Response of Wheat Genotypes to Drought Stress Stimulated by PEG

Abstract

Wheat is a cereal grain crop that is commonly cultivated and is a good source of nutrients that are beneficial to human health. In recent years, the productivity of wheat has been steadily declining, with abiotic pressures accounting for almost half of all yield losses. Drought stress is a significant limiting factor for plant development and production around the planet. The influence of polyethylene glycol (PEG) (at concentrations of 5, 10, and 15%)-induced drought stress on the morphological, physiological, and biochemical characteristics of fifteen wheat genotypes was investigated in this work. Overall, it was discovered that morphological and physiological indicators such as germination % and shoot-root lengths during the seedling stage had reduced significantly. The proline content, on the other hand, was shown to be positively correlated with the concentration of PEG treatments. There was a significant difference between the genotypes HD2733, HD2888, and RAJ3765 regarding tolerance to abiotic stress caused by drought. A further finding was that under stressful settings, the first three main components explained 56.65 percent, 65.06 percent, and 72.47 percent of the total variability in PEG treatment levels of five, ten, and fifteen percent, respectively. These collective morphological and physiological parameters, and analyses of their diverse responses, could be used for screening of drought tolerance among the 15 wheat genotypes to select for significant drought tolerance and diverse molecular responses during breeding of stress resistant forms.

1. Introduction

Wheat (Triticum aestivum L.) provides a significant proportion of required dietary calories, minerals, and around 20% of the needed protein for humans [1,2,3]. In 2018, wheat production in India was around 99.7 million tonnes (mt), with an area of 29.58 million hectares (ha) [4]. According to current estimates, the worldwide need for wheat yields is expected to rise by 50% by 2050 to feed the world’s rising population [5]. Productivity in wheat is declining because of the negative impacts of a variety of biotic and abiotic stressors [6,7].

Stresses caused by abiotic variables such as high temperatures, low temperatures, and droughts greatly reduce wheat production, resulting in an average yield loss of around 50% [8,9]. Among the most frequently occurring threats, drought stress is regarded as a severe constraint on agricultural crop production throughout the world [10]. Drought stress has negative effects on the morphological, physiological, and biochemical attributes of the wheat crop [11], and it results in a significant reduction in overall production [6,12]. In the absence of a seasonal or growth stage variation in the crop, genotypes must be evaluated at relevant and often diverse developmental phases [13].

According to predictions, drought periods are expected to become more intense and severe in the foreseeable future [14]. As a result, it is critical to increase our knowledge of how drought stress impacts the functional features of plants and their ecological relationships [15]. Imposing experimental artificial ways to generate drought stress is essential for furthering our knowledge of this phenomenon. Drought stress may be induced artificially in a variety of ways, including restricting water delivery [16], treating with abscisic acid (ABA), and using polyethylene glycol (PEG) [17]. Inducement of drought stress in plants using PEG, a non-ionic water-soluble polymer, is extensively utilized as it is not anticipated to enter the plant cells [18]. Up to this point, several publications have reported the discovery of drought-tolerant wheat genotypes by introducing varying concentrations of PEG-6000 into the plant and observing statistically significant variations in various attributes at the seedling stage [7,19,20,21]. Because it effects the growth and development of wheat via a variety of factors [8], drought stress tolerance is a difficult criterion for wheat performance. When wheat is subjected to moderate to severe water stress, it exhibits significant changes in its morpho-physiological and biochemical characteristics. This is due to changes in plant water relations, cellular oxidative stress, decreased CO₂ assimilation, damage to the membranes of affected tissues, and, in some cases, inhibition of enzyme activity [22]. For wheat species, the effects of drought on their morphological, physiological, and biochemical properties change depending on their ploidy level [23].

Lack of soil moisture influences certain morphological characteristics of wheat, including seed germination [11], shoot length [8], root length [8], tillering [24,25,26], spike number, grain number per spike [24,25,26], number of viable tillers per plant [24,25,26], and 1000 grain weight [24,25,26]. These metrics are derived from physiological characteristics such as chlorophyll concentration, relative water content, photosynthetic rate, and membrane stability index. The biochemical proline is vital in managing osmotic pressure and stabilizing cells. As a result, these metrics have the potential to be used as valid indicators for screening and selecting drought-resistant wheat genotypes [27,28]. In these circumstances, the current inquiry was carried out to determine the reaction of 15 wheat genotypes to drought stress conditions generated by PEG. To identify drought-resistant wheat genotypes that may be employed in a breeding programme for the development of drought-tolerant wheat varieties, the effects of different PEG-6000 concentrations on several morphological, physiological, and biochemical characteristics were investigated.

2. Material and Methods

Field experiments were carried out during the wheat growing season of 2016–2017 at the field research laboratory and experimental station, Department of Biotechnology, Sardar Vallabhbhai Patel University of Agriculture & Technology, Meerut, India. Fifteen bread-wheat genotypes were evaluated in this study and their details are given in

Table 1. Details of fifteen genotypes.

S. No.	Name of Variety	Pedigree	Centre	Release Year	Zone	Production Condition
1	DBW17	CMH 79A.95/3* CNO 79//Raj 3777	IIWBR (DWR), Karnal	2006	NWPZ	Irrigated, timely sown
2	DBW71	Prinia/UP 2425	IIWBR (DWR), Karnal	2013	NWPZ	Irrigated, late sown
3	HD2733	ATTILA/3/TUI/CARC//CHEN/CHTO/4/ATTILA	IARI, New Delhi	2001	NEPZ	Irrigated, timely sown
4	HD2864	DL 509-2/DL 377-8	IARI New Delhi.	2008	CZ	Irrigated, late sown
5	HD2888	C 306/T. sphaerococcum//HW 2004	IARI, New Delhi	2006	NEPZ	Rainfed, timely sown
6	HD3086	DBW 14/HD 2733// HUW 468	IARI, New Delhi	2014	NWPZ	Irrigated, timely sown
7	HUW468	CPAN-1962/TONI//LIRA’S“/PRL’S’	BHU, Varanasi	1997	NEPZ	Irrigated, timely sown
8	K9423	HP1633/KAL/UP262	CSAUAT, Kanpur	2004	NEPZ	Irrigated, late sown
9	PBW343	ND/VG 7944//KAL/BB3YACO S/4/VEE# 5S	PAU, Ludhiana	2000	NEPZ	Irrigated, timely sown
10	PBW396	CN067/MFD//M0N ‘S73/SERI	PAU, Ludhiana	2000	NWPZ	Rainfed, timely sown
11	PBW590	594/RAJ3814//W 485	PAU, Ludhiana	2009	NWPZ	Irrigated, late sown
12	RAJ3765	HD 2402/VL 639	RAU, Durgapura	1995	NWPZ	Irrigated, late sown
13	UP2425	HD2320/UP2263	GBPUAT, Pantnagar	1999	NWPZ	Irrigated, timely sown
14	WH711	ALD ‘S’HUAC//HD 2285/3/HFW-17	CCSHAU, Hissar	2002	NWPZ	Irrigated, timely sown,
15	WH1021	NYOT95/SONAK	CCSHAU, Hisar	2007	NWPZ	Irrigated, late sown

. The seeds were procured from Department of Genetics and Plant Breeding, Sardar Vallabhbhai Patel University of Agriculture and Technology, Meerut.

2.1. Plant Growth and Drought Treatment

To evaluate the wheat genotypes for various morpho-physiological and biochemical characters under drought stress conditions at the seedling stage, drought stress was induced by polyethylene glycol [19]. Fifty seeds of each genotype were surface sterilized with 0.1% of HgCl₂ for 1 min, then washed thrice with distilled water to avoid fungal contamination, and then were placed on Whatman No. 2 filter paper in 90 mm plastic Tarson Aseptic Petri dishes and were moistened with 8 mL of PEG-6000. The petri dishes were covered and incubated at laboratory conditions (27 ± 2 °C) for 15 days with three different concentrations (5%, 10% and 15% in the treatments 1, 2 and 3, respectively) and the untreated seeds were used as a control. After germination, seedlings were transferred to the rainout shelter. Experiments were conducted in a Randomized Block Design in three replicates. The dimensions of each block were 15 × 15 inches (length × breadth) and the space between the two blocks was 6 inches. The crop was maintained in the field using standard agronomic practices. Various morphological, physiological, and biochemical parameters were recorded during the seedling stage, vegetative growth stage and reproductive stage of the plants.

2.2. Observations on the Morphological Parameters

The numbers of germinated seeds were counted and recorded every 24 h for up to 10 days and the germination percentage was calculated (number of germinated seed/total number of seed × 100). The shoot length (ShL), from the shoot apex to the root apex and the root length (RL), from base of the shoot (collar region) to the root apex, were measured after 15 days of germination. Plant height (PH) was measured from the base of the plant to the tip of the spike (including awns). All the measured lengths were recorded in centimetres (cm). The number of tillers plant⁻¹ (NT) and the flag leaf area (FLA) was calculated after 20 days of anthesis stage by the leaf index method [29] as Leaf area = L × W × F; where, L = maximum length (cm), W = maximum width (cm), F = correction factor (0.747). The spike length (SL) in centimetres, spikelet number spike⁻¹ (SPS), number of grain spike⁻¹ (GPS), thousand grain weight (TW) were measured; days to heading (DTH) and days to maturity (DTM) were counted from date of seed treatment to the appearance of ears and browning of ears, respectively.

2.3. Observations on the Physiological and Biochemical Parameters

A Soil Plant Analytical Development (SPAD) chlorophyll meter (Minolta) was used to measure the relative chlorophyll (ChL) content (µg/cm²) of the leaves of each genotype at the seedling stage under stress conditions. An Infra-Red Gas Analyzer (PN), LI-6400 XT (LICOR Inc., Lincoln, NE, USA), was used to measure the photosynthetic rate (Pn) of leaves (µmol/m²sec). The relative water content (RWC) was calculated through the equation

$$\mathrm{RWC}=\frac{\mathrm{FW}-\mathrm{DW}}{\left(\mathrm{TW}-\mathrm{DW}\right)}\times 100$$

where FW = Fresh weight, TW = Turgid weight and DW = Dry weight of the leaf [30].

The membrane stability index (MSI) was determined by recording the electrical conductivity of leaf leakages in double distilled water at 40 °C and 100 °C [31]. Their electric conductivities were measured with an EC meter (Electrical Conductivity) as C1 and C2 respectively. The membrane stability index = [1 − (C1/C2)] × 100. The free proline content (PC) in leaf tissues were determined by adopting the colorimetric method [32]. The proline content was calculated as per the formula:

$$\mathrm{Proline}\left(\mathsf{\mu }\frac{\mathrm{M}}{\mathrm{g}}\mathrm{fresh}\mathrm{weight}\right)=36.2311\times \mathrm{OD}\times \frac{\mathrm{V}}{2}\times \mathrm{F}$$

where, 36.2311 is the standard curve value of proline, OD = optical density at 520 nm, V = total volume of extract in mL, F = milligram of fresh weight of leaf taken for one proline estimation, 2 = volume of aliquot taken for proline estimation.

2.4. Statistical Analysis

All the data presented are the means of three independent replicates with ±standard error (SE). Data were subjected to analysis of variance (ANOVA) and comparison of means used the Duncan’s Multiple Range test [33] performed by IBM SPSS Statistics v20 (New York, NY, USA). Pearson’s correlation coefficients were calculated separately for the control and the treatments. A principal component analysis (PCA) based on the correlation matrix was performed using SPSS to classify the variation in traits as well as the genotypes. To assess the variation in traits, the PCA biplots and boxplot were generated separately for the control and drought stress setups using R software [34].

3. Results

Analysis of variance (ANOVA) revealed significant differences among the selected wheat genotypes for all the analysed traits, except for MSI and RWC under control and drought stress treatment conditions. The mean squares from the ANOVA and significance of mean comparison (p < 0.05) are given in

Table 2. Mean squares of morphological, physiological, and biochemical traits under control, 5% PEG, 10% PEG and 15% PEG treatment condition.

		df	GP	ShL	RL	NT	DOH	PH	FLA	DOM	SL
Control	Between Groups	14	10.492 *	2.953 *	3.247 *	1.475 *	48.248 *	37.545 *	90.971 *	207.438 *	7.119 *
	Within Groups	30	0.442	0.670	1.137	0.506	0.644	6.874	9.098	3.322	0.559
	Total	34
5% PEG	Between Groups	14	93.853 *	3.957 *	2.239 *	1.363 *	49.029 *	43.955 *	69.977 *	188.046 *	6.797 *
	Within Groups	30	19.946	0.641	0.450	0.322	0.350	7.242	7.545	0.622	0.789
	Total	34
10% PEG	Between Groups	14	212.329 *	5.579 *	2.141 *	1.106	55.637 *	67.307 *	64.085 *	171.427 *	4.732 *
	Within Groups	30	14.479	0.804	0.307	0.428	0.233	5.310	4.547	0.294	1.100
	Total	34
15% PEG	Between Groups	14	562.567 *	7.602 *	2.381 *	0.887 *	36.389 *	69.697 *	61.616 *	115.958 *	5.817 *
	Within Groups	30	9.679	0.311	0.320	0.225	0.306	11.381	4.659	0.611	1.118
	Total	34
		df	SPS	GPS	TW	Pn	CHL	MSI	RWC	PROLINE
Control	Between Groups	14	12.422 *	78.527 *	21.977 *	59.308 *	14.999 *	21.019	22.444	0.192 *
	Within Groups	30	0.933	7.190	1.492	1.975	3.382	11.713	22.264	0.000
	Total	34
5% PEG	Between Groups	14	10.200 *	45.032 *	18.122 *	53.947 *	13.406 *	33.404	25.960	0.221 *
	Within Groups	30	0.867	4.406	0.390	1.000	7.723	14.676	18.650	0.000
	Total	34
10% PEG	Between Groups	14	6.413 *	72.541 *	20.797 *	51.654 *	12.708	34.150	43.407	0.244 *
	Within Groups	30	1.156	3.333	0.134	0.358	6.396	11.038	15.873	0.000
	Total	34
15% PEG	Between Groups	14	7.533 *	76.962 *	16.663 *	47.622 *	11.258	109.792 *	212.793 *	0.282 *
	Within Groups	30	0.978	3.028	0.181	0.123	8.267	5.271	12.105	0.000
	Total	34

* Significant at 5% level of probability.

.

3.1. Morphological Responses to Drought Stress

In the present study, the maximum seed GP (100%) was recorded in PBW343 and UP2425, and minimum in K9423 (94%) in control conditions (

Table 3. Mean values of morphological traits under control and 5%, 10% and 15% PEG treatment conditions.

Traits	Genotypes	Control	5% PEG	10% PEG	15% PEG
		Mean ± SE	Mean ± SE	Mean ± SE	Mean ± SE
GP	DBW17	98.44 ± 0.54 bc	76.53 ± 1.76 d	63.43 ± 1.47 c	42.60 ± 0.98 e
	DBW71	99.28 ± 0.02 ab	75.10 ± 2.60 d	62.50 ± 2.14 c	38.53 ± 1.36 e
	HD2733	98.88 ± 0.53 ab	89.23 ± 4.13 abc	79.50 ± 3.70 ab	71.00 ± 3.29 b
	HD2864	95.37 ± 0.08 efg	83.20 ± 1.44 bcd	75.17 ± 1.30 b	64.97 ± 1.13 c
	HD2888	96.32 ± 0.54 def	89.70 ± 2.08 ab	83.63 ± 1.93 a	79.97 ± 1.82 a
	HD3086	98.60 ± 0.54 b	75.50 ± 2.19 d	64.03 ± 1.88 c	44.23 ± 1.30 e
	HUW468	95.26 ± 0.41 fg	78.30 ± 2.71 d	61.57 ± 2.11 c	53.00 ± 1.85 d
	K9423	94.66 ± 0.12 g	81.57 ± 1.88 cd	76.23 ± 1.76 b	53.03 ± 1.24 d
	PBW343	100.0 ± 0.00 a	75.50 ± 3.46 d	63.50 ± 2.94 c	41.00 ± 1.91 e
	PBW396	95.90 ± 0.07 ef	79.40 ± 1.39 d	68.23 ± 1.18 c	55.03 ± 0.95 d
	PBW590	96.56 ± 0.50 de	78.57 ± 1.82 d	64.77 ± 1.47 c	43.50 ± 0.98 e
	RAJ3765	99.52 ± 0.01 ab	91.50 ± 2.66 a	85.57 ± 2.45 a	81.97 ± 2.34 a
	UP2425	100.0 ± 0.00 a	78.13 ± 3.15 d	63.70 ± 2.60 c	51.17 ± 2.05 d
	WH711	97.35 ± 0.78 cd	79.70 ± 3.70 d	61.37 ± 2.86 c	55.10 ± 2.54 d
	WH1021	95.84 ± 0.10 efg	74.43 ± 1.70 d	65.23 ± 1.53 c	61.00 ± 1.39 c
ShL	DBW17	12.30 ± 0.61 a	8.50 ± 0.06 abc	6.53 ± 0.62 bcd	5.27 ± 0.12 bc
	DBW71	12.13 ± 0.47 a	8.73 ± 0.62 ab	5.77 ± 0.30 cde	4.83 ± 0.37 cd
	HD2733	10.23 ± 0.47 c	8.97 ± 0.12 a	8.10 ± 0.20 ab	7.17 ± 0.41 a
	HD2864	10.50 ± 0.61 bc	7.37 ± 0.34 bcde	5.73 ± 0.22 cde	3.07 ± 0.61 e
	HD2888	9.57 ± 0.41 c	8.37 ± 0.09 abcd	7.33 ± 0.22 abc	6.17 ± 0.28 b
	HD3086	9.20 ± 0.50 c	7.17 ± 0.37 cde	5.17 ± 0.74 def	3.13 ± 0.03 e
	HUW468	9.30 ± 0.21 c	6.23 ± 0.90 ef	4.90 ± 0.67 def	3.93 ± 0.22 de
	K9423	10.13 ± 0.26 c	6.13 ± 0.43 ef	3.67 ± 0.30 f	3.07 ± 0.09 e
	PBW343	11.73 ± 0.83 ab	7.80 ± 0.40 abcd	4.83 ± 0.95 def	3.37 ± 0.09 e
	PBW396	9.47 ± 0.13 c	5.63 ± 0.35 f	4.33 ± 0.66 ef	3.17 ± 0.24 e
	PBW590	10.03 ± 0.03 c	5.87 ± 0.63 ef	4.40 ± 0.59 ef	3.30 ± 0.20 e
	RAJ3765	10.60 ± 0.66 bc	9.13 ± 0.39 a	8.17 ± 0.38 a	7.63 ± 0.59 a
	UP2425	10.07 ± 0.09 c	7.23 ± 0.64 bcde	5.40 ± 0.64 de	3.03 ± 0.29 e
	WH711	9.53 ± 0.49 c	6.87 ± 0.18 def	4.53 ± 0.15 ef	3.43 ± 0.34 e
	WH1021	10.07 ± 0.50 c	7.80 ± 0.52 abcd	5.90 ± 0.26 cde	3.10 ± 0.29 e
RL	DBW17	9.40 ± 0.26 abc	7.43 ± 0.12 abc	5.33 ± 0.19 abc	3.60 ± 0.25 bc
	DBW71	8.10 ± 0.29 abcde	6.60 ± 0.15 bcde	5.43 ± 0.33 abc	3.70 ± 0.31 bc
	HD2733	6.73 ± 0.72 e	4.80 ± 0.31 f	4.40 ± 0.32 cd	3.27 ± 0.39 bcde
	HD2864	8.03 ± 0.57 abcde	7.20 ± 0.30 abcd	5.20 ± 0.36 abc	2.97 ± 0.15 cdef
	HD2888	7.03 ± 0.47 e	5.90 ± 0.72 ef	4.73 ± 0.12 cd	4.07 ± 0.09 b
	HD3086	8.77 ± 0.24 abcde	6.33 ± 0.45 cde	4.47 ± 0.15 cd	2.27 ± 0.09 ef
	HUW468	7.63 ± 0.74 bcde	6.20 ± 0.44 cde	5.23 ± 0.15 abc	3.30 ± 0.62 bcde
	K9423	7.40 ± 1.72 cde	6.87 ± 0.58 abcde	4.93 ± 0.26 c	3.07 ± 0.09 bcdef
	PBW343	9.93 ± 0.19 a	8.00 ± 0.29 a	6.17 ± 0.54 ab	3.50 ± 0.23 bcd
	PBW396	9.57 ± 0.48 ab	6.03 ± 0.35 de	5.13 ± 0.28 bc	2.93 ± 0.24 cdef
	PBW590	9.17 ± 0.20 abcd	5.57 ± 0.37 ef	2.8 ± 0.12 e	2.50 ± 0.26 def
	RAJ3765	6.93 ± 0.47 e	6.60 ± 0.15 bcde	6.20 ± 0.25 a	5.57 ± 0.29 a
	UP2425	7.17 ± 0.43 de	6.70 ± 0.46 bcde	3.77 ± 0.32 de	2.00 ± 0.36 f
	WH711	8.63 ± 0.26 abcde	5.73 ± 0.27 ef	5.10 ± 0.06 c	2.07 ± 0.33 f
	WH1021	8.67 ± 0.37 abcde	7.77 ± 0.35 ab	5.17 ± 0.70 abc	3.07 ± 0.59 bcdef
NT	DBW17	4.33 ± 0.44 c	3.67 ± 0.17 d	3.50 ± 0.29 c	3.33 ± 0.33 cd
	DBW71	6.50 ± 0.76 a	5.00 ± 0.29 b	4.53 ± 0.32 bc	4.33 ± 0.17 b
	HD2733	5.67 ± 0.73 abc	4.67 ± 0.17 bcd	4.17 ± 0.60 bc	3.83 ± 0.17 bcd
	HD2864	5.83 ± 0.17 ab	5.00 ± 0.00 b	4.67 ± 0.17 abc	4.33 ± 0.33 b
	HD2888	5.83 ± 0.33 ab	4.67 ± 0.17 bcd	4.33 ± 0.17 bc	3.67 ± 0.33 bcd
	HD3086	6.67 ± 0.17 a	5.00 ± 0.58 b	4.50 ± 0.29 bc	4.00 ± 0.29 bcd
	HUW468	5.67 ± 0.33 abc	5.33 ± 0.33 ab	4.50 ± 0.76 bc	4.17 ± 0.17 bc
	K9423	6.33 ± 0.17 a	5.33 ± 0.33 ab	5.00 ± 0.29 ab	4.50 ± 0.29 b
	PBW343	6.17 ± 0.33 a	5.17 ± 0.44 ab	4.67 ± 0.17 abc	3.67 ± 0.17 bcd
	PBW396	5.83 ± 0.33 ab	4.83 ± 0.17 bc	4.33 ± 0.17 bc	3.83 ± 0.17 bcd
	PBW590	5.83 ± 0.33 ab	4.50 ± 0.58 bcd	4.00 ± 0.50 bc	3.83 ± 0.17 bcd
	RAJ3765	6.50 ± 0.58 a	6.17 ± 0.44 a	5.80 ± 0.35 a	5.33 ± 0.17 a
	UP2425	5.67 ± 0.17 abc	5.00 ± 0.29 b	4.17 ± 0.33 bc	3.90 ± 0.21 bcd
	WH711	4.67 ± 0.17 bc	3.67 ± 0.17 d	3.50 ± 0.00 c	3.33 ± 0.60 cd
	WH1021	4.67 ± 0.44 bc	3.83 ± 0.17 cd	3.50 ± 0.50 c	3.17 ± 0.17 e
DTH	DBW17	98.50 ± 0.50 a	94.17 ± 0.33 a	88.83 ± 0.44 b	84.00 ± 0.29 b
	DBW71	93.83 ± 0.33 d	88.83 ± 0.33 e	84.33 ± 0.33 f	78.83 ± 0.33 e
	HD2733	97.50 ± 0.00 ab	93.67 ± 0.44 ab	90.33 ± 0.17 a	85.83 ± 0.33 a
	HD2864	89.50 ± 0.29 e	85.33 ± 0.17 f	80.17 ± 0.17 h	75.83 ± 0.33 g
	HD2888	95.83 ± 0.33 c	93.33 ± 0.44 ab	90.17 ± 0.44 a	86.00 ± 0.00 a
	HD3086	93.67 ± 0.44 d	88.83 ± 0.33 e	84.67 ± 0.17 f	80.00 ± 0.50 d
	HUW468	89.17 ± 0.67 e	84.17 ± 0.33 g	78.50 ± 0.29 j	75.83 ± 0.33 g
	K9423	88.83 ± 0.73 e	84.17 ± 0.33 g	79.00 ± 0.29 ij	75.67 ± 0.44 g
	PBW343	96.50 ± 0.58 bc	91.83 ± 0.33 cd	88.00 ± 0.00 c	81.83 ± 0.33 c
	PBW396	88.00 ± 0.00 e	82.83 ± 0.33 h	79.33 ± 0.17 hij	76.33 ± 0.33 g
	PBW590	97.50 ± 0.00 ab	90.83 ± 0.33 d	86.17 ± 0.44 e	80.00 ± 0.29 d
	RAJ3765	88.83 ± 0.33 e	85.33 ± 0.44 f	79.50 ± 0.00 hi	77.33 ± 0.17 f
	UP2425	96.50 ± 0.76 bs	91.83 ± 0.33 cd	87.00 ± 0.29 d	80.83 ± 0.33 d
	WH711	97.67 ± 0.17 ab	92.67 ± 0.17 bc	87.50 ± 0.29 cd	81.83 ± 0.33 c
	WH1021	89.17 ± 0.67 e	84.83 ± 0.33 fg	81.67 ± 0.17 g	79.00 ± 0.00 e
PH	DBW17	81.90 ± 0.60 cd	79.03 ± 0.93 cde	72.57 ± 2.53 g	69.23 ± 1.36 e
	DBW71	79.53 ± 0.87 de	76.83 ± 0.45 de	75.67 ± 1.07 efg	72.77 ± 0.49 cde
	HD2733	85.87 ± 1.20 bc	85.57 ± 0.54 b	83.07 ± 1.77 bc	70.73 ± 2.75 de
	HD2864	81.80 ± 0.87 cd	81.57 ± 3.22 bcd	79.90 ± 1.71 cde	73.07 ± 1.13 cde
	HD2888	83.03 ± 2.00 cd	80.00 ± 1.29 cde	79.40 ± 1.71 cde	77.10 ± 0.66 bcd
	HD3086	82.47 ± 0.32 cd	81.30 ± 0.66 cd	80.40 ± 0.53 cd	77.33 ± 3.24 bc
	HUW468	81.27 ± 1.25 cde	76.67 ± 0.52 de	73.80 ± 0.85 fg	77.47 ± 1.96 bc
	K9423	84.90 ± 1.07 bc	81.67 ± 0.55 bcd	80.53 ± 0.66 cd	77.80 ± 1.62 bc
	PBW343	85.43 ± 0.88 bc	79.93 ± 1.68 cde	76.93 ± 1.54 def	72.40 ± 2.91 cde
	PBW396	84.60 ± 2.44 bcd	81.63 ± 1.69 bcd	79.10 ± 0.61 cde	73.67 ± 1.37 cde
	PBW590	76.90 ± 0.75 e	76.10 ± 2.08 e	73.70 ± 1.20 fg	72.73 ± 0.68 cde
	RAJ3765	91.00 ± 2.31 a	90.77 ± 1.24 a	89.57 ± 0.15 a	89.17 ± 2.75 a
	UP2425	89.43 ± 2.37 ab	85.40 ± 2.14 b	85.27 ± 0.87 b	80.30 ± 1.67 b
	WH711	82.80 ± 0.60 cd	81.23 ± 0.73 bcd	78.07 ± 0.37 de	74.80 ± 1.14 bcde
	WH1021	83.70 ± 2.37 cd	83.07 ± 2.28 bc	84.70 ± 1.88 b	73.53 ± 2.47 cde
FLA	DBW17	14.57 ± 1.11 e	14.39 ± 0.47 f	12.51 ± 2.61 g	9.85 ± 0.15 e
	DBW71	19.03 ± 0.87 de	17.77 ± 0.42 def	16.87 ± 0.40 def	13.99 ± 1.59 cd
	HD2733	20.86 ± 1.14 cd	16.51 ± 1.10 ef	15.42 ± 0.36 efg	14.89 ± 0.60 cd
	HD2864	26.60 ± 3.25 bc	24.11 ± 1.27 b	21.84 ± 1.14 bc	17.74 ± 1.33 c
	HD2888	23.70 ± 3.49 cd	21.84 ± 3.58 bcde	20.35 ± 0.96 bcd	16.56 ± 1.28 cd
	HD3086	25.96 ± 1.48 bc	18.37 ± 1.86 cdef	17.01 ± 1.02 def	15.81 ± 0.43 cd
	HUW468	21.29 ± 1.23 cd	22.92 ± 2.18 bcd	18.75 ± 1.87 cde	14.25 ± 1.21 cd
	K9423	24.93 ± 1.18 bc	19.09 ± 0.17 bcdef	17.84 ± 0.81 def	16.52 ± 1.17 cd
	PBW343	18.22 ± 0.88 de	16.93 ± 0.64 ef	13.75 ± 1.00 fg	13.35 ± 0.52 de
	PBW396	23.31 ± 2.32 cd	19.92 ± 2.58 bcde	18.00 ± 1.24 cde	17.43 ± 1.37 cd
	PBW590	21.02 ± 1.77 cd	19.21 ± 1.50 bcdef	16.92 ± 1.80 def	15.94 ± 0.87 cd
	RAJ3765	25.64 ± 0.68 bc	23.60 ± 1.58 bc	22.61 ± 0.19 b	21.74 ± 0.62 cd
	UP2425	37.47 ± 1.48 a	34.73 ± 1.01 a	32.05 ± 0.69 a	30.06 ± 2.04 a
	WH711	29.94 ± 0.91 b	20.57 ± 0.79 bcde	17.50 ± 1.35 def	18.10 ± 1.63 c
	WH1021	19.03 ± 1.29 de	17.09 ± 0.08 ef	15.87 ± 0.26 efg	14.70 ± 1.97 b
DTM	DBW17	120.50 ± 0.50 e	111.83 ± 0.33 h	107.83 ± 0.33 i	105.0 ± 0.29 h
	DBW71	119.50 ± 0.50 e	112.67 ± 0.17 h	107.50 ± 0.58 i	103.50 ± 0.58 i
	HD2733	130.50 ± 0.50 c	123.83 ± 0.33 d	120.33 ± 0.33 d	116.00 ± 0.29 d
	HD2864	130.33 ± 1.20 c	118.83 ± 0.33 f	115.83 ± 0.17 f	107.00 ± 0.29 g
	HD2888	110.33 ± 1.48 f	105.17 ± 0.17 i	102.00 ± 0.00 j	100.17 ± 0.33 j
	HD3086	142.00 ± 1.53 a	135.83 ± 0.60 a	128.83 ± 0.17 a	119.00 ± 0.58 b
	HUW468	129.00 ± 1.53 c	120.83 ± 0.33 e	115.33 ± 0.33 f	109.0 ± 0.29 f
	K9423	130.17 ± 1.17 c	121.17 ± 0.73 e	110.83 ± 0.44 h	107.17 ± 0.33 g
	PBW343	130.33 ± 1.20 c	118.50 ± 0.58 f	114.0 ± 0.00 g	108.83 ± 0.33 f
	PBW396	137.50 ± 0.50 b	128.50 ± 0.50 c	121.17 ± 0.17 d	114.33 ± 0.67 e
	PBW590	125.50 ± 0.50 d	115.83 ± 0.33 g	114.00 ± 0.00 g	109.83 ± 0.17 f
	RAJ3765	136.17 ± 1.30 b	130.00 ± 0.76 b	127.67 ± 0.17 b	122.83 ± 0.33 a
	UP2425	128.33 ± 0.67 cd	123.00 ± 0.50 d	118.50 ± 0.50 e	110.00 ± 1.00 f
	WH711	138.83 ± 1.42 b	128.17 ± 0.44 c	122.50 ± 0.50 c	117.33 ± 0.17 c
	WH1021	122.0 ± 0.29 e	117.00 ± 0.00 g	110.00 ± 0.00 h	107.33 ± 0.33 g
SL	DBW17	15.43 ± 0.52 e	15.07 ± 0.07 efef	14.07 ± 0.29 e	13.23 ± 0.28 de
	DBW71	15.73 ± 0.32 e	15.40 ± 0.20 def	14.73 ± 0.87 cde	14.40 ± 0.31 cde
	HD2733	18.13 ± 0.55 b	17.27 ± 0.29 bc	16.03 ± 0.23 cde	15.23 ± 0.09 bcd
	HD2864	17.50 ± 0.31 bcd	16.80 ± 0.92 cd	16.33 ± 0.87 bcd	15.43 ± 1.07 bc
	HD2888	17.27 ± 0.55 bcd	16.73 ± 0.24 cde	16.27 ± 0.64 bcd	15.70 ± 0.06 bc
	HD3086	16.73 ± 0.33 bcde	16.63 ± 0.55 cde	15.83 ± 0.67 cde	14.07 ± 0.87 cde
	HUW468	17.80 ± 0.58 bc	16.33 ± 0.07 cde	15.97 ± 0.23 cde	14.73 ± 0.68 cde
	K9423	20.03 ± 0.42 a	18.67 ± 0.37 ab	16.60 ± 1.10 bc	14.00 ± 0.23 cde
	PBW343	16.63 ± 0.38 cde	14.53 ± 0.85 f	14.43 ± 0.69 de	12.80 ± 0.53 e
	PBW396	16.80 ± 0.45 bcde	16.43 ± 0.15 cde	15.97 ± 0.23 cde	15.57 ± 0.58 bc
	PBW590	17.30 ± 0.55 bcd	16.53 ± 0.84 cde	15.93 ± 0.24 cde	15.73 ± 0.57 bc
	RAJ3765	19.80 ± 0.12 a	19.13 ± 0.44 a	18.57 ± 0.79 a	18.13 ± 0.88 a
	UP2425	20.53 ± 0.47 a	19.90 ± 0.61 a	18.00 ± 0.31 ab	17.07 ± 0.60 ab
	WH711	16.47 ± 0.32 cde	16.23 ± 0.30 cde	15.37 ± 0.43 cde	15.27 ± 0.55 bc
	WH1021	16.30 ± 0.36 de	15.33 ± 0.60 def	14.30 ± 0.49 de	13.93 ± 0.78 cde
SPS	DBW17	16.00 ± 0.58 efg	15.67 ± 0.33 cde	15.33 ± 0.33 cde	15.00 ± 1.00 bcd
	DBW71	16.67 ± 0.33 defg	16.33 ± 0.33 bcde	16.00 ± 0.58 cd	15.33 ± 0.33 bc
	HD2733	21.67 ± 0.33 a	20.67 ± 0.33 a	19.00 ± 1.00 a	18.33 ± 0.33 a
	HD2864	22.00 ± 0.00 a	21.33 ± 0.67 a	18.67 ± 0.33 a	18.33 ± 0.33 a
	HD2888	18.00 ± 0.00 bcd	17.33 ± 0.33 bc	17.00 ± 0.58 bc	16.67 ± 0.33 ab
	HD3086	15.00 ± 0.00 g	14.67 ± 0.33 e	13.67 ± 0.67 e	13.33 ± 0.88 de
	HUW468	19.00 ± 1.00 bc	17.00 ± 0.58 bcd	16.67 ± 0.33 cd	14.67 ± 0.33 cd
	K9423	17.33 ± 0.33 bcde	16.00 ± 1.00 bcde	15.33 ± 0.88 cde	14.67 ± 0.88 cd
	PBW343	17.67 ± 0.33 bcde	16.67 ± 0.67 bcd	14.67 ± 0.33 de	12.67 ± 0.33 e
	PBW396	19.33 ± 1.33 b	17.67 ± 0.33 b	17.00 ± 0.58 bc	16.33 ± 0.33 bc
	PBW590	15.67 ± 0.33 fg	15.33 ± 0.33 de	15.33 ± 0.33 cde	14.67 ± 0.33 cd
	RAJ3765	19.33 ± 0.88 b	17.33 ± 0.67 bc	17.00 ± 0.58 bc	16.33 ± 0.33 bc
	UP2425	18.00 ± 0.00 bcd	16.33 ± 0.33 bcde	16.00 ± 0.58 cd	15.33 ± 0.33 bc
	WH711	17.33 ± 0.33 bcde	15.67 ± 0.88 cde	15.00 ± 0.58 cde	14.67 ± 0.67 cd
	WH1021	16.33 ± 0.33 defg	16.00 ± 0.00 bcde	15.00 ± 1.00 cde	14.67 ± 0.88 cd
GPS	DBW17	45.17 ± 0.17 fg	44.50 ± 1.00 b	43.83 ± 1.09 b	36.50 ± 0.58 cd
	DBW71	45.53 ± 0.50 efg	44.17 ± 0.60 bc	39.67 ± 1.20 c	33.33 ± 0.33 de
	HD2733	40.83 ± 1.36 g	39.17 ± 0.33 d	36.67 ± 0.60 cd	33.67 ± 1.17 de
	HD2864	49.83 ± 3.59 cdef	41.00 ± 0.29 bcd	38.83 ± 1.09 cd	38.33 ± 0.44 c
	HD2888	53.83 ± 0.33 bc	52.17 ± 0.88 a	52.00 ± 0.58 a	50.83 ± 0.44 a
	HD3086	48.33 ± 3.18 def	43.50 ± 0.58 bc	39.00 ± 0.87 cd	36.50 ± 1.15 cd
	HUW468	41.17 ± 0.83 g	40.33 ± 1.42 cd	36.50 ± 0.50 cd	35.00 ± 1.32 cd
	K9423	52.00 ± 1.73 bcd	41.83 ± 0.44 bcd	39.00 ± 0.50 cd	36.00 ± 2.08 cd
	PBW343	55.17 ± 0.33 ab	44.00 ± 0.50 bc	36.00 ± 0.76 e	31.67 ± 1.45 e
	PBW396	52.50 ± 0.58 bcd	42.67 ± 1.30 bcd	38.67 ± 1.17 cd	35.17 ± 1.30 cd
	PBW590	49.00 ± 1.15 cdef	42.83 ± 1.92 bcd	36.33 ± 2.60 cd	34.33 ± 0.93 de
	RAJ3765	59.33 ± 1.33 a	52.50 ± 1.04 a	50.67 ± 0.17 a	46.67 ± 0.44 b
	UP2425	46.33 ± 1.01 ef	40.67 ± 3.17 bcd	37.50 ± 0.76 cd	35.33 ± 0.60 cd
	WH711	50.33 ± 1.45 bcde	42.67 ± 0.60 bcd	39.33 ± 0.83 cd	36.33 ± 0.44 cd
	WH1021	45.50 ± 0.58 efg	41.33 ± 0.17 bcd	38.67 ± 0.93 cd	36.33 ± 0.33 cd
TW	DBW17	42.02 ± 0.49 a	33.51 ± 0.35 c	30.78 ± 0.07 c	27.52 ± 0.32 d
	DBW71	37.29 ± 0.56 cde	29.91 ± 0.17 e	27.58 ± 0.12 h	24.43 ± 0.23 hi
	HD2733	40.15 ± 0.66 ab	34.23 ± 0.16 bc	32.40 ± 0.22 b	29.25 ± 0.38 b
	HD2864	39.42 ± 0.79 bc	34.05 ± 1.16 bc	28.87 ± 0.36 fg	24.78 ± 0.32 gh
	HD2888	42.37 ± 0.36 a	39.48 ± 0.22 a	35.50 ± 0.23 a	32.15 ± 0.15 a
	HD3086	38.89 ± 0.25 bcd	31.97 ± 0.22 d	27.72 ± 0.19 h	25.75 ± 0.20 f
	HUW468	37.02 ± 0.64 de	30.08 ± 0.17 e	26.25 ± 0.36 i	23.77 ± 0.29 i
	K9423	42.25 ± 0.29 a	34.79 ± 0.39 b	30.37 ± 0.25 cd	26.77 ± 0.13 e
	PBW343	42.38 ± 0.71 a	34.92 ± 0.15 b	29.87 ± 0.17 de	27.10 ± 0.18 de
	PBW396	35.22 ± 1.39 e	30.40 ± 0.13 e	25.40 ± 0.21 j	23.05 ± 0.18 j
	PBW590	35.65 ± 1.18 e	31.78 ± 0.24 d	27.72 ± 0.11 h	25.38 ± 0.26 fg
	RAJ3765	36.28 ± 0.17 e	34.17 ± 0.12 bc	32.12 ± 0.19 b	28.56 ± 0.31 bc
	UP2425	39.50 ± 0.29 bc	32.02 ± 0.16 d	29.44 ± 0.19 ef	25.96 ± 0.24 f
	WH711	41.93 ± 0.92 a	31.77 ± 0.08 d	28.75 ± 0.13 g	25.79 ± 0.17 f
	WH1021	35.83 ± 0.60 e	34.39 ± 0.12 bc	31.78 ± 0.14 b	28.35 ± 0.15 c

Means followed by the same letters (a,b,c) are not significantly different (p < 0.05) using Duncan New Multiple Range Test (DMRT’s test).

, Figure 1). The GP lies between 74.43% (WH1021) and 91.50% (RAJ3765), 61.37% (WH711) and 85.57% (RAJ3765), and 38.53% (DBW71) and 81.97% (RAJ3765), at 5%, 10% and 15% PEG treatment, respectively. The average GP in control conditions was 97.46%, which was reduced to 80.42%, 69.23% and 55.74%, under 5%, 10% and 15% PEG treatments, respectively. The ShL and RL ranged from 9.20 cm (HD3086) to 12.30 cm (DBW17), and 6.73 cm (HD2733) to 9.93 cm (PBW343), respectively in control conditions. The maximum reduction in ShL and RL was observed at the highest induced drought stress (15% of PEG). The average ShL recorded at 0% PEG (control) was 10.32 cm, which was reduced to 27.81%, 45.25% and 58.91% under 5%, 10 % and 15% PEG treatments. The average RL was 8.21 cm in control conditions and found to be reduced on an average to 5.01 cm at the 15% PEG treatment. In control conditions, the minimum NT were 4.33 (DBW17) and maximum 6.67 (HD3086). In treatment cases, NT ranged from 3.67 (WH711) to 6.17 (RAJ3765), 3.50 (WH711, WH1021) to 5.80 (RAJ3765), and 3.17 (WH1021) to 5.33 (RAJ3765), at 5%, 10% and 15% PEG concentration, respectively. The average NT was 5.74 in the control and was reduced to 16.55%, 24.39% and 31.18%, under 5%, 10% and 15% PEG treatments, respectively. The genotypes DBW71, HD3086, PBW343 and RAJ3765, were found to be the best, developing more than 6.50 tillers per plant under control conditions. The genotype RAJ3765 showed a good result with a maximum average NT of 5.33 per plant under all drought stress treatments. The average days to heading was 93.40 days in the control conditions, and reduced by 14.41% at 15% PEG treatment. The maximum number of DTH were 98.50 (DBW17) and minimum were 88.0 (PBW396) in the control conditions. For treatment cases, DTH ranged from 82.83 (PBW396) to 94.17 (DBW17), 78.50 (HUW468) to 90.33 (HD2733) and 75.67 (HUW468) to 86.0 (HD2888) days, at 5%, 10% and 15% PEG concentration, respectively. However, the genotypes HD2733, HD2888 and RAJ3765 were less vulnerable to drought stress with respect to the days to heading. The PH of all the 15 wheat genotypes was significantly decreased compared to the control in all the three stress treatments. The minimum and maximum PH was 76.90 cm (PBW590) and 91.00 cm (RAJ3765), respectively under control conditions. Average PH was 83.64 cm under control conditions, which was decreased by 2.70%, 4.94% and 9.76%, at 5%, 10 % and 15% PEG treatments, respectively. The genotypes HD2733 and UP2425 had a PH more than 85 cm, whereas the genotypes DBW 17, DBW71, HUW468, PBW343 and PBW590 were less than 80 cm at 5% PEG treatment. A PH more than 89.0 cm was recorded in RAJ3765 at 10% and 15% PEG concentration. The genotypes HD2864, HD3086, RAJ3765, UP2425 and WH711 had more than 25 cm² FLA, whereas, in DBW17, DBW71, PBW343 and WH1021 it was less than 20 cm² in the control. In treatment conditions, a maximum FLA of 34.73, 32.05 and 30.06 cm² was recorded for 5%, 10% and 15% PEG in the genotype UP2425. Further, the effect of drought treatments on flag leaf area (FLA) were varied among the genotypes, as an average leaf area was 23.44 cm² under control and was up to 28.63% less at the higher PEG (15%) treatment.

The days to maturity ranged from 110.33 (HD2888) to 142 days (HD3086) in control conditions, and 105.17 to 135.83 days at the 5% PEG treatment. In further treatments, minimum and maximum DTM were 102.0 to 128.83 days, and 100.17 to 122.83 (RAJ3765) days, in the case of 10% and 15% PEG treatments, respectively. Moreover, the average days to maturity was 128.73 days under control conditions and was found to reduce by up to 14.17% days in the 15% PEG treatment. In control conditions, minimum SL was 15.43 cm (DBW17) and maximum 20.53 cm (HD3086). In treatment cases, SL ranged from 14.53 cm (PBW343) to 19.90 cm (UP2425), 14.07 cm (DBW17) to 18.57 cm (RAJ3765), and 12.80 cm (PBW343) to 18.13 cm (RAJ3765), at 5%, 10% and 15% PEG concentration, respectively. The genotype HD3086 and HD2864 had minimum and maximum SPS in control conditions (15.0 and 22.0) and in 5% PEG (14.67 and 21.33) treatment conditions, but in the case of 10% and 15% PEG treatment, the genotype HD2733 had the maximum 19.0 and 18.33 SPS, respectively. The average SL and SPS recorded in the controls were 17.50 cm and 17.96 cm respectively, SL and SPS were decreased by 4.40%, 5.73% and 9.20%; and 10.30%, 14.17% and 14.27%, under 5%, 10 % and 15% PEG treatments, respectively. However, the genotypes RAJ3765 and HD2888 were less affected under all three drought treatments, and had only a 8.43% and 9.09% decrease in spike lengths and SPS, respectively. The GPS ranged from 40.83 (HD2733) to 59.33 (RAJ3765) in the controls, and 39.17 to 52.50 at 5% PEG treatment. In further treatment, minimum and maximum GPS were 36.0 to 52.0 and 31.67 (PBW343) to 50.83 (HD2888) days, in the case of 10% and 15% PEG treatment, respectively. The average number of grains per spike (GPS) was 48.99 in the controls and was found to reduce by up to 11.08%, 17.98% and 24.33% under 5%, 10 % and 15% PEG treatments, respectively. The TW ranged from 35.22 g (PBW396) to 42.38 g (PBW343) in the control and, the average TW (39.08 g) was recorded in the control and was decreased by 15.15%, 24.16% and 32.01%, at 5%, 10 % and 15% PEG treatments, respectively. The genotypes DBW17, HD2733, HD2888, K9423, PBW343 and WH711 performed better in respect to TW, and recorded more than 40.0 g in the control conditions. The minimum TW was recorded in DBW71 (29.91 g) at 5% PEG, and in PBW396 at 10% and 15% PEG treatment. The maximum TW was in HD2888 under all three drought stress treatments (Table 3, Figure 1).

3.2. Physiological and Biochemical Response to Drought Stress

The chlorophyll (ChL) content ranged from 45.88 (UP2425) to 53.57 (WH1021) µg/cm² in control conditions (

Table 4. Mean values of physiological and biochemical traits under control and 5%, 10% and 15% PEG treatment condition.

Traits	Genotypes	Control	5% PEG	10% PEG	15% PEG
		Mean ± SE	Mean ± SE	Mean ± SE	Mean ± SE
CHL	DBW17	47.08 ± 0.37 fg	45.65 ± 1.22 ab	44.53 ± 1.45 b	42.93 ± 0.95 ab
	DBW71	49.90 ± 1.73 bcdef	47.37 ± 1.27 ab	45.83 ± 0.77 ab	44.34 ± 1.89 ab
	HD2733	49.10 ± 0.35 cdefg	48.42 ± 0.21 ab	47.87 ± 0.68 ab	46.03 ± 0.29 a
	HD2864	48.43 ± 1.20 defg	47.65 ± 0.58 ab	46.80 ± 3.42 ab	45.68 ± 0.79 a
	HD2888	51.55 ± 0.99 abcd	51.03 ± 0.44 a	49.62 ± 0.26 a	47.30 ± 1.08 a
	HD3086	51.98 ± 0.98 abcd	47.22 ± 1.80 ab	47.87 ± 0.92 ab	44.57 ± 1.44 ab
	HUW468	52.37 ± 0.17 abc	49.65 ± 0.87 a	49.50 ± 0.81 a	46.20 ± 0.65 a
	K9423	47.63 ± 0.99 efg	46.33 ± 2.90 ab	45.40 ± 0.33 ab	45.23 ± 0.26 a
	PBW343	50.55 ± 1.46 abcdef	46.22 ± 2.31 ab	43.83 ± 1.77 b	39.62 ± 1.60 b
	PBW396	51.60 ± 0.45 abcd	47.18 ± 0.35 ab	46.12 ± 2.12 ab	43.97 ± 3.51 ab
	PBW590	50.52 ± 0.87 abcdef	50.63 ± 0.35 a	46.85 ± 1.60 ab	46.18 ± 1.56 a
	RAJ3765	50.80 ± 2.02 abcde	49.10 ± 1.32 ab	46.57 ± 1.33 ab	45.93 ± 0.91 a
	UP2425	45.88 ± 0.95 g	43.78 ± 2.16 b	43.23 ± 1.65 b	42.02 ± 2.35 ab
	WH711	52.87 ± 1.09 ab	49.33 ± 0.25 a	46.68 ± 0.57 ab	44.60 ± 1.47 ab
	WH1021	53.57 ± 0.16 a	51.08 ± 3.23 a	50.23 a ± 0.68 a	44.40 ± 2.58 ab
Pn	DBW17	17.04 ± 0.15 d	16.37 ± 1.02 d	13.12 ± 0.45 d	10.17 ± 0.19 f
	DBW71	19.62 ± 0.79 bcd	18.25 ± 0.40 bc	10.77 ± 0.27 e	9.73 ± 0.15 f
	HD2733	20.92 ± 0.59 b	20.00 ± 0.35 b	18.35 ± 0.08 b	16.38 ± 0.10 c
	HD2864	18.31 ± 0.04 cd	16.23 ± 0.02 d	14.68 ± 0.43 c	11.48 ± 0.24 e
	HD2888	21.00 ± 0.46 b	19.28 ± 0.69 b	17.78 ± 0.20 b	17.03 ± 0.22 b
	HD3086	19.58 ± 0.89 bcd	16.77 ± 0.09 cd	15.52 ± 0.34 c	13.13 ± 0.33 d
	HUW468	17.63 ± 0.40 cd	13.50 ± 0.85 e	10.20 ± 0.06 ef	8.97 ± 0.02 g
	K9423	14.47 ± 0.85 e	10.50 ± 0.15 fg	9.22 ± 0.47 fg	7.72 ± 0.26 hi
	PBW343	10.68 ± 1.52 f	10.07 ± 0.64 fg	7.48 ± 0.20 h	6.33 ± 0.12 j
	PBW396	17.95 cd ± 0.40 cd	16.17 ± 1.02 d	12.30 ± 0.44 d	11.02 ± 0.13 e
	PBW590	13.82 ± 0.48 e	11.80 ± 0.12 f	9.38 ± 0.31 fg	8.22 ± 0.12 h
	RAJ3765	25.67 ± 1.58 a	23.48 ± 0.97 a	21.12 ± 0.23 a	19.35 ± 0.43 a
	UP2425	10.72 ± 0.67 f	10.10 ± 0.00 fg	9.08 ± 0.34 g	7.43 ± 0.04 i
	WH711	10.00 ± 0.41 f	9.27 ± 0.12 g	7.93 ± 0.35 h	6.50 ± 0.09 j
	WH1021	20.02 ± 1.10 bc	17.27 ± 0.19 cd	14.75 ± 0.57 c	12.65 ± 0.18 d
MSI	DBW17	82.45 ± 1.90 bc	79.48 ± 1.84 abcde	75.95 ± 1.00 abcd	64.75 ± 1.13 cde
	DBW71	86.03 ± 2.98 abc	79.08 ± 2.74 abcde	74.37 ± 1.61 bcd	59.54 ± 1.69 f
	HD2733	88.64 ± 2.65 ab	84.41 ± 2.03 ab	80.50 ± 1.23 ab	77.48 ± 0.42 a
	HD2864	89.28 ± 0.19 a	84.73 ± 1.47 ab	81.20 ± 1.41 a	76.19 ± 1.32 a
	HD2888	89.42 ± 0.24 a	85.14 ± 1.00 a	82.09 ± 1.17 a	79.29 ± 1.11 a
	HD3086	87.50 ± 2.53 ab	82.35 ± 2.38 abcd	76.27 ± 1.16 abcd	67.58 ± 0.50 bcd
	HUW468	85.67 ± 0.50 abc	80.31 ± 2.78 abcde	76.53 ± 2.65 abc	69.55 ± 1.35 b
	K9423	86.10 ± 0.77 abd	84.07 ± 1.94 abc	78.56 ± 1.81 abc	70.79 ± 1.63 b
	PBW343	84.72 ± 2.53 abc	76.29 ± 2.07 de	72.85 ± 1.78 cd	60.60 ± 1.05 ef
	PBW396	86.13 ± 1.21 abc	78.41 ± 2.22 abcde	75.73 ± 1.31 abcd	68.70 ± 1.19 bc
	PBW590	83.57 ± 1.93 abc	76.91 ± 0.91 cde	74.60 ± 1.72 bcd	64.38 ± 1.49 de
	RAJ3765	86.48 ± 1.63 abc	80.76 ± 2.33 abcde	77.39 ± 2.23 abc	75.75 ± 1.09 a
	UP2425	80.55 ± 3.26 c	77.50 ± 3.13 bcde	72.27 ± 2.92 cd	64.10 ± 2.59 de
	WH711	82.38 ± 1.78 bc	74.30 ± 3.43 e	69.99 ± 3.23 d	71.54 ± 0.85 b
	WH1021	83.33 ± 1.92 abc	79.77 ± 0.98 abcde	78.04 ± 1.80 abc	71.14 ± 1.00 b
RWC	DBW17	84.97 ± 1.96 ab	75.93 ± 1.75 bc	67.46 ± 1.56 cde	51.86 ± 1.20 fg
	DBW71	81.45 ± 2.82 ab	78.19 ± 2.71 abc	64.74 ± 2.24 e	53.49 ± 1.85 fg
	HD2733	82.75 ± 3.82 ab	77.21 ± 3.57 abc	74.61 ± 3.45 abc	72.66 ± 3.36 ab
	HD2864	86.14 ± 1.49 ab	79.26 ± 1.37 abc	72.44 ± 1.25 abcd	68.26 ± 1.18 abc
	HD2888	88.16 ± 2.04 ab	84.52 ± 1.95 a	77.06 ± 1.78 ab	74.34 ± 1.72 a
	HD3086	81.28 ± 2.35 ab	78.51 ± 2.27 abc	70.78 ± 2.04 abcde	53.85 ± 1.55 efg
	HUW468	86.24 ± 2.99 ab	75.81 ± 2.63 bc	70.17 ± 2.43 abcde	66.45 ± 2.30 bc
	K9423	84.92 ± 1.96 ab	76.00 ± 1.76 bc	72.04 ± 1.66 abcde	66.51 ± 1.54 bc
	PBW343	86.67 ± 4.00 ab	76.26 ± 3.52 abc	69.89 ± 3.23 bcde	51.14 ± 2.36 g
	PBW396	85.99 ± 1.49 ab	79.90 ± 1.38 abc	75.36 ± 1.31 ab	59.88 ± 1.04 de
	PBW590	80.00 ± 1.85 b	76.34 ± 1.76 abc	74.74 ± 1.73 abc	52.00 ± 1.20 fg
	RAJ3765	86.43 ± 2.49 ab	79.44 ± 2.29 abc	77.89 ± 2.25 a	73.73 ± 2.13 a
	UP2425	83.79 ± 3.39 ab	78.07 ± 3.16 abc	70.90 ± 2.87 abcde	58.10 ± 2.35 def
	WH711	89.92 ± 4.15 a	80.87 ± 3.74 ab	74.05 ± 3.42 abcd	67.23 ± 3.11 bc
	WH1021	82.81 ± 1.91 ab	71.39 ± 1.65 c	66.67 ± 1.54 de	64.07 ± 1.48 cd
PROLINE	DBW17	1.50 ± 0.00 e	1.54 ± 0.01 g	1.58 ± 0.01 i	1.66 ± 0.00 g
	DBW71	1.24 ± 0.01 a	1.27 ± 0.01 i	1.33 ± 0.00 k	1.36 ± 0.01 j
	HD2733	1.81 ± 0.01 g	1.92 ± 0.01 c	2.01 ± 0.00 c	2.08 ± 0.01 ab
	HD2864	1.30 ± 0.00 f	1.35 ± 0.01 h	1.41 ± 0.00 i	1.44 ± 0.01 h
	HD2888	1.75 ± 0.01 b	1.89 ± 0.00 b	1.99 ± 0.00 b	2.09 ± 0.00 a
	HD3086	1.29 ± 0.01 f	1.36 ± 0.01 h	1.40 ± 0.01 i	1.43 ± 0.01 h
	HUW468	1.69 ± 0.01 c	1.71 ± 0.01 d	1.76 ± 0.01 d	1.82 ± 0.01 d
	K9423	1.10 ± 0.01 h	1.18 ± 0.01 j	1.22 ± 0.00 l	1.26 ± 0.01 k
	PBW343	1.23 ± 0.01 g	1.27 ± 0.01 i	1.35 ± 0.01 j	1.40 ± 0.00 i
	PBW396	1.52 ± 0.00 e	1.58 ± 0.00 f	1.59 ± 0.01 g	1.65 ± 0.00 g
	PBW590	1.60 ± 0.01 d	1.64 ± 0.01 e	1.66 ± 0.01 f	1.70 ± 0.01 f
	RAJ3765	1.76 ± 0.00 b	1.86 ± 0.01 c	1.96 ± 0.00 c	2.06 ± 0.00 c
	UP2425	1.10 ± 0.00 h	1.15 ± 0.01 j	1.21 ± 0.00 l	1.27 ± 0.00 k
	WH711	1.59 ± 0.01 d	1.64 ± 0.01 e	1.72 ± 0.01 e	1.78 ± 0.00 e
	WH1021	1.79 ± 0.01 a	1.90 ± 0.00 ab	1.99 ± 0.00 b	2.08 ± 0.00 b

Means followed by the same letters (a,b,c,e,f,g,h) are not significantly different (p < 0.05) using Duncan New Multiple Range Test (DMRT’s test).

, Figure 2). The genotype WH1021 showed maximum ChL content 51.08 µg/cm² at 5% PEG treatment and reduced to 44.40 µg/cm² under 15% PEG treatment. The maximum ChL content was 47.30 µg/cm² in HD2888 and the minimum 39.62 µg/cm² in PBW343 at 15% PEG treatment. The average ChL content was 50.26 µg/cm² in control conditions, and reduced by 4.42%, 7.02% and 11.26%, under 5%, 10 % and 15% PEG treatments, respectively. The genotypes K9423 and HD2733 were less affected, even at the highest level of stress treatment. The photosynthetic rate (Pn) was found to reduce under drought stress conditions. In the control condition, the minimum Pn was 10.0 (WH711) and the maximum 25.67 µmol/m²sec (RAJ3765) (Table 4, Figure 2). In treatment cases, Pn ranged from 9.27 (WH711) to 23.48 (RAJ3765) µmol/m²sec, 7.48 (PBW343) to 21.12 (RAJ3765) µmol/m²sec and 6.50 (WH711) to 19.35 (RAJ3765), at 5%, 10% and 15% PEG concentration, respectively. An average Pn of 17.16 µmol/m²sec was observed under the control conditions, which was decreased by 11.01%, 25.52% and 35.49%, under 5%, 10% and 15% PEG treatments, respectively. The maximum reduction in Pn of 40.31% was observed in the genotype DBW17 at 15% PEG treatment, whereas the genotypes HD2888 and HD2733 were least affected and showed only a 18.90% and 21.70% reduction.

The maximum MSI 89.42% was recorded in HD288 and the minimum in UP2425 (80.55%) in control conditions (Table 4, Figure 2). The MSI lies between 74.30% (WH711) and 85.14% (HD2888), 69.99% (WH711) and 82.09% (HD2888), and 60.60% (PBW343) and 79.29% (HD2888), at 5%, 10% and 15% PEG treatment, respectively. The average MSI under the control treatments was 85.48%, and it gradually decreased, being 6.14%, 10.59% and 18.78% less under the stress treatments. Among all the genotypes tested, HD2888 and RAJ3765 were least affected and were reduced by 11.32% and 12.40% respectively. The RWC ranged from 80.0% (PBW590) to 89.92 (WH711) in control conditions and 71.39% (WH1021) to 84.52% at 5% PEG treatment. In further treatments, the minimum and maximum RWC was 64.74% (DBW71) to 77.89% (RAJ3765) and 51.14% (PBW343) to 74.34% (HD2888), in the case of 10% and 15% PEG treatment, respectively (Table 4, Figure 2). A significant reduction in the RWC was observed as the stress was increased. The average RWC was 84.77% in the control conditions, which was 26.58% less under the stress treatments at 15% PEG. The maximum proline content under control conditions was observed in the genotype HD2733 (1.81µM/gfw), and this increased to 1.92 µM/gfw, 2.01 µM/gfw and 2.08 µM/gfw, at 5%, 10 % and 15% PEG, respectively. The minimum proline content was in the genotype UP2425 (1.10 µM/gfw) under the control conditions and increased to 1.15 µM/gfw, 1.21 µM/gfw and 1.26 µM/gfw, at 5%, 10 % and 15% PEG treatment, respectively (Table 4, Figure 2).

3.3. Correlation of Traits

Significant correlations were observed in all traits compared between the control and drought stress treatments (

Table 5. Pearson’s correlation coefficients (r) describing the association of morphological, physiological and biochemical traits of 15 wheat genotypes evaluated under drought control (lower diagonal) and 5% PEG (upper diagonal) conditions.

Control	5%PEG
		GP	ShL	RL	NT	DTH	PH	FLA	DTM	SL	SPS	GPS	TW	Pn	CHL	MSI	RWC	PROLINE
	GP	1	0.347 *	−0.348 *	0.282	0.075	.405 **	0.162	−0.003	0.341 *	0.416 **	0.454 **	0.421 **	0.434 **	0.380 *	0.648 **	0.721 **	0.423 **
	ShL	0.429 **	1	0.034	−0.079	0.357 *	0.266	−0.121	−0.21	−0.07	0.189	0.371 *	0.348 *	0.538 **	0.158	0.249	0.169	0.25
	RL	0.036	0.25	1	0.074	−0.193	0.03	0.012	−0.193	−0.192	−0.15	0.057	0.127	−0.125	−0.253	−0.142	−0.263	−0.335 *
	NT	0.146	−0.075	−0.228	1	−0.364 *	0.19	0.216	0.226	0.446 **	0.17	0.284	−0.015	0.216	−0.163	0.162	0.129	−0.178
	DTH	0.507 **	0.199	0.08	−0.234	1	−0.092	−0.083	−0.317 *	−0.138	−0.09	0.111	0.277	−0.114	−0.093	−0.121	0.183	0.054
	PH	0.321 *	0.009	−0.349 *	0.088	−0.187	1	0.343 *	0.430 **	0.468 **	0.279	0.202	0.222	0.342 *	0.027	0.136	0.057	0.198
	FLA	0.074	−0.387 **	−0.263	0.115	−0.04	0.267	1	0.143	0.611 **	0.117	−0.019	−0.07	−0.192	−0.196	0.016	0.196	−0.226
	DTM	0.091	−0.272	0.158	0.157	−0.235	0.247	0.362 *	1	0.319 *	−0.037	−0.181	−0.427 **	−0.03	−0.122	−0.121	−0.011	−0.086
	SL	0.003	−0.226	−0.473 **	0.148	−0.239	0.474 **	0.565 **	0.204	1	0.11	0.109	0.087	0.059	−0.29	0.056	0.07	−0.099
	SPS	−0.132	−0.132	−0.299 *	0.106	−0.269	0.304 *	0.208	0.133	0.299 *	1	−0.178	0.167	0.361 *	0.066	0.341 *	0.094	0.195
	GPS	0.054	0.043	0.003	0.316 *	−0.197	0.316 *	0.156	0.169	0.172	−0.007	1	0.454 **	0.457 **	0.201	0.148	0.423 **	0.285
	TW	0.12	0.139	−0.052	−0.173	0.471 **	0.075	0.018	−0.165	0.003	−0.063	0.052	1	0.232	0.145	0.355 *	0.131	0.287
	Pn	−0.039	−0.082	−0.28	0.202	−0.404 **	0.106	−0.248	−0.14	−0.017	0.268	0.053	−0.352 *	1	0.203	0.343 *	0.116	0.555 **
	CHL	−0.206	−0.352 *	0.165	−0.078	−0.193	−0.19	−0.188	0.112	−0.380 *	−0.165	0.125	−0.265	0.204	1	0.323 *	0.336 *	0.535 **
	MSI	−0.06	−0.148	−0.204	0.292	−0.19	−0.092	−0.079	−0.049	−0.013	0.305 *	0.084	0.007	0.457 **	0.126	1	0.531 **	0.114
	RWC	0.047	−0.08	0.152	−0.07	−0.046	0.109	0.119	0.016	−0.029	0.191	0.21	0.212	−0.013	0.223	0.512 **	1	0.043
	PROLINE	−0.178	−0.247	−0.132	−0.298 *	−0.018	−0.029	−0.282	−0.163	−0.17	0.185	−0.101	−0.282	0.507 **	0.476 **	0.119	0.091	1

Abbreviations: Germination percentage (GP), shoot length (ShL), root length (RL), number of tillers plant⁻¹ (NT), days to heading (DTH), plant height (PH), flag leaf area (FLA), days to maturity (DTM), spike length (SL), spikelet number spike⁻¹ (SPS), number of grain per spike (GPS), Thousand Grain Weight (TW), Photosynthesis rate (Pn), chlorophyll (CHL), Membrane stability index (MSI) and Relative water content (RWC). ** and * Correlation is significant at the 0.01 level (2-tailed) and 0.05 level (2-tailed) respectively.

and

Table 6. Pearson’s correlation coefficients(r) describing association of morphological, physiological and biochemical traits of 15 wheat genotypes evaluated under drought 10% PEG (lower diagonal) and 15% PEG (upper diagonal) treatment conditions.

10%PEG

15%PEG

GP

ShL

RL

NT

DTH

PH

FLA

DTM

SL

SPS

GPS

TW

Pn

CHL

MSI

RWC

PROLINE

GP

1

0.589 **

0.460 **

0.283

0.12

0.430 **

0.28

0.203

0.485 **

0.597 **

0.738 **

0.598 **

0.778 **

0.355 *

0.878 **

0.915 **

0.690 **

ShL

0.478 **

1

0.596 **

0.236

0.445 **

0.264

−0.071

0.171

0.281

0.413 **

0.496 **

0.597 **

0.738 **

0.245

0.397 **

0.470 **

0.600 **

RL

0.168

0.168

1

0.413 **

−0.007

0.403 **

−0.095

−0.005

0.175

0.253

0.489 **

0.400 **

0.580 **

0.063

0.233

0.333 *

0.398 **

NT

0.357 *

0.151

0.212

1

−0.426 **

0.442 **

0.262

0.258

0.362 *

0.244

0.28

−0.103

0.278

0.196

0.173

0.306 *

−0.109

DTH

−0.06

0.287

−0.258

−0.363 *

1

−0.281

−0.147

−0.141

−0.113

0.042

0.182

0.668 **

0.218

−0.035

0.095

0.007

0.355 *

PH

0.457 **

0.392 **

0.097

0.198

−0.185

1

0.547 **

0.386 **

0.424 **

0.054

0.481 **

0.147

0.345 *

0.119

0.217

0.385 **

0.106

FLA

0.18

0.033

−0.204

0.261

−0.152

0.460 **

1

0.275

0.691 **

0.205

0.197

−0.027

0.022

0.003

0.084

0.239

−0.161

DTM

0.019

0.002

0.017

0.208

−0.232

0.410 **

0.209

1

0.351 *

−0.003

−0.039

−0.15

0.256

0.032

0.185

0.167

0.181

SL

0.452 **

0.207

−0.067

0.425 **

−0.239

0.430 **

0.632 **

0.379 *

1

0.430 **

0.388 **

0.058

0.366 *

0.122

0.323 *

0.370 *

0.236

SPS

0.568 **

0.366 *

0.031

0.091

−0.081

0.201

0.247

−0.009

0.361 *

1

0.278

0.17

0.502 **

0.363 *

0.571 **

0.554 **

0.323 *

GPS

0.607 **

0.466 **

0.253

0.234

0.076

0.276

0.158

−0.155

0.239

0.156

1

0.611 **

0.669 **

0.336 *

0.609 **

0.582 **

0.492 **

TW

0.629 **

0.606 **

0.094

0.034

0.448 **

0.389 **

0.022

−0.345 *

0.088

0.174

0.603 **

1

0.590 **

0.126

0.485 **

0.445 **

0.566 **

Pn

0.689 **

0.732 **

0.153

0.237

−0.011

0.510 **

0.062

0.187

0.265

0.419 **

0.615 **

0.556 **

1

0.336 *

0.660 **

0.570 **

0.681 **

CHL

0.068

0.215

−0.096

−0.122

−0.112

−0.017

−0.141

−0.062

−0.057

0.069

0.101

0.183

0.354 *

1

0.383 **

0.380 **

0.331 *

MSI

0.727 **

0.272

0.035

0.197

−0.115

0.118

−0.003

−0.205

0.118

0.544 **

0.337 *

0.407 **

0.537 **

0.149

1

0.867 **

0.618 **

RWC

0.707 **

0.09

−0.018

0.149

0.007

0.184

0.209

0.289

0.429 **

0.410 **

0.354 *

0.206

0.288

−0.085

0.516 **

1

0.576 **

PROLINE

0.398 **

0.543 **

0.053

−0.114

0.129

0.225

−0.194

0.007

0.01

0.298 *

0.407 **

0.488 **

0.625 **

0.501 **

0.304 *

0.311 *

1

Abbreviations: Germination percentage (GP), shoot length (ShL), root length (RL), number of tillers plant⁻¹ (NT), days to heading (DTH), plant height (PH), flag leaf area (FLA), days to maturity (DTM), spike length (SL), spikelet number spike⁻¹ (SPS), number of grain per spike (GPS), Thousand Grain Weight (TW), Photosynthesis rate (Pn), chlorophyll (CHL), Membrane stability index (MSI) and Relative water content (RWC). ** and * Correlation is significant at the 0.01 level (2-tailed) and 0.05 level (2-tailed) respectively.

). The GP had a significant positive correlation with ShL, PH, DTH in the control condition, whereas it showed a negatively correlation with RL in the case of 5% PEG. Otherwise, in all the treatments, the GP had a significant positive correlation with all the traits except DTH, FLA and DTM. In the control conditions, ShL was significantly negatively correlated with FLA and ChL. In contrast, significant positive correlations of ShL were observed with DTH, GPS, TW, Pn in 5% PEG; with PH, SPS, Proline in 10% PEG; and with RL, DTH, SPS, GPS, TW, Pn, MSI, RWC and Proline in 15% PEG. The RL had a significant negative correlation with PH, SL, and SPS in the control and with Proline in the 5% PEG. Moreover, NT was negatively correlated with the proline content in the control, whereas, under the 5% PEG treatment, it had a negative correlation with DOH and a positive correlation with SL. DTH showed a significantly positive correlation with TW in control as well as drought stress conditions, whereas, negatively correlated with Pn and DTM.

Similarly, PH was positively correlated with SL under both stress and control conditions, whereas, with FLA, DTM and Pn, a positive correlation was observed only under drought stress conditions. On other hand, SL had significant positive correlation with FLA, SPS and DOM in control and PEG treatment conditions. However, DOM was negatively correlated with TW in 5% and 10% PEG, whereas, TW was positively correlated with Pn, MSI and proline content in treatment conditions. In the control and all the three treatments, Pn had a significant positive correlation with MSI and proline content, whereas, with ChL and RWC the correlation was observed only in 5% and 10% PEG. The proline content had a significant negative correlation with all physiological traits and yield related traits like SPS, GPS and TW in drought condition.

3.4. Principal Component Analysis (PCA)

The first three components explained 53.29% of the total variation under the control conditions (

Table 7. Rotated component matrix of morphological, physiochemical and biochemical traits of 15 wheat genotypes under control and 5% PEG treatment conditions. Abbreviations: see Table 5.

	CONTROL				5% PEG
Traits	PC-1	PC-2	PC-3	Traits	PC-1	PC-2	PC-3
SL	0.788	0.403	0.034	GP	0.938	0.107	−0.095
RL	−0.697	−0.036	−0.384	Pn	0.749	−0.222	−0.090
PH	0.661	0.406	0.029	MSI	0.639	0.004	0.053
SPS	0.618	−0.102	0.201	GPS	0.612	−0.201	0.286
FLA	0.594	0.493	−0.392	TW	0.603	−0.337	0.438
DTH	−0.548	0.480	0.135	PH	0.602	0.466	0.099
CHL	−0.069	−0.709	−0.468	ShL	0.565	−0.334	0.467
PRO	0.029	−0.682	−0.026	PRO	0.558	−0.494	−0.522
Pn	0.354	−0.650	0.527	SL	0.424	0.781	0.023
MSI	0.456	−0.500	0.415	FLA	0.138	0.717	0.139
ShL	−0.485	0.318	0.601	DTM	−0.034	0.633	−0.392
DTM	0.371	0.117	−0.504	NT	0.377	0.626	0.080
RWC	0.276	0.093	−0.408	RL	−0.346	−0.050	0.640
NT	0.506	0.021	0.324	CHL	0.336	−0.540	−0.594
TW	−0.109	0.555	0.065	DTH	0.049	−0.411	0.383
GPS	0.361	0.125	−0.177	RWC	0.520	0.104	0.056
GP	−0.109	0.545	0.362	SPS	0.535	0.111	−0.088
Explained variance (eigenvalue)	3.778	3.197	2.084	Explained variance (eigenvalue)	4.715	3.191	1.894
Proportion of total variance (%)	22.22	18.81	12.26	Proportion of total variance (%)	27.73	18.77	11.14
Cumulative variance (%)	22.22	41.03	53.29	Cumulative variance (%)	27.73	46.51	57.65

). The first component (PC1) accounted for 22.22% of the variation, mostly affected by SL, PH, SPS and FLA. The most effective traits in the second component (PC2) were SL, PH, FLA and DOH. The third component (PC3) was mostly influenced with the variation of ShL and Pn. In drought stress conditions, the first three principal components explained 57.65%, 65.06% and 72.47% of the total variability in Treatment 1 (5%), Treatment 2 (10%) and Treatment 3 (15%), respectively (Table 7 and

Table 8. Rotated component matrix of morphological, physiochemical, and biochemical traits of 15 wheat genotypes under 10% PEG and 10%PEG treatment conditions. Abbreviations: see Table 5.

	10% PEG				15% PEG
Traits	PC-1	PC-2	PC-3	Traits	PC-1	PC-2	PC-3
GP	0.930	0.051	−0.035	GP	0.959	−0.019	−0.160
Pn	0.889	−0.176	−0.110	Pn	0.873	−0.151	0.173
ShL	0.793	−0.316	0.121	RWC	0.862	0.026	−0.312
GPS	0.711	−0.168	0.001	MSI	0.855	−0.117	−0.394
MSI	0.709	−0.294	−0.242	GPS	0.818	−0.042	0.127
TW	0.679	−0.436	0.281	ShL	0.760	−0.278	0.401
PH	0.653	0.409	0.084	PRO	0.711	−0.430	−0.060
RWC	0.632	0.297	0.259	CHL	0.672	−0.016	−0.345
SPS	0.619	0.043	−0.027	SPS	0.658	−0.037	−0.434
PRO	0.616	−0.497	0.017	SL	0.653	0.569	−0.138
SL	0.578	0.750	0.227	TW	0.608	−0.564	0.205
FLA	0.277	0.682	0.401	DTH	0.148	−0.740	0.055
NT	0.474	0.585	−0.430	FLA	0.240	0.693	−0.214
DTH	−0.041	−0.499	0.730	NT	0.432	0.682	0.369
RL	0.160	−0.065	−0.711	PH	0.550	0.675	0.314
CHL	0.390	−0.452	−0.234	RL	0.632	−0.081	0.666
DTM	0.118	0.623	−0.014	DTM	00.244	0.464	0.060
Explained variance (eigenvalue)	6.171	3.158	1.731	Explained variance (eigenvalue)	7.62	3.12	1.59
Proportion of total variance (%)	36.30	18.58	10.18	Proportion of total variance (%)	44.80	18.32	9.35
Cumulative variance (%)	36.30	54.88	65.06	Cumulative variance (%)	44.80	63.12	72.47

). In Treatment 1, the first two principal components accounted for 46.51% of total cumulative variation. The variables GP, Pn, MSI, GPS, TW and PH had high positive loading into the PC1, while PC2 was mostly affected by PH, SL and FLA followed by DOM and NT. The third component had high correlations with TW, ShL and RL variables. In treatments 2 and 3, the first two principal components had 54.88% and 63.12% total cumulative variations respectively. In treatment 2, the GP, Pn, ShL, and GPS in PC1; SL, FLA and DOM in PC2; while the DOH in PC3 were found as the most effective traits. Similarly, in treatment 3, the GP, Pn, RWC, MSI and GPS had high positive loading into the PC1; while FLA, NT and PH in PC2; followed by ShL and RL in PC3. The relationships between the different traits and genotypes with the respective principal components are further illustrated by the principal component biplots for the control and drought treatment conditions (Figure 3A–D).

4. Discussion

Drought stress is known to cause a reduction in values for morphological traits (shoot length, root length, no. of tillers, days to heading, spike length, plant height and thousand grain weights) and affect the biological yield [19]. The wheat genotypes that were significantly tolerant to drought stress had major changes in their root system, photosynthetic rate and efficient utilization of available water. In the present study, germination percentage and seedling growth was significantly reduced with increase in the concentration of the PEG treatment. Similar findings have also been reported, where there was 98–100% germination under control conditions [11,35] but significant decreases from a maximum of 64% [36] to a lowest of 36% [37] observed with increased stress levels. The genotypes RAJ3765, HD288 and HD2733 performed better and showed maximum GP at higher PEG treatments. The induced drought stress significantly reduced the shoot and root lengths of wheat genotypes. A reduction in ShL and RL, ranging from 11.66 cm to 1.0 cm and 11.83 to 1.34 cm, with an increase in drought stress has been observed [8,11,38]. The reduction in the shoot/root lengths might be due to some disturbance posed by the osmotic stress conditions in cell division and elongation [19,39]. The number of tillers per plant has a direct contribution towards grain yield in wheat [40], and thus, it is an important trait to measure. In this study, the average number of tillers per plant was 5.74 and was found to reduce with increasing levels of drought stress. A reduction in the average tiller numbers from 4.45 to 3.36 due to severe drought stress has also been reported [26,41]. The drought stress caused reduction in PH and FLA of between 9.76% and 28.63% under stress conditions. A drastic reduction in FLA, up to 30% under stress conditions, was observed in previous studies [42]. Under drought stress, the reduction in plant height could be attributed to a decline in the cell enlargement and more leaf senescence [23,43] and the reduction in cell expansion and production of cells both are known to contribute to a loss in leaf area [44]. In the present study, a reduction of 8–16 days in DTH and 10–23 days in the number of days to maturity was observed. Likewise, 7–18 days early heading in drought conditions was also reported [42]. In accordance with the previous reports, the number of days to maturity was found to reduce as stress levels were increased. A reduced number of days to heading and days to maturity also play an important role in drought stress tolerance as they allow for drought escape [19,45,46,47]. However, the plant cycle should not be too short, because such traits will compromise yields. The average DTM under drought stress treatment condition was 98.97 days, which was slightly lower than in the control (103.13 days) [48]. It was earlier found that, the susceptible and tolerant genotypes that show early maturity under stress conditions, manifest the escape mechanism of the genotype for drought tolerance [28]. Besides, drought stress is also known to cause reduction in the spike length (SL), number of grains per spike and spikelets per spike [49,50]. The drought stress also significantly affects the grain filling, thus leading to reduced grain size and a smaller number of grains [51,52]. So ultimately this causes reduction in grain and biological yields [19,53,54]. Previously, about 19.8% reduction in the number of grains per spike under drought stress condition have been reported [50].

The varied responses by morphological and physiological features in the wheat genotypes are assumed to be attributable to differences in genotype of each variety. The genotypes HD2888 and RAJ3765 were less affected in terms of the quantitative traits like SL, SPS, GPS and TW. Fewer effects on these traits under different drought stress conditions can be considered as the phenotype of tolerant genotypes [40]. The studies on physiological responses of wheat varieties to drought stress are essential to understand the mechanisms of drought resistance. Drought induces significant alterations in wheat physiology [55]. Previous studies have showed that water stress significantly decreased the ChL content and values of other physiological traits during the different developmental stages of wheat [16,56,57]. Among all the genotypes tested, PBW343 was found to be the most sensitive to drought stress, with an observed 21.62% reduction in ChL content, otherwise HD2888 was the least affected, reduced by only 8.24%. The genotypes with highest chlorophyll content under drought stress were classified as resistant, and those with lowest ChL content as the susceptible genotypes [27]. The reduction in Pn from 20 µmol/m²sec to 6µmol/m²sec with the increase in the level of PEG-6000 concentration recorded previously [16]. In the current findings, the maximum reduction in Pn of 40.31% was observed in the genotype DBW17 at 15% PEG treatment, whereas the genotypes HD2888 and HD2733 were least affected and showed only 18.90% and 21.70% reductions. Senescence is accelerated by drought stress, which accelerates chlorophyll breakdown, resulting in a reduction in photosynthesis and the reduction in Pn ultimately leads to yield loss [54,58,59].

Under drought stress conditions, the RWC is an important indicator of the water status in wheat [60]. The drought stress could reduce the RWC up to 43% (from 88 to 45%) in bread wheat [61].

As water stress has adverse effects both on membrane structure and function [62], measurement of the membrane stability index has been considered as an important scale for selecting the drought tolerant wheat genotypes [28]. Previously, a significant decrease in MSI from 85% in the control to 50% in drought stress treatments has been reported [63]. Most importantly, the accumulation of proline in plant cells plays a crucial role in fighting drought stress due to its ability to oppose oxidative stress and is considered to be an important strategy to overcome the effects of water stress [64]. It was observed that the amount of proline content increased with the increase in the level of drought stress [65] and the genotype with the highest proline content performed better under stress conditions [28]. A significant increase of proline up to 1.37 µM/gfw was recorded under drought stress conditions [66].

A significant correlation between the yield related traits in normal and drought stress conditions may be considered as target traits during the selection process [67,68]. Significant positive correlation between cell MSI and yield related traits and, spike length with PH and SPS under both stressed and control conditions have been reported [26,69]. In the current study also, significant positive correlations were found between the morphological traits related to yield (TW, SL, SPS, GPS) and physiological traits (Pn, RWC, MSI) in treatment conditions.

Hence, the measurement of these traits may also be used as an important scale for selecting drought tolerant wheat genotypes [28]. The high correlation between a trait and component indicates that the trait is associated with the direction of the minimum or maximum amount of variability in the data set [70]. PCA biplots have been used by many researchers for the comparison of different genotypes [71,72], and some were able to reveal that the bread wheat genotypes with the larger PCA1 and lower PCA2 scores will give high yields (stable genotypes) and genotypes with the lower PCA1 and larger PCA2 scores had low yield (unstable genotype) [73,74,75].

5. Conclusions

A large range of genotypic diversity exists and confers a wide response to PEG-stimulated drought stress in wheat genotypes, according to the findings of the current research (Figure 1). PEG concentrations were observed to decrease with increasing PEG concentrations in all treatment conditions except the proline content, which was shown to rise with increasing PEG concentrations. The relationship between physiological and yield related (SPS, GPS, and TW) features was shown to be statistically significant and favourable. Evaluation of these characteristics, as well as the build-up of proline content, may be regarded as a method for the successful selection of drought resistant wheat cultivars in future research. GP, Pn, MSI, GPS, and TW were all shown to be impacted by PEG treatment under the drought treatment scenarios, suggesting that these characteristics might be used as marker traits to assess the genotypes for drought stress under the conditions studied. The genotype RAJ3765 showed favourable results in all the drought stress treatments tested, and it would be an excellent source for future research into the mechanisms of drought resistance in wheat, if it were available.