Heat Susceptibility Index Research Articles

Genotypic response to heat stress in durum wheat and the expression of small HSP genes

Heat stress is one of the major abiotic stresses that limit wheat growth and yield. To breed heat-tolerant genotypes of durum wheat, a source of tolerance needs to be identified. The objectives of this paper were to evaluate the heat tolerance of seven durum wheat genotypes and to investigate the differential expression of four sHSP genes in heat-tolerant and heat-sensitive genotypes. 14-day-old seedlings were subjected to continuous high temperature of 45 °C for 24 h in a growth chamber, while growth of control seedlings was maintained at 25 °C. Heat tolerance among durum wheat genotypes was evaluated based on heat susceptibility index (HSI). Based on HSI, Haurani 27 and Acsad 65 were categorized as heat-tolerant genotypes, while Um Qais and Noorseih genotypes were categorized as heat sensitive. Two genotypes, Dairalla 6 and Haurani nawawi, were categorized as moderately heat tolerant. The remaining genotype, Sham 1, was categorized as moderately heat resistant. In response to heat stress, changes in the expression level of four sHSP genes (TdHSP26.5, TdHSP23.5, TdHSP17.6, and TdHSP16.9) were analyzed by qRT-PCR in heat-tolerant (Haurani 27 and Acsad 65) and heat-sensitive (Um Qais and Noorseih) wheat genotypes. Heat-tolerant genotypes exhibited higher expression levels of TdHSP26.5 and TdHSP23.5 than sensitive genotypes. The expression of TdHSP17.6 was significantly up-regulated in all genotypes with almost the same extent, while TdHSP16.9 expression was significantly enhanced only in Acsad 65. The observed expression of TdHSP26.5 (plastidal) and TdHSP23.5 (mitochondrial) might contribute to heat tolerance in durum 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

Indices and their Applicability under High Temperature in Potato (<i>Solanum tuberosum</i> L.) Cultivars

The increasing temperature is going to be more vulnerable for cool season crops like potato which requires an optimum productivity temperature of 18 to 20 °C. Thus, breeding for heat tolerance has become very important. Therefore, some previously used indices for abiotic stress tolerance have been used in our study for screening of high temperature stress tolerance in potato. Three high yielding (Kufri jyoti, Kufri megha and Kufri pokraj) and two local (Rangpuria and Badami) commonly grown potato cultivars were selected for our experiment. Potato cultivars were sown under normal condition and two high temperature conditions (polyhouse and early season) and indices such as HSI (heat susceptibility index), HTI (heat tolerance index), GM (geometric mean) and HII (heat intensity index) were used to evaluate the performance of the cultivars under all the three temperature conditions. The positive and significant correlation between HTI (heat tolerance index), and GM (geometric mean) as well as with tuber yield under all the conditions revealed that these indices were efficient in selecting the high temperature tolerant potato cultivars. We recorded the equal applicability of these two indices for both high yielding and local group of potato cultivars. Our study revealed that cultivar Kufri megha and Rangpuria showed higher heat tolerance between high yielding and local cultivars respectively.

Indices and their Applicability under High Temperature in Potato (<i>Solanum tuberosum</i> L.) Cultivars

The increasing temperature is going to be more vulnerable for cool season crops like potato which requires an optimum productivity temperature of 18 to 20 °C. Thus, breeding for heat tolerance has become very important. Therefore, some previously used indices for abiotic stress tolerance have been used in our study for screening of high temperature stress tolerance in potato. Three high yielding (Kufri jyoti, Kufri megha and Kufri pokraj) and two local (Rangpuria and Badami) commonly grown potato cultivars were selected for our experiment. Potato cultivars were sown under normal condition and two high temperature conditions (polyhouse and early season) and indices such as HSI (heat susceptibility index), HTI (heat tolerance index), GM (geometric mean) and HII (heat intensity index) were used to evaluate the performance of the cultivars under all the three temperature conditions. The positive and significant correlation between HTI (heat tolerance index), and GM (geometric mean) as well as with tuber yield under all the conditions revealed that these indices were efficient in selecting the high temperature tolerant potato cultivars. We recorded the equal applicability of these two indices for both high yielding and local group of potato cultivars. Our study revealed that cultivar Kufri megha and Rangpuria showed higher heat tolerance between high yielding and local cultivars respectively.

Evaluation of agronomic and physiological traits associated with high temperature stress tolerance in the winter wheat cultivars

Post-anthesis high temperature stress is a major concern for the winter wheat producing areas in east China, especially in Shandong province. Fourteen agronomic and physiological traits were studied in 58 Chinese wheat accessions under high-temperature conditions in 2012 and 2013. High temperature stress led to reduction in grain yield and other yield component traits. Significant variations were observed for grain yield per plant (GYPP), grain weight per spike (GWS), thousand kernel weight (TKW), grain number of the main-spike, spikelet number and biological yield per plant. Among the physiological traits measured, chlorophyll content and normalized difference vegetation index showed significant variation under high temperature stress. The results indicate that heat susceptibility index estimated for TKW, GYPP, GWS and flag leaf senescence scale (FLSS) could be used as selection criteria for identifying heat tolerant genotypes for the Shandong province. The results also suggest that FLSS is a good, quick visual indicator of stay-green for field selection for heat tolerance. After harvest, TKW can be measured as final indicator of heat tolerance. The varieties Gaoyou 9415, Hemai 13, Jimai 22, Kexin 9, Shannong 8355, Taishan 23, Yannong 5286 and Zimai 7 were heat tolerant and potential germplasm for heat tolerance breeding in Shandong province and other parts of China. The results could be useful for breeding climate resilient varieties for China or other countries in the world suffering high temperature stresses during grain filling period.

Evaluation of wheat chromosome translocation lines for high temperature stress tolerance at grain filling stage.

High temperature (HT, heat) stress is detrimental to wheat (Triticum aestivum L.) production. Wild relatives of bread wheat may offer sources of HT stress tolerance genes because they grow in stressed habitats. Wheat chromosome translocation lines, produced by introgressing small segments of chromosome from wild relatives to bread wheat, were evaluated for tolerance to HT stress during the grain filling stage. Sixteen translocation lines and four wheat cultivars were grown at optimum temperature (OT) of 22/14°C (day/night). Ten days after anthesis, half of the plants were exposed to HT stress of 34/26°C for 16 d, and other half remained at OT. Results showed that HT stress decreased grain yield by 43% compared with OT. Decrease in individual grain weight (by 44%) was the main reason for yield decline at HT. High temperature stress had adverse effects on leaf chlorophyll content and Fv/Fm; and a significant decrease in Fv/Fm was associated with a decline in individual grain weight. Based on the heat response (heat susceptibility indices, HSIs) of physiological and yield traits to each other and to yield HSI, TA5594, TA5617, and TA5088 were highly tolerant and TA5637 and TA5640 were highly susceptible to HT stress. Our results suggest that change in Fv/Fm is a highly useful trait in screening genotypes for HT stress tolerance. This study showed that there is genetic variability among wheat chromosome translocation lines for HT stress tolerance at the grain filling stage and we suggest further screening of a larger set of translocation lines.

Effect of terminal heat stress on yield and yield components of bread wheat genotypes

Grain yield of wheat is severely affected by various biotic and abiotic stresses. Among the abiotic stresses, heat (terminal high temperature) is one of the major causes of low productivity in the late sown conditions in India. In the present investigation, two F2 progenies, from PBW 373 x WH 1081 and PBW 373 x PBW 343 along with their parents and four check varieties (Raj 3765, WH 730, DBW 17 and WH 711) were evaluated in field. Parents and checks were sown under normal (29 Nov., 2011) and late (3 Jan., 2012) conditions, while F2 were sown under late condition only. Data were recorded on 152 plants from each of the both crosses along with parents and check varieties for yield, yield components and physiological traits. Two factors ANOVA exhibited highly significant differences for genotypes, environments and for genotype x environment interactions for days to heading, days to anthesis, days to physiological maturity, grain filling duration, plant height, productive tillers/plant, grains/spike, 1000-grain weight, grain yield/plant, biomass/plant, harvest index and membrane thermostability (MTS). Heat susceptibility index (HSI) for 1000-grain weight and grain yield/plant was observed to be low in all tolerant genotypes (PBW 373, Raj 3765 and WH 730). The performance of heat susceptible parents was affected to more extent in late sown conditions as compared to that in tolerant parents. Grain yield/plant showed a positive correlation with plant height (0.69** and 0.28**), biomass/plant (0.98** and 0.94**) and number of productive tillers/plant (0.89** and 0.85**) in both the crosses. A wide range of variation was observed for days to heading, days to physiological maturity, grain filling duration, productive tillers/plant, grains/spike, biomass/plant, 1000-grain weight, grain yield/plant, canopy temperature depression (CTD) and MTS in first cross, while there was lesser variability in this population as compared to the previous population, for grain filling duration, 1000-grain weight, grain yield per plant, biomass, CTD and chlorophyll fluorescence. A total of 10 segregants expected to yield better performing progeny in heat stress/late sown conditions were selected from each of the two F2 populations.

Physiological traits associated with heat tolerance in bread wheat (Triticum aestivum L.).

Field experiments for evaluating heat tolerance-related physiological traits were conducted for two consecutive years using a mapping population of recombinant inbred lines (RILs) from the cross RAJ4014/WH730. Chlorophyll content (Chl) and chlorophyll fluorescence (CFL) were recorded under timely sown (TS) and late sown (LS) conditions. Late sowing exposes the terminal stage of plants to high temperature stress. Pooled analysis showed that CFL and Chl differed significantly under TS and LS conditions. The mean value of CFL (Fv/Fm) and Chl under both timely and late sown conditions were used as physiological traits for association with markers. Regression analysis revealed significant association of microsatellite markers viz., Xpsp3094 and Xgwm131 with coefficients of determination (R (2)) values for CFL (Fv/Fm) and Chl as 12 and 8%, respectively. The correlation between thousand grain weight (TGW) with Chl and CFL were 14 and 7% and correlation between grain wt./spike with Chl and CFL were 15 and 8%, respectively. The genotypes showing tolerance to terminal heat stress as manifested by low heat susceptibility index (HSI = 0.43) for thousand grain weight, were also found having very low Chl, HSI (-0.52). These results suggest that these physiological traits may be used as a secondary character for screening heat-tolerant genotypes.

Field Adaptation of Some Introduced Wheat (Triticum aestivum L.) Genotypes in Two Altitudes of Tropical Agro-Ecosystem Environment of Indonesia

Heat stress is a major environmental factor limiting wheat productivity in tropical regions such as Indonesia. The objective of this study was to investigate the adaptability of introduced wheat genotypes in tropical agro-ecosystems. Sixteen spring wheat genotypes were grown at two different altitudes i.e. low altitude (176 m asl) with an average temperature of 29.8 °C located at Leuwikopo Field Experimental Station, Bogor Agricultural University, Darmaga Bogor and high altitude (1100 m asl) with an average temperature of 20.6 °C at Cipanas Field Experimental Station (Ornamental Crop Research Station), Cianjur, West Java, Indonesia from July to November 2012. Plant height, number of tillers, flag leaf area, leaf angle, days to flowering, spike number per plant, empty spikelet number, grain weight per plant and 100 grain weight were observed following the standard methods. Heat susceptibility index was calculated based on grain weight per plant. The results showed that cultivation at a low altitude, hotter environment remarkably affected wheat growth and yield, as reflected in overall reduction of plant height, reduced number of tillers and leaf area, and ultimately reduced yield and yield components for most genotypes compared to the same measures taken at high altitude in lower temperatures. Plant growth before heading was similar in both locations, but the days to flowering was longer in high altitude than that in low altitude. High temperature stress in low altitude reduced the spike number/plant, grain weight/plant, 100 grain weight and increase number of empty spikelet/spike. Based on our results for heat susceptibility index, six genotypes, namely Sbr, Ymh, Astreb/Cbrd, Astreb/Ningma, H-20 and Nias, were characterized as heat tolerant genotypes.

Impact of wheat-Leymus racemosus added chromosomes on wheat adaptation and tolerance to heat stress.

Adaptation of wheat (Triticum aestivum L.) to high temperatures could be improved by introducing alien genes from wild relatives. We evaluated the responses of wheat-Leymus racemosus chromosome introgression lines to high temperature to determine their potentiality for developing improved wheat cultivars. Introgression lines and their parent Chinese Spring were evaluated in a growth chamber at the seedling stage and in the field at the reproductive stage in two heat-stressed environments in Sudan. Optimum and late planting were used to ensure exposure of the plants to heat stress at the reproductive stage. The results revealed the impact of several Leymus chromosomes in improving wheat adaptation and tolerance to heat. Three lines possessed enhanced adaptation, whereas two showed high heat tolerance. Two addition lines showed a large number of kernels per spike, while one possessed high yield potential. Grain yield was correlated negatively with the heat susceptibility index, days to heading and maturity and positively with kernel number per spike and triphenyl tetrazolium chloride assay under late planting. The findings suggest that these genetic stocks could be used as a bridge to introduce the valuable Leymus traits into a superior wheat genetic background, thus helping maximize wheat yield in heat-stressed environments.

Late planting heat stress on ear growth physiology of wheat

Grain yield of wheat in Bangladesh is low as it is severely affected by various biotic and abiotic stresses, among them; heat stress (terminal high temperature) is one of the major causes of lower wheat yield in Bangladesh. This paper focuses on the assessment and performance of some wheat genotypes under different temperature regimes and to fix up of suitable potential lines, for high temperature-stressed environments. Four wheat genotypes (Bijoy, BAW 1059, BAW 1064, and Sonora) were tested under normal and heat stress condition to study the influence of late planting heat stress on ear growth physiology of wheat. In membrane thermostability (MT) test, Bijoy, BAW 1059 and BAW 1064 showed less than 50% membrane injury and were considered as heat tolerant (HT) genotypes and Sonora showed more than 50% membrane injury and was considered as heat sensitive genotype (HS). The HT genotypes maintained higher level of proline both in flag leaf and kernel in late planting heat stress condition than that of normal growing condition but HS Sonora produced reverse result. In late planting heat stress condition, Sonora exhibited greater decrease in flag leaf chlorophyll (98%) than that of HT genotypes, Bijoy and BAW 1064 (64%) and BAW 1059 (70%). Due to late planting heat stress, the quantity of ear dry matter accumulation at peak and duration required to attain peak was higher in HT genotypes than the sensitive one. The HT genotypes showed longer ear growth duration, higher stem reserve utilization, higher relative grain yield and low heat susceptibility index (HSI) for grain yield under late planting heat stress condition compared to HS genotype.

Inheritance of terminal heat tolerance in two spring wheat crosses

The objective of this study was to develop an understanding about the genetics of terminal heat tolerance in wheat (Triticum aestivum L.). The minimum number of genes was assessed using Mendelian and quantitative genetic approach. Two crosses were made between heat tolerant and heat susceptible bread wheat cultivars: NW1014 × HUW468 and HUW234 × HUW468. Heat susceptible HUW468 was common in both the crosses. The F4, F5 and F6 generations were evaluated including F1 in two different dates of sowing (normal and very late) under field conditions in year 2006–07. The data was recorded for grain fill duration (GFD) and thousand-grain weight (TGW). Based on data of two dates, decline% and heat susceptibility index (HSI) of GFD and TGW were estimated. Heat tolerance in F1 showed absence of dominance. Estimation of genes using Mendelian approach in F4, F5 and F6 progenies (148–157) of the two crosses suggested that heat tolerance was governed by a minimum of three genes. Quantitative approach also indicated simil...

QTL for yield, yield components and canopy temperature depression in wheat under late sown field conditions

A wheat (Triticum aestivum L.) recombinant inbred line (RIL) population was used to identify quantitative trait loci (QTL) associated with yield, yield components, and canopy temperature depression (CTD) under field conditions. The RIL population, consisting of 118 lines derived from a cross between the stress tolerant cultivar ‘Halberd’ and heat stress sensitive cultivar ‘Karl92’, was grown under optimal and late sown conditions to impose heat stress. Yield and yield components including biomass, spikes m−2, thousand kernel weight, kernel weight and kernel number per spike, as well as single kernel characteristics were determined. In addition, CTD was measured during both moderate (32–33 °C) and extreme heat stress (36–37 °C) during grain-filling. Yield traits showed moderate to high heritability across environments with a large percentage of the variance explained by genetic effects. Composite interval mapping detected 25 stable QTL for the 15 traits measured, with the amount of phenotypic variation explained by individual QTL ranging from 3.5 to 27.1 %. Two QTL for both yield and CTD were co-localized on chromosomes 3BL and 5DL and were independent of phenological QTL. At both loci, the allele from Halberd was associated with both higher yield and a cooler crop canopy. The QTL on 3BL was also pleiotropic for biomass, spikes m−2, and heat susceptibility index. This region as well as other QTL identified in this study may serve as potential targets for fine mapping and marker assisted selection for improving yield potential and stress adaptation of wheat.

Evaluation of growth, yield, relative performance and heat susceptibility of eight wheat (Triticum aestivum L.) genotypes grown under heat stress

Eight spring wheat cultivars were evaluated under three heat stress conditions (early, late and very late) in order to identify suitable cultivars to develop heattolerant genotypes resistant to future global warming. Results from the study indicate that stress did not negatively affect flag leaf area in ‘Prodip’ and ‘Sufi’, flag leaf dry matter partitioning in ‘Prodip’, ‘BARI Gom-26’ and ‘Shatabdi’, above-ground dry matter partitioning in ‘Shatabdi’ and ‘BARI Gom-26’, seedling emergence in ‘Sufi’ and ‘BARI Gom-26’, or tiller production in ‘Sufi’ and ‘BARI Gom-26’. With respect to lower yield reduction, relative performance and heat susceptibility index (HSI), ‘Sufi’ was highly heat stress-tolerant, followed by ‘BARI Gom-26’ and ‘Shatabdi’. On the basis of HSI values in early heat stress and extremely late heat stress (corresponding to early and extremely late sowing), ‘BARI Gom-26’ (HSI=0.10, 0.65) and ‘Shatabdi’ (0.22, 0.62) were highly tolerant to early heat stress and moderately tolerant to extremely late heat stress while ‘Sufi’ was highly tolerant (0.35) to extremely late heat stress and moderately tolerant (0.51) to early heat stress. All other genotypes were susceptible to heat stress, among which ‘Gourab’ (2.19, 1.46) was the most susceptible followed by ‘Sourav’ (1.19, 1.42), ‘Prodip’ (1.03, 1.23), ‘BARI Gom-25’ (1.61, 0.89) and ‘Bijoy’ (1.04, 1.28). Thus, ‘BARI Gom-26’, ‘Shatabdi’ and ‘Sufi’ have the greatest potential to be used as high-yielding wheat genotypes under warm to hot environments and could be used in a breeding programme to develop heat-tolerant wheat.

Evaluation of bread wheat (Triticum aestivumL.) genotypes for terminal heat tolerance under different environments

Thirty five genetically diverse bread wheat genotypes were evaluated for terminal heat tolerance in three environments by altering the sowing dates viz., non stress (E1), mild heat stress (E2) and high heat stress (E3) using physiological indices. Twelve genotypes showed the consistent performance under E1 and E3 environments. Genotypic performance varied substantially over the E1 and E3 environments. Genotypes namely, HD 2733, CL 3125, HD 2189, C 306, DBW 14, WR 544, PBW 373, HD 2932, Kundan, HD 2967, HD 2997 and L 512 showed least heat susceptibility index (HSI) for grain yield ranging from 0.1 to 0.5. These genotypes also showed least HSI for other associated characters viz., canopy temperature depression, membrane stability index, 1000 grain weight and biological yield and hence can be regarded as tolerant to terminal heat stress. Since the identified genotypes can cope up the effect of heat stress, they can be utilized for developing heat tolerant genotypes

CORRELATION AND HEAT SUSCEPTIBILITY INDEX ANALYSIS FOR TERMINAL HEAT TOLERANCE IN BREAD WHEAT

Six generations namely, P1, P2, F2, F3, BC1s and BC2s (2006-07) and P1, P2, F3, F4, BC1ss and BC2ss (2007-08) developed from four parental genotypes viz. DBW 14 (heat tolerant), NP 846 (heat and drought tolerant), WH 147 and Raj 4014 (heat susceptible for late sown). All the six generations from four crosses were evaluated during Rabi 2006-07 and Rabi 2007-08 in a compact family block design with three replications on two sowing dates. Heat susceptibility index values revealed reduction in grain yield in both the years for all the generations of the four crosses. Significant estimates of correlation of grain yield with days to heading, days to anthesis and days to maturity were recorded in late sown condition during first year. While under timely sown condition spike length has high estimate correlation with grain yield in first year itself. Significant estimated were recorded for tillers per plant in both the environments in second year. Lowest yield loss was reported in backcross populations of Cross I in both years and among segregating populations of Cross IV observed to be least affected and therefore suggested to be forwarded to further generations and further selection of heat tolerant genotypes.

High temperature combined with drought affect rainfed spring wheat and barley in south-eastern Russia: Yield, relative performance and heat susceptibility index

Among all abiotic stresses, drought is undoubtedly the major factor, which, individually or combined with heat stress, limits crop productivity worldwide. Considering these facts, four spring barley and two spring wheat genotypes were evaluated under two stress (early and late) conditions in a southern arid region of Russia in order to identify suitable spring wheat and barley genotypes for that region and to assess the optimum sowing time for specific genotypes. High temperature followed by deficit soil moisture affected all stages from germination through to reproduction of crop when sown late, finally drastically reducing yield. On the other hand, due to low temperature, germination and stand establishment of crop sown early were highly affected, resulting in lower grain yield. Thus, high temperature (air and soil) followed by drought (deficit soil moisture) in the late-sown crop (from germination to reproductive stages) and low temperature in germination through vegetative stages of the early-sown crop are the most important constraints for crop production in this arid region. From the overall performance (yield, relative performance and stress susceptibility index), genotype ‘Zernograd.770’ is recommended for both early and late drought stressed areas and ‘Ratnik’ were sensitive to stress both at low temperatures when sown early and high temperatures followed by drought when sown late. Key words: High temperature, drought, spring wheat, barley, Russia.

Phenology, Growth and Yield of Three Wheat (Triticum aestivum L.) Varieties as Affected by High Temperature Stress

Wheat is the most important cereal in the world. However, due to an increasing trend of rising temperatures around the world, wheat may be exposed to greater thermal stress in the near future. Therefore, the identification and development of suitable wheat varieties is an important step to resolve this threat to production and to achieve high yield, even under high temperature stress. In this context, phenology, growth and yield of three elite varieties of wheat (‘Gourab’, ‘BARI Gom-25’ and ‘BARI Gom-26’) were evaluated under two sowing conditions: optimum (sown on November 15) and late heat stress condition (sown on December 27). All wheat varieties, when sown late, faced severe temperature stress that significantly affected phenology, growth and finally yield. Taking into consideration phenological variation, dry matter (fresh and dry weight) partitioning and grain yield, variety ‘BARI Gom-26’ performed better both in optimum and late heat stress, followed by ‘BARI Gom-25’; ‘Gourab’ performed the least. On the basis of heat tolerance parameters [relative performance (RP) and heat susceptibility index (HSI)], ‘BARI Gom-25’ (RP-79%; HSI-0.7) was the best performing variety followed by ‘BARI Gom-26’ (RP-74%; HSI-0.9) under heat stress while ‘Gourab’ (RP-61%; HSI-1.3) was sensitive to heat.

Heat tolerance in relation to acquired thermotolerance for membrane lipids in bread wheat

Cell membrane stability (CMS) and tetrazolium triphenyl chloride (TTC) test, heat susceptibility index (HSI), heat response index (HRI) and grain yield were used to evaluate diverse 28 bread wheat genotypes including parents and their progenies under normal and heat stress conditions for two years. The genotypes differed significantly for all the characters indicating considerable variation for improvement of these traits. The varieties WH 1021 had a desirable combination of grain yield and heat tolerance potential, while WH 730 had a combination of cellular thermotolerance (TTC and chlorophyll fluorescence), heat tolerance (HRI) and high grain yield under heat stress conditions. Correlation coefficients revealed that HRI was the most important trait followed by TTC because the genotype having high HRI also had high grain yield and showed better mitochondrial viability and membrane stability under heat stress. The use of the parents with high GCA effects, namely, NIAW 34 and WH 730 and WH 1021 in crossing programme for thermotolerance may provide desirable segregants for improvement of heat tolerance in material under study.

Exploring the possibility of obtaining terminal heat tolerance in a doubled haploid population of spring wheat (Triticum aestivum L.) in the eastern Gangetic plains of India

High temperature during grain filling stage causes significant yield losses to wheat in south Asia and many other parts of the world. One hundred and forty doubled haploid (DH) wheat lines (including parents), derived from the cross Berkut (heat susceptible)×Krichauff (heat tolerant), were grown in six environments comprising two dates of sowing in three consecutive years (2007–2008, 2008–2009, and 2009–2010) at Banaras Hindu University, Varanasi, India. The objective was to assess DH lines for heat tolerance and to identify superior lines under hot humid environments of the eastern Gangetic plains (EGP) of India. Considerable variation was observed for grain yield (GY), thousand grain weight (TGW), grain fill duration (GFD), and canopy temperature (CT). Likewise, considerable variation was also observed for heat susceptibility index (HSI) of GY, TGW, and GFD. The DH lines were grouped into four categories based on the HSI and around 5–10% lines were categorized as heat tolerant. A few lines yielded significantly more than the better parent and possessed good expression of other traits. The most promising 20 lines have been listed as sources of heat tolerance, with 3 lines better yielding than the superior parent Krichauff. The results demonstrated that it is possible to obtain lines that perform better for yield and yield related traits in heat stressed environments of the EGP of India.