International Journal of Advancements in Research & Technology, Volume 2, Issue 7, July-2013
ISSN 2278-7763
419
Research article
Effect of Drought Stress on the Physiology and Yield of the Pakistani Wheat Germplasms
Ammar Ali1, Nawab Ali2, Nimat Ullah2, Farman Ullah2, Muhammad Adnan3, Zahoor Ahmed
Swati1
1
Institute of Biotechnology and Genetic Engineering, KPK Agriculture University, Peshawer,
Pakistan.
2
Department of Biotechnology and Genetic Engineering, Kohat University of Science &
Technology, Kohat, Pakistan.
3
Department of Botany, Kohat University of Science & Technology, Kohat, Pakistan.
Abstract
Drought stress is the most important factor and ever-growing problem limiting wheat (Triticum
aestivum L.) productivity worldwide. Wheat has physiological mechanisms that enable them to
adapt drought stress and this adaptation may vary among different genotypes. This study was
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performed to investigate the physiological responses in twelve wheat genotypes under drought
stress to identify drought tolerant genotypes. Stress was imposed by growing the genotypes
under four irrigation treatments (T1-380 ml, T2-190 ml, T3-126 ml and T4-95 ml) with each
fifteen days interval. The results revealed that electrolytes leakage was increased and other
physiological characteristics such as turgidity, relative leaf water contents and plant yield were
decreased during the increase in drought stress. The Tatara, ZAS-08, ZAS-42 and Ghaznavi-98
wheat genotypes exhibited the normal physiology and were considered as drought tolerant
genotypes. The drought tolerant genotypes specified in this study will be grown in rain fed
regions in order to improve the crop productivity and will be used in wheat breeding programs to
produce a stress tolerant genotype.
Key words: Triticum aestivum L, Physiological characteristics, Drought stress.
Introduction
Drought stress is one of the most important factors limiting plant growth and crops production
worldwide more than any other biotic or abiotic stress
[1, 2] .
It is an ever-growing problem that
harshly limits the crop production and result in important agricultural losses especially in arid
and semiarid areas
[3] .
The response of plants to drought stress is very complicated and they
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International Journal of Advancements in Research & Technology, Volume 2, Issue 7, July-2013
ISSN 2278-7763
420
manage stress through stress avoidance approaches that depends on genotype. Plants under stress
try to maintain their metabolic and structural capacity to improve their potential under that vary
stress through modified gene expression
[4] .
Wheat is the most important food crop cultivated
throughout the world and is the major source of proteins and calories which are almost 72% in an
average diet
[5] .
The current production of wheat is not sufficient to meet the demands of rapidly
growing population
[6] .
Although, breeders are working hard to improve wheat production,
however increasing wheat production in drought environments has been more complex to
achieve [7] .
Yield components and drought resistance are controlled at independent genetic loci, therefore the
identification of physiological traits that are responsible for drought tolerance should be
considered in the breeding programs
[8] .
Breeding efficiency could be improved if existing
physiological and morphological characteristics associated with yield components under an
environmental stress could be identified and used as selection criteria for traditional plant
breeding
[9] .
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According to the previous literatures, there is an association between physiological
responses and tolerance mechanisms of plants against drought stress i.e. membrane stability
high relative water content
[11]
pigment content stability
[12, 13] .
[10]
It was reported that drought
tolerant varieties in barley maintained higher relative leaf water content (RLWC) under drought
stress
[14] .
The breeding approaches to develop new or improved cultivars against stress need a
thorough understanding of the reactions of plant tissues or organs against the specific stress.
Thus, it is very important to identify those wheat genotypes which have the ability to tolerate
water stress. These stress tolerant genotypes can be used as reliable selection criteria in the
breeding programs.
The main objective of this work was to investigate physiological traits that are associated with
drought stress in wheat genotypes and to find out the drought tolerant genotypes that could be
used for yield improvement either by introducing these genotypes in rain fed area or using in
wheat breeding programs.
Materials and Methods
Physiological Studies
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International Journal of Advancements in Research & Technology, Volume 2, Issue 7, July-2013
ISSN 2278-7763
421
Twelve wheat genotypes were chosen (Table 1) and seeds were collected from Cimmyt spring
wheat nurseries and sown under four irrigation conditions (T1-380 ml, T2-190 ml, T3-126 ml
and T4-95 ml) with each 15 days interval. After maturation, investigations were made to see the
effect of drought stress on physiological characteristics and yield trait. Physiological
characteristics (Electrolytes leakage, Turgidity, Relative leaf water contents) were measured at
three different stages i.e. 60 days, 95 days and 120 days after sowing.
Electrolytes leakage
Electrolyte leakage into the solution was measured in 5 cm2 leaf discs after exposure to various
stress treatments with a Consort C-931 conductivity meter. The leaf discs were incubated in 5 ml
double distilled water for 3 hours at 25oC with shaking and initial conductivity of the solution
was determined. Final conductivity of the solution was determined after autoclaving the samples
(100% electrolyte leakage). The amount of electrolytes leakage attributable to different growth
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conditions and varieties were estimated as a percentage of initial to final conductivity.
Electrolytes leakage was calculated by using following formula.
Electrolytes leakage (%) =
Initial reading
× 100
Final reading
Turgidity:
Calculating turgidity, weighted fresh leaf (W1) and then kept the leaf in distilled water for 24
hours and weighted again (W2). Turgidity was calculated from the following formula.
Relative leaf water contents
Turgidity (gm) = W2 − W1
To measure RLWC, third leaf on main stem of each plant was used. The samples were surface
dried gently with tissue paper, wrapped in polythene bags. Soon after arriving laboratory, leaves
were weighed to measure fresh weight (FW). The samples were then soaked in large plastic tubs
containing distilled water and were left over night at room temperature. Next morning, these
leaves were carefully bloated with tissue paper prior to the determination of turgid weight (TW).
Leaf samples were then oven dried for 48 hours at 80oC. Dried leaves were then weighed to
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International Journal of Advancements in Research & Technology, Volume 2, Issue 7, July-2013
ISSN 2278-7763
422
record dry weight (DW). Leaf water contents were calculated by following formula (Schonfeld et
al., 1988)
[15] .
RLWC =
Yield Trait
Fresh wt − dry wt
× 100
Turgid wt − dry wt
Plants were randomly selected and hand threshed separately, average number of grains per spike
and yield per plant were recorded in grams.
Results and Discussion
Drought stress affect wheat productivity grown in dry and semidry areas and reduces plant yield
more than any other environmental stress
[16-19] .
In this study, significant differences were
reported in total yield per plant (YPP) and number of grains per spike (NGPS) amongst different
varieties in drought stress. Drought stress negatively affect yield per plant and number of grains
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per spike, as drought stress increased from T1 to T4, the YPP and NGPS decreased. Yield of
wheat varieties were considerably decreased when they were allowed to grow in minimum
annual rainfall regions [20] . Highest YPP mean values were reported in decreasing order as Tatara
(7.45 gm), Ghaznavi-98 (6.40 gm), Zas-08 (6.17 gm) and Zas-42 (5.70 gm) while lowest YPP
mean values in increasing order as 26-ESWYT-124 (1.52 gm), Zas-34 (2.10 gm) and 38IBWSN-1077 (2.47 gm) (Table 2). The result revealed that Tatara, Ghaznavi-98, Zas-08 and
Zas-42 genotypes has given optimal yield per plant at all the four treatments. Similarly numbers
of grains per spike were also reduced with an increase in drought stress. Highest NGPS mean
values were reported in decreasing order as Tatara (25.9), Zas-42 (25.7), SCO-27 (24.3) and Zas08 (22.8) and lowest values in increasing order as 38-IBWSN-1059 (14.12), 38-IBWSN-1077
(14.23) and Zas-70 (14.63) (Table 2). This is also supported by the findings of Chandler and
Singh (2008) that numbers of grains per spike were decreased under drought stress
[21] .
Water
stress has been reported to affect all the yield components, mainly the number of grains per spike
and the number of spikes per plant
[22, 23] .
It has been recognized that decrease in yield and yield
components under drought stress is a key concern in developing countries of the world
The biotic and abiotic stresses target the cell membrane of plants at first
[25] ;
drought tolerant plants maintain its integrity and stability in drought stress
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[24] .
however, the
[26] .
Membrane
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International Journal of Advancements in Research & Technology, Volume 2, Issue 7, July-2013
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423
stability is important for plant growth and development as it tolerate drought stress against
plants, since drought stress caused water loss from plant tissues which damage membrane
structure and function
[27]
due to electrolytes leakage. In this study, the lowest mean values of
electrolytes leakage were reported for Zas-42 (9.22%) after 60 days of sowing which increased
to 13.5% and 15.5% after 95 and 120 days of sowing, respectively (Table 2). It revealed that
when plants progressed toward maturity, the electrolytes leakage increased gradually with an
increase in drought stress. The treatments differences were statistically significant at all the three
stages. The genotypic differences and the interaction of the treatments with genotypes (varieties)
were also significant at all the three stages. Electrolytes leakages revealed positive correlations
with drought stress at all three stages as given in Table 2. As drought stress was increased from
T 1 to T 4 , it resulted in an increase in electrolytes leakage. The leakage was due to cell
membranes rupture which becomes more permeable
[28] .
After 120 days, the lowest electrolyte
leakage was reported for ZAS-42 (15.5%), ZAS-08 (16.4%) and Tatara (17.2%). These wheat
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genotypes were considered as drought avoidant genotypes as they avoided drought stress by
maintaining cell membrane stability, resulted in low electrolytes leakage and hence given high
yield. ZAS-70, ZAS-67 and 38-IBWSN-1077 wheat genotypes have the ability of tolerating low
electrolytes leakage to produce reasonable yield. The poor yield of 38-IBWSN-1052, SCO-27
and ZAS-34 wheat genotype under drought stress was related to their inability to avoid or
tolerate stress and high electrolytes leakage that was recorded 23.8%, 23.6% and 23.4%,
respectively. The results obtained from electrolyte leakage in this study revealed that membrane
integrity of drought tolerant genotypes was stable as compared to other genotypes; this
association of electrolyte leakage and drought tolerance was also reported by other researchers
[29, 2] .
The RLWC of the leaves indicate the water condition of the cells and have important correlation
with biotic and abiotic stress tolerance
[2] .
strong association with drought tolerance
It has been reported that, RLWC of the leaves has
[30]
and it is a good indicator of drought stress than
other physiological and biochemical characteristics of the crop plants
[31] .
Our results revealed
significant differences in RLWC among varieties at three different stages and showed that,
retention ability of the plant was significantly different at different growth stages. The maximum
RLWC was reported in Tatara 88.5%, 79.3% and 74.2% after 60, 95 and 120 days of sowing,
respectively (Table 2). It showed that RLWC was decreased with the age of plant because
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International Journal of Advancements in Research & Technology, Volume 2, Issue 7, July-2013
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424
RLWC was high after 60 days in comparison to 95 and 120 days of the sowing; this is also
supported by other literatures that as plants progressed toward maturity, water retention ability
decreased
[31] .
Similarly turgidity was also decreased with an increase in drought stress, because
weight of plants was high during 60 days in comparison to 95 and 120 days. This means that
plants were more turgid at 60 days as compared to 95 and 120 days of the sowing (Table 2). This
variation in RLWC of leaf and turgidity may be due to the ability of the tested wheat genotypes
to absorb more water from soil and also to control water loss through the stomata [32] . It may also
be due to the variation in the ability of wheat genotypes to avoid stress by maintaining tissue
turgor osmotically. Highest RLWC after 120 days of sowing was reported in Zas-42 (76.8%),
Tatara (74.2%), Zas-67 (72.4%) and Zas-08 (72.0%) as given in Table 2. This revealed that, at
all the three stages, ZAS-08, ZAS-42, Tatara, and ZAS-67 maintained higher RLWC and is
considered as drought tolerant genotypes while SCO-27, 26-ESWYT-124, 38-IBWSN-1059,
ZAS-34 have low RLWC and is considered moderate drought tolerant genotypes. These results
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were supported by Schonfeld et al., (1988) that RLWC may be used as a selection criterion in
breeding for improved drought resistance in wheat genotypes [15] .
This study allowed us to recognize those physiological characteristics that are associated with
drought stress, and screen out appropriate wheat genotypes, which can be introduced in arid area
to produce high yield in drought conditions and can be further used in breeding programs to
produce a stress tolerant genotype.
Conclusion
It has been concluded that wheat yield was significantly affected by physiological traits in
drought stress conditions. With respect to physiological and yield traits, Tatara, Ghaznavi-98,
ZAS-08 and ZAS-42 wheat genotypes revealed maximum drought tolerance and can be
successfully grown in arid region without much loss of wheat productivity. Thus, screening of
drought tolerant wheat genotypes on the basis of physiological traits may be a useful tool for the
breeding programs.
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Table 1: Pedigree of the twelve wheat genotypes including 10 wheat advance lines used in this
study.
Serial
Varieties/Adv.Lines Pedigree
Breeding History
ZAS-70(16)
CGSS99B00015F-099Y-099M-
Number
1
Inqalab90*2/Tukuru
099M-31Y-OB
2
ZAS-67(15)
Inqalab90*2/Tukuru
CGSS99B00015F-099Y-099M099Y-099M-29Y-0B
3
ZAS-42(21)
Inqalab90*2/Tukuru
CGSS99B00015F-099Y-099M099Y-099M-52Y-OB
4
ZAS-08(08)
PBW343*2/Kukum
CGSS99B00041F-099Y-099M099Y-099M-34Y-OB
5
ZAS-34
6
26-WSWYT-124
7
N.A
N.A
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38-IBWSN-1098
RABE/6/WRM/4/FN/3*TH/K58/2*N/3/AU5-
CMSS95YOA33OS-0100Y-51-
6869/5/w
IDH-OY-O5B-OY
CBRD/BCN
CMSS94B00007S-0300M-
0100Y-0100M-17Y-7M-0Y
8
38-IBWSN-1059
SW89.5277/BORL95/SKAUZ
CMSS93Y03172T-19Y-010M010Y-010M-3Y-3M-OY
9
38-IBWSN-1077
KUAZ/SITE
CMSS933B01068S-9Y-010M010Y-010M-2Y-OM-2KBYOKBY-OM
10
38-IBWSN-1052
CROC-1/AE.SQUARROSA
CMSS93Y01031S-13Y-5KBY-
(205)//KAUZ/3/ATTILA
010M-010Y-5M-OKBY-OM9KBY
11
Ghaznavi-98
Jup/BJy/S/Ures
N.A
12
Tatara
Jup/ALD/S//KLT/S/3VEE/S
N.A
N. A; Not Applicable
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Table 2. The physiological characteristics of twelve wheat genotypes in mean values for different
treatments and different stages (drought stress).
After
60
days
After
95
days
After
120
days
After
60
days
After
95
days
After
120
days
After
60
days
After
95
days
After
120
days
Mean
YPP
(gm)
Mean
values
values
SCO-27
76.775
66.775
64.125
0.039
0.036
0.023
18.233
20.475
23.600
24.367
3.378
38IBWSN1052
76.125
70.450
65.475
0.037
0.033
0.014
19.342
20.750
23.867
19.875
3.257
38IBWSN1077
74.550
70.225
67.300
0.023
0.020
0.013
17.300
19.675
24.575
14.233
2.475
38IBWSN1059
68.300
63.100
60.900
0.021
0.018
0.017
15.500
17.800
18.250
14.122
4.300
26ESWYT124
70.750
62.450
59.050
0.042
0.039
0.012
16.200
19.575
19.225
19.500
1.525
ZAS-08
72.350
74.942
72.075
0.054
0.051
0.045
10.575
12.875
16.425
22.807
6.175
ZAS-34
71.250
67.450
66.450
0.039
0.036
0.020
19.892
21.825
23.425
16.735
2.105
ZAS-42
73.992
81.223
76.800
0.054
0.050
0.052
09.225
13.500
15.500
25.752
5.700
ZAS-67
71.950
77.680
72.400
0.047
0.080
0.023
16.525
20.025
21.800
16.777
2.875
ZAS-70
79.500
74.913
69.950
0.054
0.049
0.029
17.483
20.325
23.200
14.637
2.875
Ghaznavi98
78.625
71.960
68.600
0.069
0.064
0.047
13.475
16.300
20.775
18.388
6.400
Tatara
88.525
79.330
74.250
0.079
0.073
0.068
11.217
14.475
17.250
25.940
7.450
Varieties
RLWC (%)
Turgidity (gm)
Electrolytes leakage (%)
NGPS
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RLWC; Relative leaf water content, NGPS; Number of grains per spike, YPP; Yield per plant
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