Evaluation of Cotton Genotypes for Drought Tolerance and Their Correlation Study at Seedling Stage Evaluation of Cotton Genotypes for Drought Tolerance and Their Correlation Study at Seedling Stage

separated five 3) and 4) and boll and variability there may be reactions of for drought in and

without water stress [3,4] and compete for receiving moisture from deeper levels of soil than plants grown under non-stress water conditions [5][6][7][8]. Shoot length is also considerably sensitive to water stress, thus cause severe decline in shoot length [4,9]. The Root/ shoot length ratio is regarded as stress adaptive system in response to water shortage conditions; hence it is considered an important indicator for drought stress tolerance. Some physiological attributes like Relative Water Content (RWC) which measures the amount of water retained by the plant in the leaf tissue, thus high RWC in water stress conditions would be preferable to sustain water stress.
Higher RWC in leaf tissue has been considered as reliable selection criteria to evolve crop varieties for water shortage environments [10,11].
Various morphological, physiological and yield characters are being used to measure drought tolerance when they are correlated with each other. Cotton subjected to water deficient since cotton originates from areas that are often exposed to water-deficit stress [12,13]. Therefore, selection for drought tolerance is a major interest of plant breeders in cotton. A number of different morphological (leaf, stem and root growth parameters) and physiological traits (more than 30 traits) have been suggested as important selection criteria relative to drought tolerance in cotton [14]. However, none of the above physiological traits has so far been consistently correlated positively with drought tolerance [14]. The difficulty in identification of a physiological parameter as a reliable indicator of yield in drought conditions has suggested that yield performance over a range of environments should be used as the main indicator for drought tolerance [15]. Several morphological traits belonging to seedling traits have been reported showing importance in relation to water stress tolerance in cotton [2]. Such traits include taproot mass, density of lateral roots, seedling vigor, rapidity in root development and root/shoot ratio [16]. For drought tolerance, longer taproot was supported by [17]. Two schools of thought exist among the researchers regarding root length under water stress conditions. Some scientists reported that root length of plants subjected to water stress registered significant increase in root length against those plants irrigated with optimum level of water [3,4]. On the contrary, some scientists found that root length under drought conditions has decreased seriously [16].

Materials and Methods
The research was carried out in the experimental area of the and origin were studied. The experiment was carried-out in factorial design with two irrigation treatments, non-stress and water stress with four replications. The water regimes were considered as the main factor while varieties as sub-factor. All agricultural inputs and practices like spraying, fertilization, weeding, irrigation and cotton production technology were adopted as recommended for the cotton crop. The data were collected from ten tagged plants in each replication. The seedlings were t part; the plant material was screened at seedling stage against water stress with some developmental and physiological traits [17,18].
Field screening for drought tolerance at seedling stage: Two irrigation regimes i.e. non-stress in which normal irrigations were applied, first after 25 days of sowing and second at 44 days after sowing whereas in water stress treatment, the stress was imposed from sowing till 44 days of the crop growth and development. For developmental and physiological traits, the observations were recorded for shoot length (cm), root length (cm), number of lateral roots, leaf area (cm 2 ), leaf relative water content with formula RWC = [(Fresh weight-Dry weight)/(Turgid weight-Dry weight)] x 100, excised leaf water loss (ELWL%) was calculated by following [19]. with formula E LWL = (Fresh weight -wilted weight) / Dry weight x 100, stomatal conductance (mmolm -2 s -1 ) was determined in mmolm -2 s -1 by Prometer-AP4 and stomatal density (mm 2 ) by impression method according to technique developed [20]. The soil type of the experimental area was loam and sandy loam in texture.

Results and Discussion
Analysis of variance and mean performance of cotton genotypes under water stress conditions at seedling stage. The results revealed that moisture deficit inflicted considerable influence on all the developmental and physiological characters at seedling stage (Table 1). Inconsistent responses of genotypes to water stress were observed because mean squares due to treatment × genotypes interactions were significant for all the studied characters.
Analogous to these results, [21] observed significant influence of water stress on root and shoot length of 80 accessions of cotton examined. The significance of accessions × treatment interactions revealed differential response of accessions to the two moisture environments. Significant differences for stomatal conductance, water content in leaves and water loss from excised leaves due to drought stress were also noted by [22]. The mean performance of cotton genotypes for various developmental and physiological traits under water stress are discussed here under.  (Table 2).
Cultivars, Chandi, Bt-cotton and BH-160 with maximum declines in shoot length as -15.00, -13.50 and -10.75cm respectively were found rather more susceptible to drought stress conditions. In water stress, the shoot lengths of Sadori (45.15cm) followed by CRIS-134 (45.10 cm) were relatively longer. These genotypes also showed greater tolerance to drought stress due to the fact that the shoot lengths of Sadori and CRIS-134 genotypes were reduced to only -4.85 and -5.65cm respectively under drought stress conditions. Similar to our findings, [23] found that shoot length of cotton seedlings were decreased due to exposure of drought stress. [24] suggested that shoot growth modifications may influence the root growth and development, thus may interfere with the cotton susceptibility to water stress. Response of cotton genotypes to water stress involves osmotic adjustment, elasticity to photochemical apparatus and stomatal conductance; hence the nature of shoot and root growth and development determine responses of genotypes to water stress [24,25] stated that water deficiency at initial vegetative stage has substantially reduced the shoot and root dry-matter in cotton plant.  [29,30]. Generally deep-rooted plants exhibit greater drought tolerance than shallow rooted genotypes.
Therefore, first irrigation is usually delayed in cotton up to 40 (Table 3). Analogous to present results, [32]. found two drought tolerant cotton genotypes while [30]. observed six cotton genotypes which produced higher number of lateral roots indicating their drought tolerance while [33]. observed that severe water stress reduced the root proliferation.  While other groups of cultivars like CIM-496, CIM-534, and Sindh-1 showed tolerance to drought stress due to reason that leaf area of these genotypes was less affected by stress and reduction was noted as -6.50, 6.50, and -6.00cm 2 respectively. [35] in his study observed that water stress resulted in reductions of all plant organs including total plant weight. However, he stated that declines in the leaf area below the optimum leaf area index will decrease crop growth rate and total photosynthesis per plant which ultimately will decrease the yield. Under well water condition, leaf area index increases along with growth rate, but it decreases in water deficit condition due to leaf area adjustment process. [36] conducted a pot experiment in green house on two cotton varieties and observed 24% and 29% decrease in leaf area of two genotypes respectively in drought-stressed plants. [37] noted the consequence of drought stress on leaf area at various reproductive stages of cotton and concluded that drought stress decreased leaf area in all the stages of the crop except maturity.
Relative water content (RWC %): High RWC% under drought stress conditions may be preferable to maintain water balance, thus higher RWC% may be adopted as good criteria to breed plants for water stress tolerance [11]. Moisture stress tolerance can be achieved through the capability of plants to minimize evaporation via stomatal shutting and modifications in leaf phenotype [38].
In present study, drought stress caused considerable declines in RWC% of the genotypes under screening and the reduction ranged from -26.50 to -48.50% ( caused substantial decline in yield, growth and leaves water content as reported by [22]. However, some varieties recorded higher growth and yield and also sustained higher leaf water content and more photosynthesis. Leaf relative water content was observed as 69% and 45% in transgenic and wild-type plants, respectively at 10-day drought stress. Similarly, transgenic plants showed better performance due to stress responsive genes for photosynthesis, stomatal conductance, transpiration, and osmotic potential as compared to wild type [39]. Excised leaf water loss (ELWL%): The cultivars possessing ability of low rate excised leaf water loss how drought resistance.
Therefore, ELWL% was recommended as best measure for tolerance to water stresses [11]. Variable response of cotton genotypes was observed for ELWL% under water stress at seedling stage. Drought stress increased the excised leaf water loss of all the cotton genotypes in the range of -14.50 to -27.50%. The maximum reduction in ELWL% nevertheless was recorded in varieties Btcotton followed by NIAB-78 and BH-160 (Table 4). Some genotypes like CIM-496, CRIS-134 and CIM-534 showed lower ELWL% under drought stress, the relative ELWL% of these genotypes was with -13.00, -14.50 and -17.50%, hence demonstrated their stress tolerance. Analogous to our findings, [39] also observed negative effects of water stress on excised leaf water loss in water shortage conditions. Note: *RD = Relative difference between non-stress and water stress treatments.  allow sustained accumulation of dry matter and its partitioning to reproductive organs [43,44] found that the water stress lowered the stomatal conductance, thus some varieties were less affected by water stress and maintained their stomatal conductance.  Note: *RD = Relative difference between non-stress and water stress treatments.  [46] noted that stomatal density increased as water stress increased, while the maximum stomatal aperture reduced only in the severe stressed plants. [

Correlations (R) Between Development and Physiological Traits
There was a significant positive association of shoot length with root length, number of lateral roots, leaf area, relative water content and stomatal density ( Table 6). These results indicated that from excised leaves, and stomatal conductance was also significant and positive. The relationships of leaf area with characters related to evapo-transpiration are well documented. It has been stated that RWC was considered as impotent parameter for determining water status in plant leaves. The preference of RWC to be important illustration of plant water status due to genetic variation also hold true because of close alliance between relative water content and yield in water stress Available reports revealed that drought tolerant species reduce the water loss by reducing the leaf area and also restricting stomatal opening.