IDENTIFICATION MORPHOLOGICAL AND PHYSIOLOGICAL MECHANISMS OF DROUGHT TOLERANCE IN CONTASTING GENOTYPES OF RAINFED BARLEY

Abstract

Drought stress is one of the most important abiotic stresses which plays a significant role in reducing crop production around the world. In order to study morphological and physiological mechanisms of different barley genotypes under drought stress, a split-split plot experiment with RCBD design with 3 replications under rainfed and well-watered conditions were conducted using sensitive, semi-sensitive, and tolerant barley genotypes in Dryland Agriculture Research Institute in Maragheh, Iran. Results showed that almost all measured traits including LAI, stomatal conductance, membrane stability, osmotic potential, protein content, carbohydrates, SPAD readings and chlorophyll content except RWC and canopy temperature were significantly affected by drought stress. Results also showed that the amount of plant hormones including Auxin, IAA, abscisic acid, ascorbic acid, and gibberellic acid in different plant tissues were affected by water stress. The same situation was observed for non-structural carbohydrates and sucrose. In general, drought stress caused significant reduction in LAI, chlorophyll and carotenoid contents, protein content, reduction in membrane stability, increase in osmotic potential, carbohydrates, MDA and H₂O₂ in plant tissues. Barley leaves showed highest levels of Methyl linoleate and Methyl stearate under well-watered conditions. Whereas, the highest levels of Methyl palmitate and Methyl oleate was observed under drought stress conditions. This is a scavenging mechanism for ROS which protects plants against adverse effects of oxidative stress and helps tolerant genotypes to perform better under stress conditions.

Detection of genes associated with salt tolerance in wheat recombinant inbred lines population using molecular markers

Abstract

186 recombinant inbred lines derived from cross between Roshan and Superhead-II were evaluated under normal and saline conditions to identify QTLs controlling grain yield in winter bread wheat under salt stress conditions. The linkage map of this population including 484 markers (22 SSR markers and 462 DArT markers) on 20 chromosomes of wheat was prepared. 25 QTLs on 13 linkage groups (10 chromosomes) were identified for grain yield. Out of which, 10 and 15 QTLs were related to normal and saline conditions, respectively. Major QTLs for grain yield were identified on chromosomes 1A and 3B which describes 11.2 and 10.3 percent of the gain yield changes, respectively. Two major QTLs were also identified for 1000 grain weight and number of grains. Chromosomes 3B and 2D under saline and normal conditions had the highest number of QTLs. It seems that the loci on these two chromosomes have the major role in tolerance of wheat to salt stress conditions. Hence, these loci can be studied in more details in the future wheat breeding programs.

Evaluation of selected improved lines derived from cross between Roshan and SuperHead-II for salinity tolerance using morphological, physiological, and agronomical characteristics

Abstract

In order to evaluate the salt tolerance of 100 recombinant inbred lines derived from cross between Roshan and Superhead-II an experiment with alpha lattice design with two replications was conducted in Yazd (normal) and Ardekan (Sline) in 2009-2010. Total dry weight, grain weight, number of grains, 1000 grain weight, plant height, root weight, shoot biomass, stress tolerance index, and grain yield were measured. Results showed that all the measured traits were significantly affected by salt stress. The highest grain yield was observed in lines number 26, 53, 22, 89, 30, 28, 87, 66, 75, 8, 15, 49, 40, 38, 55, 29, 83, 88, 68, 27, 12, 42, 79, and 67. Regarding stress tolerance indices (SSI, TOL, STI, GMP) results showed that the best indices for evaluating salt stress tolerance were GMP and STI. The highest values for these indices were observed in lines number 7, 12, 15, 20, 27, 28, 38, 49, 83, 94, 67, 50, 37, 41, and 29. Hence these lines can be considered as salt tolerant lines. Ultimately, based on grain yield and level of salt tolerance, 10 superior lines including 26, 30, 28, 87, 15, 49, 40, 38, 29, and 83 were selected as promising lines for salt stress tolerance. These lines need to be further tested in multi-location trials. 

Evaluation of genotype × environment interaction on salinity tolerance of different wheat genotypes (Selected from PWSN-SALT)

Abstract

In order to evaluate the effects of the Genotype by Environment interaction (G×E) and to determine grain yield stability in winter bread wheat genotypes under salt stress conditions, 100 contrasting winter bread wheat genotypes (50 salt-sensitive and 50 salt-tolerant) were evaluated for salt tolerance in an experiment with alpha lattice design (10×10) with two replications in four environments in Yazd and Kerman provinces of Iran. Results of the combined analysis showed that the effect of genotype, environment and G×E were significant for plant height, number of grains per spike, and 1000 grain weight. However, the effect of genotype was not significant for grain yield. Based on mean grain yield over all environments, genotypes number 56 and 66 with 1.91 and 6.50 tones per hectare had the lowest and highest grain yield, respectively. Genotype number 53 under normal conditions and genotypes number 26, 69, and 57 under saline conditions in Kerman, had the highest and lowest grain yields, respectively. Based on regression analysis under normal and saline conditions, genotype number 95 had the general adaption ability and genotypes number 97 and 86 had specific adaptation ability under normal conditions. Results showed that genotypes number 50, 44, 95, 83, and 55 had better performance in comparison with salt-tolerant checks including Arg, Bam, and Kavir over all environments. Hence, these genotypes can be considered as salt-tolerant candidate genotypes to be used in wheat breeding programs or in PPB.

Identification of QTLs associated with salt tolerance in bread wheat cult. Roushan in cross with Falat, Sabalan, and Superhead II using DArT markers

Abstract

For identification of QTLs controlling salt tolerance and associated with grain yield, physiological and agronomical traits in three populations of winter bread wheat derived from cross between Roshan×Falat, Roshan×Sabalan, and Roshan×Superhead-II, 186 recombinant inbred lines (RILs) from cross Roshan×Superhead-II, 272 RILs from cross Roshan×Sabalan, and 319 RILs from cross Roshan×Falat, were evaluated for salt tolerance under seedling and reproductive growth stages. The linkage maps for these populations were developed using SSR and DArT markers. We found 127 QTLs in the RILs from cross Roshan×Superhead-II under normal and salt stress conditions. 25 QTLs on 13 linkage groups (10 chromosomes) including 1A₁, 2A, 4A, 5A, 7A, 2B₁, 2B₂, 2B₃, 3B, 6B₂, 6B₁, 1D, and 2D₁ were identified, which 10 and 15 QTLs were related to normal and saline conditions, respectively. The major QTLs for grain yield were on chromosomes 1A₁, and 3B sandwiched between wPT-668205 and wPT-731282, and wPT-666738 and wmc505.2 which described 11.02 and 10.30 of the total grain yield variations, respectively. Chromosomes 3B and 2D₁ showed the highest numbers of QTLs under normal and saline conditions. It seems that several clusters of QTLs for salt stress are located on these chromosomes which probably play an important role in salt tolerance of wheat. Hence, these chromosomes can be considered for further investigations in wheat breeding programs. 164 QTLs were detected in RILs population derived from cross Roshan×Falat by using composite interval mapping method. From these QTLs 110 and 54 QTLs were associated with reproductive and seedling stages, respectively. Five QTLs for grain yield (GY) were detected on chromosomes 2B1, 4D2, 5B2, 7B and 7D1 which two of them were under saline conditions. The major QTL for GY was detected on chromosome 7B sandwich between wPt-6484 and wPt-6657 which describes %14.99 of total variation in GY. We used MCMC method to identify QTLs with additive and epistatic effects as well as their interactions with environment. Finally, 44 QTLs were detected, which 28 of them associated with reproductive stage. Out of 44 QTLs, 29 QTLs showed only additive effects and 15 QTLs had both additive and environmental effects. We also detected 24 QTLs with epistatic and environmental effects. Results showed that QTLs associated with physiological traits such as shoot and root sodium content at seedling stage, in comparison with morphological traits relatively better shows the environmental (treatment) effects on plant growth and development. Biochemical pathways for accumulation of Na⁺ and K⁺ were different. In RILs population of Roshan×Sabalan, by using QTL Cartographer software 142 QTLs were detected at seedling and reproductive stages under normal and saline conditions. The major QTL for GY were detected on chromosome 2B sandwiched between wPt-3561 and wPt-0408 markers which describes %10.2 of total variation. Chromosomes 2B and 1A showed the highest numbers of QTLs at reproductive stage under normal and saline conditions. Major QTLs for some other measured traits were also detected on these chromosomes. Probably, those loci on these two chromosomes have important role in salinity tolerance of wheat which can be considered in further studies. 29 QTLs were detected for sodium concentration on 13 chromosomes where 16 and 13 QTLs were associated with sodium concentration in shoot and roots, respectively. Several QTLs for shoot and root sodium concentration were detected on chromosomes 1A, 6A, and 2B which described high percentage of phenotypic variations. For other measured traits, 17 and 5 QTL clusters were detected on different chromosomes under seedling and reproductive stages, respectively. SSR markers qwm88, gwm55, gwm526, gwm626, and gwm540 were significantly correlated with the different identified QTLs. These markers can be used in further studies for MAS.

Haplotype variation and association mapping of molecular markers associated with QTL(s) involved in tolerance to salt stress in wheat  genotypes (Selected from PWSN-SALT)

Abstract

Wheat is the most important agricultural crop of the world and Iran and considered as the main source of nutrition and health of human being. On the other hand, salinity is one of the most important limiting factors for crop production. Crop breeding for salinity tolerance is an efficient approach for yield improvement and stability under saline conditions. To study haplotype variation of the QTLs controlling salinity tolerance in winter bread wheat genotypes, 100 contrasting wheat genotypes including salt-sensitive and salt-tolerant genotypes were evaluated for salt tolerance in an incomplete block experiment with alpha lattice design with two replications under normal (ECe=4 dSm^-1) and saline (ECe=10 dsm^-1) conditions in Yazd and Kerman provinces of Iran. Results of the combined analysis showed significant differences among genotypes. Based on mean grain yield over all environments, genotypes number 26, 40, 48, 51, 49, 54, 55, 59, 60, 66, 67, 69, 73, 75, 83, 87, 89, and 94 showed better performance than salt tolerant checks including Arg, Bam, and Kavir. These genotypes were selected for further molecular, physiological and adaptation studies. Furthermore, 30 salt-tolerant and salt-sensitive lines were selected based on morphological, agronomical, phonological, and stress tolerance indices in comparison with tolerant checks for haplotype analysis using reported major QTLs for salt tolerance in wheat. Based on the results of association study of SSR markers and phenotypic traits, significant correlations between SSR markers and different measured traits were detected. Those markers with highest correlation with the phenotypic traits of interest can be used for marker assisted selection. Thus, markers Xcfa2121 and Xgwm10 at the distance 56 to 82 cM, and Xwmc296 at the distance 150 to 158.7 cM on chromosome 2A and markers Xgwm194 and Xgwm624 on chromosome 4D, due to their close correlations with the most measured traits can be introduced as suitable markers for MAS for salt tolerance in wheat. Such significant relationships in the respective regions of the chromosomes in Iranian wheat genotypes indicate that these loci have the highest probability of the presence of responsive genes for salt tolerance. Selected wheat genotypes were clustered in different haplotype groups based on QTLs detected on chromosomes 2A, 3B, 4D, and 6D. With comparison of allelic combination in the most tolerant genotypes and presence or absence of alleles of the specific markers in these genotypes we can realize the importance of different parts of QTL regions. Xgwm10, Xgwm445, Xbarc353.2, and Xgwm312 markers at the distance 56-82 cM, and Xgwm515 and Xwmc296 for the region of 150-158.7 cM on chromosome 2A were reported as the best markers associated with salt tolerance in wheat. Alleles 194, 193, 200, 205, 148, 171, and 165 bp were also reported as effective alleles in these chromosomal regions. Furthermore, marker Xwmc326 with 186 bp allele for chromosome 3B, markers Xgpw345 and Xbarc48.4 with 192 and 144 bp alleles for chromosome 4D, as well as Xbarc196 with 176 bp allele for chromosome 6D are suitable markers for breeding wheat for salt tolerance using MAS.

Evaluation of salt tolerant wheat cultivars and parental lines to understand the mechanisms involved in their salt tolerance

Abstract

To evaluate winter bread wheat cultivars and parental lines under salt stress conditions, a factorial experiment with RCBD design was conducted with 20 wheat genotypes under normal (EC of soil and water were 4.5 and 3.5 dSm^-1, respectively) and saline (EC of soil and water were 11.9 and 10.2 dSm^-1, respectively) conditions and with three replications in Yazd province of Iran. Wheat genotypes were also evaluated with SSR markers for chromosome 2A. Results showed that, Grain Yield (GY), number of grains per spike, 1000 grain weight, and number of spikes as well as Na⁺ and K⁺ concentrattions were significantly affected by salinity. Significant differences for GY were observed among genotypes under both normal and saline conditions. Bolani and Mahooti cultivars showed the highest GY under normal and saline conditions with 6.18 and 5.26, and 6.04 and 5.07 tons per hectare, respectively. Salt-sensitive cultivar Moghan-3 showed the lowest grain yield under normal (2.68 tha^-1) and saline (1.42 tha^-1) conditions. Stress tolerance indices including STI, MP, GMP, and HM were identified as the best indices for tolerance to salt stress. These indices showed positive and highly significant correlations with GY under normal and saline conditions. Among those, STI was the best tolerance index which can distinguish group A genotypes from other groups. In molecular analysis, using 22 pairs of SSR markers, polymorphism information was calculated for all the genotypes. Totally 293 alleles from 22 primers were detected on chromosome 2A and polymorphism information was calculated for each primer pairs. In this study the range for polymorphism information was estimated between 0.59-0.94 with the mean of 0.85. Number of alleles in each loci was variable between 4 to 19. The highest and lowest number of alleles was observed for markers Xgwm515 and Xgwm249, respectively. Using NTSYS software (edition 2.02) the genetic distances of the genotypes were calculated based on Dice similarity coefficient and Average Linkage Method algorithm and wheat genotypes were clustered in 5 groups. Results showed that SSR markers are efficient tools for evaluation of genetic variation in Iranian wheat genotypes. The results of this study can be used in wheat germplasm collection.

Preliminary evaluation of advanced wheat genotypes from the cross between Roshan and Superhead-II under saline and normal conditions in Yazd and Kerman

Abstract

To study salt tolerance of winter bread wheat genotypes, 373 wheat genotypes and 3 tolerant checks including Arg, Bam, and Kavir were evaluated in Yazd and Kerman provinces of Iran during 2009-2010 growing season. Plant height, spike length, peduncle length, awn length, and grain yield as well as Na⁺ and K⁺ concentrattions were measured under normal and saline conditions. Results showed that, almost all measured traits including Grain Yield (GY) were significantly affected by salinity. Arg showed the highest GY and awn length. Analysis of stress tolerance indices in tolerant checks also showed that the highest and lowest GMP and STI were belong to Arg and Kavir, respectively. Whereas, in wheat genotypes, lines number 10, 74, 32, 86, 92, 98, 114, 297, 191, 188, 300, and 326 had highest STI and GMP and GY under normal and saline conditions. Hence, these lines can be introduced as the most salt tolerant genotypes. Results of Bi-Plot analysis also confirmed these results.

Source and sink strength of different genotypes of wheat under water and non-water stress conditions during reproductive stage

Abstract

This study was carry out in two different experiments in order to investigate the effects of drought stress and plant growth regulators on different wheat cultivars. First experiment was conducted aiming to identify the yield potential of wheat cultivars under drought stress and selection of contrasting cultivars among eight cultivars for further examinations. Cultivars were Azar 2 (tolerant-dryland), Pishtaz (tolerant-irrigated), Pishgam (semi-tolerant irrigated), Sardari (tolerant-dryland), Shahriar (half tolerant-irrigated), Karaj3 (sensitive - irrigated), Gaspard (sensitive - irrigated), Marvdasht (moderately susceptible irrigated) and MV17 (sensitive - irrigated), respectively. The cultivars were cultivated in control treatments (full irrigation) and water shortage after flowering (cut of watering from booting until maturity) during 2010-2011 in the Breeding farm of Seed and Plant Improvement Institute. The experiment was conducted as split plot in RCBD with three replications which main factor was withholding watering and the sub-plots was cultivars. In order to evaluate drought stress and plant growth regulators during reproductive stage in different wheat cultivars, the second experiment was conducted as factorial experiment in RCBD with three replications in the experimental greenhouse of Agricultural Biotechnology Research Institute of Iran. Treatments were cultivars (including Pishtaz and Karaj 3), water treatment (control and water stress after flowering) and plant growth regulators (5 levels). Water stress was applied after flowering with daily weighting of the pots. Benzyl amino purine (BAP) and abscisic acid (ABA) were applied in two stages including (1) The stage of cell division (two days after flowering, T1) and (2) the beginning of grain filling (14 days after flowering, T2). The results of the experiment showed that there were significant differences between selected cultivars. In field and greenhouse Karaj 3 and Pishtaz showed similar behaviors. It was found that Pishtaz was more efficient in carbohydrate storage in grains under water stress and was efficient to remobilizing assimilate to the grains. In the stress condition IAA and ABA levels in Pishtaz was higher than Karaj 3 and it seems that hormones play a fundamental role in the production of photo assimilates and carbohydrate storage in the grains.

This study revealed that the level of IAA and ABA in the Pishtaz the under stress significantly was higher than the Karaj3. It was also found that the use of BAP at anthesis stage significantly increased endogenous IAA level in grains, while the decreased amount of endogenous ABA in grains. It also cleared that the application of ABA during anthesis stage, significantly reduces endogenous IAA while that of enhances endogenous ABA level of grains. It seems that reducing of endogenous IAA level had negative impact on sink strength (grains) by reducing the size and number of endosperm cells. This had resulted in lower grain weight and final grain yield eventually. Thus, it is suggesting that during wheat breeding programs it might be better if parents with having efficient cytokinin production capacity at anthesis stage and higher endogenous ABA level at grain filling stage (normally 14 days after anthesis) be selected. This would increase the ability of grains to more production and store assimilates, and increased remobilization of soluble carbohydrate during grain filling.

Soluble carbohydrates remobilization circumstances in tolerant and susceptible wheat genotypes to terminal drought

Abstract

The aim of the present study was to study remobilization in wheat genotypes under stress and non-stress conditions. In order to identify the growth and yield of 8 wheat cultivars  Including,  Azar 2 (tolerant-dryland), Zarin (semi-tolerant, irrigated), Pishgam (tolerance-irrigated), Sardari (tolerant-dryland), Alvand (semi-tolerant, irrigated), Gaspard (irrigated-sensitive), C-85-D-3 (semi-sensitive, irrigated) and line MV17 (Irrigated, sensitive) were planted in the control condition (full irrigation) and water stress, drought stress after flowering (inducing drought from booting stage to physiological maturity). This study was conducted in Agricultural Biotechnology Research Institute of Iran and Research and Seed and Plant Improvement Institute of Iran at the cereal farm of wheat breeding department. In the first stage of project the experiment was carried out in the form of two-factor split plot based on RCBD with three replications. The second experiment was conducted in order to supplementary studies, especially enzymes activity which involved in the remobilization. According to the results of previous experiment, two contrasting cultivars including MV17 (drought sensitive) and Pishgam (drought tolerant), were selected, base some factors such as irrigated, length of the growing period and some other morphological traits. The results evidentially showed that yield and yield components (such as the number of grains per spike, seed weight, harvest index and biomass) not only had significant genetically differences, but also under different water treatments they had more significant differences in the most measured aspects. The survey showed that in dryland cultivars (Sardari and Azar 2) and drought tolerant cultivar such as (Pishgam), had higher ability to store the soluble carbohydrates like glucose, fructose and sucrose mostly in the penultimate. Fructose was the most aboundant soluble sugar among others and had higher contents in the internodes probably used for fructans synthase. While the irrigated-sensitive varieties such as MV17, were depends on current photosynthesis, producing more soluble carbohydrates in the leaves and better ability for transferring photo-assimilates directly to the seeds. However, these ability of cultivars, highly were dependent on the availability of water, and water scarcity during grain filling stage reduces the production capacity of photo-assimilates and transferring them to grains. Results of second experiment showed that there were significant amounts of soluble sugars in the leaf and grains of susceptible cultivar MV17, and thus limitation of precursors, were not limiting factor for starch synthesis in leaves or seeds. Then probably other factors such as the strength of the sink and regulator of factors had played important roles in improvement and performance of these cultivars. Under controlled conditions, vacuolar and apoplast invertases activities were higher in the grain of MV17, whilst in drought stress conditions there were more vacuolar, apoplastic and cytosolic invertases activities in the grains of Pishgam. During cell division (First sampling) the maximum concentrations of glucose and fructose of grains were simultaneous with maximum apoplastic, cytosolic and vacuolar invertase activities. Although under controlled conditions, there was significant difference in the grain sucrose synthase activity among both cultivars, but in water stress condition the activity of this enzyme in grains of Pishgam was more than MV17. Sucrose synthase had the maximum activity during grain filling stage in both cultivars. This study showed that the drought tolerant cultivars have highly efficient enzyme activities which involvs in remobilization of carbohydrates from the leaves and internodes to the seeds, and efficient starch synthase activity in the grains simultaneously as well. Hence, it is recommended that during breeding programs for selection of superior lines, concentration of water soluble carbohydrates and activity of related enzymes should be considered.