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Article

Evaluating Physiological and Yield Indices of Egyptian Barley Cultivars Under Drought Stress Conditions

by
Wessam A. Abdelrady
1,2,
Elsayed E. Elshawy
3,
Hassan A. Abdelrahman
1,
Syed Muhammad Hassan Askri
1,
Zakir Ibrahim
1,4,
Mohamed Mansour
3,
Ibrahim S. El-Degwy
5,
Taha Ghazy
5,
Aziza A. Aboulila
6,* and
Imran Haider Shamsi
1,*
1
Zhejiang Key Laboratory of Crop Germplasm Resource, Department of Agronomy, College of Agriculture and Biotechnology, Zhejiang University, Hangzhou 310058, China
2
Department of Crop Science, Faculty of Agriculture, South Valley University, Qena 83523, Egypt
3
Barley Research Department, Field Crops Research Institute, Agricultural Research Center, Giza 85871, Egypt
4
Department of Biotechnology and Bioinformatics, Faculty of Agriculture, Lasbela University of Agriculture, Water and Marine Sciences, Uthal 90150, Pakistan
5
Agronomy Department, Faculty of Agriculture, Kafrelsheikh University, Kafr El-Sheikh 33516, Egypt
6
Genetics Department, Faculty of Agriculture, Kafrelsheikh University, Kafr El-Sheikh 33516, Egypt
*
Authors to whom correspondence should be addressed.
Agronomy 2024, 14(11), 2711; https://doi.org/10.3390/agronomy14112711
Submission received: 12 October 2024 / Revised: 13 November 2024 / Accepted: 15 November 2024 / Published: 17 November 2024
(This article belongs to the Special Issue Qualitative and Quantitative Plant Screening Measurements for Yield and Quality Enhancement)
Browse Figures
Versions Notes

Abstract

:
Climate change significantly threatens crops, mainly through drought stress, affecting barley, which is essential for food and feed globally. Ten barley cultivars were evaluated under normal and drought stress conditions during the 2019/20 and 2020/21 seasons, focusing on traits such as days to heading and maturity, plant height, number of spikes m−2, spike length, 1000-kernel weight, and biological and grain yield. Drought stress significantly reduced most of these traits. The genotypes showed significant differences in their responses to irrigation treatments, with the interaction between seasons and cultivars also being significant for most traits. The grain yield and 1000-kernel weight were among the least affected traits under drought stress, respectively. Notably, Giza138 and Giza126 showed strong drought tolerance, suitable for drought-resilient breeding. In season one, Giza126, Giza134, and Giza138 yielded 13%, 9%, and 11%, respectively, while Giza135 and Giza129 showed higher reductions at 31% and 39%. In season two, Giza126, Giza134, and Giza138 had reductions of 14%, 10%, and 13%, respectively, while Giza135 and Giza129 again exhibited higher reductions at 31% and 38%. These cultivars also showed strong performance across various stress tolerance indices, including the MP, YSI, STI, GMP, and YI. Giza 134 demonstrated the lowest values for the SDI and TOL, indicating superior drought stress tolerance. On the other hand, Giza 129 and Giza 135 were the most sensitive to drought stress, experiencing significant reductions across critical traits, including 6.1% in days to heading, 18.37% in plant height, 28.21% in number of kernel spikes−1, 38.45% in grain yield, and 34.91% in biological yield. In contrast, Giza 138 and Giza 2000 showed better resilience, with lower reductions in the 1000-kernel weight (6.41%) and grain yield (10.61%), making them more suitable for drought-prone conditions. Giza 126 and Giza 132 also exhibited lower sensitivity, with minimal reductions in days to heading (2%) and maturity (2.4%), suggesting potential adaptability to water-limited environments. Giza 126 maintained the highest root lengths and had the highest stomatal conductance. Giza 138 consistently had the highest chlorophyll content, with SPAD values decreasing to 79% under drought. Despite leading in shoot length, Giza 135 decreased to 42.59% under drought stress. In conclusion, Giza 126 and Giza 138 showed adaptability to water-limited conditions with minimal impact on phenological traits. Giza 126 had the longest roots and highest stomatal conductance, while Giza 138 consistently maintained a high chlorophyll content. Together, they and Giza 134 are valuable for breeding programs to improve barley drought tolerance.

Graphical Abstract

1. Introduction

Climate change poses a significant threat to crops, mainly through drought stress, affecting barley, which is essential for food and feeds globally [1]. Drought represents the most severe environmental limitation, leading to significantly higher yield losses than other abiotic stresses [2,3,4]. Drought affects nearly all climatic regions, with drought-prone zones comprising 16.2–41.2% of global arable land. Drought-tolerant crops and resilient agricultural practices must be developed to ensure food security and safety and adapt to the increasing frequency and severity of droughts due to climate change [5,6]. Barley is the fourth most crucial cereal crop next to wheat, rice, and maize in the cultivated area [7,8]. The area planted for barley in Egypt in 2022 was 24,500 hectares (ha), the yield reached was 3948 tons/ha, and the total production was 96,717 metric tons [9]. Moreover, barley represents the main crop in Egyptian rainfed areas. Barley can grow in highly contrasting habitats, tolerate stress conditions, and are typically cultivated as dry-land or rainfed plants [10]. Barley is an excellent genetic model for studying the mechanisms of drought stress tolerance [11,12].
Among abiotic stresses, drought stress has a major effect on plant growth and productivity by influencing many physiological and biochemical processes [13,14,15]. Generally, drought stress happens when the available water in the soil is reduced and atmospheric environments cause continuous water loss by transpiration or evaporation [16]. The top negative effect of drought stress on crops has been found to reduce biomass and yield production [17]. Many researchers have studied barley’s drought stress tolerance genetic bases [18,19]. Improving crop growth and yield under drought stress involves maintaining photosynthetic efficiency, water balance, and nutrient uptake. Testing cultivars at critical growth stages is crucial. Advanced genomic techniques and an integrative approach combining physiology, breeding, and genetics are essential for developing drought-tolerant crops [19]. Barley’s adaptation to drought stress relies on genetic variability. Key traits include root and shoot lengths, yield-related traits, the chlorophyll content, osmotic adjustment, and antioxidant enzyme activities. Breeding programs use direct and indirect selection, crossing drought-tolerant cultivars, and utilizing marker-assisted selection to enhance drought tolerance and develop resilient barley cultivars with stable yields [20]. Drought affects barley by reducing photosynthesis, causing floral abnormalities, spikelet and kernel sterility, and decreasing grain yield and quality. It leads to stomatal closure, delayed flower development, and inhibited cell division, resulting in fewer and smaller grains with a lower carbohydrate and nitrogen content [21].
Various indices are used to screen barley cultivars for drought stress tolerance, each offering different insights into their performance [22]. The Drought Susceptibility Index (DSI) measures relative yield reduction under stress, with lower values indicating higher tolerance. The Tolerance Index (TOL) assesses the absolute yield difference between stress and non-stress conditions, where lower values signify greater tolerance. Mean Productivity (MP) and Geometric Mean Productivity (GMP) focus on average and stable yields, respectively, with higher values indicating better overall performance [23]. The Stress Tolerance Index (STI) measures the yield under stress relative to the average yield under non-stress conditions, with higher values indicating better performance under stress. The Drought Resistance Index (DRI) adjusts yield ratios by the relative reduction due to stress, with higher values reflecting better drought resistance. Additionally, the Genotypic main effect and Genotype by Environment interaction (GGE) biplot method provides graphical representations to visualize genotype performance across different environments, aiding in identifying and breeding drought-tolerant barley cultivars [24]. The GGE biplot analysis has been mainly used to analyze data that can be organized into a two-way table. Depending on their graphical nature, biplot analysis was used to identify the drought stress-tolerant barley cultivars [25]. The relationship between agronomic characteristics and stress tolerance indices helps us understand the essential traits contributing to drought stress tolerance [26,27].
Recent genomic advances for drought tolerance in crops, particularly wheat and barley, integrate physiology, breeding and genetic approaches. Physiological research explores how crops adapt biochemically to drought, such as conserving water through cellular changes. Breeding techniques focus on selecting and crossing drought-resistant genotypes to develop new, high-yield drought-tolerant varieties. Genetic research employs GWAS and QTL mapping to identify specific drought-tolerant genes, while GBS generates extensive SNP data for refining these traits. Integrating these techniques supports more resilient crop development [19,28]. The present study evaluated the ten barley cultivars under normal and drought stress conditions to identify the most drought-tolerant cultivars. It also sought to investigate the associations between agronomic traits and drought stress tolerance and to facilitate the ranking of cultivars for drought tolerance by utilizing multiple parameters simultaneously.

2. Materials and Methods

2.1. Physiological Experiments

2.1.1. Plant Materials and Drought Stress Treatments

To examine drought tolerance, this study used ten cultivated barley cultivars (Table S1). Seeds were surface sterilized for 15 min with 10% commercial NaClO (0.52% active Cl) and rinsed for 30 min with tap water. Plants were grown in 2-L pots filled with clay soil for 35 days, with three replicates. Each replicate contained ten plants grown under natural field conditions. Irrigation was controlled with the following three treatments: natural irrigation (every five days after the third irrigation and complete germination with the emergence of the third leaf), moderate drought conditions, seven-day irrigation (every seven days after the third irrigation), and drought conditions ten-day irrigation (every ten days after the third irrigation). Irrigation was conducted using a half-strength Hoagland nutrient solution. Each pot received approximately 0.7 to 0.9 L of nutrient solution per irrigation event. This controlled irrigation approach enabled the precise monitoring of water dynamics throughout the drought treatment period. The Permanent Wilting Point (PWP) was determined to be 20.9%, and the Available Soil Water (AW) was 17.6%. Table S3 provides a detailed analysis of the soil composition of the potting substrate, identical to that used in the field experiment. All the chemical materials were purchased from Aladdin, Reagent Co., Ltd., Shanghai, China.

2.1.2. Chlorophyll Content, Chlorophyll Fluorescence and Stomatal Conductance

Chlorophyll content was measured in the youngest fully expanded leaves using a SPAD meter (SPAD-502 Plus, Konica Minolta, Inc., Tokyo, Japan). Chlorophyll fluorescence was measured using the LI-600 device in Tucson, AZ, USA. The Photosystem II quantum efficiency in light (ΦPSII) was measured using the LI-COR LI-600 porometer/fluorometer. For dark-adapted leaves, the device measured the maximum quantum yield (Fv/Fm). Phi was calculated using fluorescence signals from the leaf in the light-adapted mode. For the dark-adapted mode, leaves were dark-adapted for 1 h before measuring Fv/Fm. Barley seedlings were dark-adapted, and measurements were taken from the oldest and youngest fully expanded leaves using a portable fluorimeter. The maximum quantum efficiency of photosystem II (Fv/Fm) was calculated using the formula Fv/Fm = (Fm − Fo)/Fm. Measurements were conducted under saturating actinic light at 660 nm with an intensity of 1100 µmol·m−2·s−1. Stomatal conductance (gs) was measured from the youngest fully expanded leaves using a porometer. All measurements followed manufacturer instructions before the fully expanded leaves. Four replicates were randomly taken for each barley genotype under either control or drought conditions. All measurements were conducted according to the specified protocols to ensure accuracy and repeatability.

2.2. Field Experiments

The present investigation was carried out at the Agronomy Department, Faculty of Agriculture, Kafrelsheikh University, and the field experiment was conducted on the farm of Sakha Agricultural Research Station, Kafr El-Sheikh Governorate, Egypt, during the 2019/2020 and 2020/2021 seasons. Ten local barley cultivars were included in this study (Table S1). The studied cultivars were experimented with two treatments: the first (normal treatment) with three irrigations, including the planting irrigation, and the second treatment (stress treatment) with only the planting irrigation, as shown in Table S2. The cultivars investigated were sown on 15 December in the two seasons using the randomized complete block design with three replications. The depth of the water table was measured at different intervals during irrigation events. Each irrigation treatment was located separately. Each genotype was planted in an experimental unit with 6 rows 3.5 m long and 20 cm apart. All of the cultural practices, except irrigation treatments, were carried out at the proper time.
The experimental soil was categorized as clay loamy, with an average pH of 8.2 and electrical conductivity (EC) of 2.10 dSm−1. Soil water constants included a Field Capacity (FC) of 38.5%, a Permanent Wilting Point (PWP) of 20.9%, and an Available Soil Water (AW) of 17.6%. As shown in Table S3, the grains were hand drilled at the recommended seeding rate of barley in Egypt (120 kg ha−1). Each plot (4.2 m2) was sown in six rows of 3.5 m long with 20 cm between rows. A randomized complete block design with three replicates was laid out for each experiment. Traditional and cultural practices were applied as recommended by the Ministry of Agriculture (Egypt). Barley grains were sown on 15 December; the preceding crop was maize, which was grown in both seasons. Monthly mean air temperatures (°C) and rainfall (mm/month) during the growing seasons at the experimental site are shown in Table S4. Also, the amounts of water provided through the two seasons, 2019/20 and 2020/21, are shown in Table S2. Water prevention began during the tillering stage and stem elongation in most cultivars to the harvesting stage. Furthermore, rainfall was 1114 m3 ha−1 and 528.79 m3 ha−1 in seasons 2019/20 and 2020/21, respectively (Table S2). Additionally, the water table level in the two seasons was above 170 cm at 60 and 125 days after planting for the drought stress and normal irrigations. Consequently, irrigation treatments were suitable to study the effect of drought stress.
Days to heading and maturity were recorded as the mean of all plants per plot. Plant height, spike length, 1000-kernel weight (g), and number of kernels per spike (KS) were estimated as an average of 10 random spikes from the central rows. Biological yield (ton ha−1) was recorded for all harvested plants per plot−1 and converted to ton ha−1. Grain yield (ton ha−1) was noted and measured from the grains of harvested plants plot−1 after threshing and then converted to ton ha−1. Stress tolerance indices, formulae, and references used to evaluate drought stress tolerance are presented in Table S5.
Variance analysis for each season recorded to date was estimated according to Snedecor and Cochran, 1980 [29]. According to Steel and Torrie, the means of the studied cultivars were compared by the LSD test at a 5% probability level [30]. The effects of the cultivars were assumed to be fixed. The homogeneity of error variances for the two seasons and the irrigation treatments was calculated as in Levene [31]. The statistical analysis was achieved using the statistical routines presented in EXCEL 2016 [32].

3. Results

3.1. Physiological Parameters Under Drought Condition

3.1.1. Plant Growth Under Drought Conditions

Figure 1 presents the growth patterns of ten barley cultivars under drought conditions. The results indicate varying levels of drought tolerance among the different cultivars. Drought-sensitive cultivars exhibit significant stress responses, including burning the lower leaves and reducing plant length, size, and weight. These observations underscore the differential impact of drought on the cultivars, highlighting the variability in drought tolerance across the barley cultivars studied.
Under normal conditions, Giza 135 exhibits the longest shoot lengths, indicating optimal growth. In moderate drought conditions, Giza 136 (84.35%) maintained relatively high shoot lengths, demonstrating resilience, followed by Giza 2000 and Giza 129, respectively, showing moderate reductions. Under drought conditions, Giza 132 (79.53%) performs better than other varieties, demonstrating superior drought tolerance. Giza 135 consistently showed the longest shoot lengths under normal conditions, while Giza 136 exhibited strong resilience to drought stress, as shown in Figure 2a.
For root length, as presented in Figure 2b under normal conditions, Giza 126 exhibits the longest root lengths, indicating robust growth, followed by Giza 135 and Giza 136. Giza 2000 and Giza 123 also perform well. In moderate drought conditions, Giza 126, Giza 136, and Giza 123 maintained relatively high root lengths, demonstrating resilience, whereas the others showed moderate reductions. Under drought conditions, Giza 126 (61.35%), Giza 136 (45.43%), and Giza 123 (41.72%) perform better than other varieties, demonstrating superior drought tolerance. Giza 126 consistently exhibits the longest root lengths across all conditions, indicating strong resilience to drought stress, which is crucial for selecting crop varieties for varying water availability scenarios.
Under normal conditions, Giza 130 exhibited the highest shoot fresh weights, indicating optimal growth. In moderate drought conditions, Giza 132 (52.8%) maintained relatively the highest shoot fresh weight, demonstrating resilience, while Giza 2000 and Giza 138 showed moderate reductions. Under drought conditions, Giza 130 (38.1%), followed by Giza 132 and Giza 126, performed better than other varieties, such as Giza 135 and Giza 129, demonstrating superior drought tolerance. Giza 130 consistently showed the highest shoot fresh weights under normal conditions. At the same time, Giza 132 and Giza 126 exhibited strong resilience to drought stress, which is crucial for selecting crop varieties for varying water availability scenarios, as shown in Figure 2c.
For the shoot dry weight traits of the ten cultivars under normal, moderate, and severe drought conditions, all of the cultivars experienced reduced dry weight as water availability decreased, but the extent varied, indicating differences in drought tolerance. Giza 136 had the highest dry weight under normal conditions, followed by Giza 138 and Giza 135, while Giza 134 had the lowest. Under moderate drought, Giza 136 retained 74.5% of its normal weight, with Giza 132 showing exceptional tolerance by retaining 97.7%. Giza 134 had the lowest retention at 67.3%. Under severe drought, Giza 136 retained 48.9% of its normal weight, with Giza 132 and Giza 126 retaining 67.2% and 68%, respectively. Giza 135 was most affected, retaining only 31.7%. Overall, Giza 136 was the most drought-tolerant, followed by Giza 132 and 126, as shown in Figure 2d.

3.1.2. Photosynthetic Efficiency Percentage and Induction Under Drought Stress

Under normal conditions, as presented in Figure 3a,b, Giza130 (83.40%), Giza126 (82.69%), and Giza135 (82.48%) showed the highest photosynthetic efficiency. Under moderate drought conditions, efficiency slightly reduces, with Giza130 (81.65%), Giza123 (81.64%), and Giza138 (80.55%) demonstrating resilience. Drought conditions cause significant decreases, notably in Giza129 (74.88%), but Giza126 (81.03%) and Giza135 (78.58%) showed better tolerance. Giza130 performed best under optimal conditions, while Giza126 is most resilient to drought. These insights guide selecting cultivars for varying water availability, enhancing crop yield.
Under normal conditions, plants like Giza134 (79.0%), Giza138 (78.75%), and Giza129 (78.5%) exhibited superior photosynthetic induction, rapidly adjusting to changes in light intensity. Under moderate drought conditions, photosynthetic induction slightly decreases, with Giza129 (77.75%), Giza130 (77.75%), and Giza138 (77.75%) showing resilience. Drought stress significantly hinders this process, with more pronounced reductions in cultivars like Giza136 (73.75%). Despite this, Giza126 (76.5%) and Giza129 (76.75%) maintained higher induction percentages, displaying better drought tolerance. Giza134 excels under optimal conditions, while Giza126 and Giza129 show the highest resilience to drought stress.

3.1.3. Stomatal Conductance Under Drought Stress

Under drought stress conditions, the stomatal conductance of various Giza cultivars was significantly affected, showing marked reductions as the drought intensity increased. For Giza 2000, stomatal conductance decreased (50.42%) under moderate drought. Further drought stress caused a more substantial decrease (79.83%). Similarly, Giza 135 experienced a reduction of 30% under moderate drought, with stomatal conductance decreasing. Under drought stress, the reduction was even more pronounced, with stomatal conductance decreased by 87.14%. In the case of Giza 134, the stomatal conductance decreased by 48.46% under moderate drought. Under drought stress, the decrease was 90.77%. Giza 129, starting with a lower initial value, showed reductions of 57.58% under moderate drought and decreased by 66.67% under drought stress. Giza 132 showed one of the largest reductions, with stomatal conductance decreasing (67.99%) under moderate drought and decreasing (94.12%) under drought stress. Giza 123 showed a similar trend, with a reduction of 52% under moderate drought and a decrease of 89.33% under severe drought.
Giza 130 exhibited moderate reductions, with stomatal conductance decreasing by 27.93% under moderate drought and 75.68% under drought stress. In contrast, Giza 136 had the highest initial stomatal conductance reductions of 45.14% and 86.85% under moderate and full drought, respectively. Giza 138 showed a marked decrease of 70.15% under moderate drought, with stomatal conductance dropping. Under drought stress, the reduction reached 89.55%. Finally, Giza 126, which had the highest stomatal conductance in normal conditions, was reduced by 39.90% under moderate drought and 75.76% under drought stress. In summary, all cultivars exhibited a decrease in stomatal conductance as drought stress increased, with Giza 126 maintaining relatively higher values across all conditions compared to other cultivars. However, Giza 132 experienced the most significant percentage reductions under drought stress, highlighting their greater sensitivity to severe drought stress conditions Figure 3c.

3.1.4. Chlorophyll Content Under Drought Stress

Under normal conditions, the highest SPAD values were recorded for Giza 138 (39.7, 100%), indicating optimal chlorophyll content. In moderate drought conditions, Giza 138 (34.6, 87%), Giza 123 (31.1, 78.22%), and Giza 135 (30.7, 77.33%) maintain relatively high SPAD values, demonstrating resilience, whereas Giza 2000 and Giza 129 showed moderate reductions, respectively. Under drought conditions, Giza 138 (31.4, 79%), followed by Giza 135 and Giza 123, respectively, perform better than other varieties, such as Giza 2000 and Giza 129, demonstrating superior drought tolerance. Overall, Giza 138 consistently shows the highest SPAD values across all conditions, indicating strong resilience to drought stress, which is crucial for selecting crop varieties for varying water availability scenarios (Figure 3d).

3.2. Field Parameters Under Water Deficiency

3.2.1. Impact of Drought Stress on DH and DM, PH, SL and KS

For the number of days to heading (DH) in the first season, under water deficit conditions, Giza126 exhibited the lowest reduction percentage (4.1%) for the DH. At the same time, Giza138 showed the highest sensitivity with a 6.1% reduction percentage for the DH, followed by Giza134 (a 6% reduction). In the second season, Giza132 had the lowest reduction percentage (1.9%) of the DH, while Giza2000 and Giza135 showed the highest reduction percentages of 6.8% and 6.7%, respectively. Genotypes such as Giza135 and Giza129 showed high sensitivity to water deficit conditions in both seasons, with reductions of around 6%, whereas Giza126 and Giza132 exhibited relatively lower sensitivity, especially in season 2, as shown in Figure 4a.
For the days to maturity (DM), under the water deficit condition, the two varieties Giza123 and Giza138 recorded the lowest reduction percentage (1.6% and 1.1%) for the DM in the first and second seasons, respectively. On the other hand, Giza134 and Giza126 showed significant reduction percentages of 4.2% and 3.2% in the two seasons, respectively. Genotypes such as Giza134, Giza130, and Giza135 showed higher sensitivity to water deficit conditions in both seasons, with reductions of around 3%, while Giza138 and Giza136 exhibited relatively lower sensitivity. These results indicate varying levels of sensitivity and adaptability to water deficit among the genotypes, with some genotypes showing significant reductions in the DH and DM, indicating higher sensitivity to drought conditions, as shown in Figure 4b.
For the plant high trait (PH), as presented in Figure 4c, in the first season, Giza136 had the highest reduction percentage (14.02%), while the lowest percentage was recorded for Giza130 (4.47%). In the second season, Giza129 had the highest value for the PH reduction percentage (18.37%), which showed higher sensitivity, while Giza134 recorded the lowest reduction percentage (8.46%) and appeared less sensitive.
For the spike length (SL), Giza129 had the highest reduction percentage in the first and second seasons (25.48% and 26.86%, respectively), while Giza134 and Giza138 recorded the lowest SL reduction percentages, 12.93% and 8.68%, in the first and second seasons, respectively. Giza135 and Giza129 were more sensitive, while Giza138 was less sensitive, as shown in Figure 4d. For the number of kernel spikes−1 (KS), in the first and second seasons, Giza129 had the highest value of reduction percentage (28.21% and 24.43%, respectively), while, for the lowest value, Giza138 recorded the lowest rate in the first (9.28%) and second (4.76%) seasons, indicating that Giza135 and Giza129 were more sensitive. At the same time, Giza138 was less sensitive, as shown in Figure 4e.

3.2.2. Impact of Drought Stress on the Number of Spikes, KW, BY and GY

For the number of spikes m−2 in season 1, Giza123 exhibited a reduction of 12.28%. For the number of spikes m−2 in season 1, Giza129 had the highest reduction percentage (18.67%), followed by Giza135 and Giza123. Meanwhile, in season 2, the reduction percentage for the number of spikes m−2 ranged from 2.54% for Giza138 to 20.35% for Giza135. Genotypes such as Giza135 and Giza129 showed higher sensitivity, while Giza138 exhibited a lower sensitivity, as shown in Figure 5a.
For 1000-kernel weight (KW) trait, under water deficit, the lowest (1.65%) and highest (12.88%) reduction percentages were recorded for Giza2000 and Giza129, respectively, in the first season. In the second season, Giza126 exhibited the lowest KW reduction percentage (0.45%). At the same time, Giza129 had the highest reduction percentage (8.12%), indicating that genotypes such as Giza135 and Giza129 showed higher sensitivity. In contrast, Giza2000 exhibited relatively lower sensitivity, as shown in Figure 5b.
For the biological yield (BY) trait, as shown in Figure 5c, Giza129 had the highest reduction percentage (28.61%) under water deficit in the first season, followed by Giza135 (22.71%), Giza123 (19.42%), and Giza126 (17.07), which were revealed to be the most sensitive varieties. In the second season, under the same condition, Giza129 and Giza135 experienced the highest reduction percentages (34.91% and 30.78%, respectively), and the lowest reduction was recorded for Giza130, which decreased by 8.54 reduction percentage. Genotypes such as Giza135 and Giza129 showed higher sensitivity. At the same time, Giza134 exhibited relatively lower sensitivity.
For the grain yield (GY) trait in the first season, Giza129 (38.45%) followed by Giza123 (31.67%), exhibited the highest reduction percentage of GY under the water deficit condition. In season 2, Giza129 had a 37.55% reduction percentage in the GY, followed by Giza135 (31.14%) and Giza123 (22.98%). In comparison, Giza2000 had the lowest reduction percentage (9.21%), indicating that genotypes such as Giza135 and Giza129 showed higher sensitivity, while Giza134 exhibited relatively lower sensitivity, as shown in Figure 5d.

3.2.3. Drought Stress Susceptibility Index and Correlation Analysis

Table 1 presents the drought stress susceptibility indices for the cultivars under study. Giza 134, Giza 138, and Giza 126 showed the highest values in drought-stressed conditions. The high values of the YP (yield potential under non-stressed conditions), YS (yield under drought-stressed conditions), YI (Yield Index), STI (Stress Tolerance Index), and GMP (Geometric Mean Productivity) for these cultivars suggest a robust ability to sustain yield under drought, marking them as resilient options. Giza 134 stands out with the lowest values for the SDI (Stress Differential Index) and TOL (Tolerance Index), typically used to gauge sensitivity to drought stress, affirming its superior drought tolerance. In contrast, Giza 129 and Giza 135, which have DSI (Drought Susceptibility Index) values above unity and high TOL values, are identified as more sensitive to drought stress, producing lower yields under such conditions.

3.2.4. Genotype into Environment Interaction (GGE) Biplot for Grain Yield

Figure 6 visualizes the appropriate cultivars for the two seasons under normal and drought stress conditions. The lines split the biplot into eight sectors and the four environments were grouped into three main sectors. The “which-won-where” pattern showed that Giza 134 and Giza 138 were the vertex cultivars under all conditions in the two seasons, followed by Giza 126.

3.2.5. Analysis of Variance Among All Factors

Table S6 presents the traits’ mean squares for seasons, irrigation treatments, cultivars, and their interactions. Season mean squares were significant at the 0.05 or 0.01 probability levels for all traits in all situations except the spike length and biological yield. The irrigation treatments and genotype mean squares were also significant for all of the studied traits. Table S7 presents the means and ranges of reduction % due to drought stress for all studied characters during the 2019/20 and 2020/2021 seasons.
The mean squares of seasons × irrigation treatment interaction (S × Irr) being significant only for the No. days to maturity and No. of spikes m−2 indicate that the response of the studied cultivars changed from one season to another for these characters. The season × cultivars interaction variations were significant for all characters, except for days to maturity. Also, the interaction mean squares for irrigation treatments with cultivars were significant for all studied traits.

3.2.6. Mean Performance of Cultivars (Seasons and Irrigation Treatment Effects)

Normal irrigation recorded the highest mean values for all of the studied characters compared to the drought stress treatment (Table 2).

4. Discussion

4.1. Yield Components and Plant Traits Under Drought Stress

Drought response in barley, particularly in the DH and DM, is crucial in yield stability. Early heading and maturity are advantageous traits, enabling plants to avoid terminal drought stress and maintain better yields. A negative correlation between the DH and yield under drought conditions has been observed, with earlier heading cultivars generally yielding more. Similarly, earlier maturity improves drought performance. The significant genotypic variation in DH and DM indicates that breeding programs can target these traits to develop drought-tolerant barley varieties cultivars that sustain yields in water-limited environments [33].
Drought stress significantly impacts barley yield by reducing phenotypic variability. Identifying key traits for breeding is essential to enhance drought tolerance. The number of fertile spikelets and the grain number per spike are critical traits influencing the yield under drought conditions, directly affecting reproductive success and overall yield [25]. Our study proved drought stress significantly reduced barley grain yield and yield components. For instance, Giza 134 had the highest number of kernel spikes−1, while Giza 138 and Giza 2000 exhibited the best 1000-kernel weight. Conversely, Giza 123, 135, and 129 performed poorly under stress. Despite reduced plant height and spike length, the total chlorophyll content remained unaffected. Giza 126, 2000, and 127 demonstrated superior grain yields under normal and drought conditions, indicating good drought tolerance. These cultivars are promising candidates for breeding drought-resistant barley cultivars. Future research should explore the genetic mechanisms behind these traits [34].
The means and ranges of reduction percentages due to drought stress for the studied characters are listed in Table S6. The means of reduction were positive for all of the studied characters. The least affected character with the drought stress was the number of days to maturity (5.9 and 4.3%) in the first and second seasons, respectively. On the contrary, the most affected characters with drought stress were the number of spikes m−2 (19.5%) and biological yield (20.5 and 14%) in the first and second seasons, respectively. Saeidi et al., 2013 [35] found 22, 18.3, 5.9, 5.5, and 21.9% reductions in the grain yield, biomass, 1000-kernel weight, number of kernel spikes−1, and number of spikes m−2 caused by post-anthesis water deficiency. In addition, an 8.8 to 16.3% reduction in the grain yield was found under drought stress [27].
According to Mahmood et al. (2021), biomass dry matter and plant height can be used as selection criteria for grain yield performance under drought conditions [27]. This may relate to the effect of post-anthesis drought stress when plant biomass growth has reached the maximum level [26]. Many authors on barley detected reduced grain yield and yield components under drought stress [36,37,38,39]. In addition, the season × irrigation treatments × cultivars interactions were significant for all traits. Selection for genetic variability in the analyzed cultivars for drought tolerance is the most critical practice in breeding for drought stress [19]. According to the significant variance, the studied cultivars proved to be an appropriate source of genetic diversity in breeding for drought stress tolerance [40]. Our results agreed with previous studies [25,27,34].
Drought decreases the 1000-kernel weight and grain number per spike, directly affecting the yield. It also reduces the plant height. Cultivars such as Danesiah, Eram, and Yoosef have been identified as suitable for normal and drought conditions [33]. The best cultivars for biological yield were Giza 134 and Giza 138, while Giza 129 and Giza 135 performed the worst under all conditions. Giza 134 and Giza 138 were the best for grain yield, and Giza 2000 was favorable under most conditions. In contrast, Giza 129, Giza 135, and Giza 133 performed poorly under stress conditions. The reduction in grain yield is primarily attributed to drought stress affecting grain-related traits during the early grain-filling period, such as the grain weight and the number of grains [4].
Previous studies confirm drought stress reduces growth, reflected in decreased plant height, dry weight, and other growth functions [41,42]. These observations highlight the importance of selecting and breeding resilient cultivars under drought conditions, ensuring sustainable barley production in water-limited environments. In conclusion, early heading and maturity are beneficial traits for drought tolerance in barley, and significant genotypic variations in these traits can be leveraged in breeding programs. Identifying and breeding for crucial traits such as the number of fertile spikelets, kernel number per spike, and 1000-kernel weight is essential for improving yield under drought stress. Cultivars like Giza 134, Giza 138, and Giza 2000 show promise for developing drought-resistant barley cultivars. Future research should delve into the genetic mechanisms underlying these traits to enhance our understanding and breeding strategies for drought tolerance in barley. The biplot analysis appeared as a valuable screening tool to identify the stress-tolerant cultivars in wheat [43] and barley [25].

4.2. Identifying Drought-Tolerant Barley: Challenges and Key Traits

Identifying truly drought-tolerant cultivars remains challenging, with accurate phenotyping playing a critical role. Over the past several decades, assessing drought tolerance has been a central focus in crop breeding programs [44]. These efforts often involve using bi-parental populations derived from genetically diverse parents. However, the genetic diversity within barley has been significantly reduced due to long-term domestication and modern breeding practices. This reduction in diversity has constrained the identification of valuable drought-tolerant genes and has subsequently limited breeding success [45,46]. Therefore, utilizing diverse natural populations is essential for improving drought tolerance [19].
Our study screened ten cultivated barley cultivars, revealing significant variation in the shoot biomass and water content under control and drought conditions. Notably, cultivars such as Giza 138, Giza 134, and Giza 126 demonstrated superior performance under drought stress, emphasizing the potential of barley as a valuable resource for identifying genes that contribute to drought tolerance in breeding programs. This aligns with the findings of Elakhdar et al. (2023) on Giza 134, showing a 10–20% increase in yield stability through sustained growth and enhanced water retention under drought conditions. Notably, Giza 134 increases proline levels by 30%, potentially boosting the yield by up to 15% in water-limited settings. This genotype retains 90% of its photosynthetic capacity and reduces water loss by 25–30% via increased stomatal resistance, optimizing the water-use efficiency. Genetically, Giza 134 drought resilience is a valuable target for MAS, which could improve breeding efficiency by 40% by selecting over 60 drought-responsive genes. Drought tolerance is further enhanced by gamma-aminobutyric acid pathways, contributing up to 30% of drought resilience and cis-regulatory elements, which could optimize stress responses. Additionally, improved iron homeostasis in Giza 134 reduces leaf wilting by 20–25%, establishing a robust platform for developing drought-resilient barley cultivars for arid regions [47].
Evaluating the same materials under varying drought conditions is crucial to accurately identifying true drought-tolerant cultivars. Drought is a complex and gradual stressor, with its severity influenced by multiple factors, including watering, drought stress duration, irrigation methods, soil properties, and temperature [48,49]. Given the variability of drought stress across different locations and years, it is essential to conduct drought tolerance assessments across multiple locations, years, or controlled environments [50]. While efforts have been made to create consistent and reliable drought conditions, pot culture with soil provides a promising approach as it closely simulates field conditions. However, the complex nature of soil composition makes it difficult to maintain uniform water and nutrient availability [51,52]. To address this, our study was conducted under field conditions, using clay soil in the pots experiment to closely mimic natural field environments.
Our research aimed to evaluate barley cultivars under field conditions and in pots, with accurate phenotyping critical for assessing drought tolerance [53]. Traditionally, drought tolerance has been measured by yield loss under stress. However, more recent studies have focused on other traits closely associated with drought tolerance, such as morphology, biomass production, water relations, and photosynthetic activity [51,54,55]. In barley, traits such as fresh matter, dry matter, and relative water content are commonly used for this purpose [19]. Our study used reductions in the shoot fresh weight, dry weight, and water content as critical traits to screen for drought tolerance.

5. Conclusions

This study underscores the profound impact of drought stress on barley, revealing that reduced irrigation significantly diminishes most of the evaluated traits. Among these, grain yield was the most affected trait. This research underscores the critical need to select drought-resilient barley cultivars to maintain sustainable production in regions with limited water availability. The study highlights significant variation in drought tolerance among barley cultivars regarding physiological parameters. Giza 134, Giza 126, and Giza 138 displayed remarkable resilience, maintaining robust growth, photosynthetic efficiency, and chlorophyll content under drought stress. These cultivars represent excellent options for breeding efforts aimed at improving drought resistance. Conversely, cultivars like Giza 135 and Giza 129 were more susceptible to drought, exhibiting substantial declines in growth and physiological traits. This research emphasizes the importance of selecting drought-tolerant barley cultivars to ensure sustainable crop production in water-scarce environments such as Giza 134, Giza 138, and Giza 126. Future research could investigate the genetic basis of drought tolerance in these cultivars to identify tolerance-related genes or markers.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/agronomy14112711/s1, The supplementary data include several key tables providing essential information about the study. Table S1 lists the names and pedigrees of the studied cultivars. Table S2 details the water provided, expressed in m3 per hectare, throughout the barley growing seasons for both years. Table S3 presents the mechanical and chemical analyses of the experimental sites in both seasons. Table S4 presents the monthly mean air temperature (°C), relative humidity (RH%), and rainfall (mm/month) recorded at the experimental site during the 2019/20 and 2020/21 growing seasons. Table S5 outlines the stress tolerance indices, including the formulae and references used to evaluate drought stress tolerance. Table S6 shows the mean squares across the two seasons and under different water treatments. Finally, Table S7 provides the means and ranges of reduction % due to drought stress for all studied characters during the 2019/20 and 2020/2021 seasons.

Author Contributions

W.A.A.: Investigation, Methodology, Validation, Conceptualization, Data curation, and Writing—original draft. E.E.E.: Experimental work and Data curation. H.A.A.: Methodology and Software. S.M.H.A.: Methodology and Formal analysis. Z.I., M.M. and I.S.E.-D.: Formal analysis and Writing—review and editing. T.G.: Investigation and Writing—review and editing. A.A.A.: Conceptualization, Project administration, Visualization, and Writing—review and editing. I.H.S.: Supervision, Funding acquisition, Writing—original draft, and Writing—review and editing. All authors have read and agreed to the published version of the manuscript.

Funding

This research was financially supported by the International (Regional) Cooperation and Exchange Program, Research Fund for International Young Scientists, Grant No. 32250410280, the National Natural Science Foundation of China, Sino-Pakistan Project NSFC, Grant No. 31961143008, “Xingdian Talents Support Plan” Program and Jiangsu Collaborative Innovation Center for Modern Crop Production (JCIC-MCP) China.

Data Availability Statement

The article provides all the data necessary to support the findings of this study.

Conflicts of Interest

The authors declare that the research was conducted without commercial or financial relationships that could create a conflict of interest.

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Figure 1. Comparative analysis of ten cultivars under varying drought conditions. The figure illustrates the impact of normal conditions, moderate drought stress, and severe drought stress on the growth and root development of different Giza cultivars, highlighting the varying levels of drought tolerance across cultivars.
Figure 1. Comparative analysis of ten cultivars under varying drought conditions. The figure illustrates the impact of normal conditions, moderate drought stress, and severe drought stress on the growth and root development of different Giza cultivars, highlighting the varying levels of drought tolerance across cultivars.
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Figure 2. Performance and drought tolerance of ten cultivars for shoot length (cm) (a), root length (cm) (b), fresh shoot weight (c), and shoot dry weight (d). Different letters indicated significant variations among the cultivars using LSD 0.05.
Figure 2. Performance and drought tolerance of ten cultivars for shoot length (cm) (a), root length (cm) (b), fresh shoot weight (c), and shoot dry weight (d). Different letters indicated significant variations among the cultivars using LSD 0.05.
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Figure 3. Photosynthetic efficiency, Photosystem II quantum efficiency, stomatal conductance, and SPAD values of ten Giza cultivars under normal, moderate, and severe drought conditions. (a,b) show the photosynthetic efficiency and Photosystem II quantum efficiency percentages; (c) the stomatal conductance under drought stress (gsw) values; (d) SPAD values under different drought stress. Different letters indicated significant variations among the cultivars using LSD 0.05.
Figure 3. Photosynthetic efficiency, Photosystem II quantum efficiency, stomatal conductance, and SPAD values of ten Giza cultivars under normal, moderate, and severe drought conditions. (a,b) show the photosynthetic efficiency and Photosystem II quantum efficiency percentages; (c) the stomatal conductance under drought stress (gsw) values; (d) SPAD values under different drought stress. Different letters indicated significant variations among the cultivars using LSD 0.05.
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Figure 4. Mean performance of days to heading (a) and number of days to maturity (b), plant height (cm) (c), spike length (cm) (d), and number of kernel spikes−1 (e) for studied cultivars under normal and drought stress conditions across irrigation treatments and two seasons. Different letters indicated significant variations among the cultivars using LSD 0.05.
Figure 4. Mean performance of days to heading (a) and number of days to maturity (b), plant height (cm) (c), spike length (cm) (d), and number of kernel spikes−1 (e) for studied cultivars under normal and drought stress conditions across irrigation treatments and two seasons. Different letters indicated significant variations among the cultivars using LSD 0.05.
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Figure 5. Performance of the number of kernel spikes−1 (a), 1000-kernel weight (b), biological yield ha−1 (c), and grain yield ha−1 (d) for the studied cultivars under normal and drought stress conditions in the two seasons across the irrigation treatments and the two seasons. Different letters indicated significant variations among the cultivars using LSD 0.05.
Figure 5. Performance of the number of kernel spikes−1 (a), 1000-kernel weight (b), biological yield ha−1 (c), and grain yield ha−1 (d) for the studied cultivars under normal and drought stress conditions in the two seasons across the irrigation treatments and the two seasons. Different letters indicated significant variations among the cultivars using LSD 0.05.
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Figure 6. Grain yield performance and stability of ten cultivars under normal and drought stress across two seasons. A GGE biplot was used to rank 10 cultivars (G1–G10: Giza 123, Giza 126, Giza 132, Giza 134, Giza 130, Giza 136, Giza 138, Giza 2000, Giza 135, Giza 129) for grain yield across four environments: E1 (normal, 2019/20), E2 (drought stress, 2019/20), E3 (normal, 2020/21), and E4 (drought stress, 2020/21). The Average Environment Axis (AEA) indicated higher mean performance, while its perpendicular axis indicated greater variability or instability. The analysis highlighted yield performance and stability differences under normal and drought conditions.
Figure 6. Grain yield performance and stability of ten cultivars under normal and drought stress across two seasons. A GGE biplot was used to rank 10 cultivars (G1–G10: Giza 123, Giza 126, Giza 132, Giza 134, Giza 130, Giza 136, Giza 138, Giza 2000, Giza 135, Giza 129) for grain yield across four environments: E1 (normal, 2019/20), E2 (drought stress, 2019/20), E3 (normal, 2020/21), and E4 (drought stress, 2020/21). The Average Environment Axis (AEA) indicated higher mean performance, while its perpendicular axis indicated greater variability or instability. The analysis highlighted yield performance and stability differences under normal and drought conditions.
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Table 1. Estimates of a Drought Stress Susceptibility Index based on grain yield for the studied cultivars in the two seasons.
Table 1. Estimates of a Drought Stress Susceptibility Index based on grain yield for the studied cultivars in the two seasons.
CultivarsYpYsDSIYIYSISTIGMPSDITOL
Giza 1234.433.221.440.900.730.733.771.731.21
Giza 1264.413.820.701.060.870.864.101.870.59
Giza 1324.333.720.741.040.860.824.021.860.61
Giza 1344.754.300.511.200.901.044.521.900.46
Giza 1304.223.620.751.010.860.783.911.860.60
Giza 1364.283.580.861.000.840.783.911.840.70
Giza 1384.704.160.611.160.881.004.421.880.55
Giza 20004.513.880.741.080.860.894.181.860.63
Giza 1354.332.981.650.830.690.663.591.691.35
Giza 1294.302.672.000.740.620.583.391.621.63
Drought Susceptibility Index (DSI), Sensitivity Drought Index (SDI), Stress Tolerance (TOL), Geometric Mean Productivity (GMP), Stress Tolerance Index (STI), Yield Index (YI), and Yield Stability Index (YSI). A lower Stress Susceptibility Index than unity (DSI < 1) is synonymous with a high stress tolerance, while a high Stress Susceptibility Index (DSI > 1) means higher stress sensitivity.
Table 2. Mean values of the studied characters for the barely grown under water treatments (normal irrigation and drought stress) during the 2019/2020 and 2020/2021 growing seasons.
Table 2. Mean values of the studied characters for the barely grown under water treatments (normal irrigation and drought stress) during the 2019/2020 and 2020/2021 growing seasons.
VariableDHDMPHSMSLKSTKWBYGY
Year
2019/202086130108.024119.6064.8350.1812.173.96
2020/202188132107.264209.6566.0251.6812.234.06
F test****NS**NS****NS**
Irrigation treatments
Normal irrigation90.55133.81113.86435.9110.6671.6254.6013.314.43
Drought stress83.45126.97101.43395.868.6059.2347.2611.103.59
F test******************
2019/20Normal irrigation89.49133.23113.59428.4710.6471.0753.8213.254.41
Drought stress82.43125.34102.45394.188.5658.5946.5411.103.52
2020/21Normal irrigation91.61134.38114.13443.3410.6772.1855.3713.374.44
Drought stress84.48128.60100.40397.538.6359.8747.9911.093.67
LSD0.051.271.101.992.792.7890.190.880.170.07
DH = No. of days to heading, DM = No. of days to maturity, PH = plant height (cm), SM = No. spikes m−2, SL = spike length (cm), KS = No. of kernel spikes−1, TKW = 1000-kernle weight (g), BY = biological yield (ton ha−1), and GY = grain yield (ton ha−1). ‘**’ refers to significant differences at 0.01, while ‘NS’ refers to no significant differences.
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MDPI and ACS Style

Abdelrady, W.A.; Elshawy, E.E.; Abdelrahman, H.A.; Hassan Askri, S.M.; Ibrahim, Z.; Mansour, M.; El-Degwy, I.S.; Ghazy, T.; Aboulila, A.A.; Shamsi, I.H. Evaluating Physiological and Yield Indices of Egyptian Barley Cultivars Under Drought Stress Conditions. Agronomy 2024, 14, 2711. https://doi.org/10.3390/agronomy14112711

AMA Style

Abdelrady WA, Elshawy EE, Abdelrahman HA, Hassan Askri SM, Ibrahim Z, Mansour M, El-Degwy IS, Ghazy T, Aboulila AA, Shamsi IH. Evaluating Physiological and Yield Indices of Egyptian Barley Cultivars Under Drought Stress Conditions. Agronomy. 2024; 14(11):2711. https://doi.org/10.3390/agronomy14112711

Chicago/Turabian Style

Abdelrady, Wessam A., Elsayed E. Elshawy, Hassan A. Abdelrahman, Syed Muhammad Hassan Askri, Zakir Ibrahim, Mohamed Mansour, Ibrahim S. El-Degwy, Taha Ghazy, Aziza A. Aboulila, and Imran Haider Shamsi. 2024. "Evaluating Physiological and Yield Indices of Egyptian Barley Cultivars Under Drought Stress Conditions" Agronomy 14, no. 11: 2711. https://doi.org/10.3390/agronomy14112711

APA Style

Abdelrady, W. A., Elshawy, E. E., Abdelrahman, H. A., Hassan Askri, S. M., Ibrahim, Z., Mansour, M., El-Degwy, I. S., Ghazy, T., Aboulila, A. A., & Shamsi, I. H. (2024). Evaluating Physiological and Yield Indices of Egyptian Barley Cultivars Under Drought Stress Conditions. Agronomy, 14(11), 2711. https://doi.org/10.3390/agronomy14112711

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