Heat Tolerance Traits Research Articles

Effect of Temperature on Seed Germination in Spinach (Spinacia oleracea)

Breeding heat-tolerant spinach is an important project to meet the demand of increasing spinach production in heat conditions. Seed germination is the early stage to test, screen, and develop heat-tolerant spinach genotypes. The objective of this research was to determine temperature effect on the seed germination percentage and to select heat-tolerant spinach genotypes. A total of nine spinach genotypes were used in this research. The germination experiment was conducted using seven temperatures: 10, 15, 20, 25, 30, 32, and 35 °C under growth chambers. The temperature trials were conducted using completely randomized design (CRD) with three replicates. Spinach seed germination percentage varied among the nine spinach genotypes under the seven temperatures, indicating that genetic variation for heat tolerance existed in the nine spinach genotypes. ‘Donkey’, ‘Marabu’, and ‘Raccoon’ showed higher seed germination percentage with over 70% at 30 and 32 °C, indicating the three spinach genotypes had heat tolerance for germination. However, all spinach genotypes except ‘Ozarka II’ dropped their germination percentages sharply to less than 30%; ‘Ozarka II’ had 63% germination under 35 °C, indicating it is a good source of heat tolerance for seed germination. The higher germination percentages above 30 °C of ‘Ozarka II’, ‘Donkey’, ‘Marabu’, and ‘Raccoon’ may indicate their potential as donors of heat-tolerant traits in spinach breeding program.

Phenotypic characterization of specific adaptive physiological traits for heat tolerance in wheat

Phenotyping for high temperature stress tolerance in the field presents a challenge due to its interaction with other environmental factors. High temperature stress is one of the devastating abiotic stresses, which severely affect various physiological and biochemical processes. An experiment was conducted for phenotypic characterization of specific adaptive physiological traits for heat tolerance in ten wheat genotypes under normal (timely sown) and terminal high temperature (late sown) environments. The rate of photosynthesis was significantly higher in varieties HUW 234, HD 2932, HD 2864 and WH 1124 under timely sown condition, which also synchronized with yield. Higher net photosynthesis contributed in translocation of photo-assimilates to developing sink. Under late sown condition, relative water content, membrane stability index was lower compared to timely sown condition in all the genotypes due to high temperature induced injury. Canopy temperature depression at 15 days after anthesis had significant positive correlation with grain yield under timely sown condition compared to late sown conditions. The reproductive attributes were significantly higher under timely sown condition compared to late sown terminal high temperature environment in all the genotypes. However, the genotypic variation clearly appeared under both the growing conditions. The genotypes HD 2932, HD 2864, HD 3095, HI 8703 and HUW 234 exhibited greater heat tolerance efficiency and sustained higher yield under prevailing high temperature conditions particularly at grain filling and development stages.

Interleukin-2 ((IL-2) gene polymorphism and association with heat tolerance in Nigerian goats

Interleukin-2 (IL-2) serves as a potent immuno-modulator, and plays a unique role in both the activation and maintenance of immune responses and in lymphocyte development. Gene polymorphism in IL-2 gene in three major Nigerian goat breeds [West African Dwarf (WAD), Red Sokoto (RS) and Sahel (SH)] was analysed by restriction fragment length polymorphisms (RFLP). The restriction enzyme, DraI was utilized. The association between the polymorphic site and some heat tolerant traits were also investigated in a total of 157 animals comprising 59 WAD, 69 RS, and 29 SH goats of both sexes. The IL-2 sequence displayed a 98% nucleotide identity with the referenced Cahi-IL-2 AY603404.1 orthologous sequence in GenBank. The phylogenetic trees revealed largely species-wise clustering, while the RS and SH goats were closer compared to the WAD goats. DraI genotype frequencies were in Hardy-Weinberg Equilibrium (P<0.05). The expected heterozygosity (H), which is a measure of gene diversity in the goat populations, ranged from 0.26 to 0.28. The heterozygote (TA) had a comparative advantage over the homozygote (AA) in terms of rectal temperature (39.21±0.08 (TT) and 38.86±0.13 (TA); P<0.05). The SH goats also displayed greater resistance to thermal stress compared to the RS and WAD goats. There were varying sex and interaction effects on the thermal indices. The present findings may find application in the selection of superior animals for resistance to heat stress as well as provide insight to questions about evolution, ecology and conservation of Nigeria indigenous goats.

Effect of Irrigation Timing on Root Zone Soil Temperature, Root Growth and Grain Yield and Chemical Composition in Corn

High air temperatures during the crop growing season can reduce harvestable yields in major agronomic crops worldwide. Repeated and prolonged high night air temperature stress may compromise plant growth and yield. Crop varieties with improved heat tolerance traits as well as crop management strategies at the farm scale are thus needed for climate change mitigation. Crop yield is especially sensitive to night-time warming trends. Current studies are mostly directed to the elevated night-time air temperature and its impact on crop growth and yield, but less attention is given to the understanding of night-time soil temperature management. Delivering irrigation water through drip early evening may reduce soil temperature and thus improve plant growth. In addition, corn growers typically use high-stature varieties that inevitably incur excessive respiratory carbon loss from roots and transpiration water loss under high night temperature conditions. The main objective of this study was to see if root-zone soil temperature can be reduced through drip irrigation applied at night-time, vs. daytime, using three corn hybrids of different above-ground architecture in Uvalde, TX where day and night temperatures during corn growing season are above U.S. averages. The experiment was conducted in 2014. Our results suggested that delivering well-water at night-time through drip irrigation reduced root-zone soil temperature by 0.6 °C, increase root length five folds, plant height 2%, and marginally increased grain yield by 10%. However, irrigation timing did not significantly affect leaf chlorophyll level and kernel crude protein, phosphorous, fat and starch concentrations. Different from our hypothesis, the shorter, more compact corn hybrid did not exhibit a higher yield and growth as compared with taller hybrids. As adjusting irrigation timing would not incur an extra cost for farmers, the finding reported here had immediate practical implications for farm scale adaptation to hot environments.

Evaluation of vigor and winter hardiness of black raspberry breeding populations (Rubus occidentalis) grown in the southeastern US

Demand for fresh berry products continues to grow in the United States; however, commercial raspberry production in the southeastern US is difficult because cultivars are not well adapted to the warm climate and fluctuating winter temperatures, where heat degrades plant vigor and fruit quality, and warm spells in mid to late winter can cause low chilling plants to break bud too early. Recent research about the health benefits of a polyphenolic-rich diet has led to a resurgence of interest and breeding efforts in black raspberry, and is the driving factor for this particular research. Two half-sib populations, ORUS 4304 and ORUS 4305 (307 progeny total) were planted in Jackson Springs, North Carolina in 2012. From fall 2012-spring 2015, a number of traits were measured on each plant, among them vigor, winter hardiness, and heat damage, analyzed in several different ways. Plant vigor increased or decreased over harvest seasons based on individual differences in the segregating plant population, but also showed correlations with temperature, i.e., less vigorous plants were more susceptible to damage by heat or cold. Overall, ORUS 4305 was less vigorous than ORSU 4304. As is the case with most raspberries grown in the southeast, vigor in general is expected to decrease over time; however, certain individuals show transgressive segregation for the trait. Linkage mapping for both populations is underway to identify and validate QTL for vigor, winter hardiness, heat tolerance, and other traits within black raspberry. Ultimately, we hope to gain a more complete understanding of black raspberry physiology and genetics to make breeding commercial quality cultivars a possibility in the southeast.

Quantitative Trait Loci Associated with Physiological Traits for Heat Tolerance in Creeping Bentgrass

Identification of heat‐stress‐related quantitative trait loci (QTL) is important for selecting heat‐tolerant germplasm. The aim of this study was to identify QTL markers by associating major physiological traits related to heat tolerance to specific regions of the genome in a population of creeping bentgrass (Agrostis stolonifera L.) with linkage maps and genetic variability for heat tolerance. Phenotypic variation in visual turf quality (TQ) ratings, leaf chlorophyll content (CHL), leaf membrane stability, and canopy temperature depression (CTD) were evaluated under heat‐stress conditions in 2‐yr field trials (2008 and 2009), greenhouses, and controlled‐environmental growth chambers. Phenotypic assessment demonstrated the segregation and variation of heat tolerance in the population and allowed for the association of traits in specific regions of the genome. Quantitative trait loci for every trait were found across the two parental linkage maps, with a total of 32 QTL for all traits. A number of QTL regions were associated with multiple traits, such as on linkage groups 2.2, 4.1, and 4.2 of the L93‐10 linkage map and linkage groups 3.1 and 5.1 of the 7418‐3 linkage map. Quantitative trait loci identified in this study may be implemented in future studies to identify markers for use in marker‐assisted selection to improve heat tolerance or to help elucidate mechanisms regulating heat tolerance in creeping bentgrass.

Single nucleotide polymorphisms in ATP1A1 gene and their association with thermotolerance traits in Sahiwal and Karan Fries cattle

Expression of stress genes under thermal stress partially explain the relatively higher thermal adaptability of indigenous breeds compared to exotic breeds of cattle. ATP1A1 gene is one of such gene that encodes for a1 isomer of Na+, K+- ATPase enzyme for Na+- coupled transport of metabolites, nutrients, ions and represents a plausible candidate for heat tolerance traits. Present study was designed to compare SNP variations in ATP1A1 gene and to evaluate their association with respiration rate, rectal temperature and heat tolerance coefficient in Sahiwal (51) and Karan Fries (50) cows maintained at Livestock Research Centre of National Dairy Research Institute, Karnal. Two SNPs (T27008243C and A27008223G) were identified in both the dairy cattle breeds. Association of each SNP genotype was analyzed using Generalized Linear Model procedure in Statistical Analysis System (SAS). Sahiwal cows with TT (15.91±1.89b) at T27008243C locus had lowest RR compared to TC genotypes (18.25±1.77ab) and CC genotype (19.24±1.52a), while in Karan Fries cows RR for AA genotype at A27008223G locus was lower (28.85±1.96b) compared to GG genotype (32.37±2.51a). Thus, the study indicated that the TT genotype at T27008243C locus in Sahiwal and AA genotype at 27008223 locus in Karan Fries cows are desirable genotypes for genetic adaptability under heat stress.

Genetic Analysis of Yield and Yield-Attributing Traits for High Temperature Resistance in Tomato

ABSTRACTHigh temperatures can significantly reduce tomato (Solanum lycopersicum L) yield. A 5 × 5 diallel cross was used under high temperatures in a greenhouse to estimate combining ability and understand the genetic basis of tomato genotypes under heat stress. Additive gene action was predominant in governing most heat-tolerant morphological traits; yield was governed by nonadditive gene action. A cross involving high × high general combining ability (gca) or high × low gca had better specific combining ability (sca) effects. The genetic components and proportions studies showed heat tolerance was governed by nonadditive gene action and is a dominant trait. The parental variance (Vr) and parent–offspring covariance (Wr) relationship (Wr–Vr) indicated that heat tolerance traits were governed by overdominance. Significant correlation occurred between yield and yield-attributing traits. Heterosis was high for yield and most yield-attributing traits. Heterosis breeding involving crosses with high gca parents ‘CLN1621E × Nagcarlan’ and ‘BL1176 × Nagcarlan’ could be used to improve tomato for yield during heat stress. Selection for heat tolerance traits should be in early generations followed by selection for yield.

Novel SNP identification in exon 3 of HSP90AA1 gene and their association with heat tolerance traits in Karan Fries (Bos taurus × Bos indicus) cows under tropical climatic condition.

Heat shock proteins (HSPs) act as molecular chaperones those are preferentially transcribed in respose to heat stress and the polymorphism in HSP genes associated with heat tolerance traits in cows. HSP90AA1 gene has been mapped on Bos taurus autosome 21 (BTA-21) and spans nearly 5368 bp comprising of 11 exons out of which the first exon does not translate. The present study was done on Karan Fries (5/8 HF × 3/8 Tharparkar) cows reared in tropical climate with the objectives of identifying single-nucleotide polymorphisms (SNPs) in targeted regions (exon 3) of HSP90AA1 gene and analyzing their association with heat tolerance traits in Karan Fries cows. Respiration rate (RR) and rectal temperature (RT) were recorded once daily for four consecutive days during probable extreme hours in different seasons or temperature humidity index (THI), viz., winter, spring, and summer. For detecting single-nucleotide polymorphisms, sequence data were analyzed using BioEdit software (version 7.2). Comparative sequence analysis of HSP90AA1 gene showed point mutation, viz., g.1209A>G (exon 3) as compared to Bos taurus (NCBI Ref Seq: AC_000178.1). Association analysis indicated that THI was influenced (P < 0.01) by RR, RT, and HTC. Similarly, SNPs at locus g.1209A>G were categorized into three genotypes, i.e., AA, AG, and GG, and the least squares means (LSMEANS) of RR, RT, and HTC for GG (homozygous) genotype were significantly lower (P < 0.01) than AA (homozygous) and AG (heterozygous) genotypes. These findings may partly suggest that cows with GG genotypes were favored for heat tolerance trait, which can be used as an aid to selection for thermo-tolerance Karan Fries cows for better adaptation in subtropical and tropical hot climate.

Breeding for plant heat tolerance at vegetative and reproductive stages.

Key messageThermotolerant crop research.Global warming has become a serious worldwide threat. High temperature is a major environmental factor limiting crop productivity. Current adaptations to high temperature via alterations to technical and management systems are insufficient to sustain yield. For this reason, breeding for heat-tolerant crops is in high demand. This review provides an overview of the effects of high temperature on plant physiology, fertility and crop yield and discusses the strategies for breeding heat-tolerant cultivars. Generating thermotolerant crops seems to be a challenging task as heat sensitivity is highly variable across developmental stages and processes. In response to heat, plants trigger a cascade of events, switching on numerous genes. Although breeding has made substantial advances in developing heat-tolerant lines, the genetic basis and diversity of heat tolerance in plants remain largely unknown. The development of new varieties is expensive and time-consuming, and knowledge of heat tolerance mechanisms would aid the design of strategies to screen germplasm for heat tolerance traits. However, gains in heat tolerance are limited by the often narrow genetic diversity. Exploration and use of wild relatives and landraces in breeding can increase useful genetic diversity in current crops. Due to the complex nature of plant heat tolerance and its immediate global concern, it is essential to face this breeding challenge in a multidisciplinary holistic approach involving governmental agencies, private companies and academic institutions.

Combining ability studies for heat tolerance traits in bread wheat [Triticum aestivum (L.) em. Thell

A set of 28 hybrids were developed involving eight diverse parents (HD 2687, DBW 17, PBW 373 ,Raj 3765, Raj 3077, Raj 4037, Raj 4083and RKA 501) by using diallel mating system without reciprocals. The 28 F 1 ’s and 8 parents were grown in Randomized Block Design with two replications during rabi 2008-09. Analysis of variance revealed that variance due to genotypes, parents, parents vs . crosses and crosses were highly significant and significant for all the traits studied. Significant mean squares due to general combining ability and specific combining ability in pooled analysis revealed significance of both additive and dominance gene effects in inheritance of all the heat tolerance traits in wheat. The low predictability ratio revealed that all the characters studied were predominantly controlled by non- additive genes action. The present study has identified desirable parents RKA 501, PBW 373, Raj 3077, Raj 3765 and HD 2687 for most of the heat tolerant parameters. The importance of additive but mainly non-additive gene action is highlighted. Improvement in heat injury and other heat tolerant parameters should be possible by resorting to biparental mating followed by recurrent selection or by diallel selective mating.

Dissection of heat tolerance mechanism in tropical maize

Identification of diverse inbred lines and selection of heat tolerant genotypes based on key secondary traits that influence the grain yield is of great importance. In the present study, correlation coefficient and path analysis were used to identify potential traits for heat tolerance. The results on correlation studies revealed that grain yield per plant had positive relationship with number of kernels per cob (0.833), shelling percentage (0.592), chlorophyll content (0.575), plant height, ear height, 100-seed weight, pollen shed duration and cob length. The traits like days to 50% tasseling (−0.383), days to 50% silking (−0.382), anthesis silk interval (−0.381), senescence and cell injury (%) were negatively associated with grain yield. Further, path analysis showed that the number of kernels per cob had highest positive direct (0.6689) and indirect effect via chlorophyll content and days to 50% tasseling on grain yield followed by shelling percentage through number of kernels per cob, days to 50% tasseling and chlorophyll content. Cluster analysis based on phenotypic data showed presence of three main groups. The first group (GI) consisted of four inbred lines (5.1%) which were superior to mean of 75 inbred lines in respect of all the traits. The selection of genotypes based on number of kernels per cob, anthesis silk interval, shelling percentage, chlorophyll content, plant height and ear height will indirectly increase the maize yield under heat stress.

Characterization of wheat genotypes using morpho- physiological traits for heat tolerance

Constant or transitory high temperatures affect plant growth and development inducing diverse morphological and physiological changes in plants which ultimately causes yield decrease. The traits like relative injury (RI%), chlorophyll content, canopy temperature depression (CTD), heat susceptibility index (HSI), 1000-kernel weight (TKW), grain filling duration (GFD) were used in present study to assess the capability of plants to tolerate heat stress. The study revealed that the evaluated wheat genotypes showed variable degree of tolerance against heat for different traits. On the basis of morpho-physiological traits such as RI, chlorophyll content at 15 days after anthesis (DAA), CTD at 15 DAA, HSI, TKW, GFD, genotypes HD2329 x HD2967 (19.2%), WH1021 (−21.7%), JOB666 X WH1105 (−37.5%), WH1124 X HD2967 (0.55), HD2891 (2.1%) and WAXWING X HD2967 (−2.15%) were identified as the most heat tolerant genotypes for respective characters. For grain yield out of 54 wheat genotypes, DBW90, HD2329, UP2843 × HD2967, WH1124 × HD3059, WH1124 × HD2967, MACS6272 × WH1105, MACS6272 × HD2967, HD2891 × WH1105 and UP2338 were classified as heat tolerant.

Single nucleotide polymorphisms in Heat Shock Protein (HSP) 90AA1 gene and their association with heat tolerance traits in Sahiwal cows

Heat Shock Proteins (HSPs) are group of proteins which are synthesized during heat stress. HSP genes have been reported to be associated with heat tolerance and production performance in cattle. HSP90AA1 gene has been mapped on Bos taurus autosome 21 (BTA 21) and spans nearly 5368 bp comprising 11 exons out of which first exon does not translate. The present study was carried out in Sahiwal cows (n=100) with the objectives to identify SNPs in targeted regions (exon 3, 7, 8 &amp; 11) of HSP90AA1 gene and to analyze their association with heat tolerance traits in Sahiwal cows. Respiration rate (RR) and rectal temperature (RT) was recorded once during probable extreme hours in winter, spring and summer season. Further, heat tolerance coefficient (HTC) also calculated to see the adaptability of the animals during the period of heat stress. On the basis of comparative sequence analysis, total five SNPs were revealed at position of A1209G, A3292C, T4935C, T5218C and A5224C in the targeted region of HSP90AA1 gene. Out of these, only two SNPs at A1209G and A3292C loci were found significantly associated with heat tolerance traits in Sahiwal cows. Whereas, THI has a highly significant associated with RR, RT and HTC in all the seasons. At A1209G locus in Sahiwal cows for traits RR, genotype AA (18.40±0.46a), AG (19.60±0.85b) and GG (21.18± 0.64ab) and trait HTC AA (1.78±0.04a), AG (1.85±0.03b) and GG (1.91± 0.02c) differ significantly (p&lt;0.01) while trait RT, AG (38.32±0.10b) and GG (38.27±0.08ab) didn’t differ significantly. For a locus A3292C for traits RR, genotype AA (21.55±1.01a), AC (19.66±1.59b) and CC (18.40±1.03c) differ significantly (p&lt;0.05), while traits RT, genotype AA (38.41±0.12), AC (38.28±0.20) and CC (37.96±0.15) didn’t differ significantly. For trait HTC, AA (1.93±0.04a), AC (1.85±0.06b) and CC (1.79±0.05c) found significantly (p&lt;0.05) differ with each other. Our study indicated that Sahiwal cows of AA and AC genotype had better thermo-tolerance capacity, which had been useful for genetic improvement of Sahiwal cattle for heat tolerance traits.

Growth and photosynthesis of Upland and Pima cotton: response to drought and heat stress

The effects of drought and heat stress on physiology of two common cotton species, Gossypium hirsutum L. (Upland) and G. barbadense L. (Pima) were investigated in this study. Four consecutive 28-day pot experiments were carried out in a fully controlled growth chamber under four temperatures (25, 30, 35 and 40°C), while two water treatments (well-watered and drought) were imposed for 10 days to both cotton species. Growth according to dry matter accumulation of G. barbadense was more limited by sole drought conditions (50%), whereas heat stress was more remarkable on growth of G. hirsutum (64%). Chlorophyll (Chl) a and b content were more temperature-sensitive in G. hirsutum than G. barbadense under well-watered conditions. The most noticeable decrease in droughtinduced rates of photosynthesis rate (P n ), transpiration rate (E) and stomatal conductance (g s ) were recorded under 35°C, although genotypic variation was found under 25°C. Higher water use efficiency was associated with higher temperature. Relative decrease in Chl a content, g s and maximal quantum efficiency of PSII exhibited by both spe cies were distinctive physiological traits for heat and drought tolerance.

Novel SNPs in HSPB8 gene and their association with heat tolerance traits in Sahiwal indigenous cattle.

Heat shock proteins (HSPs) are expressed in response to heat stress, and the polymorphism in HSP genes at single-nucleotide level has been reported to be associated with heat tolerance and production performance traits in cattle. HSPB8 gene has been mapped on Bos taurus autosome 17 (BTA-17) spanning nearly 13,252 bp and comprising three exons and two introns. The present study was conducted in Sahiwal cows (n = 108) reared in subtropical climate with the objectives to identify SNPs in all three exons and part of intron 1 of HSPB8 gene and to analyze their association with heat tolerance traits in Sahiwal cows. Respiration rate (RR) and rectal temperature (RT) were recorded once during probable extreme hours in different seasons or Temperature-Humidity Index (THI), i.e., winter, spring, and summer. Heat tolerance coefficient (HTC) was also calculated to check the adaptability of the animals during the period of heat stress. The comparative sequence analysis revealed a total two single-nucleotide polymorphisms (SNPs), i.e., g.507G>A in exon 1 and g.881T>C in intron 1 of HSPB8 gene. Out of these two identified SNPs, only one SNP, i.e., g.507G>A, was found to be significantly associated with heat tolerance indicator traits (RR, RT, and HTC) in Sahiwal cows. The perusal of results across different seasons showed the significant (P < 0.01) difference in RR, RT, and HTC between winter, spring, and summer seasons. RR, RT, and HTC were found to be significantly lower (P < 0.01) in GA as compared to GG genotype of g.507G>A SNP of HSPB8 gene. However, in case of another SNP, i.e., g.881T>C, located on intron 1, the RR, RT, and HTC were having non-significant association with the different genotypes, i.e., TT and TC. These findings may partly suggest that GA genotype of SNP g.507G>A of HSPB8 gene has a probable role in heat tolerance in Sahiwal cattle and can therefore be utilized as a marker in propagation of thermo-tolerance cattle in hot tropical and subtropical climate. Nevertheless, the involvement of other regulatory mechanisms cannot be overruled.

Evaluate of SSRs for Heat Tolerance using Korean Major Wheat Cultivars and Heat Resistant Turkey Resources

High temperature is one of major environmental stress. Heat tolerance managing is difficult through the phenotypic selection, so marker assistant selection (MAS) using molecular markers like as RAPD, SSR etc. was tried to select useful traits for heat tolerance. Fourteen SSR markers reported by previous research were selected for this research. We tried to evaluate 14 SSR markers for MAS using 31 useful wheat resources including 24 crossing line from Turkey, six Korean wheat cultivars and Chinese spring. The average of the number of alleles and PIC values in this study were 6.14 and 0.64, respectively. Two major clades and four sub clades were grouped by phylogenetic tree using UPGMA. Four Korean wheat cultivars were distinct from other Turkey resources in the phylogenetic dendrogram. From the results, we expected that these markers were able to adapt to screening wheat genotyping for heat tolerance.

Novel SNPs in ATP1B2 Gene and their Association with Heat Tolerance Indicator Traits in Sahiwal Cattle

Heat Shock Proteins (HSPs) are expressed in response to heat stress and the polymorphism in HSP genes at single nucleotide level is reported to be associated with heat tolerance and production performance traits in cattle. ATP1B2 gene was mapped to Bos taurus autosome 19 (BTA 19) spanning nearly 4310bp, comprising 7 Exons and 6 Introns. The present study was conducted in Sahiwal cows (n=108) raised under sub-tropical climate with the objectives to identify SNPs in targeted regions (Intron 2,4 and Exon 3,5) of ATP1B2 gene and to analyze their association with heat tolerance traits in Sahiwal cows. Respiration rate (RR) and rectal temperature (RT) were recorded during probable extreme hours in winter, spring and summer seasons. Heat tolerance coefficient (HTC) was also calculated to check the adaptability of the animals during the period of heat stress. The comparative sequence analysis revealed a total of two SNPs in Intron 2 of ATP1B2 gene i.e. g.2243G&gt;A and g.2366T&gt;C. Out of these two identified SNPs, only one SNP i.e. g.2243G&gt;A was found to be significantly (PC, RR, RT and HTC were having non-significant association with the different genotypes i.e. TT and TC. These findings may partly suggest that AA and GA genotype of SNP g.2243G&gt;A of ATP1B2 gene can be utilized as potential marker for propagating thermo-tolerant cattle.

Genetic polymorphisms within exon 3 of heat shock protein 90AA1 gene and its association with heat tolerance traits in Sahiwal cows.

Aim:The present study was undertaken to identify novel single nucleotide polymorphism (SNP) in Exon 3 of HSP90AA1 gene and to analyze their association with respiration rate (RR) and rectal temperature (RT) in Sahiwal cows.Materials and Methods:The present study was carried out in Sahiwal cows (n=100) with the objectives to identify novel SNP in exon 3 of HSP90AA1 gene and to explore the association with heat tolerance traits. CLUSTAL-W multiple sequence analysis was used to identify novel SNPs in exon 3 of HSP90AA1 gene in Sahiwal cows. Gene and genotype frequencies of different genotypes were estimated by standard procedure POPGENE version 1.32 (University of Alberta, Canada). The significant effect of SNP variants on physiological parameters, e.g. RR and RT were analyzed using the General Linear model procedure of SAS Version 9.2.Results:The polymerase chain reaction product with the amplicon size of 450 bp was successfully amplified, covering exon 3 region of HSP90AA1 gene in Sahiwal cows. On the basis of comparative sequence analysis of Sahiwal samples (n=100), transitional mutations were detected at locus A1209G as compared to Bos taurus (NCBI GenBank AC_000178.1). After chromatogram analysis, three genotypes AA, AG, and GG with respective frequencies of 0.23, 0.50, and 0.27 ascertained. RR and RT were recorded once during probable extreme hours in winter, spring, and summer seasons. It was revealed that significant difference (p<0.01) among genetic variants of HSP90AA1 gene with heat tolerance trait was found in Sahiwal cattle. The homozygotic animals with AA genotype had lower heat tolerance coefficient (HTC) (1.78±0.04a), as compared to both AG and GG genotypes (1.85±0.03b and 1.91±0.02c), respectively. The gene and genotype frequencies for the locus A1209G were ascertained.Conclusions:Novel SNP was found at the A1209G position showed all possible three genotypes (homozygous and heterozygous). Temperature humidity index has a highly significant association with RR, RT, and HTC in all the seasons. Perusal of results across different seasons showed the significant (p<0.01) difference in RR, RT, and HTC among winter, spring, and summer seasons. Genetic association with heat tolerance traits reveals their importance as a potential genetic marker for heat tolerance traits in Sahiwal cows.

Screening and validation of tomato genotypes under heat stress using Fv/Fm to reveal the physiological mechanism of heat tolerance

Cultivation of tomatoes at high temperatures negatively affects growth and yield. Our aim was to screen tomato genotypes under heat stress for differences in the maximum quantum efficiency of photosystem II (Fv/Fm) and uncover the physiological traits for heat tolerance in a three-step process. Initially, 67 tomato genotypes were ranked according to Fv/Fm. Two genotypes with higher Fv/Fm (heat-tolerant group) and two genotypes with lower Fv/Fm (heat-sensitive group) were selected from the initial screening. Second, the physiological responses of the four genotypes to seven days of heat stress (36/28°C) were analyzed in detail. Third, pollen germination and fruit set of the four genotypes were investigated at high temperature conditions in the field. The results showed that the heat-tolerant group maintained higher leaf pigment content and higher total phenolic content (TPC) than the heat-sensitive group under heat stress. The heat-tolerant group maintained unaltered stomata and pore area and net photosynthesis rate (PN) but increased stomatal conductance (gs) under heat stress compared with the control. Chloroplasts in the heat-tolerant group maintained a normal shape, whereas the chloroplasts in the heat-sensitive group became swollen with decomposed starch grain after heat stress. The heat-tolerant group exhibited a higher pollen germination rate (%), longer pollen tube length and higher fruit set rate compared with the heat-sensitive group at high temperatures in the field. Thus, we concluded that Fv/Fm is an early indicator of heat stress tolerance and that the responses of tomatoes to heat stress were identical in widely different growing conditions. The stay-green trait, improved ability of stomata regulation and higher contents of reactive oxygen species scavengers seemed to be part of the protective mechanisms in heat-tolerant tomatoes.