Post-anthesis Drought Research Articles

Improved tolerance to post-anthesis drought stress by pre-drought priming at vegetative stages in drought-tolerant and -sensitive wheat cultivars

Wheat crop endures a considerable penalty of yield reduction to escape the drought events during post-anthesis period. Drought priming under a pre-drought stress can enhance the crop potential to tolerate the subsequent drought stress by triggering a faster and stronger defense mechanism. Towards these understandings, a set of controlled moderate drought stress at 55–60% field capacity (FC) was developed to prime the plants of two wheat cultivars namely Luhan-7 (drought tolerant) and Yangmai-16 (drought sensitive) during tillering (Feekes 2 stage) and jointing (Feekes 6 stage), respectively. The comparative response of primed and non-primed plants, cultivars and priming stages was evaluated by applying a subsequent severe drought stress at 7 days after anthesis. The results showed that primed plants of both cultivars showed higher potential to tolerate the post-anthesis drought stress through improved leaf water potential, more chlorophyll, and ribulose-1, 5-bisphosphate carboxylase/oxygenase contents, enhanced photosynthesis, better photoprotection and efficient enzymatic antioxidant system leading to less yield reductions. The primed plants of Luhan-7 showed higher capability to adapt the drought stress events than Yangmai-16. The positive effects of drought priming to sustain higher grain yield were pronounced in plants primed at tillering than those primed at jointing. In consequence, upregulated functioning of photosynthetic apparatus and efficient enzymatic antioxidant activities in primed plants indicated their superior potential to alleviate a subsequently occurring drought stress, which contributed to lower yield reductions than non-primed plants. However, genotypic and priming stages differences in response to drought stress also contributed to affect the capability of primed plants to tolerate the post-anthesis drought stress conditions in wheat.

Evaluation of Bread Wheat Genotypes under Normal and Post-anthesis Drought Stress Conditions for Agronomic Traits

Evaluation of Bread Wheat Genotypes under Normal and Post-anthesis Drought Stress Conditions for Agronomic Traits

The sowing date and post-flowering water status affect the sugar and grain production of photoperiodic, sweet sorghum through the regulation of sink size and leaf area dynamics

The combined production of grain and sugar by sorghum requires efficient leaf C acquisition (source) and allocation to productive sinks, namely the stem and the panicle. Photoperiod sensitivity, which regulates plant phenology and growth, is also likely to be a key regulator of such C source-sink relationships, while it is crucial to drought adaptation. This study set out to evaluate the contribution of plant leaf area and stem growth to the production of grain and sugar by sweet, photoperiodic sorghum depending on the sowing date and post-flowering water availability. Twelve West African accessions were studied in the field in Senegal during two consecutive rainy seasons, comparing two sowing dates and post-anthesis water regimes (irrigated, or not). Plant growth and development were monitored weekly up to flowering. Organ size and biomass, stem juiciness and sweetness were characterized at flowering and maturity. At flowering, early sowing enhanced plant leaf area, stem dry weight and sugar production, and plant leaf area expressed per unit of stem dry weight was positively correlated to stem sweetness, suggesting that a high pre-flowering source-to-sink ratio favors early sugar accumulation. Overall, a late sowing date reduced sugar and grain production more than post-anthesis drought, whereas early sowing enhanced both types of production. No post-anthesis competition was found between grain filling and stem sugar accumulation. However, under drought conditions, the maintenance of combined production was better for the most leaf stay-green accessions. It is suggested that the combined production of sugar and grain by sweet, photoperiodic sorghum in response to the sowing date and post-anthesis drought is firstly sink-driven but that source (plant leaf area) dynamics can enhance stem sugar accumulation and its maintenance under drought conditions. These results provide further insight into the traits to be combined in dual-purpose ideotypes dedicated to drought-prone environments.

Tolerance of Durum Wheat Cultivars to Postanthesis Drought Conditions as Affected by Seed Priming, Bio-Fertilizer and Potassium Application

The present study aimed to investigate the tolerance of different durum wheat (Triticum turgidum ssp. durum Desf.em. Musn) genotypes to drought stress at heading to maturity stage under the influence of drought alleviation treatments.The field work was carried out at Fuka Research Station, Faculty of Desert and Environmental Agriculture, AlexandriaUniversity, Matrouh Branch Egypt, in 2012/2013 and 2013/2014 winter seasons. The experimental design was split-plot,with four replicates where the main plots included six treatments as follows: 1) Spraying with potassium, 2) Priming withcalcium chloride, 3) Bio-fertilization with HALEX® 4) Seed hydro-priming, 5) Sowing of dry seed (these five treatmentswere subjected to drought by holding irrigation at postanthesis) and 6) Control (irrigation all season). The sub-plotsincluded the three durum wheat genotypes. The results revealed insignificant variation for applied treatments on allstudied characters, except for 100-grain weight, in the two seasons. Cultivars showed significant variations in LAI (at 80DAS), dry weight of spikes (at 50 % heading and 30 days later) and number of grains spike-1 in the two seasons.Interaction between drought alleviation treatments and cultivars was insignificant, for all studied characters in the twoseasons. Also, wheat plants, irrigated all season, gave the highest 100-grain weight (5.31 and 6.48 g) in the two seasons,respectively. On the other hand, Sohag 3 was superior (0.23 and 0.25) to Marjawi (0.19 and 0.21) in LAI, in the twoseasons, respectively. In addition, Beni Suef 5 gave the highest significant dry weight of spikes and number of grainsspike -1 in the two seasons. Drought susceptibility index (DIS) values revealed that seed priming with CaCl2 and watertolerated drought at postanthesis stage and gave comparable grain yield to that of control. Beni Suef 5 and Marjawishowed higher tolerance to drought than Sohag 3.

How do timing, duration, and intensity of drought stress affect the agronomic performance of winter rye?

Abstract Winter rye ( Secale cereale L.) will be especially affected by drought induced yield losses in Central and Eastern Europe in the future because it is predominantly cultivated on low-fertile soils with a poor water-holding capacity. In order to examine the performance of winter rye under different drought conditions, field experiments were carried out during the years 2011, 2012, and 2013 near Braunschweig, Germany. Two sets of genotypes were tested under severe, mild, pre-anthesis, and post-anthesis drought stress in rain-out shelters as well as under rainfed and well-watered conditions. The grain, straw, and total above ground biomass yields, harvest index, grain yield components, leaf area index (LAI), and phenological characteristics were examined, as well as phenotypic correlations between grain yield and further characteristics. Drought induced grain yield reduction ranged from 14 to 57%, while straw yield and harvest index were lesser affected by drought than the grain yield. Under drought conditions, fully ripe was reached up to twelve days earlier than under non water-limited conditions. Pre-anthesis drought mainly reduced spikes m −2 and kernels spike −1 while drought during grain filling reduced the 1000-kernel weight (TKW) only. The grain yield was positively associated with straw yield, spikes m −2 , and kernels spike −1 under water limited conditions while the TWK was only positively associated with grain yield under drought during grain filling. Consequently, high pre-anthesis biomass as well as high numbers of spikes m −2 and kernels spike −1 are especially important for obtaining high grain yields under water-limited conditions. Focusing on these traits is, therefore, recommendable for developing drought tolerant rye genotypes.

Assessment of genetic diversity and estimation of genetic parameters for remobilization related traits of wheat under drought conditions

In order to evaluate genetic variability and estimation of remobilization related traits in wheat using biometrical genetic techniques an experiment was conducted in a randomized complete blocks design with three replicates under post-anthesis drought stress conditions in the Campus of Agriculture and Natural Resources, Razi University, Kermanshah, Iran during 2011-2012 cropping season. The results of analysis of variance showed significant differences between the genotypes for all studied traits except current photosynthesis (CP) and current photosynthesis share into kernel yield (CPSKY). High genetic gain and broad sense heritability estimates were observed for penultimate remobilization share into kernel yield (PenRSKY) and internodes remobilization share into kernel yield (IRSKY) indicating high genetic potential, low effect of environment and predominant role of additive gene effect on their expression. Spike dry matter remobilization (SDMR), spike dry matter remobilization efficiency (SDMRE) and spike remobilization share into kernel yield (SRSKY) exhibited the highest phenotypic and genetic positive correlation with kernel yield (KY). Moreover, the highest genotypic and phenotypic covariance was observed between kernel yield (KY) and SDMR, CP, SDMRE and SRSKY, respectively. The highest environmental covariance was identified between kernel yield (KY), peduncle dry matter remobilization (PedDMR) and penultimate dry matter remobilization (PenDMR), respectively. High co-heritability was detected between SDMRE and PedDMR, PedDMRE and PenDMR and between peduncle remobilization share into kernel yield (PedRSKY) and internodes dry matter remobilization efficiency (IDMRE), suggesting that selection of either of the traits would simultaneously affect the others, positively.

The yield of wheat genotypes associated with yield components under irrigated and drought stress after anthesis

Although water deficiency is one of the major problems affecting crop production, including wheat, studying water limiting effects on yield components and their relationships with grain yield can facilitate breeding programs for selecting high-yielding genotypes under drought stress conditions. In this regard, 21 bread wheat genotypes were evaluated using two field experiments (post-anthesis drought stress and normal conditions). The experiments were arranged as randomized complete block designs with three replications during 2009–2011. There were significant differences among the genotypes in their traits under both conditions. Under irrigated conditions, genotypes KAYSON/GLENNSON//ATTILA and CHAM//PTZ NISKA/VT, and under drought stress conditions, genotypes CHAM//PTZ NISKA/VT and PASTOR/3/VORONA produced the highest yields. The grain yield had positive and high correlations with the biological yield, harvest index, number of spikes per square meter (m2), and number of kernels per spike under normal conditions and with the harvest index, number of kernels per spike, and spike length under drought stress conditions. Path analysis indicated that the maximum positive direct effect on grain yield under both conditions was contributed namely by the harvest index, number of kernels per spike, and spike length. These traits should be considered as the promising traits in wheat improvement programs.

Relationship between carbon isotope discrimination and grain yield of rainfed winter wheat in a semi-arid region

Carbon isotope discrimination (CID) has been suggested as an indirect selection criterion for grain yield under drought stress in wheat (Triticum aestivum L.). However, the association between CID and grain yield varies greatly among different studies. In this study, conducted in western Kansas, a temperate semi-arid region, the genetic variation of grain CID and its association with grain yield and other agronomic traits were examined using 43 preliminary and 15 advanced breeding lines under dryland conditions. The 43 preliminary breeding lines were tested in three environments while the 15 advanced breeding lines were tested in one environment. Results showed that both preliminary and advanced breeding lines had significant genetic variations and relatively small coefficients of variation in grain CID, indicating grain CID as a promising trait for selection in wheat breeding programs. In the trials for the preliminary breeding lines, the association between grain CID and grain yield was significant (P < 0.05) and positive in all three environments with Pearson correlation coefficients ranging from 0.34 to 0.74. This correlation was stronger in a trial with expected post-anthesis drought stress. However, there was only a weak positive correlation between grain CID and grain yield in the trial for the advanced breeding lines. Winter injury may have confounded the grain CID and yield relationship. This study also revealed a significant (P < 0.05) and negative correlation between grain CID and grain protein content in all four trials with Pearson correlation coefficients ranging from −0.43 to −0.65, suggesting a possible impact on baking quality while selecting high grain CID. Therefore, our results suggest that grain CID could be useful for grain yield prediction in semi-arid areas with moderate drought stress. However, precaution should be taken for selecting grain CID because of the effect of environment on its association with grain yield and its negative correlation with protein content.

Drought adaptation of stay-green sorghum is associated with canopy development, leaf anatomy, root growth, and water uptake.

Stay-green sorghum plants exhibit greener leaves and stems during the grain-filling period under water-limited conditions compared with their senescent counterparts, resulting in increased grain yield, grain mass, and lodging resistance. Stay-green has been mapped to a number of key chromosomal regions, including Stg1, Stg2, Stg3, and Stg4, but the functions of these individual quantitative trait loci (QTLs) remain unclear. The objective of this study was to show how positive effects of Stg QTLs on grain yield under drought can be explained as emergent consequences of their effects on temporal and spatial water-use patterns that result from changes in leaf-area dynamics. A set of four Stg near-isogenic lines (NILs) and their recurrent parent were grown in a range of field and semicontrolled experiments in southeast Queensland, Australia. These studies showed that the four Stg QTLs regulate canopy size by: (1) reducing tillering via increased size of lower leaves, (2) constraining the size of the upper leaves; and (3) in some cases, decreasing the number of leaves per culm. In addition, they variously affect leaf anatomy and root growth. The multiple pathways by which Stg QTLs modulate canopy development can result in considerable developmental plasticity. The reduction in canopy size associated with Stg QTLs reduced pre-flowering water demand, thereby increasing water availability during grain filling and, ultimately, grain yield. The generic physiological mechanisms underlying the stay-green trait suggest that similar Stg QTLs could enhance post-anthesis drought adaptation in other major cereals such as maize, wheat, and rice.

Stay-green alleles individually enhance grain yield in sorghum under drought by modifying canopy development and water uptake patterns.

Stay-green is an integrated drought adaptation trait characterized by a distinct green leaf phenotype during grain filling under terminal drought. We used sorghum (Sorghum bicolor), a repository of drought adaptation mechanisms, to elucidate the physiological and genetic mechanisms underpinning stay-green. Near-isogenic sorghum lines (cv RTx7000) were characterized in a series of field and managed-environment trials (seven experiments and 14 environments) to determine the influence of four individual stay-green (Stg1-4) quantitative trait loci (QTLs) on canopy development, water use and grain yield under post-anthesis drought. The Stg QTL decreased tillering and the size of upper leaves, which reduced canopy size at anthesis. This reduction in transpirational leaf area conserved soil water before anthesis for use during grain filling. Increased water uptake during grain filling of Stg near-isogenic lines (NILs) relative to RTx7000 resulted in higher post-anthesis biomass production, grain number and yield. Importantly, there was no consistent yield penalty associated with the Stg QTL in the irrigated control. These results establish a link between the role of the Stg QTL in modifying canopy development and the subsequent impact on crop water use patterns and grain yield under terminal drought.

Wheat seedlings growth response to water deficiency and how it correlates with adult plant tolerance to drought

SUMMARYImproving resistance to water and osmotic stresses at the seedling stage is becoming a much more important target for wheat breeders due to an increase in the frequency and severity of drought occurrences at the crop establishment and tillering phases in many wheat growing areas of the world. Ninety-six diverse wheat genotypes were laboratory tested for germination and growth response under osmotic stress induced by polyethylene glycol (PEG). Germination percentage, mean germination time, coleoptile length, shoot length and shoot growth rate were compared under stress (−0·4 MPa) and control (0·0 MPa) conditions. The same genotypes were previously grown in field trials exposed to drought stress during the anthesis and/or grain filling growth stage along with control (optimum) conditions. Grain yield (GY) and 19 other traits of agronomic importance (earliness, stem-related traits, number of kernels, mass of 1000 grains, etc.) were recorded. All seedling traits under PEG-induced water stress showed the highest relationship with the stem and stem-related traits of adult plants. To study the correlation between stress tolerance in the seedling and reproductive stages, three stress indices (tolerance index (TOL), stress susceptibility index (SSI) and stress tolerance index (STI)) for the seedling traits and GY under pre- and post-anthesis drought stress were calculated, based on a mean trait value obtained under stress and the corresponding trait value under control conditions. The ranking of the genotypes based on TOL and STI from seedling traits was found in most cases to be significantly correlated with the ranking of genotypes based on TOL and STI from GY, respectively.

Identification of quantitative trait loci contributing to yield and seed quality parameters under terminal drought in barley advanced backcross lines

Drought is a major limiting factor for barley production, especially in the primary areas of its cultivation. Wild barley represents a major source of favourable alleles for increasing the genetic variation for multiple traits including resistance to both biotic and abiotic stresses. We used advanced backcross quantitative trait locus (AB-QTL) analysis of a BC3-doubled haploid population developed between the cultivated parent Brenda (Hordeum vulgare ssp. vulgare) and the wild accession HS584 (H. vulgare ssp. spontaneum) to study the contribution of wild barley in improving various agronomic and seed quality traits under post-anthesis drought. The experiment was carried out at two different locations (IPK, Gatersleben and Nordsaat, Bohnshausen) and terminal drought was imposed by withholding water or spraying with potassium iodide at 10 days after flowering under greenhouse or field conditions, respectively. QTL analysis indicated that wild barley contributed favourably to most of the traits studied under both control and drought conditions. A total of seven hot-spot QTL regions with co-localizing QTL for various traits harboured more than 80 % of the stable QTL detected in the present study. For yield and thousand-grain weight and their respective drought tolerance indices, most of the QTL were derived from Brenda. On the other hand, for traits like seed length and seed nitrogen content, all the QTL were contributed by HS584, the parent having higher trait value. A significantly reduced carbon/nitrogen (C/N) ratio in the selected contrasting inferior lines compared to superior ones suggests that C/N ratio could be a potential parameter for screening not just seed quality parameters but also grain weight performance under terminal drought.

Appraisal of some physiological traits in two wheat cultivars subjected to terminal drought stress during grain filling

In a greenhouse experiment, two winter wheat ( Triticum aestivum L.) varieties differing in post anthesis drought resistance, tolerant (cv. Zagros) and sensitive (cv. Marvdasht), were subjected to either well-watered (WW) or water-stressed (WS) from anthesis to maturity. All physiological parameters were affected by drought stress. Results show that water deficits enhanced the senescence by accelerating loss of leaf chlorophyll and soluble proteins and the loss was more in Marvdasht than Zagros. The net CO2 assimilation rate (P N ) in flag leaves during water deficit displayed a strict correlation with the drought sensitivity of the genotypes and showed an early reduction in Marvdasht. The effect of drought on grain yield was primarily due to the significant reduction in grain weight, particularly in drought-sensitive Marvdasht. The results indicate that the main physiological factor associated with yield stability of Zagros under drought stress may be attributed to the capacity for chloroplast activity in the flag leaf, which apparently allows sustained P N of flag leaf during grain filling under drought stress. Keywords: Assimilate, chlorophyll, flag leaves, grain yield, wheat ( Triticum aestivum L.)

Evaluation of Drought Tolerant in Some Wheat Genotypes to Post-anthesis Drought Stress

Water deficit is the major cause of wheat (Triticum aestivum L.) yield losses in Iran and many other regions where the crop is not normally irrigated. The aim of the present study was to evaluate the ability of several selection indices to identify drought-resistant wheat genotypes. Twenty-one bread wheat genotypes were evaluated under two field experiments (post-anthesis drought stress and normal conditions). The experiments were arranged in a randomized complete block design with three replications in two successive growing seasons (2007/2008 and 2008/2009). The results showed that yields in the normal conditions were positively correlated with yields in the stress conditions. Several genotypes with good performance under both conditions were identified. Correlation analysis indicated that the most suitable drought tolerance criteria for screening substitution genotypes were mean productivity (MP), geometric mean productivity (GMP) and stress tolerance index (STI) (Group A genotypes) and when the stress was severe, stress susceptibility index (SSI) was found to be more useful index in discriminating resistant genotypes. Based on different drought indices, genotypes G4, G14 and G9 had the best ranking. In addition bi-plot and cluster analysis cleared superiority of these three genotypes in both seasons.

Antioxidant Defence System in Chickpea (Cicer arietinum L.): Influence by Drought Stress Implemented at Pre- and Post-anthesis Stage

Significant differences in the antioxidant system of the leaves of four chickpea (Cicer arietinum L.) genotypes differing in tolerance to drought were observed in a pot experiment. Drought stress was imposed at pre- and post- anthesis stage (50 and 65 days after sowing). We studied the effect of drought stress on hydrogen peroxide (H2O2) content, lipid peroxidation and antioxidant enzyme activities in four chickpea genotypes viz., Tyson, ICC 4958, JG 315 and DCP 92-3. Drought treatment significantly increased hydrogen peroxide accumulation and lipid peroxidation, which indicated the extent of oxidative injury posed by stress conditions. Enzyme activities of Superoxide Dismutase (SOD), Peroxidase (POX), Catalase (CAT) and Ascorbate Peroxidase (APX) increased in chickpea leaves as a consequence of drought conditions and all the enzyme activities were significantly higher in drought stressed genotypes i.e., Tyson and ICC 4958 than in JG 315 and DCP 92-3. Relationship between Lipid Peroxidation (LPO), Hydrogen peroxide (H2O2), Superoxide Dismutase (SOD), Catalase (CAT), Peroxidase (POX) and Ascorbate Peroxidase (APX) was determined in order to find out whether these parameters can be used as selection criteria for drought tolerance in this crop. Early drought stress (pre-anthesis drought) was found to be more damaging than the late drought stress (post-anthesis drought).

Relationship of Endogenous ABA and IAA to Accumulation of Grain Protein and Starch in Two Winter Wheat Cultivars under Post-anthesis Water Deficit

Accumulation of protein and starch in grain is a key process determining grain yield and quality in wheat. Under drought endogenous plant hormone levels will change and may have an impact on the yield and quality of wheat. In a greenhouse experiment, two winter wheat (Triticum aestivum L.) varieties differing in post anthesis drought resistance, tolerant (cv. Zagros) and sensitive (cv. Marvdasht), were subjected to either well-watered (WW) or water-stressed (WS) from anthesis to maturity. On the 7, 15 (grain enlargement stage) and 31 (grain filling stage) days after anthesis (DAA), endogenous abscisic acid (ABA) and indole-3-acetic acid (IAA) were determined in grain of wheat plants by enzyme linked immunosorbent assay (ELISA). The patterns of hormonal changes were similar in two varieties. The ABA levels were much higher under water deficit than well water treatment. In comparison grain ABA levels in all sampling stages was more in Marvdasht than Zagros. The endogenous grains IAA content display a marked reduction by the time and the water stress aggravated this reduction in both cultivars, however, the depresstion was more in drought-sensitive than drought-tolerant. The relationship between yields and contents of starch and protein in grains and levels of two hormones in sink organ indicated that the changes in yield and content of grain starch and protein under water withholding were associated with the reduced IAA and elevated ABA level in grains. It was proposed that the changed levels of endogenous hormones under drought post-anthesis might indirectly affect protein and starch accumulation in grains by influencing the regulatory enzymes and processes.

Effect of Post Anthesis Drought on Certain Agronomical Characteristics of Wheat under Two Different Nitrogen Application Conditions

A field experiment was conducted to evaluate effect of drought stress at the post anthesis stage on a bread wheat cultivar, Gonen, during the 2009-10 and 2010-11 growing seasons. Plants were covered with a rainout shelter after the post anthesis stage to prevent rain. Nitrogen fertilizers were applied at two different ways during the plant growth. The experiment was arranged in split block with three replications. Grain yield was 2445 kg/ha under the control condition whereas 1755 kg/ha under the drought condition. High amount of early application of nitrogen fertilizer resulted in 21.6 % increase in grain yield. Drought after flowering stage caused 5.2 % and 20.7 % reduction in thousand kernel weight and kernel number respectively. But there were no significant effects of nitrogen treatments on these traits. Plant height, tiller number, spike number, spikelet and kernel number, single plant yield, spike and stem weight decreased as a result of drought stress after post anthesis while only tiller number and spike number interacted with nitrogen treatments under the stress condition. The results suggested that early application of nitrogen leads to sufficient plant growth and root development resulting in a better adaptation to the post anthesis drought conditions.

زارع، رقم جدید گندم نان برای کاشت در شرایط آبیاری معمول و تنش خشکی پس از مرحله گلدهی در مناطق سرد ایران

Zareh was primarily received as an introduction wheat within the Winter Wheat Observation Nursery for Irrigated Areas (WWON-IR) with pedigree of 130L1.11//F35.70/Mo73/4/Ymh/Tob//Mcd/3/Lira from CIMMYT-Turkey in 2001-02 cropping season. Zareh was tested as C-83-8 in yield trials under normal irrigation and post-anthesis drought stress conditions in cold regions of Iran. It outyielded Shahryar (national check cultivar) under normal irrigation (7550 vs. 7254 kgha-1) and post-anthesis drought stress conditions (4893 vs. 4328 kgha-1), so it is recommended for cultivation under both conditions. Zareh is a winter wheat with red kernel. Its average height is 98 cm and it is resistant to the yellow rust. Its average thousand kernel weight under normal irrigation and drought condition was 40 and 31 gram, respectively. Zareh has grains with average protein and gluten content of 11.4% and 31.5%, respectively. Zareh was officially released in September 2010 for cultivation in cold regions of Iran with post-anthesis drought stress conditions.

Does Increased Leaf Appearance Rate Enhance Adaptation to Postanthesis Drought Stress in Sorghum?

ABSTRACTIncreased leaf appearance rate (LAR) could reduce preanthesis water use of sorghum [Sorghum bicolor (L.) Moench] by restricting plant size via reduced tillering. The aim of this paper was to assess LAR as a potential pathway for adaptation to postanthesis drought stress. Four hybrids with different LAR were grown in four semicontrolled experiments under well‐watered conditions or postanthesis drought stress and in two irrigated field experiments. Observations included leaf area dynamics, transpiration, transpiration efficiency (TE), leaf N, biomass, and grain yield. ATx642 hybrids (0.0306 leaf °C d−1) had significantly greater LAR than AQL39 hybrids (0.0279 leaf °C d−1) and this increased early main shoot vigor. Under low plant density, this reduced tiller number and hence leaf area and biomass around anthesis. As hybrids had similar TE and differed little in phenology, this can reduce preanthesis water use. Water availability at flag leaf determined grain number per plant (adjusted R2 = 0.80, p &lt; 0.01) and hence grain yield. However, the effect of increased LAR on reduced plant size was temperature dependent. Under high temperature, genotypic differences in tillering were reduced and main shoot leaf number increased more in hybrids with greater LAR. This increased responsiveness of leaf number could increase plant size and water use at anthesis. Hence, greater LAR may confer drought adaptation only in specific environments unless it is also associated with critical aspects of biomass partitioning.

QTL analysis for thousand-grain weight under terminal drought stress in bread wheat (Triticum aestivum L.)

Grain yield under post-anthesis drought stress is one of the most complex traits, which is inherited quantitatively. The present study was conducted to identify genes determining post-anthesis drought stress tolerance in bread wheat through Quantitative Trait Loci (QTLs) analysis. Two cultivated bread wheat accessions were selected as parental lines. Population phenotyping was carried out on 133 F2:3 families. Two field experiments and two experiments in the greenhouse were conducted at IPK-Gatersleben, Germany with control and post-anthesis stress conditions in each experiment. Thousand-grain weight was recorded as the main wheat yield component, which is reduced by post-anthesis drought stress. Chemical desiccation was applied in three experiments as simulator of post-anthesis drought stress whereas water stress was applied in one greenhouse experiment. Analysis of variance showed significant differences among the F2:3 families. The molecular genetic linkage map including 293 marker loci associated to 19 wheat chromosomes was applied for QTL analysis. The present study revealed four and six QTLs for thousand-grain weight under control and stress conditions, respectively. Only one QTL on chromosome 4BL was common for both conditions. Five QTLs on chromosomes 1AL, 4AL, 7AS, and 7DS were found to be specific to the stress condition. Both parents contributed alleles for drought tolerance. Taking the known reciprocal translocation of chromosomes 4AL/7BS into account, the importance of the short arms of homoeologous group 7 is confirmed for drought stress.