Heat Tolerance Index Research Articles

Combining Ability and Gene Action Controlling Grain Yield and Its Related Traits in Bread Wheat under Heat Stress and Normal Conditions

High temperature is a major environmental stress that devastatingly affects wheat production. Thenceforth, developing heat-tolerant and high-yielding wheat genotypes has become more critical to sustaining wheat production particularly under abrupt climate change and fast-growing global population. The present study aimed to evaluate parental genotypes and their cross combinations under normal and heat stress conditions, exploring their diversity based on dehydration-responsive element-binding 2 gene (DREB, stress tolerance gene in response to abiotic stress) in parental genotypes, and determining gene action controlling yield traits through half-diallel analysis. Six diverse bread wheat genotypes (local and exotic) and their 15 F1 hybrids were evaluated at two different locations under timely and late sowing dates. Sowing date, location, genotype, and their interactions significantly impacted the studied traits; days to heading, chlorophyll content, plant height, grain yield, and its attributes. Cluster analysis classified the parents and their crosses into four groups varying from heat-tolerant to heat-sensitive based on heat tolerance indices. The parental genotypes P2 and P4 were identified as an excellent source of beneficial alleles for earliness and high yielding under heat stress. This was corroborated by DNA sequence analysis of DREB transcription factors. They were the highest homologies for dehydrin gene sequence with heat-tolerant wheat species. The hybrid combinations of P1 × P5, P1 × P6, P2 × P4, and P3 × P5 were detected to be good specific combiners for grain yield and its attributes under heat stress conditions. These designated genotypes could be used in wheat breeding for developing heat-tolerant and climate-resilient cultivars. The non-additive genetic variances were preponderant over additive genetic variances for grain yield and most traits under both sowing dates. The narrow-sense heritability ranged from low to moderate for most traits. Strong positive associations were detected between grain yield and each of chlorophyll content, plant height, number of grains/spike, and thousand-grain weights, which suggest their importance for indirect selection under heat stress, especially in early generations, due to the effortlessness of their measurement.

Tolerance to high temperature at reproductive stage: Trade‐offs between phenology, grain yield and yield‐related traits in wild and cultivated barleys

AbstractHigh‐temperature stress at the reproductive stage poses a substantial constraint on cereal production worldwide. This study was conducted to assess tolerance to terminal high‐temperature stress in 45 wild (Hordeum vulgare ssp. spontaneum) genotypes, four cultivars (H. vulgare ssp. vulgare), 98 F3 and 79 BC1F2 families derived from hybridization of a high‐temperature tolerant wild genotype and a susceptible cultivar ‘Mona’. Results of analysis of variance showed significant genotypic and high‐temperature stress effects on all the traits studied. Approximately one quarter of the wild genotypes originating from a warmer climate were slightly affected by high‐temperature stress. Grain yield strongly correlated (p < .01) with stress tolerance, yield stability and heat tolerance indices. The reduction in the reproduction period caused by high temperature was much higher in cultivated genotypes than in wild ones. Grain number and weight were the most effective yield components to screen high‐temperature tolerant F3 and BC1F2 families. In conclusion, strategies like escape/avoidance are being used primarily to cope with heat stress by cultivars, whereas adaptive strategies such as tolerance are being implemented by wild barley.

Impact of environmental factors on physiological adaptability, thermo-tolerance indices, and productivity in Jersey crossbred cows.

Environmental stressors such as temperature, humidity, rainfall, photoperiod, etc. under tropical conditions are some of the important limiting factors for optimum expression of production and reproduction in dairy cows. The present study evaluated changes in cardinal physiological responses, heat tolerance indices, and milk yield in Jersey crossbred cows due to abiotic stress. Climograph was developed using daily maximum and minimum temperatures, humidity, and rainfall at livestock farm over a period of 15 years. Seasons significantly (P < 0.01) influenced cardinal physiological responses and thermal adaptability of Jersey crossbred cows. Diurnal environmental variations between morning and afternoon of the shed caused increase in body temperature, pulse, and respiration rate by 0.59-0.91%, 4.95-7.18%, and 9.73-32.37%, respectively. Thermal adaptability of cows showed significant (P < 0.01) higher deviations from perfect state of adaptability during summer, monsoon, and post-monsoon as compared to winter and spring seasons. The responsiveness and ranking of cows were dissimilar among 3 heat tolerance indices, viz., Iberia heat tolerance index, Benezara's coefficient of adaptability, and Dairy Search Index (DSI). Enhanced respiration rate was the most important observable bio-indicator to poor thermal adaptability. Good thermo-tolerant cows had 8.86% higher (P < 0.05) monthly milk yield per cow than poorly adapted ones. Findings of this study suggest that deviations in cardinal physiological responses across the seasons are very reliable and simple estimates for evaluating levels of thermo-tolerance in crossbred cows.

Phenotypic Selection and Bulked Sergeant Analysis for 1000-Kernel Weight under Heat Stress in Durum Wheat

Divergent phenotypic selection for 1000-kernel weight (TKW) was performed under heat stress in a population of 120 F7 recombinant inbred lines (RILs) of durum wheat. The direct response to selection for TKW and correlated response in grain yield per plant (GYP) were assessed under favorable and heat stress conditions. Considerable genetic variations were found among the tested RILs for TKW and GYP. Under heat stress, mean TKW of F7 RILs selected in the high and low directions were 62.28 and 34.42g, respectively. Positive and highly significant responses to selection were obtained for TKW in the high (14.92 and 16.29%) and low (20.78 and 26.88%) directions under favorable and heat stress conditions, respectively. Selection for higher TKW produced positive and highly significant correlated response in GYP under heat stress (11.05%), whereas selection for lower TKW produced positive and highly significant correlated responses in GYP under favorable (11.13%) and heat stress (19.33%) conditions. High realized heritability estimates were obtained for TKW (0.74 and 0.75) and GYP (0.65 and 0.71) under favorable and heat stress conditions, respectively. F8 RILs derived from selection for higher TKW showed higher heat tolerance index (averaged 1.20) than RILs selected for lower TKW (0.52), indicating the usefulness of selection for higher TKW in improving heat tolerance. Bulked segregant analysis with 40 simple sequence repeats (SSR) markers identified seven positives alleles located on 2A (1), 3B (2), 4A (1), 5A (1), 6A (1) and 7B (1) chromosomes that were associated with higher TKW as an indicator for heat tolerance.

Evaluation of Triticum durum–Aegilops tauschii derived primary synthetics as potential sources of heat stress tolerance for wheat improvement

AbstractAddressing the impact of heat stress during flowering and grain filling is critical to sustaining wheat productivity to meet a steadily increasing demand from a rapidly growing world population. Crop wild progenitor species of wheat possess a wealth of genetic diversity for several biotic and abiotic stresses, and morphological traits and can serve as valuable donors. The transfer of useful variation from the diploid progenitor, Aegilops tauschii, to hexaploid wheat can be done through the generation of synthetic hexaploid wheat (SHW). The present study targeted the identification of potential primary SHWs to introduce new genetic variability for heat stress tolerance. Selected SHWs were screened for different yield-associated traits along with three advanced breeding lines and durum parents as checks for assessing terminal heat stress tolerance under timely and late sown conditions for two consecutive seasons. Heat tolerance index based on the number of productive tillers and thousand grain weight indicated that three synthetics, syn9809 (64.32, 78.80), syn14128 (50.30, 78.28) and syn14135 (58.16, 76.03), were able to endure terminal heat stress better than other SHWs as well as checks. One of these synthetics, syn14128, recorded a minimum reduction in thousand kernel weight (21%), chlorophyll content (2.56%), grain width (1.07%) despite minimum grain-filling duration (36.15 d) and has been selected as a potential candidate for introducing the terminal heat stress tolerance in wheat breeding programmes. Breeding efforts using these candidate donors will help develop lines with a higher potential to express the desired heat stress-tolerant phenotype under field conditions.

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.

Bioregulators application improved heat tolerance and yield in chickpea (Cicer arietinum L.) by modulating zeaxanthin cycle

Chickpea is sensitive to heat stress and generally experiences high temperature during reproductive phase. Therefore, terminal heat stress is key constraints for its production. Exogenous application of bioregulators is an option to improve heat tolerance and yield. Therefore, an experiment was carried out using two contrasting Desi type (JG 14) and Kabuli type (Pusa 1108) chickpea varieties with an objective to interlink bioregulators induced heat tolerance with zeaxanthin pigments cycle. Experiment was comprising two main treatments i.e. Normal (18th November) and late (20th December) sown conditions for exposing the crop to high temperature and four sub-treatments (Foliar application of bioregulators viz ABA (10 ppm), BA (40 ppm), SA (100 ppm), thiourea (1000 ppm) and water spray (as control) prior to flowering. Under high temperature condition, reduction in leaf photosynthesis, photosynthetic pigments, chlorophyll fluorescence parameters, yield and its attributes was recorded. Foliar application of bioregulators augmented the grain yield by improving the photosynthetic rate (PN), photosynthetic pigments including zeaxanthin, maximum quantum yield of PS II (Fv/Fm), non-photochemical quenching, heat tolerance index, yield attributes and reducing the level of violaxanthin and heat susceptibility index over the control (water) under late sown condition which in turn suggested that bioregulators induced the heat tolerance by activating operation of zeaxanthin pigments cycle in chickpea. Moreover, Kabuli chickpea variety responded better to bioregulators than Desi type particularly under heat stress condition.

Assessment of Heat Tolerance in Some Wheat Species and Interspecific Hybrids

Twelve accessions including two diploid, four tetraploid and six hexaploid genotypes were used in this study to assess heat tolerance in wheat. All possible crosses were made and the resulted hybrids with their parents were subsequently evaluated for heat tolerance in two sowing dates. Evaluation was based on 1000 grain weight, grain yield per plant, cell membrane thermostability and tetrazolium chloride reduction. Results revealed significant variability among wheat genotypes and hybrids in all evaluated traits under favorable and heat stress conditions. However, tetraploid genotypes showed the highest performance under heat stress followed by hexaploid and diploid genotypes, respectively. According to results of heat tolerance index, one tolerant and one susceptible parent from each ploidy level along with 6 related interspecific hybrids were chosen to be involved in molecular analysis. Target region amplification polymorphism (TRAP) markers were used based on fixed primers of heat shock protein genes. TRAP clearly confirmed the morpho-physiological findings and generated a dendrogram which was quietly like that of morpho-physiological data. TRAP was able to generate one and five specific bands for diploid and hexaploid genotypes respectively, while no specific bands were generated for tetraploid. In addition, the different genomes showed some shared bands between each other revealing their relationship. Interestingly, two specific bands for tolerant genotypes of different ploidy level were generated which were absent in all susceptible genotypes. Findings herein are of high importance and could help in successive breeding programs for wheat improvement.

Thermoregulatory capacity of Santa Inês hair ewes of different genotypes associated with coat colors raised in a hot environment

ABSTRACT The relationship between hair color characteristics and thermoregulatory responses in ewes raised in hot environment were evaluated. 15 Santa Inês hair ewes of different genotypes associated with coat colors (light brown, dark brown and black) with body weight of 41.2 ± 8.1 kg were evaluated during three consecutive days. Rectal temperature (RT, °C) and coat surface temperature (CST, °C) of seven anatomical points (front, back, croup, loin, side, thigh, and belly) were measured during the morning and afternoon periods. Thermoregulatory responses were recorded along with meteorological variables. Heat tolerance index (HTI) and thermal gradient (TG, °C) were estimated for each genotype. RT and CST were influenced by periods of the day (P < 0.05), being higher in the afternoon, but TG did not differ (P > 0.05) between periods. HTI, CST, and TG were equal (P > 0.05) among the three genotypes. Only RT was higher in animals with dark brown coats compared to light brown, but equal to the black coat. It was observed that animals with black or dark brown hairs have a strong association between the CST under study, and yet these had an inverse behavior with the RT. Animals with a darker coat tend to trigger heat dissipation in various anatomical regions of the body, presenting dynamics in thermoregulatory responses in relation to those with lighter coats. Santa Inês ewes have heat dissipation mechanisms as a function of different genotypes associated with coat colors, but have the same thermoregulatory aspects to maintain homeostasis, demonstrating an excellent adaptive mechanism in a hot environment.

Possible involvement of xanthophyll cycle pigments in heat tolerance of chickpea (Cicer arietinum L.)

Chickpea being a winter season crop often experiences heat stress during reproductive phase. For chickpea production, terminal heat stress is one of the major constraints. Plants have built up numerous mechanisms to combat the heat stress. We considered the photosynthetic pigments for heat tolerance. Therefore, in order to investigate the heat tolerance in relation to photosynthetic pigments, a field trial was carried out having 4 contrasting genotypes namely BG 240 and JG 14 (relatively heat tolerant), SBD 377 (moderately tolerant) and ICC 1882 (relatively heat sensitive). Heat stress was imposed by altering the sowing date i.e. normal (18th November) and late sown (18th December). Under delayed sown condition, heat stress was faced by crop starting from flowering stage to crop maturity. Under heat stress condition, heat tolerant genotypes BG 240 and JG 14 maintained higher level of membrane stability, RWC (%), osmolytes, dry matter partitioning, grain yield, heat tolerance index and had higher values of zeaxanthin, quantum yield of PS II (Fv/Fm ratio), non-photochemical quenching (NPQ), photosynthetic rate, level of photosynthetic pigments (chlorophylls and carotenoids) and lower level of violaxanthin, and lipid peroxidation as compared to heat sensitive one (ICC 1882). In addition to this, Fv/Fm ratio and NPQ exhibited positive relationship with heat tolerance which suggested the involvement of xanthophyll cycle pigments in chickpea heat tolerance.

Wheat Variety Improvement for Climate Resilience

High temperature stress unfavorably affects plant growth and reduces grain yield (GY). This study was conducted with an aim to identify the terminal heat tolerance of one hundred and two wheat genotypes with three checks. They were sown under normal (non-stress) and late (stress) conditions at Regional Agricultural Research Station (RARS), Tarahara; RARS, Nepalgunj and National Wheat Research Program (NWRP), Bhairahawa, Nepal. The trial was sown in Augmented design during 2014/15 winter season as a Nepal heat tolerance wheat screening nursery (NHTWSN). Grain yield, maturity, stress susceptibility and tolerant indices were estimated to assess the heat tolerance of the genotypes. Combined analysis among the tested wheat lines (102 new entries + 3 checks) showed that KACHU//KIRITATI/WBLL1 ((Heat tolerance index (HTI) = 1.78) possessed the highest level of heat tolerance, followed by SLVS /3/ CROC_1/ AE.SQUARROSA (224)// OPATA/5/ VEE/LIRA//BOW/3/BCN/4/KAUZ/6/ 2*KA/NAC//TRCH (HTI=1.57) while SUP152/VILLA JUAREZ F2009 (HTI=0.83) appeared to be the least heat tolerant. Correlation analysis showed that yield under stress environment had positive (r=0.083) and significant (p&lt;0.05) association with that of non-stress environment. Grain yield (Kg/ha) under both environments had significant positive correlation with mean productivity (MP), geometric mean productivity (GMP) and HTI. Thirty seven wheat genotypes possessing heat tolerance will be considered in further heat tolerance trial and can also be used directly in varietal development and in the crossing program to breed more heat tolerant genotypes.

Screening the FIGS Set of Lentil (Lens culinaris Medikus) Germplasm for Tolerance to Terminal Heat and Combined Drought-Heat Stress

Lentil (Lens culinaris Medikus) is one of the most important cool season food legume crops grown in many countries. Seeds are typically rich in protein, fiber, prebiotic carbohydrates and minerals, such as iron and zinc. With changing climate and variability, the lentil crop faces frequent droughts and heat stress of varying intensity in its major production zones. In the present study, a set of 162 lentil accessions selected through the Focused Identification of Germplasm Strategy (FIGS) were screened for tolerance to heat stress and combined heat-drought stresses under field conditions at two contrasting locations, namely Marchouch and Tessaout in Morocco. The results showed a significant genotypic variation for heat tolerance and combined heat-drought tolerance among the accessions at both locations. Based on the heat tolerance index (HTI), accessions, namely ILL 7833, ILL 6338 and ILL 6104, were selected as potential sources of heat tolerance at Marchouch, and ILL 7814 and ILL 8029 at Tessaout. Using the stress tolerance index (STI), ILL 7835, ILL 6075 and ILL 6362 were identified as the most tolerant lines (STI &gt; 1) at Marchouch, and ILL 7814, ILL 7835 and ILL 7804 (STI &gt; 1) at Tessaout, under the combined heat-drought stress conditions. Accession ILL 7835 was identified as a good source of stable tolerance to heat stress and combined heat-drought stress at both locations.

A potential seedling-stage evaluation method for heat tolerance in Indian mustard (Brassica juncea L. Czern and Coss).

Heat stress is one of the major limitations to crop productivity. In the present study, an efficient method of screening was adopted for identification of heat tolerantIndian Mustard genotypes by applying 4-day cycle of heat stress to seedlings. Thirty-four genotypes were screened based upon lipid peroxidation and survival percentage and classified them into five different classes according to membership function value (MFV) for response against high temperature. The maximum and minimum value of mean MFV were 0.89 (highly heat tolerant, TPM1) and 0.12 (highly heat sensitive, JM2), respectively. The coefficient of determination (R 2) between the mean MFV and the heat tolerance index (HTI) of MDA content, survival percentage was 0.914 and 0.808 suggesting that these parameters are reliable traits to evaluate the heat tolerance of Brassica juncea genotypes. The evaluation method was further validated using identified contrasting genotypes and assessment of heat stress associated biochemical parameters. Results showed efficient recovery of tolerant genotype as compared to sensitive genotype. Expression profiling of heat stress-related genes (HSP21 and HSFA7A) showed significant upregulation in the tolerant genotype (TPM1) (9.73- and 4.87-fold, respectively) as compared to the sensitive genotype (JM2) (4.18- and 1.73-fold, respectively) under heat stress condition. The results imply development of an efficient screening method which is useful for evaluation and breeding of thermo-tolerant B. juncea.

Variation for Heat Tolerance During Seed Germination in Diverse Carrot [Daucus carota (L.)] Germplasm

Carrot production is constrained by high levels of heat stress during the germination stage in many global regions. Few studies have been published evaluating the effect of heat stress on carrot seed germination or screening for genetic heat stress tolerance. The objectives of this study were to evaluate the response of diverse carrot germplasm to heat stress, identify heat-tolerant germplasm that may be used by plant breeders, and define the appropriate temperature for assessing heat tolerance in germinating carrot seed. To identify an appropriate screening temperature, three commercial hybrids and an open pollinated variety were evaluated at five temperatures (24, 32.5, 35, 37.5, and 40 °C). In preliminary studies, 35 °C was identified as the optimal temperature for screening heat tolerance of carrot seed. Cultivated and wild carrot plant introductions (PIs) (n = 270) from the U.S. Department of Agriculture (USDA) National Plant Germplasm System (NPGS) representing 41 countries, inbred lines from the USDA Agricultural Research Service (n = 15), and widely grown commercial hybrids (n = 8) were evaluated for heat tolerance under heat stress and nonstress conditions (35 °C and 24 °C, respectively) by calculating absolute decrease in percent germination (AD), inhibition index (II), relative heat tolerance (RHT), and heat tolerance index (HTI). All measurements of heat tolerance identified significant differences among accessions; AD ranged from −13.0% to 86.7%, II ranged from 35.7% to 100.0%, RHT ranged from 0 to 1.36, and HTI ranged from 0.0 to 1.45. The broad-sense heritability (H2) calculations ranged from 0.64 to 0.86 for different traits, indicating a moderately strong genetic contribution to the phenotypic variation. Several wild carrot accessions and inbred lines displayed low levels of heat tolerance, whereas cultivated accessions PI 643114 (United States), PI 652400 and PI 652403 (Turkey), PI 652208 (China), and PI 652403 (Russia) were most heat tolerant. This is the first evaluation of heritability for heat stress tolerance during carrot seed germination, the first measure of HTI, and the first correlation calculation between heat and salt tolerance during germination in carrot.

Genetic variations, heritability, heat tolerance indices and correlations studies for traits of bread wheat genotypes under high temperature

PurposeThe purpose of this paper was to study the genetic variability, heritability, heat tolerance indices and phenotypic and genotypic correlation studies for traits of 250 elite International Center for Agricultural Research in the Dry Areas (ICARDA) bread wheat genotypes under high temperature in Wad Medani, Center in Sudan.Design/methodology/approachBread wheat is an important food on a global level and is used in the form of different products. High temperature associated with climate change is considered to be a detrimental stress in the future on world wheat production. A total of 10,250 bread wheat genotypes selected from different advanced yield trials introduction from ICARDA and three checks including were grown in two sowing dates (SODs) (1st and 2nd) 1st SOD heat stress and 2nd SOD non-stress at the Gezira Research Farm, of the Agricultural Research Corporation, Wad Medani, Sudan.FindingsAn alpha lattice design with two replications was used to assess the presence of phenotypic and genotypic variations of different traits, indices for heat stress and heat tolerance for 20 top genotypes and phenotypic and genotypic correlations. Analysis of variance revealed significant differences among genotypes for all the characters. A wide range, 944-4,016 kg/ha in the first SOD and 1,192-5,120 kg/ha in the second SOD, was found in grain yield. The average yield on the first SOD is less than that of the secondnd SOD by 717.7 kg/ha, as the maximum and minimum temperatures were reduced by 3ºC each in the second SOD when compared to the first SOD of the critical stage of crop growth shown.Research limitations/implicationsSimilar wide ranges were found in all morpho-physiological traits studied. High heritability in a broad sense was estimated for days to heading and maturity. Moderate heritability estimates found for grain yield ranged from 44 to 63.6 per cent, biomass ranged from 37.8 to 49.1 per cent and canopy temperature (CT) after heading ranged from 44.2 to 48 per cent for the first and secondnd SODs. The top 20 genotypes are better than the better check in the two sowing dates and seven genotypes (248, 139, 143, 27, 67, 192 and 152) were produced high grain yield under both 1st SOD and 2nd SOD.Practical implicationsThe same genotypes in addition to Imam (check) showed smaller tolerance (TOL) values, indicating that these genotypes had a smaller yield reduction under heat-stressed conditions and that they showed a higher heat stress susceptibility index (SSI). A smaller TOL and a higher SSI are favored. Both phenotypic and genotypic correlations of grain yield were positively and significantly correlated with biomass, harvest index, number of spikes/m2, number of seeds/spike and days to heading and maturity in both SODs and negatively and significantly correlated with canopy temperature before and after heading in both SODs.Originality/valueGenetic variations, heritability, heat tolerance indices and correlation studies for traits of bread wheat genotypes under high temperature

Supra‐optimal growth temperature exacerbates adverse effects of low Zn supply in wheat

AbstractRising temperatures are a major threat to global wheat production, particularly when accompanied by other abiotic stressors such as mineral nutrient deficiencies. This study aimed to quantify the effects of supra‐optimal temperature on growth, photosynthetic performance, and antioxidative responses in bread wheat cultivars grown under varied zinc (Zn) supply. Two bread wheat cultivars (Triticum aestivum L., cvs. Lasani‐2008 and Faisalabad‐2008) with varied responsiveness to Zn supply and drought tolerance were cultured in nutrient solution with low (0.1 µM) or adequate (1.0 µM) Zn under optimal (25/20°C day/night) or supra‐optimal (36/28°C day/night) temperature regimes. Supra‐optimal temperature severely reduced root but not shoot biomass, whereas low Zn reduced shoot as well as root biomass. Shoot‐to‐root biomass ratio was reduced under low Zn but increased under supra‐optimal temperature. Supra‐optimal temperature inhibited root elongation and volume particularly in plants supplied with low Zn. In both cultivars, Zn efficiency index was reduced by supra‐optimal temperature, whereas heat tolerance index was reduced by low Zn supply. Supra‐optimal temperature decreased photosynthesis, quantum yield, and chlorophyll density in low‐Zn but not in adequate‐Zn plants. In comparison, low Zn decreased specific activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX) and increased glutathione reductase (GR), where supra‐optimal temperature increased SOD, decreased GR and did not change APX activity in leaves and roots. Moreover, supra‐optimal temperature severely reduced shoot Zn concentration and Zn uptake per plant specifically under adequate Zn supply. Overall, supra‐optimal temperature exacerbated adverse effects of low Zn supply, resulting in severe reductions in growth traits viz. shoot and root biomass, root length and volume, and consequently impeded Zn uptake, enhanced oxidative stress and impaired photosynthetic performance. Adequate Zn nutrition is crucial to prevent yield loss in wheat cultivated under supra‐optimal temperatures.

Screening maize (Zea mays L.) inbred lines for basal and acquired thermotolerance

Maize (Zea mays L.) is the most important cereal crop in Africa. However, its production is under serious threat due to the increasing occurrence of abiotic stress factors such as heat stress. In this study, 18 maize inbred lines were screened for basal and acquired thermotolerance using the water bath and growth chamber techniques, respectively. Based on the water bath technique, highly significant differences (P<0.001) in coleoptile growth among the inbred lines under heat stress, non-stress (control) and across environments were observed. Coleoptile growth was used to calculate heat tolerance index (HTI) of each inbred line. Based on the results, EM86Y, EM578Y, HM63Y, HM1472Y and AO595Y were depicted as tolerant to basal heat stress. With regards to the growth chamber study, three stress indices, namely, HTI, heat susceptibility index (HSI) and tolerance (TOL) were used to determine inbred lines exhibiting acquired thermotolerance. Results obtained showed that EM88Y and KO315Y were tolerant, while HM48Y and CM321Y were semi-tolerant to acquired heat stress. Basal thermotolerance is useful prior to emergence, while acquired thermotolerance is effective after crop emergence. Combining these mechanisms of tolerance in single inbred lines is highly recommended.

Seasonal variations in physiological response and heat tolerance indices of Sahiwal, HF x Sahwial crossbred and Hill (Badri) Cattle under farm conditions of Uttarakhand

Present investigation was conducted on Sahiwal, crossbred (Sahiwal x Holstein Friesian) and Hill (Badri) cattle to study the effect of season on physiological response and heat tolerance indices under farm condition in foot hills of Uttarakhand. Physiological responses of eighteen primiparous lactating cows (four in each group) were recorded daily in morning (9:00 am) and evening (3:00 pm) for 20 days in summer, rainy and winter season. Heat tolerance indices like Temperature humidity index, Iberia heat tolerance coefficient, Benezara coefficient of adaptability and Dairy search index were calculated. There was a significant (P≤0.05) difference between mean morning and evening rectal temperature (RT), respiration (RR) and pulse rate (PR) between indigenous and crossbred cows during summer and rainy season. Also significant (P≤0.05) difference was found between winter vs. summer/ rainy season with respect to morning and evening RT, RR and PR in all the groups. Crossbred cows had RT, RR and PR than indigenous counterparts in all the season. In winter all physiological parameters were significantly (P≤0.05) lower than summer/ rainy season in all the groups. Heat tolerance indices indicated that Sahiwal cows were more heat resistant than Hill (Badri) cows and crossbred cows, the least heat resistant during summer and rainy season. Moreover, during winter season none of the groups were under climatic stress. Study indicated that indigenous breeds were more adaptive to the stressful climatic condition in foot hills of Uttarakhand.

Gene Action and Combining Ability of Cellular Thermotolerance in Bread Wheat (Triticum aestivumL.)

Heat stress is one of the most important factors limiting growth and productivity of wheat. In the present study, gene action, general (GCA) and specific (SCA) combining ability of cellular thermotolerance were studied in a nine-parent half diallel cross of bread wheat evaluated under normal (1 st sowing date) and heat stress (late sowing date) conditions. The cellular thermotolerance was estimated based on cell membrane thermostability (CMS) and tetrazolium chloride (TTC) reduction. Grain yield/plant (GYP), 1000-kernel weight (TKW), stem diameter (STD) and heat tolerance index (HTI) were measured. Compared with their parents, F1 hybrids significantly produced higher GYP, CMS, TTC and HTI. Highly significant mean squares of GCA and SCA effects were observed for all traits with GCA mean squares being much larger than that of SCA. Highly significant additive (a) and non-additive (b) gene actions were observed for all the traits with a predominance of the additive gene actions. However, the dominance genetic variance of CMS and TTC was greater than the additive variance. Moderate to high narrow-sense heritability was obtained for CMS (0.52), TTC (0.57) and HTI (0.71). GYP was significantly correlated with CMS (r = 0.62), TTC (r = 0.63) and HTI (r = 0.60). A highly significant positive correlation was obtained between CMS and TTC (r = 0.73), supporting that CMS and TTC could be used as efficient criteria for selecting wheat genotypes under heat stress. The parents P9, P1 and P2 were identified as best general combiners for CMS, TTC and HTI respectively. Six crosses were identified as best promising combinations for CMS (P1 × P8 and P5 × P9), TTC (P4 × P9 and P5 × P6) and HTI (P1 × P2 and P8 × P9). Thus, inclusion these superior genotypes into breeding programs could be useful for improvement of heat tolerance in wheat.

Expression of Mn-SOD and Cu,Zn-SOD of Sahiwal and Karan-Fries in response to acute heat exposure

The present study aimed to investigate the expression of Mn-SOD and Cu,Zn-SOD mRNA in lymphocytes of Sahiwal and Karan-Fries during acute thermal exposure. Six numbers each of Sahiwal and Karan-Fries heifers in the age group of 2–2.5 years were exposed at 40±1°C and 50% relative humidity inside a psychrometric chamber for 4 h in a day. Respiration rate, heart rate and rectal temperatures were recorded to calculate heat tolerance index by calculating Dairy Search Index (DSI). Blood samples were collected at 0, 1, 2, 3 and 4 h of heat exposure for estimation of Mn-SOD and Cu,Zn-SOD mRNA expression by RT-PCR. DSI of Sahiwal was not influenced by heat exposure even after 4 h of heat exposure. After 1 h of heat exposure, DSI of Karan-Fries increased which further escalated after 3 h of exposure in Karan-Fries. Mn-SOD expression increased after 4 h and 2 h of heat exposure in Sahiwal and Karan-Fries respectively, however the expression declined after 3 h of exposure in Karan-Fries. Expression of Cu,Zn-SOD mRNA of Sahiwal and Karan-Fries was not influenced by heat exposure. The study revealed better equipped antioxidant system of Sahiwal than Karan-Fries in response to acute thermal exposure.