Environ. Control Biol., 52 (4), 227231, 2014
DOI: 10.2525/ecb.52.227
Original Paper
Effects of Shading on Growth and Photosynthetic Potential of
Greengram (Vigna radiata (L.) Wilczek) Cultivars
Takuya ARAKI1, Thay Thay OO2 and Fumitake KUBOTA3
1
Faculty of Agriculture, Ehime University, Matsuyama, Ehime 7908566, Japan
2
Yezin Agricultural University, Naypyidaw, Myanmar
3
Faculty of Agriculture, Kyushu University, Fukuoka 8128581, Japan
(Received May 24, 2014; Accepted August 12, 2014)
The effects of shading on growth and photosynthetic potential was analyzed with 8 cultivars with greengram (Vigna
radiata (L.) Wilczek). Plants grown in 5 L pots were subjected to 2-week shading treatment and after 2-week recovery by
removing a black-cheese cloth. Photosynthetic potential was evaluated by electron transport rate sealed on the both leaf surfaces by vaseline, which is close relationship to gross photosynthetic rate because CO2 released by the reaction of
photorespiration is recycled by stroma in chloroplast. Shading treatment reduced total dry weight of all cultivars. In particular, significant reduction in total dry weight was found in Nyangoo, Magwe and VC. Leaf specific area under shading treatment showed increment tendency and remarkable increase in this parameter was found in Nyangoo and VC, which cultivars
decreased total dry weight under shading, indicating that shading treatment lead to thin of the leaf thickness. The ratio of
plant height to diameter of stem was significantly decreased in R-288-8, Kanti and Yezin-5 by shading, indicating the restriction of succulent growth under shading condition and these cultivars are superior in lodging resistance to other cultivars.
Photosynthetic rate as evaluated by electron transport rate sealed by vaseline was decreased by shading treatment. The extent of decrease in photosynthetic potential was found cultivaral difference. According to these results, Kanti is capable of
applicable to the highest in resistance to shading and its recovery.
Keywords : electron transport rate, greengram, gross photosynthetic rate, photochemical system II, shading
INTRODUCTION
Light is an indispensable resource for plant growth because the light energy supplied from the sun is the basic
factor that regulates growth rate, organ development or
structure, function and behavior. The adaptation and acclimation to light environment is also critical to the plant survival and production efficiency in any ecosystem.
In particular, photosynthetic active radiation is the
major factor regulating photosynthesis and other physiological processes in plants, and hence the dry matter production and yield depend on photosynthetic active radiation
to a great extent (Rao and Mitra, 1988). In general, plants
grown in high light intensity and adapted to this condition
have been known to reduce the photosynthetic rate under
the shading condition. But if we can select a cultivar that
performs a stable photosynthesis under different light intensities, it will be a greater advantage to get high and stable
productivity under the natural environments.
Islam (1993) reported that Vigna radiata was greatly
affected by shading, and the total dry weight per plant decreased with an increase in shading ratio, and this trend
continued till the maturity stage. The low economic yield
of greengram in intercropping conditions is largely attributed to the less solar energy supply by shading during the
entire life cycle. The cultivation of greengram character-
ized by having an early maturity is allowed to be successfully grown before and after rice cropping, or intercropping
with sugarcane (Pookpakdi, 1978). However, in the summer season, the irradiance fluctuation frequently occurs,
and it may cause the yield instability for greengram species
(Karim et al., 2003). The resistance to low light intensity
or shading is important factor for greengram cultivars
grown under the agro-forestry cropping system and
intercropped with such a tall plant as sugarcane plants.
Although numerous studies have been carried out on
photosynthetic light responses in many crops, yet the effects of irradiance intensities on the photosynthetic apparatus of carbon assimilation and photochemical systems in a
leaf have not been sufficiently studied, especially in tropical grain legumes (Karim et al., 2003). The accumulation
of knowledge on the shading response or adaptation, and
mechanisms of shading resistance is important as the foundation of improving and stabilizing the yield of leguminous
crops grown in Myanmar.
Many of the smallholders farming system in Myanmar
were so far characterized by variable seasonal rainfall and
poor soil fertility with minimal external inputs of nitrogen
and phosphorous. This results in reducing crop yields to
extremely low levels. However, recently, the efforts to improve soil fertility have been begun introducing leguminous
species into the farming systems of many rural communities. The nitrogen benefit from legumes in intercropping
Corresponding author : Takuya Araki, fax: 81
89946
9526,
e-mail : araki@agr.ehime-u.ac.jp
Vol. 52, No. 4 (2014)
T. ARAKI ET AL.
systems is depending on the symbiotic activity. The importance of legume variety in nitrogen nutrition in
intercropping systems in Myanmar not yet been sufficiently
documented.
In the intercropping combination with tall and short
species, the amount of light that is received by short species
such as greengram is greatly influenced by the plant population density of the taller partner crops. Under such circumstances, shade-resistant legumes become valuable to
get higher yield. Of the legume crops grown in Myanmar,
greengram is a promising grain legume that given much attention from farmers for its high price and short growth duration. Thus, the successful introduction of this legume
species is expected to bring a greater advantage from the
intercropping system.
In order to raise and stabilize the yield of greengram
in Myanmar, various technological improvements are necessary for the intercropping and cultivar breeding.
However, very few reports are available on the effect of
shading on growth and photosynthetic activity in
greengram. It is an important factor to search greengram
cultivars that have the ability to tolerate partial shading for
intercropping with sugarcane and pigeon pea. However, refined techniques for evaluating shade tolerance have not yet
developed in Myanmar. By identifying genotypic differences for resistance to shading condition, to obtain new information which is indispensable for the improvement of
cropping system unique in Myanmar will be expected.
In many studies, photosynthetic rate measured with a
leaf of full open stomata is evaluated as a potential standard
of photosynthetic activity of the leaf. The measurement of
photosynthetic is a time taking operation because it is necessary to keep the stomata at a sufficient openness, and
hence, measurements of many leaves are difficult (Kubota
et al., 1991). Thus, photosynthetic measurements under
stomatal resistance free conditions may indicate the potentiality of crop for photosynthesis. In this study, the photosynthetic activities of greengram cultivars were accurately
and quickly estimated from ETR of sealed leaves according
to the method described by Haimeirong et al. (2002). The
objective of this study is to compare the cultivar features in
growth responses and electron transport rate under shading
treatment for developing the shade-resistant genotype.
MATERIALS AND METHODS
Plant materials and treatment
The experiment was conducted during August to
September, 2006 at Kyushu University, Japan, using eight
greengram cultivars: two landraces (cvs. Magwe,
Nyaungoo) are from China, six Myanmar promising
cultivars (cvs. Yezin-4, Daumo, R288-8, Kanti, Yezin-5
and VC 1973A) are released from Central Agricultural
Research Institute in Myanmar.
The pre-germinated seeds were sown in a 5 L pot
filled with sandy loam soil. Then, the young shoots were
thinned to one plant per pot for each cultivar after germination. The plants were grown outdoors under natural light
conditions for 30 days after sowing. The experiments were
designed with four replications. The pots were divided into
two groups. One group was continuously grown under the
natural light condition, control, and the other group was
subjected to the low light condition, shading. The shading
treatment was conducted at 30 days after sowing and was
divided into two stages, 2- week shading and 2-week recovery. Shading was carried out by placing pots under the
frames covered with a black cheese-cloth to get 60% of full
sunlight. During the recovery stage, the black cheese-cloth
was removed and then the pots were returned back under
natural light for two weeks.
Measurements of growth parameters and electron
transport rate
Four plants for each treatment and cultivars were harvested before and after 2 weeks shading, and were measured leaf area per plant with an automatic area meter
(Model AAM 8, Hayashi Denko, Japan). The plants harvested were dried at 80°C for 3 days and were measured
dry matter weight per plant. Chlorophyll degree of a leaf
is an index determined as SPAD value by the chlorophyll
meter (SPAD-502, Konica-Minolta, Japan), leaf area per
plant, specific leaf area (SLA), plant height and diameter
ratio under the control and shaded conditions were measured before and after the shading.
To observe the relationship between gross photosynthetic rate under 2% O2 level (Pg 2%) and electron
transport rate sealed on both leaf surfaces with vaseline
ETRvase), the measurement of photosynthetic rate was
conducted at 390 mol mol1 of CO2 concentration, 2% O2
level and photosynthetic photon flux densitiy (PPFD)
range from 200 to 700 mol m2 s1 . The temperature,
relative humidity and air flow rate were similar as described in Araki et al. (2014). The calculation equations for
ETR and Pg were the same as those described in Araki et
al. (2012).
In this experiment, the uppermost fully expanded
leaves were used for the determination of ETR of sealed
leaf and measured at two weeks after the shade and the recovery treatments. According to the method described by
Haimeirong et al. (2002), both surfaces of a leaf were
sealed with vaseline to stop the gas exchange between the
leaf and the atmosphere; hence the functions of both photosynthetic assimilation (CO2 uptake) and photorespiration
(CO2 release) are restricted within the leaf. After both
functional rates became equally balanced, electron transport rate of PSII in sealing leaves was monitored within 15
min with a fluorescence probe (PAM-2000, Walz,
Germany) at different PPFD levels (200, 300, 400, 500 and
600 mol m2 s1).
RESULTS AND DISCUSSION
The growth parameters, leaf, stem, root and total dry
weights under the control and shading conditions are shown
in Table 1. The accumulation of dry matter in crops frequently has a close relationship with LA. As a result of reduction in leaf dry weight under shading, total dry weight
was declined especially in cvs. Nyaungoo, Magwe and
VC. The reduction in stem and root dry weight was also
Environ. Control Biol.
SHADING EFFECT OF GREENGRAM
Table 1
Cultivaral difference in dry matter weight, leaf area, leaf specific area (SLA), the ratio of plant height to stem diameter (H/D)
and SPAD values of greengram cultivars under the control and shading conditions.
Dry matter weight
Cultivar
Treatment
Nyangoo
Control
Shade
Magwe
Control
Shade
Yezin-4
Control
Shade
Daumo
Control
Shade
R-288-8
Control
Shade
VC
Control
Shade
Kanti
Control
Shade
Yezin-5
Control
Shade
Leaf
(g plant1)
Stem
(g plant1)
3.8
2.5*
(67)
4.2
3.2ns
(76)
2.7
3.0ns
(111)
3.3
3.1ns
(94)
3.1
2.7ns
(87)
3.7
2.4*
(66)
2.7
3.0ns
(110)
3.3
3.1ns
(94)
2.1
1.8ns
(86)
2.6
2.5ns
(96)
2.7
2.2ns
(80)
2.1
2.3ns
(108)
2.0
2.1ns
(107)
2.2
1.9ns
(87)
2.7
2.6ns
(95)
2.1
2.0ns
(94)
Root
(g plant1)
1.1
0.5**
(44)
1.4
0.6***
(45)
1.1
0.8*
(73)
0.9
0.5**
(59)
1.0
0.9ns
(91)
1.1
0.5***
(42)
1.1
0.8ns
(73)
0.9
0.8ns
(90)
Leaf
Total
(g plant1)
area
(m2 plant1)
7.1
4.8*
(68)
8.3
6.4*
(77)
6.6
6.0ns
(92)
6.3
6.0ns
(94)
6.0
5.7ns
(94)
7.0
4.9**
(69)
6.6
6.4ns
(98)
6.4
6.0ns
(93)
16.1
14.2ns
(88)
15.0
12.5ns
(83)
14.6
13.6ns
(93)
12.1
13.1ns
(108)
12.3
12.1ns
(98)
13.0
13.6ns
(105)
15.9
19.8**
(125)
15.7
18.7ns
(119)
SLA
(cm2 g1)
423
561*
(133)
355
391ns
(110)
533
446ns
(84)
365
422ns
(115)
396
448ns
(113)
343
540**
(157)
580
650ns
(112)
473
600*
(127)
SPAD
H/D
3.9
6.2**
(158)
2.2
5.7***
(257)
3.5
5.2*
(148)
3.5
5.7**
(116)
4.9
5.6ns
(115)
2.5
5.7**
(227)
4.9
5.5ns
(114)
3.9
4.4ns
(112)
value
51.6
45.2ns
(88)
36.4
43.1ns
(118)
35.3
39.6ns
(112)
35.3
37.9ns
(107)
29.8
46.0**
(155)
33.9
33.7ns
(99)
47.1
49.4ns
(105)
44.2
49.2ns
(111)
Values in the parentheses are percent of shading treatment to control.
***, **, * and ns represent significant varietal differences and not significant at 0.1%, 1%, 5% level, respectively.
attributed to the reduction in total dry weight in these
cultivars. Particularly, remarkable reduction in root dry
weight was found in these cultivars, which corresponded to
42 to 45% as compared to that under control. Dry weight
of individual organs was not significantly different between
the control and shaded plants in cvs.Yezin-4, R288-8, Kanti
and Yezin-5 and their total dry weight ranged 92 to 98% of
the control. An additional feature of these cultivars was
greater leaf area under the shaded condition (Table 1).
Chlorophyll plays a key role in determining the light
absorption efficiency within a leaf. The chlorophyll degree
was influenced by shading. In all the cultivars except
cultivar VC and Nyaungoo, SPAD values were increased
during the shading treatment. In particular, the value of R288-8 under shading was significantly higher than those
under control. Many previous studies have been reported
that chlorophyll per unit leaf area increased under low
PPFD, which allowed increasing the absorption of photosynthetic active radiation and enhancing the assimilation
efficiency (Nilsen and Orcutt, 1996; Pearcy, 1998; Evans
and Pooter, 2001).
Kubota et al. (1992) stated that SLA was increased
with reduction in light intensity in both Vigna radiata and
Vigna mungo. The similar response was found in this experiment and SLA of all the cultivars except cv.Yezin-4,
was increased under shaded condition. According to the report of Björkman (1981), the shaded plant generally had a
higher SLA, because the leaves were characterized by having larger layer of palisade cells. This may cause the increase in the number of chlorophylls, by which the
photosynthetic rate per unit leaf area increased at low light
Vol. 52, No. 4 (2014)
intensity.
Greengram plants were elongated in height by shading, and this may reduce the physical strength of the plant,
and cause to increase lodgings (Kubota and Abdul, 1992).
The ratio of plant height to stem diameter (H/D) is used as
an indicator for lodging resistance. In this study, H/D ratio
differed between the cultivars, and the smallest values were
found in Yezin-5 (Table 1). This may suggest that this
cultivar have an increased lodging resistance because of
keeping a larger stem diameter under the shaded condition.
Net photosynthetic rate measured in the normal atmospheric air containing 21% O2 did not show a linear relationship with ETR in C3 leaves, because the functional strength
of photorespiration in leaves greatly affects the photosynthetic electron distribution (Krall et al., 1991). But
photorespiration restricted in the air of low O2 concentration, the sink for electrons transported from the
photosystem is limited to the CO2 assimilation function,
and hence a close relationship appears between the rate of
CO2 assimilation without photorespiration and ETR (Krall
and Edwards, 1992). Light responses in Pg2%, ETR2%
and ETRvase in a young active leaf were determined at a
leaf temperature of 30°C in the PPFD range from 200 to
700 mol m2 s1 . Pg2% increased with an increase in
PPFD, having a turning point at about 600 mol m2 s1
(Fig. 1A). Both ETR2% and ETRvase had an almost the
same response pattern to light intensity (Fig. 1B).
The relationship between Pg2% and ETRvase for three
greengram cultivars, Kanti, Yezin-4 and VC grown under
the control and shading are shown in Fig. 2. Under each
measurement condition, ETRvase showed a close positive
T. ARAKI ET AL.
Fig. 1
Fig. 2
Fig. 3
Changes in Pg 2% (A) and ETR 2% and ETRvase (B) of greengram under different light intensities.
Relationships between Pg 2% and ETRvase of three greengram cultivars (A) and control and shaded plants (B). **(P0.01)
Cultivaral difference of ETRvase under different light intensities in shaded and recovery plants of Nyangoo, Magwe, Yezin-4 and
Kanti under control, shade and recovery. A and B; Nyangoo, C and D; Yezin-4, E and F; Magwe, G and H; Kanti.
relationship with Pg2%. This means that Pg2% is accurately estimated from ETRvase, which can be used as an indicator to estimate the photosynthetic activity of greengram
cultivars in different PPFD. However, the accuracy of estimated values might gradually decrease as the PPFD increases beyond 600 mol m2 s1 , because energy
dissipation mechanisms such as the Mehler reaction may
become more activated (Oberhuber and Edwards, 1993).
By using ETRvase, the photosynthetic potential of different
cultivars was estimated within the PPFD range of 200
600
mol m2 s1 (Fig. 3).
ETRvase was determined under the control, shading
and recovery conditions to identify the varietal difference.
Four cultivars measured ETRvase in Fig.3 were selected
based on the results of the changes in total dry matter
weight to shading; cultivars of shading sensitive were
Nyangoo and Magwe, and those of resistance were Yezin-4
and Kanti. The varietal differences in ETRvase response
were observed in both shaded and recovery conditions.
Among the eight cultivars, ETRvase of a leaf was the highest in cvs. R288-8, Kanti and Yezin-5 and kept a stable
level in both shading and recovery conditions (data not
shown). However, ETRvase of cvs. Nyaungoo, Magwe,
Yezin-4, Daumo and VC may be greatly reduced under
shading and are very sensitive to light intensity fluctuation.
In cv. Magwe, a large reduction in ETRvase was observed in shaded plant but it recovery level was higher than
control plant after two weeks. On the other hand, a
Environ. Control Biol.
SHADING EFFECT OF GREENGRAM
significant reduction of total dry weight was also found in
this cultivar and it may be suggested that this cultivar may
sensitive to changing light environment. The reduction degree of ETRvase under shading condition showed same
level as that of total dry matter weight, which suggests that
the measurement of ETR sealed on both leaf surfaces with
vaseline is available to efficient screening for shading resistant cultivars.
Cultivars used in this study may be divided into some
groups according to the results. Firstly, we could divide the
response in total dry weight to shading into two groups,
that is, shading sensitive cultivars were Nyangoo, Magwe
and VC, and shading resistant ones were Yezin-4, Daumo,
R288-8, Kanti and Yezin-5. The former three cuiltivars
(shading sensitive) possessed common feature of shading
response, decrease in root dry weight and maintenance of
leaf area. However, this group was further divided into two
groups by the results of ETRvase. Magwe was sensitive in
ETRvase to shading, while the others, Nyangoo and VC
were non-sensetive. Latter five cultivars were further also
divided some groups based on growth and photosynthetic
features. Yezin-4 and Daumo showed the increment in
H/D with the maintenance of total dry matter weight under
shading condition, which feature could lead to lodging.
The residual three cultivars, R288-8, Kanti and Yezin-5
maintained H/D and photosynthetic feature. It seems that
the classification of cultivars based on dry matter production and photosynthetic features under shading conditions
may be available for application of genetic resources such
as breeding.
The results of the present study agree with the finding
of Haimeirong et al. (2002) and they were reported that
ETR of sealed leaf is able to be used as one of the photosynthetic indicators for leaves of C3 crops. Varietal difference of ETRvase response to shading was significantly
different in greengram cultivars and it seems to be possible
to improve shade-resistant cultivars for intercropping.
However, there is a little information about sealed leaf
method and further study is necessary to improve the resistant cultivars. The order of shading resistance from high to
low is as follow; cvs. Kanti, Yezin-5, R288-8, Yezin-4,
Daumo, VC, Magwe and Nyaungoo.
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