Targeted improvement of the wheat genome by marker-assisted selection and understanding its homoeologous gene evolution and expression balance

Increasing global demand for wheat, due to burgeoning human population, increased use in feed, and ethanol production requires improved cultivars to substantially increase its productivity. The objectives of this study were to: i) understand mechanism(s) controlling the unique gene expression balance in the polyploid wheat that may have led to its adaptation and success as a major crop plant, and ii) to make cultivar improvement more targeted, precise, and fast through marker-assisted selection. In silico analysis, confirmed by single stranded conformation polymorphism (SSCP), revealed that more than 91% of the hexaploid wheat genes are expressed from two or more homoeologues. Expression of only 9% of the genes was from one of the three homoeologues. In general, the proportion of expressed copies decreased with the increase in structural copy number. Homoeologous gene expression was further influenced by the physical location of the genes on the chromosomes. Short arms of wheat chromosomes appear to be functionally different from long arms. Expresion of all three homoeologues was favored in the proximal regions of the short arms but in the long arms, the terminal regions were favored. The most significant observation was that tissue specific expression patterns for 87% of the wheat genes were different for different homoeologues. More genes and more homoeologues/gene were expressed in the root tissue and the least number were expressed in meiosis and early stages of flowering. The maximum tissue-specific homoeologous gene expression was observed during flowering and seed development stages and the least was observed in roots. About 30% of the genes showed altered methylation or expression pattern in response to homoeologue copy number change, suggesting that expression of these genes is interdependent among homoeologues. Sequence changes among homoeologues showed a distinct pattern that was common to all genes studied. The middle of the coding region exhibited the least proportion of sequence changes. Accounting for codon usage, the ratio of synonymous to non-synonymous changes did not show any increase in synonymous changes which would be expected due to selection pressure. We therefore postulated that wheat and perhaps other higher eukaryotes possess a mechanism to protect translated parts of the genes from sequence change(s), irrespective of their function. The applied part of my research focused on targeted use of marker-assisted selection for rapid introgression of single genes into popular cultivars. Using marker assisted backcross breeding; we individually transferred seven pest resistance genes into seven winter wheat lines to develop 28 advanced breeding lines. We also optimized a marker-assisted background selection based method of gene introgressions. After testing various approaches by simulations, we incorporated the available information on the distribution of genes and recombination on wheat chromosomes to develop a marker-assisted background selection method to accomplish ≥96% recovery of recurrent parent genome (RPG) in two backcrosses

Enhancing Crop Gene Pools with Beneficial Traits Using Wild Relatives

This review covers genetic resources from wild relatives; barriers and approaches to interspecific gene transfer; beneficial traits from wild relatives that contribute to the gene pool; biotechnological approaches to increase the utilization of wild relatives in crop improvement; and some results of usage of wild relatives in plant breeding

Elucidating and Mapping Heat Tolerance in Wild Tetraploid Wheat (Triticum turgidum L.)

Identifying reliable screening tools and characterizing tolerant germplasm sources is essential for developing wheat (Triticum aestivum L.) varieties suited for the hot areas of the world. Our objective was to evaluate heat tolerance of promising wild tetraploid wheat (Triticum turgidum L.) accessions that could be used as sources of heat tolerance in common- and durum-wheat (Triticum durum) breeding programs. We screened 109 wild tetraploid wheat accessions collected by the International Center for Agriculture Research in the Dry Areas (ICARDA) from the hottest wheat growing areas in Africa and Asia, as well as, two common wheat checks for their response to heat stress by measuring damage to the thylakoid membranes, flag leaf temperature depression (FLTD), and spike temperature depression (STD) during exposure to heat stress for 16 beginning at anthesis. Measurements were taken on the day of anthesis then 4, 8, 12, and 16 days post anthesis (DPA) under controlled optimum and heat-stress conditions. Individual kernel weight (IKW) and heat susceptibility index (HSI) measurements were also obtained. Prolonged exposure to heat stress was associated with increased damage to thylakoid membranes, as indicated by the high ratio of constant fluorescence (O) to peak variable fluorescence (P). A positive and significant correlation was found between O/P ratio and both FLTD and STD under heat-stress conditions. A negative and significant correlation was found between FLTD and HSI and between STD and HSI based on the second and third measurements (4 and 8 DPA). Correlations obtained after the third measurement were not significant because heat-stress accelerated maturity and senescence. For a pedigree-based mapping strategy a family approach was then developed by crossing and back-crossing heat-tolerant and heat-susceptible germplasm. A set of 800 lines resulting from the pedigree-based family approach was phenotyped using FLTD, chlorophyll content and yield and its components under heat stress. Genotyping of these lines was accomplished using simple sequence repeat (SSRs) markers. Some QTLs associated with heat stress tolerance were identified. This study identified potential heat-tolerant wild tetraploid wheat germplasm and QTL conditioning heat tolerance that can be incorporated into wheat breeding programs to improve cultivated common and durum wheat

Advances in Wheat Genetics: From Genome to Field: Proceedings of the 12th International Wheat Genetics Symposium

plant genetics; plant genomics; agricultur

Differential Response to Foliar Pathogens in Wheat as a Consequence of Cytoplasmic Substitution

Wheat alloplasmic lines are plants where the cytoplasmic genome of one wheat species was substituted by those of a wild relative, while maintaining the original nucleus. Our project studied differential responses of various alien cytoplasm in a specific nuclear background to various pathogens to identify NC interaction effects on biotic stress tolerance. This study analyzed fifty selected alloplasmic lines that were tested for disease response to Pyrenophora tritici-repentis isolates Br15 and Pti2. Results indicate that Ae. bicornis cytoplasm with nuclei donor of Chris and Selkirk provides increased resistance to tan spot isolate Br15. Puccinia triticina was used in determining differential responses between alloplasmic and euplasmic lines. A bulk set of four leaf rust isolates indicated Aegilops heldreichii cytoplasm with Chris nucleus provides resistance to the susceptible euplasmic line Chris and showed increased resistance to both tan spot isolates. These data indicates that cytoplasmic variability can improve resistance to plant diseases

Improvement of Australian wheat grain functionality for breadmaking by introgression of novel high-molecular weight glutenin subunits into Australian cultivars

Bread wheat (Triticum aestivum) is one of the most important cereal crops in the world. It is an important component of human diet, chiefly as the main ingredient of the many available presentations of bread and noodles around the world. Wheat flour can produce dough with visco-elasticity properties, which is essential for bread making. Glutenin, a group of grain storage proteins, confers these visco-elasticity properties of dough. From the food production point of view, it is also called functional protein since it regulates end product quality. The breadmaking quality of Australian wheat cultivars can be enhanced by improving grain glutenin protein content. In this thesis, a range of HMW glutenin protein manipulation was conducted utilising introgression lines containing various alleles of the 1Ay high-molecular-weight glutenin subunit (HMW-GS) gene - which is silenced in current Australian wheat cultivars. Wheat lines expressing two 1Ay HMW glutenin subunit alleles, 1Ay21* and 1AyT1, sourced from Italian hexaploid wheat germplasm, were successfully introgressed into a range of commercial Australian cultivars and advanced to the BC4F4 generation before further rounds of selfing were conducted to generate nearly-isogenic lines (NILs) carrying the introgressed genes. The F1 generation was developed by reciprocal crossing of the Australian cultivars with Ay donor wheat lines. MALDI-TOF mass spectrometry and SDS-PAGE were used to confirm introgression of the target 1Ay HMW-GS at each generation. Ay introgression NILs were developed through conventional breeding process that’s why may have change some unwanted gene effects on plants growth habit, grain and protein quality. The influence of different alleles of 1Ay on relative HMW GSs composition, HMW‐ /LMW‐GSs ratio, end‐use quality and grain yield has been evaluated from plants grown in small-scale glasshouse experiments and large-scale field trials. NIR and HPLC analyses were used for protein quantification. Extensograph, farinograph, and baking tests were carried out to evaluate dough and bread quality. Because of traditional breeding, there has been a greater possibility of passing unwanted genes in advance generations. That is why, the agronomic performance on 1Ay allele introgression lines have also been examined though large-scale field trial. Expression of the novel Ay subunits in the NILs was stable in the Australian environment, as evidenced by the analysis results of grain from two years of field trials. No significant differences were observed between the reciprocal crossing NILs in terms of agronomic traits and grain protein attributes based on small scale quality test. However, introgression of the expressed 1Ay subunit genes led to an overall increase in protein and glutenin contents and resulted in significant increases of various end-product quality parameters. The level of changes was variable between the cultivar’s background. The active 1Ay21* subunit increased the amount of total protein by up to 15.4%, gluten content by up to 10%, glutenin content by up to 5%, the HMW-to-LMW-GS ratio and hence improved the dough extensibility (21%) without affecting the expression levels of the other subunits at Bonnie Rock background. On the other hand, expressed 1Ay21* increased polymeric protein (UPP%) by up to 14.3%, and improved dough strength by up to 28% respectively in Livingston background NILs. The Lincoln-derived Ay21* NILs showed increased grain protein% by up to 9% and grain yield up to 10%, indicating that protein content and grain yield can be increased simultaneously by introgressing the expressed Ay21* gene which shows great potential to ultimately increase Australian wheat productivity and value without increasing production costs. NILs at Lincoln bacground also showed increased UPP% by up to 24%, bread volume by up to 28%. The thesis also studied the allelic effect of expressed 1Ay gene that showed the two alleles have different levels of potential in improving grain, dough and baking qualities. On the other hand 1AyT1 subunit increased total grain protein by up to 9%, dough elasticity (Rmax) increased by up to 24%, reduced dough mixing time by up to 23% and increased bread volume by up to 2.4% (rapid-dough protocol) compared to the recurrent parent Livingston. Since this study demonstrated significant variation between two expressed 1Ay alleles (Ay21* and AyT1) allele in influencing protein and end product quality another novel expressed Ay allele (AyT2) from an Israeli wheat tetraploid line also cloned and characterised. NILs were also generated in three Australian wheat cultivars Yitpi, Kukri and Livingston by integrating this novel expressed 1Ay HMW-GS, as for the other two Ay alleles. Result showed that the open reading frame of AyT2 is 1830 bp long and encodes a 608-residue polypeptide. 1AyT2 introgression NILs showed that UPP% increased by up to 50% and seed size increased by up to 36%. The wheat lines developed in the current study and carrying the novel Ay HMW-GS genes have the potential to become new varieties or be used as parent lines by breeding programs to improve grain protein content and composition, thus improving viscoelastic properties of dough and therefore quality of baking products. Such improvement would in turn contribute toward enhancing the marketability of Australian wheat in global markets

Genetic diversity in elite lines and landraces of CIMMYT spring bread wheat and hybrid performance of crosses among elite germplasm

Wheat (Triticum aestivum) is one of the major cereals in the world. During the past years, the world consumption of wheat increased up to nearly 600 million tones, whereas wheat production continuously decreased. Due to land limitations, new production gains must be achieved from improved plant management systems as well as from the development of high yielding varieties. The International Maize and Wheat Improvement Center (CIMMYT) employs different strategies to enhance yield potential in wheat especially for developing countries. For instance, the wheat breeding program focuses on defined mega-environments (MEs), assuming similar growing conditions in certain countries. In the search for useful alleles, breeders often turn back to wild relatives of wheat stored in the CIMMYT gene bank. With the production of synthetic hexaploid bread wheat (SHWs), characteristics from T. durum and T. tauschii can be combined and via backcrossing incorporated into modern breeding materials. Wheat landraces (LCs) are an additional reservoir of resistances to pests and diseases as well as for environmental adaptation. The production of wheat hybrids is seen as a further option to improve yield potential. A considerable amount of genetic diversity among the materials is a prerequisite for all strategies. Due to the worldwide importance of CIMMYT wheat varieties, they represent a suitable source to examine different breeding strategies in wheat. The main objective of our research was to determine the genetic diversity in modern wheat breeding materials and genetic resources at CIMMYT. Specific research questions were: (i) Is the systematic breeding targeted for different MEs reflected in the genetic diversity among breeding lines (Experiment 1)? (ii) Does the production of SHWs (Experiment 2) and the use of LCs (Experiment 3) enhance the genetic variation in modern breeding materials? (iii) Does the development of hybrids represent an option to improve yield potential in wheat? (iv) Is it possible to predict levels of heterosis with the determination of genetic distance (GD) among hybrid parents? (v) Do genomic and EST- derived SSRs differ in the measurement of genetic diversity (Experiments 1 and 3)? (vi) Are GD values based on SSRs correlated with the coefficient of parentage (COP) (Experiments 1 to 4)? In Experiment 1, a total of 68 CIMMYT advanced breeding lines was analyzed with 99 SSRs, of which 51 were EST- and 46 genomic derived SSRs. A high level of genetic diversity (GD = 0.41) was observed among the breeding lines. The majority of variation (91%) was detected among lines targeted to one specific ME, which indicates a broad genetic base of the current CIMMYT breeding materials. Principal coordinate analysis (PCoA) could clearly separate the lines, but they clustered independently from their target MEs. Main explanations are: (i) alleles were selected that provide fitness to several MEs, (ii) adaptation depends only on a small number of genes that were not detected with the SSRs applied, or (iii) too few cycles of selection were considered to separate the germplasm. In Experiment 2, a total of 11 SHWs, 7 recurrent parent lines, and 13 families of backcross-derived lines (SBLs) were analyzed with 90 SSRs. The SHWs clustered far from the SBLs and the recurrent parents in the cluster analyses and PCoA, and formed a distinct germplasm pool with high allelic variation. Two families of SBLs were tested for a selective advantage of the SHW alleles. Six SSRs revealed non-Mendelian inheritance, indicating that the genomic region of SHWs was actively selected for. Thus, the production of SHWs provides a promising approach for the enhancement of genetic variation in modern breeding materials. In Experiment 3, gene bank accessions of 36 LCs from different countries and a total of 119 accessions from nine LCs populations collected in Turkey and Mexico were analysed with 44 and 76 SSRs, respectively. Both LC materials revealed high allelic variation (GD = 0.69 and 0.54). The 36 LC accessions could not be separated according to their continent of origin. An unexpected relationship was observed between the Chilean LC ?Trigo africano? and the Nigerian LCs ?Dikwa?. All of the nine LC populations could be discriminated except for two Turkish LCs collected from the same location. In accordance with previous studies, considerable genetic variation was observed within the LC populations. Our results contributed a lot to the characterisation of the LCs and generated important knowledge for the management of seed bank accessions. In Experiment 4, a total of 112 wheat hybrids and their 22 parental lines were evaluated at two locations in Mexico for grain yield, plant height, days to flowering and maturity. The level of heterosis varied between -15.3% and 14.1%, but was generally too low to compensate for the high costs of hybrid seed production. The correlations between mid-parent values and hybrid performance, as well as between parental line per se performance and general combining ability were significant (P < 0.01) for all traits, and particularly high for grain yield (r = 0.86 and 0.91). PCoA based on 113 SSR markers revealed three groups of parents. However, the correlations of GDs and COPs with the values of heterosis were negative and not significant. Thus, the prospects of large-scale cultivation of hybrid wheat in developing countries are low. The correlations between GDs and COP in Experiments 1 and 3 were generally significant but low. This can be explained by unrealistic assumptions in the calculation of COPs, which ignore the effects of selection and genetic drift. Similarly to genomic SSRs, EST-SSRs did not reflect functional diversity. The latter revealed lower degrees of polymorphism than genomic SSRs in all experiments, but the allele designation was simpler and more reliable. Across all experiments, our study demonstrates that plant breeding does not inevitably lead to a loss of genetic diversity. We confirmed that CIMMYT?s breeding strategies contributed to a successful increase in genetic variation. These results provide useful information to wheat breeders in CIMMYT and other national programs, regarding the use of wild relatives and landraces for the enhancement of the genetic base of wheat germplasm. In addition, our research provides a base of knowledge for future association studies, identification of useful alleles, and their use in marker-assisted selection.Weizen (Triticum aestivum) ist eine der wichtigsten Getreidearten der Welt. Während in den letzten Jahren der Weizenverbrauch weltweit auf knapp 600 Mio. t anstieg, ist die Produktion rückläufig. Ein erneuter Produktionszuwachs kann angesichts weltweit limitierter Anbauflächen nur über verbesserte Anbauverfahren und die Züchtung verbesserter Weizensorten erfolgen. Mit verschiedenen Strategien versucht das Internationale Institut für Mais und Weizenzüchtung (CIMMYT) in Mexiko das Ertragspotential des Weizens speziell in Entwicklungsländern zu erhöhen. Aufgrund der in vielen dieser Länder vergleichbaren Anbaubedingungen züchtet das Weizenprogramm u.a. für definierte Makro-Umwelten (MEs). Auf der Suche nach wertvollen Allelen greifen die CIMMYT-Züchter häufig auf Wildtypen in der Genbank zurück. Mit der Erzeugung von synthetischen Weizen (SHWs) werden Eigenschaften von T. durum und T. tauschii kombiniert und anschließend mittels Rückkreuzungen in modernes Zuchtmaterial von T. aestivum eingebracht. Landrassen (LCs) stellen ein zusätzliches Reservoir für Resistenzen und verbesserte Umweltanpassung dar. Die Züchtung von Hybridweizen wird als weitere Option zur Erhöhung des Ertragspotentials angesehen. Die genetische Diversität im Ausgangsmaterial ist gleichermaßen wichtig für alle diese Züchtungsstrategien. Aufgrund seiner weltweiten Bedeutung stellt das Weizenmaterial des CIMMYT eine ausgezeichnete Quelle zur Untersuchung der verschiedenen Optionen für die Weizenzüchtung dar. Hauptzielsetzung der vorliegenden Studie war die Erforschung der genetischen Diversität in aktuellem Zuchtmaterial und genetischen Ressourcen des CIMMYT. Im Einzelnen wurden folgende Fragestellungen bearbeitet: (1) Spiegelt sich die systematische Züchtung für verschiedene MEs in der genetischen Diversität zwischen Weizenlinien wieder (Experiment 1)? (2) Kann durch die Erzeugung von SHWs (Experiment 2) bzw. die Nutzung von LCs (Experiment 3) eine Erweiterung der genetischen Variation in modernem Zuchtmaterial erreicht werden? (3) Welche Möglichkeiten zur Anhebung des Ertragspotentials bietet die Erzeugung von Hybriden (Experiment 4)? (4) Inwieweit kann mit der Bestimmung genetischer Distanzen (GD) zwischen Elternlinien die Heterosis in Weizenhybriden vorausgesagt werden? (5) Zeigen genomische und EST-abgeleitete SSRs Unterschiede in der Bestimmung genetischer Diversität (Experimente 1 bis 4)? (6) Ist die genetischer Diversität, berechnet anhand von SSRs, mit dem Abstammungskoeffizienten (COP) korreliert (Experimente 1 und 3)? In Experiment 1 wurden 68 Hochleistungslinien mit 99 SSR Markern untersucht, von denen 51 EST- und 46 genomische SSRs waren. Es wurde ein hohes Ausmaß an genetischer Diversität ermittelt (GD = 0,41). Der Hauptteil der genetischen Variation (91%) wurde innerhalb der für MEs gezüchteten Linien gefunden, was auf eine außerordentliche Breite des CIMMYT-Zuchtmaterials hinweist. In der Hauptkoordinatenanalyse (PCoA) gruppierten die Linien unabhängig von ihrer Anpassung an fünf MEs. Mögliche Ursachen dafür sind: (a) Es wurden Allele selektiert, welche hohe Fitness in mehreren MEs bewirken; (b) die für die Anpassung verantwortlichen Allele wurden nicht mit den untersuchten SSRs erfasst; (c) die Selektion auf Anpassung an die MEs erstreckte sich über zu wenige Selektionszyklen. In Experiment 2 wurden 11 SHWs, 7 rekurrente Elternlinien (BWs) und 13 davon abgeleitete Familien von Rückkreuzungslinien (SBLs) mit 90 SSRs untersucht. Anhand einer Clusteranalyse und PCoA konnten die SHWs eindeutig von den SBLs sowie BWs getrennt werden. Sie stellen somit einen eigenständigen Pool an Genmaterial mit hoher Allelvariation dar. Zwei SBL-Familien wurden auf einen selektiven Vorteil der SHW-Allele getestet. Sechs SSRs zeigten dabei eine signifikante Abweichung von den unter Mendelscher Vererbung erwarteten Genfrequenzen, was auf eine gerichtete Selektion der SHW-Allele schließen lässt. Die Erzeugung von SHWs bietet somit ein Potential zur Erweiterung der genetischen Variation in modernem Zuchtmaterial. In Experiment 3 wurden Akzessionen von 36 LC aus verschiedenen Ländern sowie 119 Akzessionen von neun LC-Populationen aus der Türkei und Mexiko mit 44 bzw. 76 SSRs analysiert. Beide Materialgruppen zeigten ein hohes Maß an genetischer Diverstät (GD = 0,69 bzw. 0,54). Die 36 LCs konnten nicht entsprechend ihren Ursprungskontinenten getrennt werden. Jedoch wurde eine bisher unbekannte Beziehung zwischen einer chilenischen und nigerianischen LC aufgedeckt. Mit Ausnahme zweier türkischer LC-Populationen konnten alle neun untersuchten LCs differenziert werden. Der Großteil der genetischen Variation wurde jedoch innerhalb der LC-Populationen ermittelt. Die Ergebnisse dieses Experiments leisteten somit einen wesentlichen Beitrag zur Charakterisierung der LCs und führten zu wichtigen Erkenntnissen für das künftige Management von Genbank?Akzessionen. In Experiment 4 wurden 112 Weizenhybriden sowie deren Elternlinien in zwei mexikanischen Umwelten für Ertrag, Wuchshöhe, Blütezeit und Reife evaluiert. Die Heterosiswerte für Ertrag schwankten zwischen -15,3% und 14,1% und waren im Durchschnitt zu niedrig, um die höheren Produktionskosten für das Hybridsaatgut zu amortisieren. Die Korrelationen zwischen Elternmittel und Hybridleistung sowie Eigenleistung und Testkreuzungsleistung der Hybrideltern waren signifikant und für alle Merkmale inklusive Ertrag sehr hoch (r = 0,86 bzw. 0,91). Mit Hilfe von 113 SSRs konnten die Elternlinien in drei Gruppen eingeteilt werden. Die Korrelation zwischen GD und Heterosis war jedoch niedrig und nicht signifikant. Nach diesem Ergebnis sind die Aussichten für den potentiellen Erfolg von Hybridweizen in Entwicklungsländern als gering einzustufen. In Experiment 1 und 3 waren die Korrelationen zwischen den GD und COP-Werten signifikant aber niedrig. Dies beruht vermutlich auf unrealistischen Annahmen bei der Berechnung des COP, da hierbei Selektion und genetische Drift ignoriert werden. Im Vergleich zu genomischen SSRs spiegelten auch EST-SSRs keine funktionelle Diversität wieder. Die EST-SSRs waren in allen Experimenten weniger polymorph, jedoch einfacher auszuwerten als die genomischen SSRs. Über alle Experimente hinweg zeigt unsere Studie, dass Pflanzenzüchtung nicht notwendigerweise zum Verlust genetischer Variation führen muss. Sie belegt, dass die am CIMMYT verfolgten Strategien erfolgreich zu einer Verbreiterung der genetischen Variation beitragen. Die Ergebnisse geben den Weizenzüchtern am CIMMYT und in nationalen Zuchtprogrammen wertvolle Hinweise zur Nutzung von Wildarten bzw. Landsorten für die Erweiterung der genetischen Basis bei Weizen. Zudem bieten sie eine Basis für weitere Assoziationskartierungsstudien zur Identifizierung von wertvollen Allelen und deren Nutzung im Rahmen der marker-gestützten Selektion

Elucidating and Mapping Heat Tolerance in Wild Tetraploid Wheat (Triticum turgidum L.)

Identifying reliable screening tools and characterizing tolerant germplasm sources is essential for developing wheat (Triticum aestivum L.) varieties suited for the hot areas of the world. Our objective was to evaluate heat tolerance of promising wild tetraploid wheat (Triticum turgidum L.) accessions that could be used as sources of heat tolerance in common- and durum-wheat (Triticum durum) breeding programs. We screened 109 wild tetraploid wheat accessions collected by the International Center for Agriculture Research in the Dry Areas (ICARDA) from the hottest wheat growing areas in Africa and Asia, as well as, two common wheat checks for their response to heat stress by measuring damage to the thylakoid membranes, flag leaf temperature depression (FLTD), and spike temperature depression (STD) during exposure to heat stress for 16 beginning at anthesis. Measurements were taken on the day of anthesis then 4, 8, 12, and 16 days post anthesis (DPA) under controlled optimum and heat-stress conditions. Individual kernel weight (IKW) and heat susceptibility index (HSI) measurements were also obtained. Prolonged exposure to heat stress was associated with increased damage to thylakoid membranes, as indicated by the high ratio of constant fluorescence (O) to peak variable fluorescence (P). A positive and significant correlation was found between O/P ratio and both FLTD and STD under heat-stress conditions. A negative and significant correlation was found between FLTD and HSI and between STD and HSI based on the second and third measurements (4 and 8 DPA). Correlations obtained after the third measurement were not significant because heat-stress accelerated maturity and senescence. For a pedigree-based mapping strategy a family approach was then developed by crossing and back-crossing heat-tolerant and heat-susceptible germplasm. A set of 800 lines resulting from the pedigree-based family approach was phenotyped using FLTD, chlorophyll content and yield and its components under heat stress. Genotyping of these lines was accomplished using simple sequence repeat (SSRs) markers. Some QTLs associated with heat stress tolerance were identified. This study identified potential heat-tolerant wild tetraploid wheat germplasm and QTL conditioning heat tolerance that can be incorporated into wheat breeding programs to improve cultivated common and durum wheat