Heat Tolerant Genotypes Research Articles

Physiological traits for evaluating heat‐tolerance of Australian spring wheat cultivars at elevated CO2

AbstractHigh temperatures and increasing CO2 concentrations are a major threat to global wheat (Triticum aestivum L.) production, demanding the development of heat‐tolerant wheat cultivars. Plant physiological traits are potential surrogates for evaluating genetic variation for crop stress tolerance. This research evaluated 23 Australian wheat cultivars and two breeding lines for heat‐tolerance by characterising the associated physiological traits. The interactive effects of heat‐stress and elevated CO2 were studied under controlled greenhouse conditions and delayed sowing in the field with exposure to higher temperature. Physiological changes, pollen viability and grain yield were assessed. A significant correlation was observed between physiological and agronomical traits under high temperature at 35°C and elevated CO2 at 800 µl L−1, providing evidence of adaptation to high temperatures in some genotypes. Variation in stomatal conductance, transpiration rate, canopy temperature, leaf chlorophyll and photosynthesis were associated with maintenance of pollen viability and grain yield at high temperatures. Of the genotypes assessed, seven were classified as heat tolerant at both ambient and elevated CO2 and nine were heat susceptible while the remainder showed a variable response to CO2 at high temperatures. Field data confirmed the heat responses of the most heat‐tolerant and susceptible genotypes. The heat tolerant genotypes identified are candidates for further breeding and selection to improve adaptation to a changing climate.

Wheat genotypes tolerant to heat at seedling stage tend to be also tolerant at adult stage: The possibility of early selection for heat tolerance breeding

Wheat production is seriously influenced by extreme hot weather, which has attracted increasing attention. It is important to compare wheat responses to heat at seedling and reproductive stages, to explore the potential relationship between the performances at different growing stages and the possibility of early selection to accelerate heat tolerance breeding. In this study, forty wheat genotypes were screened under heat stress at both seedling and adult stages. It was found that root lengths at seedling stage were severely reduced by heat stress with significant variations among wheat genotypes. Heat-tolerant genotypes at seedling stage showed less root length decrease than susceptible ones. Wheat genotypes tolerant at seedling stage showed higher yield at adult stage after heat treatment. The performances of wheat genotypes screened under heat stress at seedling and adult stages were ranked by seedling damage index and adult damage index. A significant positive relationship was found between heat tolerance at seedling stage and at adult stage (r = 0.6930), suggesting a similar tolerant/susceptible mechanism at different plant growth stages and the possibility of early selection at seedling stage for breeding heat tolerance. Extremely tolerant and susceptible genotypes with consistent performances at seedling and adult stages were genetically compared and associated SNP markers and linked candidate genes were identified.

Tomato (Solanum lycopersicum L.) Genotypes Respond Differently to Long-Term Dry and Humid Heat Stress

Tomato production in coastal areas in West Africa is constrained by heat stress. There is currently limited empirical evidence on the extent of the effect of heat stress on tomato yield in the sub-region. In this study, we assessed the effects of heat stress on yield and yield components among 16 tomato genotypes with varying heat tolerance status and explored the potential of stress tolerance indices to identify heat tolerant genotypes. The experiments were conducted under three temperature and humidity regimes, namely optimal season (28.37/23.71 °C and 71.0/90.4% day/night), long-term mild and humid (greenhouse, 30.0/26.2 °C and 77.6/97.2%), and long-term mild and dry (open field, 31.50/28.88 °C and 66.72/77.82%) heat stress (HS). All genotypes exhibited significantly higher fruit set percentage, fruit number per plant, fruit weight, and fruit weight per plant in the optimal season compared to both heat stress conditions. In general, the genotypes demonstrated higher performance under dry HS (i.e., HS in open field HSO) than humid HS (i.e., HS in greenhouse HSG). Fruit set decreased by 71.5% and 68.3% under HSG and HSO, respectively, while a reduction of 75.1% and 50.5% occurred in fruit weight per plant under HSG and HSO, respectively. The average sum of ranks values from nine stress tolerance indices and fruit weight per plant (used as proxy trait of yield) identified CLN2498D, CLN3212C, CLN1621L, and BJ01 as heat tolerant under HSG and BJ01, BJ02, Fla.7171, and P005 as heat tolerant under HSO. Fruit weight per plant under long-term heat stress (Ys) and optimal growing conditions (Yp) were suitable to select high performing genotypes under HSO, HSG, and optimal conditions while relative stress index, yield stability index, yield index, stress susceptibility index, and harmonic mean were suitable to select heat tolerant genotypes under either HSG or HSO. Our findings shed light on the extent of the effect of HS on tomato production in the off-season in coastal areas in West Africa and provide new insight concerning the heat tolerance status of the evaluated tomato genotypes.

Effect of endogenous gibberellic acid content on physiological and yield related traits in late sown wheat

Terminal heat stress is becoming major factors in limiting wheat production with increasing evidence of heat stress in present scenario of climate change. Plant hormones are key player in determining plant response to these stresses from perception of stress to final adoptive response. Gibberellic acid is one of the major plant hormone playing crucial role in plant development from germination to seed development, but there is huge gap in knowledge about its role under heat stress. Present study was conducted in late sown wheat (i.e. on 5th January)to examine the inter-relationship between leaf gibberellic acid (GA3) level at reproductive stage with physiological and yield related traits under heat stress in 40 wheat genotypes. Genotypes were categorized into three classes namely tolerant, intermediate and sensitive based on heat stress tolerance ability for further analysis. The diversity in endogenous GA3 concentration was found among the cultivars. The unique inverse relationship between GA3 level in flag leaf and tolerance level of genotypes was found in this study through regression analysis (p<0.05). The path analysis showed that GA3 had direct negative influence on test weight under heat stress conditions. Thus, investigations of mechanism of GA3 influence on sink capacity have the potential to develop heat tolerant genotype and increase wheat production under heat stress.

Identification of Heat Tolerant Cotton Lines Showing Genetic Variation in Cell Membrane Thermostability, Stomata, and Trichome Size and Its Effect on Yield and Fiber Quality Traits.

Heat stress in cotton reduces its productivity. The development of heat-tolerant cotton varieties having resilience against changing climate is feasible. The purpose of this study was to probe the genetic variability in upland cotton for heat tolerance, the association of cell membrane thermostability (CMT), stomata, and trichome size with cotton adaptation to high temperature and effective breeding strategy to advance the valued traits. Relative cell injury percentage (RCI%) in studied genotypes ranged from 39 to 86%. Seventeen genotypes were found heat tolerant on the basis of low RCI%, heat susceptibility index (HSI<1), higher number of boll/plant, and seed cotton yield (SCY). Scanning electron microscopy (SEM) of heat-tolerant genotypes revealed the presence of different size of stomata (21.57 to 105.04 μm2) and trichomes (177 to 782.6 μm) on leaves of selected genotypes. The regression analysis showed a strong and negative association of RCI% and stomata size with SCY. However, no association was observed between the trichome size, yield, and fiber traits. On the overall location basis, a significant genotype × environment interaction was observed. All selected genotypes produced a higher SCY as compared with check varieties. But the stability analysis showed that the high yielding genotypes NIA-M-30, NIA-80, NIA-83, and CRIS-342 were also wide adaptive with unit regression (bi∼1) and non-significant deviation from the regression line (S2d∼0). The ability for the combination of some heat-tolerant genotypes was estimated by using the line × tester method among nine hybrids along with their 3 testers (i.e., male) and 3 lines (i.e., females). Genotypes, CRIS-342 and NIA-Perkh, were observed as best general combiners for SCY with a negative general combining ability effects for RCI%. Five hybrids showed a positive specific combining ability and heterotic effects for studied traits and also found lowest for HSI. RCI% and SCY/plant displayed higher estimates of heritability and genetic advance, indicating the heritability due to additive gene effects and chances of effective selection. The identified heat-tolerant and wide adaptive germplasm can be further advanced and utilized in cotton breeding programs for developing heat-tolerant cultivars. Selection criteria involving CMT and stomata size concluded to be an effective strategy for the screening of heat-tolerant cotton.

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.

Growth and Yield Performances, Pathogenicity, Heat Tolerance, Antioxidant Activity, and Pungency Level of Anthracnose Resistant and Heat Tolerant Inbreed Lines and F1 Genotypes of Chili Pepper (Capsicum Annuum)

Growth and Yield Performances, Pathogenicity, Heat Tolerance, Antioxidant Activity, and Pungency Level of Anthracnose Resistant and Heat Tolerant Inbreed Lines and F1 Genotypes of Chili Pepper (Capsicum Annuum)

Morphological, biochemical and molecular insights on responses to heat stress in chilli

Four heat susceptible and four heat tolerant genotypes of chilli were grown under high temperature as well as control conditions to study the morphological, biochemical and molecular changes occurring in them due to high temperature stress. It was observed that high temperature did not have significant effect on vegetative growth in chilli however the reproductive growth was significantly affected and was manifested as reduction in fruit length, fruit width, fruit weight and number of seeds per fruit. The detrimental effect was more pronounced in heat susceptible chilli genotypes. Tolerant genotypes accumulated more amounts of protein as well as proline and displayed higher activities of antioxidant enzymes like SOD (superoxide dismutase) and POD (peroxidase) in order to combat the high temperature stress. Out of seven Capsicum annuum specific heat shock proteins studied, three genes namely CaHSP 832 (HSP 83), Ca HSP 703(HSP70) and Ca HSP 2272 (small HSP) showed significant differences in expression level between tolerant and susceptible genotypes thereby suggesting their utility in discriminating the genotypes for their tolerance to heat stress.

Performance of Heat Tolerant Maize Genotypes under Moisture Stress during Rainy Season in Karnataka

This research was formulated to study the response of heat tolerant genotypes to prolonged period of water stress prevalent under rainfed situation. The trial was conducted at Agricultural Research Station, Dhadesugur, University of Agricultural Sciences, Raichur, Karnataka, India, during rainy season (kharif) 2019. The present study comprised of three stress tolerant genotypes (RCRMH 2, RCRMH 3 and RCRMH 4) with four moisture stress stages (imposed between 20-40, 40-60, 60-80 and 80-100 DAS) which were sown during June, July and August, and the design employed was Randomized complete block design. The results revealed that superior performance of RCRMH 3 (5321 kg ha-1) over other genotypes whether stressed or not, but all the genotypes were on par with each other in terms of physiological parameters viz., proline accumulation, relative water content, canopy temperature, NDVI, relative chlorophyll content and ASI, and these parameters exhibited good correlation with yield and hence found ideal for stress studies. The present study indicated that these cultivars sustain maize production under moisture stress condition and therefore, are suitable to semiarid region characterized by inclement weather.

Proteome changes and associated physiological roles in chickpea (Cicer arietinum) tolerance to heat stress under field conditions.

Interrogative proteome analyses are used to identify and quantify the expression of proteins involved in heat tolerance and to identify associated physiological processes in heat-stressed plants. The objectives of the study were to identify and quantify the expression of proteins involved in heat tolerance and to identify associated physiological processes in chickpea (Cicer arietinum L.) heat-tolerant (Acc#7) and sensitive genotype (Acc#8) from a field study. Proteomic and gene ontological analyses showed an upregulation in proteins related to protein synthesis, intracellular traffic, defence and transport in the heat-tolerant genotype compared to the susceptible one at the warmer site. Results from KEGG analyses indicate the involvement of probable sucrose-phosphate synthase (EC 2.4.1.14) and sucrose-phosphate phosphatase (EC 3.1.3.24) proteins, that were upregulated in the heat-tolerant genotype at the warmer site, in the starch and sucrose pathway. The presence of these differentially regulated proteins including HSP70, ribulose bisphosphate carboxylase/oxygenase activase, plastocyanin and protoporphyrinogen oxidase suggests their potential role in heat tolerance, at flowering growth stage, in field-grown chickpea. This observation supports unaltered physiological and biochemical performance of the heat-tolerant genotypes (Acc#7) relative to the susceptible genotype (Acc#8) in related studies (Makonya et al. 2019). Characterisation of the candidate proteins identified in the current study as well as their specific roles in the tolerance to heat stress in chickpea are integral to further crop improvement initiatives.

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

Bread wheat genotypes phenotypic characterization under late sowing heat stress and genetic diversity analysis of selected heat tolerant genotypes

Wheat is one of the earliest cultivated plants and second major cereal crop of the world that contains human food essentials. Due to climatic variations, crop is exposed to severe environmental conditions. Rising global temperature is expected to result in severe climate shift in future. High temperature exerts negative effects on wheat phenology and grain production. Selection of heat tolerant wheat germplasm is the best stress management strategy. Present research was planned to conduct field-based evaluation of 100 wheat genotypes under normal and heat stress conditions. The data of twelve phenotypic traits was recorded under control and heat stress trials. There were diverse variations observed among genotypes for morphological characters. The high yielding selected wheat lines 68.111-56, CHEN-84, CHEN-74, IWA8611400-65, CHEN-95, CHEN-96, CHEN-86, CHEN-80, 68.111-60 and CHEN-92 were subjected to DNA fingerprinting with Simple Sequence Repeat markers viz; WMC 18, CFA2129, WMC 367, CFD 48, WMC44 and WMC 798. The genetic diversity ranged from 0 to 0.25 with an average value of 0.06. Unweighted pair group of arithmetic means cluster analysis grouped these lines into clusters. Most of the genetic diversity was observed for CHEN-74 and CHEN-96 in cluster. The study has identified genetically diverse, heat tolerant and high yielding wheat genotypes with possible exploitation in development of climate smart wheat varieties.

Nitric oxide secures reproductive efficiency in heat-stressed lentil (Lens culinaris Medik.) plants by enhancing the photosynthetic ability to improve yield traits.

Rising temperatures, globally and locally, would be detrimental for cool- and summer-season food legumes, such as lentil (Lens culinaris Medik.). Lentil is highly sensitive to supra-optimal temperatures (> 30°C), particularly during reproductive growth, resulting in flower and pod losses. Thus, suitable strategies are needed to introduce heat tolerance in this legume. Here, we evaluated the efficacy of nitric oxide (NO)-applied as foliar treatment of 1mM sodium nitroprusside (SNP), twice (one day before final exposure to high temperature, and again five days later)-on heat-stressed (32/20°C) lentil genotypes, differing in heat sensitivity. As a result of heat stress, endogenous NO increased significantly in heat-tolerant genotypes (46-62% in leaves and 66-68% in anthers, relative to the respective controls), while it decreased in heat-sensitive (HS) genotypes (27-30% in leaves and 28-33% in anthers, relative to the respective controls). Foliar supplementation with SNP markedly increased endogenous NO in leaves and anthers of both the control and heat-treated plants. Heat stress significantly accelerated phenology, damaged membranes, chlorophyll, chlorophyll fluorescence, cellular viability, and decreased leaf water status, carbon fixing and assimilating ability, less so in plants treated with SNP. Heat stress plus SNP significantly improved carbon fixation (as RuBisCo activity) and assimilation ability, (as sucrose concentration (in leaves and anthers), sucrose synthase and vacuolar acid invertase activity, reducing sugars), as well as osmolyte accumulation (proline and glycine betaine) in leaves and anthers. Moreover, SNP-treated plants had significantly less oxidative damage-measured as malondialdehyde and hydrogen peroxide concentrations-in leaves and anthers, relative to the respective control. Reproductive function-assessed as pollen grain germination and viability, stigma receptivity, and ovular viability-decreased markedly in plants exposed to heat stress alone, more so in HS genotypes, but increased significantly with SNP treatment as a consequence of improved leaf and anther function, to significantly increase the pod and seed numbers in heat-stressed lentil plants, relative to heat-stress alone.

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;

Morpho-Physiological Traits and Functional Markers Based Molecular Dissection of Heat-Tolerance in Urdbean.

Urdbean (Vigna mungo L. Hepper) is one of the important pulse crops. Its cultivation is not so popular during summer seasons because this crop is unable to withstand excessive heat stress beside lack of humidity in the atmosphere. Therefore, a panel of 97 urdbean diverse genotypes was assessed for yield under stress and non-stress conditions with an aim to identify heat tolerant genotypes. This study identified 8 highly heat tolerant and 35 highly heat sensitive genotypes based on heat susceptibility index. Further, physiological and biochemical traits-based characterization of a group of six highly heat sensitive and seven highly heat tolerant urdbean genotypes showed genotypic variability for leaf nitrogen balance index (NBI), chlorophyll (SPAD), epidermal flavnols, and anthocyanin contents under 42/25°C max/min temperature. Our results showed higher membrane stability index among heat tolerant genotypes compared to sensitive genotypes. Significant differences among genotypes for ETR at different levels of PAR irradiances and PAR × genotypes interactions indicated high photosynthetic ability of a few genotypes under heat stress. Further, the most highly sensitive genotype PKGU-1 showed a decrease in different fluorescence parameters indicating distortion of PS II. Consequently, reduction in the quantum yield of PS II was observed in a sensitive one as compared to a tolerant genotype. Fluorescence kinetics showed the delayed and fast quenching of Fm in highly heat sensitive (PKGU 1) and tolerant (UPU 85-86) genotypes, respectively. Moreover, tolerant genotype (UPU 85-86) had high antioxidant activities explaining their role for scavenging superoxide radicals (ROS) protecting delicate membranes from oxidative damage. Molecular characterization further pinpointed genetic differences between heat tolerant (UPU 85-86) and heat sensitive genotypes (PKGU 1). These findings will contribute to the breeding toward the development of heat tolerant cultivars in urdbean.

Response of contrasting bread wheat genotypes for heat and drought stress tolerance for rhizospheric soil properties

Aim: The study aimed at investigating differential response of contrasting bread wheat genotypes for heat and drought stress towards changes in chemical and microbial components of rhizospheric soil for developing climate resilient wheat varieties. Methodology: Rhizospheric soils were studied for changes in pH, electrical conductivity, cations, anions, micro-elements, major-elements, organic carbon and organic matter, and plant growth promoting rhizobacteria(PGPRs) abundance at booting and anthesis stages of growth in four contrasting genotypes during 2017-18 and 2018-19 crop seasons Results: The contrasting genotypes (HD2967 and WH730) for heat tolerance exhibited significant interaction between genotype and stage of growth for Na+, K+ and nitrogen, while genotypes (HUW468 and C306) for drought tolerance exhibited it for available nitrogen only. Significant difference for Ca2+, Mg2+, iron, manganese, nitrogen and potassium levels were recorded in drought stress related genotypes at two stages of growth. The heat tolerant genotype showed 2.54 and 10.67 folds enhancement in population of N2 fixing and spore forming bacteria at anthesis compared to sensitive genotypes, while drought tolerant genotype showed 1.51, 1.07 and 6.26 folds in P-solubilizing, N2 fixing and general bacterial abundance. Interpretation: Contrasting genotypes for heat and drought stresses responded differently for chemical properties and abundance of PGPRs in rhizospheric soils.

Identification of small open reading frames (sORFs) associated with heat tolerance in nitrogen-fixing root nodules of Phaseolus vulgaris wild-type and cv BAT93

Common bean is an important legume crop and a major source of protein for low-income groups around the world. Legumes have the ability to engage symbiotic interactions with nitrogen-fixing soil bacteria. In this study, next-generation sequencing technology was used to perform transcriptome analyses of a yet unexplored group of peptides encoded by small open reading frames (sORFs; &lt; 150 codons) in nitrogen-fixing symbiotic nodules of two heat-tolerant genotypes of common bean (Phaseolus vulgaris L): the cultivar BAT93 and a wild genotype (named P. vulgaris 7) from the south of Mexico. After heat stress, total RNA was isolated and used for transcriptome analysis. Sixty differentially expressed sORFs were identified between control and heat stress treatments. The expression profiles of these sORFs suggest that, regardless the evolutionary closeness between P. vulgaris BAT93 and P. vulgaris 7, each genotype has independently adapted their molecular signaling pathways to survive heat stress. The dataset developed may provide a useful resource for future genetic and genomic studies in these species

Effect of Late Seeding Warmer Condition on Phenology and Yield of Wheat

Four wheat variety/genotype (BARI Gom-26, BAW-1202, BAW-1182 and BARI Gom-27) were tested under three heat stress regimes (normal, moderate and severe) to evaluate the effect of late seeding warmer condition on phenology and yield of wheat, as well as to identify suitable cultivars to develop heat-tolerant genotypes at Hajee Mohammad Danesh Science and Technology University (HSTU), Dinajpur during November, 2016 to April, 2017. Results revealed that genotype BAW-1182 and BAW-1202 showed greater thermostability of cell membrane with acceptable yield performance under heat stress condition. The order of tolerance based on heat susceptibility index (based on grain yield) was BAW-1182&gt;BAW-1202&gt;BARI Gom-27&gt;BARI Gom-26 under heat stress conditions. Thus, BAW-1182 and BAW-1202 have the greatest potential to be used as high-yielding wheat genotypes under warm to hot environments and could be used in a breeding programme to develop heat-tolerant wheat.&#x0D; Bangladesh Agron. J. 2021, 24(1): 13-23

Improving thermotolerance in Gossypium hirsutum by using signalling and non-signalling molecules under glass house and field conditions

The climate change and global warming driven rise in temperature and unpredictable occurrence of heat waves impede cotton plants growth and development. Therefore, environmental friendly thermotolerance strategies are required to sustain optimum crop yield under stressful conditions. Reports on heat stress impacts on plant water relations, gas exchange attributes and physiological parameters, at different reproductive stages of cotton, under controlled and natural conditions are lacking. To investigate the impact of temperature and exogenous application of elicitors, a medium heat tolerant cotton genotype was exposed to control/optimal (30/20 °C), medium (38/24 °C) and high (45/30 °C) temperature stress at squaring, flowering and boll formation stages. Plants were staggered to April (early), May (normal) and June (late) sowing dates under field conditions. Growth regulators, salicylic acid (SA-50 ppm), bio-stimulant moringa leaf extract (MLE-30 times diluted) and signaling molecules, i.e. hydrogen peroxide (H2O2 -30 ppm) and ascorbic acid (ASA-70 ppm), were applied foliarly one day prior to temperature stress treatments. Several physio-biochemical parameters, such as leaf non-enzymatic antioxidant, gas exchange attributes and water relations were measured seven-days after exposure to medium and high temperature regimes. Elevated temperature (45/30 °C) increased the content of total soluble proteins (TSP), activity of glutathione reductase (GR), radical scavenging capacity (DPPH%) and H2O2 generation by 64 %, 26 %, 39 % and 57 %, respectively, compared with optimal temperature plants (control). Similarly, the stomatal conductance (GS), seed index and ginning out turn (GOT%) were reduced by 49 %, 47 % and 44 %, respectively under the high temperature regime compared with control temperature regime. Gas exchange components, water relations, seed index and GOT were also reduced under medium and high temperature regimes. Among the exogenous applications, H2O2 showed profound alleviation of temperature stress, followed by ASA and MLE. Foliar application of H2O2 increased TSP, GR and DPPH% by 1.16 folds, 70 % and 82 % (averaged across during three reproductive stages); while, GS, seed index and GOT were increased by 45 %, 20 %, 22 % under high temperature stress over the control plants of the same thermal regime. In conclusion, oxidative burst and antioxidant activities were increased, whereas stomatal conductance, seed index and GOT were reduced with increasing temperature from 30/20 °C to 38/24 °C and from 38/24 °C to 45/30 °C. On the other hand, H2O2 improved thermotolerance of cotton plants via maintaining cellular redox balance, gas exchange attributes, and further enhanced seed weight and ginning out turn under medium and high temperature regimes.

Discovery of miRNAs and Development of Heat-Responsive miRNA-SSR Markers for Characterization of Wheat Germplasm for Terminal Heat Tolerance Breeding.

A large proportion of the Asian population fulfills their energy requirements from wheat (Triticum aestivum L.). Wheat quality and yield are critically affected by the terminal heat stress across the globe. It affects approximately 40% of the wheat-cultivating regions of the world. Therefore, there is a critical need to develop improved terminal heat-tolerant wheat varieties. Marker-assisted breeding with genic simple sequence repeats (SSR) markers have been used for developing terminal heat-tolerant wheat varieties; however, only few studies involved the use of microRNA (miRNA)-based SSR markers (miRNA-SSRs) in wheat, which were found as key players in various abiotic stresses. In the present study, we identified 104 heat-stress-responsive miRNAs reported in various crops. Out of these, 70 miRNA-SSR markers have been validated on a set of 20 terminal heat-tolerant and heat-susceptible wheat genotypes. Among these, only 19 miRNA-SSR markers were found to be polymorphic, which were further used to study the genetic diversity and population structure. The polymorphic miRNA-SSRs amplified 61 SSR loci with an average of 2.9 alleles per locus. The polymorphic information content (PIC) value of polymorphic miRNA-SSRs ranged from 0.10 to 0.87 with a mean value of 0.48. The dendrogram constructed using unweighted neighbor-joining method and population structure analysis clustered these 20 wheat genotypes into 3 clusters. The target genes of these miRNAs are involved either directly or indirectly in providing tolerance to heat stress. Furthermore, two polymorphic markers miR159c and miR165b were declared as very promising diagnostic markers, since these markers showed specific alleles and discriminated terminal heat-tolerant genotypes from the susceptible genotypes. Thus, these identified miRNA-SSR markers will prove useful in the characterization of wheat germplasm through the study of genetic diversity and population structural analysis and in wheat molecular breeding programs aimed at terminal heat tolerance of wheat varieties.