The human population is projected to reach 9.8 billion by 2050 (United Nations, 2017), requiring 100 to 110% more food in 2050 than in 2005 (Tilman et al., 2011). However, a decrease in crop yields due to climate change (Lobell and Field, 2007; Zhao et al., 2022) poses a significant challenge in ensuring adequate food production for a growing population (Tito et al., 2018). Earth’s average temperature is predicted to rise by 1.1-6.4°C due to increased greenhouse gases during the next century (Yamori et al., 2014). Increasing temperatures are anticipated to hinder advancements in addressing food insecurity by diminishing agricultural yields in the upcoming decades (Kroeger, 2023). The rise in temperature demands crops to grow and produce well at temperatures above their optimal. Potatoes are among the many crops affected by increased temperatures and climate change.

Potato is a cool season crop that produces tubers (the edible part, underground modified stems used for nutrient storage and propagation). Temperature and photoperiod regulate potato tuberization and yield (Dutt et al., 2017). However, temperature has been cited as the single most crucial uncontrollable factor affecting the growth and yield of potatoes (Levy and Veilleux, 2007). Potato plants can tolerate day temperatures of about 32°C without significant loss in total biomass production (Minhas et al., 2006); however, a temperature of 25°C has been considered optimum for vegetative growth and 24°C for photosynthesis (Timlin et al., 2006). The most temperature-critical growth stages in potatoes are tuber initiation and bulking. Night temperatures above 18°C reduce tuberization, whereas temperatures beyond 25°C (Bushnell, 1925) may result in no tuberization. Several reports have shown tuber yield and quality deterioration due to heat stress (temperatures beyond the upper limit of the optimum tuberization - 20°C) (Lafta and Lorenzen, 1995; Hancock et al., 2014; Aien et al., 2017; Paul et al., 2017; Obiero et al., 2019). Heat stress damage is more apparent in tubers than in shoots (Lafta and Lorenzen, 1995). Moreover, the growth stage at which heat stress occurs has an even more significant implication on the cultivar’s response to high temperatures. The effect of heat stress is more pronounced in the early stages of tuber formation than in later stages. Heat stress at early stages results in drastic tuber yield reductions (Rykaczewska, 2013) and at later stages leads to quality deterioration (Kim et al., 2017). The effect of heat stress was more deleterious under long days than under short days; complete inhibition of tuber formation in the variety Désirée was observed when grown at 16:8 h (day: night) photoperiod and 32/22°C (day/night) temperature (Wolf et al., 1990).

Heat stress impacts both potato yield and tuber quality (external as well as internal), causing deformities like elongation, bottlenecks, second-growth, chain tuberization, gemmations, and knobs during tuber bulking (Rykaczewska, 2013). Assessment of tubers’ secondary growth and physiological defects needs to be incorporated into heat tolerance studies of potatoes since total yield alone may not be the only indicator of tolerance (Rykaczewska, 2015). High temperatures during plant growth often shorten the dormancy period of potato tubers (Wurr, 1992; Levy and Veilleux, 2007; Struik et al, 2007). The effects of high temperatures on potatoes are aggravated when coupled with water deficiency, resulting in significant yield loss (Levy, 1986). Rykaczewska, 2015 reported that combined heat and drought stress reduced the yield of a sensitive cultivar by over 50%, whereas the more tolerant variety experienced a yield reduction of about 25%.

The effects of heat stress vary according to genotype, occurrence time, duration, and intensity of high temperatures. Potato cultivars differ in their responses to heat stress (Levy, 1986; Ghosh et al., 2000; Ahn et al., 2003). Popular varieties like Russet Burbank, Atlantic, and Yukon Gold are known to be sensitive to internal heat necrosis or internal brown spots. The frequency and severity of such defects increase when they experience high day and night temperatures early in the growing season, combined with low rainfall (Yencho et al., 2008). The tolerance of potatoes towards heat stress is explained by various biochemical and transcriptional factors differing in genotypes (Morpurgo and Ortiz, 1988).

Potato-growing regions in the world are changing (Jennings et al., 2020; Devaux et al., 2021). While new areas are added, traditional regions face challenges in growing potatoes. To meet the current production level, around 12.5% of the current potato production climate (43 million hectares) is required to be shifted to newer regions (Fumia et al., 2022). However, developing heat-tolerant potato varieties is the practical solution to sustain and expand production, aiding food security in the face of climate change and global warming (Hijmans, 2003; Pradel et al., 2019; Devaux et al., 2021). Heat-tolerant varieties are projected to increase the potential yields by more than 5% in most areas and 10% in tropical regions and parts of the USA and Canada (Hijmans, 2003). Manipulating planting dates and developing tolerant varieties are crucial strategies, as shown in a simulation study (Naz et al., 2022).

Of the 156 countries worldwide that plant potatoes (FAO, 2019), heat stress is reported in various places, including tropical highlands. Lavras in Brazil (Lambert et al., 2006); San Ramón in Peru (Khan et al., 2015; Benavides et al., 2017; Raymundo et al., 2018; Muñoa et al., 2022); Jalandhar in India (Bhardwaj et al., 2022), Western Australia in Australia (Obiero et al., 2022) are considered heat stress sites for the selection of heat-tolerant potatoes. Some unexpected areas, like Ontario, Canada, have also been reported to experience heat during the potato growing season. Potato yield decreased by 17.2% in 2016 compared with the production in 2015 in Ontario, Canada, due to extremely high temperatures during the 2016 summer (Tang et al., 2018). High-temperature stress will be more common in the future (Battisti and Naylor, 2009; Monneveux et al., 2014; Lehretz et al., 2021), emphasizing the need for developing heat-tolerant varieties (Bashir et al., 2023). Screening potato genotypes for heat tolerance under appropriate conditions is a reliable method to select clones enriched with favorable traits/genes that allow them to overcome heat stress. The Texas A&M Potato Breeding Program has been selecting potatoes under high-temperature stress (>30°C) for several decades at two main locations in the Panhandle region of Texas, Springlake and Dalhart, and has released several potato clones that could be considered heat-tolerant.

This study was performed to 1) evaluate if Texas field locations used by the Texas A&M Potato Breeding Program are suitable for heat stress screening (objective 1), 2) assess if planting time at the most stressful location should be modified to improve heat stress screening (objective 2), and 3) identify tuber traits affected by heat stress under field conditions and compare them with those observed under controlled greenhouse conditions (objective 3). The goal is to identify appropriate settings (field locations, planting dates, contrasting greenhouse conditions) to evaluate potato clones for heat stress and to identify reliable heat tolerant and sensitive checks for future potato heat tolerance studies. Heat-tolerant potato clones are desired to cope with the future global warming scenario and extend potato production to warmer areas.

Our research subjected potatoes to prolonged heat stress in field and greenhouse experiments, aligning with studies by Tang et al., 2018 and Bashir et al., 2023. Unlike many short-term heat stress treatments, we employed extended periods throughout the crop cycle, consistent with findings that temperatures above 25°C stress potatoes. Temperature regimes used by Boguszewska-Mańkowska et al., 2020; Zhang et al., 2021, and Rykaczewska, 2015 reflect similar stress conditions. Some of the field sites that reported heat stress on potatoes are San Ramón, Peru, and Lavras, Brazil. San Ramón frequently experiences heat stress (Khan et al., 2015; Benavides et al., 2017; Raymundo et al., 2018; Muñoa et al., 2022) with an average day/night temperature of 28/23°C (Benavides et al., 2017) but fluctuating between 16 to 36°C (Muñoa et al., 2022). In Lavras, Brazil, the mean maximum and minimum temperatures are 28.5 and 16.5°C, respectively (Lambert et al., 2006). Both the locations in our study encounter prolonged periods of temperature exceeding 25°C throughout the crop period and often reaching above 40°C (Gautam et al., 2024). High temperatures inhibit potato tuber growth and development in short- and long-day conditions (Wheeler and Tibbitts, 1986), with the inhibitory effect more significant in long-day conditions (Van Dam et al., 1996; Jackson, 1999) as in our study. Although there are reports of episodes of heat stress during germination, tuber initiation, and bulking or maturation, few sites observe a constant increase in temperature from planting to harvest, as in our case. Springlake exhibits a steady rise in temperature and photoperiod throughout the crop period. While Dalhart also faces high temperatures, the photoperiod consistently decreases from tuberization to harvest, mitigating some adverse effects of heat on tuber development. Springlake’s combination of high temperature and increased photoperiod during crop growth positions it uniquely. This scenario may become more prevalent in the future due to climate change in the northern hemisphere potato-producing region. Therefore, the field sites we utilized could serve as representative of future temperature scenarios for most potato-growing regions in the Northern hemisphere. The GGE biplot on the relationship of environments (type 10) also reveals that Springlake environments are more consistent and can discriminate clones, primarily based on tuber defect traits ( Supplementary Figure 6 ), thus making it suitable for future heat stress-related studies.

Environment, cultivar, and their interaction jointly dictate yield capacity (Benavides-Cardona et al., 2022), with environment notably impacting traits like yield and tuber dry matter. A yield reduction of 13% in Brazil (Patino-Torres et al., 2021) was recorded, while in Bangladesh, reductions ranged from 4.5% to 34.8% (Mahmud et al., 2021) due to heat stress. The yield in the current study was higher in field and greenhouse experiments exposed to less heat stress, consistent with findings from previous reports. Our study, conducted under more stressful conditions, observed a substantial 67% (43% to 84%) yield reduction between Dalhart and Springlake, with no significant reduction observed with different planting times at Springlake. Greenhouse conditions in 2021 led to an 18% yield reduction, and a similar study reported a 24% reduction under comparable conditions (Rykaczewska, 2015). Potato clones had significantly higher total yields in Dalhart than in Springlake. Lower temperatures within the 12-28°C favorable range correspond to higher potato yields, indicating an increased harvest index (Wheeler and Tibbitts, 1986). Our greenhouse experiments showed that heat stress reduced the harvest index of potatoes by ~8% in 2020 and 20.5% in 2021 ( Supplementary Table 7 ). The conditions in 2021 were more contrasting than in 2020 in the greenhouses. Thus, a greater harvest index reduction (from normal to heat stress) was realized in 2021. Under high-temperature conditions, the potato plants had greater aerial mass, resulting in a lower harvest index. The above-ground dry mass increased by 53% in 2020 and 67% in 2021. This increase in above-ground dry mass could be explained by the increased plant height (~33% in 2020 and 30% in 2021) and a decrease in leaf area by 73% in 2021 ( Supplementary Table 7 ). Photoassimilates were diverted to aerial rather than underground parts (tubers) under heat-stress conditions. Several reports (Wolf et al., 1990; Hancock et al., 2014; Aien et al., 2017) corroborate this.

There are reports of tuber quality deterioration in potatoes due to heat stress. High temperatures inhibit tuber formation, deform tubers, and cause chain tuber formation, secondary growth, and premature sprouting (Bodlaender, 1963; Levy and Veilleux, 2007; Rykaczewska, 2015; Zhang et al., 2021). Tuber deformities include knobby tubers, heat sprouts, chained tubers, and growth cracks. Knobby tubers result from interrupted growth, resulting in shape deformation with irregularly shaped secondary growth or bumps, while heat sprouts occur when tubers sprout prematurely due to heat exposure. Chained tubers form when tuber growth is periodically interrupted, and growth cracks emerge when the tuber splits and heals (Hutchinson, 1969; Van Den Berg et al., 1990). Heat stress conditions can lead to tuber deformities, with reported percentages varying from 0% to 40% (Rykaczewska, 2015) and 9.6% to 16.1% (Patino-Torres et al., 2021). Genotypes vary in their capacity to tolerate heat, and sensitive varieties can suffer a substantial marketable yield loss. This study presents the first comprehensive quantification of various tuber defects in potatoes under prolonged field and greenhouse heat stress. Tuber defects prevalent under heat-stress field conditions were similarly observed in heat-stress greenhouse conditions, highlighting the correlation between high temperatures and tuber defects. The dissection of defects into categories like heat sprouts, chain tubers, knobs, and growth cracks, along with their distribution with non-marketable tubers, is novel. While Dalhart had consistent internal tuber defect percentages (~16%), Springlake exhibited variability (5-23%) across years, suggesting multifactorial influences on defect expression. Despite Atlantic’s high total and marketable yields, it exhibited a high percentage of internal defects, particularly internal heat necrosis, indicating susceptibility to high temperatures.

Heat stress in potatoes can decrease yield due to multiple factors. Elevated temperatures during tuber formation decreased the number of tubers per plant (Zhang et al., 2021), and in extreme cases, tuber initiation is inhibited. Additionally, heat stress may delay tuber initiation, resulting in the formation of numerous smaller tubers instead of larger ones (Mahmud et al., 2021), as we found in our experiments. Dalhart produced a higher number of large tubers than Springlake. The conditions in Dalhart favored better initiation of tuberization and bulking than Springlake. Late planting in Springlake reduced tuber weight, indicating reduced assimilate allocation to tubers, although the number of tubers remained unaffected. The greenhouse trials corroborate the results from the field. Less extreme conditions in 2020 did not show significant differences in tuber number and weight, but more contrasting conditions in 2021 showed significant differences. Lafta and Lorenzen (1995) observed that high temperatures caused fewer tubers to be formed. However, some studies, like that of Borah and Milthorpe (1962) and Struik et al. (1989), report that more tubers are formed at higher temperatures (Struik, 2007). There was more than double (99% to 143%) increase in tuber numbers, with individual tuber mass ranging from 58% to 98% of the control when six cultivars of potatoes were grown under heat stress for 14 days (Rykaczewska, 2015). At first glance, the results seem contradictory: Heat stress could reduce the average number of tubers per plant or increase the number per plant. The severity and timing of heat stress and genotypic differences for time to tuber initiation could explain the results. In some clones, high temperatures around the developmental stage of tuber initiation could inhibit tuber formation or severely reduce the number of tubers formed. However, clones with very early initiation of tuberization could escape heat stress. On the other hand, clones with later tuber initiation could end up with a higher number of smaller tubers.

Increased temperatures affect the dry matter distribution in potatoes, favoring above-ground growth over underground tubers (Marinus and Bodlaender, 1975). It is assimilate partitioning, not the total plant productivity, that is affected by high temperature, as confirmed by an increase in translocation of radiolabeled C to vegetative organs (leaves and stems) along with a decrease towards the tubers (Wolf et al., 1990). We confirmed this discriminatory partitioning of assimilates through the harvest index. The reduced harvest index under heat stress confirms assimilates diversion to aerial parts over economic tubers. An indirect method of estimating tuber dry matter can be done by measuring the specific gravity of tubers (Nzaramba et al., 2013). Our specific gravity measurements in field and greenhouse settings and tuber dry matter assessments in greenhouse trials show a decrease due to heat stress. Higher specific gravity is desired in potatoes, especially in processing types, as it indicates higher dry matter in the tuber and less oil absorption in fried/processed products. The specific gravity of potatoes decreases with high-temperature stress (Teixeira et al., 2015; Andrade et al., 2021; Fernandes Filho et al., 2021). Various studies indicate a drastic reduction in tuber dry matter when potatoes are grown above 20-25°C (Levy and Veilleux, 2007; Aien et al., 2017; Kim and Lee, 2019; Obiero et al., 2019). Dalhart was more favorable than Springlake regarding specific gravity. Planting dates did not have significant differences in the specific gravity of the samples tested in Springlake, indicating similar heat stress conditions during both planting dates. However, the clones showed significant differences in specific gravity in the field and greenhouse trials. The majority of variation explained by clones in all three trials indicate genetic control of the trait. Thus, observing more genetic control of specific gravity would allow breeders to develop varieties with high specific gravity and, therefore, high dry matter. The synthesis of high levels of endogenous gibberellins, which reduces the partitioning of assimilates to the tubers and impedes the synthesis of starch and tuber-specific proteins, has been associated with the reduction of tuber dry matter under high temperatures (Lovell and Booth, 1967).

Potato dormancy is regulated by a combination of genetic factors, environment, physiology, and hormones (Sonnewald and Sonnewald, 2014). The current study showed that dormancy in potatoes is mainly controlled genetically. However, location and growth conditions (planting dates and temperatures) influenced tuber dormancy. High temperatures during tuber growth in the field lead to reduced dormancy, indicating physiological aging (Midmore and Roca, 1992; Van Ittersum et al., 1992; Suttle, 2007). In a study, varieties Premier Russet and Ranger Russet, when exposed to high temperatures (29°C), shortened their dormancy compared to normal (16°C) temperature during the tuber maturity stage (Zommick et al., 2014). In 2020, with less extreme temperatures, the effects on dormancy in potato clones were not fully realized. However, the subsequent 2021 trial revealed that extreme temperatures significantly shortened dormancy in the potato clones. On its extreme effect, high temperature can break dormancy in tubers still growing in the field, often termed “heat sprouts” (Levy and Veilleux, 2007; Zhang et al., 2021). Greenhouse experiments and field trials showed consistent results. In both settings, more extreme conditions (Springlake, late planting and heated conditions in 2021) led to shorter dormancy in potato clones than milder conditions (Dalhart, regular planting and normal conditions in 2021). The shortening of dormancy and heat sprouting in the field due to heat stress is likely associated with the gibberellin biosynthesis pathway (Zhang et al., 2021). Many studies consider postharvest temperatures critical for prolonging tuber dormancy in potatoes; however, the importance of temperatures during growth can be highlighted through studies like ours.

Our results were consistent with findings that the environment explains a significant part of the variation for traits like total yields, marketable yield, and dry matter, while genotypes contribute substantially (Sood et al., 2020). Based on the range of observed characteristics, we propose three levels of potato heat tolerance. The first level pertains to a clone’s ability to yield, the second level involves producing high yield without external deformities, and the third level encompasses the production of tubers free from both external and internal defects. Russet Burbank consistently displayed poor marketable yield, whereas Vanguard Russet emerged as a top-yielding variety with more marketable tubers across various environments. Reveille Russet exhibits unique traits such as long dormancy and late emergence. Its late emergence may mask its potential heat tolerance (Gautam et al., 2021). Early exposure to high temperatures and premature tuber harvesting can reduce tuber marketable yield, specific gravity, dry matter, and dormancy. Despite successful evaluation in lab conditions (Gautam et al., 2021), assessing Reveille Russet for heat tolerance in the field and greenhouse remains challenging due to its shorter growth period. In greenhouse trials, Sierra Gold and Yukon Gold were identified as high-yielding clones using a multi-trait stability index, with shorter maturation periods than other russet varieties. Russet Burbank’s sensitivity to heat stress in Texas growing sites is consistent with its optimal temperature of 17.5°C (Yandell et al., 1988) for yield. Increased heat sprouting in later stages of crop maturity (Rykaczewska, 2015) suggests its correlation with prolonged heat stress, explaining its lesser detection in greenhouse trials due to shorter growth periods (90 days) compared to 100 or more days in the field. Considering various measured traits, Vanguard Russet stands out for its high marketable tuber yield, average tuber weight, and long dormancy with few internal defects. Conversely, Russet Burbank exhibited low marketable tuber yield and many small tubers, along with reduced specific gravity under heat stress. Although Atlantic produced a high yield of external defect-free tubers, it was sensitive to internal defects, indicating heat susceptibility. These results are effectively summarized using GGEbiplot type 3: Which won Where plot ( Supplementary Figure 7 ) and multi-trait stability index plots ( Figure 11 ), confirming the consistent performance of Vanguard Russet across field and greenhouse experiments.

Potato plants grown in the Panhandle region of Texas (represented by the Springlake and Dalhart locations) face temperatures exceeding 25°C during the growing season. Both locations are suitable for heat stress screening. Springlake stands out as the most stressful site for heat stress evaluation, and regular planting time is suitable for heat stress screening. Greenhouse trials confirmed field findings on the effect of heat stress on tuber yield, quality, and dormancy. Vanguard Russet is a reliable heat-tolerant reference. Russet Burbank and Atlantic can be used as sensitive checks due to their high incidence of external (Russet Burbank) and internal (Atlantic) defects. Heat stress during the potato growing season significantly reduces marketable yield, increases external and internal tuber defects, alters the chemical composition (lower specific gravity, dry matter, starch, higher percent of simple sugars), and reduces dormancy. Heat-tolerant cultivars are less affected by the detrimental effects of heat stress.

Some limitations of this study include the difficulty of achieving normal/ideal potato growing conditions (25/15°C) under greenhouse conditions. The normal/ideal conditions were moderately stressful. A possible confounding effect was the inclusion of genotypes from different plant maturity groups and market classes. Under greenhouse conditions, all clones were harvested at 90 DAP, and some clones did not achieve full potential (i.e. Reveille Russet). Despite the study’s limitations, key messages on the effect of heat stress in potatoes can be drawn, and they are useful for further investigations on screening genotypes for heat tolerance and understanding the underlying mechanism of heat tolerance in potatoes using potato clones contrasting for heat tolerance.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

SG: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Visualization, Writing – original draft, Writing – review & editing. DS: Data curation, Formal analysis, Investigation, Methodology, Project administration, Writing – original draft, Writing – review & editing. JK: Data curation, Formal analysis, Investigation, Methodology, Project administration, Writing – original draft, Writing – review & editing. MV: Conceptualization, Funding acquisition, Investigation, Methodology, Project administration, Resources, Supervision, Visualization, Writing – original draft, Writing – review & editing.