Evaluation of drought tolerance in cotton (Gossypium hirsutum L.) genotypes under irrigated and rainfed conditions

Introduction

Cotton (Gossypium hirsutum L.) is a globally significant cash crop valued for its fiber, oil, and seed by-products. It contributes substantially to the agricultural economy, particularly in arid and semi-arid regions. However, the crop is increasingly vulnerable to abiotic stresses, especially drought, which has emerged as a major constraint on productivity in rainfed ecosystems (Tuteja et al., 2007; Reddy et al., 2017) [16,15] . Inadequate and erratic rainfall patterns during the crop growth period adversely affect key physiological and reproductive processes, leading to substantial yield losses. Drought stress influences cotton at various growth stages, reducing photosynthetic efficiency, altering leaf water potential, and impairing reproductive success by decreasing boll retention and seed filling (Karam et al., 2006; Basal et al., 2009) [14,10] . The extent of these effects varies depending on the intensity and timing of water deficit as well as genotypic adaptability. Thus, breeding for drought resilience in cotton is a pressing need in the context of climate change and increasing water scarcity. Effective drought screening requires a multi-trait approach, combining morphological, physiological, and yield-based parameters. Traits such as relative water content (RWC), plant height, boll number, dry matter accumulation, and yield under stress are commonly used indicators (Blum, 2011) [11] . Furthermore, stress indices like the Drought Susceptibility Index (DSI) and Yield Stability Ratio (YSR) provide quantitative assessments of genotype performance across environments (Fischer & Maurer, 1978) [13] . Advanced visualization tools such as heatmaps and biplots also facilitate the interpretation of complex, multivariate data sets in genotype evaluation (Fernandez, 1992) [12] .

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In this study, twenty cotton genotypes were evaluated under irrigated and rainfed conditions to identify lines with enhanced drought tolerance. The objectives were to (i) assess genotypic variability in morphological and physiological traits under drought, (ii) determine yield stability through stress indices, and (iii) identify superior genotypes suitable for drought-prone environments and breeding programs.

Material and Methods

Experimental Site and Design

The study was conducted under field conditions using a Randomized Complete Block Design (RCBD) with three replications at University of Agricultural Sciences, Dharwad. Two moisture regimes were imposed irrigated and rainfed. Each genotype was sown in 4-row plots (6 m length), with 75 cm row and 30 cm plant spacing. Standard agronomic practices were followed uniformly across treatments.

Plant Material

Twenty cotton genotypes of diverse genetic backgrounds were evaluated viz., ARB-815, Sahana, ARB-757, SSB- [7] , who emphasized yield component stability under stress as a critical drought-tolerance indicator.

Phenological Traits

The onset of key phenological stages, including 50% squaring, flowering, and boll opening, was influenced by moisture availability (Table 2). On average, flowering occurred 3 days earlier and boll opening 1 day earlier under rainfed conditions. Such early phenology is commonly observed in stress-adaptive genotypes employing a drought escape strategy. Genotypes like Sahana, ARB-757, and CPD-814 showed earlier flowering and boll opening, whereas ARB-760 and HAG-811 exhibited delayed flowering. Delay under rainfed conditions may be attributed to reduced metabolic activity under drought stress, consistent with Reddy et al. (2004) [6] .

Plant Growth (Height)

Plant height declined under rainfed conditions at all observed stages (105, 120, and 170 DAS), with the highest reduction (11.91%) at 105 DAS (Table 3). The maximum decline at early stages may indicate sensitivity to moisture stress during vegetative growth. Genotypes CPD-755, SSB-5, and KH-138 experienced substantial reductions (>20%) in height at early stages, while LH-1968 and HAG-811 maintained plant height with minimal reductions (<5%). This suggests better early vigor and growth maintenance under limited water availability in the latter genotypes.

Total Dry Matter Accumulation

Drought stress significantly affected biomass accumulation (Table 4). The average reduction in total dry matter (TDM) was 25.6%, with NH-615 and GSHV-99/307 showing reductions over 40%, indicating poor biomass productivity under stress. In contrast, CPD-814 and Sahana maintained higher TDM, suggesting efficient photosynthetic activity and better water use efficiency. The capacity to accumulate biomass under limited water supply is critical for yield potential, especially under rainfed agriculture, as emphasized by Turner et al. (2001) [8] .

Relative Water Content (RWC)

RWC, a key physiological indicator of plant water status, showed consistent reductions under rainfed conditions (Table 5). The mean reduction was 9.4% at 95 DAS, 7.0% at 132 DAS, and 3.2% at 160 DAS, showing a declining trend as plants matured. Genotypes GK-147, ARB-815, and GBHV-184 maintained high RWC under stress, suggesting efficient osmotic adjustment or deeper rooting systems. In contrast, NH-615, LH-1968, and CSH-7106 had significant drops, especially at early stages, reflecting their vulnerability. These patterns are consistent with Blum (2011) [11] , who stated that higher RWC under drought is often associated with better cellular hydration and drought tolerance.

Drought Indices

Three drought screening indices were calculated Plant Height Stress Index (PHSI), Yield Stability Ratio (YSR), and Drought Susceptibility Index (DSI) ( The biplot (Fig. 1) illustrates the clustering of genotypes based on yield and DSI. This visual differentiation confirms that genotypes with low DSI and high yield performance under rainfed conditions are ideal for selection and breeding.

Heatmap Analysis of Drought Tolerance Traits:

The heatmap effectively identified drought-resilient and droughtsensitive cotton genotypes based on a combination of morphological, physiological, and yield-related traits. It highlighted that GSHV-99/291, GK-147, ARB-815 and SSB-5 are consistently tolerant and suitable for breeding efforts aimed at improving drought resilience. These insights complement trait-specific analyses and reinforce the value of integrated screening approaches in crop stress physiology.

References

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