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Effect of shading on plant development, yield and fruit quality of sweet pepper grown under conditions of high temperature and radlation
Scientia Horticulturae, 29 (1986) 31--35
31
Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
EFFECT OF SHADING ON PLANT DEVELOPMENT, YIELD AND FRUIT QUALITY OF SWEET PEPPER GROWN UNDER CONDITIONS OF HIGH TEMPERATURE AND RADIATION
I. R Y L S K I and M. S P I G E L M A N Institute of Field and Garden Crops, Agricultural Research Organization, The Volcani Center, Bet Dagan (Israel) Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel,No. 1438-E, 1985 series (Accepted for publication 6 January 1986)
ABSTRACT Rylski, I. and Spigelman, M., 1986. Effect of shading on plant development, yield and fruit quality of sweet pepper grown under conditions of high temperature and radiation. Scientia Hortic., 29: 31--35. The effect of different levels of shading of sweet pepper under high solar radiation (> 600 cal cm -2 day -1) at 2 different spacings during the summer months in the northwestern Negev desert of Israel (31°N) was investigated. When light intensity was reduced, plant height, number of nodes and leaf size increased. However, shading inhibited the development of lateral shoots on the main stem of the plant below the first terminal flower. The changes in plant development due to shading affected fruit set, number of fruits per plant, fruit location on the plant, fruit development and yield. The lateral shoots which developed under high light intensity provided 25% of the total yield, whereas only a few fruits were picked from the lateral shoots of plants under low light intensity. The lowest number of fruits per plant was obtained under 47% shading at 5 plants m -2 density, under 47 and 26% shading at 6.7 plants m -~ density. Under shading, individual fruits were larger and had a thicker pericarp. Shading reduced sun-scald damage of the fruits from 36% in full sunlight to 3--4% under 26 and 47% shading. The highest yield of high-quality fruits was obtained with 12--26% shade. Keywords: fruit development; fruit quality; fruit set; shading; sun scald; sweet pepper.
INTRODUCTION The effect of light intensity on p e p p e r plant d e v e l o p m e n t has previously b e e n i n v e s t i g a t e d m a i n l y o n y o u n g p l a n t s , o r u n d e r r e l a t i v e l y l o w light intensity conditions, where additional lighting increased plant growth and y i e l d ( H o r i e t al., 1 9 6 8 ; Deli a n d T i e s s e n , 1 9 6 9 ; B e d d i n g , 1 9 7 1 ) . U n d e r high s o l a r r a d i a t i o n c o n d i t i o n s , s h a d i n g a t an e a r l y stage o f p l a n t d e v e l o p m e n t i n c r e a s e d cell d i v i s i o n a n d v o l u m e in leaves a n d w h o l e p l a n t d r y m a t t e r , a n d
0304-4238/86/$03.50
© 1986 Elsevier Science Publishers B.V.
32
also positively affected fruit growth and yield (Schoch, 1972). The objective of the present study, conducted under high solar radiation conditions, was to investigate sweet pepper plant development, in association with yield and fruit quality, as affected by shading throughout the growing season. MATERIALS AND METHODS
The effect of shading was investigated in the summer, under field conditions with natural light at Besor, in the northwestern Negev desert. Temperature and radiation data at Besot for the experimental period are given in Table I. Pepper plants cultivar 'Maor' were grown under a screen supported by an aluminium frame structure, 12 m wide, 138 m long and 2.5 m high. The length was divided into 16 plots, each 8 m in length. The long axis of the structure was oriented in the north--south direction. The flux density of the solar radiation was modified by covering the structure with polyethylene screens, except for 20 cm below the roof and 20 cm above the ground. This covering allowed free air movement in all directions, in order to minimize possible differences in air temperature under the various screens. Plots were distributed in the structure in four randomized split blocks. One half of the plots were planted with two double rows on 2.4-m-wide beds, five plants per m2; the other half was planted with three rows on 1.8-m-wide beds, 6.7 plants per m 2. In all plots the within-row spacing was 0.3 m. The screens were installed in June, 1 week after planting, to eliminate effects of the screens on plant establishment. Data on plant development were obtained by measurements of 12 60-dayold plants, grown at the 5 plants m -2 density, in all shading treatments. Plant height, number of flowering nodes, and number of lateral shoots with at least one flower that developed below the first terminal flower were recorded. On the same plants, the leaf area of the leaves between the 1st and 2nd flowering nodes, between the 2nd and 3rd nodes, between the 3rd and 4th nodes was measured with an Area-meter LI 3050 A. This way, all the leaves were included, from the first terminal flower to the fourth flowering node.
TABLE I Climatic data at Besor during the experimental season ( m o n t h l y means, as recorded by the Israel Meteorological Service)
Month
May June July
Temperature max. (°C) Mean
Extreme
Temperature min. (oc) Gobal Bright radiation sunshine M e a n Extreme (cal c m -2 day-') (h day-')
29.7 30.0 31.8
41.0 40.7 36.0
15.0 17.2 20.5
10.0 13.0 17.0
632 692 664
11.3 12.2 12.0
33 The fruits were picked when red-ripe, counted and weighed. Total, marketable and top-grade quality yield and sun-scald damage fruits were recorded. From each shading treatment, 200 marketable fruits were examined for fruit weight, length, diameter, pericarp thickness and the number of seeds. RESULTS AND DISCUSSION
Plant development records taken under different levels of shading showed that plant height, number of flower nodes and leaf size increased as light intensity decreased (Table II). The increase in plant height of shaded plants was a result of both internode elongation and node number. The apical growth was strongest under the lowest radiation. However, shading reduced the development of lateral shoots on the main stem of the plants. In shaded plants, the leaves were bigger than those in full light. Under the lowest lightintensity conditions, the total leaf area measured between the first and the fourth flower node was a b o u t 60% greater than that on plants grown in full light. T A B L E II S w e e t p e p p e r p l a n t d e v e l o p m e n t as a f f e c t e d b y various levels o f s h a d i n g ( 6 0 days a f t e r planting) ~ Shading 2 (%)
0 12 26 47
Plant height (cm)
29.9c 30.3 c 35.9b 40.2 a
Number of flower nodes
5.6b 5.6 b 6.0ab 6.2 a
N u m b e r of side s h o o t s 3
6.2a 5.5 a b 5.0b 3.7 c
T o t a l leaf area ( c m 2) at f l o w e r n o d e No. ( f r o m t h e base) 2
3
4
96b 129 a 136a 142 a
179c 210 bc 237ab 285 a
241c 2 9 6 bc 321b 399 a
Values f o l l o w e d b y d i f f e r e n t letters differ significantly at P = 0.05. 2 M e a n daily s h a d i n g c a l c u l a t e d for 21 J u n e , at l a t i t u d e 31°N. 3 S h o o t s b e l o w first f l o w e r i n g n o d e .
Vegetative growth influenced fruit set and fruit growth. In all treatments fruit set was concentrated, but under high light-intensity conditions, the fruits were obtained as a result of fruit set at the lst--3rd flowering nodes, and on the lateral branches. The latter gave 25% of the total yield in this treatment, whereas only a few fruits were picked from the lateral branches of plants under low light intensity. The lowest number of fruits per plant was obtained under 47% shading at 5 plants m -2 density, and under 47 and 26% shading at the 6.7 plants m -2 density (Table III). However, decreased fruit set caused by shading did not lower the yield level, as expressed by weight per unit area. Under shading, individual fruits weighed more, were
34 T A B L E III Sweet pepper yield and fruit quality at two planting densities as affected by various levels of shading I Shading 2 (%)
N u m b e r of fruits per plant
Mean fruit wt. (g)
Yield (kg m -s)
% of total yield
Total
Marketable
Top-grade quality
Sun-scalded fruit
5 plants m -~ 0 8.1 a 12 8.5 a 26 7.7 a 47 5.4 b Mean 7.4 A
86 97 108 111 100
c b a a A
3.1 3.9 4.1 3.0 3.5
b a a b B
2.0 3.1 3.7 2.9 2.9
c b a b B
57 63 79 77 69
c b a a A
36 20 8 2 16
a b c d A
6,7 plants m -2 0 7.1 ab 12 7.9 a 26 6.4 b 47 4.8 c Mean 6.5 B
94 104 112 113 106
b a a a A
4.2 5.3 4.7 3.6 4.4
bc a ab c A
2.7 4.4 4.6 3.5 3.8
c a a b A
58 72 82 74 71
c b a b A
36 16 4 3 15
a b c c A
Values followed by different letters differ significantly at P = 0.05 (lower case) and P = 0.01 (capital letters), between densities. 2 Mean daily shading calculated for 21 J u n e at latitude 31°N. T A B L E IV Sweet pepper fruit d e v e l o p m e n t as affected by various levels of shading (200 marketable fruits per t r e a t m e n t ) ~ Shading s (%)
N u m b e r of seeds per fruit
Fruit with > 400 seeds (%)
Fruit weight (g)
Fruit length (cm)
Fruit diameter (cm)
Pericarp thickness (mm)
0 12 26 47
244 287 302 304
10.8 21.3 24.1 28.7
104 111 123 129
72.4 73.0 74.7 78.5
66.4 67.4 70.1 70.3
41.7 43.3 43.4 47.5
b a a a
d c b a
c c b a
c b a a
c b b a
1 Values followed by different letters differ significantly at P = 0.05. Mean daily shading calculated for 21 J u n e at a latitude of 31°N.
larger
in both length and diameter, and the pericarp was thicker (Table IV). The highest total yield at both planting densities was harvested from 12 and 26% shaded plots, which also gave highest marketable yield at 6.7 plants m -2 p l a n t e d , w h i l e 2 6 % s h a d i n g g a v e t h e h i g h e s t m a r k e t a b l e yield at 5 p l a n t s m -2. A t t h e h i g h e r p l a n t d e n s i t y , f e w e r f r u i t s w e r e s e t p e r p l a n t , b u t b o t h t o t a l a n d m a r k e t a b l e y i e l d in t h i s t r e a t m e n t w e r e h i g h e r . N o i n t e r a c t i o n was found between plant density and light intensity.
35
Yield level was controlled by fruit set and fruit growth. It seems that the fruit size was affected by plant development, mainly leaf size (Schoch, 1972) and seed number per fruit (Rylski, 1973). In shaded plants, there were approximately 20% more seeds per fruit and 29% fruits with more than 400 seeds, in comparison with 11% of such fruits developed on plants grown in full light (Table IV). In addition, plants grown in full light developed many side branches on the main shoot below the first terminal flower, which caused a change in plant habitus. The lower side branches on the main shoot bent under the fruit weight, thus opening the plant canopy and exposing it to high radiation. This effect increased sun scald, causing damage of 36% of the fruit, a low percentage of top-grade fruits, and a low marketable yield. The differences in the number of side branches and their development between shaded plants and those grown in full light can be explained by the differences in their apical growth. In the shaded plants the apical growth was strong, and this prevented side-shoot sprouting and development (Rylski and Halevy, 1972). The response of pepper plants to shading will probably vary in different geographical areas, seasons and cultivars, and from different agricultural practices such as planting density, irrigation, fertilization, and other factors. In the present experiment, conducted under high light intensity (> 600 cal cm-2 day-~) with 'Maor' (blocky California type), the highest yield of topquality fruit was obtained when the light intensity was decreased by 12-26% shading, even when the fruit-set percentage was lower. Similar results were obtained with tomatoes, which were sensitive to low light intensity as regards flower and fruit malformation, but which gave the highest yield (both total and marketable) when grown under 25% shade (Sagi, 1979).
REFERENCES Bedding, A.J., 1971. Supplementary illumination -- an economically sound proposition. Grower, 76: 530--534. Deli, Y. and Tiessen, H., 1969. Interaction of temperature and light intensity on flowering of Capsicum frutescens vat. grossum cv. 'California Wonder'. J. Am. Soc. Hortic. Sci., 94: 349--351. Hod, Y., Tatsumi, M. and Shiraishi, K., 1968. Studies on the growth of vegetables in relation to light conditions. II. The effects of prolonged illumination on the growth of vegetables. Hiratsuka, Jpn. Hortic. Res. Stn. Bull., 7 : 1 7 3 - - 1 8 5 (in Japanese with English summary). Rylski, I., 1973. Effect of night temperature on shape and size of sweet pepper (Capsicum annuum L.). J. Am. Soc. Hortic. Sci., 98: 149--152. Rylski, I. and Halevy, A.H., 1972. Factors controlling the readiness to flower of buds along the main axis of pepper (Capsicum annuum L.). J. Am. Soc. Hortic. Sci., 97: 309--312. Sagi, A., 1979. Influence of solar radiation intensities on flowering, fruit set and fruit development in tomatoes. M.S. Thesis, The Hebrew University of Jerusalem, Faculty of Agriculture, Rehovot, Israel, 72 pp. (in Hebrew with English summary). Schoch, P.G., 1972. Effects of shading on structural characteristics of the leaf and yield of fruit in Capsicum annuum L. J. Am. Soc. Hortic. Sci., 97 : 461--464.
31
Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
EFFECT OF SHADING ON PLANT DEVELOPMENT, YIELD AND FRUIT QUALITY OF SWEET PEPPER GROWN UNDER CONDITIONS OF HIGH TEMPERATURE AND RADIATION
I. R Y L S K I and M. S P I G E L M A N Institute of Field and Garden Crops, Agricultural Research Organization, The Volcani Center, Bet Dagan (Israel) Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel,No. 1438-E, 1985 series (Accepted for publication 6 January 1986)
ABSTRACT Rylski, I. and Spigelman, M., 1986. Effect of shading on plant development, yield and fruit quality of sweet pepper grown under conditions of high temperature and radiation. Scientia Hortic., 29: 31--35. The effect of different levels of shading of sweet pepper under high solar radiation (> 600 cal cm -2 day -1) at 2 different spacings during the summer months in the northwestern Negev desert of Israel (31°N) was investigated. When light intensity was reduced, plant height, number of nodes and leaf size increased. However, shading inhibited the development of lateral shoots on the main stem of the plant below the first terminal flower. The changes in plant development due to shading affected fruit set, number of fruits per plant, fruit location on the plant, fruit development and yield. The lateral shoots which developed under high light intensity provided 25% of the total yield, whereas only a few fruits were picked from the lateral shoots of plants under low light intensity. The lowest number of fruits per plant was obtained under 47% shading at 5 plants m -2 density, under 47 and 26% shading at 6.7 plants m -~ density. Under shading, individual fruits were larger and had a thicker pericarp. Shading reduced sun-scald damage of the fruits from 36% in full sunlight to 3--4% under 26 and 47% shading. The highest yield of high-quality fruits was obtained with 12--26% shade. Keywords: fruit development; fruit quality; fruit set; shading; sun scald; sweet pepper.
INTRODUCTION The effect of light intensity on p e p p e r plant d e v e l o p m e n t has previously b e e n i n v e s t i g a t e d m a i n l y o n y o u n g p l a n t s , o r u n d e r r e l a t i v e l y l o w light intensity conditions, where additional lighting increased plant growth and y i e l d ( H o r i e t al., 1 9 6 8 ; Deli a n d T i e s s e n , 1 9 6 9 ; B e d d i n g , 1 9 7 1 ) . U n d e r high s o l a r r a d i a t i o n c o n d i t i o n s , s h a d i n g a t an e a r l y stage o f p l a n t d e v e l o p m e n t i n c r e a s e d cell d i v i s i o n a n d v o l u m e in leaves a n d w h o l e p l a n t d r y m a t t e r , a n d
0304-4238/86/$03.50
© 1986 Elsevier Science Publishers B.V.
32
also positively affected fruit growth and yield (Schoch, 1972). The objective of the present study, conducted under high solar radiation conditions, was to investigate sweet pepper plant development, in association with yield and fruit quality, as affected by shading throughout the growing season. MATERIALS AND METHODS
The effect of shading was investigated in the summer, under field conditions with natural light at Besor, in the northwestern Negev desert. Temperature and radiation data at Besot for the experimental period are given in Table I. Pepper plants cultivar 'Maor' were grown under a screen supported by an aluminium frame structure, 12 m wide, 138 m long and 2.5 m high. The length was divided into 16 plots, each 8 m in length. The long axis of the structure was oriented in the north--south direction. The flux density of the solar radiation was modified by covering the structure with polyethylene screens, except for 20 cm below the roof and 20 cm above the ground. This covering allowed free air movement in all directions, in order to minimize possible differences in air temperature under the various screens. Plots were distributed in the structure in four randomized split blocks. One half of the plots were planted with two double rows on 2.4-m-wide beds, five plants per m2; the other half was planted with three rows on 1.8-m-wide beds, 6.7 plants per m 2. In all plots the within-row spacing was 0.3 m. The screens were installed in June, 1 week after planting, to eliminate effects of the screens on plant establishment. Data on plant development were obtained by measurements of 12 60-dayold plants, grown at the 5 plants m -2 density, in all shading treatments. Plant height, number of flowering nodes, and number of lateral shoots with at least one flower that developed below the first terminal flower were recorded. On the same plants, the leaf area of the leaves between the 1st and 2nd flowering nodes, between the 2nd and 3rd nodes, between the 3rd and 4th nodes was measured with an Area-meter LI 3050 A. This way, all the leaves were included, from the first terminal flower to the fourth flowering node.
TABLE I Climatic data at Besor during the experimental season ( m o n t h l y means, as recorded by the Israel Meteorological Service)
Month
May June July
Temperature max. (°C) Mean
Extreme
Temperature min. (oc) Gobal Bright radiation sunshine M e a n Extreme (cal c m -2 day-') (h day-')
29.7 30.0 31.8
41.0 40.7 36.0
15.0 17.2 20.5
10.0 13.0 17.0
632 692 664
11.3 12.2 12.0
33 The fruits were picked when red-ripe, counted and weighed. Total, marketable and top-grade quality yield and sun-scald damage fruits were recorded. From each shading treatment, 200 marketable fruits were examined for fruit weight, length, diameter, pericarp thickness and the number of seeds. RESULTS AND DISCUSSION
Plant development records taken under different levels of shading showed that plant height, number of flower nodes and leaf size increased as light intensity decreased (Table II). The increase in plant height of shaded plants was a result of both internode elongation and node number. The apical growth was strongest under the lowest radiation. However, shading reduced the development of lateral shoots on the main stem of the plants. In shaded plants, the leaves were bigger than those in full light. Under the lowest lightintensity conditions, the total leaf area measured between the first and the fourth flower node was a b o u t 60% greater than that on plants grown in full light. T A B L E II S w e e t p e p p e r p l a n t d e v e l o p m e n t as a f f e c t e d b y various levels o f s h a d i n g ( 6 0 days a f t e r planting) ~ Shading 2 (%)
0 12 26 47
Plant height (cm)
29.9c 30.3 c 35.9b 40.2 a
Number of flower nodes
5.6b 5.6 b 6.0ab 6.2 a
N u m b e r of side s h o o t s 3
6.2a 5.5 a b 5.0b 3.7 c
T o t a l leaf area ( c m 2) at f l o w e r n o d e No. ( f r o m t h e base) 2
3
4
96b 129 a 136a 142 a
179c 210 bc 237ab 285 a
241c 2 9 6 bc 321b 399 a
Values f o l l o w e d b y d i f f e r e n t letters differ significantly at P = 0.05. 2 M e a n daily s h a d i n g c a l c u l a t e d for 21 J u n e , at l a t i t u d e 31°N. 3 S h o o t s b e l o w first f l o w e r i n g n o d e .
Vegetative growth influenced fruit set and fruit growth. In all treatments fruit set was concentrated, but under high light-intensity conditions, the fruits were obtained as a result of fruit set at the lst--3rd flowering nodes, and on the lateral branches. The latter gave 25% of the total yield in this treatment, whereas only a few fruits were picked from the lateral branches of plants under low light intensity. The lowest number of fruits per plant was obtained under 47% shading at 5 plants m -2 density, and under 47 and 26% shading at the 6.7 plants m -2 density (Table III). However, decreased fruit set caused by shading did not lower the yield level, as expressed by weight per unit area. Under shading, individual fruits weighed more, were
34 T A B L E III Sweet pepper yield and fruit quality at two planting densities as affected by various levels of shading I Shading 2 (%)
N u m b e r of fruits per plant
Mean fruit wt. (g)
Yield (kg m -s)
% of total yield
Total
Marketable
Top-grade quality
Sun-scalded fruit
5 plants m -~ 0 8.1 a 12 8.5 a 26 7.7 a 47 5.4 b Mean 7.4 A
86 97 108 111 100
c b a a A
3.1 3.9 4.1 3.0 3.5
b a a b B
2.0 3.1 3.7 2.9 2.9
c b a b B
57 63 79 77 69
c b a a A
36 20 8 2 16
a b c d A
6,7 plants m -2 0 7.1 ab 12 7.9 a 26 6.4 b 47 4.8 c Mean 6.5 B
94 104 112 113 106
b a a a A
4.2 5.3 4.7 3.6 4.4
bc a ab c A
2.7 4.4 4.6 3.5 3.8
c a a b A
58 72 82 74 71
c b a b A
36 16 4 3 15
a b c c A
Values followed by different letters differ significantly at P = 0.05 (lower case) and P = 0.01 (capital letters), between densities. 2 Mean daily shading calculated for 21 J u n e at latitude 31°N. T A B L E IV Sweet pepper fruit d e v e l o p m e n t as affected by various levels of shading (200 marketable fruits per t r e a t m e n t ) ~ Shading s (%)
N u m b e r of seeds per fruit
Fruit with > 400 seeds (%)
Fruit weight (g)
Fruit length (cm)
Fruit diameter (cm)
Pericarp thickness (mm)
0 12 26 47
244 287 302 304
10.8 21.3 24.1 28.7
104 111 123 129
72.4 73.0 74.7 78.5
66.4 67.4 70.1 70.3
41.7 43.3 43.4 47.5
b a a a
d c b a
c c b a
c b a a
c b b a
1 Values followed by different letters differ significantly at P = 0.05. Mean daily shading calculated for 21 J u n e at a latitude of 31°N.
larger
in both length and diameter, and the pericarp was thicker (Table IV). The highest total yield at both planting densities was harvested from 12 and 26% shaded plots, which also gave highest marketable yield at 6.7 plants m -2 p l a n t e d , w h i l e 2 6 % s h a d i n g g a v e t h e h i g h e s t m a r k e t a b l e yield at 5 p l a n t s m -2. A t t h e h i g h e r p l a n t d e n s i t y , f e w e r f r u i t s w e r e s e t p e r p l a n t , b u t b o t h t o t a l a n d m a r k e t a b l e y i e l d in t h i s t r e a t m e n t w e r e h i g h e r . N o i n t e r a c t i o n was found between plant density and light intensity.
35
Yield level was controlled by fruit set and fruit growth. It seems that the fruit size was affected by plant development, mainly leaf size (Schoch, 1972) and seed number per fruit (Rylski, 1973). In shaded plants, there were approximately 20% more seeds per fruit and 29% fruits with more than 400 seeds, in comparison with 11% of such fruits developed on plants grown in full light (Table IV). In addition, plants grown in full light developed many side branches on the main shoot below the first terminal flower, which caused a change in plant habitus. The lower side branches on the main shoot bent under the fruit weight, thus opening the plant canopy and exposing it to high radiation. This effect increased sun scald, causing damage of 36% of the fruit, a low percentage of top-grade fruits, and a low marketable yield. The differences in the number of side branches and their development between shaded plants and those grown in full light can be explained by the differences in their apical growth. In the shaded plants the apical growth was strong, and this prevented side-shoot sprouting and development (Rylski and Halevy, 1972). The response of pepper plants to shading will probably vary in different geographical areas, seasons and cultivars, and from different agricultural practices such as planting density, irrigation, fertilization, and other factors. In the present experiment, conducted under high light intensity (> 600 cal cm-2 day-~) with 'Maor' (blocky California type), the highest yield of topquality fruit was obtained when the light intensity was decreased by 12-26% shading, even when the fruit-set percentage was lower. Similar results were obtained with tomatoes, which were sensitive to low light intensity as regards flower and fruit malformation, but which gave the highest yield (both total and marketable) when grown under 25% shade (Sagi, 1979).
REFERENCES Bedding, A.J., 1971. Supplementary illumination -- an economically sound proposition. Grower, 76: 530--534. Deli, Y. and Tiessen, H., 1969. Interaction of temperature and light intensity on flowering of Capsicum frutescens vat. grossum cv. 'California Wonder'. J. Am. Soc. Hortic. Sci., 94: 349--351. Hod, Y., Tatsumi, M. and Shiraishi, K., 1968. Studies on the growth of vegetables in relation to light conditions. II. The effects of prolonged illumination on the growth of vegetables. Hiratsuka, Jpn. Hortic. Res. Stn. Bull., 7 : 1 7 3 - - 1 8 5 (in Japanese with English summary). Rylski, I., 1973. Effect of night temperature on shape and size of sweet pepper (Capsicum annuum L.). J. Am. Soc. Hortic. Sci., 98: 149--152. Rylski, I. and Halevy, A.H., 1972. Factors controlling the readiness to flower of buds along the main axis of pepper (Capsicum annuum L.). J. Am. Soc. Hortic. Sci., 97: 309--312. Sagi, A., 1979. Influence of solar radiation intensities on flowering, fruit set and fruit development in tomatoes. M.S. Thesis, The Hebrew University of Jerusalem, Faculty of Agriculture, Rehovot, Israel, 72 pp. (in Hebrew with English summary). Schoch, P.G., 1972. Effects of shading on structural characteristics of the leaf and yield of fruit in Capsicum annuum L. J. Am. Soc. Hortic. Sci., 97 : 461--464.