the plants were grown at 25°C for the first 8 weeks, the following 3 weeks at 20°C had less effect on tuberous root formation. No tuberous roots were formed under 25 °C for I l weeks. The first 2 or 4 weeks at 20°C followed by 9 or 7 weeks at 25°C, respectively, had no e f f e ~ but half of the plants formed tuberous roots when given the first 8 weeks at 20 ° C. Experiment
2. - -
The percentage of tuberous root formation was high under short days at 20 and 25°C in 'UPS-99' and 'UPS-I 21', which are both photosensitive varieties for flowering (Table 3 ). Tuberous root formation was obE x , n e r i m e n t 3. - -
TUBEROUS ROOT FORMATION IN WINGED BEAN
5
TABLE 3 Effects of photoperiod and temperature on tuberous root formation of photo-sensitive and photoinsensitive varieties for flowering Temperature (°C)
20 25 30
Daylength (h)
16 8 16 8 16 8
Photo-sensitive for flowering
Photo-insensitive for flowering
'UPS-99'
"UPS- 121'
"KUS-5'
'KUS- I 0"
%t
NO. 2
%
No.
%
No.
%
No.
0 92 0 100 0 0
0 1.0 0 1.0 0 0
0 100 20 100 0 0
0 1.7 1.6 1.2 0 0
81 100 100 100 0 0
1.2 1.6 1.0 1.2 0 0
100 100 100 1O0 34 0
1.6 2.4 1.0 1.6 0.8 0
i% of plants with tuberous roots. ~No. of tuberous roots per plant. There were no significant differences on number of tuberous roots per plant in any treatment and variety by Duncan's multiple range test, 5% level.
Fig. 2. Tuberous roots o f ' K U S - 1 0 ' formed under !ong days at 20°C.
6
H. OKUBO ET AL.
served not only under short days but also under long days at 20 and 25 °C in 'KUS-5' and 'KUS-10', which are piioto-insensitive varieties for flowering, although the number of tuberous roots formed under long days was less than that under short days but not statistically different. Figure 2 shows the tuberous roots of'KUS-10' formed under long days at 20 ° C. Tuberous root formation was alse observed at 30°C under short days in 'KUS-10'. DISCUSSION
Effects of daylength on tuberous root formation ~gree with those of a previous investigation (Wong, 1981 ), and indicate that winged bean is basically a short-day plant for tuberous root formation. Winged bean is one of several tropical tuberous root crops, which are short-d:~y plants for tuberous root formation. Tuberous root formation is also promoted by short clays in dahlia (Zimmerman and Hitchcock, 1929; Moser and Hess, 1968 ), and a photoperiod of about 12 h may be optimal for tuberous root growth in sweet potato (McDavid and Alamu, 1980 ) and in cassava (Bolhuis, 1966 ). The fact that tuberous root formation occurred under long days at 20°C suggests that low temperature may be also an inductive factor. Herath and Ormrod (1979) and Wong ( 1981 ) concluded that temperature is as important as photoperiod in controlling flowering in winged bean, but their conclusion seems to be restricted to flowering behavior only under inductive short days. No flowering occurred under long days irrespective of temperature. However, flowering of'UPS-99' under a 13 h daylength at 20 ° C but not at 25 and 30°C (Uemoto et ai., 1982) indicates that temperature can have a role in flowering. Wong ( 1981 ) reported that tuberous root formation in winged bean is highly influenced by photoperiod but that temperature did nut appear to affect it. He used the Malaysian selection, cultivar 'M14/4', whereas 'UPS' varieties were used here, and there may be varietal differences in the temperature response of tuberous root formation. Moser and Hess ( 1968 ) concluded that the short-day requirement for tuberous root formation in dahlia was not altered by low temperature. Our results indicate that the induction of tuberous root formation in winged bean is affected by relatively low temperature (20°C), and that the plants must first reach a certain age. This is like the response of flowering and induction of tuberous root formation to photoperiod in winged bean (Wong, 1981 ). The daylength requirement for tuberous root formation seems to parallel that for flowering; photo-sensitive lines for flowering are also photo-sensitive for tuberous root formation, and photo-insensitive lines for flowering are photo-insensitive for tuberous root formation. The ability of'KUS-I 0' to form tuberous root under short days at 30°C may be related to the fact that less
TUBEROUS ROOT FORMATION IN WINGED BEAN
7
flower or pod drop occurred during growth at high temperature in 'KUS' varieties than in others (S. Uemoto, unpublished data, 1983 ). Zimmerman and Hitchcock (1929) studied the effect ofdaylength on flowering and tuberous root formation in some varieties of dahlia. All varieties examined formed tuberous roots under short days. Flowering was independent, however, of tuberous root formation; some flowered and formed tuberous roots concurrently under short days, while some flowered independently ofdaylength. There are many varieties of dahlia that flower throughout the long days of summer, such as pompon types. In some species, the formation of storage organs such as bulbs, corms, tubers and tuberous roots is under the control of daylength. The photoreceptor for the perception of daylength is phytochrome, and the mechanism is probably very similar to that for the photoperiodic control of flowering (VincePrue, 1975, 1985 ). In flowering of winged bean, the photoperiodic response is a characteristic that is controlled by a few major genes and some modifying polygenes (Uemoto et al.. 1982 ). This may also be the case in tuberous root formation. The selection of photo-insensitive varieties of winged bean for flowering will also result in selection for tuberous root formation.
REFERENCES Boihuis, G.G., 1966. Influence of length of illumination period on root formation in cassava, Manihot utilissima Pohl. Neth. J. Agric. Sci., 14:251-254. Claydon, A., 1975. A review of the nutritional value of the winged bean Psophocarpus tetragonolobus (L.) DC. with special reference to Papua New Guinea. Sci. New Guinea, 3:103-114. Herath, H.M.W. and Ormrod, O.P., 1979. Effects of temperature and photoperiod on winged beans (Psophocarpus tetragonolobus (L.) D.C. ). Ann. Bot., 43: 729-736. Kahn, T.N., 1978. Variation, ecology and cultural practices of the winged bean. Proc. I st International Seminar on Winged Bean, Philippine Council for Agriculture and Resources Research, Los Banos, pp. 3-11. Masefield, G.B., 1973. Psophocarpus tetrag¢,nolobus- - a crop with a future? Field Crop Abstr., 26: 157-160. McDavid, C.R. and Alamu, S., 1980. Effect of daylength on the growth and development of whole plants and rooted leaves of sweet potato (Ipomer, hatatas). Trop. Agric. (Trinidad), 57:113-119. Moser, B.C. and Hess, C.E., 1968. The physiology of tuberous root development in dahlia. Proc. Am. Soc. Hortic. Sci., 93: 593-603. Poulter, N.H., 1982. Some characteristics of the roots of the winged bean [Psophocarpus tetragonolobus (L.) DC.]. J. Sci. Food Agric., 33:107-114. Uemoto, S., Fujieda, K., Nonaka, M. and Nakamote, Y., 1982. Effect~ ofphotoperiod and temperature on the raceme budding of winged beans (Psophocarpus tetragonolobus). Bull. Inst. Trop. Agric. Kyushu Univ., 5: 59--70. Vince-Prue, D., 1975. Photoperiodism in plants. McGraw-Hill, London, 444 pp. Vince-Prue, D., 1985. Photoperiod and hormones. In: R.P. Pharis and D.M. Reid (Editors), Encyclopedia of Plant Physiology New Series Vol. 11, Hormonal Regulation of Develop-
8
H. OKUBO ET AL.
ment Ill. Role of Environmental Factors. Springer-Verlag, Berlin/Heidelberg/New York/ Tokyo, pp. 308-364. Wong, K.C., 198 I. Environmental factors affecting the growth, flowering and tuberization in winged bean (Psophocarpus tetragono!obz4s (L.) D.C. ). Paper presented at the 2nd International Seminar of Winged Bean, Colombo. Zimmerman, P.W. and Hitchcock, A.E., 1929. Root formation and flowering of dahlia cuttings when subjected to different day lengths. Bot. Gaz., 87: l - l 3.
Effects of photoperiod and temperature on tuberous root formation in winged bean
( Psophocarpus tetragonolobus ) Hiroshi Okubo, Teruyuki Masunaga~, Hirotsugi Yamashita 2 and Shunpei Uemoto 3 Laboratory of Horticuhural Science, Faculty of Agriculture, Kyushu University, Fukuoka 812, Japan (Accepted I 1 July 1991 )
ABSTRACT Okubo, H., Masunaga, T., Yamashita, H. and Uemoto, S., 1992. Effects of photoperiod and temperature on tuberous root formation in winged bean (Psophocarpus tetragonolobus). Scientia Hortic., 49: 1-8. Effects of photoperiod and temperature on tuberous root formation in some winged bean varieties were investigated. Tuberous root formation was induced by short days. Relatively low temperature (20°C) also caused formation of tuberous root even under long days, but both lower (15°C) and higher temperatures (25°C) did not. Plants must reach a ce~ain age for tuberous root induction by temperature. The daylength requirement for tuberous root formation in photo-sensitive and insensitive varieties seems to closely parallel that for flowering. Keywords: photoperiod; Psophocarpus tetragonolobus; temperature; tuberous root; winged bean.
INTRODUCTION
Winged bean (Psophocarpus tetragor.olobus) has recently been recognized as a nutritious crop because its immature pods, mature seeds and leave.; are rich in protein (Masefield, 1973; Claydon, 1975 ). The tuberous roots of the crop are also reported to contain a higher percentage of protein on a dry weight basis than any other ti'opical root crop known, such as taro, yam, cassav~ and sweet potato (Claydon, 1975). Tuberous roots of winged bean are a highly prized food in some parts of Papua New Guinea and Burma where they are peeled, baked or boiled and then eaten as a snack (Poulter, 1982 ). t Present address: Ukiha Agricultural Extension Office, Yoshiimachi 839-13, Fukuoka Prefecture, Japan. 2present address: Kumamoto Prefecture Office, Kumamoto 862, Japan. ~Present address: Oita Junior College, Oita 870, Japan.
© 1992 Elsevier Science Publishers B.V. All rights reserved 0304-4238/92/$05.00
2
H. OKUBO ET AL.
Having originated in the tropical regions, winged bean is essentially a typical short-day plant for flower initiation (Kahn, 1978; Herath and Ormrod, 1979 ). For the purpose of producing young pods as a new vegetable in Japan, many efforts have been made in our laboratory to select photoperiod-insensitive varieties for flower induction. Several completely photo-insensitive varieties for summer pod production in open fields (KUS (Kyushu University Selections) varieties) were also produced (S. Uemoto, unpublished data, 1983). It has been reported that tuberous root formation was affected more by daylength than by temperature, and that short days are necessary to initiate tuberous root formation almost irrespective of the temperature (Wong, 1981 ). Wong ( 1981 ) also showed that, unlike the flowering response to photoperiod, tuberous root development continued irrespective of daylength once the stimulus was received. Greater dry matter accumulation was found to occur at a daylength of 14 h than at I l h (Herath and Ormrod, 1979 ). Since winged bean has been traditionally cultivated only within tropical or subtropical zones where daylength is short, there is little informatio, on the response of tuberous root formation to photoperiod, temperature or combination treatments. The present paper is concerned with the effects of photoperiod and temperature on tuberous root formation in some winged bean varieties. MATERIALS AND METHODS 1. ~ Two varietie:; of winged bean, cultivars 'UPS-122' and 'UPS45' (UPS, University of Papua New Guinea Selections) were used. Seeds were sown on 2 November and germinated at 30°C. Young seedlings were potted in sand and grown until the third trifoliate leaf stage ( 18 November) in a glasshouse. They were subjected to 15, 20, 25 and 30°C with relative humidity of 80 +_5% in the phytotron of the Biotron Institute, Kyushu University under short and long days. Short days (8 h) were provided by covering the growing plants from 17:00 h to 09:00 h of the following day. Long days were achieved by extending the daylength to 16 h with white fluorescent lamps. On 8 February, they were transferred into the glasshouse at a minimum temperature of 15 °C and daylength treatments were continued until the measurement of tuberous root formation on 20 February.
Experiment
Effects of temperature under long days ( 16 h ) were examined. Seeds of 'LIPS-!22' were germinated on 4 November and. grown to the third trifoliate leaf stage (20 November) at 25°C. After this initial period, the plants were potted and subjected to experimental conditions in the phytotron for an additional I I weeks as follows: (A) 20°C for I I weeks; (B) 20°C for 8 weeks then 25°C for 3 weeks; (C) 20°C for 4 weeks then 25°C for 7 weeks; (D) 20°C for 2 weeks then 25°C for 9 weeks; (E) 25°C for I l weeks; (F) 25°C for 8 weeks then 20°C for 3 weeks; (G) 25°C for 4 weeks Experiment
2. - -
TUBEROUS ROOT FORMATION IN WINGFD BEAN
3
then 20°C for 7 weeks; (H) 25°C for 2 weeks then 20°C for 9 weeks. Measurements were made on 7 February. 3. m Tuberous root formation in photo-sensitive (cultivars 'UPS99' and "UPS- 121') and photo-insensitive varieties for flowering (cultivars 'KUS-5' and 'KUS-10'), was examined in response to photoperiod and temperature. Seeds were sown on 25 June and germinated at 30°C. After germination they were potted and grown in the phytotron at 20, 25 and 30°C under 8 and 16 h daylength until 30 September. In all the experiments, the plants were fed with rautrient solution containing N/P2Os/K20 ( 15:8:17 ) as required. All flowers ~ere removed. Tuberous root formation was defined as the formation of a localized region of visibly thickened adventitious roots.
Experiment
RESULTS
Growth of seedlings of both 'UPS-122' and 'UPS-45' was inhibited at a constant temperature of 15 °C. Shoot growth of both varieties was more vigorous under long than short days. Figure 1 shows the tuberous roots of'UPS-122' formed under short day at 20°C. One hundred percent tuberous root formation was observed in both varieties under short days at 20 and 25 °C, and at 30°C only 'UPS-45' formed tuberous roots at low percentage (Table 1 ). Tuberous root formation also occurred in both varieties under long days at 20°C, but not at 25 and 30°C. Experiment
1. ~
Fig. 1. Tuberous root development of'UPS-122' as affected by short days (right) and long days (left) at 20 ° C.
4
H. OKUBOET AL.
TABLE I Effect of photoperiod and temperature on tuberous root formation of~UPS - 122' and 'UPS-45' Temperature (°C)
15
Daylength (h)
16 8 16 8 16 8 16 8
20 25 30
'UPS-122'
'UPS-45"
% of plants with tuberous roots
No. of tuberous roots per plant
% of plants with tuberous roots
No. of tuberous roots per plant
0 0 37.5 100 0 100 0 0
0 0 3.0a 5.4a 0 4.8a 0 0
0 0 10 100 0 100 0 20
0 0 1.0a 1.6ab 0 2.3b 0 1.0a
Mean separation within columns by Duncan's multiple range test, 5% level. TABLE 2 Effect of temperature on tuberous root formation of'U PS-122' under long days Treatment
% of plants with tuberous roots
No. of tuberous roots per plant
20°C 20°C 20°C 20°C
for i ! weeks for 8 weeks and 25°C for 3 weeks for 4 weeks and 25°C for 7 weeks tbr 2 weeks and 25°C for 9 weeks
60 50 0 0
2.0abe i.6ab 0 0
25 ° C for I ! weeks 25'~C for 8 weeks and 20°C for 3 weeks 25°C for 4 weeks and 20°C for 7 weeks 25°C for 2 weeks and 20°C for 9 weeks
0 20 89 90
0 0.5a 2,9bc 4.1c
Mean separation by Duncan's multiple range test, 5% level.
The highest percentages of tuberous root formation were obtained when the plants were given the first 2 or 4 weeks at 25°C, and were then transferred to 20°C (Table 2). When the plants were grown at 25°C for the first 8 weeks, the following 3 weeks at 20°C had less effect on tuberous root formation. No tuberous roots were formed under 25 °C for I l weeks. The first 2 or 4 weeks at 20°C followed by 9 or 7 weeks at 25°C, respectively, had no e f f e ~ but half of the plants formed tuberous roots when given the first 8 weeks at 20 ° C. Experiment
2. - -
The percentage of tuberous root formation was high under short days at 20 and 25°C in 'UPS-99' and 'UPS-I 21', which are both photosensitive varieties for flowering (Table 3 ). Tuberous root formation was obE x , n e r i m e n t 3. - -
TUBEROUS ROOT FORMATION IN WINGED BEAN
5
TABLE 3 Effects of photoperiod and temperature on tuberous root formation of photo-sensitive and photoinsensitive varieties for flowering Temperature (°C)
20 25 30
Daylength (h)
16 8 16 8 16 8
Photo-sensitive for flowering
Photo-insensitive for flowering
'UPS-99'
"UPS- 121'
"KUS-5'
'KUS- I 0"
%t
NO. 2
%
No.
%
No.
%
No.
0 92 0 100 0 0
0 1.0 0 1.0 0 0
0 100 20 100 0 0
0 1.7 1.6 1.2 0 0
81 100 100 100 0 0
1.2 1.6 1.0 1.2 0 0
100 100 100 1O0 34 0
1.6 2.4 1.0 1.6 0.8 0
i% of plants with tuberous roots. ~No. of tuberous roots per plant. There were no significant differences on number of tuberous roots per plant in any treatment and variety by Duncan's multiple range test, 5% level.
Fig. 2. Tuberous roots o f ' K U S - 1 0 ' formed under !ong days at 20°C.
6
H. OKUBO ET AL.
served not only under short days but also under long days at 20 and 25 °C in 'KUS-5' and 'KUS-10', which are piioto-insensitive varieties for flowering, although the number of tuberous roots formed under long days was less than that under short days but not statistically different. Figure 2 shows the tuberous roots of'KUS-10' formed under long days at 20 ° C. Tuberous root formation was alse observed at 30°C under short days in 'KUS-10'. DISCUSSION
Effects of daylength on tuberous root formation ~gree with those of a previous investigation (Wong, 1981 ), and indicate that winged bean is basically a short-day plant for tuberous root formation. Winged bean is one of several tropical tuberous root crops, which are short-d:~y plants for tuberous root formation. Tuberous root formation is also promoted by short clays in dahlia (Zimmerman and Hitchcock, 1929; Moser and Hess, 1968 ), and a photoperiod of about 12 h may be optimal for tuberous root growth in sweet potato (McDavid and Alamu, 1980 ) and in cassava (Bolhuis, 1966 ). The fact that tuberous root formation occurred under long days at 20°C suggests that low temperature may be also an inductive factor. Herath and Ormrod (1979) and Wong ( 1981 ) concluded that temperature is as important as photoperiod in controlling flowering in winged bean, but their conclusion seems to be restricted to flowering behavior only under inductive short days. No flowering occurred under long days irrespective of temperature. However, flowering of'UPS-99' under a 13 h daylength at 20 ° C but not at 25 and 30°C (Uemoto et ai., 1982) indicates that temperature can have a role in flowering. Wong ( 1981 ) reported that tuberous root formation in winged bean is highly influenced by photoperiod but that temperature did nut appear to affect it. He used the Malaysian selection, cultivar 'M14/4', whereas 'UPS' varieties were used here, and there may be varietal differences in the temperature response of tuberous root formation. Moser and Hess ( 1968 ) concluded that the short-day requirement for tuberous root formation in dahlia was not altered by low temperature. Our results indicate that the induction of tuberous root formation in winged bean is affected by relatively low temperature (20°C), and that the plants must first reach a certain age. This is like the response of flowering and induction of tuberous root formation to photoperiod in winged bean (Wong, 1981 ). The daylength requirement for tuberous root formation seems to parallel that for flowering; photo-sensitive lines for flowering are also photo-sensitive for tuberous root formation, and photo-insensitive lines for flowering are photo-insensitive for tuberous root formation. The ability of'KUS-I 0' to form tuberous root under short days at 30°C may be related to the fact that less
TUBEROUS ROOT FORMATION IN WINGED BEAN
7
flower or pod drop occurred during growth at high temperature in 'KUS' varieties than in others (S. Uemoto, unpublished data, 1983 ). Zimmerman and Hitchcock (1929) studied the effect ofdaylength on flowering and tuberous root formation in some varieties of dahlia. All varieties examined formed tuberous roots under short days. Flowering was independent, however, of tuberous root formation; some flowered and formed tuberous roots concurrently under short days, while some flowered independently ofdaylength. There are many varieties of dahlia that flower throughout the long days of summer, such as pompon types. In some species, the formation of storage organs such as bulbs, corms, tubers and tuberous roots is under the control of daylength. The photoreceptor for the perception of daylength is phytochrome, and the mechanism is probably very similar to that for the photoperiodic control of flowering (VincePrue, 1975, 1985 ). In flowering of winged bean, the photoperiodic response is a characteristic that is controlled by a few major genes and some modifying polygenes (Uemoto et al.. 1982 ). This may also be the case in tuberous root formation. The selection of photo-insensitive varieties of winged bean for flowering will also result in selection for tuberous root formation.
REFERENCES Boihuis, G.G., 1966. Influence of length of illumination period on root formation in cassava, Manihot utilissima Pohl. Neth. J. Agric. Sci., 14:251-254. Claydon, A., 1975. A review of the nutritional value of the winged bean Psophocarpus tetragonolobus (L.) DC. with special reference to Papua New Guinea. Sci. New Guinea, 3:103-114. Herath, H.M.W. and Ormrod, O.P., 1979. Effects of temperature and photoperiod on winged beans (Psophocarpus tetragonolobus (L.) D.C. ). Ann. Bot., 43: 729-736. Kahn, T.N., 1978. Variation, ecology and cultural practices of the winged bean. Proc. I st International Seminar on Winged Bean, Philippine Council for Agriculture and Resources Research, Los Banos, pp. 3-11. Masefield, G.B., 1973. Psophocarpus tetrag¢,nolobus- - a crop with a future? Field Crop Abstr., 26: 157-160. McDavid, C.R. and Alamu, S., 1980. Effect of daylength on the growth and development of whole plants and rooted leaves of sweet potato (Ipomer, hatatas). Trop. Agric. (Trinidad), 57:113-119. Moser, B.C. and Hess, C.E., 1968. The physiology of tuberous root development in dahlia. Proc. Am. Soc. Hortic. Sci., 93: 593-603. Poulter, N.H., 1982. Some characteristics of the roots of the winged bean [Psophocarpus tetragonolobus (L.) DC.]. J. Sci. Food Agric., 33:107-114. Uemoto, S., Fujieda, K., Nonaka, M. and Nakamote, Y., 1982. Effect~ ofphotoperiod and temperature on the raceme budding of winged beans (Psophocarpus tetragonolobus). Bull. Inst. Trop. Agric. Kyushu Univ., 5: 59--70. Vince-Prue, D., 1975. Photoperiodism in plants. McGraw-Hill, London, 444 pp. Vince-Prue, D., 1985. Photoperiod and hormones. In: R.P. Pharis and D.M. Reid (Editors), Encyclopedia of Plant Physiology New Series Vol. 11, Hormonal Regulation of Develop-
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ment Ill. Role of Environmental Factors. Springer-Verlag, Berlin/Heidelberg/New York/ Tokyo, pp. 308-364. Wong, K.C., 198 I. Environmental factors affecting the growth, flowering and tuberization in winged bean (Psophocarpus tetragono!obz4s (L.) D.C. ). Paper presented at the 2nd International Seminar of Winged Bean, Colombo. Zimmerman, P.W. and Hitchcock, A.E., 1929. Root formation and flowering of dahlia cuttings when subjected to different day lengths. Bot. Gaz., 87: l - l 3.