Heat Tolerant Genotypes Research Articles

From landraces to haplotypes, exploiting a genomic and phenomic approach to identify heat tolerant genotypes within durum wheat landraces

Dry and hot climates severely impact wheat yields, necessitating the development of innovative solutions to accelerate the breeding and selection of more adaptable durum wheat genotypes. The aim of this study was to identify new wheat ecotypes that can bridge the gap between commercial varieties and adaptability to ongoing climate change. In this study, advanced genomic and phenomic techniques were combined to characterize a set of durum wheat landraces derived from single seed descent (SSD). This approach enabled the identification of novel variability in the TdHsp26-A1 and -B1 genes. As a result, 38 durum wheat genotypes were analyzed using targeted enrichment PCR, leading to the identification of 17 novel haplotype combinations with SNPs in the TdHsp26 genes. The response of these SSD haplotypes to heat stress was characterized at both the seedling and tillering growth stages. Phenotypic analysis of contrasting genotypes led to the selection of two distinct genotypes: SSD69 and SSD397. During heat stress, SSD69 exhibited altered accumulation of H2O2 and MDA content under both growth conditions, providing new insights into the oxidative response to heat stress. Additionally, this work identifies phenotypic traits that are suitable for detecting differences between variants. The geographic distribution of the different alleles aligned with the spread of durum wheat from its center of origin.

Variation among Blackgram (Vigna mungo L.) Genotypes for Antioxidant Defence System and Yield under High Temperature Stress

Background: Blackgram is a short duration pulse crop which is sensitive to high temperatures. Raising global temperatures are becoming a serious threat to the production of blackgram by altering biochemical processes at cellular level. Hence, the present investigation was carried out for better understanding of genotypic variability and the biochemical mechanisms governing heat stress tolerance which can help in identifying heat tolerant blackgram genotypes that can yield better under climate change scenarios. Methods: Thirty blackgram genotypes selected from temperature induction response technique were evaluated for biochemical efficiency under natural high temperature conditions during summer, 2022 and 23. Field experiment was conducted at Agricultural College Farm, Acharya N.G Ranga Agricultural University, Agricultural College, Bapatla. Biochemical and yield parameters were recorded at flowering and the data were analyzed statistically and pooled. Result: The results of the study revealed that the genotypes TBG-129, LBG-1015, PU-1804 and PU-31 recorded higher seed yield indicating their ability to withstand high temperatures by up-regulating various biochemical pathways involved in increased production of proline, carotenoids and antioxidant defense enzymes that might have scavenged the free radicals that were produced due to high temperature stress, thereby preventing lipid peroxidation. Lower seed yield was recorded in TBG-125 and LBG-1023 which might be due to oxidative damage caused by higher accumulation of free radicals and poor scavenging activity of antioxidant enzymes. Moreover, the results of correlation analysis revealed that all the biochemical traits such as proline, carotenoids and antioxidant defense enzymes showed positive association with seed yield except free radicals and malondialdehyde. The principal component analysis results revealed considerable variability among the traits accounting for 80.0%. The genotypes TBG-129, LBG-1015, PU-1804 and PU-31 can be used in breeding programmes for development of heat tolerant genotypes.

Assessing Heat Stress Tolerance of Wheat Genotypes through Integrated Molecular and Physio-Biochemical Analyses

Heat as an abiotic stress significantly impairs the sustainable productivity of wheat (Triticum aestivum L.). To determine the tolerance of genotypes to heat stress, a comprehensive approach should be used that integrates simultaneous phenotyping and genotyping analyses. The aim of this study is to identify local heat-tolerant genotypes using simple sequence repeat (SSR) markers and evaluate the selected genotypes under field conditions for their tolerance to heat stress. Of the 12 SSR markers that showed polymorphism, eight were associated with six important traits. The use of hierarchical cluster analysis (HC) based on SSR markers led to the identification of 13 genotypes that showed varying results and were grouped into three distinct heat tolerance classes: tolerant (T), moderately tolerant (MT), and sensitive (S). The results showed that heat stress had a significant effect on 19 traits under this study, with significant variation in tolerance to heat stress between genotypes. The tolerant genotypes exhibited a range of average thousand-kernel weight (TKW) values between 40.56 and 44.85, while the sensitive genotype (Yecora Rojo) had an average TKW of 35.45. Furthermore, the tolerant genotypes showed two to three times higher levels of antioxidants compared to the sensitive genotypes when exposed to heat stress. Among the traits analyzed, six showed a favorable combination of high heritability (>60%) and genetic gain (>20%). Through the integration of principal component analysis and stepwise multiple linear regression, it was determined that six traits (grain yield, 1000-kernel weight, plant height, intercellular carbon dioxide, flag leaf area, and grain filling duration) revealed differences between the 13 genotypes. HC analysis of the six traits resulted in the same division of genotypes into three main categories as observed in an HC analysis based on SSR markers. It is worth noting that Saudi wheat, including KSU106, KSU105, and KSU115 as local genotypes, in addition to the 16HTWYT-22 genotype, showed higher heat tolerance compared to the other genotypes tested, indicating its potential suitability for agriculture in Saudi Arabia. These results contribute to breeding programs focused on developing heat-tolerant wheat varieties and accelerate progress in wheat productivity improvement programs.

Cowpea: Prospecting for Heat-Tolerant Genotypes

Selecting genotypes tolerant to high temperatures is an important measure for agricultural maintenance and production in climate change scenarios. Thus, this study aimed to select cowpea genotypes tolerant to increased air temperature. A total of 20 cowpea genotypes were used, cultivated under temperature regimes of 20–26–33 °C and 24.8–30.8–37.8 °C in a completely randomized experimental design under a 2 × 20 factorial scheme (temperature regimes × genotypes). The BRS Inhuma, Bico-de-Ouro-17-45, BRS Guariba, and BRS Imponente genotypes did not show significant differences in the analyzed physiological responses to the increase in air temperature. The BRS Inhuma, Bico-de-Oouro-17-19, Bico-de-Ouro-17-44, Bico-de-Ouro-17-45, BRS Guariba, and BRS Imponente genotypes showed increased temperature tolerance as thermal stress did not affect production. The Pingo-de-Ouro-17-48, MNC00-595F-27, MNC06-895E-1, and MNC09-981B-2 genotypes reduced water efficiency by −26.85, −25.19, −40.04, and −60.37%, respectively, due to the increase in temperature. The results obtained in this work represent a pre-selection of genotypes that are tolerant to high temperatures, with the BRS Inhuma, Bico-de-Ouro-17-45, BRS Guariba, and BRS Imponente genotypes indicated as tolerant to increased temperatures based on the interaction of physiological and productive responses. There is an urgent need to select cowpea genotypes tolerant to increased temperature to maintain production in climate change scenarios and ensure agricultural systems’ sustainability and food security.

Genotypic Selection Using Quantitative Trait Loci for Better Productivity under High Temperature Stress in Tomato (Solanum lycopersicum L.)

High temperature stress affects tomato production both in tropical and sub-tropical environments worldwide. To explore genetic variation for heat tolerance in tomato, 329 transcontinental tomato genotypes were evaluated at the Ministry of Municipality and Environment (MME) greenhouses near Doha, Qatar, where the average daytime temperature was 38 °C with a big fluctuation during the tomato growth season. A preliminary phenotypic analysis identified a panel of 71 hybrid and pure-line tomato genotypes for more detailed studies. The selected subset was examined in the greenhouse using a randomized complete block design under heat stress. The materials were phenotyped for fruit size, fruit weight, fruit hardness, fruit locules, fruit set, total soluble solids (TSS), and fruit yield. Significant phenotypic differences among genotypes were observed for all the traits assessed. To explore the genetic basis of the variation among the examined genotypes, the subset was genotyped using 104 SNP markers identified in previous heat-tolerance genome-wide association studies (GWAS). Nineteen QTL-associated SNP markers could reliably select heat-tolerant genotypes in terms of better fruit yield, fruit set, and TSS. These markers are located on chromosome 1, 5, 6, 8, 9, and 12. Interestingly, two clusters of markers on chromosome 6 were linked to significant effects on yield, fruit set, and TSS under high temperature. Eighteen out of nineteen SNP markers were mapped within a gene body. Based on the phenotypic and the genotypic analysis, an elite set of five genotypes was selected for approval for heat stress environments in Qatar. The aim of the present work is to provide significant results that are exploitable not only in the Qatar region but also worldwide. Specifically, the 19 molecular markers identified in this study can serve as useful tools for breeders in selecting heat-tolerant material.

Effects of high temperature on grain quality and enzyme activity in heat-sensitive versus heat-tolerant rice cultivars.

High-temperature (HT) stress significantly affects the quality of rice (Oryza sativa L.), although the underlying the mechanism remains unknown. Therefore, in the present study, we assessed protein components, amino acids, mineral element levels, starch biosynthesis enzyme activity and gene expression of two heat-sensitive and two heat-tolerant genotypes under HT treatment during early (from 1 to 10 days, T1) and mid-filling (from 11 to 20 days, T2) after anthesis. Except for one cultivar, most rice varieties exhibited increased levels of amylose, chalky degree and protein content, along with elevated cracked grains and pasting temperatures and, consequently, suppressed amino acid levels under HT stress. HT treatment also increased protein components, macro- (Mg, K, P and S) and microelements (Cu, Zn, and Mo) in the rice flour. Both HT treatments reduced the activity of ADP-glucose pyrophosphate, ground-bound starch synthase, as well as the relative ratio of amylose to total starch, at the same time increasing starch branch enzyme activity. The expression levels of OsAGPL2, OsSSS1 and OsSBE1 in all varieties exhibited the same trends as enzyme activity under HT treatment. High temperatures negatively affected rice quality during grain filling, which is related to heat tolerance and grain shape. Altered enzymatic activity is crucial to compensate for the lowered enzyme quality under heat stress. © 2024 Society of Chemical Industry.

Integrated physiological and genetic data reveal key-traits for heat tolerance in tomato

As global temperatures continue to rise, high summer temperatures severely affect crop growth, reducing yield and quality. The projections of annual declines in crop yield require more in-depth multidisciplinary studies on plant tolerance to abiotic stresses. As tomato is a major crop in the Mediterranean region, its response to heat stress has become important to be addressed in order to identify those traits affecting stress tolerance. In this study, physiological and genomic analyses were performed on two heat-tolerant genotypes (LA3120 and E42) grown at high temperatures during the entire life cycle. The results showed that heat stress diversely affected gas exchange and fluorescence parameters in the two genotypes. In particular, E42 regulated the photosynthetic machinery under heat stress by modulating the electron transport chain, whereas LA3120 was less affected by the applied stress. Genotyping data obtained from a GBS (genotyping by sequencing) analysis were used to explore the genetic variability of both genotypes with the aim of identifying candidate genes that might regulate their stress response. These results further deepen our understanding of the physiological mechanisms activated in response to heat stress and allowed to select key traits that could be used in breeding program to select thermotolerant tomato genotypes.

A Multimodal and Temporal Network-Based Yield Assessment Method for Different Heat-Tolerant Genotypes of Wheat

A Multimodal and Temporal Network-Based Yield Assessment Method for Different Heat-Tolerant Genotypes of Wheat

Evaluation of Blackgram (Vigna mungo L.) Genotypes for Dry Matter Partitioning, Reproductive Efficiency and Yield under High Temperature Stress

Background: In the present climate change scenario, the rising temperatures are imposing severe threat to blackgram production leading to marked reduction in yield potential.The reduction in the yield potential is mainly due to reproductive failures caused by heat stress. Keeping this in view, the present study was carried out to find out the reasons behind reproductive failures and identify the genotypes that yield better under heat stress. Methods: Thirty blackgram genotypes selected from temperature induction response technique were evaluated for reproductive efficiency under natural high temperature conditions. Field experiment was conducted at Agricultural College Farm, Acharya N.G Ranga Agricultural University, Agricultural College, Bapatla. Dry matter partitioning, reproductive efficiency and yield traits were recorded at flowering and the data were analyzed statistically and pooled. Result: Genetic variability was observed among the blackgram genotypes with respect to dry matter partitioning, reproductive efficiency and yield traits under high temperature stress conditions. Among the 30 genotypes tested for thermotolerance, the genotypes TBG-129, PU-1804 and LBG-1015 were found to withstand high temperature stress at reproductive stage by possessing higher dry matter, number of flowers per plant, pollen viability, pollen germination percentage, pollen load on stigma, stigma receptivity, flower to pod setting percentage and higher yield. Correlation analysis revealed a strong positive association of total dry matter and all the reproductive efficiency characteristics with seed yield under heat stress conditions. The PCA results revealed considerable variability among the traits accounting for 86.6% of total variability. The genotypes TBG-129, PU-1804 and LBG-1015 can be potentially used as donors in the breeding programmes for the development of heat tolerant genotypes.

Tolerance indices based evaluation of wheat (Triticum aestivum) genotypes under terminal heat stress conditions

Present study was carried out during winter (rabi) seasons of 2021–22 and 2022–23 at Crop Research Centre, Sardar Vallabhbhai Patel University of Agriculture and Technology, Meerut, Uttar Pradesh to evaluate the terminal heat tolerance ability of 30 wheat (Triticum aestivum L.) genotypes using 8 heat stress tolerance indices. The results indicate that 12 genotypes showed low yield reduction as compared to average yield reduction. The stress susceptibility index (SSI) was observed as robust indicator for identifying heat-tolerant genotypes. Stress tolerance index (TOL) was observed crucial which reflects genotype's ability to maintain grain yield under terminal heat stress. Analysis of correlation revealed positive relationships between grain yield under normal and stress conditions, suggesting that best-performing genotypes under normal conditions also perform well under terminal heat stress conditions. Principal component analysis and biplot analysis further confirmed the importance of studied tolerance indices for identification of heat tolerance genotypes. PC1 was associated with yield potential and heat tolerance, while PC2 was associated with stress susceptibility. Based on analysis, genotypes, viz. DBW14, DBW90, HD2864, HD2932, HD2985, HS375, HUW234, RAJ4083, WH1021, WH1124, DBW71 and PBW757 exhibited higher terminal heat stress tolerance. Cluster analysis revealed two major clusters, cluster I contained 12 heat tolerant genotype while cluster II was consisting 18 heat susceptible genotypes. The SSI and TOL index were found promising indices for identification of heat tolerant genotypes of wheat.

Heat stress induced cytosine methylation in the coding region of Rubisco activase (Rca) reveals its genotype-specific expression in contrasting wheat genotypes

Rising environmental temperature has become a major concern in global wheat production since it has critical effects on plant growth,development and yield. Elevated temperatures have become. Further understanding of the processes behind the development of heattolerance is necessary for significant agricultural crops. Cytosine methylation in DNA plays an essential function in epigenetic regulation of gene expression at various developmental stages and environmental stress in plants. In this study, we report the comparative analysis of cytosine methylation in the coding region of the Rubisco activase (Rca) gene in heat tolerant (RAJ3765) and heat susceptible (HUW510)genotypes of wheat in four growth stages under control and heat-stressed conditions in CG, CHG and CGG contexts. We found that the overall 5-mC increased due to heat stress in HUW510 during tillering (25%), boot stage (25%), heading (48%) and anthesis (50%) as compared to RAJ3765 during tillering (21%), boot stage (4%), heading (4%) and anthesis (11%). Additionally, gene expression profiling by using qPCR at the different plant growth stages also showed the decline in the gene expression in the leaf samples in both the genotypes due to heat stress, with a minimum in the susceptible genotype at the anthesis stage. The study will increase the knowledge on the molecular regulation of photosynthetic pathways by cytosine methylation which would assist in selection and manipulation of heat tolerance in wheat.

Dissecting wheat above-ground architecture for enhanced water use efficiency and grain yield in the subtropics

BackgroundGrowing wheat under climate change scenarios challenges, scientists to develop drought and heat-tolerant genotypes. The adaptive traits should therefore be explored and engineered for this purpose. Thus, this study aimed to dissect surface traits and optimizing the leaf architecture to enhance water use efficiency (WUE) and grain yield. Twenty-six wheat genotypes were assessed for five novel leaf traits (NLTs: leaf prickle hairs, groove type, rolling, angle and wettability) under normal, drought and heat conditions following triplicated factorial randomized complete block design (RCBD). The data for NLTs, physiological traits (stomatal conductance, WUE, transpiration, and photosynthesis), and standard morphological and yield traits were recorded. Leaves were sampled at the stem elongation stage (Zadoks 34) to measure the leaf water content (%), contact angle, and to obtain pictures through scanning electron microscopy (SEM). The air moisture harvesting efficiency was evaluated for five selected genotypes. The ideotype concept was applied to evaluate the best-performing genotypes.ResultsThe correlation analysis indicated that long leaf prickle hairs (> 100 μm), short stomatal aperture and density (40–60 mm− 2), inward to spiral leaf rolling, medium leaf indentation, low contact angle hysteresis (< 10°), and cuticular wax were positively associated with WUE. This, in turn, was significantly correlated to grain yield. Thus, the genotypes (E-1) with these traits and alternate leaf wettability had maximum grain yield (502 g m− 2) and WUE supported with high photosynthesis rate, and relative water content (94 and 75% under normal and stress conditions, respectively). However, the genotype (1-hooded) with dense leaf hairs on edges but droopy leaves, spiral leaf rolling, and lighter groove, also performed better in terms of grain yield (450 g m− 2) under heat stress conditions by maintaining high photosynthesis and WUE with low stomatal conductance and transpiration rate.ConclusionThe SEM analysis verified that the density of hairs on the leaf surface and epicuticular wax contributes towards alternate wettability patterns thereby increasing the water-use efficiency and yield of the wheat plant. This study paves a way towards screening and and developing heat and drought-tolerant cultivars that are water-saving and climate-resilient.

Genome-wide expression analysis of novel heat-responsive microRNAs and their targets in contrasting wheat genotypes at reproductive stage under terminal heat stress.

Heat stress at terminal stage of wheat is critical and leads to huge yield losses worldwide. microRNAs (miRNAs) play significant regulatory roles in gene expression associated with abiotic and biotic stress at the post-transcriptional level. In the present study, we carried out a comparative analysis of miRNAs and their targets in flag leaves as well as developing seeds of heat tolerant (RAJ3765) and heat susceptible (HUW510) wheat genotypes under heat stress and normal conditions using small RNA and degradome sequencing. A total of 84 conserved miRNAs belonging to 35 miRNA families and 93 novel miRNAs were identified in the 8 libraries. Tae-miR9672a-3p, tae-miR9774, tae-miR9669-5p, and tae-miR5048-5p showed the highest expression under heat stress. Tae-miR9775, tae-miR9662b-3p, tae-miR1120a, tae-miR5084, tae-miR1122a, tae-miR5085, tae-miR1118, tae-miR1130a, tae-miR9678-3p, tae-miR7757-5p, tae-miR9668-5p, tae-miR5050, tae-miR9652-5p, and tae-miR9679-5p were expressed only in the tolerant genotype, indicating their role in heat tolerance. Comparison between heat-treated and control groups revealed that 146 known and 57 novel miRNAs were differentially expressed in the various tissues. Eight degradome libraries sequence identified 457 targets of the differentially expressed miRNAs. Functional analysis of the targets indicated their involvement in photosynthesis, spliceosome, biosynthesis of nucleotide sugars and protein processing in the endoplasmic reticulum, arginine and proline metabolism and endocytosis. This study increases the number of identified and novel miRNAs along with their roles involved in heat stress response in contrasting genotypes at two developing stages of wheat.

Variation in Physiological Traits of Blackgram (Vigna mungo L.) Genotypes under High Temperature Stress

Background: Blackgram is one of the important short duration pulse crop which is sensitive to high temperatures. The rising global temperatures are threatening the yield of blackgram by altering the physiological processes at cellular level. Keeping this in view, the present investigation was carried out for better understanding of genotypic variability and the physiological mechanisms governing heat stress tolerance which can help in identifying heat tolerant blackgram genotypes that can yield better under climate change scenarios. Methods: Thirty blackgram genotypes selected from temperature induction response technique were evaluated for physiological efficiency under natural high temperature conditions during summer, 2022 and 2023. Field experiment was conducted at Agricultural College Farm, Acharya N.G Ranga Agricultural University, Agricultural College, Bapatla. Physiological and yield parameters were recorded at flowering and the data were analyzed statistically and pooled. Result: Significant genetic variability was observed among the blackgram genotypes with respect to all the physiological traits under high temperature stress conditions. Among the 30 genotypes tested for thermotolerance, the genotypes TBG-129, PU-1804, LBG-1015, PU-31 and TBG-104 were found to withstand high temperature stress at reproductive stage by maintaining higher total chlorophyll, carotenoids, chlorophyll stability index, total biomass production, cooler canopies resulting into higher canopy temperature depression, less membrane injury index values and higher yield. Correlation analysis revealed a strong positive correlation for all the physiological traits with seed yield except membrane injury index under heat stress conditions. The PCA results revealed considerable variability among the traits accounting for 82.65% of total variability. The genotypes TBG-129, PU-1804, LBG-1015 and TBG-104 can be potentially used as donors in the breeding programmes for the development of heat tolerant genotypes.

Evaluation of Desi Chickpea (Cicer arientinum L.) Landraces for Heat Tolerance using Morpho-phenological Traits and Stress Tolerance Indices (STI)

Background: Chickpea is a globally important commercial crop and a key source of protein for vegetarian populations. Though chickpea was domesticated at least 3000 years ago, research into abiotic stress tolerance has been limited compared to cereals. Methods: An experiment was conducted with a set of seventy-one genotypes of Desi chickpea (Cicer arietinum L.) to isolate high temperature tolerant genotypes using randomized block design (RBD) under two different sowing conditions (normal and late/terminal heat stress) and two growing seasons (rabi-2017-18 and 2018-19) at the Pulses Research Station of Junagadh Agricultural University. The screening of heat tolerant genotypes was done based on nine morpho-phenological traits, stress tolerance indices and correlation amongst them. Result: The heat tolerant genotypes of chickpea had less percentage of reduction in numbers of pods, seed yield per plant and 100-seeds weight. Five genotypes viz., ICC 4958, ICC 14595, ICC 8318, GG 4 and ICCV 92944 were identified as highly heat tolerant on the basis of HSI and YSR. These tolerant genotypes and screening criteria’s can be of great importance to identify donor parents to develop new cultivars for the farmers growing chickpea in the heat prone regions.

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.&#x0D; 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.

Heat tolerance indices as tools for characterizing resilient wheat (&lt;i&gt;Triticum aestivum&lt;/i&gt;) RILs population under thermal stress

The escalating impact of heat stress on agriculture due to climate change has necessitated the development of heat- tolerant crop varieties. To address this, a study was carried out at research farm of CCS Haryana Agricultural University, Hisar, Haryana during winter (rabi) seasons of 2018–19 and 2019–20 under two different environments (normal and late sown). Evaluation of multiple stress indices and their relationship with grain yield per plot was done using 200 recombinant inbred lines (RILs) of wheat (Triticum aestivum L.). Positive correlation was observed between grain yield and stress tolerance index, mean productivity, geometric mean productivity, harmonic mean and mean relative performance, while negative correlations existed with heat susceptibility index, tolerance, stress susceptibility index and reduction under stress conditions. Stepwise regression analysis revealed the importance of mean productivity, yield index, geometric mean productivity, stress tolerance index, and reduction in predicting grain yield. Principal Component Analysis highlighted the significance of tolerance and reduction in explaining the variance, with PC-1 labeled as the resilience and stress tolerance component and PC-2 as the yield stability and performance component. These findings were able to select 13 most heat tolerant RILs, performing better than national level check genotype WH730 and emphasized the role of stress indices especially HSI and TOL in characterizing genotypic responses to heat stress and guiding the selection of heat-tolerant genotypes for sustainable crop improvement. In the context of heat stress tolerance, understanding and harnessing transgressive segregants could lead to the development of crop varieties that not only tolerate, but thrive in challenging environments, ensuring sustainable food production under changing climatic conditions.

A Genome-wide association study identifies candidate genes for heat tolerance in adult cucumber (Cucumis sativus L.) plants

Heat stress causes overgrowth, leaf dryness and fruit malformation, which negatively impacts cucumber quality and yield. Yet, in spite of the devastating consequences of this abiotic stress, few genes for heat tolerance in cucumber have been identified. Here, the heat injury indices of 88 cucumber accessions representing diverse ecotypes were collected in two open-field environments, with naturally occurring high temperatures over two years. Seventeen of the 88 accessions were identified as highly heat-tolerant. Using a genome-wide association study, five loci (gHII3.1, gHII3.2, gHII3.3, gHII4.1 and gHII6.1) on three chromosomes associated with heat tolerance were detected. Pairwise linkage disequilibrium correlation, sequence polymorphisms, and qRT-PCR analyses at these loci, identified five candidate genes predicted to be casual for heat stress response in cucumber. CsaV3_3G04883, CsaV3_4G029050 and CsaV3_6G005370 each had nonsynonymous SNPs, and were significantly up-regulated by heat stress in the heat-tolerant genotypes. CsaV3_3G031890 was also induced by heat stress, but in the heat-sensitive genotypes, and sequence polymorphism was only found in the promoter region. Identifying these candidate genes lays a foundation for understanding cucumber thermotolerance mechanisms. Our study is one of the few to examine heat stress in adult cucumber plants and it therefore fills a critical gap in knowledge. It is also an important first-step towards accelerating the breeding of robust heat-tolerant varieties.

Photosynthesis in newly developed leaves of heat-tolerant wheat acclimates to long-term nocturnal warming.

We examined photosynthetic traits of pre-existing and newly developed flag leaves of four wheat genotypes grown in controlled-environment experiments. In newly developed leaves, acclimation of the maximum rate of net CO2 assimilation (An) to warm nights (i.e. increased An) was associated with increased capacity of Rubisco carboxylation and photosynthetic electron transport, with Rubisco activation state probably contributing to increased Rubisco activity. Metabolite profiling linked acclimation of An to greater accumulation of monosaccharides and saturated fatty acids in leaves; these changes suggest roles for osmotic adjustment of leaf turgor pressure and maintenance of cell membrane integrity. By contrast, where An decreased under warm nights, the decline was related to lower stomatal conductance and rates of photosynthetic electron transport. Decreases in An occurred despite higher basal PSII thermal stability in all genotypes exposed to warm nights: Tcrit of 45-46.5 °C in non-acclimated versus 43.8-45 °C in acclimated leaves. Pre-existing leaves showed no change in An-temperature response curves, except for an elite heat-tolerant genotype. These findings illustrate the impact of night-time warming on the ability of wheat plants to photosynthesize during the day, thereby contributing to explain the impact of global warming on crop productivity.

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.