Browsing by Subject "Fusarium head blight"

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Effects of non-adapted quantitative trait loci (QTL) for Fusarium head blight resistance on European winter wheat and Fusarium isolates
(2010) Ohe, Christiane von der; Miedaner, Thomas
Fusarium head blight (FHB), caused by Fusarium graminearum and F. culmorum, is a devastating disease responsible for tremendous damage in wheat fields and contamination of grain with mycotoxins deoxynivalenol (DON) and nivalenol (NIV), rendering the harvest unsafe for human and animal consumption. The variability of Fusarium populations is high and changes in aggressiveness, chemotypes or species within and among Fusarium populations are known. Stable FHB resistance combined with high yield is one main target in wheat breeding programs. Mapping studies detected several quantitative trait loci (QTL) for FHB resistance in non-adapted sources, such as Sumai3 from China. The two most important and commonly used major QTL are located on chromosome 3BS (Fhb1) und 5A (Qfhs.ifa-5A). However, negative side effects of non-adapted resistance sources introgressed in elite winter wheat material are feared in Europe. Furthermore, the stability of the QTL effect against changing Fusarium populations is unknown. The objectives of this research were to analyze whether (1) the QTL Fhb1 and Qfhs.ifa-5A introgressed from a non-adapted resistance source into two winter wheat varieties have possible side effects on agronomic and quality performance, (2) 3-ADON and 15-ADON chemotypes are significantly different in their aggressiveness and DON production, (3) competition among Fusarium isolates in mixtures exists, and if so, how the resistant host will influence this competition. In conclusion, both resistance QTL are effective and stable in elite spring and winter wheat backgrounds. For improvement of FHB resistance both QTL are valuable, but Qfhs.ifa-5A would suffice for European breeding programs. Due to chemotype shifts, 3-ADON isolates could pose a greater risk to food safety than 15-ADON but breeding and use of highly resistant lines can reduce the risks associated with DON in wheat. Accordingly, resistant spring wheat lines were less affected by the tested Fusarium isolates and mixtures and, therefore, confirmed a high stability of these QTL. Directed selection of highly aggressive isolates due to the resistance QTL seems to be unlikely in the short term.
Genomics-assisted breeding strategies for quantitative resistances to Northern corn leaf blight in maize (Zea mays L.) and Fusarium diseases in maize and in triticale (× Triticosecale Wittm.)
(2021) Galiano Carneiro, Ana Luísa; Miedaner, Thomas
Fusarium head blight (FHB) in triticale (× Triticosecale Wittm.), Gibberella ear rot (GER) and Northern corn leaf blight (NCLB) in maize (Zea mays L.) are devastating crop diseases causing yield losses and/or reducing grain quality worldwide. Resistance breeding is the most efficient and sustainable approach to reduce the damages caused by these diseases. For all three pathosystems, a quantitative inheritance based on many genes with small effects has been described in previous studies. Hence, this thesis aimed to assess the potential of genomics-assisted breeding strategies to reduce FHB, GER and NCLB in applied breeding programs. In particular, the objectives were to: (i) Dissect the genetic architecture underlying quantitative variation for FHB, GER and NCLB through different quantitative trait loci (QTL) and association mapping approaches; (ii) assess the potential of genomics-assisted selection to select superior triticale genotypes harboring FHB resistance; (iii) phenotype and characterize Brazilian resistance donors conferring resistance to GER and NCLB in multi-environment trials in Brazil and in Europe; and (iv) evaluate approaches for the introgression and integration of NCLB and GER resistances from tropical to adapted germplasm. The genome-wide association study (GWAS) conducted for FHB resistance in triticale revealed six QTL that reduced damages by 5 to 8%. The most prominent QTL identified in our study was mapped on chromosome 5B and explained 30% of the genotypic variance. To evaluate the potential of genomic selection (GS), we performed a five-fold cross-validation study. Here, weighted genomic selection increased the prediction accuracy from 0.55 to 0.78 compared to the non-weighted GS model, indicating the high potential of the weighted genomic selection approach. The successful application of GS requires large training sets to develop robust models. However, large training sets based on the target trait deoxynivalenol (DON) are usually not available. Due to the rather moderate correlation between FHB and DON, we recommend a negative selection based on genomic estimated breeding values (GEBVs) for FHB severity in early breeding stages. In the long-run, however, we encourage breeders to build and test GS calibrations for DON content in triticale. The genetic architecture of GER caused by Fusarium graminearum in maize was investigated in Brazilian tropical germplasm in multi-environment trials. We observed high genotype-by-environment interactions which requires trials in many environments for the identification of stable QTL. We identified four QTL that explained between 5 to 22% of the genotypic variance. Most of the resistance alleles identified in our study originated from the Brazilian tropical parents indicating the potential of this exotic germplasm as resistance source. The QTL located on chromosome bin 1.02 was identified both in Brazilian and in European trials, and across all six biparental populations. This QTL is likely stable, an important feature for its successful employment across different genetic backgrounds and environments. This stable QTL is a great candidate for validation and fine mapping, and subsequent introgression in European germplasm but possible negative linkage drag should be tackled. NCLB is another economically important disease in maize and the most devastating leaf disease in maize grown in Europe. Virulent races have already overcome the majority of known qualitative resistances. Therefore, a constant monitoring of S. turcica races is necessary to assist breeders on the choice of effective resistances in each target environment. We investigated the genetic architecture of NCLB in Brazilian tropical germplasm and identified 17 QTL distributed along the ten chromosomes of maize explaining 4 to 31% of the trait genotypic variance each. Most of the alleles reducing the infections originated from Brazilian germplasm and reduced NCLB between 0.3 to 2.5 scores in the 1-9 severity scale, showing the potential of Brazilian germplasm to reduce not only GER but also NCLB severity in maize. These QTL were identified across a wide range of environments comprising different S. turcica race compositions indicating race non-specific resistance and most likely stability. Indeed, QTL 7.03 and 9.03/9.04 were identified both in Brazil and in Europe being promising candidates for trait introgression. These major and stable QTL identified for GER and NCLB can be introgressed into elite germplasm by marker-assisted selection. Subsequently, an integration step is necessary to account for possible negative linkage drag. A rapid genomics-assisted breeding approach for the introgression and integration of exotic into adapted germplasm has been proposed in this thesis. Jointly, our results demonstrate the high potential of genomics-assisted breeding strategies to efficiently increase the quantitative resistance levels of NCLB in maize and Fusarium diseases in maize and in triticale. We identified favorable QTL to increase resistance levels in both crops. In addition, we successfully characterized Brazilian germplasm for GER and NCLB resistances. After validation and fine mapping, the introgression and integration of the QTL identified in this study might contribute to the release of resistant cultivars, an important pillar to cope with global food security.
Inheritance of quantitative resistance and aggressiveness in the wheat/Fusarium pathosystem with emphasis on Rht dwarfing genes
(2010) Voß, Hans-Henning; Miedaner, Thomas
Fusarium head blight (FHB), or scab, is one of the most devastating fungal diseases affecting small-grain cereals and maize, causing severe yield losses and contamination of grain with mycotoxins such as deoxynivalenol (DON) worldwide. Fusarium graminearum (teleomorph Gibberella zeae) and Fusarium culmorum are the most prevalent Fusarium species in wheat production in Central and Northern Europe. Breeding for increased resistance to FHB in wheat is considered the most effective strategy for large scale disease management and mycotoxin reduction. Height reducing Rht genes are extensively used in wheat breeding programmes worldwide in order to improve lodging resistance and yield potential, with Rht-D1b being the most important Rht allele in Northern Europe. However, their individual effects on FHB resistance are yet unclear. Due to the incremental approach to increase host resistance the question arises whether the Fusarium pathogen has the capability to adapt by increased aggressiveness and/or increased mycotoxin production. Therefore, the objectives of the present study were to investigate the effects on FHB resistance of Rht-D1b and additional Rht alleles, the segregation variance for FHB resistance and identification of FHB resistance QTL in subsequent mapping analyses in three crossing populations segregating for the semi-dwarfing Rht-D1b allele and two sets of isogenic wheat lines. Regarding the pathogen, the study aims to determine the segregation variance in two F. graminearum crosses of highly aggressive parental isolates and to examine the stability of host FHB resistance, pathogen aggressiveness and the complex host-pathogen-environment interactions in a factorial field trial. All experiments were conducted on the basis of multienvironmental field trials including artificial inoculation of spores. The presence of Rht-D1b resulted in 7-18% reduction in plant height, but considerably increased FHB severity by 22-53% within progenies from three tested European elite winter wheat crosses. In the following QTL mapping analyses the QTL with the strongest additive effects was located at the Rht-D1 locus on chromosome arm 4DS and accordingly coincided with a major QTL for plant height in all three wheat populations. On total, a high number of 8 to 14 minor QTL for FHB reaction that were found in the three populations which emphasised the quantitative inheritance of FHB resistance in European winter wheat. The detected QTL mostly showed significant QTL-by-environment interactions and often coincided with QTL for plant height. By means of isogenic lines in the genetic background of the variety Mercia, Rht-D1b and Rht-B1d significantly increased mean FHB severity by 52 and 35%, respectively, compared to the wild-type (rht). Among the Maris Huntsman data set, the Rht alleles increased mean FHB severity by 22 up to 83%, but only the very short lines carrying Rht-B1c or Rht-B1b+Rht-D1b showed significance. The analyses of 120 progenies of the crosses from each of the highly aggressive parental F. graminearum isolates revealed significant genetic variation for aggressiveness, DON and fungal mycelium production following sexual recombination. This variation resulted in stable transgressive segregants towards increased aggressiveness in one of the two progeny. The factorial field trial, including eleven F. graminearum and F. culmorum isolates varying in aggressiveness and seven European elite winter wheat varieties, varying in their FHB resistance level, displayed no significant wheat variety × isolate interaction. Nevertheless, isolates possessing increased aggressiveness significantly increased FHB severity and DON production at a progressive rate on varieties with reduced FHB resistance. In conclusion, the analysed Rht alleles led to differently pronounced negative effects on FHB resistance that strongly depended on the genetic background. However, significant genetic variation for FHB resistance exists for selection and, thus, to largely counteract these effects by accumulating major and minor FHB resistance QTL. Significant genetic variation for aggressiveness among F. graminearum and the capability to increase its level of aggressiveness beyond yet known levels simply by sexual recombination may lead to long term erosion of FHB resistance. The rate at which increased aggressiveness develops will depend on the selection intensity and whether it is of constant, episodic or balanced nature. Consequently, the selection pressure imposed on the pathogen should be minimized by creating and maintaining a broad genetic base of FHB resistance that relies on more than one genetically unrelated resistance source by combining phenotypic and marker-assisted selection to achieve a sustainably improved FHB resistance in wheat breeding.
Molecular and genetic analyses of aggressiveness in Fusarium graminearum populations and variation for Fusarium head blight resistance in durum wheat
(2011) Talas, Firas; Miedaner, Thomas
Fusarium head blight (FHB) is a devastating disease of wheat, barley and other cereals, which affects all wheat-growing areas of the world. The most prevalent species are Fusarium graminearum Schwabe (teleomorph: Gibberella zeae (Schweinitz) Petch) and Fusarium culmorum (W. G. Smith) Saccardo. Wheat breeding for FHB resistance has become the most effective and cost efficient strategy to combat this disease. Assisting long term stable breeding programs need a better understanding of the biology and dynamic changes of the population structure. Deoxyninalenol (DON) has the most economical impact among the other mycotoxin secreted by this fungus. Several chemotypes characterizes F. graminearum isolates. All chemotypes (3-ADON, 15-ADON, and NIV) were detected in Europe. The prevalent chemotype in Germany and UK is 15-ADON. Population structure is the result of evolutionary forces acting on the population in time and space together with mutation, recombination, and migration enhancing the genetic variance of a population, random drift and the selection reducing it. Aggressiveness in F. graminearum denotes the quantity of disease induced by a pathogenic isolate on a susceptible host in a non-race specific pathosystem, and is measured quantitatively. The quantitative traits such as aggressiveness and DON production mirror both the environmental changes and the genetic variation. Several genes are responsible for DON production; majority of these genes are grouped in TRI5 cluster. Few genes are known to be associated with F. graminearum aggressiveness such as MAP kinase genes, RAS2, and TRI14. Association between single nucleotide polymorphism and genetic variation of aggressiveness and DON production traits provide a clear identification of quantitative participation of different SNPs in expressing the trait. Also, this approach provides a good method to test the association between candidate genes and the traits. The objectives of this research were to (1) screen some durum wheat landraces for FHB resistance; (2) determine the genetic and chemotypic structure of natural population of F. graminearum in Germany; (3) determine the phenotypic variation in Aggressiveness and DON production, which come out one farmer wheat field; (4) compare the phenotypic variation and genetic variation occurring in one wheat field; and (5) associate the phenotypic traits with SNPs in candidate genes. Screening for FHB resistance was performed on sixty-eight entries form the Syrian landraces. The main characters of selection for resisting FHB disease are low mean value of infection and stability in different environments. Four genotypes (ICDW95842, ICDW92330, ICDW96165, Chahba) had small mean FHB value, small value of deviation form regression, and regression coefficient close to zero. These genotypes were considered as candidate resistant sources of FHB for further agronomic performance analysis through backcrossing generation. The causal agent of FHB in Germany is F. graminearum s.s. with a dominating rate of 64.9 % (out of 521 Fusarium spp. isolates). Nonetheless, the three chemotypes were detected in Germany and some times within one wheat field. The 15-ADON chemotype dominated the populations of F. graminearum s.s. in Germany followed by 3-ADON then NIV chemotype (92, 6.8, and 1.2%, respectively). High genetic diversity (Nei?s gene diversity ranged form 0.30 to 0.58) was detected on a single wheat field scale. Analysis of molecular variance (AMOVA) revealed a higher variance within populations (71.2%) than among populations (28.8%). Populations of F. graminearum s.s. in Germany display a tremendous genetic variation on a local scale with a restricted diversity among populations. Surprisingly the phenotypic variation of aggressiveness and DON production revealed a similar partitioning scale as the genetic variation. In other words, analyses of variance (ANOVA) revealed a higher variance within populations (72%) than between (28%) populations. The wide spectrum of aggressiveness (i.e., from 18 to 39%) and DON production (from 0.3 to 23 mg kg-1) within single wheat field simulate the global variation in both traits. Consequently, associating the observed variation of aggressiveness and DON production with detected single nucleotide polymorphism (SNPs) in some candidate genes revealed few but significant associations. According to Bonferroni-Holm adjustment, three SNPs were associated significantly with the aggressiveness, two in MetAP1 and one in Erf2 with explained proportions of genotypic variance (pG) of 25.6%, 0.5%, and 13.1%, respectively. One SNP in TRI1 was significantly associated with DON content on TRI1 (pG=4.4). The rapid decay of the LD facilitate a better high resolution of the association approach and is in turn suggest the need of higher number of SNP marker to facilitate a genome wide association study. The linkage disequilibrium between unlinked genes suggests the involvement of these genes in the same biosynthesis network. In conclusion, building wheat breeding program for FHB resistance depend initially on identifying sources of resistance among wheat varieties or wild relatives. Moreover, understanding the population structure of the pathogen and the selection forces causing genetic alteration of the population structure enable us employ a sufficient increase of the host resistance. Keeping such a balanced equilibrium between increasing host resistance and changes occur in genetic structure of F. graminearum population would insure no application of additional selection pressure. Further association of candidate genes with aggressiveness can provide effective information of the population development. Continuous observation of Fusarium population?s development is needed to insure a stable management of Fusarium head blight disease.
Prospects of genomic selection for disease resistances in winter wheat (Triticum aestivum L.)
(2019) Grote, Cathérine Pauline; Miedaner, Thomas
Die Ziele dieser Arbeit waren (i) die erstmalige Evaluierung des Effekts des Zwerggens Rht24 auf FHB- und STB-Resistenzen, Wuchshöhe und Ährenschieben im Vergleich zum weit genutzten Locus Rht-D1, (ii) die Untersuchung des Potenzials der nichtadaptierten QTL Fhb1 und Fhb5 für die Entwicklung von Kurzstrohweizen, (iii) die Analyse der Vorhersagegenauigkeit von GS innerhalb und zwischen Familien durch die Anwendung der beiden Modelle RR-BLUP (ridge-regression best linear unbiased prediction) und wRR-BLUP (weighted RR-BLUP) und (iv) die Berechnung des Selektionsgewinns bzw. die Bestimmung der korrekt selektierten Top-10 %-Genotypen für FHB- und STB-Resistenzen durch GS. Die Ergebnisse dieser Studie zeigten, dass das gibberellinsäuresensitive Zwerggen Rht24 auf Chromosom 6 die Wuchshöhe um durchschnittlich 8,96 cm senkte, ohne dabei die FHB- und STB-Resistenzen oder den Zeitpunkt des Ährenschiebens ungünstig zu beeinflussen. Demgegenüber senkte das weitläufig verwendete Allel Rht-D1b die FHB-Resistenz um durchschnittlich 10,05 Prozentpunkte in einer Winterweizenpopulation bestehend aus acht biparentalen Familien, die für diese Resistenzloci segregierten. Diese Arbeit hat zusätzlich aufgezeigt, dass die Resistenzallele von Fhb1 und Fhb5 die FHB-Anfälligkeit um 6,54 bzw. 11,33 Prozentpunkte reduzierten und somit bereits allein das nicht-adaptierte Allel Fhb5b in der Lage ist, den negativen Effekt von Rht-D1b auf die FHB-Resistenz im untersuchten Material auszugleichen. Das verdeutlicht, dass die Wahl der Zwerg- und Resistenzgene in Zuchtprogrammen, in denen FHB-Resistenz ein Selektionsmerkmal ist, von entscheidender Bedeutung ist. In dieser Studie wurde des Weiteren das Potenzial der GS innerhalb und zwischen Familien untersucht. Die Vorhersagegenauigkeiten innerhalb einer Familie waren für alle Zielmerkmale höher als die zwischen Familien und unterschieden sich zwischen den einzelnen Familien und Vorhersagekonstellationen. Die stärkere Gewichtung von signifikanten Markern durch das wRR-BLUP-Modell führte zu einer Verbesserung der Vorhersagegenauigkeit im Vergleich zum weit genutzten RR-BLUP-Modell, wenn einzelne Gene, wie Rht-D1, oder Major-QTL, wie Fhb5, vorhanden waren. In dieser Studie wurden die genomisch geschätzten Zuchtwerte (GEBVs) von 2.500 ungeprüften Genotypen bestimmt, basierend auf einer partiell verwandten Trainingspopulation von 1.120 Genotypen. Die 10 % FHB- und STB-resistentesten Linien und eine zufällige Stichprobe wurden unter Berücksichtigung der Wuchshöhe genomisch selektiert und phänotypisch in einem vierortigen Feldversuch evaluiert. Für die FHB-Resistenz wurde ein Selektionserfolg von 10,62 Prozentpunkten relativ zur zufällig selektierten Populationsstichprobe ermittelt. Die GS erhöhte die STB-Resistenz allerdings nur um 2,14 Prozentpunkte. Auch die Selektion von neuen Kreuzungseltern auf der Basis von GS erscheint nicht ausreichend zuverlässig, da nur 19 % der Top-10 %-Individuen korrekt selektiert wurden. Zusammenfassend stellt die GS ein wertvolles Werkzeug dar, um den Zuchtfortschritt für die komplex vererbte FHB-Resistenz über kürzere Zyklen und größere Populationen zu unterstützen. In Kombination mit der Nutzung geeigneter Zwerggene und des nicht adaptierten QTL Fhb5 kann dadurch eine Steigerung der FHB-Resistenz im Winterweizen erzielt werden.
Quantitative-genetic evaluation of resistances to five fungal diseases in a large triticale diversity panel (×Triticosecale)
(2022) Miedaner, Thomas; Flath, Kerstin; Starck, Norbert; Weißmann, Sigrid; Maurer, Hans Peter
The man-made cereal triticale was fully resistant to the biotrophic diseases powdery mildew, leaf rust, yellow rust, and stem rust from its introduction in Europe in the mid-1970s until about 1990. In the following years, new races that were able to infect at least some triticale genotypes developed in all four pathogen populations, and resistance breeding came into focus. Here, we analyzed 656 winter triticale cultivars from 12 countries for resistance to these biotrophic diseases and Fusarium head blight (FHB) at up to 8 location-year combinations (environments). FHB ratings were corrected for plant height and heading stage by comparing three statistical methods. Significant (p < 0.001) genetic variances were found for all resistances with moderate to high entry-mean heritabilities. All traits showed a normal distribution, with the exception of stem rust, where the ratings were skewed towards resistance. There were no substantial correlations among the five disease resistances (r = −0.04 to 0.26). However, several genotypes were detected with multi-disease resistance with a disease rating below average for all five diseases simultaneously. In future, such genotypes must be selected primarily to cope with future challenges of less pesticide use and global climate change.