Measure Of Heat Tolerance Research Articles

Genes and models for estimating genetic parameters for heat tolerance in dairy cattle.

Dairy cattle are highly susceptible to heat stress. Heat stress causes a decline in milk yield, reduced dry matter intake, reduced fertility rates, and alteration of physiological traits (e.g., respiration rate, rectal temperature, heart rates, pulse rates, panting score, sweating rates, and drooling score) and other biomarkers (oxidative heat stress biomarkers and stress response genes). Considering the significant effect of global warming on dairy cattle farming, coupled with the aim to reduce income losses of dairy cattle farmers and improve production under hot environment, there is a need to develop heat tolerant dairy cattle that can grow, reproduce and produce milk reasonably under the changing global climate and increasing temperature. The identification of heat tolerant dairy cattle is an alternative strategy for breeding thermotolerant dairy cattle for changing climatic conditions. This review synthesizes information pertaining to quantitative genetic models that have been applied to estimate genetic parameters for heat tolerance and relationship between measures of heat tolerance and production and reproductive performance traits in dairy cattle. Moreover, the review identified the genes that have been shown to influence heat tolerance in dairy cattle and evaluated the possibility of using them in genomic selection programmes. Combining genomics information with environmental, physiological, and production parameters information is a crucial strategy to understand the mechanisms of heat tolerance while breeding heat tolerant dairy cattle adapted to future climatic conditions. Thus, selection for thermotolerant dairy cattle is feasible.

Impact of hot weather on animal performance and genetic strategies to minimise the effect

Dairy cows in Australia and New Zealand are generally kept outdoors, making them susceptible to weather variability and in particular heat stress. In this paper, we review (1) exploiting genetic variability to improve heat tolerance, (2) genotype by environment interactions, i.e. suitability of high merit cows to weather variability and (3) how novel phenotyping and genomics can help improve heat tolerance. Selection for heat tolerance is a permanent and cumulative strategy and especially useful in grazing situations where management practices, such as cooling mechanisms, are sometimes impractical. Australia was the first country in the world to release breeding values for heat tolerance in dairy cattle nationally in 2017. The breeding value captures genetic variation in the reduction of milk production traits with rising temperature and humidity. The breeding values have been validated in independent studies (in Victoria, Australia, and California, USA), showing that thermotolerant cows maintain a lower core body temperature under hot and humid conditions. Genotype by environment interactions for traits sensitive to heat is only a concern for farms in very extreme conditions and therefore affect only a small proportion of individuals (those in the extreme 5th percentile). Heat tolerance is a complex trait in that in addition to milk traits, health and fertility may also be affected. Next-generation heat tolerance breeding values may include sensor device information in addition to changes in milk composition, or other measurable biomarkers. This is especially useful when measured in genotyped female populations. Research into novel ways of measuring heat tolerance could transform the way we select for this trait and capture more of the complexity of this trait. To be successful in this area, multi-disciplinary collaboration among animal scientists is likely to facilitate this goal. Combining genomics, traditional and novel measures of heat tolerance with intermediate metabolic biomarkers and prioritised genetic variants could be a way to capture the complexity of thermotolerance in future heat tolerance breeding values. Finally, selecting cows that are resilient to variability in weather is feasible and heat tolerance is a good example of this.

Temporal specific coevolution of Hsp70 and co-chaperone stv expression in Drosophila melanogaster under selection for heat tolerance.

Heat shock proteins (Hsps) have long been candidates for ecological adaptation given their unequivocal role in mitigating cell damage from heat stress, but linking Hsps to heat tolerance has proven difficult given the complexity of thermal adaptation. Experimental evolution has been utilized to examine direct and correlated responses to selection for increased heat tolerance in Drosophila, often focusing on the major Hsp family Hsp70 and/or the master regulator HSF as a selection response, but rarely on other aspects of the heat shock complex. We examined Hsp70 and co-chaperone stv isoform transcript expression in Australian D. melanogaster lines selected for static heat tolerance, and observed a temporal and stv isoform specific, coordinated transcriptional selection response with Hsp70, suggesting that increased chaperone output accompanied increased heat tolerance. We hypothesize that the coordinated evolutionary response of Hsp70 and stv may have arisen as a correlated response resulting from a shared regulatory hierarchy. Our work highlights the complexity and specificity of the heat shock response in D. melanogaster. The selected lines examined also showed correlated responses for other measures of heat tolerance, and the coevolution of Hsp70 and stv provide new avenues to examine the common mechanisms underpinning direct and correlated phenotypic responses to selection for heat tolerance.

Use of multiple stress indices as a measure of heat tolerance in wheat accessions

Wheat is a crop of global significance, grown in diversified environments. Heat stress affects a number of morpho-physiological traits in crops including wheat. A set of 40 wheat accessions along with four checks were screened for heat tolerance based on various stress indices. The present study was undertaken during rabi 2018-19 in randomized block design having three replications at CCS Haryana Agricultural University, Hisar under two dates of sowing i.e. 24 th November and 24 th December . Significant variance was observed among genotypes based on HSI of all the traits except plant height and spike length. Based on HSI and TOL, the accessions DT 126, DT 46, DT 142, DT 102 and DT 124 were found to be most tolerant to heat stress, whereas on the basis of HRI, HTI, MP and GMP, the promising accessions identified were DT 116, DT 101, DT 181, WH 1124, HD 3059 and DT190. The accessions identified as heat tolerant would form an important resource for the development of high yielding varieties under heat stress condition. Correlation coefficients based on HSI of different traits revealed significant positive association of grain yield per plant with biological yield per plant, harvest index, NDVI 1, tillers per plant and 1000 grain weight, denoting that these traits can be used effectively, for selection of heat tolerant genotypes. Grain yield was found to be positively correlated with the indices viz ., HRI, HTI, MP and GMP while, negatively with HSI and TOL under stress condition. The stress indices used under study were recognized as paramount for identifying cultivars with high tolerance to heat stress.

Cell Membrane Stability as a Measure of Heat Tolerance in Hexaploid and Tetraploid Wheat

A comparison was made of the physiological and morphological differences between Inqlab-91 (hexaploid) and Langdon (tetralpoid) wheat genotypes in response to high temperature stress applied at third leaf stage of growth. Electrolytes leakage technique was used to detect differences in the heat sensitivities of leaves of Inqlab-91 and Langdon. This method showed that at both 35 or 40°C Inqlab-91 was more heat tolerant than Langdon.

Putative Markers associated with Grain weight under Terminal Heat Stress in Bread-Wheat (Triticum aestivum L.)

Terminal heat tolerance is an important breeding target in wheat. Methods of selection for heat tolerance in wheat are limited. The most common approach is the evaluation of yield in nurseries grown under heat stress. The objective of this study was to estimate inheritance of heat tolerance and the grain character in bread wheat by combining molecular marker analysis. The tolerance in bread wheat using a cross between genotypes that were identified previously were utilized to identify SSR markers that are linked to traits associated with terminal heat tolerance. Grain wt. was used as a measure of heat tolerance because this trait was highly correlated with tolerance levels of genotypes. Genotypes WH730 and RAJ4014 were used as tolerant and sensitive parents respectively for generating mapping populations against the study of terminal heat stress respectively. A Recombinant Inbred Line (RIL) mapping population derived from the heat sensitive genotype RAJ4014 and heat tolerant genotype WH730 was evaluated for the heat stress over two years in a replicated trial under timely sown (TS) and late sown (LS) field conditions. The parental lines were screened with approximately 300 SSR (μsatellite) markers out of which about 20% showed polymorphism. Parents and their Recombinant inbred lines (RILs) screened by microsatellite markers for finding allelic variation. Xgwm48, Xgwm55 and Xcfd29 are three markers suggested an application of marker-assisted selection for wheat improvement under terminal heat tolerance.

Physiological thermal limits predict differential responses of bees to urban heat-island effects.

Changes in community composition are an important, but hard to predict, effect of climate change. Here, we use a wild-bee study system to test the ability of critical thermal maxima (CTmax, a measure of heat tolerance) to predict community responses to urban heat-island effects in Raleigh, NC, USA. Among 15 focal species, CTmax ranged from 44.6 to 51.3°C, and was strongly predictive of population responses to urban warming across 18 study sites (r2 = 0.44). Species with low CTmax declined the most. After phylogenetic correction, solitary species and cavity-nesting species (bumblebees) had the lowest CTmax, suggesting that these groups may be most sensitive to climate change. Community responses to urban and global warming will likely retain strong physiological signal, even after decades of warming during which time lags and interspecific interactions could modulate direct effects of temperature.

GENETIC VARIATION IN RELATIVE CELL INJURY FOR BREEDING UPLAND COTTON UNDER HIGH TEMPERATURE STRESS

The objective of present study was to examine the presence of variation in relative cell injury percentage (RCI%), as a measure of heat tolerance in sample of G. hirsutum germplasm and also to investigate genetic basis, if any, of RCI% under heat stress. For this purpose, response of 70 cotton varieties/lines was studies to optimum and high temperature, and RCI% was measured at reproductive stage. Data showed differing responses of the germplasm to the two temperature regimes. On the basis of similarities MNH 552, FH 100 and NIAB 111 were screened out as tolerant whilst Cedix ST-362 (GL), LRA 5166 and 4F were identified as susceptible varieties. Three sets of crosses involving tolerant × susceptible varieties were made according to generation mean technique. Six generations of each cross was field planted under optimum and high temperature and at reproductive stage RCI% was again measured. Genetic analysis of the data showed the predominant effect of additive component in the inheritance of RCI% under both the temperature regimes and consequently estimates of h2ns were high in three crosses. These estimates were used to calculate response to selection in F3 population that appear to be encouraging. The results of present investigation suggest that RCI% could be used as effective selection criteria for selecting the plants with lower value of RCI%.

Multivariate analysis of adaptive capacity for upper thermal limits in Drosophila simulans

Thermal tolerance is an important factor influencing the distribution of ectotherms, but our understanding of the ability of species to evolve different thermal limits is limited. Based on univariate measures of adaptive capacity, it has recently been suggested that species may have limited evolutionary potential to extend their upper thermal limits under ramping temperature conditions that better reflect heat stress in nature. To test these findings more broadly, we used a paternal half-sibling breeding design to estimate the multivariate evolutionary potential for upper thermal limits in Drosophila simulans. We assessed heat tolerance using static (basal and hardened) and ramping assays. Our analyses revealed significant evolutionary potential for all three measures of heat tolerance. Additive genetic variances were significantly different from zero for all three traits. Our G matrix analysis revealed that all three traits would contribute to a response to selection for increased heat tolerance. Significant additive genetic covariances and additive genetic correlations between static basal and hardened heat-knockdown time, marginally nonsignificant between static basal and ramping heat-knockdown time, indicate that direct and correlated responses to selection for increased upper thermal limits are possible. Thus, combinations of all three traits will contribute to the evolution of upper thermal limits in response to selection imposed by a warming climate. Reliance on univariate estimates of evolutionary potential may not provide accurate insight into the ability of organisms to evolve upper thermal limits in nature.

Estimation of genetic parameters for morpho-physiological traits under terminal heat tolerance in bread wheat (Triticum aestivumL.)

Winter wheat is adversely impacted by the effects of high temperature stress in many wheat-producing areas. Increasing productivity under heat stress conditions requires the development of high temperature-tolerant wheat cultivars. The identification and measurement of traits conferring high temperature tolerance and an understanding of genetic variability and gene regulation of these traits are essential for the development of high temperature-tolerant germplasm. Understanding the genetic basis of tolerance to high temperature is important for improving the productivity of wheat (Triticum aestivum L.) in regions where the stress occurs. The objective of this study was to estimate the genetic parameters for morpho-physiological characters viz. number of days to heading, days to maturity, tillers/plant, grain number, 1000 grain weight, grain yield, membrane stability and chlorophyll stability index under terminal heat stress which was created by delayed sowing of the crop. Four cultivars, DBW 16, Hindi 62 (heat-tolerant) and WH147, WH711 (heat-susceptible), were crossed as WH147 × DBW 16 and Hindi 62 × WH711 to produce F1, F2, and F3 populations, and their grain-filling duration (GFD) at 35 ° C day was determined as a measure of heat tolerance. Results indicated that significant variations were observed among different F 2 plant of both wheat crosses in respect of all yield attributes under heat stress environment. The SSR marker analysis was applied for the screening of the four parents for the polymorphism under stress condition. Products from 25 primer pairs among 50 simple sequence repeat (SSR) pairs were polymorphic between the parents. The polymorphic markers will be subjected for the genetic analysis of F 2 and F 3 population of the respective crosses under study.

Thermostability of Cell Membranes as a Measure of Heat Tolerance and Relationship to Flowering Delay in Chrysanthemum

Identification of heat-tolerant chrysanthemum [Dendranthema ×grandifolia (Ramat.) Kitamura] genotypes for commercial production in hot areas of the world is desirable. The extent to which electrolyte leakage from chrysanthemum leaf discs, measured using a test for cell membrane thermostability (CMT), could be related to the delay in flowering induced by heat in the field-grown plants was determined. The relationship between the relative injury (RI) occurring in leaf tissue discs of chrysanthemum cultivars and treatment temperature was sigmoidal. A single temperature treatment at 50 °C resulted in injury values near the midpoint of the sigmoidal response curve and showed the greatest sensitivity in detecting genotypic differences in heat tolerance. The cultivars with a low RI value are those with the greater CMT and shorter heat-induced delay to flowering.

Thermal tolerance trade-offs associated with the right arm of chromosome 3 and marked by the hsr-omega gene in Drosophila melanogaster.

Drosophila melanogaster occurs in diverse climatic regions and shows opposing clinal changes in resistance to heat and resistance to cold along a 3000 km latitudinal transect on the eastern coast of Australia. We report here on variation at a polymorphic 8 bp-indel site in the heat shock hsr-omega gene that maps to the right arm of chromosome 3. The frequency of the genetic element marked by the L form of the gene was strongly and positively associated with latitude along this transect, and latitudinal differences in L frequency were robustly associated with latitudinal differences in maximum temperature for the hottest month. On a genetic background mixed for genes from each end of the cline a set of 10 lines was derived, five of which were fixed for the L marker, the absence of In(3R)P and 12 kb of repeats at a second polymorphic site at the 3' end of hsr-omega, and five that were fixed for the S marker, In(3R)P and 15 kb of hsr-omega repeats. For two different measures of heat tolerance S lines outperformed L lines, and for two different measures of cold tolerance L lines outperformed S lines. These data suggest that an element on the right arm of chromosome 3, possibly In(3R)P, confers heat resistance but carries the trade-off of also conferring susceptibility to cold. This element occurs at high frequency near the equator. The alternate element on the other hand, at high frequency at temperate latitudes, confers cold resistance at the cost of heat susceptibility.

Quantitative and molecular characterization of heat tolerance in hexaploid wheat

Understanding the genetic basis of tolerance to high temperature is important for improving the productivity of wheat (Triticum aestivum L.) in regions where the stress occurs. The objective of this study was to estimate inheritance of heat tolerance and the minimum number of genes for the trait in bread wheat by combining quantitative genetic estimates and molecular marker analyses. Two cultivars, Ventnor (heat-tolerant) and Karl92 (heat-susceptible), were crossed to produce F1, F2, and F3populations, and their grain-filling duration (GFD) at 30/25 °C 16/8 h day/night was determined as a measure of heat tolerance. Distribution of GFD in the F1 and F2 populations followed the normal model (χ2, p > 0.10). A minimum of 1.4 genes with both additive and dominance effects, broad-sense heritability of 80%, and realized heritability of 96%for GFD were determined from F2 and F3 populations. Products from 59primer pairs among 232 simple sequence repeat (SSR) pairs were polymorphic between the parents. Two markers, Xgwm11 andXgwm293, were linked to GFD by quantitative trait loci (QTL) analysis of the F2 population. The Xgwm11-linked QTL had only additive gene action and contributed 11% to the total phenotypic variation in GFD in the F2population, whereas the Xgwm293-linked QTL had both additive and dominance action and contributed 12% to the total variation in GFD. The results demonstrated that heat tolerance of common wheat is controlled by multiple genes and suggested that marker-assisted selection with microsatellite primers might be useful for developing improved cultivars.

Influence of Prestress Environment on Annual Bluegrass Heat Tolerance1

Annual bluegrass (Poa annua L.) turf quality is reduced during periods of high temperature. To predict heat stress injury and develop improved prestress maintenance practices, an understanding of the seasonal variation in annual bluegrass heat tolerance and the influence of soil moisture on heat tolerance is crucial. Annual bluegrass growing in the field on a Drummer silty clay loam (fine silty, mixed, mesic Typic Haplaquolls) was sampled on 23 dates over two growing seasons and brought to a laboratory for exposure to high temperature. Prestress environmental conditions (air and soil temperature, soil matric potential, plant water potential, daylength, rainfall and irrigation) were monitored. Plants were enclosed in plastic bags, exposed for 30 min to temperatures in the range 40 to 48°C in a water bath and placed in a greenhouse for a 2‐week recovery period. The dry weight of the stressed plants expressed as a percentage of the controls (heat tolerance indices, HTI) was used as a measure of heat tolerance. In a second experiment, field plots of annual bluegrass were maintained for one growing season under either a dry (rainfall plus irrigation to prevent severe wilting) or moist (dry treatment plus 10‐mm irrigation every other day) soil regime. Plants were stress‐tested on five dates when differences in soil matric potentials existed between treatments, and on five dates when matric potentials were identical (saturated soil). Turfgrass color, quality, and rooting depth were monitored. The best equation fitted to HTI using the results of the first experiment was: y = 15.6 ✕ A + 9.85 ✕ B − 0.22 ✕ A2 − 0.31 ✕ B2 − 0.25 ✕ A ✕ B ✕ 194.71 (R2 = 0.78, p = 0.0001), where A = mean maximum daily air temperature (°C) for the 2 days preceding sampling and B = mean total precipitation (mm) of the period 2 through 4 days prior to sampling. The second experiment revealed a nonsignificant trend for annual bluegrass maintained under moist soil conditions to be less heat tolerant than that under dry conditions. No differences were found due to treatment in rooting depth which negatively correlated (r = −0.83) with the soil temperature at 10 cm. Because of reduced turfgrass quality with the dry soil conditions, there appeared to be little potential for increasing heat tolerance through irrigation management.