Genetic analysis of low-temperature tolerance in winter wheat

Winter wheat has a higher yield over spring sown wheat and has many ecological and agronomic advantages. However, low temperature (LT) stress is one of the major abiotic factors which limit increased crop production. LT­-tolerance in winter wheat is a quantitative trait and molecular and genetic evidence suggest that LT-tolerance is governed by a number of genes with complex interactions. In order to identify and characterize the chromosomal regions conferring LT-tolerance, a doubled haploid (DH) mapping population was utilized from two winter wheat parents Norstar and Cappelle-desprez which have an identical vrn-1 locus but differ in their potential LT-tolerance (Båga et al., 2006a; 2006b). Norstar has an LT50 of -21°C and Cappelle-Desprez has an LT50 of -13°C (Båga et al., 2006a; 2006b). In this study, molecular markers such as simple sequence repeats (SSRs) and amplified fragment length polymorphisms (AFLPs) were used to construct a linkage map of a Norstar x Cappelle-desprez cross and to identify markers and regions associated with LT-tolerance. A linkage map was assembled with a total genetic length of 2292 cM comprising 443 SSR and 197 AFLP markers. A major QTL (Quantitative trait loci- a region of DNA that is associated with a phenotypic trait) for LT-tolerance was identified on chromosome 5A which has been associated with a cluster of C-repeat binding factors (CBFs). The QTL identified in this study is similar to the Fr-2 locus in diploid and hexaploid wheat, also associated with LT tolerance. A previously constructed Norstar BAC library (Ratnayaka et al., 2005) was screened to identify putative CBF clones. Mapping of the CBF positive clones to the major QTL identified on chromosome 5A will help in identifying the key CBF gene(s) contributing to the LT-tolerance trait

Wheat-barley hybridization – the last forty years

Abstract Several useful alien gene transfers have been reported from related species into wheat (Triticum aestivum), but very few publications have dealt with the development of wheat/barley (Hordeum vulgare) introgression lines. An overview is given here of wheat 9 barley hybridization over the last forty years, including the development of wheat 9 barley hybrids, and of addition and translocation lines with various barley cultivars. A short summary is also given of the wheat 9 barley hybrids produced with other Hordeum species. The meiotic pairing behaviour of wheat 9 barley hybrids is presented, with special regard to the detection of wheat– barley homoeologous pairing using the molecular cytogenetic technique GISH. The effect of in vitro multiplication on the genome composition of intergeneric hybrids is discussed, and the production and characterization of the latest wheat/barley translocation lines are presented. An overview of the agronomical traits (b-glucan content, earliness, salt tolerance, sprouting resistance, etc.) of the newly developed introgression lines is given. The exploitation and possible use of wheat/barley introgression lines for the most up-to-date molecular genetic studies (transcriptome analysis, sequencing of flow-sorted chromosomes) are also discussed

Breeding winter durum wheat for Central Europe : assessment of frost tolerance and quality on a phenotypic and genotypic level

Durum wheat (Triticum durum) is a tetraploid wheat that is used for pasta and other semolina products. Quality standards for semolina requested by the pasta industry are very high. Different characteristics should come with the cereal as raw material for an optimal end product. Vitreosity, the glassy and amber quality feature of durum wheat kernels, is an indicator for high semolina yield. The complex protein-starch matrix of glassy kernels breaks the grain into the typical semolina granulate instead of flour during milling. Humid conditions, like late summer rains in Central Europe, have a huge effect on this characteristic, changing this matrix irreversibly. Such processes in the kernel are less understood and challenge plant breeders to find genotypes with improved vitreosity. A set of F5 winter durum wheat lines (Chapter 2) was used to investigate the relationship between protein content and vitreosity as well as the impact of humidity on the stability of the trait. A method to evaluate the mealy part in kernels was improved and enabled to test for the influence of humidity on vitreosity. Furthermore, it was revealed that the vitreosity of a durum wheat kernel depends on the protein content up to a specific threshold as well as on the genotypic potential to form the complex endosperm matrix. The ability to maintain this kernel quality under humid conditions also highly depends on the genetics of a variety. In the Mediterranean region, durum wheat is grown as autumn-sown spring type. The mild winters as well as rain during spring allow the plants to develop well, and the dry summers enable an early harvest in June. Durum wheat production in Central Europe, on the other hand, is confronted with harsh winters and recurring severe frosts. The lack of a sufficient frost tolerance in combination with high quality, forces farmers to use the spring type with a spring sowing. Growing winter durum instead of spring durum wheat, would allow an autumn sowing. Using the winter type in this growing area, could have several advantages like an increased yield and stability due to a prolonged growing time. Further, the constant soil coverage would prevent soil erosion and the growth vigor of winter durum has advantages against weeds. The success of winter durum breeding depends on frost tolerance as a key factor for varieties with excellent winter survival. Discontinuous occurrence of frosts across years and protective snow coverage, however, limit the phenotypic selection for this trait under field conditions. Greenhouses or climate chambers could be used as alternative to test under the necessary conditions, but those fully-controlled tests are time consuming and labor-intensive. The Weihenstephaner Auswinterungsanlage are wooden boxes with movable glass lids used as a semi-controlled test. Plants are exposed to all seasonal conditions, including frost stresses, in this test, but they can be protected from snow coverage. While this method is already successfully used to test for frost tolerance in bread wheat, the application in durum wheat has not been evaluated yet. The frost tolerance scorings of winter durum elite lines (F5 and F6) based on the Weihenstephaner Auswinterungsanlage were compared to the field evaluation (Chapter 3). It was demonstrated that this semi-controlled test produces reliable and highly heritable (h2 = 0.83-0.86) frost tolerance data. The correlation of those results compared with the field data (r = 0.71) suggests this semi-controlled test as an indirect selection platform. Since it is now possible to test cost-efficient at early stages for frost tolerance, the next challenge was to determine whether the kernel quality or the grain yield suffers from an increased frost tolerance. In a survey with F5 winter durum elite lines, no negative association between frost tolerance and quality or other important agronomic traits could be found in European breeding material (Chapter 4). In order to support classical plant breeding, which relies predominantly on phenotypic data and parental information, molecular markers can be taken into account. Molecular markers can provide an in-depth look into the genetic architecture of traits, enable the determination of the relatedness of genotypes, identify the genetic variation in a population, or can assess the effect of geographic selection preferences. Furthermore, it is possible to assist knowledge-based selection. This improves plant breeding programs on a genetic level. The population structure in spring durum has already been examined with molecular methods in several studies. Winter durum, on the other hand, was only analyzed as a small group as part of spring durum studies or in groups of landraces. A highly diverse and unique panel of 170 winter durum and 14 spring durum lines was analyzed using a genotyping-by-sequencing (GBS) approach. A total of 30,611 markers, well distributed across the chromosomes, were obtained after filtering for marker quality. A principal coordinate analysis and a cluster analysis were applied. Together they revealed the absence of a major population structure (Chapter 5). The lines, however, grouped in a certain way, depending on their origin, associated with decreasing quality and increasing frost tolerance moving from South to Continental Europe. These groups allow breeders to conduct targeted crosses to further improve the frost tolerance in the Central European material. Another possibility is to build heterotic groups for hybrid breeding. The linkage disequilibrium (LD) decay was within 2-5 cM, indicating a high diversity in winter durum. The high marker density together with the extent of LD observed in this analysis allows to perform high-resolution association mapping in the present winter durum panel. The 30,611 markers and additional markers for candidate genes in frost tolerance were used to assess the genetic architecture of frost tolerance in durum wheat (Chapter 6). A major QTL was identified on chromosome 5A, likely being Frost Resistance-A2 (Fr-A2). Additional analysis of copy number variation (CNV) of CBF-A14 at Fr-A2 support this conclusion. CBF-A14 CNV explains about 90% of the proportion of genotypic variance. Two markers found in the QTL region were combined into a haploblock and enabled to capture the genetic variance of this QTL. Furthermore, the frequency of the QTL allele for frost tolerance shows a latitudinal gradient which is likely associated with winter conditions. In summary, the selection tools for vitreosity and frost tolerance provided in this study create a platform for winter durum breeding to select for high quality genotypes with excellent winter survival utilizing phenotypic as well as genotypic information.Durumweizen (Triticum durum) gehört zu den tetraploiden Weizen und wird für die Herstellung von Pasta und anderer Grießprodukte verwendet. Die geforderten Qualitätsstandards der Pasta-Industrie sind hierbei sehr hoch. Das Rohprodukt muss über verschiedenste Eigenschaften verfügen. Ein wichtiger Indikator für eine hohe Grießausbeute ist die Glasigkeit, sichtbar als typischer glasiger Bernsteincharakter des Durumkornes. Die komplexe Protein-Stärke Matrix des Endosperms veranlasst das glasige Korn während des Mahlprozesses in Gries anstelle von Mehl zu zerfallen. Feuchte Bedingungen, wie Spätsommerregen in Zentraleuropa, haben einen starken Einfluss auf diese Korneigenschaft und verändern hierbei irreversibel die Endospermmatrix. Über diese Vorgänge im Korn ist nur wenig bekannt, was die Selektion auf Glasigkeit erschwert. Daher wurden F5 Winterdurumlinien verwendet (Kapitel 2), um die Zusammenhänge von Proteingehalt und Glasigkeit sowie den Einfluss von Feuchte auf die Glasigkeit zu untersuchen. Eine verbesserte Bestimmungsmethode der Glasigkeit ermöglichte es, die Veränderung der visuellen Struktur des Korns unter feuchten Bedingungen besser zu verstehen. Des Weiteren wurde festgestellt, dass die Ausprägung der Glasigkeit bis zu einem bestimmten Minimal-Proteingehalt des Kornes durch letzteren stark beeinflusst wird. Außerdem spielt das genetische Potenzial, glasige Körner zu bilden und diese auch stabil zu erhalten, eine wichtige Rolle. Im Mittelmeerraum wird Durumweizen als Sommerform im Herbst gesät. Milde Winter und Frühjahrsregen erlauben eine starke Pflanzenentwicklung, und trockene Sommer ermöglichen eine frühe Juniernte. Die Hartweizenproduktion in Zentraleuropa ist jedoch mit starken Wintern und wiederkehrenden Frösten konfrontiert. Das Fehlen von Sorten, die eine ausreichende Frosttoleranz mit hoher Qualität kombinieren, zwingt die Landwirte zu einer Frühjahrsaussaat. Würde man jedoch Winterdurum anstelle von Sommerdurum anbauen, könnte eine Herbstaussaat verwendet werden. Vorteile wären zum Beispiel eine Ertragssteigerung, wie auch eine verbesserte Ertragsstabilität. Eine kontinuierliche Bodenbedeckung würde Bodenerosion vermeiden und der Wachstumsvorsprung der Winterform hätte Vorteile hinsichtlich Unkräutern. Die Frosttoleranz ist ein wichtiger Bestandteil für eine gute Überwinterung und spielt eine Schlüsselrolle für eine erfolgreiche Winterdurum-Züchtung. Das unregelmäßige Auftreten von Frost über die Jahre und isolierende Schneedecken, erschweren hierbei eine regelmäßige Selektion auf dieses Merkmal unter Feldbedingungen. Als Alternative könnten z.B. Klimakammern genutzt werden, solche Methoden sind aber zeitaufwändig und arbeitsintensiv. Die Weihenstephaner Auswinterungsanlage sind im Feld aufgestellte Holzkisten mit einem bewegbaren Glasdach. Die Pflanzen werden hier allen natürlichen Wetterbedingungen ausgesetzt, unter anderem Froststress da das Dach die Bildung einer Schneedecke verhindert. Diese Methode wird bereits erfolgreich im Weichweizen eingesetzt, wurde aber bisher noch nicht für Durumweizen evaluiert. Frosttoleranzdaten für Winterdurum (F5 und F6 Linien) wurden mittels der Auswinterungsanlage, wie auch auf dem Feld erhoben und verglichen (Kapitel 3). Es konnte gezeigt werden, dass die Auswinterungsanlage nachvollziehbare und hoch erbliche (h2 = 0.83-0.86) Daten produziert, welche zudem mit den Feldergebnissen stark korrelierten (r = 0.71). Das macht die Auswinterungsanlage zu einer vielversprechenden Plattform für eine Selektion auf Frosttoleranz. Da es nun möglich ist, kostengünstig und zeitsparend bereits in frühen Generationen auf Frosttoleranz zu testen, war es wichtig, zu ermitteln, wie sich Frosttoleranz auf die Kornqualität und ertrag auswirkt. In einer Studie mit F5 Elite-Winterdurum konnte keine negative Assoziierung zwischen diesen Merkmalen festgestellt werden (Kapitel 4). Klassische Pflanzenzüchtung basiert primär auf phänotypischen Daten und Informationen der Eltern. Mit molekularen Markern kann die Selektion tiefgreifender unterstützt werden. Molekulare Marker können einen Einblick in die genetische Architektur von Merkmalen geben, ermöglichen den Verwandtschaftsgrad zwischen Genotypen zu bestimmen, identifizieren die genetische Variation innerhalb einer Population oder beschreiben den Effekt von geografischen Selektionspräferenzen. Des Weiteren unterstützen sie eine wissensbasierte Selektion. Die Nutzen von molekularen Markern kann die Pflanzenzüchtung beschleunigen und präziser machen. Sommerdurum wurde bereits mit Markern in einigen Populationsstudien untersucht, wohingegen Winterdurum nur in kleinen Gruppen solcher Studien mituntersucht oder Gruppen von Landrassen verwendet wurden. Ein hoch diverses und einmaliges Set aus 170 Winterdurum und 14 Sommerdurum wurde mittels eines Genotyping-by-Sequencing Ansatzes untersucht. Nach einer Qualitätsanalyse ergaben sich daraus 30,611 Marker, welche gut über alle Chromosomen verteilt waren. Eine multidimensionale Skalierung und eine Clusteranalyse ergaben, dass es keine größere Populationsstruktur gibt (Kapitel 5). Die Linien gruppierten sich aber zu einem gewissen Grad anhand ihrer Herkunft, assoziiert mit einer sinkenden Qualität und einer steigenden Frosttoleranz von Südeuropa nach Kontinentaleuropa. Solche Cluster erlauben es Züchtern, gezielte Kreuzungen zwischen diesen Gruppen zu machen, um die Frosttoleranz im Zentraleuropäischen Material weiter zu verbessern. Eine andere Möglichkeit wäre es, diese Cluster beizubehalten, um daraus heterotische Gruppen für den Einsatz von Hybriden zu nutzen. Das Kopplungsungleichgewicht (LD) fiel innerhalb von 2-5 cM unter den Schwellenwert, was eine breite genetische Varianz in Winterdurum signalisiert. Die hohe Markerdichte zusammen mit der Ausdehnung des LD erlaubt, eine hochauflösende Assoziationskartierung in diesem Winterdurum Set durchzuführen. Die 30,611 Marker, inklusive zusätzlicher Marker für Kandidaten-Gene der Frosttoleranz, wurden verwendet, um die genetische Architektur von Frosttoleranz innerhalb von Hartweizen zu analysieren (Kapitel 6). Ein neuer QTL wurde auf Chromosom 5A entdeckt und entspricht dem Frost Resistance-A2 (Fr-A2). Weitere Analysen von CBF-A14 am Fr-A2 Lokus, welches in verschiedene Kopien vorkommt (CNV), unterstützen diese Annahme. CBF-A14 CNV erklärt etwa 90% der genetischen Varianz. Zwei Marker die mit der Region des QTL assoziiert sind, wurden zu einem Haploblock zusammengefasst und ermöglichen es die genetische Varianz des QTL zu erfassen. Die Frequenz des QTL-Allels für Frosttoleranz verteilte sich entlang der geographischen Herkunft der Genotypen. Zusammenfassend kann festgestellt werden, dass die neu erarbeiteten Selektionsmethoden für Glasigkeit und Frosttoleranz in dieser Studie eine gute Basis für die Auswahl neuer Winterdurumlinien mit hoher Qualität und guter Winterhärte bilden. Hierbei kann auf phänotypische und genotypische Informationen zurückgegriffen werden

Dissection of drought tolerance mechanism in wheat plant

As wheat is one of the three major crops in the world, improving its drought tolerance is crucial for human beings to develop sustainable food in the context of global climate change. This review updates the studies on wheat exposed to drought stress. In this work, the physiological responses of wheat plants under water deficit are discussed from different angles. A comprehensive description of droughttolerance mechanisms in wheat plants is given. The current state of researches on drought-related traits is reviewed. To further demonstrate the genetic basis of wheat drought tolerance, some knowledge of the powerful genetic research tool, Genome-wide Association study, is elaborated on. In addition, this review also summarizes multiple potential approaches for further studies on drought-related candidate genes. The results obtained utilizing those advanced technologies in this area so far are thoroughly illustrated. Finally, the challenges of investigating wheat genotypes in drought condition and mixtures of natural abiotic stresses are discussed. Traditional difficulties and novel progress in the wheat root system investigation are elaborated

Meta-Analysis of Wheat QTL Regions Associated with Heat and Drought Stress

Heat and drought are the two most important environmental constraints to wheat production globally, are often present simultaneously and will become more severe with global climate change. This presents a unique challenge to wheat scientists who must work to develop wheat cultivars that are productive and adapted to future environmental conditions. A number of recent studies have reported quantitative trait loci (QTL) associated with heat and drought tolerance, as well as QTL for stress adaptive traits such as the availability of stem carbohydrates or crop canopy temperature. The objective of this study was to perform a meta-analysis of these QTL to identify regions of the wheat genome that are consistently associated with tolerance to heat and drought. To identify Meta-QTL (MQTL), a QTL database was developed from 30 studies targeted at heat and drought stressed environments. The positions of individual QTL were projected onto a consensus genetic map based on the presence of common molecular markers and a 95% confidence interval (CI) was calculated for each QTL. After positioning the individual QTL, the software `Biomercator v2.1\u27 was used to predict the location and CI of MQTL based on maximum likelihood. In total, 854 QTL were reported for 80 different traits. This included 502 for drought stress, 234 for heat stress, and 118 adaptive trait QTL in non-stressed environments. These QTL were grouped into 66 MQTL regions distributed throughout the wheat genome. Most regions co-localized for both heat and drought stress, although both drought and heat stress specific MQTL regions were also identified. Using the traits present within MQTL it was possible to genetically model Stress Trait Expression Pathways (STEPs) that can be used to identify target alleles and physiological traits for improvement through breeding

Plant breeding for organic farming: current status and problems in Europe

Compendium is a part of Deliverable 4 of 6th FP SSA project “Environmental friendly food production system: requirements for plant breeding and seed production” (ENVIRFOOD) and contains information about current status and problems in EU regarding to organic plant breeding

QTL Analysis and Trait Dissection in Ryegrass (\u3cem\u3eLolium\u3c/em\u3e Spp.)

Key points Molecular marker-based genetic analysis permits the dissection of complex phenotypes through resolution of the locations of pleiotropic and interacting genetic factors. Several QTLs for agronomically important characters such as flowering time, winter hardiness and forage quality have been identified in perennial ryegrass by molecular marker-based map analysis. Some QTLs were putatively orthologous to those for equivalent traits in cereals. The identification of co-location between QTLs and functionally-associated genetic markers is critical for the future implementation of marker-assisted selection programs

Characterisation of selected bread wheat (Triticum aestivum L.) genotypes for drought tolerance based on SSR markers, morpho-physiological traits and drought indices.

Master of Science in Plant Breeding. University of KwaZulu-Natal, Pietermaritzburg, 2018.Bread wheat (Triticum aestivum L.) and durum wheat (T. turgidum L. var. durum) are staple cereal food crops worldwide. In South Africa, bread wheat is the second most economically important cereal after maize. Drought stress associated with climate change is a major cause of the yield gap in wheat production in South Africa. Drought tolerant wheat cultivars are yet to be developed and released in the country. Wheat improvement for drought tolerance is one of the major breeding goals in South Africa. Integrative pre-breeding techniques involving genotypic and phenotypic characterisation ensure an accurate selection of potential drought tolerant parents for breeding. Therefore, the specific objectives of the current study were: 1) to determine the genetic diversity and population structure of forty-seven diverse bread wheat genotypes introduced from the International Maize and Wheat Improvement Center (CIMMYT) using ten selected polymorphic Simple Sequence Repeat (SSR) markers, 2) to characterise fifteen bread wheat genotypes introduced from CIMMYT using physiological and morphological traits, and 3) to assess drought tolerance amongst fifteen selected bread wheat genotypes using nine drought tolerance indices. Genetic diversity and population structure of 47 CIMMYT derived bread wheat genotypes were examined using 10 SSR molecular markers. All the SSR markers used in the study were highly polymorphic. The highest PIC values were recorded for XGWM 132, WMS 179 and WMS 30 with 0.93, 0.89 and 0.89, respectively. Cluster analysis detected 3 distinct clusters with Clusters A and C consisting of most diverse genotypes. Two distinct heterotic patterns were identified to select unique parents for crosses. Analysis of molecular variance (AMOVA) detected significant genetic diversity among populations, among individuals and within individuals with explained percentage variance of 3%, 37% and 60%, respectively. Genetic diversity and population stratification was mainly due to private alleles detected. Based on detected genetic variability, a total of 15 genotypes were selected and subjected for phenotypic characterisation. The selected genotypes included SYM2016-037, SYM2016-038, SYM2016-029, SYM2016-010 and SYM2016-012 from Cluster A, SYM2016-044, SYM2016-004, SYM2016-016, SYM2016-019, SYM2016-014, SYM2016-008, SYM2016-006 and SYM2016-047 from Cluster B and SYM2016-042 and SYM2016-027 from Cluster C. The above selected 15 bread wheat genotypes were evaluated under field and greenhouse conditions using a randomised complete block design with 3 replications. Drought stress was imposed as follows: 1 week before 50% heading (WBH) and 1 week after 50% heading (WAH). A fully-irrigated water regime (NS, non-stress) was used as a comparative control. Genotypes were evaluated using 2 physiological and 8 morphological traits. Significant differences (P < 0.05) were detected among genotypes and genotype x test environment interaction. Genotype effect was significant for days to flowering, days to maturity, plant height, number of productive tillers, number of spikelets per spike, grain number and 100 grain weight. Genotype x test environment interaction was significant for canopy temperature, days to flowering, days to maturity, plant height, number of spikelets per spike, grain number, 100 seed weight and the yield. Significant correlations were detected between yield and days to flowering, days to maturity, plant height, number of productive tillers, number of spikelets per spike, grain number and 100 seed weight under greenhouse condition. The number of productive tillers per plant and the number of spikelets per spike were positively associated with yield under field evaluation. Principal component analysis revealed PC1 to be consistently associated with yield, 100 seed weight and number of spikelets per spike. Days to flowering and maturing, plant height and canopy temperature were positively associated with either PC2 or PC3 under greenhouse and field conditions. A yield penalty was noted for early flowering and maturing genotypes such as SYM2016-014, SYM2016-027 and SYM2016-029 relative to late flowering and maturing genotypes SYM2016-016, SYM2016-037 and SYM2016-006. Crossing of these complementary lines and continuous selection of progenies is essential to develop early maturing genotypes with stable and high yield potential. In this study, days to flowering and maturity, plant height, canopy temperature and 100 seed weight were favourable traits to screen genotypes for drought tolerance. Screening for drought tolerance under greenhouse condition was more reliable than under field evaluation. The above 15 wheat genotypes were evaluated using 9 drought tolerance indices based on yield data. The drought indices used were drought resistance (DR), mean productivity (MP), harmonic mean of yield (HM), stress susceptibility index (SSI), stress tolerance index (STI), tolerance index (TOL), yield index (YI), yield reduction index (YR) and yield stability index (YSI). Analysis of variance detected significant differences among genotypes (P < 0.001) and genotype by water regime interaction (P < 0.01) affecting yield response. Significant differences were also recorded among genotypes (P < 0.05) for DR, HM, MP, STI, YI and YSI. Consistent mean genotype ranking was recorded for HM, MP, STI, SSI and YI enabling selection of genotypes SYM2016-006, SYM2016-016 and SYM2016-037. PC analysis detected high variation of 82.2% among genotypes, with percentage variation partitioned as follows: 42.64% for PC1, 22.37% for PC2 and 12.18% for PC3. Both PC and bi-plot analyses revealed strong associations between HM, MP, STI, YI and yield under drought stressed and non-stressed conditions. High yielding genotypes such as SYM2016-006, SYM2016-016 and SYM2016-037 scored higher values for HM, MP, STI, YI and yield under drought stressed and non-stressed conditions. DR was associated with early maturing genotypes such as SYM2016-014, SYM2016-029 and SYM2016-38. These genotypes were considered as potential parents for future wheat breeding programmes emphasizing drought tolerance