Article
Evaluation of Drought Tolerance of Some Wheat (Triticum
aestivum L.) Genotypes through Phenology, Growth, and
Physiological Indices
M. Kaium Chowdhury 1, M. A. Hasan 2, M. M. Bahadur 2, Md. Rafiqul Islam 3, Md. Abdul Hakim 4,
Muhammad Aamir Iqbal 5, Talha Javed 6,7, Ali Raza 8, Rubab Shabbir 6, Sobhy Sorour 9, Norhan E. M. Elsanafawy 9,
Sultana Anwar 10, Saud Alamri 11, Ayman EL Sabagh 9,12,* and Mohammad Sohidul Islam 13,*
Agricultural Training Institute, Department of Agricultural Extension, Gaibanda 5700, Bangladesh;
kaium24bcs@gmail.com
2 Department of Crop Physiology & Ecology, Hajee Mohammad Danesh Science and Technology University,
Basherhat 5200, Bangladesh; mdabuhasan@yahoo.com (M.A.H.); mmbhstu@yahoo.com (M.M.B.)
3 Agronomy Division, Regional Agricultural Research Station, Bangladesh Agricultural Research Institute,
Pabna 6600, Bangladesh; rafiq_bari2@yahoo.com
4 Department of Agricultural Chemistry, Hajee Mohammad Danesh Science and Technology University,
Dinajpur 5200, Bangladesh; ahakimhstu.upm@gmail.com
5 Department of Agronomy, Faculty of Agriculture, University of Poonch Rawalakot,
Rawalakot 12350, Pakistan; aamir1801@yahoo.com
6 College of Agriculture, Fujian Agriculture and Forestry University, Fuzhou 350002, China;
mtahaj@fafu.edu.cn (T.J.); rubabshabbir28@gmail.com (R.S.)
7 Department of Agronomy, University of Agriculture, Faisalabad 38000, Pakistan
8 Fujian Provincial Key Laboratory of Crop Molecular and Cell Biology, Oil Crops Research Institute,
Center of Legume Crop Genetics and Systems Biology/College of Agriculture,
Fujian Agriculture and Forestry University (FAFU), Fuzhou 350002, China;
alirazamughal143@gmail.com
9 Department of Agronomy, Faculty of Agriculture, Kafrelsheikh University, Kafr El-Shaikh 33516, Egypt;
sobhysor@yahoo.com (S.S.); noraudy2020@gmail.com (N.E.M.E.)
10 Department of Agronomy, University of Florida, Gainesville, FL 32601, USA; sultana.anwar@yahoo.com
11 Department of Botany and Microbiology, College of Science, King Saud University,
Riyadh 12211, Saudi Arabia; saualamri@ksu.edu.sa
12 Department of Field Crops, Faculty of Agriculture, Siirt University, Siirt 56100, Turkey
13 Department of Agronomy, Hajee Mohammad Danesh Science and Technology University,
Dinajpur 5200, Bangladesh
* Correspondence: ayman.elsabagh@agr.kfs.edu.eg (A.E.S.); shahid_sohana@yahoo.com (M.S.I.)
1
Citation: Chowdhury, M.K.;
Hasan, M.A.; Bahadur, M.M.;
Islam, M.R.; Hakim, M.A.;
Iqbal, M.A.; Javed, T.; Raza, A.;
Shabbir, R.; Sorour, S.; et al.
Evaluation of Drought Tolerance of
Some Wheat (Triticum aestivum L.)
Genotypes through Phenology,
Growth, and Physiological Indices.
Agronomy 2021, 11, 1792. https://
doi.org/10.3390/agronomy11091792
Academic Editor: Bujun Shi
Received: 18 August 2021
Accepted: 1 September 2021
Published: 7 September 2021
Publisher’s Note: MDPI stays neutral with regard to jurisdictional
claims in published maps and institutional affiliations.
Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
Abstract: Increasing human population and changing climate, which have given rise to frequent
drought spells, pose a serious threat to global food security, while identification of high yielding
drought tolerant genotypes remains a proficient approach to cope with these challenges. To offer a
methodology for the evaluation of the drought-tolerant wheat genotypes based on the pheno-physiological traits, a field experiment was executed, entailing four wheat genotypes viz. BARI Gom 26,
BAW 1158, BAW 1167, and BAW 1169 and two water conditions viz. control treatment (three times
irrigation at 20, 50, and 70 DAS, i.e., 100% field capacity) and stressed treatment (no irrigation during the entire growing season). The results revealed that drought stress drastically reduced the days
to booting, heading, anthesis and physiological maturity, relative water content (RWC), chlorophyll
content, canopy temperature depression (CTD), and photo-assimilates-spike dry matter (SDM),
grains spike−1 and grain yield of all wheat genotypes. In addition, the genotypes BAW 1167 and
BARI Gom 26 remained more prone to adverse effects of drought as compared to BAW 1169 and
BAW 1158. Furthermore, DS induced biosynthesis of compatible solutes such as proline, especially
in BAW 1169, which enabled plants to defend against oxidative stress. It was inferred that BAW
1169 remained superior by exhibiting the best adaptation as indicated by the maximum relative
values of RWC, total chlorophyll, CTD, proline content, SDM, grains spike−1, and grain yield of
wheat. Thus, based on our findings, BAW 1169 may be recommended for general adoption and
Agronomy 2021, 11, 1792. https://doi.org/10.3390/agronomy11091792
www.mdpi.com/journal/agronomy
Agronomy 2021, 11, 1792
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utilization in future wheat breeding programs aimed at developing potent drought-tolerant wheat
genotypes to ensure food security on a sustainable basis.
Keywords: drought stress; wheat genotypes; phenological traits; physiological indices; drought tolerance
1. Introduction
Wheat (Triticum aestivum L.) of the family Gramineae is a popular grain crop of ancient origin. It constitutes one of the most important trade commodities as one-fifth of the
world’s wheat production is traded globally [1]. Wheat provides 21% of the food calories
and 20% of the protein for more than 4.5 billion people in 94 countries, and as a global
food crop, it contributes to food security for many countries. The annual production of
wheat is estimated to be around 600 million Metric tons, which makes it the third largest
crop in the world after corn (Zea mays L.) and rice (Oryza sativa L.) [2]. The yield is a complex trait that is strongly influenced by environmental stresses. The increasing yield potential has indisputable importance in solving the wheat food deficit, especially in Bangladesh. Under a changing climate, environmental stresses have emerged as the main
threats to staple crop production. Recently, wheat production has been adversely influenced by the progressive global climatic changes and increasing shortage of water resources, coupled by the worsening of the eco-environment, which has compromised the
nutritional security of the increasing population [3]. Among the environmental stresses,
water scarcity or drought stress during the growing season and common stress in most
arid and semi-arid areas severely reduces yield. In Bangladesh, it is generally grown under rain-fed conditions during the dry winter (November to April). The soil moisture retention, owing to monsoon rains, supports vegetative growth of wheat plants, however
the reproductive stage is adversely affected with the depletion of the residual soil moisture [4]. Thus, drought stress (DS) incidence limits wheat productivity more severely than
any other environmental stress [5].
DS adversely affects plant establishment and consequently growth and development.
Cell enlargement and assimilates partitioning are hindered by DS [6]. Under extreme conditions, it may severely disturb several metabolic processes, resulting in diminished photosynthesis, impeded cell enlargement and division, and finally passed on the cells [6]. DS
at the reproductive stage is more harmful to plant metabolic processes compared to the
vegetative growth stage. This is because DS at anthesis markedly reduces photosynthesis,
reproductive development, and finally grain yield [4,7]. However, this problem is feared
to be further augmented due to climate change as global warming manifested through
rising temperatures can potentially lead to a serious decline in soil moisture-holding capacity. Several management approaches have been proposed to combat DS, but there has
been little work for screening out drought tolerant genotypes for cultivation in droughtprone areas. The selection of drought tolerant genotypes has been as the economically
viable and biologically superior approach to boost wheat production in moisture deficient
regions [8]. Genotypes should be tested for their drought tolerance based on phenology,
morphology, physiology, and biochemical behavior at different growth stages from germination to maturity (tillering, jointing, booting, anthesis, grain filling, and physiological
maturity stages) due to their variable responses to DS. Plants can tolerate by changing
their physiological functions under drought stress, such as less reduction in water content
[9], chlorophyll content [10], membrane stability [11], photosynthetic activity [12], dry
matter production [11], higher accumulation of soluble sugars [13], proline content [10],
amino acids [14], and enzymatic and non-enzymatic activities [15] to protect against oxidative stress. Therefore, drought-tolerant indices should be determined that can be used
to identify DS tolerant and susceptible genotypes. The testing of crop genotypes for
drought tolerance on their physiological response to DS may serve as the potent approach
Agronomy 2021, 11, 1792
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to screen out well development of new cultivars [16], but it involves a deeper understanding of the yield determining process [17]. In addition, evaluating the physiological
changes occurring under DS may lead to genetic improvement of drought tolerant genotype. It remains a vital challenge to develop drought tolerant genotypes while maintaining higher yields, while selection of drought tolerant genotypes to serve as donor parents
prerequisites any future breeding program. However, immense research and knowledge
gaps exist pertaining to wheat genotypes evaluation on tolerance indices, phenology, and
physiological traits under DS. Thus, we hypothesized that wheat genotypes might respond differently in terms of phonological and physiological traits to DS owing to varying
genetic potential and screening of most superior genotypes that can boost wheat production under changing climate. The present field experiment was aimed to evaluate physiological and phenological traits in wheat genotypes under DS conditions for sorting out the
most drought tolerant genotype for general adoption in the region.
2. Material and Methods
2.1. Location and Duration
The experiment site used was the research farm of the Department of Crop Physiology and Ecology (CPE), Hajee Mohammad Danesh Science and Technology University
(HSTU), Dinajpur, Bangladesh (25°39′ N latitude and 88°41′ E longitude with a 37.58 m
altitude) [18]. The experimental site falls in the agro-ecological zone (AEZ-1) of Old Himalayan Piedmont Plain. The experiment was executed during the winter season from November to April 2018.
2.2. Soil
The experimental field was a medium-high land belonging to the non-calcarious dark
gray floodplain soil. The soil is sandy loam under the Order Inceptisol and belongs to the
Ranishankail series. It is classified as Non-Calcareous Brown Floodplain Soil with Piedmont alluvium parent material [18]. The soil is characterized as acidic in nature, having a
field capacity of 25.8%, permanent wilting point at 12.0%, and bulk density of 0.86–1.07 g
cm−3. The organic matter content of the soil is low (0.69). The physical and chemical properties of the experimental soil up to the depth of 15 cm were studied to know the initial
status (Tables 1 and 2) before conducting the experiment.
Table 1. General characteristics of soil of the experimental site.
General Characters
Location
AEZ
General Soil type
Parent material
Soil series
Drainage
Flood level
Topography
Description
Crop Physiology and Ecology, HSTU, Dinajpur
Old Himalayan Piedmont Plain (AEZ-1)
Non-Calcareous Brown Floodplain Soil
Piedmont alluvium
Ranishankail
Moderately well-drained
Above flood level
High land
Table 2. Initial soil physical and chemical properties of experimental fields and their interpretation according to fertilizer
recommendation guide [19].
Soil Characters
Sand (%)
Silt (%)
Analytical
Value
Critical
Level
Physical properties
60.00
27.00
-
Range of Value Used
Soil Test Values
within the Interpretation
Interpretation
Class
-
-
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Clay (%)
Textural class
Bulk density(g/cc)
Field capacity (%)
Permanent wilting point
Soil pH (1:1.25, Soil: H2O)
Organic matter (%) (Wet oxidation method)
CEC (meq/100g soil) (BaCl2- compulsive exchange method)
Total nitrogen (%) (Micro-Kjeldahl method)
Available phosphorus (µg g−1) (Molybdate
blue ascorbic acid method)
Exchangeable potassium (meq100 g−1 soil)
(Flame photometer method)
Available sulphur (µg g−1)
(Turbidity method using BaCl2)
Available boron (µg g−1) (Calcium chloride
extraction method)
Available zinc (µg g−1) (Atomic Absorption
Spectrophotometer method)
13.00
Sandy loam
0.86–1.07
25.8
12.0
Chemical properties
5.40–5.50
0.69
-
-
-
Low
-
5.60
-
Low
-
0.07
0.12
Low
≤0.09
16.75
10.00
Medium
7.51–15.0
0.17
0.12
Low
0.18–0.27
17.53
10.00
Medium
15.10–22.50
0.15
0.20
Very low
≤0.15
0.88
0.60
Low
0.45–0.90
N.B.: Analysis of initial soil samples was performed from Soil Resources and Development Institute (SRDI), Dinajpur,
Bangladesh.
2.3. Climate
The experimental site is situated in the sub-tropical region receiving a major portion
of rainfall during the months from May to September and scant rainfall during the rest of
the year. In this study, the weather data, including temperature, rainfall, and relative humidity (RH) during November to April of the HSTU campus were recorded at the HSTU
Meteorological Station, HSTU, Dinajpur (Table 3). The average maximum and minimum
temperature, RH, and rainfall were 25.4 and 15.22 °C, 82.0%, and 8.00 mm, respectively.
Rainfall occurred extremely at 55–61 DAS, i.e., grain filling stage.
Table 3. Weather data during the growing period of wheat at the HSTU campus, Dinajpur.
Months
November
December
January
February
March
April
Relative Humidity
(%)
87
85
72
78
81
89
Temperature
Minimum (°C)
Maximum (°C)
15.9
25.6
10.9
21.9
9.6
18.8
14.7
25.2
17.5
29.7
22.7
30.9
Total Rainfall (mm)
0.0
0.0
4.0
8.0
3.0
33.0
Source: Meteorological Station, HSTU, Dinajpur.
2.4. Experimental Design and Treatments
The experiment was conducted in a split plot design with three replications. The unit
plot size was 4.0 m × 2.5 m. The spacing between plots and blocks were 0.75 and 1.0 m,
respectively. The main plots contained well-watered (WW) condition (three irrigation at
20, 50, 70 days after sowing-DAS) and drought stress condition (no irrigation), while subplots had four wheat genotypes viz., (i) BARI Gom 26, (ii) BAW 1158, (iii) BAW 1167, and
(iv) BAW 1169. Wheat genotypes and their pedigree history are presented in Table 4.
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Table 4. Wheat genotypes and their pedigree/selection history used for the present study.
Sr. No.
Genotypes
1
BARI Gom 26 (BAW 1064)
2
3
4
BAW 1158
BAW 1167
BAW 1169
Pedigree/Selection History
Variety, ICTAL123/3/RAWAL87//VEE/HD2285
BD(JOY) 86-0JO-3JE-010JE-010JE-HRDI-RC5DI
BAW 968/SHATABDI
BL 3877 = KAUZ/STAR/CMH 81.749//BL 2224
SHATABDI/BAW 923
BARI: Bangladesh Agricultural Research Institute; BAW: Bangladesh Wheat, SHATABDI: Wheat variety.
2.5. Experimentation
A power tiller was employed for plowing the experimental field, which was leveled
by harrowing and laddering carefully. Afterward, weeds and previous crop leftovers
were manually removed to demark main plots, sub-plots, and blocks. Fertilizers including
N, P, K, S, Zn, and B were applied at the rate of 90-85-66-20-2-0.5 kg ha−1, respectively, in
the form of urea (N: 46%), triple supper phosphate (TSP: 50% P2O5), murate of potash (MP:
60% K2O), gypsum (S: 18%) and boric acid (B: 17%), respectively. Full doses of all fertilizers except N (one-third) were incorporated thoroughly into the soil as basal dose. The
remaining N was further split into two doses for application at 20 and 50 days after sowing
(DAS). Wheat seeds of all genotypes were sown using 120 kg ha−1 seed rate in 20 cm apart
rows. A shallow irrigation was applied in all plots just after sowing for promoting uniform
germination and seedling establishment. Plots were irrigated three times (at 21, 50, and 70
DAS) for WW treatment, and the remaining plots were not irrigated throughout the growing period and protected from rainfall by using rainout shelter (transparent polythene
sheet) to maintain DS condition. After sowing, care was taken against birds up to 15 days.
The crop was kept weed-free, and to control diseases, Tilt 250 EC was sprayed regularly
at 15 days intervals after 30 days of sowing.
2.6. Data Collection
2.6.1. Phenological Indices
During the crop cycle, the dates of booting, heading, anthesis, and physiological maturity were recorded using the scale proposed by [20].
2.6.2. Physiological Indices
Relative Water Content (RWC)
The RWC in the flag leaves was determined at 12 days after anthesis (DAA). The leaf
lamina, after collecting from the field was sealed immediately in plastic bags and quickly
transferred to the laboratory. Fresh weight (FW) was taken immediately, and the leaves
were placed in distilled water in test tubes. Turgid weight (TW) was obtained after soaking leaves in water for about 24 h at room temperature. Dry weight (DW) was obtained
after oven drying the leaf samples at 80 °C for 72 h. The values of the fresh, turgid, and
dry weights of the flag leaves were used to calculate the RWC according to the following
formulae used by [21].
RWC (%) =
Fresh weight Dry weight
× 100%
Turgid weight Dry weight
Chlorophyll Estimation
At 8 and 24 DAA, the chlorophyll content of the flag leaf was determined by the
protocol of [22]. The leaf samples of 1 mg were taken from different flag leaf positions.
The samples were grinded with the help of mortar and pestle and subsequently chlorophyll was extracted using aqueous acetone (80%). Later, the suspension was placed in
centrifuge tubes, and centrifuged (CENTRIFUGE, DSC-158T 220, RPM 3200, AMPS 2;
Agronomy 2021, 11, 1792
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Made in Taiwan R.O.C.) for 3 min. Then, a clear green solution was extracted from the
colorless residue. The solution’s optical density was measured using 80% acetone with the
help of spectrophotometer at 645 and 663 nm. Leaf’s total chlorophyll was determined by
employing the following formulae [22]:
Total chlorophyll (mg g−1 FW) = [20.2(D645+8.02(D663)] × [v/(1000 ×
w)]
Where, V = final volume of filtrated extract;
W = weight of fresh leaf;
D645 = absorbance at 645 nm wavelength;
D663 = absorbance at 663 nm wavelength.
Canopy Temperature Depression (CTD)
The difference between ambient air temperature and canopy temperature in degree
centigrade is known as CTD. The handheld infra-red thermometer (Model: Crop TRAC
item no. 2955L-Spectrum Technologies, Inc. Beijing-10000, China) was used to measure
this trait from approximately 50 cm above the canopy at a 30° angle from the horizon. The
CTD was recorded at 16 DAA under bright sunlight and negligible wind conditions by
using the following formula [23].
CTD (°C) = Ambient Temperature (Ta) − Canopy Temperature (Tc)
Estimation of Proline
Proline content of flag leaf and kernel in all wheat genotypes were estimated at 16
DAA following the standard method [24]. Flag leaves and spikes from each replication of
each genotype were collected and immediately kept in the ice-bag and brought to the Laboratory. The kernels from the spike were separated, and 0.5g of fresh weight of both flag
leaf and kernels were taken for proline estimation. At first, ninhydrin reagent was prepared and utilized for proline estimation within two hours of preparation. To prepare
ninhydrin reagent, 30 mL glacial acetic acid and 20 mL 6M orthophosphoric acid was
mixed with 1.25 g of ninhydrin. It was subsequently heated and stirred gently to dissolve,
but the temperature was not allowed to exceed 70 °C. Proline standards (0, 2, 4, 6, 8, 10,
12, 14, 16, 18, and 20 µg/mL) were prepared with distilled water. Using mortar and pestle,
0.5g fresh sample was grinded and thoroughly homogenized in 3% sulpho salicylic acid
(10 mL) until digestion of plant material. The filtration of homogenate was performed
using filter paper (Whatman No. 2). Then, in a Pyrex test tube, filtrate (2 mL) and standard
proline solution were reacted with ninhydrin reagent (2 mL) and glacial acetic acid (2 mL).
These were subsequently boiled in water bath that was covered with aluminum foil to
hamper evaporation for 1 h at 100 °C. Subsequently, cooling of mixture in ice bath was
performed and toluene (4 mL) was added in each tube with the help of a dispenser. The
shaking of each tube was for 15–20 s with the help of an electrical shaker was performed
to allow the layers to separate. The spectrophotometer (SPECTRO UV-VIS RS Spectrophotometer, Labo Med, Inc.) at 520 nm, having pure toluene as a blank, was used for absorbance of the layer. From a standard curve, proline content was estimated on a fresh weight
basis by following the below equation:
Proline (µmoles/g of fresh plant materials) = {(µg proline/mL × ml toluene)/115.5 µg/µmoles}/(g sample/5)
Measurement of Photo-Assimilates
To quantify spike dry matter (SDM) accumulation pattern, three spikes from main
shoot were cut at anthesis stage with 4 days interval under normal and water deficit conditions. The samples were kept in an oven at 80 °C for 72 h and subsequently weighed
using an analytical balance (Model EK 300 i). The samples were collected from an area of
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1.5 m × 1 m from the center of each plot by cutting the plant at ground level at the harvesting stage. Ten plant samples from each treatment were taken, and the weight of spikelets
spike−1 was measured. The samples were dried under the sun, threshed and cleaned manually and grain weight was taken after drying in the sun. Grain yield was expressed in t
ha−1 with moisture adjusted at 12%.
2.7. Statistical Analysis
The recorded data were subjected to statistical analyses by partitioning the total variance using computer run statistical program “MSTAT-C” (Statistical software packages
developed by the Crop and Soil Sciences Department, Michigan State University, East
Lansing, MI, USA) [25]. The significance among treatment means were compared by employing Duncun’s Multiple Range Test (DMRT) at p ≤ 5% level of probability.
3. Results and Discussion
3.1. Phenological Characteristics
3.1.1. Days to Booting (DB)
The DS significantly influenced the DB in the present study by hastening the booting
stage for three days earlier (Table 5). The time required to attain the booting stage varied
significantly among the genotypes. In DS, the genotype BAW 1169 required the maximum
days (55.33 d) to attain a booting stage that was statistically similar to BAW 1158 (54.65
d). Conversely, BAW 1167 required the minimum days (46.42 d) to attain the booting
stage, followed by BARI Gom 26 (50.23 d). The results are certified by Maman et al. [26],
who reported earlier that water deficit stress accelerates the booting stage. This may be
due to DS slowing down photosynthesis and translocation of photosynthates (demonstrated by SDM), and this affects overall plant development, which is reflected by the
overall shortening of the DB. DS may shorten the DB and accelerate the senescence of
wheat genotypes [27]. The plants of BAW 1169 genotype strive to complete their growth
period as early as possible to cope with drought stress conditions.
Table 5. Effect of DS on days required to attain different phenophases in different wheat genotypes.
Treatment
Well watered
Water stress
CV (%)
BARI Gom 26
BAW 1158
BAW 1167
BAW 1169
CV (%)
BARI Gom
26
BAW 1158
BAW 1167
BAW 1169
WW
DS
WW
DS
WW
DS
WW
DS
Days to Booting
Days to Heading
Water levels
63.54 a
59.23 b
1.52
Genotypes
50.23 b
59.85 b
54.65 a
63.56 a
46.42 b
58.96 b
55.33 a
66.23 a
1.24
2.00
Genotypes × Water levels
49.72 b
60.23 b
46.85 c
56.63 c
56.61 a
65.43 a
54.96 ab
63.85 a
48.96 b
59.11 b
45.65 c
54.63 c
57.23 a
67.11 a
56.42 a
65.81 a
51.21 a
49.11 a
1.41
Days to Anthe- Days to Physiological Masis
turity
75.22 a
70.54 b
1.77
107.78 a
101.41 b
1.57
71.24 b
75.63 a
68.42 b
75.63 a
0.75
103.58 b
105.11 a
102.62 b
106.21 a
0.66
75.22 a
70.06 b
74.23 a
72.40 ab
72.23 ab
66.30 c
75.84 a
74.16 a
106.62 a
99.15 c
107.98 a
104.16 ab
104.25 b
94.04 d
108.83 a
105.77 a
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CV (%)
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1.24
2.00
0.75
0.66
In a column, values having same letter(s) within main effects and interaction effect did not differ significantly by DMRT
at p ≤ 5% level; CV: coefficient of variation.
3.1.2. Days to Heading (DH)
There was a significant difference in DH for the genotypes under water treatments.
DS reduced the days required for heading from 63.54 to 59.23 d (Table 5). DS has been
shown to hasten the growth stage and causes a significant reduction in the number of DH
[11]. Remarkable variations regarding the DH were also observed among the genotypes.
For characterizing genotypes, recording and analysis of DH is a useful tool. DS generally
decreased the days required to initiate heading or flowering due to the early start of the
reproductive stage [28]. However, the genotype BAW 1169 required the maximum DH
(66.23 d), which was statistically similar to BAW 1158 (65 d), while the minimum days
required for heading (58.63 d) were recorded in BAW 1167 (58.96 d) followed by BARI
Gom 26 genotypes (60.05 d). In DS conditions, the earliest heading (54.63 d) was recorded
in BAW 1167 followed by BARI Gom 26 (56.63 d), but the maximum days (65.81 d) were
recorded in BAW 1169 followed by BAW 1158 (63.85 d). No significant variation between
WW and DS regarding the DH in both BAW 1169 and BAW 1158 genotypes. Drought
sensitive genotypes tend to switch to heading earlier under DS, and therefore have a shortened life cycle, whereas drought-tolerant varieties showed non-significant difference in
the heading time [29], and by considering this observation, BAW 1169 and BAW 1158 were
considered as DS tolerant genotypes. Early heading has also been considered as an indicator of increased tolerance to drought in semi-arid locations [30], a major drought escaping mechanism, particularly in terminal drought stresses in durum and bread wheat [31],
and yield improvement [32]. In rain-fed conditions, earlier flowering of wheat tends to
provide balanced moisture consumption at pre- and post-anthesis stages, which promote
grain filling. Wheat varieties having earlier flowering were matured in lesser time and
thus partially escaped from drought; thus, such varieties tend to complete their life cycle
before dehydration caused by high temperatures. Our results are as well in agreement
with those of previous researchers [27,33], where they reported that DS significantly reduced the DH of bread and durum wheat genotypes. Nevertheless, there is a contradictive
finding, according to which no remarkable variation on the DH of bread wheat varieties
due to DS was observed in another study [34]. Hence, plants acclimatization with the soil
moisture availability by matching the growth duration is vital for producing grain yield
as per varietal potential [35]. The phenological development stages of plants are successfully matched with the periods of soil moisture availability, i.e., crop growth season is
shortened to escape the drought stress [6]. Optimum water supply at booting and flowering, heading, and milking stages enhanced the crop yield [36]. Therefore, the selection of
early maturing genotypes has also been believed to be an effective strategy for minimizing
the losses of yield from DS, and less distressed genotypes to DH are considered as tolerant.
3.1.3. Days to anthesis (DA)
Days to anthesis significantly differed between the irrigated and non-irrigated conditions ranging from 70.54 to 75.22 d. Wheat genotypes pronouncedly effected the number
of days required to attain anthesis (Table 5). The maximum days (75.65 and 75.63 d) were
required to attain the anthesis stage in BAW 1169 and BAW 1158, respectively. On the
contrary, the minimum days were required in BAW 1167 (68.42 d). A significant interaction was found between water levels and wheat genotypes on the number of DA. However, in DS conditions, the maximum number of DA (74.16 d) was recorded in BAW 1169,
which differed significantly with other genotypes, and the minimum DA (66.30 d) was
recorded in BAW 1167 among all genotypes. No remarkable variation on DA of BAW 1158
and BAW 1169 due to DS was observed in this study. Pre-anthesis period is highly sensitive for obtaining grain yield attributes such as the number of grain per spike [37], while
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grains weight depends largely on post-anthesis period. The reduced grain-filling time allows terminal stress avoidance, while in comparison, longer duration triggers stem reserves utilization for grain filling under stress. The improvement of cultivar yield under
DS resulted from a more extended grain filling duration [38]. Previous findings [27,33]
concerning the number of DA have shown that DS significantly reduced the DA of wheat
genotypes, as observed in the present study. Wheat genotypes escape DS by earlier heading and maturing, which indicates as the characteristics of drought-tolerant genotypes
[30]. In addition, DS enhances senescence by accelerating chlorophyll degradation, leading to a decrease in leaf area and photosynthesis [39]. These observations corroborate our
findings pertaining to reduced SDM. There is evidence that stay-green phenotypes with
delayed leaf senescence under drought conditions can improve their tolerance performance [40]. Although, the grain-filling rate is determined mostly by genetic factors, and
the grain-filling duration is controlled by environmental factors [41]. The DS accelerated
the anthesis stage of all genotypes, but tolerant genotypes delayed anthesis almost similar
to normal plants in this study. Similarly, findings have been earlier reported by various
researchers [42,43], therefore, based on longer DA of BAW 1169 and BAW 1158, these
might be declared drought tolerant genotypes.
3.1.4. Days to Physiological Maturity (DPM)
The phenological development duration of wheat genotypes constitutes one of the
most pertinent factors for grain yield estimation under any specific environment [44]. The
growth period duration interacts with phenological development, leading to higher grain
yield owing to balanced consumption of resources, especially moisture, and by reducing
the adverse effects of environmental stresses through shortening of growth periods [45].
Days required to physiological maturity showed a significant relationship within the
growing condition, wheat genotypes, and their interaction (Table 5). Plants physiologically matured 6.37 d earlier owing to DS over control plants. BAW 1169, BAW 1158, and
BARI Gom 26 required the maximum days (106.21, 105.11, and 103.58 d, respectively) to
attain physiological maturity, whereas BAW 1167 required the minimum days (102.12 d).
In DS, the highest DPM was obtained in BAW 1169 (105.77 d), followed by BAW 1158
(104.16 d), and the minimum was recorded in BAW 1167 (94.04 d). Wheat genotypes escaped DS by finishing their life cycle in advance and matured earlier, which may be due
to the genetic divergence. DS-induced reductions of DPM in wheat genotypes have been
reported in various research [39,46], presumably due to the senescence of canopy earlier.
The decrease in maturity days under DS might be controlled by the lowering of nutrients
in the plants (data not shown), which decreased chlorophyll in leaves (see 3.2.2. Chlorophyll Content) due to the lack of nitrogen needed for the assimilation. The loss of the
chloroplast integrity in the leaf causes the early senescence in DS that ultimately leads
plants to mature early. In the present study, DS decelerated the physiological maturity
stage of BAW 1169 and BAW 1158 as affirmed tolerant genotypes, which were supported
by several researchers [42,43,47], with less reduction of DPM in response to DS.
3.2. Physiological Indices
3.2.1. Relative Water Content (RWC)
RWC is an important characteristic that measures water status in plants reflecting the
ongoing metabolic activities in tissues and that may be used as a reliable indicator of
drought tolerance. The RWC in flag leaf at 12 DAA was profoundly affected by DS in all
wheat genotypes (Table 6). However, the RWC was decreased under DS, but all the genotypes recorded varying levels of reduction. As compared to control, the highest reduction (8.42%) due to DS was recorded in BAW 1167, then BARI Gom 26 (7.70%), and the
lowest (2.59%) was in BAW 1169, and slightly higher in BAW 1158 (3.47%). The results
indicated that genotypes BAW 1169 and BAW 1158 maintained a greater amount of water
in the leaves under DS than the other two genotypes. A less reduction of RWC in response
Agronomy 2021, 11, 1792
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to DS has been noted for drought-tolerant genotypes [48]. The results of our study were
in close agreement with the findings obtained by [49], who reported that wheat plants
subjected to DS significantly reduced the RWC. Reduction of RWC in leaves might be
associated with the loss of water as well as the variations of water uptake among the genotypes. Increased leaf water retention (LWR) through less reduction of RWC due to DS
could be attributed to rolling of leaves, which results in serious decline of exposed surface
area, and thus might be used as an indicator for determining the drought tolerance potential of crop plants [50]. Genotypes that established high LWR under DS tend to have significantly higher potential for preserving water balance in leaves, which reflects their DS
tolerance. As DS leads to scarcity of water in the root zone, plants slow down water loss
by closing stomata for surviving under DS. Therefore, RWC and leaf rolling hold perspectives for utilization in breeding programs aimed at improving the drought tolerance and
boosting genetic potential for higher grain yields [51]. In addition, RWC shows strong
positive correlations with water use efficiency (WUE), whereas the transpiration rate expresses negative correlation with WUE under drought stress [52]. RWC in leaves is responsive to DS and correlates with drought tolerance [53], and is a better indicator of DS
than any indices of plants [54]. Genotypes may have the ability to absorb water from the
soil or the ability of stomata to reduce the loss of water under DS. Wheat plants under DS
conditions decreased dry matter production and RWC [55], showing that RWC and photosynthetic rates were positively correlated [56], and high RWC (higher osmotic regulation and lesser tissues cell walls elasticity) indicates DS tolerance [57]. Under DS, reduction of RWC indicates turgor pressure decline in plant cells, which leads to growth retardation [58]. In response to DS, roots generate chemical signals, which leads to stomatal
closure and reduction in stomatal conductance [59]. Variation of RWC among the genotypes may be owing to diverse genetic potential for absorbing water from the rhizosphere
and extending the depth of roots to exploit lower soil horizons for moisture extraction
[60]. Plants strive to alleviate the damaging effects of stress by altering their metabolism
to cope with stress. However, the genotypes with reduced leaf water loss due to DS are
believed to be more drought tolerant [34], and RWC may be used as a useful indicator in
order to screen out wheat genotypes having superior drought tolerance. As far as RWC is
concerned, the genotype BAW 1169 followed by BAW 1158 may be suggested as droughttolerant, owing to a minimum relative reduction of RWC.
Table 6. Effect of DS on the relative water content in the flag leaf of different wheat genotypes at 12 DAA.
Genotypes
Water Levels
Well watered
Water stress
Well watered
BAW 1158
Water stress
Well watered
BAW 1167
Water stress
Well watered
BAW 1169
Water stress
Level of significance
CV (%)
BARI Gom 26
Relative Water Content (RWC)
%
% Change Over Normal
87.96 b
81.19 d
−7.70
88.17 ab
85.11 c
−3.47
91.41 a
83.71 cd
−8.42
89.56 a
87.24 b
−2.59
*
1.28
In a column, values having same letter(s) did not differ significantly by DMRT at p ≤ 5% level; * indicates significant at 5%
level of probability.
3.2.2. Chlorophyll Content
In order to screen out drought-tolerant wheat genotypes, Chl content has been assessed successfully by many researchers [61]. Drought tolerant genotypes maintain high
Agronomy 2021, 11, 1792
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Chl content [62], essential for photosynthesis, and higher Chl content that is lower reduction due to DS in wheat genotypes is voted as tolerant genotypes [61]. In addition, Chl has
been regarded as a vital chloroplast component, which is crucial for photosynthesis and
photosynthetic rate [63]. It is an indicator of the photosynthetic activity, biosynthesis of
assimilates [64], and senescence [65]. However, the Chl content in flag leaves of wheat
genotypes was significantly influenced by water regimes at 8 and 24 DAA (Table 7). Due
to DS, the Chl content was remarkedly reduced in all wheat genotypes at 8 DAA, and the
reduction was lesser in genotypes BAW 1169 (8.40%) and BAW 1158 (9.76%) compared to
BAW 1158 (16.60%) and BARI Gom 26 (17.25%). The Chl content at 24 DAA was also profoundly reduced due to DS in all wheat genotypes following previous trends, and the
reduction was minimum in BAW 1169 (14.85%) and BAW 1158 (15.91%) than BAW 1158
(32.56%) and BARI Gom 26 (33.97%). The rate of reduction due to DS at 24 DAA was
higher than 8 DAA, as the plants suffer adversely owing to DS at a later stage with the
depletion of soil moisture. The result obtained from this study indicated that genotypes
BAW 1169 and BAW 1169 possessed higher content of Chl at both observation stages than
the remaining genotypes under DS. Chl content in the flag leaves of barley decreased under DS [66], and a more pronounced reduction is noted in drought susceptible wheat genotypes [67]. The inhibition of Chl synthesis and the inability of sensitive wheat genotypes
to withstand DS has been noted [68]. Our results contradict the earlier findings [69] as
they reported that the Chl content in the stressed leaves of wheat increased as compared
to non-stressed leaves, and this may happen under moderate water stress. Acute DS hampers photosynthesis by destroying Chl components, damaging the photosynthetic systems, along with decreasing the uptake of nutrients from soil solution and translocation
within crop plants [63,70]. Furthermore, DS also damages the thylakoid membranes [71],
adversely affecting Chl synthesis, accumulation, and distribution of assimilates [72]. The
Chl content of the leaf may be used as an index for source evaluation; therefore, Chl content decline under DS has been considered as a pronounced non-stomatal limiting factor
[73]. Additionally, Chl content has been recognized as an index to determine plants tolerance to DS [74], Chl reduction in response to water deficit is regarded as a sign of oxidative
stress damage caused by chlorophyllase enzymes [75]. Furthermore, proline biosynthesis
from glutamate precursor may also be inferred as the reason to decrease the Chl content
under DS [76], as observed in our research (Tables 8 and 9). From overall information, it
may be concluded that BAW 1169 is a tolerant genotype since it contains the highest
amount of Chl than the other genotypes.
Table 7. Effect of DS on the flag leaf chlorophyll content of different wheat genotypes at 8 and 24 DAA.
Genotypes
Water Levels
Well watered
Water stress
Well watered
BAW 1158
Water stress
Well watered
BAW 1167
Water stress
Well watered
BAW 1169
Water stress
Level of significance
CV (%)
BARI Gom 26
Chlorophyll Content in Flag Leaf at 8 Chlorophyll Content in Flag Leaf at
DAA
24 DAA
%
Change
Over
% Change Over
mg g−1 FW
mg g−1 FW
Normal
Normal
2.55 a
2.09 b
2.11 cd
−17.25
1.38 d
−33.97
2.44 b
2.20 a
2.20 c
−9.76
1.85 c
−15.91
2.49 b
2.15 ab
2.06 d
−16.60
1.45 d
−32.56
2.62 a
2.29 a
2.40bc
−8.40
1.95 bc
−14.85
**
*
2.20
3.50
In a column, values having same letter(s) did not differ significantly by DMRT at p ≤ 5% level; DAA indicates days after
anthesis, FW indicates fresh weight; * indicates significant at 5% level of probability; ** indicates significant at 1% level of
probability.
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3.2.3. Canopy Temperature Depression (CTD)
The CTD has been considered a reliable tool to assess drought tolerance in crop
plants. It entails difference between air (ambient) temperature (Ta) and leaf (canopy) temperature (Tc), while the higher CTD values indicate better stress tolerance. Under DS,
plants strive to adapt resistance strategies by a descending trend of physiological indices
such as RWC, Chl content, CTD °C, etc., for minimizing the loss of water [77]. However,
DS pronouncedly influenced CTD at 16 exhibited by wheat genotypes (Table 8). Wheat
genotypes under WW condition maintained 8.60 to 9.53 °C CTD, and the highest CTD was
recorded in BAW 1169 (9.53 °C), which was statistically similar to BARI Gom 26 (9.40 °C),
while BAW 1158 showed the lowest CTD (8.60 °C) that was statistically equal to BAW
1167 (8.73 °C). The DS condition significantly reduced CTD values wheat genotypes under
investigation, as the reduction was more pronounced in BAW 1167 (41.23%), indicating
its drought sensitivity followed by BARI Gom 26 (36.49%), and the lowest was in BAW
1169 (23.71%), signifying the most tolerant genotype. The results from this study indicated
that BAW 1167 and BARI Gom 26 were more affected than BAW 1169 and BAW 1158. The
CTD decrease under drought stress is probably due to an increase in respiration and a
decrease in transpiration as a result of stomatal closure. These results are consistent with
previously reported results in which DS significantly influenced the CTD of wheat genotypes. In addition, Tc has been regarded as vital indicator of water status in crop plants
and holds merit for being a non-destructive technique for estimating stomatal conductance alterations under DS [78]. The water transpiration increment in response to moisture
scarcity can decrease the temperature of plant surfaces and vice-versa [79]. Stressed wheat
plants showed higher Tc in comparison to optimally watered plants [80]. Relatively lower
Tc observed in DS plants indicates potential for absorbing higher soil moisture that assists
plant to maintain optimal water status [81]. Our results indicated that the genotypes BAW
1169 and BAW 1158 (tolerant) exhibited cooler canopy in response to DS in comparison to
the genotypes BAW 1167 and BARI Gom 26 (sensitive).
Table 8. Effect of DS on the CTD of different wheat genotypes at 16 DAA.
Genotypes
Water Levels
WW
DS
WW
DS
WW
DS
WW
DS
BARI Gom 26
BAW 1158
BAW 1167
BAW 1169
Level of significance
CV (%)
Canopy Temperature Depression (CTD)
(°C)
% Change Over Control
9.40 ab
5.97 e
−36.49
8.60 c
6.30 e
−26.74
8.73 bc
5.13 f
−41.23
9.53 a
7.27 d
−23.71
**
3.82
-
In a column, values having same letter(s) did not differ significantly by DMRT at p ≤ 5% level; ** indicates significant at
1% level of probability.
3.2.4. Proline Content
Proline accumulation under DS is one of the common features in plants [82], which
serves as critical osmolyte biosynthesized in response to abiotic stresses, including DS
[83]. Generally, genotypes are selected as drought-tolerant, having higher proline content
in DS than in normal conditions. However, flag leaves proline content varied among
wheat genotypes at 16 DAA under DS (Table 9). The proline content in flag leaves was
increased in all genotypes due to DS, and the highest increment was recorded in BAW
1169 (24.02%) over BAW 1158 (21.55%), BARI Gom 26 (10.53%), and BAW 1167 (8.19%),
Agronomy 2021, 11, 1792
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respectively. The proline content in the kernel was also increased in all the genotypes due
to the influence of DS. The highest increment over control (WW) was recorded in BAW
1169 (20.16%), followed by BAW 1158 (18.00%), and the lowest was in BAW 1167 (3.54%),
trailed by BARI Gom 26 (4.25%). The results indicated that BAW 1169 and BAW 1158
maintained the maximum amount of proline content in the flag leaf and kernel than BARI
Gom 26 and BAW 1167 genotypes under DS conditions. The proline content in bread
wheat genotypes significantly increased under stress, as reported in earlier research [84].
In addition, plant cells achieve osmotic adjustment by accumulating compatible solutes
such as proline in the cytoplasm and serve as an osmoprotectant [85]. It helps to control
N storage, stabilize membrane, and scavenge different free radicals, along with buffering
cellular redox potential to cope with abiotic stresses [86]. Under DS, proline performs role
of metal chelator, antioxidative protection and signaling [83]. The accumulation of proline
in DS plants can also serve as sensor of drought injury along with its prime role in stress
tolerance mechanisms [84]. It has the potential to protect crop plants from oxidative damage, which is the main strategy of plants to avoid detrimental effects of water deficit stress.
High proline levels enable plants to attain low water potential, and thus imparts tolerance
against moisture deficiency by increasing the biosynthesis of intermediate enzymes [85].
In a recent study, it was observed that wheat genotypes alleviate DS by overproduction
of two special amino acids, namely L-cysteinylglycine and fructoselysine, to tolerate
drought [14]. The plants’ potential for accumulating the proline under DS depends on
genetic potential of variety along with severity and duration of stresses. Few plant species
have potential to biosynthesize enough proline to cope with adverse effects of abiotic
stresses [86]. However, the genetic disparity of such osmotic changes can be a useful tool
for the selection of drought-tolerant wheat genotypes [87]. Higher accumulation of proline
content in BAW 1169 and BAW 1158 due to DS indicates as relatively tolerant genotypes,
and it may be associated to better osmotic adjustment of plants, which prevents degradation of macromolecules and different vital cell membranes [59,88].
Table 9. Effect of DS on the proline content in flag leaf and kernel of wheat genotypes at 16 DAA.
Genotypes
Water Levels
Well watered
Water stress
Well watered
BAW 1158
Water stress
Well watered
BAW 1167
Water stress
Well watered
BAW 1169
Water stress
Level of significance
CV (%)
BARI Gom 26
Proline Content in Flag Leaf
% Change Over
µmole g−1 FW
Normal
1.90 c
2.10 a
10.53
1.81 d
2.20 a
21.55
1.83 d
1.99 b
8.19
1.79 d
2.22 a
24.02
*
4.04
Proline Content in Kernel
% Change Over
µmole g−1 FW
Normal
2.60 cd
2.71 c
4.25
2.50 d
2.95 b
18.00
2.54 d
2.64 c
3.94
2.58 d
3.10 a
20.16
*
2.56
In a column, values having same letter(s) did not differ significantly by DMRT at p ≤ 5% level; FW indicates fresh weight;
* indicates significant at 1% level of probability.
3.3. Accumulation of Photo-Assimilates
3.3.1. Spike Dry Matter (SDM)
Under optimal and moisture scarce conditions, a sigmoid way for accumulation of
dry matter (DM) in spike was noted in wheat genotypes (Figure 1). Under WW conditions,
the ear DM weight was observed to increase gradually in BARI Gom 26 (4.57 g) followed
by BAW 1158 (4.03 g) and BAW 1167 (3.98 g) at 44 DAA, the last observing stage in this
study. The remaining BAW 1169 genotype was observed to increase in SDM weight (3.56
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g) up to 40 DAA, and thereafter declined. Under DS, the DM accumulation in the spike
increased in all wheat genotypes up to a certain DAA, such as BARI Gom 26 and BAW
1158, which increased up to 40 DAA and then declined, and BAW 1167 increased up to 36
DAA and thereafter declined tremendously. Whereas, in the case of BAW 1169, the DM
increased gradually with increasing plant age (DAA). The declining tendency of DM after
attaining the highest level may be due to respiratory loss of spike. Hence, it is indicated
that the wheat grains of BAW 1167, BARI Gom 26, and BAW 1158 dried quickly and attained physiological maturity earlier as compared to BAW 1169. The sigmoid way involving accumulation of dry matter under DS has also been reported earlier [69,89]. The DS
condition leads to reduced plant growth, which is reflected in plant height, leaf area, dry
weight, and other growth functions [42,90], reduced Chl content, photosynthetic rate, and
TDM [14,39,91]. The reduction of SDM may be attributed to profound respiratory losses
in the spike. DS in crop field decreased CO2 uptake [92], leaf gas exchange capacity [93],
and photochemical reactions and photosynthetic metabolism [94]; consequently, these
might have reduced DM in plants. Our results showed that DS reduced the RWC (Table
6), Chl content (Table 7), and CTD (Table 8), resulting in reduced SDM; BAW 1169 maintained higher values among all genotypes under DS.
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
BARI Gom 26
0.5
0.0
5.0
Well watered
Water stress
0 4 8 1216 20 24 28 32 36 40 44
Days after anthesis
Spike dry weight (g spike-1)
Spike dry weight (g spike -1)
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
BAW 1158
0.5
0.0
0 4 8 121620242832364044
Days after anthesis
15 of 21
5.0
5.0
4.5
4.5
4.0
Spike dry weight (g spike -1)
Spike dry weight (g spike -1)
Agronomy 2021, 11, 1792
4.0
3.5
3.5
3.0
3.0
2.5
2.5
2.0
2.0
1.5
BAW 1167
1.0
0.5
1.5
BAW 1169
1.0
0.5
0.0
0 4 8 12162024283236 4044
0.0
Days after anthesis
0 4 8 12 16 20 24 28 32 36 40 44
Days afetr anthesis
Figure 1. Effect of DS on the spike dry weight of different wheat genotypes at different DAA.
3.3.2. Dry Weight of Grains Spike−1
Significant variation was found in grain dry weight spike−1 by the interaction effect
of water levels and wheat genotypes (Table 10). At WW condition, BARI Gom 26 produced the maximum dry weight of grains spike−1 (3.45 g spike−1), while the lowest corresponding value was recorded for BAW 1158 (2.96 g spike−1), which was statistically similar
to BAW 1167 (2.97 g spike−1). In DS, the grain dry weight spike−1 was reduced significantly
in all wheat genotypes, and the degree of reduction was maximum in BAW 1167 (11.78%)
followed by BARI Gom 26 (8.33%) than that of BAW 1169 (3.26%) and BAW 1158 (3.38%).
The results indicated that genotypes BAW 1169 and BAW 1158 were relatively less affected by water deficit stress than the other two genotypes. DS leads to reduced plant
growth reflected in leaf area, dry weight, spike length, number of grains spige−1 and grain
weight [39,42,89,90]. High Chl content under DS indicates lower intensity of photosynthetic apparatus’s photo-inhibition, therefore decreasing losses of carbohydrates for
grains development [95]. A higher number of the fertile floret, which is transferred into a
higher number of potential grain spike−1, may depend on several factors under DS such
as reduced phenological indices (Table 5), RWC (Table 6), Chl content (Table 7) etc., consequently reduced grain size, and finally reduced grain weight spike−1 greatly in BAW
1167 and BARI Gm 26. Most likely at the sink level, DS adversely affects the grain yield
potential by decreasing fertile grains and the size spike−1 in BAW 1167 and BARI Gm 26
(sensitive) genotypes.
Table 10. Effect of DS on the grain dry weight spike−1 and grain yield of different wheat genotypes.
Genotypes
BARI Gom 26
BAW 1158
BAW 1167
Water Levels
Well watered
Water stress
Well watered
Water stress
Well watered
Grain Dry Weight Spike−1
% Change Over
g Spike-1
Normal
3.60 a
3.30 b
−8.33
2.82 d
2.76 d
−2.13
2.97 c
-
t ha−1
5.58 a
3.64 d
5.56 a
4.23 c
5.07 b
Grain Yield
% Change Over
Normal
−34.77
−23.92
-
Agronomy 2021, 11, 1792
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Water stress
Well watered
BAW 1169
Water stress
Level of significance
CV (%)
2.62 e
3.07 c
2.97 c
**
1.88
−11.78
−3.26
-
3.27 d
5.65 a
4.39 c
**
2.67
−35.50
−22.30
-
In a column, values having same letter(s) did not differ significantly by DMRT at p ≤ 5% level ** indicates significant at 1%
level of probability.
3.3.3. Grain Yield
The grain yield of wheat genotypes was significantly influenced by water conditions
in the field (Table 10). At WW condition, the grain yield ranged from 5.65 to 5.07 t ha−1,
while BAW 1169 provided the highest yield (5.65 t ha−1), which was statistically identical
to BARI Gom 26 (5.58 t ha−1), and BAW 1158 (5.56 t ha−1). The lowest yield was found in
BAW 1167 (5.07 t ha−1). Grain yield was reduced in all wheat genotypes due to DS, and
the extent of reduction was maximum in BAW 1167 (35.50%) and BARI Gom 26 (34.77%)
than BAW 1169 (22.30%) and BAW 1158 (23.92%) over control (WW), indicating that the
two previous genotypes were more susceptible to DS. The results indicated that less reduction of grain yield in BAW 1169 and BAW 1158 genotypes owing to DS was a result of
drought tolerance. Other studies also showed that a stress environment reduces grain
yield in wheat compared to control [33,96]. DS had unusual effects on the grain yield,
depending on the developmental stage in which it occurs. TGW and grain yield were remarkably reduced when DS was imposed at pre-anthesis, post-anthesis, anthesis, booting,
and anthesis with reduced grain-filling period [39,97]. Significant reduction in grain yield
due to post-anthesis water stress may result from a reduction of the production of photoassimilates (source limitation), power of the sink to absorb photo-assimilates and the grain
filling duration. DS at post-anthesis severely reduced grain yield (98%), which depends
upon the severity of stress and growth stage in which the drought condition was imposed
[96,98]. The improvement of yield in wheat and barley under DS has resulted from a prolonged grain filling period, high chlorophyll content, and a more sustained turgor or combination of them [99]. The incidence of DS at early and later growth stages severely affected wheat growth, which alters water-utilizing capacity and ultimately results in substantially reduced yield [100]. The anthesis stage is highly vulnerable to DS as it affects
the pollen grain viability, which in turn, reduces the number of grains spike−1 [101]. The
highest grain yield in BAW 1169 and BAW 1158 under DS in this study may be related to
less reduction of life span (Table 5), RWC (Table 6), total Chl (Table 7), CTD (Table 8),
SDM (Figure 1) and increasing proline (Table 9), as supported by many researchers
[86,88,102,103]. The yield variation under DS can be attributed to the diverse genetic background among the genotypes [103–105], and activated genes in response to drought exhibited variation in their expression [106].
4. Conclusions
In this study, the drought stress remarkably decreased the phenological indices such
as days to booting, heading, anthesis, etc. in all wheat genotypes. However, the reduction
was comparatively lower in BAW 1169 and BAW 1158 genotypes than BAW 1167 and
BARI Gom 26 indicating their superiority in terms of drought tolerance. In addition, better
RWC, Chl and proline contents in flag leaf and kernel along with CTD were noted in BAW
1169 and BAW 1158 genotypes. Furthermore, yield attributes including SDM and grain
weight spike−1, along with grain yield, were significantly reduced in BAW 1167 and BARI
Gom 26 genotypes than that of BAW 1169 and BAW 1158. Finally, longer growth duration,
greater stability of flag leaf chlorophyll, water retention capability in leaves, ability to keep
the canopy cooler, higher proline level, greater SDM, and better grains spike−1 under DS
contributed to drought tolerance of wheat genotypes, which might be inferred to be
Agronomy 2021, 11, 1792
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ranked as BAW 1169 > BAW 1158 > BARI Gom 26 > BAW 1167 in decreasing order of
drought tolerance.
Author Contributions: Conceptualization, M.A.H. (M. A. Hasan), M.M.B., S.S., and M.K.C.; methodology, M.A.H., S.S. and M.K.C.; software, M.A.H. and M.K.C.; validation, M.A.H., M.K.C.,
M.M.B., and M.S.I.; formal analysis, M.A.H. (M. A. Hasan) and M.K.C.; investigation, M.K.C. and
M.A.H. (M. A. Hasan); resources, M.A.H.; data curation, M.K.C., M.A.H. (Md. Abdul Hakim), and
M.S.I.; writing—original draft preparation, M.K.C., M.A.H. (M. A. Hasan), and M.S.I.; writing—
review and editing, A.A., T.J., R.S., M.S.I., M.R.I., M.A.I., M.A.H. (Md. Abdul Hakim), M.B., I.A.I.,
A.R., S.A. (Sultana Anwar), and E.M.A.; visualization, M.S.I.; supervision, M.A.H.; project administration, M.A.H.; funding acquisition, S.A. (Sultana Anwar), S.A. (Saud Alamri), M.S., M.B., E.M.A.,
I.A.I., and A.E.S. All authors have read and agreed to the published version of the manuscript.
Funding: Researchers supporting project number (RSP-2021/194), King Saud University, Riyadh,
Saudi Arabia.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: Not applicable.
Acknowledgement: The authors would like to extend their sincere appreciation to the researchers
supporting project number (RSP-2021/194), King Saud University, Riyadh, Saudi Arabia.
Conflicts of Interest: The authors declare no conflict of interest.
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