Pigments and Epicuticular Wax in Wheat Spikelets and Grains Under Terminal Heat-Stress

Growth, development and productivity of wheat are significantly influenced by heat stress. Terminal heat stress (prevalence of heat stress at anthesis and grain-filling stages) leads to reduction in productivity and quality of wheat grains. Being photosynthetically active, ear of wheat plant is beneficial, particularly under terminal heat stress. This study investigated a few ear related morpho-physiological traits across twenty-nine wheat genotypes under terminal heat stress condition. Genotypic variability was quantified for different traits and contrasting genotypes were identified. Intra-ear competition was noticed at morphological level. Ear traits such as; low temperature of ear surface (for better and sustained photosynthesis), more stomatal density on glumes (for keeping ear temperature low via transpiratory cooling), longer awns (for higher surface area of ear, faster grain growth rate and more width of ear due to broader spikelets with more florets) and higher succulency of ear (for more ear length and number of grains in ear) supported for higher grain yield under terminal heat stress. Total projected surface area of ear was calculated from the images of ear and thereby a new image-based method is developed. This study clearly suggested that thermal imaging of ear can be used as a non-destructive and rapid screening/phenotyping technique to evaluate the physiological performance and thermo-tolerance status across the diverse genotypes/populations of wheat under heat stress condition. Lastly, inter-relationships among different ear related traits are summarized along with the suggestions for future lines of work that can help in making wheat more thermo-tolerant.

Climate change will be one of the most critical dangers to agriculture in the coming years. On average, abiotic stresses account for 50% of the production losses in agricultural production. Terminal stress is a major environmental issue limiting wheat production in the majority of wheat-growing regions across the world. The term "terminal heat stress" refers to a rise in temperature (> 30°C) after anthesis during grain development which impairs the process of grain filling in wheat. Rising temperatures shorten the vegetative and reproductive periods of the wheat crop, but the reproductive stage is more vulnerable than the vegetative. The major portion of India, including the north-eastern plain zone, the central zone, and the peninsular zone, experienced terminal stress over the summer. There are numerous solutions available for mitigating the harmful effects of terminal heat stress on wheat crops. Adjusting sowing time is one of the most impactful agronomic techniques. Wheat planting methods such as conservation tillage, bed sowing, conventional tillage plus mulch, and surface residue preservation are considered suitable alternatives for mitigating terminal stress. Moreover, irrigation at a critical period reduces terminal heat stress and boosts wheat grain development. Foliar spraying of osmoprotectants such as KNO3, Thiourea, Zn, and many others during anthesis and post-anthesis can also help in alleviating the effects of high-temperature stress on wheat crops.

Terminal heat stress (THS) causes abrupt modulation in the expression of stress-related proteins in developing seeds. These differential expressions are thought to enhance thermotolerance. Hence, a field experiment was conducted with three spring wheat genotypes, Raj 4014 (heat sensitive), K 7903 (heat escaper) and WH 730 (heat tolerant), for the identification of THS-associated proteins. To expose the plants to different levels of temperatures at the time of grain filling, the crop was sown during the second week of November and during the first week of January. The average ambient temperatures during the grain growth phase between anthesis and physiological maturity were 25.5 °C and 24.9 °C when sown in November and 31.3 °C and 32.0 °C when sown in January in 2012–2013 and 2013–2014, respectively. SDS-PAGE revealed considerable differences in grain proteome at different stages of grain filling in response to THS. Results showed that RAJ 4014 and K 7903 had very high homology in terms of qualitative pattern of protein bands as compared to WH 730. RAJ 4014 and K 7903 showed the expression of two new THS-responsive proteins (~ 40 and 105 kDa) at 7 days post anthesis (DPA) under THS. These protein bands appeared in WH 730 subsequently at 14 DPA but with low intensity. While protein bands of ~ 90 and 42 kDa appeared in K 7903 at 7 DPA, other two genotypes showed these bands at 14 DPA under both normal and THS conditions. These information could help in designing a strategy for developing heat-tolerant cultivars in molecular breeding programmes.

Terminal heat stress (HS) is a key barrier for wheat grain yield and quality. Various physiochemical and molecular parameters such as photosynthetic rate, expression analysis and activity of starch synthase (SS), total starch, amylose and amylopectin content, total amylolytic activity, and total antioxidant capacity (TAC) were analysed in wheat cvs.HD3059 (thermotolerant) and BT-Schomburgk (thermosusceptible) at grain-fillingstage under HS (32°C and 40°C, 1h). The decrease in photosynthetic rate was observed under HS. Expression analysis of the SS gene at transcript level showed downregulation in both the wheat cvs.HD3059 and BT-Schombugk under HS (32°C and 40ºC, 1h) as compared to the control. Although the downregulation of SS gene transcript expression was less in HD3059 than BT-Schombugk. Both the cultivars showed decrease in starch synthase activity and starch content under HS and the overall content was higher in HD3059, compared to BT-Schomburgk. Higher total amylolytic activity and amylose content were observed in BT-Schomburgk. Scanning electron microscopy (SEM) showed un-structured starch granules under HS. Total antioxidant capacity (TAC) was found higher in HD3059 (14.07mM FeSO4 gm-1 FW) compared to BT-Schomburgk (8.89mM FeSO4 gm-1 FW) under HS (40ºC, 1h). Findings suggest that HS during grain filling stage had more severe impact on the overall physiochemical properties of the wheat grain. Thus the starch bisynthesis pathway associated gene(s) could be exploit to enhance the yield and quality of wheat under heat stress.

Terminal heat stress (HS) has adverse effect on the quantity and quality of wheat grains, as evident from the reduction in the yield. Plant has inherited tolerance mechanism to protect itself from the environmental stresses by modulating the expression and activity of stress associated genes (SAGs)/proteins (SAPs) which protect the plant from the damage caused by HS. Heat shock transcription factor (HSF) regulates the expression of SAGs in plant under HS. Bioinformatics and phylogenetic characterization of wheat showed the presence of 56 HSFs classified into three groups—A, B, and C. The regulation of Plant HSFs basically takes place at transcriptional, post-transcriptional, translational, and post-translation levels. It also undergoes post-translational modifications such as phosphorylation, ubiquitination, and Small Ubiquitin-like MOdifier (SUMO)-mediated degradation. The expression of Heat Shock Protein (HSP) genes in response to various stimuli is regulated by HSFs. HSF1 has been reported to be the master regulator for cytoprotective HSPs expression. HSF potentially bind and activate his own promoters as well as the promoters of other members of their gene family. HSFs perceive the elevation in temperature through different signaling molecules like H2O2, kinases and ultimately increase the expression of HSPs and other SAPs inside the cell in order to protect the nascent protein from denaturation. HSFs, being placed at pivotal position, needs to be further identified, characterized and manipulated using the advanced genetic tools in order to regulate the expression of potential genes involved in defense mechanism of plants under stress. It can also be used as potential molecular marker in wheat breeding program.

ABSTRACTHeat and drought are two important constraints to global wheat productivity; understanding the genotypic responses for quality parameters under harsh production conditions (drought and heat) is very important for developing nutrient‐dense wheat varieties. A set of 15 modern bread wheat (Triticum aestivum L. subsp. aestivum) and durum wheat (Triticum turgidum subsp. durum) cultivars were tested in nine environments, including three different production conditions (normal, heat and drought) during 2020–21. Genotype stability performance for yield, nutrition and quality parameters is assessed using multienvironment trials through AMMI and GGE Biplot analysis. We discovered intriguing stress dynamics in grain zinc content (Zn) and grain iron content (Fe). Under heat stress, zinc concentration increases but decreases under drought stress, while iron does the opposite. Selecting zinc, starch and kernel weight under terminal heat stress can boost yield. Protein content and yield are inversely related, making it difficult for breeders to optimise both traits. G × E interactions and stability indices across all environments have found genotypes with high‐yielding stable genotypes, G12 (MP1358) (42.09 ppm) and G5 (HI1544) (42.41 ppm) have high Fe content. G12 (MP1358) (14.98%) ranked highest in protein concentration. Meanwhile, for Zn content, G11 (MACS 4058) (45.23 ppm) and G15 (WH730) (42.44 ppm) were top performers across environments. G7 (HI 1636) and G12 (MP1358) stand out as a win‐win genotype for their high potential and stability in yield, protein, Zn and Fe content. Our study shows the complex relationships and possible suggestions for targeted breeding programmes under heat and drought stress conditions to improve wheat grain quality and micronutrient profiles without yield loss.

Heat is an important abiotic stress during wheat (Triticum aestivum L.) grain‐filling in South Asia. A study was undertaken to determine effectiveness of selection for reduction in 1000‐kernel weight (TKWR) under heat stress to increase grain yield. Selection was made for low and high TKWR and selected progenies were evaluated in timely and late seeded trials at two locations in Nepal in 2003. One thousand kernel weight (TKW), biomass yield, grain yield, harvest index (HI), grain‐filling duration (GFD) and area under spot blotch progress curve per day (AUDPC/day) were examined. The low and high TKWR groups did not differ significantly for TKW, biomass yield, grain yield, HI, days to heading, GFD and AUDPC/day under timely seeding. However, low TKWR lines showed higher TKW, biomass yield, grain yield, HI, and GFD and lower AUDPC/day than the lines with high TKWR under late seeding. Realized heritability estimates for TKWR ranged from 0.68 to 0.85. The findings show that selection for low TKWR could be used as an indirect selection criterion to identify high grain yielding lines under terminal heat stress.

Nitrogen (N) deficiency and heat stress (HS) are major abiotic stresses that affect the quantity and quality of wheat grains. This study was conducted to examine wheat varietal response to RSI and RNDVI at the anthesis stage and their relationship to yield and yield-related traits under variable N supply and terminal heat stress. Twelve wheat varieties were evaluated in 2016–2017 and 2017–2018 at the National Agricultural Research Centre (NARC), Islamabad, Pakistan. The experiment was divided into three sets, i.e., N120 (120 kg N/ha), N60 (60 kg N/ha) and N0 (0 kg N/ha), based on the nitrogen fertilizer application. The physiological and yield-related parameters were recorded. Mean grain yield for all twelve varieties, averaged from two years of data, ranged between 1655.0 and 3890.1 kg/ha. Maximum RSI (0.99), RNDVI (1.03) and GY (3890.9 kg/ha) were recorded for FSD-08, while AARI-11 showed minimum RSI (0.50), RNDVI (0.56) and GY (1396.40 kg/ha). In the present study, mean CTD was lower, at N0 (3.57 °C), followed by N60 (5.07 °C) and N120 (5.47 °C) on average for the two years of data. The strong positive correlation of RSI and RNDVI with grain yield at R2 = 0.73 and R2 = 0.49 suggest that these parameters can be used as efficient and precise selection criteria for identifying nitrogen-use-efficient wheat varieties under terminal heat-stress conditions. This work will help the researchers to identify and develop nitrogen-use-efficient and thermos-tolerant wheat cultivars by minimizing the negative impacts of heat stress at the anthesis stage.

Wheat is one of the most common staple foods in the world. According to national agricultural research, an entire 40% of wheat grain quality has been decreased due to wheat diseases. The wheat disease mainly affects the wheat plant. Sometimes, the wheat disease damages the whole wheat plant. When the whole wheat plant is damaged, the quality of wheat grain is decreased. There are different varieties of wheat diseases such as fungal, bacterial, and virus-based diseases. One of the most common loose smut fungal diseases that decrease the grain quality in each wheat spikelet. Therefore, the identification of wheat diseases is important. In this paper, an automatic system for the identification of loose smut wheat disease along with its severity is proposed. The identification system uses 2000 RGB images which have been collected from secondary sources. Among all datasets, a total of 800, 700 images have been randomly selected for training and testing purposes in the Mask RCNN model. Through Labelme software, the images are labelled with ground and truth labels. During identification, our proposed system achieves a 97.8% F1 score for loose smut identification with bounding boxes. The severity of loose smut has been calculated through the disease severity index. With the help of DSI, a total of 63% severity for loose smut has been estimated in different wheat spikelets.

BackgroundWheat spike architecture is a key determinant of multiple grain yield components and detailed examination of spike morphometric traits is beneficial to explain wheat grain yield and the effects of differing agronomy and genetics. However, quantification of spike morphometric traits has been very limited because it relies on time-consuming manual measurements.ResultsIn this study, using X-ray Computed Tomography imaging, we proposed a method to efficiently detect the 3D architecture of wheat spikes and component spikelets by clustering grains based on their Euclidean distance and relative positions. Morphometric characteristics of wheat spikelets and grains, e.g., number, size and spatial distribution along the spike can be determined. Two commercial wheat cultivars, one old, Maris Widgeon, and one modern, Siskin, were studied as examples. The average grain volume of Maris Widgeon and Siskin did not differ, but Siskin had more grains per spike and therefore greater total grain volume per spike. The spike length and spikelet number were not statistically different between the two cultivars. However, Siskin had a higher spikelet density (number of spikelets per unit spike length), with more grains and greater grain volume per spikelet than Maris Widgeon. Spatial distribution analysis revealed the number of grains, the average grain volume and the total grain volume of individual spikelets varied along the spike. Siskin had more grains and greater grain volumes per spikelet from spikelet 6, but not spikelet 1–5, compared with Maris Widgeon. The distribution of average grain volume along the spike was similar for the two wheat cultivars.ConclusionThe proposed method can efficiently extract spike, spikelet and grain morphometric traits of different wheat cultivars, which can contribute to a more detailed understanding of the sink of wheat grain yield.

Terminal thermal stress, occurring under varying climatic conditions, significantly reduces wheat yield by affecting fertilization and grain filling processes. Wheat crop damage from terminal heat stress may be lessened by the use of biostimulants. The purpose of this study is to apply fulvic acid topically to wheat in order to reduce the effects of heat stress. Wheat crops were subjected to high temperature stress during booting and initial stages of grain in in-vivo, with heat stress applied in staggered intervals in the main plot. Different concentrations of fulvic acid (water spray, 1.25 mg L-1, 2.50 mg L-1, and 3.75 mg L-1) were applied under natural and heat stress conditions during the booting and initial stages of grain of wheat. Heat stress during booting and grain filling phases notably decreased chlorophyll content, growth related parameters and productive tillers. The impact was more significant during the booting stage compared to the filling stage of grain. Application of fulvic acid at concentrations of 3.75 mg L-1 and 2.50 mg L-1 during heat stress at booting and grain filling stages substantially increased chlorophyll content and growth related parameters compared to water spray and 1.25 mg L-1 fulvic acid. These findings imply that fulvic acid applied directly to wheat under heat stress causes thermotolerance, which has a beneficial impact on biochemical and physiological processes.

Improving terminal heat tolerance is an issue of top priority in wheat breeding in the present era of climate change. Present study was carried out to identify the association among traits of economic importance under terminal heat stress environment. The grain yield/sq. meter under terminal heat stress environment recorded highly significant positive correlation both at genotypic and phenotypic level with grain weight/spike, number of spike/sq. meter, harvest index and 1000-grain weight in both the crop seasons. Path coefficient analysis carried out using genotypic correlation coefficients revealed that days to heading contributing maximum positive direct effect towards grain yield under terminal heat stress environment followed by grain filling duration. Other characters contributing positive direct effects towards grain yield were grain weight/spike, number of spike/sq. meter, harvest index and biological yield/sq. meter under both the crop season. Thus, for improving the wheat grain yield under terminal heat stresses conditions, breeder should aim for selecting genotypes with bold grains or high grain weight /spike, more number of tillers/sq. meter, higher harvest index and longer grain filling duration.

Numbers of environmental stresses influence plant growth and development, which limits agricultural production and productivity, globally. High heat stress is a major factor that significantly reduced the wheat grain yield. Terminal heat stress adversely affects wheat plants resulting in low productivity. The ability of the plant material to mitigate the heat stress on yield may depend on the association between yield and other traits, and the variability of a trait will help identify desirable genotypes in a breeding program. For this purpose, sixty-four bread wheat genotypes were evaluated to assess genetic variability, heritability, correlations and path coefficient analysis of the traits. As result, highly significant differences in genotypes for all 15 morpho-physiological traits were observed. GCV and PCV exceeded 42% for total chlorophyll content and 16% for Main spike weight. Grain yield/plot was significantly and positively associated with spike length, spike weight, number of grains/spike, number of spikelets/spike, 1000-grain weight, biological yield/plot, GGR, total chlorophyll content and number of productive tillers/meter. As conclusion, the production of wheat in heat-stressed environment is greatly enhanced by the selection of key morphological and physiological features associated with grain yield. Five genotypes, P13833, P13828, P13031, P13723, and P13726, had high yields under heat stress condition and ought to be utilized as parents in breeding programs.

Northwest Himalayan agriculture is strongly influenced by climate change/variability, and the agriculture is often affected due to several climatic/weather components. This chapter reviews the magnitude of climate change in few important places in terms of change in temperatures, rainfall and glaciers retreat. Due to the fragile nature of mountain ecosystem, the impact of climate change/variability is higher, and this severity can be seen through the different biotic, abiotic stresses. Because of changes in climatic conditions, the microclimate of crop ecosystem is expected to change, which influences the pest and disease spectrum and also its dynamics. The changing climate may favour some pests (sucking pest) and diseases (wheat yellow rust, rice blast, etc.) and suppress some others. New pest (rice brown plant hopper) and disease (maize Phyllosticta and zonate leaf spot) infestations are already been reported in Himalayan hills. The shift in crop season may influence the availability and abundance of pollinators which is a major concern for pollination in cross-pollinated crops. Impact assessment of climatic components with rice-wheat cropping system showed that the higher mean, maximum and minimum temperatures during winter season resulted in poor wheat grain yield, whilst lower mean, maximum and minimum temperatures resulted in poor rice grain yield. Due to weather variability, the drought, cold and terminal heat stresses and extreme weather events often resulted in severe yield losses in rice, garden pea, wheat, ragi, lentil, bhindi, rajmash, French bean, buckwheat and horse gram. Perhaps, most seriously, due to the observed and predicted climate change, there is high uncertainty in crop production in the near future, and adequate attention has to be given to sustain the NW Himalayan agriculture.

The main objectives of the present study were to evaluate the influence of terminal heat stress on the physical, chemical, rheological, textural and baking properties of wheat. Four varieties were evaluated using diverse physical methods, chemical methods, rheological methods (Farinograph, Mixograph, RVA), and also tested by bread making quality. For this purpose, four genotypes Millat-11, Punjab-11, V-07096, and V-10110 with recommended date of sowing, late sowing grains were milled and analyzed for their physico-chemical, rheological and textural analysis. Two sowing dates significantly influenced grain morphology i-e; grain length (6.2 to 6.5 mm), grain width (3.2 to 3.6 mm), 1000 grain weight (36.7 to 48.7 g) and test weight (70 to 75.17 kg/ hL). Particle size index varied from 17.81 to 26.84% significantly differed along with grain hardness in the range of 59.33 to 69.33 HI. The chemical constituents were found significantly different such as moisture content (10.05-11.38%), crude protein (11.54-13.05%, crude fat (0.41-0.52%), crude fiber (0.34-0.50%), ash contents (1.23-1.68%) and falling number of 482-621 seconds. Minerals of different elements ranged like zinc 21.42-26.78 ppm, copper (38.05-48.89 ppm), calcium (31.60-46.52 ppm), iron (3.47-6.68 ppm) and manganese (456.44-645.84 ppm) respectively.