Drought Tolerance In Cotton Research Articles

Construction of a cotton VIGS library for functional genomics study.

To facilitate cotton functional genomics studies and identify cotton genes mediating biotic and abiotic stress responses, we report here a detailed protocol of construction of a VIGS library from diploid cotton Gossypium raimondii. Sequencing of the representative colonies revealed that the library covers a significant percentage of unique cotton genes. Based on the number of colonies in the primary library, it is estimated that this VIGS library is about 50× coverage of predicted cotton protein-coding genes. As a proof-of-concept experiment, we further describe a protocol to identify the genetic determinants involved in cotton drought tolerance using this VIGS library. The cotton VIGS library established here provides a unique opportunity to identify essential cotton genes in various stress responses and developmental growth regulation.

Effect of Water Stress on the Growth and Yield of Cotton Crop (<i>Gossypium hirsutum</i> L.)

Cotton is one of the most important fibre crops playing a key role in economic and social affairs of the world. Water is a critical factor which influences on growth and yield of the cotton crop. Scarcity of water has put tremendous pressure on scientists to introduce drought tolerant cotton varieties. This study was aimed to determine water stress effects on the growth and yield of cotton. The present study was carried out to examine the effect of number of irrigations on the growth and yield of cotton during 2014. The field trial was conducted at the Experimental Fields of Agronomy Section, Agriculture Research Institute, Tandojam, Pakistan. A three replicated Randomized Complete Block Design (RCBD) was employed to layout the experiment having plot size of 2.5 m × 5 m (12.5 m2). Four cotton varieties i.e. NIAB-78, Shahbaz-95, Sindh-1 and TH-224/87 were chosen for this study based on their frequent farmer usage. All the agronomic practices were performed according to standard procedures. Results showed that all the growth and yield components of cotton were significantly (P 0.05) affected by irrigation frequencies. The cotton crop irrigated six times at 21 days interval showed better results with 138.16 cm plant height, 1.45 monopodial branches per plant, 21.83 sympodial branches per plant, 44.58 bolls per plant, 33.86% G.O.T., and 26.97 mm staple length, 149.84 g seed cotton yield per plant and 2271.16 kg·ha-1 seed cotton yield. This study concluded that variety NIAB-78 showed superiority over Shahbaz-95, Sindh-1 and TH-224/87 in almost all the characters of economic importance, and the cotton crop received 6 irrigations at 21 days interval resulted in significantly economical overall performance as compared with 5 irrigations or 4 irrigations with higher seed cotton yield.

Identification of drought-responsive genes in a drought-tolerant cotton (Gossypium hirsutum L.) cultivar under reduced irrigation field conditions and development of candidate gene markers for drought tolerance

Cotton productivity is affected by water deficit, and little is known about the molecular basis of drought tolerance in cotton. In this study, microarray analysis was conducted to identify drought-responsive genes in the third topmost leaves of the field-grown drought-tolerant cotton (Gossypium hirsutum L.) cultivar Acala 1517-99 under drought stress conditions. Water stress was imposed by withholding irrigation for 9 days in the early squaring stage, which resulted in 10–15 % reduction in plant growth compared to the well-watered plants. A total of 110 drought-responsive genes (0.5 % of the total genes) were identified, 79 % (88 genes) of which were drought-repressed and 21 % (22 genes) were drought-induced. The drought-induced genes were grouped into six functional categories including stress-related (ten genes, nine of which encode heat shock proteins), metabolism (three genes) and one gene each for transcription factor, proline biosynthesis and cellular transport. The drought-repressed genes were classified into 14 functional categories, comprising metabolism (20 genes), cellular transport (12 genes), stress-related (12 genes), regulation of gene expression (nine genes), transcription factor (four genes), signal transduction (seven genes) and two genes each for biosynthesis of secondary compounds, cell wall, fatty acids/lipids and chlorophyll, and protein degradation. Most of the genes have been reported in other plants as drought-tolerant/responsive. The responsiveness of 19 selected drought-responsive genes was validated by quantitative RT-PCR. Furthermore, primers were developed and assayed for all the drought-responsive genes to develop single-strand conformation polymorphic markers, many of which were found to be correlated with drought tolerance. This report represents the first study on integration of a transcriptome analysis to develop molecular markers that are associated with drought tolerance in cotton.

Genome-Wide Functional Analysis of Cotton (Gossypium hirsutum) in Response to Drought

Cotton is one of the most important crops for its natural textile fibers in the world. However, it often suffered from drought stress during its growth and development, resulting in a drastic reduction in cotton productivity. Therefore, study on molecular mechanism of cotton drought-tolerance is very important for increasing cotton production. To investigate molecular mechanism of cotton drought-resistance, we employed RNA-Seq technology to identify differentially expressed genes in the leaves of two different cultivars (drought-resistant cultivar J-13 and drought-sensitive cultivar Lu-6) of cotton. The results indicated that there are about 13.38% to 18.75% of all the unigenes differentially expressed in drought-resistant sample and drought-sensitive control, and the number of differentially expressed genes was increased along with prolonged drought treatment. DEG (differentially expression gene) analysis showed that the normal biophysical profiles of cotton (cultivar J-13) were affected by drought stress, and some cellular metabolic processes (including photosynthesis) were inhibited in cotton under drought conditions. Furthermore, the experimental data revealed that there were significant differences in expression levels of the genes related to abscisic acid signaling, ethylene signaling and jasmonic acid signaling pathways between drought-resistant cultivar J-13 and drought-sensitive cultivar Lu-6, implying that these signaling pathways may participate in cotton response and tolerance to drought stress.

Polyamine Metabolism of the Cotton Flower and Its Sub-tending Leaf under Water-Deficit Stress in the Field

Polyamines, putrescine, spermidine and spermine are low molecular weight polycations implicated in flowering and seed set and plants’ responses under adverse environmental conditions. Research in other crops has shown that polyamine metabolism is greatly affected by water-deficit stress, however, no information exists on cotton (Gossypium hirsutum L.). A field study was conducted in 2011 in two contrasting locations (Fayetteville, AR, and Lubbock, TX) in order to investigate the effect of water-deficit stress during flowering on polyamine metabolism of the cotton flower and its subtending leaf. Treatments consisted of control (well watered) and water-stress (irrigation withheld for two weeks at the onset of flowering) in a split plot design. First day white flowers and their subtending leaves were collected at the end of each week of the stress period for determination of polyamine concentrations. Water-deficit stress resulted in significant increases in PUT and SPD levels of pistils and leaves compared to the control. However, pistil and leaf SPM content significantly increased under drought conditions in one location and remained unaltered in the other one. Leaf and pistil polyamine metabolism of cotton appeared to be greatly affected by limited water supply, however further research is needed to elucidate the ways polyamines can be used to increase cotton drought tolerance.

Physiological Mechanism of Nitrogen Mediating Cotton (<i>Gossypium hirsutum</i> L.) Seedlings Growth under Water-Stress Conditions

The objective of this investigation was to study the effects of nitrogen on tolerance to water-stress in cotton (Gossypium hirsutum L.) seedlings. Growth chamber studies with pots of washed sand were carried out in Fayetteville, USA, and Nanjing, Chinawith three water conditions (well-watered, drought-stressed, and waterlogging), and three nitrogen rates, low nitrogen (16 mM, approximately 224 mg N·l–1 water), medium nitrogen (24 mM, approximately 448 mg N·l–1 water) and high nitrogen (32 mM, approximately 672 mg N·l–1 water), respectively. The results showed that water-stress treatments reduced plant biomass, C/N ratio, root vigor and leaf photosynthesis (Pn). The plant response to water-stress resistance was affected by nitrogen, and was correlated with the activities of antioxidant enzymes. The changes of anti-oxidant enzymes was the highest in the low nitrogen rate in the drought-stressed and waterlogged cotton seedlings. Malondialdehyde (MDA) content increased significantly in the water-stress treatments, and was the lowest in the low nitrogen rate. There was a significant reduction of N accumulation under water stress. Low-nitrogen treatmentincreased C accumulation, while high-nitrogen treatment decreased N accumulation. Root vigor was decreased by water stress, and was highest in the low-nitrogen rate. After terminating the water stress, N application promoted root vigor, especially in waterlogged seedlings. The trends of Pn weresimilarto that of root vigor. These results suggested that low N application may contribute to cotton drought tolerance by enhancing the activity of antioxidant enzymes and conse-quently decreasing lipid peroxidation, and enhancing root vigor. However, higher N should be applied to waterlog- ging-stressed cotton seedlings after terminating waterlogging.

Genome-wide transcriptomic analysis of cotton under drought stress reveal significant down-regulation of genes and pathways involved in fibre elongation and up-regulation of defense responsive genes

Cotton is an important source of natural fibre used in the textile industry and the productivity of the crop is adversely affected by drought stress. High throughput transcriptomic analyses were used to identify genes involved in fibre development. However, not much information is available on cotton genome response in developing fibres under drought stress. In the present study a genome wide transcriptome analysis was carried out to identify differentially expressed genes at various stages of fibre growth under drought stress. Our study identified a number of genes differentially expressed during fibre elongation as compared to other stages. High level up-regulation of genes encoding for enzymes involved in pectin modification and cytoskeleton proteins was observed at fibre initiation stage. While a large number of genes encoding transcription factors (AP2-EREBP, WRKY, NAC and C2H2), osmoprotectants, ion transporters and heat shock proteins and pathways involved in hormone (ABA, ethylene and JA) biosynthesis and signal transduction were up-regulated and genes involved in phenylpropanoid and flavonoid biosynthesis, pentose and glucuronate interconversions and starch and sucrose metabolism pathways were down-regulated during fibre elongation. This study showed that drought has relatively less impact on fibre initiation but has profound effect on fibre elongation by down-regulating important genes involved in cell wall loosening and expansion process. The comprehensive transcriptome analysis under drought stress has provided valuable information on differentially expressed genes and pathways during fibre development that will be useful in developing drought tolerant cotton cultivars without compromising fibre quality.

QTL mapping for physiology, yield and plant architecture traits in cotton (Gossypium hirsutum L.) grown under well-watered versus water-stress conditions

Increasing scarcity of irrigation water is a major threat to sustainable production of cotton ( Gossypium hirsutum L.). Identifying genomic regions contributing to abiotic stress tolerance will help develop cotton cultivars suitable for water-limited regions through molecular marker-assisted breeding. A molecular mapping F 2 population was derived from an intraspecific cross of the drought sensitive G. hirsutum cv. FH-901 and drought tolerant G. hirsutum cv. RH-510. Field data were recorded on physiological traits (osmotic potential and osmotic adjustment); yield and its component traits (seedcotton yield, number of bolls/plant and boll weight); and plant architecture traits (plant height and number of nodes per plant) for F 2 , F 2:3 and F 2:4 generations under well-watered versus water-limited growth conditions. The two parents were surveyed for polymorphism using 6500 SSR primer pairs. Joinmap3.0 software was used to construct linkage map with 64 polymorphic markers and it resulted into 35 markers mapped on 12 linkage groups. QTL analysis was performed by composite interval mapping (CIM) using QTL Cartographer2.5 software. In total, 7 QTLs (osmotic potential 2, osmotic adjustment 1, seedcotton yield 1, number of bolls/plant 1, boll weight 1 and plant height 1) were identified. There were three QTLs ( qtl OP-2, qtl OA-1, and qtl PH-1) detected only in water-limited conditions. Two QTLs ( qtl SC-1 and qtl BW-1) were detected for relative values. Two QTLs ( qtl OP-1 and qtl BN-1) were detected for well-watered treatment. Significant QTLs detected in this study can be employed in MAS for molecular breeding programs aiming at developing drought tolerant cotton cultivars.

Construction of SSH Library and Its Analyses of Cotton Drought Associated Genes under Drought Stress

A forward cDNA-SSH library was established by suppression subtractive hybridization using seedling leaf of Handan 177,a drought-tolerant cotton(Gossypium hirsuutm L.) inbred line,among which 300 positive clones were selected for sequenc-ing.After detection by PCR for each clone,each single clone was sequenced.Totally 284 available sequences and 202 uniESTs which 28 were contigs and 174 were singlets were obtained by cluster analyses of the ESTs sequencing.The results of BlastN showed that 156 uniESTs had homologous sequences in GenBank database while the other 46 had no protein homologous.The BlastX results indicated that 116 uniESTs had significant protein homology and 40 uniESTs were unknown proteins and putative proteins.KOBAS mapped 33 ESTs of the 202 uniESTs to 55 KEGG pathways,in which there were 23 pathways at P-value0.05.This study suggested that there were closely relationships with cotton drought tolerance among pyruvate metabolism,glyoxylate and dicarboxylate metabolism.A large group of drought stress-induced genes were found in the cDNA library,which involved in many metabolism pathways such as signal transduction,energy metabolism,protein metabolism,nucleic acid metabolism,photo-synthesis,transmembran.And some genes related to drought tolerance were found,such as malate synthase genes(MS1,0001_C12;MS2,0002_F01) and malate dehydrogenase genes(Md1,001_C12;Md2,002_F01),some transcription factors like NAC(001_C08),BZR1/BES1(003_G04),zinc finger protein genes(zfp,003_C06),and the translationally controlled tumor protein gene(TCTP,002_C04).

Constructing SSH Library of Cotton Under Drought Stress and Analysis of Drought Associated Genes

A forward cDNA-SSH library was constructed from a drought-tolerant cotton ( Gossypium hirsutum L.) inbred line, Handan 177, to understand the expressions of drought-induced genes. Using suppression subtractive hybridization method, a total of 2300 positive clones were obtained, of which 300 clones were selected for PCR validation and sequencing. Among these clones, 284 were available sequences. According to clustering analysis of the expressed sequence tag (EST), 202 uniESTs were found, including 28 contigs and 174 singlets. The result of BlastN showed that 156 uniESTs had homologous sequences in GenBank database. The result of BlastX indicated that 116 uniESTs had high homology with proteins with known functions, and 40 uniESTs showed high similarities with unknown proteins or putative proteins. Thirty-three uniESTs were located into 55 KEGG pathways using KOBAS software, including 23 pathways at a significant level ( P < 0.05). These significant pathways were mainly related to pyruvate metabolism (15%) and glyoxylate and dicarboxylate metabolism (12%). A large group of drought-induced genes were detected in the cDNA library, which were involved in signal transduction, energy metabolism, protein metabolism, nucleic acid metabolism, photosynthesis, and transmembrane transport. Some of them were associated with drought tolerance, such as malate synthase genes ( MS1, 0001_C12 and MS2, 0002_F01), malate dehydrogenase genes ( Md1, 001_C12 and Md2, 002_F01), NAC type transcription factor (001_C08), BZR1/BES1 (003_G04), zinc finger protein gene ( zfp, 003_C06), and translationally controlled tumor protein gene ( tctp, 002_C04).

Drought Tolerance in Cotton: Involvement of Non‐enzymatic ROS‐Scavenging Compounds

AbstractCompounds with reactive oxygen species (ROS)‐scavenging ability were studied. High‐performance liquid chromatography (HPLC) pattern of polyphenols, contents of proline and carotenoids, and antiradical (AR) capacity were determined. The malonyldialdehyde (MDA) level was also assessed. Tolerant and sensitive cotton genotypes were compared, grown in the Aegean region of Turkey at normal (field capacity) and limited (1/3 field capacity) water supply. Chlorogenic acid isomers and flavonoids were identified in HPLC pattern of polyphenols. At normal water supply, the tolerant genotype was distinguished by a higher content of all polyphenol types, higher proline, carotenoids and AR capacity and lower MDA level compared with the sensitive genotype. In plants subjected to water deficit, a decline of all polyphenol compounds, carotenoids and AR capacity was observed. However, this response was less pronounced in the tolerant than in the sensitive genotype, i.e. despite the stress conditions imposed, the tolerant plants maintained a more effective defence system. The data are corroborated by the weaker structural membrane damage in the drought‐exposed tolerant vs. sensitive genotype, according to the MDA test. Hence, diverse chemical types are involved in the non‐enzymatic ROS‐scavenging system of cotton plants and can be related to the drought tolerance of this important crop.

Genotypic variation for drought tolerance in cotton

Increasing scarcity of irrigational water is a major threat to sustainable production of cotton (Gossypium hirsutum L.). It could be resolved by developing drought-tolerant cultivars. Osmotic adjustment and cellular membrane stability are well-documented traits that help to sustain yield under drought in cereals. However, their utility in cotton is not well established. Here, we studied genotypic variability and relationships among osmotic adjustment, cell membrane stability and productivity traits under field-induced water stress at the flowering stage. We evaluated a set of cotton germplasm comprising 32 cotton genotypes under contrasting water regimes for measurements of productivity including seedcotton yield, number of bolls per plant and boll weight, and physiological attributes such as osmotic adjustment and cell membrane stability in two field trials. The mean reduction in seedcotton yield due to water deficit was 20 and 43% in 2003 and 2004, respectively. Genotypes differed considerably for relative yield losses due to water stress ranging from 20 to 74%. Significant association between number of bolls and seedcotton yield under a water-limited regime suggests boll retention as the principal determinant of yield in a water-deficit-stress environment. Cell membrane stability varied significantly among the cotton genotypes; however, its association with productivity measurements was not significant in the water-limited regime. The significant positive correlation found between cell membrane stability and osmotic adjustment implicates the role of osmolytes in the protection of various cellular functions, including those associated with cellular membranes. Moderate but significant differences for osmotic adjustment were found among the genotypes in both years. Osmotic adjustment was positively associated with seedcotton yield under the water-limited regime and inversely correlated with the drought susceptibility index. These results demonstrated the contribution of osmotic adjustment in sustaining yield under water-deficit stress in cotton. Thus, like cereals, osmotic adjustment may be useful as a selection criterion in breeding programs with the objective of improving drought tolerance and yield in cotton under water-limited environments; however, the role of cell membrane stability as a drought-tolerant trait requires further investigation.

Different drip irrigation regimes affect cotton yield, water use efficiency and fiber quality in western Turkey

Decreasing in water availability for cotton production has forced researchers to focus on increasing water use efficiency by improving either new drought-tolerant cotton varieties or water management. A field trial was conducted to observe the effects of different drip irrigation regimes on water use efficiencies (WUE) and fiber quality parameters produced from N-84 cotton variety in the Aegean region of Turkey during 2004 and 2005. Treatments were designated as full irrigation (T 100, which received 100% of the soil water depletion) and those that received 75, 50 and 25% of the amount received by treatment T 100 on the same day (treatments T 75; T 50 and T 25, respectively). The average seasonal water use values ranged from 265 to 753 mm and the average seed cotton yield varied from 2550 to 5760 kg ha −1. Largest average cotton yield was obtained from the full irrigation treatment (T 100). WUE ranged from 0.77 kg m −3 in the T 100 to 0.98 kg m −3 in the T 25 in 2004 growing season and ranged from 0.76 kg m −3 in the T 100 to 0.94 kg m −3 in the T 25 in 2005 growing season. The largest irrigation water use efficiency (IWUE) was observed in the T 25 (1.46 kg m −3), and the smallest IWUE was in the T 100 treatment (0.81 kg m −3) in the experimental years. A yield response factor ( k y) value of 0.78 was determined based on averages of two years. Leaf area index (LAI) and dry matter yields (DM) increased with increasing water use for treatments. Fiber qualities were influenced by drip irrigation levels in both years. The results revealed that well-irrigated treatments (T 100) could be used for the semi-arid climatic conditions under no water shortage. Moreover, the results also demonstrated that irrigation of cotton with drip irrigation method at 75% level (T 75) had significant benefits in terms of saved irrigation water and large WUE indicating a definitive advantage of deficit irrigation under limited water supply conditions. In an economic viewpoint, 25.0% saving in irrigation water (T 75) resulted in 34.0% reduction in the net income. However, the net income of the T 100 treatment is found to be reasonable in areas with no water shortage.

Differential responses of the enzymes involved in proline biosynthesis and degradation in drought tolerant and sensitive cotton genotypes during drought stress and recovery

The relative water content (RWC), free proline levels and the activities of enzymes involved in proline metabolism were studied in drought tolerant (Ca/H 680) and drought sensitive (Ca/H 148) genotypes of cotton (Gossypium hirsutum L.) during induction of water stress and posterior recovery. Water stress caused a significant increase in proline levels and P5CS activity in leaves of both tolerant and sensitive genotypes, whereas the activity of P5CR increased minimally and the activity of OAT remains unchanged. The activity of PDH decreased under drought stress in both the genotypes. The leaf of tolerant genotype maintained higher RWC, photosynthetic activity and proline levels, as well as higher P5CS and P5CR activities under water stress than that of drought sensitive genotype. The drought induced proline levels and activities of P5CS and P5CR declined and tend to be equal to their respective controls, during recovery, whereas the PDH activity tends to increase. These results indicate that induction of proline levels by up regulation of P5CS and down regulation of PDH may be involved in the development of drought tolerance in cotton.

Genotypic variation for drought tolerance in cotton ( Gossypium hirsutum L.): Leaf gas exchange and productivity

Although water-limited environments are detrimental to cotton growth and productivity worldwide, identification of cotton ( Gossypium hirsutum L.) genotypes that are less sensitive to drought may improve productivity in drought prone areas. The objective of the study was to assess genotypic variation for drought tolerance in cotton varieties using physiological attributes as selection criteria, and to determine the relationship of physiological attributes with productivity traits. The association of target physiological traits for drought tolerance (photosynthetic rate ( P n), stomatal conductance ( g s), and transpiration rate ( E)) with productivity traits under well-watered (W 1) and water-limited (W 2) regimes was analyzed using 32 public cotton cultivars/bred lines in two field experiments conducted during the normal cotton growing seasons 2003 and 2004. Seed cotton yield (SCY) and biological yield (BY) were markedly affected under W 2 regime in all cultivars except the outstanding performance of CIM-1100 and RH-510 proving their superiority to other cultivars in drought tolerance. Conversely, FH-901, FH-634, and FH-2000 were high yielding under W 1 regime; however, exhibited a sharp decline in yield under W 2 regime. A positive correlation between SCY and BY under water stress ( r=0.44 in 2003; r=0.69 in 2004) indicates that BY is also a primary determinant of SCY under water stress and genetic improvement of BY under water-limited environment may also improve SCY. P n, g s, and E were significantly reduced by water stress. Substantial genotypic variation for gas exchange attributes existed among the cotton cultivars. A positive association ( P<0.01) was observed between g s and E under both regimes in both years indicating the prevalence of stomatal control of transpiration. The positive association ( P<0.01) between P n and g s in both years in W 2 regime indicates also a major role of stomatal effects in regulating leaf photosynthesis under water-limited conditions. P n was significantly correlated with SCY ( P<0.01) and BY ( P<0.05 in 2003; P<0.01 in 2004) in W 2 regime; however, the level of these associations was not significant in W 1 regime. These findings demonstrate that association of P n with productivity is effective under water-limited environment and may be useful as a selection criterion in breeding programs with the objective of improving drought tolerance and SCY under water-limited environments. Moreover, association between SCY and BY under water stress suggests that genetic improvement of BY under water stress may also improve SCY.

Increase of glycinebetaine synthesis improves drought tolerance in cotton

The tolerance to drought stress of the homozygous transgenic cotton (Gossypium hirsutum L.) plants with enhanced glycinebetaine (GB) accumulation was investigated at three development stages. Among the five transgenic lines investigated, lines 1, 3, 4, and 5 accumulated significantly higher levels of GB than the wild-type (WT) plants either before or after drought stress, and the transgenic plants were more tolerant to drought stress than the wild-type counterparts from young seedlings to flowering plants. Under drought stress conditions, transgenic lines 1, 3, 4, and 5 had higher relative water content, increased photosynthesis, better osmotic adjustment (OA), a lower percentage of ion leakage, and less lipid membrane peroxidation than WT plants. The GB levels in transgenic plants were positively correlated with drought tolerance under water stress. The results suggested that GB may not only protect the integrity of the cell membrane from drought stress damage, but also be involved in OA in transgenic cotton plants. Most importantly, the seedcotton yield of transgenic line 4 was significantly greater than that of WT plants after drought stress, which is of great value in cotton production.

Development of a Screening Method for Drought Tolerance in Cotton Seedlings

The key to an efficient screening method is the ability to screen large amounts of plant material in the shortest time possible. Due to the complexity of drought tolerance, a quick and effective screen for this trait has yet to be established. The research reported herein was designed to evaluate a screening method for drought tolerance in cotton (Gossypium hirsutum L.) seedlings. Twenty‐one converted race stocks (CRS) and two cultivars were evaluated for seedling drought tolerance (SDT) on an individual plant basis. Genotypes were evaluated October–November 2004 and February–March 2005 under greenhouse conditions. Seedlings were subjected to three sequential cycles of drought at 15 d after planting (DAP). Drought cycles consisted of withholding water until the moisture content of indicator ‘Deltapine 491’ (DP 491) plants had an average volumetric water content of 0.07. Plants then were watered to saturation and allowed to drain to field capacity and percent survival recorded after 48 h. Genotypes differed in their percent survival following three consecutive drought cycles. Drought cycles 2 and 3 did not contribute to the separation of genotypes. DP 491 was the most tolerant genotype evaluated. The drought tolerance of the CRS was similar to that of ‘Acala 1517–99’. CRS M‐9044–0165 was the most stable genotype, according to an analysis of the difference in percentage of survival for each genotype across the two experiments.

Seedling Drought Tolerance in Upland Cotton

Combining root morphological and plant physiological traits associated with drought tolerance should result in improved drought resistance in cotton (Gossypium hirsutum L.). This study was designed to evaluate the response of root growth of selected Converted Race Stocks (CRS), TAM94L‐25, and ‘Lankart 142’ (LK 142) under water stress and nonstressed conditions, and to compare their excised leaf water loss (ELWL). Two putative seedling drought tolerant and two putative nonseedling drought tolerant CRS lines, plus TAM94L‐25 and LK 142, were grown with and without moisture stress in a greenhouse at College Station, TX, in 2002 and 2003. The robust rooting CRS, M‐9044‐0031‐R and M‐8744‐0175‐R, had longer tap root length (RL), higher lateral root number (LRN), greater total root dry weight (TRDW), greater root weight per unit length of tap root (W/L), and greater shoot dry weight (SDW) than the nonrobust CRS M‐9044‐0045‐NR and M‐9044‐0057‐NR, and LK 142 regardless of water regime. Two cycles of seedling drought resulted in an increase in LRN in M‐9044‐0057‐NR, TAM94L‐25, and LK 142. SDW and TRDW were highly correlated and SDW was associated with W/L. The excised leaf water loss (ELWL) tended to be greater in the NR CRS lines when measured at 30‐m intervals for 8 h. Results suggested (i) that root parameters, initial water content (IWC), and ELWL, could be used as a reliable selection criteria for drought tolerance and (ii) that day‐neutral CRS accessions could be used as a source of useful genetic variability for a cotton drought tolerance improvement program.

Expression of selected drought-related genes and physiological response of Greek cotton varieties

Drought-tolerant cotton varieties are very important for Greece and throughout the world. Four Greek cotton varieties (Zeta 2, Zeta 5, Korina and Eva) and an Australian variety (Siokra L23) were subjected to three water-stress levels (0.0, -0.1 and -0.3 MPa). Morphological and physiological parameters studied were plant height, total leaf area, shoot, root and total plant fresh and dry weights, stomatal resistance (SR), water potential (Ψ w), and relative water content. Siokra L23 was confirmed to be the most drought-tolerant variety based on its high SR and Ψ w , it's having the smallest total leaf area, and expression of drought-tolerance-related genes. The Greek cotton varieties were ranked from most to least drought tolerant as follows: Eva, Korina, Zeta 2, Zeta 5.Molecular responses of the cotton varieties were studied by investigating the expression of five drought-tolerance-related genes, namely, trehalose-6-P synthase, heat-shock protein calmodulin-binding homolog, late embryogenesis abundant (Lea) proteins 14A and 5D, and NAD(P)H oxidase. Reverse transcription-polymerase chain reaction was performed utilizing total RNA samples isolated after a 4-d drought treatment (i.e. at the end of the stress period). Heat-shock protein calmodulin-binding homolog was induced by water stress in drought-tolerant varieties (Eva and Siokra L23) and Zeta 2. This correlation between physiological and molecular data for this gene allows it to be used in cotton breeding programs. Trehalose-6-P synthase and NAD(P)H oxidase genes were not expressed in almost all varieties and treatments. In contrast, the Lea genes showed, with minor exceptions, expression that was independent of variety and treatment. Eva and Korina varieties should be used under conditions of water shortage, whereas Zeta varieties provide a significant advantage to the grower when planted under conditions of high water availability.

Variation in carbon isotope discrimination and other traits related to drought tolerance in upland cotton cultivars under dryland conditions

The search for traits related to drought resistance is a main step in the selection of cotton with improved performance under limited water supply. The effect of cultivar and drought conditions on the physiological traits, such as carbon isotope discrimination (Δ), photosynthesis ( A), transpiration ( E), stomatal conductance ( g s), leaf osmotic potential ( ψ o) and leaf-water content (LWC), were studied in Andalucia, Spain. The morphological traits, such as leaf area and specific leaf weight (SLW), were also evaluated. In the initial study performed with three cotton cultivars, positive associations between Δ and A, E and g s were observed under increasing water stress. The A/ g s ratio was negatively associated with Δ, and a strong negative correlation was observed between SLW and Δ. In a further experiment, using a wider group of cultivars, an apparent genotypic variation in Δ was observed in plants after withholding irrigation. Genotypic variation was found for gas exchange ( A, E, g s) and leaf variables (LWC, SLW, ψ o). No relationship was found between Δ and gas exchange or leaf-related traits. Considering both samplings as situations of different water availability, and plotting the data together, a low but positive correlation was observed between Δ and g s or LWC, and negative between Δ and A/ g s. A remarkable correlation between LWC and gas exchange traits was found, whereas SLW was negatively correlated with A, A/ E, and LWC. In dryland trials (1996 and 1997), the genotypic variation in LWC was positively associated with Δ. Under these conditions, an association between genotypic variation in Δ and A or A/ E was observed. A positive correlation between yield and Δ was detected in 1996. Carbon isotope discrimination might be a useful tool for selecting drought-tolerant cotton genotypes but more studies are required to define more precisely the sampling conditions and the influence of factors affecting Δ and its relationship to crop yield.