Heat Tolerance In Wheat Research Articles

QTLs and Potential Candidate Genes for Heat Stress Tolerance Identified from the Mapping Populations Specifically Segregating for Fv/Fm in Wheat.

Despite the fact that Fv/Fm (maximum quantum efficiency of photosystem II) is the most widely used parameter for a rapid non-destructive measure of stress detection in plants, there are barely any studies on the genetic understanding of this trait under heat stress. Our aim was to identify quantitative trait locus (QTL) and the potential candidate genes linked to Fv/Fm for improved photosynthesis under heat stress in wheat (Triticum aestivum L.). Three bi-parental F2 mapping populations were generated by crossing three heat tolerant male parents (origin: Afghanistan and Pakistan) selected for high Fv/Fm with a common heat susceptible female parent (origin: Germany) selected for lowest Fv/Fm out of a pool of 1274 wheat cultivars of diverse geographic origin. Parents together with 140 F2 individuals in each population were phenotyped by Fv/Fm under heat stress (40°C for 3 days) around anthesis. The Fv/Fm decreased by 6.3% in the susceptible parent, 1–2.5% in the tolerant parents and intermediately 4–6% in the mapping populations indicating a clear segregation for the trait. The three populations were genotyped with 34,955 DArTseq and 27 simple sequence repeat markers, out of which ca. 1800 polymorphic markers mapped to 27 linkage groups covering all the 21 chromosomes with a total genome length of about 5000 cM. Inclusive composite interval mapping resulted in the identification of one significant and heat-stress driven QTL in each population on day 3 of the heat treatment, two of which were located on chromosome 3B and one on chromosome 1D. These QTLs explained about 13–35% of the phenotypic variation for Fv/Fm with an additive effect of 0.002–0.003 with the positive allele for Fv/Fm originating from the heat tolerant parents. Approximate physical localization of these three QTLs revealed the presence of 12 potential candidate genes having a direct role in photosynthesis and/or heat tolerance. Besides providing an insight into the genetic control of Fv/Fm in the present study, the identified QTLs would be useful in breeding for heat tolerance in wheat.

High Precision Temperature Controlling AGPase in Wheat Affecting Yield and Quality Traits

Adenosine diphosphate glucose pyrophosphorylase (AGPase) is the rate limiting enzyme of starch biosynthesis that directly affects the wheat productivity. AGPase and grain growth rate (GGR) discerned to be following strict temperature regimen in wheat disomic chromosome substitution (DCS) lines. The first half of grain filling period had chromosome 1B and 2D as prominent players, whereas second half was mainly controlled by chromosomes 6A and 5B. Chromosome 2D had major contribution towards yield in a specific temperature range of 23 ± 1.5 °C during initial stages of grain filling which can serve as an effective early screening tool for terminal heat tolerance in wheat. Chromosome 2D with highest amylose content can also be utilized to produce low digestibility flour. Grain yield was found to be significantly associated with spikes/plant, grains/spike, grain weight/spike and plant biomass. Further, path analysis indicated that though grains/spike had less direct effect on grain yield but its indirect impact on grain yield via AGPase-21 activity was high.

Biochemical Defense Response: Characterizing the Plasticity of Source and Sink in Spring Wheat under Terminal Heat Stress.

Wheat is highly prone to terminal heat stress (HS) under late-sown conditions. Delayed- sowing is one of the preferred methods to screen the genotypes for thermotolerance under open field conditions. We investigated the effect of terminal HS on the thermotolerance of four popular genotypes of wheat i.e. WR544, HD2967, HD2932, and HD2285 under field condition. We observed significant variations in the biochemical parameters like protein content, antioxidant activity, proline and total reducing sugar content in leaf, stem, and spike under normal (26 ± 2°C) and terminal HS (36 ± 2°C) conditions. Maximum protein, sugars and proline was observed in HD2967, as compared to other cultivars under terminal HS. Wheat cv. HD2967 showed more adaptability to the terminal HS. Differential protein-profiling in leaves, stem and spike of HD2967 under normal (26 ± 2°C) and terminal HS (36 ± 2°C) showed expression of some unique protein spots. MALDI-TOF/MS analysis showed the DEPs as RuBisCO (Rub), RuBisCO activase (Rca), oxygen evolving enhancer protein (OEEP), hypothetical proteins, etc. Expression analysis of genes associated with photosynthesis (Rub and Rca) and starch biosynthesis pathway (AGPase, SSS and SBE) showed significant variations in the expression under terminal HS. HD2967 showed better performance, as compared to other cultivars under terminal HS. SSS activity observed in HD2967 showed more stability under terminal HS, as compared with other cultivars. Triggering of different biochemical parameters in response to terminal HS was observed to modulate the plasticity of carbon assimilatory pathway. The identified DEPs will enrich the proteomic resources of wheat and will provide a potential biochemical marker for screening wheat germplasm for thermotolerance. The model hypothesized will help the researchers to work in a more focused way to develop terminal heat tolerant wheat without compromising with the quality and quantity of grains.

Using satellite data to identify the causes of and potential solutions for yield gaps in India’s Wheat Belt

Food security will be increasingly challenged by climate change, natural resource degradation, and population growth. Wheat yields, in particular, have already stagnated in many regions and will be further affected by warming temperatures. Despite these challenges, wheat yields can be increased by improving management practices in regions with existing yield gaps. To identify the magnitude and causes of current yield gaps in India, one of the largest wheat producers globally, we produced 30 meter resolution yield maps from 2001 to 2015 across the Indo-Gangetic Plains (IGP), the nation’s main wheat belt. Yield maps were derived using a new method that translates satellite vegetation indices to yield estimates using crop model simulations, bypassing the need for ground calibration data. This is one of the first attempts to apply this method to a smallholder agriculture system, where ground calibration data are rarely available. We find that yields can be increased by 11% on average and up to 32% in the eastern IGP by improving management to current best practices within a given district. Additionally, if current best practices from the highest-yielding state of Punjab are implemented in the eastern IGP, yields could increase by almost 110%. Considering the factors that most influence yields, later sow dates and warmer temperatures are most associated with low yields across the IGP. This suggests that strategies to reduce the negative effects of heat stress, like earlier sowing and planting heat-tolerant wheat varieties, are critical to increasing wheat yields in this globally-important agricultural region.

Identification of heat tolerant wheat lines showing genetic variation in leaf respiration and other physiological traits

A total of 140 diverse spring wheat lines were characterized for agronomic and physiological traits under hot field conditions, and a subset of thirteen were selected for dark leaf respiration studies (Rd). These genetic resources included synthetic-derived lines, landraces, landrace-derived lines, bread wheats, and durum wheats. Initial phenotyping showed that better heat-adapted genotypes (best yielding) exhibited high early biomass (assessed by normalized difference of vegetative index, NDVI), high grainfilling rates, and low canopy temperatures. As for other studies Rd increased as temperature increased (within the range of 15–40 °C), and decreased with plant age. Correlations between Rd and leaf temperature ranged between 0.50 and 0.85. Rd was negatively associated with yield when recorded at 30–35 °C during anthesis and grainfilling. Comparisons between wheat groups showed that synthetic-derived materials expressed lower leaf respiration rates and larger yields than the other groups at warm temperatures.

Genome-wide identification and analysis of biotic and abiotic stress regulation of small heat shock protein (HSP20) family genes in bread wheat

Small Heat Shock Proteins (sHSPs)/HSP20 are molecular chaperones that protect plants by preventing protein aggregation during abiotic stress conditions, especially heat stress. Due to global climate change, high temperature is emerging as a major threat to wheat productivity. Thus, the identification of HSP20 and analysis of HSP transcriptional regulation under different abiotic stresses in wheat would help in understanding the role of these proteins in abiotic stress tolerance. We used sequences of known rice and Arabidopsis HSP20 HMM profiles as queries against publicly available wheat genome and wheat full length cDNA databases (TriFLDB) to identify the respective orthologues from wheat. 163 TaHSP20 (including 109 sHSP and 54 ACD) genes were identified and classified according to the sub-cellular localization and phylogenetic relationship with sequenced grass genomes (Oryza sativa, Sorghum bicolor, Zea mays, Brachypodium distachyon and Setaria italica). Spatio-temporal, biotic and abiotic stress-specific expression patterns in normalized RNA seq and wheat array datasets revealed constitutive as well as inductive responses of HSP20 in different tissues and developmental stages of wheat. Promoter analysis of TaHSP20 genes showed the presence of tissue-specific, biotic, abiotic, light-responsive, circadian and cell cycle-responsive cis-regulatory elements. 14 TaHSP20 family genes were under the regulation of 8 TamiRNA genes. The expression levels of twelve HSP20 genes were studied under abiotic stress conditions in the drought- and heat-tolerant wheat genotype C306. Of the 13 TaHSP20 genes, TaHSP16.9H-CI showed high constitutive expression with upregulation only under salt stress. Both heat and salt stresses upregulated the expression of TaHSP17.4-CI, TaHSP17.7A-CI, TaHSP19.1-CIII, TaACD20.0B-CII and TaACD20.6C-CIV, while TaHSP23.7-MTI was specifically induced only under heat stress. Our results showed that the identified TaHSP20 genes play an important role under different abiotic stress conditions. Thus, the results illustrate the complexity of the TaHSP20 gene family and its stress regulation in wheat, and suggest that sHSPs as attractive breeding targets for improvement of the heat tolerance of wheat.

Overexpression of wheat ferritin gene TaFER-5B enhances tolerance to heat stress and other abiotic stresses associated with the ROS scavenging

BackgroundThe yield of wheat (Triticum aestivum L.), an important crop, is adversely affected by heat stress in many regions of the world. However, the molecular mechanisms underlying thermotolerance are largely unknown.ResultsA novel ferritin gene, TaFER, was identified from our previous heat stress-responsive transcriptome analysis of a heat-tolerant wheat cultivar (TAM107). TaFER was mapped to chromosome 5B and named TaFER-5B. Expression pattern analysis revealed that TaFER-5B was induced by heat, polyethylene glycol (PEG), H2O2 and Fe-ethylenediaminedi(o-hydroxyphenylacetic) acid (Fe-EDDHA). To confirm the function of TaFER-5B in wheat, TaFER-5B was transformed into the wheat cultivar Jimai5265 (JM5265), and the transgenic plants exhibited enhanced thermotolerance. To examine whether the function of ferritin from mono- and dico-species is conserved, TaFER-5B was transformed into Arabidopsis, and overexpression of TaFER-5B functionally complemented the heat stress-sensitive phenotype of a ferritin-lacking mutant of Arabidopsis. Moreover, TaFER-5B is essential for protecting cells against heat stress associated with protecting cells against ROS. In addition, TaFER-5B overexpression also enhanced drought, oxidative and excess iron stress tolerance associated with the ROS scavenging. Finally, TaFER-5B transgenic Arabidopsis and wheat plants exhibited improved leaf iron content.ConclusionsOur results suggest that TaFER-5B plays an important role in enhancing tolerance to heat stress and other abiotic stresses associated with the ROS scavenging.

Terminal heat stress-responsive genes analysis in heat susceptible HDR77 genotype of wheat (Triticum aestivum L.) by using semi-quantative RTPCR

Abiotic stresses particularly heat stress constitutes a serious threat to the world food production in bread wheat. In the present study, candidate gene expression analysis of HDR77 genotype (which is a susceptible genotype based on electrolyte leakage experiment) was carried out and only those candidate genes which were showing two fold change differences were selected from previous research papers These genes were run over cDNA of HDR 77genotype used as template and intensity of bands was checked by semi-quantative RT PCR. Few genes like HSP 80 gene, MADS WP12 gene, HSP 26.6B gene, WRKY53b gene, WRKY72-a gene, HSP26 gene and WRKY 72b gene were upregulated whereas TaVRT- MADS gene, NAC gene and WRKY 10 gene were down-regulated . The heat stress responsive genes will increase our understanding of molecular basis for heat tolerance in different wheat genotypes and future improvement of heat tolerance in wheat and other crops.

Assessment of DNA Polymorphism and Genetic Diversity among Heat Tolerant and Susceptible Wheat (Triticum aestivum L.) Varieties by ISSR Markers

Assessment of DNA Polymorphism and Genetic Diversity among Heat Tolerant and Susceptible Wheat (<i>Triticum aestivum</i> L.) Varieties by ISSR Markers

Influence of elevated CO2 and temperature on physiological traits and yield attributes of heat tolerant wheat genotype Halna grown inside open top chambers

Both CO2 and temperature caused significant changes in crop productivity. An experiment was conducted wherein wheat was grown inside open top chambers (OTCs) in order to determine the effects of elevated atmospheric carbon dioxide (CO2) and temperature on physiology and yield attributes of wheat genotype Halna. Halna was grown with two levels of carbon dioxide, i.e., ambient (400 ppm) and elevated (500 ± 20 ppm) and two levels of temperature, i.e., ambient, and ambient +2 °C during the Rabi (November–April) season of 2014–2015 at ICAR-RCER, Patna, India. The study revealed that elevated CO2 improved water use efficiency by 26.3%, photosynthetic rate by 14.6%, relative water content (RWC) by 15.9%, membrane stability index (MSI) by 6.6%, leaf area (LA) by 4.6%, plant height by 2.53% and grain yield by 26.9% as compared to ambient, while the activity of antioxidant enzymes were decreased, i.e., catalase by −12.59% and peroxidase by −21.04%. However, elevation of temperature by 2 °C decreased the photosynthetic rate by 15.9%, LA by 8.7% and grain yield by 11.7% but activity of CAT (+64.8%), and POX (+7.2%) were increased as compared to ambient condition. Simultaneous elevation of both (CO2 and temperature) caused non-significant increase in leaf area, number of grains ear−1, 1000 grain weight and grain yield as compared to ambient condition. The results indicated that elevated CO2 had positive effects, whereas elevated temperature had negative effects and with simultaneous elevation of CO2 and temperature, elevated CO2 nullified the negative effects of elevated temperature on photosynthetic characteristics and yield components of Halna.

Phenotypic characterization of specific adaptive physiological traits for heat tolerance in wheat

Phenotyping for high temperature stress tolerance in the field presents a challenge due to its interaction with other environmental factors. High temperature stress is one of the devastating abiotic stresses, which severely affect various physiological and biochemical processes. An experiment was conducted for phenotypic characterization of specific adaptive physiological traits for heat tolerance in ten wheat genotypes under normal (timely sown) and terminal high temperature (late sown) environments. The rate of photosynthesis was significantly higher in varieties HUW 234, HD 2932, HD 2864 and WH 1124 under timely sown condition, which also synchronized with yield. Higher net photosynthesis contributed in translocation of photo-assimilates to developing sink. Under late sown condition, relative water content, membrane stability index was lower compared to timely sown condition in all the genotypes due to high temperature induced injury. Canopy temperature depression at 15 days after anthesis had significant positive correlation with grain yield under timely sown condition compared to late sown conditions. The reproductive attributes were significantly higher under timely sown condition compared to late sown terminal high temperature environment in all the genotypes. However, the genotypic variation clearly appeared under both the growing conditions. The genotypes HD 2932, HD 2864, HD 3095, HI 8703 and HUW 234 exhibited greater heat tolerance efficiency and sustained higher yield under prevailing high temperature conditions particularly at grain filling and development stages.

Grain yield, adaptation and progress in breeding for early-maturing and heat-tolerant wheat lines in South Asia

Maintaining wheat productivity under the increasing temperatures in South Asia is a challenge. We focused on developing early maturing wheat lines as an adaptive mechanism in regions suffering from terminal heat stress and those areas that require wheat adapted to shorter cycles under continual high temperature stress. We evaluated the grain yield performance of early-maturing heat-tolerant germplasm developed by CIMMYT, Mexico at diverse locations in South Asia from 2009 to 2014 and estimated the breeding progress for high-yielding and early-maturing heat-tolerant germplasm in South Asia. Each year the trial comprised of 28 new entries, one CIMMYT check (Baj) and a local check variety. Locations were classified by mega environment (ME); ME1 being the temperate irrigated locations with terminal high temperature stress, and ME5 as hot, sub-tropical, irrigated locations. Grain yield (GY), days to heading (DTH) and plant height (PH) were recorded at each location. Effect of temperature on GY was observed in both ME1 and ME5. Across years, mean minimum temperatures in ME1 and mean maximum temperatures in ME5 during grain filling had significant negative association with GY. The ME1 locations were cooler that those in ME5 in the 5 years of evaluations and had a 1–2t/ha higher GY. A mean reduction of 20days for DTH and 20cm in PH was observed in ME5. Negative genetic correlations of −0.43 to −0.79 were observed between GY and DTH in South Asia during 2009–2014. Each year, we identified early-maturing germplasm with higher grain yield than the local checks. A positive trend was observed while estimating the breeding progress across five years for high-yielding early-maturing heat tolerant wheat compared to the local checks in South Asia. The results suggests the potential of the high-yielding early-maturing wheat lines developed at CIMMYT in improving wheat production and maintaining genetic gains in South Asia.

Truncation of grain filling in wheat (Triticum aestivum) triggered by brief heat stress during early grain filling: association with senescence responses and reductions in stem reserves.

Short heat waves during grain filling can reduce grain size and consequently yield in wheat (Triticum aestivum L.). Grain weight responses to heat represent the net outcome of reduced photosynthesis, increased mobilisation of stem reserves (water-soluble carbohydrates, WSC) and accelerated senescence in the grain. To compare their relative roles in grain weight responses under heat, these characteristics were monitored in nine wheat genotypes subjected to a brief heat stress at early grain filling (37°C maximum for 3 days at 10 days after anthesis). Compared with the five tolerant varieties, the four susceptible varieties showed greater heat-triggered reductions in final grain weight, grain filling duration, flag leaf chla and chlb content, stem WSC and PSII functionality (Fv/Fm). Despite the potential for reductions in sugar supply to the developing grains, there was little effect of heat on grain filling rate, suggesting that grain size effects of heat may have instead been driven by premature senescence in the grain. Extreme senescence responses potentially masked stem WSC contributions to grain weight stability. Based on these findings, limiting heat-triggered senescence in the grain may provide an appropriate focus for improving heat tolerance in wheat.

Identification of heat stress tolerant genotypes in bread wheat

Heat stress affects a number of physiological and morphological traits in crops. The present study was undertaken to identify heat tolerant wheat genotypes based on their response for days to flowering and days to maturity. A set of 95 wheat genotypes was evaluated under normal and late sowing conditions. Data analysis revealed that location, sowing time and genotype has marked effect on days to flowering; and sowing time and genotype has significant effect on days to maturity. Based on the time taken by the genotypes to flower and mature under late sowing condition, six genotypes showing heat tolerance in at least two locations were found to be resistant. Heat susceptibility index value was used to identify a total of thirteen genotypes as tolerant to heat for both the traits. The genotypes identified as heat tolerant would form an important resource for the development of high-yielding varieties under heat stress.

Wheat leaf lipids during heat stress: II. Lipids experiencing coordinated metabolism are detected by analysis of lipid co-occurrence.

Identifying lipids that experience coordinated metabolism during heat stress would provide information regarding lipid dynamics under stress conditions and assist in developing heat-tolerant wheat varieties. We hypothesized that co-occurring lipids, which are up-regulated or down-regulated together through time during heat stress, represent groups that can be explained by coordinated metabolism. Wheat plants (Triticum aestivum L.) were subjected to 12 days of high day and/or night temperature stress, followed by a 4-day recovery period. Leaves were sampled at four time points, and 165 lipids were measured by electrospray ionization-tandem mass spectrometry. Correlation analysis of lipid levels in 160 leaf samples from each of two wheat genotypes revealed 13 groups of lipids. Lipids within each group co-occurred through the high day and night temperature stress treatments. The lipid groups can be broadly classified as groups containing extraplastidic phospholipids, plastidic glycerolipids, oxidized glycerolipids, triacylglycerols, acylated sterol glycosides and sterol glycosides. Current knowledge of lipid metabolism suggests that the lipids in each group co-occur because they are regulated by the same enzyme(s). The results suggest that increases in activities of desaturating, oxidizing, glycosylating and acylating enzymes lead to simultaneous changes in levels of multiple lipid species during high day and night temperature stress in wheat.

Screening for heat tolerance in spring wheat (Triticum aestivum l.)

The present investigation was undertaken to identify the promising heat tolerant lines and to evaluate their heat stress responses. Twenty five spring wheat genotypes were studied in non-stressed (optimum sowing) and stressed (late sowing) environments. The experiments were conducted at Regional Wheat Research Centre, Bangladesh Agricultural Research Institute, Gazipur, during the cropping season of 2009-10. Randomized complete block design was used with three replications. Yield and yield contributing phenological and physiological characters varied among the genotypes under both optimum and late sowing conditions. Ground cover, grain filling duration, canopy temperature at grain filling and biomass production were severely affected by the heat stress leading to low grain yield under late sowing condition. G-12, G-13, G-14, G-18, and G-19 were identified as heat tolerant genotypes based on their relative performance in yield components, grain yield and heat susceptibility indices. Present genotypes are found to be ideal candidates to be used in developing heat tolerant wheat varieties. Tropical Agricultural Research and Extension 17(1): 2014: page 26-37

Characterization of heat tolerance in wheat cultivars and effects on production components

Abstract: There is a need for heat tolerant wheat cultivars adapted to the expansion of cultivation areas in warmer regions due to the high demand of this cereal for human consumption. The objective of this study was to evaluate the effect of high temperatures on grain yield and yield components of wheat and characterize heat tolerant wheat genotypes at different development stages. The genotypes were evaluated in the field with and without heat stress. High temperatures reduced the number of spikelets per spike (21%), number of grains per spike (39%), number of grains per spikelet (23%), 1000-grain weight (27%) and grain yield (79%). Cultivars MGS 1 Aliança, Embrapa 42, IAC 24-Tucuruí and IAC 364-Tucuruí III are the most tolerant to heat stress between the stages double ridge and terminal spikelet; MGS 1 Aliança, BRS 264, IAC 24-Tucuruí, IAC 364-Tucuruí III and VI 98053, between meiosis and anthesis; and BRS 254, IAC-24-Tucuruí, IAC-364-Tucuruí III and VI 98053, between anthesis and physiological maturity. High temperatures reduce grain yield and yield components. The number of grains per spike is the most reduced component under heat stress. The genotypes differed in tolerance to heat stress in different developmental stages.

Heat tolerance around flowering in wheat identified as a key trait for increased yield potential in Europe under climate change.

To deliver food security for the 9 billon population in 2050, a 70% increase in world food supply will be required. Projected climatic and environmental changes emphasize the need for breeding strategies that delivers both a substantial increase in yield potential and resilience to extreme weather events such as heat waves, late frost, and drought. Heat stress around sensitive stages of wheat development has been identified as a possible threat to wheat production in Europe. However, no estimates have been made to assess yield losses due to increased frequency and magnitude of heat stress under climate change. Using existing experimental data, the Sirius wheat model was refined by incorporating the effects of extreme temperature during flowering and grain filling on accelerated leaf senescence, grain number, and grain weight. This allowed us, for the first time, to quantify yield losses resulting from heat stress under climate change. The model was used to optimize wheat ideotypes for CMIP5-based climate scenarios for 2050 at six sites in Europe with diverse climates. The yield potential for heat-tolerant ideotypes can be substantially increased in the future (e.g. by 80% at Seville, 100% at Debrecen) compared with the current cultivars by selecting an optimal combination of wheat traits, e.g. optimal phenology and extended duration of grain filling. However, at two sites, Seville and Debrecen, the grain yields of heat-sensitive ideotypes were substantially lower (by 54% and 16%) and more variable compared with heat-tolerant ideotypes, because the extended grain filling required for the increased yield potential was in conflict with episodes of high temperature during flowering and grain filling. Despite much earlier flowering at these sites, the risk of heat stress affecting yields of heat-sensitive ideotypes remained high. Therefore, heat tolerance in wheat is likely to become a key trait for increased yield potential and yield stability in southern Europe in the future.

Heat tolerance indicators in Pakistani wheat (Triticum aestivum L.) genotypes

Abstract The effect of high temperature stress on six wheat cultivars exposed to 35-40 °C for 3 h each day for five consecutive days was examined. High temperature significantly affected total proline, soluble protein content, membrane stability index (MSI), yield, and various yield components, and had a direct effect on growth and other physiological attributes of wheat at anthesis and the milky seed stages. The wheat cultivar AS- 2002 achieved better osmotic adjustment by accumulating more leaf proline. Higher MSI was also observed in AS-2002, as well as Inqalab-91. The anthesis growth stage was found to be more sensitive to heat stress than seed development at the milky stage. Overall heat stress reduced yield 75% at anthesis and 40% at the milky stage. AS-2002 performed better on the basis of yield and yield components. Seed weight per spike was highest in AS- 2002, and lowest in SH-2002. The cumulative response of AS-2002 was better on the basis of physiological and yield attributes. In addition to yield, plant breeders should also include proline and MSI as selection parameter in the breeding program for development of heat tolerant wheat cultivars. Most of the evaluated wheat cultivars/lines were developed for cultivation in the rainfed areas of Pakistan.

Effect of cytoplasmic diversity on post anthesis heat tolerance in wheat

To study the cytoplasmic effects on heat tolerance, the nuclear genomes of ten alloplasmic lines were substituted by four or five backcrosses using ‘Karl 92’, ‘Ventnor’, ‘U1275’ and ‘Jagger’ as the recurrent parent. During the final backcross, reciprocal crosses were made to develop cytoplasmic near isogenic lines. Sixty-eight BC5F1/BC4F1 lines and their parents were evaluated in growth chambers for post anthesis heat tolerance. Plants were grown in the greenhouse and subjected to heat stress in growth chambers 10 days after anthesis for 14 days. Growth chambers were maintained at 35/30 °C for heat stress treatment. To create an optimum temperature treatment, the greenhouse was maintained at 20/15 °C. Effects of high temperature on chlorophyll content and Fv/Fm (photosystem II measuring parameter) were significantly affected by different cytoplasms. Seven cytoplasms showed improved tolerance to heat with at least one recurrent parent. These results indicate that cytoplasmic variations can contribute to an increase in chlorophyll content and quantum efficiency of photosystem II of wheat during heat stress, and also highlight the importance of the interaction between cytoplasmic and nuclear genes. The role of cytoplasm may be considered in wheat breeding programs aimed at improving heat tolerance, but the nature of the interaction between cytoplasm and nuclear gene content warrants further investigation.