Genetic Variations In Heat Tolerance Research Articles

Quantitative Trait Loci for Heat Stress Tolerance in Brassica rapa L. Are Distributed across the Genome and Occur in Diverse Genetic Groups, Flowering Phenologies and Morphotypes.

Heat stress events during flowering in Brassica crops reduce grain yield and are expected to increase in frequency due to global climate change. We evaluated heat stress tolerance and molecular genetic diversity in a global collection of Brassica rapa accessions, including leafy, rooty and oilseed morphotypes with spring, winter and semi-winter flowering phenology. Tolerance to transient daily heat stress during the early reproductive stage was assessed on 142 lines in a controlled environment. Well-watered plants of each genotype were exposed to the control (25/15 °C day/night temperatures) or heat stress (35/25 °C) treatments for 7 d from the first open flower on the main stem. Bud and leaf temperature depression, leaf conductance and chlorophyll content index were recorded during the temperature treatments. A large genetic variation for heat tolerance and sensitivity was found for above-ground biomass, whole plant seed yield and harvest index and seed yield of five pods on the main stem at maturity. Genetic diversity was assessed on 212 lines with 1602 polymorphic SNP markers with a known location in the B. rapa physical map. Phylogenetic analyses confirmed two major genetic populations: one from East and South Asia and one from Europe. Heat stress-tolerant lines were distributed across diverse geographic origins, morphotypes (leafy, rooty and oilseed) and flowering phenologies (spring, winter and semi-winter types). A genome-wide association analysis of heat stress-related yield traits revealed 57 SNPs distributed across all 10 B. rapa chromosomes, some of which were associated with potential candidate genes for heat stress tolerance.

Inheritance of heat tolerance in perennial ryegrass (Lolium perenne, Poaceae): evidence from progeny array analysis.

BackgroundHeat stress is considered one of the most important environmental factors influencing plant physiology, growth, development, and reproductive output. The occurrence and damage caused by heat stress will likely increase with global climate change. Thus, there is an urgent need to better understand the genetic basis of heat tolerance, especially in cool season plants.Materials and MethodsIn this study, we assessed the inheritance of heat tolerance in perennial ryegrass (Lolium perenne L. subspecies perenne) , a cool season grass, through a comparison of two parental cultivars with their offspring. We crossed plants of a heat tolerant cultivar (Kangaroo Valley) with plants of a heat sensitive cultivar (Norlea), to generate 72 F1 hybrid progeny arrays. Both parents and their progeny were then exposed to heat stress for 40 days, and their photosynthetic performance (Fv/Fm values) and leaf H2O2 content were measured.ResultsAs expected, Kangaroo Valley had significantly higher Fv/Fm values and significantly lower H2O2 concentrations than Norlea. For the F1 progeny arrays, values of Fv/Fm decreased gradually with increasing exposure to heat stress, while the content of H2O 2 increased. The progeny had a wide distribution of Fv/Fm and H 2O2 values at 40 days of heat stress. Approximately 95% of the 72 F1 progeny arrays had Fv/Fm values that were equal to or intermediate to the values of the two parental cultivars and 68% of the progeny arrays had H2O2 concentrations equal to or intermediate to their two parents.ConclusionResults of this study indicate considerable additive genetic variation for heat tolerance among the 72 progeny arrays generated from these crosses, and such diversity can be used to improve heat tolerance in perennial ryegrass cultivars. Our findings point to the benefits of combining physiological measurements within a genetic framework to assess the inheritance of heat tolerance, a complex plant response.

The wheat Seven in absentia gene is associated with increases in biomass and yield in hot climates.

Wheat (Triticum aestivum L.) productivity is severely reduced by high temperatures. Breeding of heat-tolerant cultivars can be achieved by identifying genes controlling physiological and agronomical traits when high temperatures occur and using these to select superior genotypes, but no gene underlying genetic variation for heat tolerance has previously been described. We advanced the positional cloning of qYDH.3BL, a quantitative trait locus (QTL) on bread wheat chromosome 3B associated with increased yield in hot and dry climates. The delimited genomic region contained 12 putative genes and a sequence variant in the promoter region of one gene, Seven in absentia, TaSINA. This was associated with the QTL's effects on early vigour, root growth, plant biomass, and yield components in two distinct wheat populations grown under various growth conditions. Near isogenic lines carrying the positive allele at qYDH.3BL underexpressed TaSINA and had increased vigour and water use efficiency early in development, as well as increased biomass, grain number, and grain weight following heat stress. A survey of worldwide distribution indicated that the positive allele became widespread from the 1950s through the CIMMYT wheat breeding programme but, to date, has been selected only in breeding programmes in Mexico and Australia.

Natural variation of physiological traits, molecular markers, and chlorophyll catabolic genes associated with heat tolerance in perennial ryegrass accessions

BackgroundIdentification of genetic diversity in heat tolerance and associated traits is of great importance for improving heat tolerance in cool-season grass species. The objectives of this study were to determine genetic variations in heat tolerance associated with phenotypic and physiological traits and to identify molecular markers associated with heat tolerance in a diverse collection of perennial ryegrass (Lolium perenne L.).ResultsPlants of 98 accessions were subjected to heat stress (35/30 °C, day/night) or optimal growth temperature (25/20 °C) for 24 d in growth chambers. Overall heat tolerance of those accessions was ranked by principal component analysis (PCA) based on eight phenotypic and physiological traits. Among these traits, electrolyte leakage (EL), chlorophyll content (Chl), relative water content (RWC) had high correlation coefficients (− 0.858, 0.769, and 0.764, respectively) with the PCA ranking of heat tolerance. We also found expression levels of four Chl catabolic genes (CCGs), including LpNYC1, LpNOL, LpSGR, and LpPPH, were significant higher in heat sensitive ryegrass accessions then heat tolerant ones under heat stress. Furthermore, 66 pairs of simple sequence repeat (SSR) markers were used to perform association analysis based on the PCA result. The population structure of ryegrass can be grouped into three clusters, and accessions in cluster C were relatively more heat tolerant than those in cluster A and B. SSR markers significantly associated with above-mentioned traits were identified (R2 > 0.05, p < 0.01)., including two pairs of markers located on chromosome 4 in association with Chl content and another four pairs of markers in association with EL.ConclusionThe result not only identified useful physiological parameters, including EL, Chl content, and RWC, and their associated SSR markers for heat-tolerance breeding of perennial ryegrass, but also highlighted the involvement of Chl catabolism in ryegrass heat tolerance. Such knowledge is of significance for heat-tolerance breeding and heat tolerance mechanisms in perennial ryegrass as well as in other cool-season grass species.

Identification and characterization of novel homeodomain leucine zipper (HD-Zip) transcription factors associated with heat tolerance in perennial ryegrass

The homeodomain leucine zipper (HD-Zip) family transcription factors play roles in regulating plant development and responses to abiotic stress; however, how HD-Zip genes are associated with plant heat tolerance is unclear. The objectives of this study were to characterize HD-Zip I genes in perennial ryegrass (Lolium perenne), analyze the expression pattern under different abiotic stresses and identify novel HD-Zip I members associated with genetic variations in heat tolerance. A total of 13 HD-Zip I genes were identified in the transcriptome of perennial ryegrass. A comprehensive phylogenetic tree of HD-Zip I proteins in perennial ryegrass, Arabidopsis and rice was constructed. Motif analysis between LpHD-Zip I and OsHD-Zip I by MEME was characterized. LpHD-Zip I had close evolutionary relationship to OsHD-Zip I, and HD-Zip I may be subject to functional differentiation between monocotyledons and dicotyledons. qPCR analysis of 13 HD-Zip I genes showed these genes expressed at different levels in roots and leaves. These genes also showed various expression levels under different abiotic stresses (cold, heat, salt and osmotic). Physiological responses of heat-sensitive lines (321681 and 418714) and heat-tolerant lines (231565 and 275660) of perennial ryegrass to heat stress were evaluated. Differential expression levels of four genes (LpHOX6, -8, -21 and -24) were detected between heat-sensitive and heat-tolerant lines. LpHOX6, -8 and -24 expression levels were negatively associated with heat tolerance while LpHOX21 was positively associated with heat tolerance of perennial ryegrass. This is the first study demonstrating the association of four members of the HD-Zip I family (LpHOX6, -8, -21, and -24) with genetic variations in heat tolerance.

Capturing genetic variability and selection of traits for heat tolerance in a chickpea recombinant inbred line (RIL) population under field conditions

Chickpea is the most important pulse crop globally after dry beans. Climate change and increased cropping intensity are forcing chickpea cultivation to relatively higher temperature environments. To assess the genetic variability and identify heat responsive traits, a set of 296 F8–9 recombinant inbred lines (RILs) of the cross ICC 4567 (heat sensitive) × ICC 15614 (heat tolerant) was evaluated under field conditions at ICRISAT, Patancheru, India. The experiment was conducted in an alpha lattice design with three replications during the summer seasons of 2013 and 2014 (heat stress environments, average temperature 35 °C and above), and post-rainy season of 2013 (non-stress environment, max. temperature below 30 °C). A two-fold variation for number of filled pods (FPod), total number of seeds (TS), harvest index (HI), percent pod setting (%PodSet) and grain yield (GY) was observed in the RILs under stress environments compared to non-stress environment. A yield penalty ranging from 22.26% (summer 2013) to 33.30% (summer 2014) was recorded in stress environments. Seed mass measured as 100-seed weight (HSW) was the least affected (6 and 7% reduction) trait, while %PodSet was the most affected (45.86 and 44.31% reduction) trait by high temperatures. Mixed model analysis of variance revealed a high genotypic coefficient of variation (GCV) (23.29–30.22%), phenotypic coefficient of variation (PCV) (25.69–32.44%) along with high heritability (80.89–86.89%) for FPod, TS, %PodSet and GY across the heat stress environments. Correlation studies (r = 0.61–0.97) and principal component analysis (PCA) revealed a strong positive association among the traits GY, FPod, VS and %PodSet under stress environments. Path analysis results showed that TS was the major direct and FPod was the major indirect contributors to GY under heat stress environments. Therefore, the traits that are good indicators of high grain yield under heat stress can be used in indirect selection for developing heat tolerant chickpea cultivars. Moreover, the presence of large genetic variation for heat tolerance in the population may provide an opportunity to use the RILs in future-heat tolerance breeding programme in chickpea.

Differential Responses of Amino Acids and Soluble Proteins to Heat Stress Associated with Genetic Variations in Heat Tolerance for Hard Fescue

Amino acid and protein metabolism are interrelated and both play important roles in plant adaptation to heat stress. The objective of this study was to identify amino acids and soluble proteins associated with genetic variation in heat tolerance of hard fescue (Festuca trachyphylla). According to a previous screening experiment, the hard fescue cultivars Reliant IV and Predator were selected as heat-tolerant and heat-sensitive cultivars, respectively. Plants of these two hard fescue cultivars were exposed to heat stress at 38/33 °C (day/night) or optimal temperature at 21/18 °C in growth chambers. Each cultivar had four replications under each temperature, and the experimental design was a split-plot design, temperature as the main plots and cultivars as the subplots. Under heat stress, ‘Reliant IV’ exhibited higher turf quality (TQ) and greater membrane stability than ‘Predator’. In response to heat stress, total amino acid content increased, whereas total soluble protein content decreased in both cultivars. The greater accumulation of amino acids in ‘Reliant IV’ was contributed by the greater increase of proteins involved in the glycolysis and the tricarboxylic acid (TCA) cycle that provided carbon skeleton for amino acid synthesis. ‘Reliant IV’ leaves exhibited greater extent of increases in the content of six individual amino acids (histidine, glutamine, proline, threonine, aspartate, and tryptophan) than ‘Predator’ under heat stress. Several soluble proteins were upregulated in response to heat stress, to a greater extent in ‘Reliant IV’ than ‘Predator’, including the proteins involved in photosynthesis, protein folding, redox hemostasis, stress signaling, stress defense, cell organization, and metabolism. These differentially accumulated free amino acids and soluble proteins could be associated with the genetic variation in heat tolerance of hard fescue.

Candidate Genes and Molecular Markers Correlated to Physiological Traits for Heat Tolerance in Fine Fescue Cultivars.

Heat stress is one of the major abiotic factors limiting the growth of cool-season grass species during summer season. The objectives of this study were to assess genetic variations in the transcript levels of selected genes in fine fescue cultivars differing in heat tolerance, and to identify single nucleotide polymorphism (SNP) markers associated with candidate genes related to heat tolerance. Plants of 26 cultivars of five fine fescue species (Festuca spp.) were subjected to heat stress (38/33 °C, day/night temperature) in controlled environmental growth chambers. Physiological analysis including leaf chlorophyll content, photochemical efficiency, and electrolyte leakage demonstrated significant genetic variations in heat tolerance among fine fescue cultivars. The transcript levels of selected genes involved in photosynthesis (RuBisCO activase, Photosystem II CP47 reaction center protein), carbohydrate metabolism (Sucrose synthase), energy production (ATP synthase), growth regulation (Actin), oxidative response (Catalase), and stress protection (Heat shock protein 90) were positively correlated with the physiological traits for heat tolerance. SNP markers for those candidate genes exhibited heterozygosity, which could also separate heat-sensitive and heat-tolerant cultivars into clusters. The development of SNP markers for candidate genes in heat tolerance may allow marker-assisted breeding for the development of new heat-tolerant cultivars in fine fescue and other cool-season grass species.

Genetic Variation for Tolerance to Terminal Heat Stress in Dasypyrum villosum

Heat stress substantially reduces the grain yield and quality of wheat (Triticum aestivum L., 2n = 6x = 42, AABBDD genome) and poses a major challenge to sustaining productivity because of global warming. Across wheat‐growing regions in the United States and globally, wheat often experiences terminal heat stress during the postflowering period. Dasypyrum villosum, a wild relative of wheat, has been a useful genetic resource for the improvement of several traits in wheat. Here we report a first survey of terminal heat tolerance in D. villosum. Twenty accessions of D. villosum from seven countries and three common wheat cultivars (checks) were compared. Agronomic traits including single kernel weight, total grain weight, grain number, and shoot weight were evaluated in both nonstress (22°C day, 17°C night) and heat stress (36°C day, 30°C night) conditions in two independent experiments. The results showed that there was significant genetic variation for heat tolerance during the grain‐filling period in D. villosum and that single kernel weight was less affected by heat stress in D. villosum than in common wheat. Three accessions, TA10228 and TA10225 originating in Italy and TA2172 in Turkey, showed the highest terminal heat tolerance. This work suggests that D. villosum may be a useful novel resource for the improvement of heat tolerance in common wheat.

Differential profiles of membrane proteins, fatty acids, and sterols associated with genetic variations in heat tolerance for a perennial grass species, hard fescue (Festuca Trachyphylla)

Cellular membrane composition controls membrane stability, affecting plant tolerance to abiotic stress. The objectives of this study were to examine differential changes in membrane constituents (sterol, fatty acid and membrane protein) in response to heat stress for a cool-season perennial grass species, hard fescue (Festuca trachyphylla) and identify major membrane constituents associated with the genetic variations in heat tolerance for two varieties contrasting in heat tolerance. Plants of heat-tolerant ‘Reliant IV’ and heat-sensitive ‘Predator’ were exposed to heat stress at 38/33°C (day/night) in growth chambers. Under heat stress, ‘Reliant IV’ showed better turf quality, greater membrane stability and higher photochemical efficiency compared to ‘Predator’. Leaf membranes of ‘Reliant IV’ showed greater increase of ethyl sterols (fucosterol, stigmasterol, sitosterol and avenasterol), and two fatty acids [oleic acid (18:1) and linoleic acid (18:2)] under heat stress compared to those for ‘Predator’. Several membrane proteins were less down-regulated or more up-regulated by heat stress in ‘Reliant IV’ than in ‘Predator’, including down-regulated proteins involved in electron transport of photosynthesis (ATP synthase subunits and cytochrome b6-f complex iron-sulfur subunit), signaling (lectin-domain containing receptor kinase A4.2), and protein modification (S-acyltransferase), and up-regulated proteins involved in carboxylation in photosynthesis (Rubisco activase beta form) and stress defense (disease resistance protein 1). These differentially accumulated sterols, fatty acids, and proteins in cellular membranes could contribute to the differential level of heat tolerance between the two varieties of hard fescues. These compounds could be used as biomarkers to select for heat-tolerant germplasm in hard fescues.

Effect of Temperature on Seed Germination in Spinach (Spinacia oleracea)

Breeding heat-tolerant spinach is an important project to meet the demand of increasing spinach production in heat conditions. Seed germination is the early stage to test, screen, and develop heat-tolerant spinach genotypes. The objective of this research was to determine temperature effect on the seed germination percentage and to select heat-tolerant spinach genotypes. A total of nine spinach genotypes were used in this research. The germination experiment was conducted using seven temperatures: 10, 15, 20, 25, 30, 32, and 35 °C under growth chambers. The temperature trials were conducted using completely randomized design (CRD) with three replicates. Spinach seed germination percentage varied among the nine spinach genotypes under the seven temperatures, indicating that genetic variation for heat tolerance existed in the nine spinach genotypes. ‘Donkey’, ‘Marabu’, and ‘Raccoon’ showed higher seed germination percentage with over 70% at 30 and 32 °C, indicating the three spinach genotypes had heat tolerance for germination. However, all spinach genotypes except ‘Ozarka II’ dropped their germination percentages sharply to less than 30%; ‘Ozarka II’ had 63% germination under 35 °C, indicating it is a good source of heat tolerance for seed germination. The higher germination percentages above 30 °C of ‘Ozarka II’, ‘Donkey’, ‘Marabu’, and ‘Raccoon’ may indicate their potential as donors of heat-tolerant traits in spinach breeding program.

Genetic Variation for Heat Tolerance in Primitive Cultivated Subspecies of Triticum turgidum L.

High temperature (heat) stress is a major constraint for the productivity of crops worldwide. Wheat (Triticum spp.) is particularly vulnerable to high temperature stress compared to other crops. The principal way to mitigate heat damage is to develop heat-tolerant varieties by identifying heat-tolerant germplasm and employing the tolerant lines in breeding programs. The objectives of this study were to investigate the genetic variation for heat tolerance in primitive cultivated subspecies of tetraploid wheat Triticum turgidum L. (AABB genome) and to identify heat-tolerant genotypes. Thirty-eight tetraploid wheat accessions belonging to five subspecies collected from 19 countries were studied for heat tolerance in day/night temperatures of 36/30°C beginning at anthesis. Several lines were classified as heat-tolerant based on small reductions in seed number, single-kernel weight, and total grain weight, as well as slow chlorophyll degradation under heat stress. T. turgidum subsp. polonicum IG110572 from Algeria, T. turgidum subsp. dicoccum IG45067 from Oman, and T. turgidum subsp. dicoccum IG45393 from Eritrea had responses similar to the reference heat-tolerant hexaploid wheat, ‘Kauz’. These heat-tolerant accessions may be useful to breeding programs for the improvement of heat tolerance in tetraploid or hexaploid wheat.

Genetic Variation for Heat Tolerance During the Reproductive Phase in Brassica rapa

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

Heritability of Heat Tolerance in Zebra Mussel Veligers

Previous work has suggested that zebra mussel populations differ in temperature tolerance and researchers have hypothesized that these differences have been caused by natural selection. For selection to act on a phenotypic character such as heat tolerance, there must be additive genetic variation for the character within populations. Individuals must have different alleles at loci that contribute to measurable differences in the phenotypic character of interest. We tested the hypothesis that heat tolerance of zebra mussel veligers has an additive genetic component and is therefore heritable. We used a full-sib, half-sib design with a large number of full-sib families (20), half-sib families (5), and offspring (averaging 41) per family (estimated power, β = 0.75). We exposed family groups to a lethal temperature of 34°C and determined individual time-to-death. Our best estimate of heritability (which can range from 0 to 1) was −0.125 (±0.095), which implies that heritability of heat tolerance among veligers was extremely low. These results are surprising given the high genetic diversity reported for North American zebra mussel populations. A lack of additive genetic variation for heat tolerance within the studied population means that heat tolerance of the veliger stage is not likely to increase further via natural selection. Further studies examining both the veliger and adult stages, and examining populations in different watersheds are required to show whether this lack of variation is widespread among North American zebra mussel populations.