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Global climate changes have led to frequent and recurrent heat stress, which has seriously affected the world maize production. The experiment presented in this paper was carried out during the maize‐growing season in 2021 and 2022 at the Huang–Huai–Hai Region Maize Science and Technology Innovation Center (36°09′N, 117°09′E) in Tai'an, Shandong province, China. The test site is located in the semi‐humid warm temperate continental monsoon climate zone, soil is brown loam. We selected different heat‐sensitive maize varieties: heat‐tolerant variety Zhengdan 958 (ZD958) and heat‐sensitive variety Xianyu335 (XY335) to study the stress effects of high temperature on the development of tassel in the key stage of its differentiation (the 12‐leaf stage, V12). We found that exposure to heat stress during the V12 stage significantly reduced the tassel size and the anther dehiscence area, making it difficult to disperse pollen, thus effectively reducing pollen production. In addition, heat stress had significant negative effects on pollen development, resulting in deformed pollen and lower pollen viability and germination rate. Our results also showed that heat stress significantly increased the activities of key reactive oxygen species‐scavenging enzymes including superoxide dismutase, peroxidase and catalase, and that the malondialdehyde and H2O2 content in tassels exposed to heat stress were significantly higher than those control group, where it should be noted that for the XY335, these effects were more pronounced than for the ZD958. The endogenous hormone content of tassels exhibited a variety of responses. After heat stress, the zeatin and salicylic acid content in tassels of both maize varieties were significantly lower than those in the respective control groups, while the abscisic acid and gibberellin acid content were significantly higher. With respect to the jasmonic acid and 3‐indoleacetic acid content, the two maize varieties exhibited opposite responses: in tassels from ZD958 plants subjected to heat stress were higher than those in the respective control group, while in tassels from XY335 plants, they were lower. The observed changes in protective enzyme activities and endogenous hormone contents induced by heat stress significantly affected the development of maize tassels and significantly reduced the amount, activity and germination rate of pollen. [ABSTRACT FROM AUTHOR]

Oilseed rape (Brassica napus) or Canola is an important oilseed crop produced and consumed globally. The predicted increase in the frequency of high‐temperature events associated with climate change poses a threat to Canola productivity. In the present work, we report the impact of short‐term heat stress on the reproductive fitness and yield components of Canola. Short heat stress episodes, especially above 36°C, resulted in diminished reproductive fitness due to reduced pollen viability and germinability. Heat stress exposure led to asynchronous male and female development and suppressed pollen development in developing buds. As the temperature increased above 32°C, the seed production decreased significantly. Temperatures beyond 38°C resulted in >50% reduction in total seed production and seed weight. Short‐term heat stress also reduced yield components, seed vigour and post‐harvest seed characteristics. Biochemical investigations of the seeds harvested from heat‐stressed (40°C for 12 hr) plants showed decreased oil content along with a variable fatty acid composition. The omega‐6/omega‐3 ratios increased in response to heat stress indicated a possible decline in oil nutritional quality. Understanding the impact of short heat stress episodes can provide efficient heat tolerance screening tools and pave the way for developing heat stress‐tolerant B. napus varieties. [ABSTRACT FROM AUTHOR]

High temperature during flowering increasingly reduces maize yield with warming climate. Heat tolerance of maize is however not fully understood in the aspect of flowering characteristics and yield stability, especially in the female flowering patterns. Temperature-controlled greenhouse studies were conducted to test heat tolerances of four inbred lines and five hybrids, including 30/20 and 40/30°C treatments during 15 days bracketing the silking stage. Field studies were conducted to determine yield stabilities of five hybrids at three stations including four field environments. In greenhouse study, fertility rate and kernel number per ear (KN/ear) of nine genotypes reduced from 34.41-83.03% and 162.0-653.7 at 30/20°C to 0.68-23.13% and 0.3-332.5 at 40/30°C, respectively, mainly due to reduced pollen shed weight (PSW), pollen viability (PV) and silking rate (SR) at 40/30°C. Hybrids Chang7-2×Qi319 and Chang7-2×Xian2 showed significantly higher yields and KN/ear at 30/20°C, but only Chang7-2×Qi319 performed better at 40/30°C. In field studies, Chang7-2×Xian2, Xian2×Zheng58, Qi319×Xian2 and Chang7-2×Qi319 were winning hybrids at specific environments. Chang7-2×Xian2 showed the highest yield potential due to the larger ear size and KN/ear but a lower yield stability because of the lower PSW and PV. Chang7-2×Qi319 combined high-yield potential and high-yield stability, which can be explained by large PSW, high PV and SR, and stable flowering pattern at different environments. Female flowering pattern (e.g. silking dynamics) is also a key determinant of high temperature tolerance and yield stability in maize. Hence, maize male and female organs should be equally concerned when achieving high and stable yield under different adverse environments in warming climate. [ABSTRACT FROM AUTHOR]

High temperatures and increasing CO2 concentrations are a major threat to global wheat (Triticum aestivum L.) production, demanding the development of heat‐tolerant wheat cultivars. Plant physiological traits are potential surrogates for evaluating genetic variation for crop stress tolerance. This research evaluated 23 Australian wheat cultivars and two breeding lines for heat‐tolerance by characterising the associated physiological traits. The interactive effects of heat‐stress and elevated CO2 were studied under controlled greenhouse conditions and delayed sowing in the field with exposure to higher temperature. Physiological changes, pollen viability and grain yield were assessed. A significant correlation was observed between physiological and agronomical traits under high temperature at 35°C and elevated CO2 at 800 µl L−1, providing evidence of adaptation to high temperatures in some genotypes. Variation in stomatal conductance, transpiration rate, canopy temperature, leaf chlorophyll and photosynthesis were associated with maintenance of pollen viability and grain yield at high temperatures. Of the genotypes assessed, seven were classified as heat tolerant at both ambient and elevated CO2 and nine were heat susceptible while the remainder showed a variable response to CO2 at high temperatures. Field data confirmed the heat responses of the most heat‐tolerant and susceptible genotypes. The heat tolerant genotypes identified are candidates for further breeding and selection to improve adaptation to a changing climate. [ABSTRACT FROM AUTHOR]

High temperatures and increasing CO2 concentrations are a major threat to global wheat (Triticum aestivum L.) production, demanding the development of heat‐tolerant wheat cultivars. Plant physiological traits are potential surrogates for evaluating genetic variation for crop stress tolerance. This research evaluated 23 Australian wheat cultivars and two breeding lines for heat‐tolerance by characterising the associated physiological traits. The interactive effects of heat‐stress and elevated CO2 were studied under controlled greenhouse conditions and delayed sowing in the field with exposure to higher temperature. Physiological changes, pollen viability and grain yield were assessed. A significant correlation was observed between physiological and agronomical traits under high temperature at 35°C and elevated CO2 at 800 µl L−1, providing evidence of adaptation to high temperatures in some genotypes. Variation in stomatal conductance, transpiration rate, canopy temperature, leaf chlorophyll and photosynthesis were associated with maintenance of pollen viability and grain yield at high temperatures. Of the genotypes assessed, seven were classified as heat tolerant at both ambient and elevated CO2 and nine were heat susceptible while the remainder showed a variable response to CO2 at high temperatures. Field data confirmed the heat responses of the most heat‐tolerant and susceptible genotypes. The heat tolerant genotypes identified are candidates for further breeding and selection to improve adaptation to a changing climate. [ABSTRACT FROM AUTHOR]

There has been little research on crop lodging and yield determination in response to varying degrees of heat stress in canola. This research aimed to examine root morphology, pod fertility, seed yield and crop lodging of two canola genotypes subjected to normal temperature (23/17°C, light/dark, as CK), and three elevated temperature regimes imposed at flowering for a short term (10 days), namely CK+2 (25.0/22.0°C, light/dark), CK+4 (27.0/24.0°C) and CK+6 (29.0/26.0°C), in a controlled growth facility. Elevated temperature treatment, CK+4 and CK+6, displayed a significant adverse effect on seed yield and stem lodging. Compared to the CK, a significant yield loss of 35.6% and 48.7% in CK+4 and CK+6, respectively, was mainly due to poor pod fertility. This was evident from the smaller number of total filled pods (−21% in the CK+4 and −25% in the CK+6), low success ratio of pod developed (−25%, CK+4 and −29%, CK+6) and poor pollen viability (−36%, CK+4 and −50%, CK+6), averaged across both genotypes. Lateral root development was sensitive to the elevated temperature treatment, showing significant reductions in the lateral root morphology (8.0%–28.5%), while the taproot was relatively tolerant to the elevated temperature stress. A strong relationship between root electrical capacitance and lateral root morphology (R2 >.74**) indicates that electrical measurements could be used as a non‐destructive method for evaluating root parameters under elevated temperatures. Higher risk of stem lodging (21.4% lower stem safety factor) compared to the CK was evident under severe elevated temperature stress, as ascribed from the reduced stem bending strength that was caused by the deteriorating stem mechanical properties such as decreased flexural rigidity and weakened vascular bundle size (i.e. stunted fibre cell, and thinned size of fibre wall, deteriorated secondary xylem and smaller secondary phloem). These results were further verified by the principal component analysis and structural equation model. The root lodging risk was not influenced by the elevated temperature regime, primarily due to the unaffected anchorage strength and height of the centre of gravity. This information will be useful in improving lodging resistance and alleviating the related impact of heat stress in canola. [ABSTRACT FROM AUTHOR]

With a warming climate, heat events occur more frequently especially during flowering of many crops which increasingly threatens food security. The maximum temperature thresholds (TTmax) for different flowering processes and kernel formation, however, are not explicit in maize (Zea mays L.). For this, a temperature‐controlled experiment was conducted including two maize hybrids ZD958 and XY335 that were widely grown in China and six temperature levels (maximum/minimum temperature; 30/20, 32/22, 34/24, 36/26, 38/28 and 40/30℃ for 14 consecutive days bracketing the silking stage). Both tasseling and pollen shedding time were advanced with elevated temperature, but silking time was advanced from 30/20 to 36/26℃ and then delayed with further temperature increase, thus extending anthesis–silking interval (ASI). Silking rate was significantly reduced to 63% at 40/30℃ for ZD958 but maintained at 88%–95% for XY335 compared to that at 30/20℃. Pollen shed weight and pollen viability decreased with elevated temperature with larger reductions in XY335 than in ZD958. Hence, ZD958 and XY335 are female and male flower sensitive hybrids, respectively. Silking rate, pollen shed number and ASI were the most important constraints to kernel formation under HT stress. TTmax for seed set of both hybrids were estimated to be ~38℃, and different flowering processes have respective TTmax. These detailed information are important to uncover heat impacts on maize and increase simulation accuracy when modelling heat effects on maize yield. Besides, more attentions need to be directed at female flower sensitivity when breeding and/or selecting heat‐tolerant maize hybrids. [ABSTRACT FROM AUTHOR]

With the expected increase of abiotic stress under global climate change, significant research has been devoted to how abiotic stress will affect crop production. To date, there has been little research on the stage sensitivity of short‐term heat stress to crop lodging and yield determination in canola. This research was conducted in a controlled growth facility and aimed to examine root morphology, pod fertility, seed yield and crop lodging of two contrasting canola genotypes subjected to a short‐term heat stress (27.0/24.3°C, light/dark), imposed respectively at three growth stages, rosette vegetative stage (RVHT), early flowering stage (EFHT) and late flowering stage (LFHT), in comparison with non‐stressed control (CK) (23/17°C). The results demonstrate that heat stress imposed at RVHT and LFHT was less detrimental to seed yield and lodging resistance. However, EFHT showed significant adverse effects on both, which was further confirmed by redundancy analysis (RDA) and structural equation modelling (SEM). Compared with the CK, EFHT resulted in a yield loss of 43%, which was mainly due to poor pod fertility, less number of filled pods (−28%), decreased pollen viability (−38%) and a lower success ratio of filled pods (−29%). The taproot was found to be relatively tolerant to heat stress, but lateral roots were sensitive to heat stress at EFHT and LFHT. Root capacitance could be used as a non‐destructive method for evaluating lateral root morphology. Compared with the CK, EFHT displayed a high risk of stem lodging, as indicated by a 27% lower safety factor. This was mainly attributed to the reduced stem bending strength that was caused by the deterioration of stem mechanical properties under EFHT, as illustrated by SEM. Root lodging resistance was not altered by any stages of short‐term heat stress, as the taproot remained stable. [ABSTRACT FROM AUTHOR]

Abstract: With the changing climatic scenario and increasing global mean temperature, heat stress became a major limiting factor for today's agriculture. To identify the underlying mechanism associated with heat tolerance in peanut, two experiments (field and growth chamber) were conducted with four genotypes (ICGS 44, GG 7, AK 159 and DRG 1) having differential high temperature stress sensitivity. Field grown plants under three different temperature (D1, D2 and D3) regimes simulated three temperature treatment effects with a variability of 3–4/4–5°C in mean day/night temperature, respectively. In growth chamber, imposition of heat shock (10°C above ambient inside growth chamber) revealed not only rapid induction (within 0.5 hr) of HSPs, especially small HSPs (HSP 17, HSP 40) in tolerant genotypes, but also its sustenance for longer duration (2 hr), which might help them to have better physiological adaptation strategies under high temperature stress. This was evident from significant advancement in phenophases observed with increase in temperature by 15–18 days at physiological maturity, while pollen viability and membrane stability reduced below 50% and 41%, respectively in DRG 1 with increase in mean day/night temperature. Maintenance of higher photosynthesis and transpiration rate and stomatal conductance helped the tolerant genotype ICGS 44 to keep relatively cooler canopy and higher photosynthates, ensuring better physiological condition in this genotype under heat stress. Significant increase (~2.5‐fold) in inositol and hexoses (glucose and fructose) content and reduction (>50%) in sucrose content in leaf tissues indicated degradation of storage carbohydrates for improved osmotic adjustment especially in tolerant genotypes under elevated temperature. [ABSTRACT FROM AUTHOR]

Cotton-producing regions throughout the world often experience high night temperatures (HNTs), affecting flowering and yield in cotton ( Gossypium hirsutum). The objective of this study was to quantify the effects of high nighttime temperatures on the physiological and biochemical characteristics of cotton during the floral bud and flowering stages. Growth chamber experiments were conducted in 2011-2012 and treatments included a control (day/night temperature of 32/24 °C) and two HNT treatments (32/29 °C from 8:00 pm to 12:00 am) for 3 weeks from the beginning of each phenological stage, i.e., first floral bud (B1) and first flower (F1). The results indicated that increased night temperatures (NTs) during the floral bud and flowering stages increased the rate of flower production per plant. However, no increase was observed in the final number of reproductive structures because the rate of floral abortion also increased for both treatments compared to the control. Additionally, the increase in night temperature during the floral bud stage reduced the sucrose content in the flower, resulting in decreased pollen viability and premature abortion of reproductive structures while the onset of flowering period was also delayed and lower accumulation of reproductive dry matter was observed. HNTs during the flowering stage reduced the number of seeds per locule and the number of seeds per boll. In general, higher than optimum NTs affected sucrose metabolism of the cotton flower and consequently its pollen viability. As a result the flowering period was delayed and a reduction in reproductive dry matter accumulation was observed due to premature abortion of reproductive structures. Finally, cotton is more sensitive to HNT at floral bud stage and this finding may be important to adjust cotton planting date, management and breeding. [ABSTRACT FROM AUTHOR]

We investigated heat tolerance at the reproductive stage in six spring-type B. rapa accessions and one B. juncea accession as a control. Plants were subjected to two temperature treatments for seven days in controlled environmental rooms, beginning one day before the first open flower on the main stem inflorescence. The high-temperature treatment ranged from 25 °C to 35 °C during 16 h light and 25 °C during 8 h dark. The control temperature treatment was set at 23 °C during 16 h light and 15 °C during 8 h dark. Soil moisture was maintained at close to field capacity to avoid drought stress. Main stem buds that emerged during the treatment period were tagged, and pod and seed production was recorded at each reproductive node. Leaf temperature depression and leaf conductance increased in the high-temperature treatment which indicated that plants were not drought stressed. A leafy vegetable type of B. rapa from Indonesia was the most tolerant to high temperature, as defined by its ability to set seed equally well in the control and high-temperature treatments, followed by an oilseed type from Pakistan. Pollen viability remained above 87 % in all accessions and treatments. We conclude that bud number and length, and pod number produced under high temperatures, might provide a useful preliminary screen for high-temperature tolerance and that B. rapa may be a valuable source of heat tolerance in canola ( B. napus). [ABSTRACT FROM AUTHOR]

High temperature ( HT) stress is one of the major environmental factors influencing yield of soybean ( Glycine max L. Merr.) in the semi-arid regions. Experiments were conducted in controlled environments to study the effects of HT stress on anatomical changes of pollen and their relationship to pollen function in soybean genotype K 03-2897. Objectives of this study were to (a) quantify the effect of HT stress during flowering on pollen function and pod set and (b) observe the anatomical changes in pollen grains of soybean plants grown under HT stress. Plants were exposed to HT (38/28 °C) or optimum temperature ( OT, 28/18 °C) for 14 days at flowering stage. HT stress significantly decreased in vitro pollen germination by 22.7 % compared to OT. Pollen from HT stress was deformed; it had a thicker exine wall and a disintegrated tapetum layer. HT stress decreased pod set percentage (35.2 %) compared to OT. This study showed that decreases in pollen in vitro germination by HT stress were caused by anatomical changes in pollen, leading to decreased pod set percentage under HT stress. [ABSTRACT FROM AUTHOR]

The grain legume grass pea ( Lathyrus sativus L.) is adapted to drought-prone environments, but the extent and mechanisms of its tolerance are not well understood. In a pot experiment, water deficit was imposed on plants by withholding water from first flowering until predawn leaf water potential (LWPpd) was −3.12 MPa. Water deficit reduced dry matter, seed yield, harvest index and water use efficiency by 60 %, 87 %, 67 % and 75 %, respectively, when compared with the controls. Flower production stopped when LWPpd fell to −1.8 MPa. At LWPpd−1.5 MPa, only 25 % of flowers resulted in filled pods (compared with 95 % filled pods in the control) with the rest aborted as flowers (48 %) or pods (27 %). Filled pods had more aborted ovules than controls, resulting in 29 % less seeds per pod. Water deficit reduced pollen viability, germination and the number of pollen tubes reaching the ovary by 13 %, 25 % and 31 %, respectively. Emergence from seeds produced from water-deficient plants was 21 % less than controls, but seedling shoot dry mass was 18 % higher, in accordance with the 19 % higher seed mass. The sensitivity of flowering to drought limited pod numbers but enabled plants to retain existing pods and develop near-normal seeds with low β- N-oxalyl- l-α-β-diaminopropionic acid toxin concentrations. This trait is useful for farming systems reliant on harvested seed for the next crop and in cases where seed size influences the value of the product. [ABSTRACT FROM AUTHOR]

In A-lines of sorghum ( Sorghum bicolor L. Moench), seed production under field conditions with manual pollination is generally lower than that in self-pollinated B-lines. This may be associated with floral differences. Six pairs of A/B-lines and four R-lines were evaluated during 2005 and 2006 at Montecillo, State of México (2240 m altitude). Rachis length, number of primary branches and fertile flowers per panicle, 100-seed weight, seed number, seed yield and seed set per panicle were evaluated. In the A-lines, the pistil characteristics were also measured and in the male-fertile lines, the size of anthers and the amount and size of viable pollen were recorded. Compared with the A- and B-lines, the R-lines exhibited significantly higher (P ≤ 0.05) numbers of flowers, seed set and seed yield per panicle and they also produced more pollen grains of larger size and with greater viability during their longer flowering period (FP). Between A- and B-lines, there were differences (P ≤ 0.05) in most of the yield traits, which also interacted with year. The proportion of viable pollen in B- and R-lines (75 %) was not considered to be a factor that might account for their low seed production. Chilling temperatures (3.5–8.4 °C) during the FP could have affected stigma receptivity in the three different line types and thus may have reduced seed set in the male-fertile lines. [ABSTRACT FROM AUTHOR]

Pollen formation in rice ( Oryza sativa L.) is highly vulnerable to environmental stresses such as heat, chilling and drought. In rice plants exposed to drought during male reproductive development, the most obvious damage often observed is a decline in the number of engorged pollen and grain set. This has been well characterized in rice under chilling and to a lesser extent under drought stress. Moreover, detailed literature on the immediate effects of drought on developing young microspores in rice is still limited. Here, we report findings from experiments on rice plants exposed to water deficit for three consecutive days during early stages of anther development. When the osmotic potential of the growing medium was equal to or less than −0.5 MPa, as induced by polyethylene glycol, the leaf water potential was significantly lowered and grain set was reduced. A strong correlation between grain set and viable young microspores (P < 0.001, r2 = 0.8223) indicates that water deficit immediately reduced fertility of rice plants at the time of exposure. This result suggests a new underlying mechanism of water deficit-induced pollen abortion in rice. [ABSTRACT FROM AUTHOR]