Heat-tolerant Cultivars Research Articles

Eustomabreeding, interspecific hybridization and cytogenetics

The development of novel ornamental cultivars requires phenotypic and genetic variation. Interspecific hybridization is an important tool to achieve this variation. Eustoma grandiflorum (Raf.) Shinner, commonly known as lisianthus, has gained importance among ornamental crops, as cut-flower or potted plant, due to the shape of its flowers, which after several years of breeding resembles those of the rose; however, the color of lisianthus flowers ranges from white to purple, including greenish, rose and blue, and many forms with colored eyes, rings and brushes. The genus is endemic to America, and it distributes from the southern United States to Central America, including the Caribbean islands. E. grandiflorum is restricted to the southern United States and to northern Mexico. E. exaltatum (L.) Salisb. Ex G. Don distributes from central Mexico to Central America. Lisianthus breeding began around 50 years ago, and due to an indirect selection, many of the available cultivars nowadays, are susceptible to high temperatures, and if the plantlets are exposed to temperatures above 25°C they might rosette. In this respect, in order to achieve genetic variation and produce heat tolerant Eustoma cultivars, we conducted a breeding program, which includes interspecific hybridization among E. grandiflorum and E. exaltatum, the last being found in its natural habitat at an average temperature above 25°C during summer. Many crosses were performed in both directions, and F1, BC1 and S1 generations were achieved, showing outstanding ornamental traits, such as different color patterns, stem and flower size and heat tolerance. Furthermore, chromosome counts and chromosome identification were possible through in situ hybridization of rDNA and retrotransposon probes to metaphasic chromosomes in both species.

High Resolution Mapping of QTLs for Heat Tolerance in Rice Using a 5K SNP Array

BackgroundHeat stress is one of the major abiotic threats to rice production, next to drought and salinity stress. Incidence of heat stress at reproductive phase of the crop results in abnormal pollination leading to floret sterility, low seed set and poor grain quality. Identification of QTLs and causal genes for heat stress tolerance at flowering will facilitate breeding for improved heat tolerance in rice. In the present study, we used 272 F8 recombinant inbred lines derived from a cross between Nagina22, a well-known heat tolerant Aus cultivar and IR64, a heat sensitive popular Indica rice variety to map the QTLs for heat tolerance.ResultsTo enable precise phenotyping for heat stress tolerance, we used a controlled phenotyping facility available at ICAR-Indian Institute of Wheat and Barley Research, Karnal, India. Based on ‘days to 50% flowering’ data of the RILs, we followed staggered sowing to synchronize flowering to impose heat stress at uniform stage. Using the Illumina infinium 5K SNP array for genotyping the parents and the RILs, and stress susceptibility and stress tolerance indices (SSI and STI) of percent spikelet sterility and yield per plant (g), we identified five QTLs on chromosomes 3, 5, 9 and 12. The identified QTLs explained phenotypic variation in the range of 6.27 to 21. 29%. Of these five QTLs, two high effect QTLs, one novel (qSTIPSS9.1) and one known (qSTIY5.1/qSSIY5.2), were mapped in less than 400 Kbp genomic regions, comprising of 65 and 54 genes, respectively.ConclusionsThe present study identified two major QTLs for heat tolerance in rice in narrow physical intervals, which can be employed for crop improvement by marker assisted selection (MAS) after development of suitable scorable markers for breeding of high yielding heat tolerant rice varieties. This is the first report of a major QTL for heat tolerance on chromosome 9 of rice. Further, a known QTL for heat tolerance on chromosome 5 was narrowed down from 23 Mb to 331 Kbp in this study.

Development of a new heat tolerance assay system for rice spikelet sterility

Background Reduction in rice yield caused by high temperature-induced spikelet sterility has been a serious concern in rice production. To date, several screening methods have been used, although their reproducibility is sometimes poor due to artifacts mainly caused by varietal differences in heading dates and panicle heights (i.e., the distance from the lamps).MethodsWe have developed a novel assay system for heat-induced spikelet sterility by using artificial rice paddies in phytotrons to conduct a highly reproducible assay throughout a year. Plants restricted to the main culm were treated under a series of heat conditions, and height uniformity of each plant was ensured by using height-adjustable pots.ResultsResults suggested that a 3-day heat treatment of 35 °C-day/29 °C-night cycles was the most suitable condition. Under the treatment, two distinct groups were identified among nine heat tolerant cultivars, with no varietal difference in panicle temperature, indicating that the system is capable of eliminating the varietal difference in panicle temperature.ConclusionsIt is concluded that the assay system would be a powerful tool for selecting heat tolerant varieties, as well as the analysis of genetic factors from various cultivars, eliminating potential artifacts.

Wheat multiple synthetic derivatives: a new source for heat stress tolerance adaptive traits.

Heat stress is detrimental to wheat (Triticum aestivum L.) productivity. In this study, we aimed to select heat-tolerant plants from a multiple synthetic derivatives (MSD) population and evaluate their agronomic and physiological traits. We selected six tolerant plants from the population with the background of the cultivar ‘Norin 61’ (N61) and established six MNH (MSD population of N61 selected as heat stress-tolerant) lines. We grew these lines with N61 in the field and growth chamber. In the field, we used optimum and late sowings to ensure plant exposure to heat. In the growth chamber, in addition to N61, we used the heat-tolerant cultivars ‘Gelenson’ and ‘Bacanora’. We confirmed that MNH2 and MNH5 lines acquired heat tolerance. These lines had higher photosynthesis and stomata conductance and exhibited no reduction in grain yield and biomass under heat stress compared to N61. We noticed that N61 had relatively good adaptability to heat stress. Our results indicate that the MSD population includes the diversity of Aegilops tauschii and is a promising resource to uncover useful quantitative traits derived from this wild species. Selected lines could be useful for heat stress tolerance breeding.

Effects of heat stress on photosynthetic characteristics and chloroplast ultrastructure of a heat-sensitive and heat-tolerant cultivar of wucai (Brassica campestris L.)

The hot climate of southern China from late summer to early fall is one of the major factors limiting the yield and quality of wucai (Brassica campestris L.). To study the effects of high temperature on the growth and development of wucai, two cultivars (heat-sensitive ‘WS-6’ and heat-tolerant ‘WS-1’) were subjected to three heat stress treatments for 5 days. The two cultivars were evaluated for plant growth, photosynthetic characteristics, oxidative damage, and activities of antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT). Heat stress treatments higher than 30 °C resulted in significant changes for both cultivars in plant growth (plant height, stem diameter, and single plant weight) and photosynthetic performance [net photosynthetic rate (PN), stomatal conductance (gs), intercellular CO2 concentration (Ci), and leaf transpiration rate (E)]. The chlorophyll (Chl) content was markedly reduced by heat stress, inhibiting photochemical activity. However, larger decreases in growth and photosynthetic parameters occurred under heat stress in WS-6, compared with WS-1. Furthermore, microscopy also revealed greater severity of damage to the photosynthetic apparatus and membrane system of WS-6 under heat stress, compared with WS-1. These effects were probably due to a greater accumulation of reactive oxygen species (ROS) and malondialdehyde (MDA) in WS-6, relative to WS-1. Moreover, higher photochemical efficiency of photosystem II (PSII) and greater activities of antioxidant enzymes were present in WS-1, compared with WS-6. Our results indicated that the extent of heat stress damage in wucai was cultivar dependent. The heat-tolerant cultivar WS-1 had a greater capacity for self-protection and self-regulation under heat stress.

Syringaldazine peroxidase stimulates lignification by enhancing polyamine catabolism in wheat during heat and drought stress

Six wheat cultivars, namely PBW 343, PBW 550 (stress susceptible), PBW 621, PBW 175 (drought tolerant), C 306 and HD 2967 (heat tolerant), were used in this study to evaluate the effect of heat and drought stress on the activities of peroxidases (POXs), diamine oxidase (DAO), polyamine oxidase (PAO) and arginine decarboxylase (ADC) and ornithine decarboxylase (ODC) in relation to contents of polyamines (PAs), lipid peroxide and lignin. High temperature (HT) elevated activities of syringaldazine peroxidase (SPX), guaiacol peroxidase (GPX) and coniferyl alcohol peroxidase (CPX) in heat tolerant cultivars while, drought stress accentuated ADC/ODC activities in drought tolerant cultivars. Both heat and drought stress enhanced activities of DAO and PAO alongwith contents of H2O2 in PBW 175 and C 306. Amongst studied POXs, SPX activity was relatively more and coincided well with lignin content under HT stress while, the levels of ADC/ODC paralleled with putrescine and spermidine contents under drought stress. Higher build up of thiobarbituric acid reactive substances in cultivars PBW 343 and PBW 550 indicated their membrane instability during both the stresses. Our results revealed that SPX mediated lignification leading to higher cell wall rigidity under heat stress and drought increased PAs involved in ROS scavenging due to presence of positive charges which can bind strongly to the negative charges in cellular components such as proteins and phospholipids and thereby stabilize the membranes under stress conditions.

Evaluation of potato (<i>Solanum tuberosum</i> L.) genotypes for yeild and tuber quality related traits at Lowland, Dire Dawa, Eastern Ethiopia

Potato ( Solanum tuberosum L.) produces more nutritious food on less land with short period of time, but the production in lowland areas is limited by high temperatures, because the crop is adapted to cool climates and perform best at about 20°C. The production of potato at lowland areas demands to develop heat tolerant cultivars adaptable specific to high temperatures. Therefore, this research was conducted with the objectives of evaluating the yield and tuber quality related traits of 26 potato genotypes and estimating the genetic diversity under heat stress. The experiment was conducted at Dire Dawa in 2012 during the hottest months with >26 0 C and >33 0 C daily average and highest temperatures, respectively. Genotypes were planted in Randomized Block Design with three replications. The presence of significant differences among potato genotypes were observed for 12 tuber yield and tuber quality related traits. The genotypes produced 7.41 to 24.3 and 4.44 to 22.52 t ha -1 total and marketable tuber yields, respectively, with tuber dry matter content ranged from 14.89 to 20.96%. The highest yields and tuber dry matter content were obtained from heat tolerant genotype (Vivadial). Heritability and expected genetic advance ranged from 22.35 to 87.65 and 15.24 to 54.97%, respectively, while genotypic and phenotypic coefficient of variations ranged from 13.63 to 85.54 and 16.78 to 90.97%, respectively. All the variability components values were medium to high for all traits suggested that selection genotypes on the basis of their performance was effective method to improve the crop in lowland areas. The genotypes were clustered in three groups of which Cluster I and II consisting of 11and 14 genotypes, respectively, while Vivadial formed solitary Cluster III. The research results demonstrated the existence of wider genetic variations among the potato genotypes and the higher chance of developing cultivars adaptable to lowland areas. Keywords: Cluster, Heat tolerant, Genetic variability, Genotypes, Variability components

Susceptibility of Faba Bean (Vicia faba L.) to Heat Stress During Floral Development and Anthesis

Experiments were conducted over 2 years to quantify the response of faba bean (Vicia faba L.) to heat stress. Potted winter faba bean plants (cv. Wizard) were exposed to temperature treatments (18/10; 22/14; 26/18; 30/22; 34/26 °C day/night) for 5 days during floral development and anthesis. Developmental stages of all flowers were scored prior to stress, plants were grown in exclusion from insect pollinators to prevent pollen movement between flowers, and yield was harvested at an individual pod scale, enabling effects of heat stress to be investigated at a high resolution. Susceptibility to stress differed between floral stages; flowers were most affected during initial green‐bud stages. Yield and pollen germination of flowers present before stress showed threshold relationships to stress, with lethal temperatures (t 50) ˜28 °C and ~32 °C, while whole plant yield showed a linear negative relationship to stress with high plasticity in yield allocation, such that yield lost at lower nodes was partially compensated at higher nodal positions. Faba bean has many beneficial attributes for sustainable modern cropping systems but these results suggest that yield will be limited by projected climate change, necessitating the development of heat tolerant cultivars, or improved resilience by other mechanisms such as earlier flowering times.

High temperature-tolerant tomato lines: bioactive compounds

High global temperatures will be a great challenge for agricultural production in the near future. Therefore, adaptation of agricultural crops to the high temperatures or development of new heat-tolerant crops with known bioactive compounds is an important strategy for nutritional health and crop improvement programs. In this context, the bioactive compounds of newly developed high temperature-tolerant tomato lines were investigated in terms of lycopene, β-carotene, ascorbic acid and phenolic compounds to assist breeders for the selection of high temperature tolerant tomato varieties with high nutritional quality. Nineteen tomato lines, including control varieties from the “Turkey F1 Hybrid vegetable variety and quality line development” project and the GAP Agricultural Research Institute, were selected for the investigation. Line 11 was superior in lycopene and β-carotene content, while line 18 was superior in ascorbic acid content as compared to control varieties Cansun F1 and Alsancak RN F1. Urfa 2012 and line 28 were found to have the highest numbers of phenolic compounds. Chlorogenic acid, naringenin, trans-ferulic acid and rutin were key phenolic compounds detected in each of the tomato lines. These newly released tomato lines can be used as value-added germplasm or parent sources to develop new heat-tolerant cultivars in breeding programs or as commercial cultivars for their superior functional qualities.

Differential responses to high temperature during maturation in heat-stress-tolerant cultivars of Japonica rice

High-temperature stress during the grain-filling stage reduces grain quality of rice, and this is a serious problem in Japan, especially in the Kyushu region. To solve this problem, various heat-tolerant cultivars have been bred, such as ‘Nikomaru’, ‘Kumasannochikara’, ‘Genkitsukushi’, ‘Sagabiyori’, and ‘Otentosodachi’. When cultivated under high temperature after flowering, these heat-tolerant cultivars had lower percentages of chalky grains than in the heat-sensitive cultivar ‘Hinohikari’. All the heat-tolerant cultivars markedly decreased the nonstructural carbohydrate content in the stem under the high temperature compared to control condition during early grain-filling stage, which is considered to be a common trait of heat tolerance. Notably, ‘Sagabiyori’, ‘Genkitsukushi’, and ‘Nikomaru’ maintained a nucellar epidermis at 17 days after flowering (DAF) under high temperature, whereas the nucellar epidermis disappeared in ‘Hinohikari’. In addition, the expression of AGPS2b, thought to be a rate-limiting enzyme in starch synthesis, in ‘Kumasannochikara’, ‘Otentosodachi’, and ‘Nikomaru’ did not decrease under high temperature, whereas ‘Hinohikari’, ‘Sagabiyori’, and ‘Genkitsukushi’ could not maintain expression of the gene at 17 DAF. Moreover, the expression of Amy3E, a starch-degradation-related gene considered to induce grain chalkiness, in ‘Kumasannochikara’ at 17 DAF was not increased by high temperature. These results suggest that the heat-stress-tolerant cultivars have various mechanisms for dealing with high-temperature stress.

Breeding for plant heat tolerance at vegetative and reproductive stages.

Key messageThermotolerant crop research.Global warming has become a serious worldwide threat. High temperature is a major environmental factor limiting crop productivity. Current adaptations to high temperature via alterations to technical and management systems are insufficient to sustain yield. For this reason, breeding for heat-tolerant crops is in high demand. This review provides an overview of the effects of high temperature on plant physiology, fertility and crop yield and discusses the strategies for breeding heat-tolerant cultivars. Generating thermotolerant crops seems to be a challenging task as heat sensitivity is highly variable across developmental stages and processes. In response to heat, plants trigger a cascade of events, switching on numerous genes. Although breeding has made substantial advances in developing heat-tolerant lines, the genetic basis and diversity of heat tolerance in plants remain largely unknown. The development of new varieties is expensive and time-consuming, and knowledge of heat tolerance mechanisms would aid the design of strategies to screen germplasm for heat tolerance traits. However, gains in heat tolerance are limited by the often narrow genetic diversity. Exploration and use of wild relatives and landraces in breeding can increase useful genetic diversity in current crops. Due to the complex nature of plant heat tolerance and its immediate global concern, it is essential to face this breeding challenge in a multidisciplinary holistic approach involving governmental agencies, private companies and academic institutions.

Comparative study of diversity based on heat tolerant-related morpho-physiological traits and molecular markers in tall fescue accessions.

Heat stress is a critical challenge to tall fescue (Festuca arundinacea Schreb.) in many areas of the globe and variations in genetic structure and functional traits is for the efficient breeding programs on developing heat tolerant cultivars. Tolerant-related morpho-physiological traits and simple sequence repeat (SSR) markers were employed to survey genetic diversity in greenhouse and growth chamber trials. 100 tall fescue accessions, including 8 commercial cultivars and 92 natural genotypes, showed a high variation in phenotypic performance under heat stress. Based on standardized heat tolerant-related morpho-physiological data, all tall fescue accessions were clustered into five groups. The accessions with similar heat tolerance were likely to be clustered in the same group. The highest genetic diversity was obtained for accessions from Africa judged by Nei’s gene diversity (0.2640) and PIC (0.2112). All grass accessions could be divided into three major groups based on SSR markers, which was partially congruous to the geographical regions and history of introduction. A low correlation was found between morpho-physiological traits and SSR markers by Mantel test. The patterns in morpho-physiological trait variations and genetic diversity associated with heat tolerance were useful to design breeding programs for developing heat stress resistance in tall fescue.

Genome-Wide Transcriptome Analysis During Anthesis Reveals New Insights into the Molecular Basis of Heat Stress Responses in Tolerant and Sensitive Rice Varieties.

Rice is one of the main food crops in the world. In the near future, yield is expected to be under pressure due to unfavorable climatic conditions, such as increasing temperatures. Therefore, improving rice germplasm in order to guarantee rice production under harsh environmental conditions is of top priority. Although many physiological studies have contributed to understanding heat responses during anthesis, the most heat-sensitive stage, molecular data are still largely lacking. In this study, an RNA-sequencing approach of heat- and control-treated reproductive tissues during anthesis was carried out using N22, one of the most heat-tolerant rice cultivars known to date. This analysis revealed that expression of genes encoding a number of transcription factor families, together with signal transduction and metabolic pathway genes, is repressed. On the other hand, expression of genes encoding heat shock factors and heat shock proteins was highly activated. Many of these genes are predominantly expressed at late stages of anther development. Further physiological experiments using heat-tolerant N22 and two sensitive cultivars suggest that reduced yield in heat-sensitive plants may be associated with poor pollen development or production in anthers prior to anthesis. In parallel, induction levels of a set of heat-responsive genes in these tissues correlated well with heat tolerance. Altogether, these findings suggest that proper expression of protective chaperones in anthers is needed before anthesis to overcome stress damage and to ensure fertilization. Genes putatively controlling this process were identified and are valuable candidates to consider for molecular breeding of highly productive heat-tolerant cultivars.

Association of SSR markers with functional traits from heat stress in diverse tall fescue accessions.

BackgroundHeat stress is a critical threat to tall fescue in transitional and warm climate zones. Identification of association between molecular markers and heat tolerance-related functional traits would promote the efficient selection of heat tolerant tall fescue cultivars. Association analysis of heat tolerance-related traits was conducted in 100 diverse tall fescue accessions consisting of 93 natural genotypes originating from 33 countries and 7 turf-type commercial cultivars.ResultsThe panel displayed significant genetic variations in growth rate (GR), turfgrass quality (TQ), survival rate (SR), chlorophyll content (CHL) and evapotranspiration rate (ET) in greenhouse and growth chamber trials. Two subpopulations were detected in the panel of accessions by 1010 SSR alleles with 90 SSR markers, but no obvious relative kinship was observed. 97 and 67 marker alleles associated with heat tolerance-related traits were identified in greenhouse trial and growth chamber trial (P < 0.01) using mix linear model, respectively. Due to different experimental conditions of the two trials, 2 SSR marker alleles associated with GR and ET were simultaneously identified at P < 0.01 level in two trials in response to heat stress.ConclusionHigh-temperature induced great variations of functional traits in tall fescue accessions. And the identified marker alleles associated with functional traits could provide important information about heat tolerance genetic pathways, and be used for molecular assisted breeding to enhance tall fescue performance under heat stress.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0494-5) contains supplementary material, which is available to authorized users.

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 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.

Effects of climate change on cultivation patterns of spring maize and its climatic suitability in Northeast China

To learn the effects of climate change on cultivation patterns of spring maize and its suitability will benefit the strategic decisions for future agricultural adaptation. In this paper, based on the daily data from 68 meteorological stations and 82 agro-meteorological observation stations in Northeast China between 1961 and 2010, the cultivation pattern of spring maize and its climatic suitability in Northeast China were investigated. The agricultural climatic suitability theory was applied. The specific growth phases of spring maize that were most sensitive to environmental limitations were further divided into four stages: from germination to emergence, from emergence to jointing, from jointing to tasseling, and from tasseling to maturity. The average resource suitability index (Isr) was established to evaluate the effects. Higher values of Isr indicate a higher degree of climatic resource suitability. Over the past five decades, the northern planting boundaries of different maturities (late, medium-late, medium, medium-early and early) of spring maize varieties in Northeast China all markedly extended northward and eastward. Of all the varieties, the medium-late maturity variety had the most expanded planting area. This further illustrated the importance of promoting medium-late range heat-tolerant cultivars of spring maize in reducing the unfavorable effect of climate change in the near future in Northeast China. In addition, the most significant extension was found in the early 21st century. Moreover, the southern planting boundaries of unsuitable planting spring maize areas continually compressed northward from the Tonghe County of Heilongjiang Province (128°49′, 46°21′) to the Huma County of Heilongjiang Province (124°11′, 51°26′). Climate change affected not only the planting patterns of spring maize, but also the climatic suitability of spring maize. Significant temporal and spatial changes of Isr from 1961 to 2010 were found. The Isr showed increasing trends, which increased by 0.19 in Heilongjiang Province, 0.16 in Jilin Province and 0.12 in Liaoning Province. Spatial differences of Isr were obvious, with high values shifting northeastward over the past 50 years, indicating more efficient suitability of agricultural climatic resources in Northeast China.

Evaluation of Some Wheat Hybrids under Normal and Heat Stress Conditions

Heat shocks at anthesis are one of the major limitations in wheat productivity in many countries worldwide including Pakistan. Present investigations were designed to battle out this calamity which may further be exploited in breeding heat tolerant cultivars. Seven parents including tolerant, moderately tolerant and susceptible but high yielders were utilized for this purpose and later hybridized in a 7 ×7 diallel fashion. Analysis of variance revealed significant variability for all the parameters studied. Highest value of negative and desirable significant heterosis and heterobeltiosis for plant height was shown by the cross combinations Weebli-1 × Uqab-2000, Inqilab-91 × Shalimar-88 under normal conditions and under stress by the hybrids Uqab-2000 × Weebli-1, Shalimar-88 × Maya/Pavon. Maximum positive heterosis for tillers per plant was recorded by the cross combination Shalimar-88 × Chenab-2000 (12.04%) and maximum positive and highly significant heterobeltiosis was recorded by the cross combination Shalimar-88 × Chenab-2000 (11.46%). Under stress for tillers per plant none of the crosses showed positive estimates. Maximum positive heterosis for 100- grain weight was shown by the cross combination Chenab-2000 × Inqilab-91 (28.22%). Maximum positive heterosis under stress for 100-grain weight was shown by the cross Inqilab-91 × Weebli-1 (23.35%) followed by Chenab-2000 × Inqilab-91 (22.22%). Maximum positive heterosis for grain yield under normal conditions was manifested by the cross combinations Uqab-2000 × Punjab-85 (28.70%) and under stress maximum positive heterosis was recorded by cross combination Shalimar-88 × Uqab-2000 (27.02%). The results of heterosis and heterobeltiosis estimation revealed that the hybrid vigor is available in the current experiment for all the traits and selection of desirable hybrids is the best way to improve the grain yield of bread wheat. Many cross combinations in the current studies may be utilized following pedigree or bulk method to develop heat tolerant wheat varieties because of their ability to perform well under normal and heat stress conditions.

Mapping QTL for the traits associated with heat tolerance in wheat (Triticum aestivum L.).

BackgroundHigh temperature (heat) stress during grain filling is a major problem in most of the wheat growing areas. Developing heat tolerant cultivars has become a principal breeding goal in the Southern and Central Great Plain areas of the USA. Traits associated with high temperature tolerance can be used to develop heat tolerant cultivars in wheat. The present study was conducted to identify chromosomal regions associated with thylakoid membrane damage (TMD), plasmamembrane damage (PMD), and SPAD chlorophyll content (SCC), which are indicative of high temperature tolerance.ResultsIn this study we have reported one of the first linkage maps in wheat using genotype by sequencing SNP (GBS-SNP) markers to extreme response to post anthesis heat stress conditions. The linkage map was comprised of 972 molecular markers (538 Bin, 258 AFLPs, 175 SSRs, and an EST). The genotypes of the RIL population showed strong variation for TMD, SCC and PMD in both generations (F10 and F9). Composite interval mapping identified five QTL regions significantly associated with response to heat stress. Associations were identified for PMD on chromosomes 7A, 2B and 1D, SCC on 6A, 7A, 1B and 1D and TMD on 6A, 7A and 1D. The variability (R2) explained by these QTL ranged from 11.9 to 30.6% for TMD, 11.4 to 30.8% for SCC, and 10.5 to 33.5% for PMD. Molecular markers Xbarc113 and AFLP AGCTCG-347 on chromosome 6A, Xbarc121 and Xbarc49 on 7A, gwm18 and Bin1130 on 1B, Bin178 and Bin81 on 2B and Bin747 and Bin1546 on 1D were associated with these QTL.ConclusionThe identified QTL can be used for marker assisted selection in breeding wheat for improved heat tolerance in Ventnor or Karl 92 genetic background.Electronic supplementary materialThe online version of this article (doi:10.1186/s12863-014-0097-4) contains supplementary material, which is available to authorized users.

Molecular cloning and in-silico characterization of high temperature stress responsive pAPX gene isolated from heat tolerant Indian wheat cv. Raj 3765.

BackgroundHeat stress leads to accelerated production of reactive oxygen species (ROS) which causes a huge amount of oxidative damage to the cellular components of plants. A large number of heat stress related genes as HSPs, catalases, peroxidases are overexpressed at the time of stress. A potent stress responsive gene peroxisomal ascorbate peroxidase (TapAPX) obtained from heat stress (42°C) responsive subtractive cDNA library from a thermo tolerant wheat cv. Raj3765 at anthesis stage was cloned, characterized and its role was validated under heat stress by proteomics and in-silico studies. In the present study we report the characterization at molecular and in-silico level of peroxisomal TapAPX gene isolated from heat tolerant wheat cultivar of India.ResultsqPCR studies of TapAPX gene displayed up to 203 fold level of expression at 42°C heat stress exposure. A full length cDNA of 876 bp obtained by RACE deduced a protein of 292 amino acid residues which gives a complete 3D structure of pAPX by homology modeling. TapAPX cDNA was cloned in expression vector pET28 (a+) and the recombinant protein over-expressed in E. coli BL21 showed highest homology with APX protein as deduced by peptide mass fingerprinting.ConclusionsTapAPX gene from wheat cv Raj3765 has a distinct role in conferring thermo tolerance to the plants and thus can be used in crop improvement programmes for development of crops tolerant to high temperature.Electronic supplementary materialThe online version of this article (doi:10.1186/1756-0500-7-713) contains supplementary material, which is available to authorized users.