Crop Heat Stress Research Articles

The cost of mismanaging crop heat stress with irrigation: Evidence from the mid-south USA

Field level data from a voluntary water use reporting program in the Delta region of Mississippi (MS), USA, provides empirical evidence that crop growers increase the amount of groundwater pumped for irrigation during periods of high temperature (degree days above 32 C). Regression analysis reveals that growers apply excess irrigation to cope with high temperature conditions while growing season evapotranspiration and precipitation are not significant factors in their decision of how much irrigation to apply. The existing literature indicates that excess water does not alleviate the harmful effect of extreme heat, making the excess irrigation wasteful and costly. Additional degree days above 32 C are associated with a 4.6 mm increase in irrigation depth (46 m3ha−1). This result may be partially explained by the fact that most farmers use visual cues (such as leaf folding which correlate with air temperature) to initiate irrigation events regardless of soil moisture contents. To quantify the impact of this mismatch, we estimate that shifting the underlying sensitivity in the farmers’ minds by 1 C would reduce groundwater pumpage by 800862 mega liters across the Delta region of Mississippi, USA. The monetary cost of mismanaging heat stress with excessive irrigation is estimated at a minimum of over US$33 million per year. We further identify two additional possible distortions affecting the demand for irrigation groundwater: (i) overestimated benefits from irrigation; and (ii) underestimated groundwater pumping cost. The policy implication is that more efforts and incentives should be placed for programs that affect the producers’ water management mindset, such as "Master Irrigator" programs that will reduce or eliminate the identified groundwater distortions and optimize benefits from irrigation.

Object-oriented analysis as a foundation for building climate storylines of compounding short-term drought and crop heat stress

IntroductionCrops are vulnerable to precipitation and heat extremes during late spring through summer.MethodsWe analyzed for a north-central U.S. region short-term drought and agricultural heat stress during April-May-June-July. We used the 4-km Parameter Elevation Regression on Independent Slopes Model (PRISM) for observations, aggregated to a 25-km grid, and two 25-km Regional Climate Model version 4 (RegCM4) simulns used either GFDL- or MPI-GCM boundary conditions. We chose 1981-2000 as our contemporary time period, and 2041-2060 as our scenario time period, which used the Representative Concentration Pathway 8.5 emissions scenario. We used object-oriented analysis to identify events of interest in observations and simulations by identifying objects in a space-time domain that meet specified criteria, such as exceeding a heat-stress temperature threshold. The event diagnosis allowed analysis of compound events, occurring when temperature and drought objects overlap.ResultsIdentified objects yielded events that can undermine agricultural productivity and which are thus relevant to decision makers, making them building blocks for possible climate storylines. The observations and simulations showed similar spatial distributions of event frequencies across the analysis region. However, the simulations attained this distribution by having fewer events that tend to cover larger areas compared to observed events, suggesting that the effective resolution of the simulations was coarser than their 25-km grids. Short-term drought frequency increased and heat-stress frequency decreased in transitioning to the scenario climate. When compounding occurred heat-stress events generally preceded the short-term drought events. The overlapping, compound events tended to be more extreme compared to non-overlapping events of either type.DiscussionThe information yielded projected changes in these agriculturally motivated events. One prominent conditional behavior emerging from the work was that a heat-stress event should be a warning to watch for potential drought, as both could compound each other to more intense levels.

Unveiling climate change impacts on agricultural sustainability: insights from the united states

Climate change poses significant threats to agricultural systems, necessitating a comprehensive understanding of its impact for effective adaptation strategies. This study examines the influence of climate change on agriculture in the United States, primarily focusing on temperature shifts and precipitation variations. Utilizing historical data and climate projections, we analyse trends in mean temperature and precipitation patterns from 1950 to 2020. The results indicate a noteworthy increase in annual mean temperature over the years, attributed to climate change. This rise in temperature has multifaceted implications, including heat stress in crops and exacerbation of drought conditions. The study also explores the complex relationship between precipitation patterns and climate change, highlighting regional variations and potential shifts in future precipitation trends. By projecting data under SSP 1-1.9 emission scenario, we assess potential changes in mean temperatures, hot days, and precipitation for 2040-2059 periods. In conclusion, this study sheds light on the interplay between climate change and agricultural systems, emphasizing the need for adaptive strategies to secure food production and mitigate potential risks. The findings underscore the urgency of proactive measures to safeguard agricultural sustainability and resilience in the face of evolving climatic conditions.

Physiological Response of Tomato and Cucumber Plants to Micro-Spray in High-Temperature Environment: A Scientific and Effective Means of Alleviating Crop Heat Stress

Drought and heat stresses are severe threats to crop production and food security in arid and semi-arid regions of the globe, especially during the summer. This study investigates the effects of micro-spray on micro-climatic and physiological characteristics of cucumber and tomato plants for four growing seasons (two growing seasons each (cucumber: 2017 and 2018 and tomato: 2021 and 2022)). The experiment was conducted in a Venlo-type greenhouse where plants were irrigated with a combined micro-spray and drip irrigation (MSDI) system (1 min for tomato (seven times a day) and 2 mins (four times a day) for cucumber) and drip irrigation (DI). Both plants’ growth and physiological parameters were recorded at the end of the experiment. Moreover, the experimental results showed that plant height and stem diameter increased under MSDI in all seasons. In addition, a micro-spray duration of 2 min decreased the average daily air temperature (Ta) and leaf temperature (T1) by 0.8 °C and 4.9 °C, respectively, and increased the average daily relative humidity (RH) by 4.3%. However, a micro-spray duration of 1 min reduced the average daily Ta and T1 by 0.76 °C and 4.6 °C, respectively, but the increase in RH (2.7%) was much lower than that in the single micro-spray duration of 2 min. In addition, the net leaf photosynthetic rate (Pn), the effective quantum yield of PSII (ΦPSII), and the stomatal conductance (Gs) of both plants increased under MSDI compared with DI. A K-means analysis showed that MSDI could eliminate the adverse effects of sunlight stress on cucumbers and tomatoes. MSDI increased the yield of cucumber and tomato plants by 18.9% and 40.4%, respectively. The fruit weight of cucumber (2017) and tomato (2021) under MSDI did not increase significantly compared to DI, which indicates that MSDI mitigated heat stress, prevented flowers from being burned, and increased the number of fruits. The results also suggested that the total soluble solids in the cucumbers and tomatoes showed no significant differences (p > 0.05) between the two treatments in four seasons. In conclusion, the MSDI system can be an appropriate strategy for the irrigation needs and climate control of plants grown in greenhouses during the hot season.

A Comprehensive Review on Climate Change Adaptation Strategies and Challenges in Agriculture

This review examines the impact of climate change on Indian agriculture and adaptation strategies. Climate change, driven by human activities, poses challenges like rising temperatures and extreme weather events. Rising temperatures can induce heat stress in crops, leading to reduced yields and poor quality produce. Farmers use adaptation measures like altering planting dates and developing climate-resilient crops. Changing rainfall patterns, erratic or insufficient rainfall can trigger drought conditions, parching farmlands and causing crop failures. On the other hand, excessive rainfall can result in flooding, which damages crops and soil, disrupting agricultural operations especially during the monsoon. Soil conservation, precision agriculture, and urban food production initiatives promote food security and resource recycling. Addressing water scarcity requires improved irrigation and efficient water management. Climate change affects agricultural pests population and threatening global food security. Various adaptation strategies, including traditional practices, resource-conservation technologies, and socio-economic interventions, are being implemented. Climate-smart agriculture technologies like precision agriculture increase yields and resilience. Success depends on regional suitability, economic viability, and collective implementation. Agriculture operates within a complex socio-ecological system with uncertainties in policy, economics, and climate. Site-specific climate-smart agriculture practices are crucial for smallholders' resilience and food security. Publicly provided agricultural extension services can help adopt these technologies, but barriers like financial constraints and cultural factors must be considered. This review emphasizes the need for comprehensive, context-specific approaches to address vulnerabilities in Indian agriculture to climate change and ensure a sustainable future for food production and smallholder livelihoods.

Reproductive-Stage Heat Stress in Cereals: Impact, Plant Responses and Strategies for Tolerance Improvement.

Reproductive-stage heat stress (RSHS) poses a major constraint to cereal crop production by damaging main plant reproductive structures and hampering reproductive processes, including pollen and stigma viability, pollination, fertilization, grain setting and grain filling. Despite this well-recognized fact, research on crop heat stress (HS) is relatively recent compared to other abiotic stresses, such as drought and salinity, and in particular, RSHS studies in cereals are considerably few in comparison with seedling-stage and vegetative-stage-centered studies. Meanwhile, climate change-exacerbated HS, independently or synergistically with drought, will have huge implications on crop performance and future global food security. Fortunately, due to their sedentary nature, crop plants have evolved complex and diverse transient and long-term mechanisms to perceive, transduce, respond and adapt to HS at the molecular, cell, physiological and whole plant levels. Therefore, uncovering the molecular and physiological mechanisms governing plant response and tolerance to RSHS facilitates the designing of effective strategies to improve HS tolerance in cereal crops. In this review, we update our understanding of several aspects of RSHS in cereals, particularly impacts on physiological processes and yield; HS signal perception and transduction; and transcriptional regulation by heat shock factors and heat stress-responsive genes. We also discuss the epigenetic, post-translational modification and HS memory mechanisms modulating plant HS tolerance. Moreover, we offer a critical set of strategies (encompassing genomics and plant breeding, transgenesis, omics and agronomy) that could accelerate the development of RSHS-resilient cereal crop cultivars. We underline that a judicious combination of all of these strategies offers the best foot forward in RSHS tolerance improvement in cereals. Further, we highlight critical shortcomings to RSHS tolerance investigations in cereals and propositions for their circumvention, as well as some knowledge gaps, which should guide future research priorities. Overall, our review furthers our understanding of HS tolerance in plants and supports the rational designing of RSHS-tolerant cereal crop cultivars for the warming climate.

Genetic Improvement of Heat Stress Tolerance in Cereal Crops

Crop heat stress is a threat to food supply, with heatwaves expected to increase in frequency and intensity globally. In addition to yield loss, heat stress dramatically reduces fertility and seed-setting rate, grain quality and weight, and seed germination and growth. Genetic variability for heat stress tolerance can be used in breeding programs to develop tolerant genotypes. The availability of genome assemblies with high-confidence sequences for many cereal crops, including rice, maize, wheat and barley, now allows the identification of heat stress tolerance-associated genes and gene networks. This review focuses on synthesizing current advances in understanding the detrimental effects of heat stress on cereal crop production at the physiological and genetic levels. It provides an account of available genomic resources, genetic variation, candidate genes, and molecular markers for heat stress tolerance. Lastly, this review offers insight into crop genetic improvement for heat stress tolerance, including germplasm screening in glasshouse and field trials, marker-assisted selection, mapping genomic loci and identification of candidate genes, and genomic-assisted breeding.

Canopy temperature and heat stress are increased by compound high air temperature and water stress and reduced by irrigation – a modeling analysis

Abstract. Crop yield is reduced by heat and water stress and even more when these conditions co-occur. Yet, compound effects of air temperature and water availability on crop heat stress are poorly quantified. Existing crop models, by relying at least partially on empirical functions, cannot account for the feedbacks of plant traits and response to heat and water stress on canopy temperature. We developed a fully mechanistic model, coupling crop energy and water balances, to determine canopy temperature as a function of plant traits, stochastic environmental conditions, and irrigation applications. While general, the model was parameterized for wheat. Canopy temperature largely followed air temperature under well-watered conditions. But, when soil water potential was more negative than −0.14 MPa, further reductions in soil water availability led to a rapid rise in canopy temperature – up to 10 ∘C warmer than air at soil water potential of −0.62 MPa. More intermittent precipitation led to higher canopy temperatures and longer periods of potentially damaging crop canopy temperatures. Irrigation applications aimed at keeping crops under well-watered conditions could reduce canopy temperature but in most cases were unable to maintain it below the threshold temperature for potential heat damage; the benefits of irrigation in terms of reduction of canopy temperature decreased as average air temperature increased. Hence, irrigation is only a partial solution to adapt to warmer and drier climates.

Novel approaches to mitigate heat stress impacts on crop growth and development

Heat stress is a major constraint to crop production and food security. The incidence of heat stress in crops has increased due to rapid changes in the global climate. Heat stress has a tremendous impact on crop growth and productivity due to its direct and indirect effects on water. Therefore, it is important to understand the morphological, physiological, biochemical, molecular, and ecological basis of heat stress in crop plants to minimize its impact on food production. Several genes alter their expression, proteins, and transcription factors to cope with heat stress. Adverse effects on macromolecules and genes change the signaling pathways for heat stress resistance. In the early phase of heat stress, plants regulate their immunity and plant nutrition management to alleviate the heat stress. All the self management of plants gets fail in severe heat stress situation to overcome from heat stress condition a judicious combination of conventional breeding and new technologies will help plants to cope efficiently with heat stress, including maintaining/enhancing yield to contribute to the nutritional requirements of the growing population. A better understanding of plant responses to heat stress has practical implications for remedies and management.

Assessing the impacts of recent-past climatic constraints on potential wheat yield and adaptation options under Mediterranean climate in southern Portugal

Wheat yield potentials under rainfed Mediterranean conditions have been long limited by late-in-season occurrence of enhanced water deficits and high temperatures, coinciding with sensitive reproductive stages. Present study aims to quantify and separate the impacts of two main abiotic stresses (drought & heat) on potentially attainable wheat yields, in a typical Mediterranean environment of southern Portugal (Alentejo) over 1986—2015. We also evaluate how possible adaptation options could mitigate potential yield losses (reduce the gap between actual and potential yield). Previously calibrated STICS soil-crop model is used for these purposes, which has been satisfactorily evaluated herein for yield simulations using additional field data before running at regional level. By coupling with high-resolution gridded soil and climate datasets, STICS simulations reliably reproduce the inter-annual variability of 30-year regional yield statistics, together with reasonable estimations of experimental potential yields. Therefore, the model is useful to explore the source of yield gap in the region. The quantified impacts, though with some uncertainties, identify the prolonged terminal drought stress as the major cause of yield gap, causing 40–70% mean potential yield losses. In contrast, a short-duration of crop heat stress (≥38 °C) during late grain-filling phase only results in small-to-moderate reductions (up to 20%). Supplemental Irrigation (SI) during reproductive stages provides good adaptive gains to recover potential yield losses by 15–30%, while the proposed early-flowering cultivar is more useful in escaping the terminal heat stress (5–15% adaptive gains) than avoiding prolonged drought stress. In addition, advancing sowing date generally favours wheat production with a robust spatial-temporal pattern. Therefore, combined options based on application of SI, using balanced early-flowering cultivar and early sowing date, may contribute to considerably reduce local yield gap, where current yields can account for 60% of potential yields (26–32% without adaptation). Regional impact assessment and adaptation modelling studies are essential to support agricultural policy development under climate change and variability. The recommended combined adaptation may also represent a promising adaptation strategy for rainfed wheat cropping system in other regions with similar Mediterranean conditions. However, the existing spatial-temporal variability of adaptation response highlights the need to address adaptation strategies at a more detailed local scale with better flexible design.

Quantifying irrigation cooling benefits to maize yield in the US Midwest.

Irrigation is an important adaptation strategy to improve crop resilience to global climate change. Irrigation plays an essential role in sustaining crop production in water-limited regions, as irrigation water not only benefits crops through fulfilling crops' water demand but also creates an evaporative cooling that mitigates crop heat stress. Here we use satellite remote sensing and maize yield data in the state of Nebraska, USA, combined with statistical models, to quantify the contribution of cooling and water supply to the yield benefits due to irrigation. Results show that irrigation leads to a considerable cooling on daytime land surface temperature (-1.63°C in July), an increase in enhanced vegetation index (+0.10 in July), and 81% higher maize yields compared to rainfed maize. These irrigation effects vary along the spatial and temporal gradients of precipitation and temperature, with a greater effect in dry and hot conditions, and decline toward wet and cool conditions. We find that 16% of irrigation yield increase is due to irrigation cooling, while the rest (84%) is due to water supply and other factors. The irrigation cooling effect is also observed on air temperature (-0.38 to -0.53°C) from paired flux sites in Nebraska. This study highlights the non-negligible contribution of irrigation cooling to the yield benefits of irrigation, and such an effect may become more important in the future with continued warming and more frequent droughts.

Molecular and genetic bases of heat stress responses in crop plants and breeding for increased resilience and productivity.

To ensure the food security of future generations and to address the challenge of the 'no hunger zone' proposed by the FAO (Food and Agriculture Organization), crop production must be doubled by 2050, but environmental stresses are counteracting this goal. Heat stress in particular is affecting agricultural crops more frequently and more severely. Since the discovery of the physiological, molecular, and genetic bases of heat stress responses, cultivated plants have become the subject of intense research on how they may avoid or tolerate heat stress by either using natural genetic variation or creating new variation with DNA technologies, mutational breeding, or genome editing. This review reports current understanding of the genetic and molecular bases of heat stress in crops together with recent approaches to creating heat-tolerant varieties. Research is close to a breakthrough of global relevance, breeding plants fitter to face the biggest challenge of our time.

English

English

Unravelling efficient applications of agriculturally important microorganisms for alleviation of induced inter-cellular oxidative stress in crops

Abiotic stresses like high temperature, cold, freezing, drought, salinity, flooding or oxidizing agents cause significant loss in the crop yield and quality. Abiotic stresses cause reactive oxygen species (ROS) production such as singlet oxygen (1O2), hydrogen peroxide (H2O2), superoxide radical (O2•−), hydroxyl radical (OH-), etc., that leads to a significant reduction of crop yield. A major source of ROS production in plants through aerobic metabolism is chloroplast, mitochondria, and peroxisome. The tripartite interactions involving Trichoderma- Phytopathogen-Host have received less attention in contrast to the plant–antagonist, plant–pathogen or pathogen–antagonist interactions. This article explores the possibilities of employing thermotolerant strains of agriculturally important microorganisms (AIMs) for alleviating the oxidative stress induced due heat stress in crops by modulating oxidative and defense network of the host.

Global heat stress on health, wildfires, and agricultural crops under different levels of climate warming

The effects of heat stress are spatially heterogeneous owing to local variations in climate response, population density, and social conditions. Using global climate and impact models from the Inter-Sectoral Impact Model Intercomparison Project, our analysis shows that the frequency and intensity of heat events increase, especially in tropical regions (geographic perspective) and developing countries (national perspective), even with global warming held to the 1.5 °C target. An additional 0.5 °C increase to the 2 °C warming target leads to >15% of global land area becoming exposed to levels of heat stress that affect human health; almost all countries in Europe will be subject to increased fire danger, with the duration of the fire season lasting 3.3 days longer; 106 countries are projected to experience an increase in the wheat production-damage index. Globally, about 38%, 50%, 46%, 36%, and 48% of the increases in exposure to health threats, wildfire, crop heat stress for soybeans, wheat, and maize could be avoided by constraining global warming to 1.5 °C rather than 2 °C. With high emissions, these impacts will continue to intensify over time, extending to almost all countries by the end of the 21st century: >95% of countries will face exposure to health-related heat stress, with India and Brazil ranked highest for integrated heat-stress exposure. The magnitude of the changes in fire season length and wildfire frequency are projected to increase substantially over 74% global land, with particularly strong effects in the United States, Canada, Brazil, China, Australia, and Russia. Our study should help facilitate climate policies that account for international variations in the heat-related threats posed by climate change.

Quantifying the response of wheat yields to heat stress: The role of the experimental setup

Previous studies suggested a wide range of sensitivities of wheat yields to heat stress around anthesis. The aim of this study was to improve the understanding of the reasons of the disagreement by testing the response of wheat yield and yield components to differences in the method of heating, the temperature measurement point and soil substrate under sole heat and combined heat and drought stress around anthesis. Growth chamber experiments performed at different sites showed that increasing of the ambient air temperature at anthesis corresponding to a temperature sum of 12000 °C min above 31 °C resulted in a significant yield reduction of −24% for plants grown on sandy soil substrate but not for those grown on a soil with high soil water holding capacity. The grain yield of wheat also declined by −16% for sandy soil substrate but at a much lower level of heat stress when the temperature of the ears was increased by infrared heaters (a temperature sum of 1900 °C min above 31 °C). The yield reduction increased significantly under combined heat and drought compared to sole heat stress. Grain number significantly declined in all experiments with heat stress and combined heat and drought stress at anthesis. Single grain weight increased with heat stress around anthesis and partly compensated for lower grain numbers of pots containing a soil with high soil water holding capacity but not in experiments with sandy soil substrate. We demonstrate, based on data from previous heat stress studies, that statistical relationships between crop heat stress and yield loss become stronger when separating the data according to the soil used in the experiments. Our results suggest that the differences in the yield response to heat may be caused by additional drought stress which is difficult to avoid in heat stress experiments using sandy soil substrate. We conclude that differences in the experimental setup of heat stress experiments substantially influence the crop response to heat stress and need to be considered when using the data to calibrate crop models applied for climate change impact assessments.

Physical robustness of canopy temperature models for crop heat stress simulation across environments and production conditions

Despite widespread application in studying climate change impacts, most crop models ignore complex interactions among air temperature, crop and soil water status, CO2 concentration and atmospheric conditions that influence crop canopy temperature. The current study extended previous studies by evaluating Tc simulations from nine crop models at six locations across environmental and production conditions. Each crop model implemented one of an empirical (EMP), an energy balance assuming neutral stability (EBN) or an energy balance correcting for atmospheric stability conditions (EBSC) approach to simulate Tc. Model performance in predicting Tc was evaluated for two experiments in continental North America with various water, nitrogen and CO2 treatments. An empirical model fit to one dataset had the best performance, followed by the EBSC models. Stability conditions explained much of the differences between modeling approaches. More accurate simulation of heat stress will likely require use of energy balance approaches that consider atmospheric stability conditions.

Heat stress is overestimated in climate impact studies for irrigated agriculture

Climate change will increase the number and severity of heat waves, and is expected to negatively affect crop yields. Here we show for wheat and maize across Europe that heat stress is considerably reduced by irrigation due to surface cooling for both current and projected future climate. We demonstrate that crop heat stress impact assessments should be based on canopy temperature because simulations with air temperatures measured at standard weather stations cannot reproduce differences in crop heat stress between irrigated and rainfed conditions. Crop heat stress was overestimated on irrigated land when air temperature was used with errors becoming larger with projected climate change. Corresponding errors in mean crop yield calculated across Europe for baseline climate 1984–2013 of 0.2 Mg yr−1 (2%) and 0.6 Mg yr−1 (5%) for irrigated winter wheat and irrigated grain maize, respectively, would increase to up to 1.5 Mg yr−1 (16%) for irrigated winter wheat and 4.1 Mg yr−1 (39%) for irrigated grain maize, depending on the climate change projection/GCM combination considered. We conclude that climate change impact assessments for crop heat stress need to account explicitly for the impact of irrigation.

Identification of High-Temperature Tolerant and Agronomically Viable Tomato (S. lycopersicum) Genotypes from a Diverse Germplasm Collection

The aim of most crop heat stress tolerance improvement programs is to increase productivity, not just survival, under high-temperature. Two cycles of experiments were conducted on forty four diverse tomato (S. lycopersicum) lines collected from UC Davis. These included one genotype each of the wild species S. pimpinellifolium (LA0373), S. Pennellii (LA0716) and S. chillense (LA1930). Experiments were conducted in both a growth-chamber and a polytunnel house. Three physiological parameters; stomatal conductance, electrolyte leakage (EL) and chlorophyll fluorescence were used to evaluate the first cycle materials in a growth chamber. Two-month old tomato plants were exposed to heat stress of 44°C for four hours and traits were assessed prior to and following heat shock treatment. Electrolyte leakage differentiated the materials best and was therefore used in subsequent evaluations. In the second cycle of evaluation, the agronomic superiority of the more heat tolerant materials was assessed using an Agronomic Superiority Index (Ag Index) calculated using Euclidean distance for fruit set %, fruit yield, plant dry weight and EL. Plants were grown hydroponically in cocopeat bags in a tunnel house for two crop seasons. The temperature in the tunnel house was maintained using natural sunlight and controlled ventilation. The Ag Index successfully identified heat tolerant and agronomically superior genotypes and fruit yield and the Ag Index were strongly correlated (R2=0.96). Two lines, LA4284 and LA3847, were classified as superior for heat tolerance and agronomic performance. The EL response in the growth chamber and the tunnel house was significantly correlated (R2=0.30), thus validating the use of EL for screening. Histological studies on the selected lines confirmed that pollen development was significantly impaired by heat stress.

Persistence of limited-transpiration-rate trait in sorghum at high temperature

A limited-transpiration (TRlim) trait has been identified in many crop species, including sorghum (Sorghum bicolor (L.) Moench), that results in restricted transpiration rate under high vapor pressure deficits (VPD). The benefit of TRlim is that under high midday-VPD conditions crop water loss is limited so that there is water conservation and positions the crop to better withstand later-season drought. Previous studies performed at 31°C found that TRlim was commonly expressed among sorghum genotypes. It was also found that those lines with low VPD breakpoints for expression of the TRlim trait exhibited insensitivity in transpiration rate to being fed silver ions. However, it is uncertain how applicable these previous results obtained at 31°C might be at higher temperature that may exist at midday in regions where sorghum is commonly grown. The current study tested for the expression of TRlim at 37°C in 16 sorghum genotypes previously found to express the trait at the lower temperature. Only three of the genotypes sustained expression of TRlim at 37°C. These results indicate that for environments where temperature may commonly reach or exceed 37°C, sorghum genotypes have been favored that acclimate to the high temperature by losing the TRlim trait. In conditions in which very high temperatures threaten crop heat stress, those genotypes that lose the TRlim trait at high temperature may be more desirable since increasing transpiration rates at these temperatures can result in leaf cooling. The silver test failed to discriminate genotypes for expression of the TRlim trait at high temperature.