Heat Tolerant Wheat Genotypes Research Articles

The Response of Different Bread Wheat Genotypes (Triticum aestivum L.) to Temperature Changes

Increased temperature is a major yield declining factor in wheat production. Current study was intended to evaluate the impact of increased temperature on the pre and post reproductive major yield attributing biometrical traits through the use of stress tolerance indices and trait reduction ratio (%) of all the traits studied. A set of 27 genotypes including 2 check entries viz., Shriram 303 and HD 2967 was evaluated in two separate trials, timely sown (non-stress) and late sown (heat stress) conditions in RBD design with three replications during rabi 2020-21 at the agriculture research farm of Rama university, Kanpur. Significant dropping in major yield attributing traits have Such as grain yield/plant, grain yield/spike and tillers/plant exhibited 54.41%, 39.31 % and 34.22% reduction, respectively thought the estimation of trait reduction ration (%) specially for the trials conducted under the late sown (heat stress) condition as compared to the normal sown trial. Five stress tolerance indices viz., susceptibility index (HSI), mean productivity (MP), tolerance (TOL), heat tolerance index (STI) and trait stability index (TSI) have been estimated to find out the heat stress tolerance and susceptible genotypes for grain yield under high temperature stress conditions.
 Correlation estimates of different heat stress tolerance indices with grain yield in non-stress condition (timely sown) exhibited significant positive association with MP (0.766**), HTI (0.622**), TSI (0.414*), and TOL (0.284). Though, under heat stress condition (late sown), grain yield displayed a significant positive correlation with HTI (0.713**), MP (0.707**), TOL (0.517**), TSI (0.656**) and negative correlation with HSI (-0.608**). Through the correlation analysis estimates, four heat stress indices viz. HSI (heat susceptibility index), MP (mean productivity), STI (stress tolerance index) and TSI (trait stability index) have been used in assorting the heat tolerant wheat genotypes. Current estimates directed that 14 genotypes (PBW 152, HUW-206, WL-2, WL-8, WL-13, DBW-71, DBW-39, WH-1105, HUW-318, PBW-154, ALWL-5, WL-14, PBW-502 and Shriram 303) were heat tolerant genotypes while 8 genotypes (Jamuni, F 2004, Allahabad Local, Black, U. P Local, YOUDA, U. P B2425 and HD 2967) have been observed high temperature susceptible. While WH-1105 and PBW-154 have been observed high yielding genotypes under heat stress environment. Therefore, genotypes WH-1105 and PBW-154 were acknowledged as a suitable genotype for late sown trial. Further, these two genotypes could be utilize in breeding programme to develope heat tolerant varieties of wheat.

Assessment of genetic diversity for heat tolerance in advanced breeding lines of bread wheat (Triticum aestivum L. em.Thell.)

Food security and public health are becoming major concerns for the global leaders due to climate change. The uneven distribution of rainfall and temperature has increased the global food demand with quality food. The current study was carried out for analysis of genetic diversity among 64 bread wheat genotypes for heat tolerance based on 21 morpho-physiological traits. The sixty four genotypes were grouped into five different clusters. Maximum number of genotypes was in cluster V (17) with lowest intra cluster distance (3.866) followed by cluster II (15), I (14), III and IV (each having 9 genotypes). Genotypes of cluster IV and I were more genetically diverse due to maximum inter cluster distance between them (8.873). The cluster II was designated as “highly tolerant” while cluster I and V as “moderately tolerant” and “highly sensitive” respectively, to heat stress on the basis of comparison of cluster mean values for yield and its major contributing traits like, peduncle length, flag leaf length, grain filling duration and so on. By collating their mean performance, the genotypes P-13348, P-13676, P-13820 and P- 14114 were found to be more heat tolerant in cluster II. Similarly, genotypes P-13808, P-13638 and P-14050 were found more moderately tolerant among cluster I genotypes and genotypes P-14106, P-14112 and P-14121 were most sensitive among the cluster V genotypes to terminal heat stress.

Heat stress tolerance indices for identification of the heat tolerant wheat genotypes

Heat stress is one of the major challenges in wheat cultivation because it coincides with the flowering period and limits the crop productivity. This study was conducted for evaluation of 50 wheat genotypes to identify the heat stress tolerant genotypes for improvement of stress tolerance. All genotypes were cultivated for two consecutive years (2018–2020) under normal and late sown conditions. The results of the study revealed that the combined analysis of variance indicated significant variations among genotypes for all the studied stress indices. The reduction in mean grain yield of all genotypes under stress condition as compared to non-stress condition, indicating that the heat stress significantly affect the grain yield. The correlation analysis showed that the negative correlation of tolerance index and stress susceptibility percentage index with the grain yield of genotypes under heat stress condition (Ys) and a highly positive correlation of stress tolerance index, mean productivity, geometric mean, harmonic mean and mean relative performance with grain yield (Yp and Ys) under both conditions, helped accurately to identify the desirable genotypes. From the results obtained from principal component, biplot and cluster analysis, it was reported that HD 2967, WH 1249, HI 1617, WH 1202, WH 1021 and WH 1142 are suitable and good yielding genotypes under both conditions. Thus, above genotypes can be used for cultivation at high temperature or as genetic resources for introducing genetic variations in wheat genotypes to improve stress tolerance.

The Terminal Heat Stress and its Effect on Yield and Yield Contributing Traits of Wheat (Triticum aestivum L.) Genotypes

An experiment was conducted with wheat genotypes NWL-14, K-9162, NWL-1014, NWL-12-2, NWL-12-4, NWL-10-4, K-910-30, NWL-4035, DBW-16, DBW-187, NWL-12 (3) T, Halna, HD-2967 to evaluate heat tolerant in wheat at instructional farm and in the laboratory of Crop Physiology & Plant Molecular Biology and Genetic Engineering, Acharya Narendra Deva University of Agriculture and Technology, Kumarganj, Ayodhya, India, during rabi season of 2021-2022. Heat stress was induced by delayed sowing 45 days from normal date of sowing (02 December 2022)-(17 January 2023) so that delay sown wheat genotypes could experience heat stress at reproductive stage. Heat tolerant wheat genotypes screened on the basis of Relative Water Content, Catalase activity, plant height, tiller number, number of grains per spike, test weight and grain yield per plant over control under heat stress condition. Heat stress reduces the the growth and yield irrespective of wheat genotypes but heat tolerant genotypes Halna, NWL-1293)T, NWL 10-2 and NWL-12-4 showed less reduction over susceptible ones. Relative water content, proline and catalase activity can be used as a physiological screening indices for heat tolerant genotypes.

Agro-Physiological Indices and Multidimensional Analyses for Detecting Heat Tolerance in Wheat Genotypes

Increasing atmospheric temperature can significantly reduce global wheat productivity; despite a mounting demand for wheat grain supplies. Developing genotypes with superior performance under current and future hot climates is a key challenge for wheat breeders. Multidimensional tools have supported plant breeders in increasing the genetic stability rate of agro-physiological indices that influence wheat productivity. We used 25 agro-physiological indices to classify 20 bread wheat genotypes for their heat stress tolerance. Agro-physiological indices and multidimensional analyses to identify differences in genetic and phenotypic were used, combining these analyses to reach selection criteria of accurate and credible. The 25 studied indices reflected high genotypic and environmental variations. We used 16 indices, which have brought together high heritability and genetic gain as indicators for screening heat-tolerant genotypes. Based on the seven principal comprehensive indices of (D value), wheat genotypes were classified into three highly heat-tolerant, four heat-tolerant, six moderately heat-tolerant, five heat-sensitive, and two highly heat-sensitive wheat genotypes. Based on four critical indices [grain yield (GY), grain-filling duration (GFD), spike length (SL) and canopy temperature (CT)] obtained from stepwise multiple linear regression (SMLR), the genotypes were grouped as four genotypes highly heat-tolerant, six heat-tolerant, two moderately heat-tolerant, four heat-sensitive and four highly heat-sensitive. The classification D value and SMLR distances were significantly correlated based on the Mantel test, with a perfect match in nine genotypes. SMLR indicated that a mathematical equation for the evaluation of wheat heat tolerance was established: GY = 0.670 + 0.504 × GFD + 0.334 × SL − 0.466 × CT (R2 = 0.739; average prediction accuracy of 94.12%). SMLR-based classification of wheat genotypes for heat tolerance was further verified through discriminant analysis, which showed that prior and posterior classification was identical in eighteen genotypes. Cross-validation showed that prior and posterior classification was identical in thirteen genotypes. Based on this study, we can recommend tolerated new wheat lines (DHL25, DHL05, DHL23 and DHL08) and cultivar Pavone-76 as a promising genetic source for heat-tolerant breeding programs.

Screening of bread wheat genotypes for heat tolerance using artificial and natural environment

Increasing temperature because of climate change is one of the leading constraints to wheat productivity by adversely affecting its growth and development. Global warming would push the wheat cultivation further into heat stressed environment in future which may ultimately cause yield loss. This research directed for determination of heat tolerance level among different wheat genotypes to establish selection criteria under high temperature to select promising wheat genotypes for breeding. Hundred wheat accessions including 97 lines from international Maize and wheat improvement centre’s (CIMMYT) heat nurseries and three local checks were assessed for tolerance against high temperature in glass house and open field. In glass house, at seedling stage data was recorded for fresh shoot weight, dry shoot weight, leaf relative water content and electrolyte leakage. In open field data for heat and yield related traits were recorded and subjected to mean square analysis. Studied traits were pooled through cluster analysis. Results showed that these traits have potential to discriminate heat tolerant and susceptible genotypes. Variances between genotypes were highly significant for all investigated traits under both circumstances. Accessions HTSBWON-15-0002, HTSBWON-15-0029, HTSBWON-15-0040, HTSBWON-15-0079, HTSBWON-15-0087, HTSBWON-15-0089 and Faisalabad-08 performed good for heat and yield related traits particularly electrolyte leakage and leaf relative water content. Hence, based on analysis it could be deduced that these genotypes may be used in hybridization programs for development of heat tolerant wheat genotypes with high yield potential.

The Effects of Brief Heat During Early Booting on Reproductive, Developmental, and Chlorophyll Physiological Performance in Common Wheat (Triticum aestivum L.).

Rising temperatures due to climate change threaten agricultural crop productivity. As a cool-season crop, wheat is heat-sensitive, but often exposed to high temperatures during the cultivation period. In the current study, a bread wheat panel of spring wheat genotypes, including putatively heat-tolerant Australian and CIMMYT genotypes, was exposed to a 5-day mild (34°C/28°C, day/night) or extreme (37°C/27°C) heat stress during the sensitive pollen developmental stage. Worsening effects on anther morphology were observed, as heat stress increased from mild to extreme. Even under mild heat, a significant decrease in pollen viability and number of grains per spike from primary spike was observed compared with the control (21°C/15°C), with Sunstar and two CIMMYT breeding lines performing well. A heat-specific positive correlation between the two traits indicates the important role of pollen fertility for grain setting. Interestingly, both mild and extreme heat induced development of new tillers after the heat stress, providing an alternative sink for accumulated photosynthates and significantly contributing to the final yield. Measurements of flag leaf maximum potential quantum efficiency of photosystem II (Fv/Fm) showed an initial inhibition after the heat treatment, followed by a full recovery within a few days. Despite this, model fitting using chlorophyll soil plant analysis development (SPAD) measurements showed an earlier onset or faster senescence rate under heat stress. The data presented here provide interesting entry points for further research into pollen fertility, tillering dynamics, and leaf senescence under heat. The identified heat-tolerant wheat genotypes can be used to dissect the underlying mechanisms and breed climate-resilient wheat.

Evaluation of some bread wheat genotypes for heat tolerance under terminal heat stress conditions

Terminal heat stress leads to significant yield reduction in wheat. Thus, the determination of heat tolerant genotypes is of major importance in wheat breeding program. The present study was conducted at Shandaweel agricultural research station, Sohag, Egypt during 2019/2020 and 2020/2021 growing seasons, to evaluate twelve bread wheat genotypes under normal sowing (20 November) and late sowing (30 December) dates, the experiment set up as a randomized complete block design with three replications. Results revealed that late sowing (terminal heat stress) had a significant adverse impact on agronomic, physiological traits and grain carbohydrate content. The genotype Shandaweel 2, followed by Giza 171 and Sids 14 performed better than other genotypes for grain yield under the normal sowing. On the other side, Shandaweel 2 outperformed the tested genotypes under the late sowing. Based on heat susceptibility index (HSI), the cultivars Sids 12, Misr 2, Sakha 95 and genotype Shandaweel 2 showed HSI<1 and they can be labeled as heat tolerant genotypes, while Sids 14, Misr 1, Giza 171 and Misr 3 showed HSI>1 and they can be considered as heat sensitive cultivars. GGE biplot analysis and ranking of genotypes revealed that the new line Shandaweel 2 was the an ideal genotype in terms of yielding ability and stability and it was suitable for planting under normal and late sowing conditions, while Giza 171 was suitable for planting under the normal sowing. The GYT biplot and superiority index showed that Shandaweel 2 and Giza 171 had the best traits profile.

Heat tolerant wheat genotypes for late sown conditions identified on the basis of physiological traits

Heat tolerant wheat genotypes for late sown conditions identified on the basis of physiological traits

Effect of Heat Stress for Agro-Economic Traits in Bread Wheat (Triticum Aestivum L.) Genotypes

In the scenario of increasing global warming, heat stress received more importance. Un- fortunately, Pakistan is also in the line of most heat affected countries of the world. In this regard, wheat being a most important staple edible crop of Pakistan is highly affected by heat stress. For combating this situation, a study was carried-out on ten bread wheat genotypes viz. Moomal, Mehran, Imdad-05, Anmol- 91, Benazir, TJ-83, SKD-1, TD-1, Abadgar and Hamal at the Experimental Field, Department of Plant Breeding and Genetics, Sindh Agriculture University, Tandojam. The experiment was laid-out in a randomized complete block design (factorial arrangement) with three replications during Rabi season, 2016-17 in order to assess the response of wheat genotypes to terminal heat stress tolerance. Wheat genotypes were evaluated in two sowing dates viz., on 24th November as a normal planting and late planting on 31th December, 2016 considered as heat stress condition. The analysis of variance revealed significant differences among the genotypes under both sowing dates indicating suitability of the experiment to improve bread wheat genotypes for heat tolerance. Reductions in various traits were observed in late planting which indicated visible effects of heat stress on agro-economic traits. On an average plant height (cm), tillers/plant, spike length (cm), spikelets/spike, grains/spike, 1000-grain weight (g) and grain yield/plant (g) were declined by -4.63, -2.49, -3.04, -4.35, -16.29, -14.08 and -9.09 units respectively under the heat stress conditions, while the wheat genotypes like TJ-83, SKD-1 and Mehran showed minimum reductions under heat stress conditions for various traits suggesting their heat tolerance, nonetheless cultivars Moomal and Benazir expressed maximum declines under heat stress expressing their susceptibility to heat stress conditions. The remaining genotypes were found as moderately heat stress tolerant.&#x0D;

Evaluation of Physiological and Morphological Traits for Improving Spring Wheat Adaptation to Terminal Heat Stress.

Wheat crop experiences high temperature stress during flowering and grain-filling stages, which is termed as “terminal heat stress”. Characterizing genotypes for adaptive traits could increase their selection for better performance under terminal heat stress. The present study evaluated the morpho-physiological traits of two spring wheat cultivars (Millet-11, Punjab-11) and two advanced lines (V-07096, V-10110) exposed to terminal heat stress under late sowing. Early maturing Millet-11 was used as heat-tolerant control. Late sowing reduced spike length (13%), number of grains per spike (10%), 1000-grain weight (13%) and biological yield (15–20%) compared to timely sowing. Nonetheless, higher number of productive tillers per plant (19–20%) and grain yield (9%) were recorded under late sowing. Advanced lines and genotype Punjab-11 had delayed maturity and better agronomic performance than early maturing heat-tolerant Millet-11. Advanced lines expressed reduced canopy temperature during grain filling and high leaf chlorophyll a (20%) and b (71–125%) contents during anthesis under late sowing. All wheat genotypes expressed improved stem water-soluble carbohydrates under terminal heat stress that were highest for heat-tolerant Millet-11 genotype during anthesis. Improved grain yield was associated with the highest chlorophyll contents showing stay green characteristics with maintenance of high photosynthetic rates and cooler canopies under late sowing. The results revealed that advanced lines and Punjab-11 with heat adaptive traits could be promising source for further use in the selection of heat-tolerant wheat genotypes.

Interrelationships among different grain characteristics of wheat grown under optimum and late sowning date conditions in the Eastern Indo-Gangetic plains of India

Wheat growth has been severely affected by increases in global temperature. The Eastern Indo-Gangetic Plains of India face similar constraints due to the traditional wheat–rice cropping system where wheat planting is often delayed leading to high temperature induced terminal heat stress. Grain characters like grain length, width, area along with starch synthesis are affected severely during heat stress. Considering the importance of grain traits, we screened the response of 55 wheat genotypes under terminal heat stress conditions to ten grain characteristics. We found that the means of all the grain traits were reduced in heat stress conditions. The effect of heat stress shows a significantly reduced grain width and perimeter, but the extent of damage is less on different grain starch characteristics e.g., grain starch area (GSA), grain starch length (GSL) and grain starch volume (GSV). Stepwise multiple regression analysis revealed that grain starch area and grain volume are the best predictors of yield under optimum sowing date conditions whereas, grain width is the best predictor under late sowing date conditions. Interrelationship studies among ten grain characters showed that the genotypes with higher levels of grain starch characteristics (GSA, GSL and GSV) in combination with the five grain size characters (grain length, grain width, grain perimeter, grain area, A/B-type starch granules) under late sowing date conditions should be promoted for the cultivation of wheat in heat stress prone areas. The present study identified and recommends some heat tolerant wheat genotypes in terms of higher yield and grain starch characteristics namely, CRPW-33, CRPW-17, CRPW-12, CRPW-126 and CRPW-21.

Screening of wheat germplasm for terminal heat tolerance under hyper-arid conditions

Due to intensive cropping system, late planting of wheat is very common which causes plants to suffer due to terminal heat stress. To adapt and mitigate the adverse effect of heat on wheat, researchers want to develop heat-tolerant wheat genotypes. Therefore, a set of 11 germplasms of wheat was sown in normal period (November 25) as well as in late period (December 25) at Instructional Farm of Swami Keshwanand Rajasthan Agricultural University, Bikaner. Various physiological, gas exchange and yield attributes were measured at different crop growth stages. Results showed that days to anthesis (DTA), relative water content (RWC), membrane stability index (MSI), photosynthetic pigments, photosynthetic rate (A), stomatal conductance (gs), internal CO2 concentration (ci), water use efficiency (WUE) and yield attributes were reduced, whereas transpiration rate (E) was increased under late sown as compared to normal. Most of the physiological and yield characters showed superiority (highest/lowest) in germplasm entry no. 26 followed by 43 and 58. Heat susceptibility index (HSI) was the lowest, whereas chlorophyll stability (CSI) and heat tolerance index (HTI) were the highest recorded in entry 26 followed by 43. Heat-tolerant germplasm could be selected on the basis of high RWC, MSI, photosynthetic pigments, CSI, A, gs, ci, WUE, yield components and HTI, and low E and HSI. In the present investigation, entry no. 26 (IC279317), 43 (IC335971) and 58 (IC336816) were found the best suited germplasm under heat stress. These germplasms supposed to carry the heat-tolerant genes and may be used for further heat tolerance breeding.

Development and validation of heat-responsive candidate gene and miRNA gene based SSR markers to analysis genetic diversity in wheat for heat tolerance breeding

Being a major staple food crop of the world, wheat provides nutritional food security to the global populations. Heat stress is a major abiotic stress that adversely affects wheat production throughout the world including Indo-Gangatic Plains (IGP) where four wheat growing countries viz., India, Bangladesh, Nepal and Pakistan produce 42% of the total wheat production. Therefore, identification of heat stress responsive molecular markers is imperative to marker assisted breeding programs. Information about trait specific gene based SSRs is available but there is lack of information on SSRs from non-coding regions. In the present study, we developed 177 heat-responsive gene-based SSRs (cg-SSR) and MIRgene-based SSR (miRNA-SSR) markers from wheat genome for assessing genetic diversity analysis of thirty- six contrasting wheat genotypes for heat tolerance. Of the 177 SSR loci, 144 yielded unambiguous and repeatable amplicons, however, thirty-seven were found polymorphic among the 36 wheat genotypes. The polymorphism information content (PIC) of primers used in this study ranged from 0.03-0.73, with a mean of 0.35. Number of alleles produced per primer varied from 2 to 6, with a mean of 2.58. The UPGMA dendrogram analysis grouped allwheat genotypes into four clusters. The markers developed in this study has potential application in the MAS based breeding programs for developing heat tolerant wheat cultivars and genetic diversity analysis of wheat germplasm. Identification of noncoding region based SSRs will be fruitful for identification of trait specific wheat germplasm.

Genotype Environment Interaction (G &amp;#215; E) of Heat Tolerant Wheat Genotypes over Locations and Years

Twenty heat tolerant wheat genotypes were evaluated in three heat stress environments of Bangladesh such as Wheat Research Center (WRC), Nashipur, Dinajpur, Regional Wheat Research Center, BARI, Gazipur, Regional Wheat Research Center, RARS, Jashore in 2015-2016. The experiments were conducted in RCBD with three replications in 2015-2016. The stability and response to change of location and sowing time of the genotypes were assessed through AMMI model and regression coefficient analysis on seven characters, viz. days to heading, days to maturity, plant height (cm), spikes m-2, grains spike-1, 1000-grain weight (g) and yield (kg·ha-1). Among the linear interactions, sowing time alone exerted the maximum sum of square (335,388,000.00**) and among the non-linear interactions, location × year paid the highest effect (7,676,490.00**), which was followed by year × location × sowing time interaction (3,956,500.00**). The highest grain yield (4475.3 kg·ha-1) was obtained from the genotype G13, followed by the genotypes G17 (4460.8 kg·ha-1) and G19 (4404.7 kg·ha-1). The genotype G8 had the smallest interaction effect, while the genotype G14 followed by G10 responded vigorously to amelioration. The genotypes G13, G18 and G19 showed averagely high yield and showed stability over the environmental modifications. The other two genotypes G20 and G12 exhibited great reduction of yield potential under unfavorable environment. The environment 121 proceeded by J121 and G131 appeared as favorable environments. The genotypes G13 and G19 produced high yield (kg·ha-1) in the favorable environments. The genotypes G16 and G18 high IPCa1 scores, indicated sensitive to mega-environmental changes. The best genotype with respect to environment was genotype G13. Genotypes G17 and G19 were best for site E1; genotypes G14, G16 and G18 were best for site E2.

Screening for heat tolerant genotypes in bread wheat (T. aestivum L.) using stress tolerance indices

Heat is a major stress that severely affects wheat productivity. The objective of the current study was estimating the effect of heat stress during the grain-filling stage for screening heat tolerant wheat genotypes by measuring six stress tolerance indices for grain yield and also measured the % of decline on other important traits. A set of 190 wheat genotypes along with four local checks were evaluated in two separate experiments, one under normal condition (timely sown) and the other under heat stress condition (late sown) in augmented block design at the research farm of Department of Genetics and Plant Breeding, C.C.S. University, Meerut (U.P) during rabi season of 2014-2015. The calculation of % declines revealed that there was a significant decline in the performance of traits under heat stress environment (late sown) in comparison to a normal environment (timely sown). Three traits, namely grain yield/plant, biological yield/plant and grain weight/ spike showed 57.15 %, 53.66 % and 47.73 % decline, respectively under heat stress environment indicating that above mentioned three traits are highly affected by heat stress. To evaluate the susceptible and tolerant genotypes for grain yield under heat stress environment, six stress tolerance indices viz. heat susceptibility index (HSI), mean productivity (MP), tolerance (TOL), stress tolerance index (STI), trait stability index (TSI) and trait index (TI) were calculated based on the grain yield under normal (timely sown) and stress (late sown) environments. The results of correlation between stress tolerance indices and grain yield in normal environment showed a significant positive relationship with MP (0.822**), STI (0.568**), TSI (0.316**), HSI (0.314**), TI (0.188*) and TOL (0.084). However, in stress environment, grain yield showed a significant positive correlation with TI (1.000**), STI (0.907**), MP (0.713**) and TOL (0.129) and negative correlation with HSI (-0.860**) and TSI (-0.808**). Based on the correlation analysis, we have selected four stress indices viz. HSI (heat susceptibility index), MP (mean productivity), STI (stress tolerance index) and TI (trait index) for their use in the selection of heat tolerant wheat genotypes. The results indicated that 9 genotypes (G51, G64, G71, G114, G119, G134, G139, G148 and G150) were heat tolerant and 12 genotypes (G1, G3, G7, G27, G38, G40, G77, G107, G136, G160, G171 and G187) were highly heat susceptible. The genotype G77 was the most heat sensitive genotype while genotype G119 and G139 showed a high yield under heat stress environment. Therefore, genotypes G119 and G139 were identified as a suitable genotype under late sowing environment and can be recommended for heat stress environment. Further, these two genotypes may be also employed in breeding programs aimed for developing heat tolerant varieties of wheat.

Assessment of terminal heat tolerance based on agro-morphological and stress selection indices in wheat

A study was conducted to quantify the effects of terminal heat stress on yield and component traits for two consecutive years under normal and late sown environments. Analysis of variance indicated significant differences among genotypes for most of the studied traits. Tiller/meter (T/M) and grain yield were the most affected traits (>30% reduction), whereas traits like grain filling rate (GFR), grain number per spike (GNPS) and thousand kernel weight (TKW) were less affected (<15%) under heat stress. The traits, viz. GFR, GNPS, TKW, T/M and spike weight, as well as the relative change in these traits exhibited positive and significant correlation with yield and yield stability index (YSI), while negative and significant correlation with heat susceptibility index (HSI) and kernel weight reduction percentage (KWR) under heat stress. Based on HSI, KWR, and YSI indices, genotypes WH 1021, NW 1014 and NW 2036 were identified as the heat tolerant, while HD 3086, HD 2967 and HD 3059 were identified to be highly productive under both normal and heat stress environments based on STI and mean yield across the environments. The above selected genotypes also showed high mean performance for GFR and TKW under heat stress and could be used for breeding wheat genotypes for heat tolerance.

Genetic differentiation of selected drought and heat tolerant wheat genotypes using simple sequence repeat markers and agronomic traits

Development of wheat (Triticum aestivum L.) varieties with increased yield potentials that are adapted to drought and heat stresses requires genetically differentiated and complementary parents. The present study established genetic profiles of heat and drought tolerant wheat genotypes through SSR loci and agronomic traits for breeding. Fourteen candidate wheat genotypes selected from the International Maize and Wheat Improvement Centre (CIMMYT) and a local variety were genotyped using 10 diagnostic SSR markers. Further, the genotypes were evaluated for agronomic performance under non-stressed (NS) and drought-stressed (DS) conditions. The mean gene diversity of 0.75 confirmed genetic diversity of evaluated wheat genotypes. Analysis of molecular variance accounted for 75 and 25% of the variation within and among genotypes respectively. Significant differences were observed for assessed agronomic traits under NS and DS conditions. There were significant (p < 0.01) correlations between grain yield and plant height (r = -0.42) and spike length (r = 0.39) under DS conditions. Cluster analysis allocated test genotypes to three genetic groups and aided selection of genetically unrelated and high-yielding heat and drought tolerant genotypes such as SM04, SM19 and SM32. These are useful germplasm for developing breeding populations for improved yield gains.

English

Wheat (Triticum aesum L.) production in Bangladesh is often impaired by heat stress. Therefore, it has been a priority to develop heat tolerant wheat variety for Bangladesh. An investigation was carried out to evaluate locally cultivated wheat genotypes for heat tolerance based on morpho-physiological and molecular markers. A pot experiment was carried out with ten locally cultivated wheat genotypes. Heat treatment was imposed, 5 days after anthesis, in a plant growth chamber at 35°C and 70% RH for 3 days. The heat stress affected all the yield contributing characters and ultimately led to a reduction in grain yield. BARI gom-29, BARI gom-30 and BARI gom-28 emerged as heat tolerant variety on the basis of susceptibility index and tolerance efficiency. While, Shatabdi, BARI gom-23, BARI gom-26 and BARI gom-24 were heat susceptible. Twenty six wheat genotypes were screened for heat tolerance through seven linked SSR markers that generated 44 alleles among the 26 wheat genotypes with an average of 6.28 alleles per locus. Overall polymorphism information content (PIC) and Nei’s gene diversity were 0.68 and 0.72, respectively. Similarity indices based unweighted pair group method with arithmetic mean (UPGMA) analysis separated 26 genotypes into five different clusters. Two morphologically identified tolerant genotypes namely BARI gom-29, BARI gom-30 and one moderate genotype BARI gom-22 were grouped in cluster 2. Therefore, these three varieties can be suitable for cultivation in the north-western part of Bangladesh as heat tolerant cultivars. Key words: Diversity, heat tolerance efficiency, heat susceptibility index, SSR marker.

Cell membrane stability- an important criterion for selection of heat tolerant genotypes in wheat (Triticum aestivum L.)

Cell membrane stability, grain filling rate, grain filling duration, canopy temperature and grain yield were used to evaluate performance of 100 diverse bread wheat (Triticum aestivum L.) genotypes under timely sown and late sown heat stress conditions for two cropping season. The genotypes differed significantly for all the traits show-ing considerable variation for improvement of characters. The genotypes WH1165 had significant high grain yield (14.6* g and 11.4g) and (11.3* g and 11.4* g) followed by cell membrane stability under timely sown and heat stress conditions, respectively indicating potential tolerance against heat stress. Correlation coefficients revealed that cell membrane stability (0.451**) and (0.639**) in timely sown and in late sown conditions, respectively were the most important trait followed by grain filling rate (0.882** and 0.744**) under timely sown and late sown conditions respec-tively. Results revealed that bread wheat genotypes which had high value of cell membrane stability had high grain yield showed potential photorespiration and high grain filling rate under heat stress condition. Twenty two genotypes WH1021, WH1155, VL803, WH787, NW1014, Raj3765, HD1869, 2042, WH1124, HD2285, WH1133, HUW234, 4066, Sonak, UP2425, UP2473, PBW503, PBW373, PBW533, SGP13, HD2643 and WH789 were identified as heat tolerant genotypes based on their relative performance in yield components, grain yield and heat susceptibility indi-ces. These genotypes were found to be ideal candidates to be used in developing heat tolerant wheat varieties. Canopy temperature, membrane thermostability and grain filling rate have also shown strong correlation with grain yield. Because of this association, these traits constitute the best available ‘tool’ for genetic improvement of wheat suitable for cultivation under heat stressed environments. Thus, these could be used as indirect selection criteria for developing heat tolerant wheat genotypes that would provide sufficient yields to meet the ever increasing wheat demand.