1,133 research outputs found
Genome Properties and Prospects of Genomic Prediction of Hybrid Performance in a Breeding Program of Maize
No full textMaize (Zea mays L.) serves as model plant for heterosis research and is the crop where hybrid breeding was pioneered. We analyzed genomic and phenotypic data of 1254 hybrids of a typical maize hybrid breeding program based on the important Dent x Flint heterotic pattern. Our main objectives were to investigate genome properties of the parental lines (e. g., allele frequencies, linkage disequilibrium, and phases) and examine the prospects of genomic prediction of hybrid performance. We found high consistency of linkage phases and large differences in allele frequencies between the Dent and Flint heterotic groups in pericentromeric regions. These results can be explained by the Hill-Robertson effect and support the hypothesis of differential fixation of alleles due to pseudo-overdominance in these regions. In pericentromeric regions we also found indications for consistent marker-QTL linkage between heterotic groups. With prediction methods GBLUP and BayesB, the cross-validation prediction accuracy ranged from 0.75 to 0.92 for grain yield and from 0.59 to 0.95 for grain moisture. The prediction accuracy of untested hybrids was highest, if both parents were parents of other hybrids in the training set, and lowest, if none of them were involved in any training set hybrid. Optimizing the composition of the training set in terms of number of lines and hybrids per line could further increase prediction accuracy. We conclude that genomic prediction facilitates a paradigm shift in hybrid breeding by focusing on the performance of experimental hybrids rather than the performance of parental lines in testcrosses
Albrecht Fitness Studio Business Plan
No full textThis business outlines what it would take to develop a designer fitness studio in Charlotte, NC. The plan contains all key aspects of a business plan, from an executive summary to a cash flow statement. The author is also the acting CEO of the company Albrecht Fitness and plans to follow through with the plan in the next 5 years. This business plan proposes an $80,000 loan needed from potential investors. The components of this business plan outline the company's potential profitability, key strategies, and overall business model
Small RNA-based prediction of hybrid performance in maize
No full textAbstract Background Small RNA (sRNA) sequences are known to have a broad impact on gene regulation by various mechanisms. Their performance for the prediction of hybrid traits has not yet been analyzed. Our objective was to analyze the relation of parental sRNA expression with the performance of their hybrids, to develop a sRNA-based prediction approach, and to compare it to more common SNP and mRNA transcript based predictions using a factorial mating scheme of a maize hybrid breeding program. Results Correlation of genomic differences and messenger RNA (mRNA) or sRNA expression differences between parental lines with hybrid performance of their hybrids revealed that sRNAs showed an inverse relationship in contrast to the other two data types. We associated differences for SNPs, mRNA and sRNA expression between parental inbred lines with the performance of their hybrid combinations and developed two prediction approaches using distance measures based on associated markers. Cross-validations revealed parental differences in sRNA expression to be strong predictors for hybrid performance for grain yield in maize, comparable to genomic and mRNA data. The integration of both positively and negatively associated markers in the prediction approaches enhanced the prediction accurary. The associated sRNAs belong predominantly to the canonical size classes of 22- and 24-nt that show specific genomic mapping characteristics. Conclusion Expression profiles of sRNA are a promising alternative to SNPs or mRNA expression profiles for hybrid prediction, especially for plant species without reference genome or transcriptome information. The characteristics of the sRNAs we identified suggest that association studies based on breeding populations facilitate the identification of sRNAs involved in hybrid performance
Epistasis in an Elite Maize Hybrid and Choice of Generation for Inbred Line Development
No full textSecond cycle breeding, utilizing backcross and F2 generations, has become the predominant type of line development program in the U.S. maize (Zea mays L.) industry. Epistasis and linkage have been identified as possible limits to progress from selection in F2 and backcross populations. Objectives of this study were to determine the importance of epistasis in an elite maize hybrid and to determine the appropriate generation for initiation of inbred line development. Six generations of progeny were developed from B73 and B84: the two parental generations, Pl (B73) and P2 (B84); the F2 generation [(B73 × B84) F2]; the BCP1 generation [(B73 × B84) × B73]; the BCP2 generation [(B73 × B84) × B84]; and the F2-Syn 8 generation (the F2 generation random mated for eight generations). Testcross progeny were produced by crossing random S9 plants from each of the six generations onto the inbred tester Mo17. One-hundred progeny of F2 × Mo17 and F2-Syn 8 × Mo17 and 50 progeny of BCP1 × Mo17 and BCP2 × Mo17, as well as the parental testcrosses, were harvested. The experiment was evaluated at four locations in 1990 and three locations in 1991. Epistatic effects were significant for grain yield and grain moisture, and accounted for 21 and 18% of the variation among generation means, respectively. The genetic variance and heritability for grain yield ranked F2-Syn 8 > F2 > BCP1 > BCP2, but differences among generations were not significant. The predicted gains for each generation ranked in agreement with the heritability. Under low selection intensities (a = 20%), the predicted mean (usefulness) ranked the generations BCP22 > F2 >> F2-Syn 8 > BCPI. Under high selection intensity (a = 1%), usefulness ranked the generations F2 > F2-Syn 8 > BCP2 > BCP1. The choice between F2and backcrosses as source populations is primarily a function of selection intensity. Our results suggest little to no advantage of random mating the F2 before initiating selection and inbreeding.This article is published as Lamkey, Kendall R., Bruce J. Schnicker, and Albrecht E. Melchinger. "Epistasis in an elite maize hybrid and choice of generation for inbred line development." Crop science 35, no. 5 (1995): 1272-1281. doi: 10.2135/cropsci1995.0011183X003500050004x. Posted with permission.</p
Molecular Genetic Diversity among Progenitors and Derived Elite Lines of BSSS and BSCB1 Maize Populations
No full textThe maize (Zea mays L.) populations Iowa Stiff Stalk Synthetic (BSSS) and Iowa Corn Borer Synthetic No. 1 (BSCB1) have undergone reciprocal recurrent selection (RRS) since their establishment in 1949. This study focused on molecular genetic variation of the progenitor inbred lines used to synthesize BSSS and BSCB1 as well as elite inbred lines derived from different cycles of selection. Our objectives were to investigate changes in allele frequencies and genetic diversity from progenitors to derived lines and evaluate trends in genetic diversity among elite lines derived from early and advanced selection cycles. Genotypic data for 105 restriction fragment length polymorphism (RFLP) loci were collected from four groups: 16 progenitors and 18 elite lines derived from BSSS, 12 progenitors and 7 elite lines derived from BSCB1. Each progenitor group had a broad genetic base but both were genetically similar. The groups of derived lines diverged substantially from each other. A larger Roger's distance was found between the groups of lines derived from advanced cycles than between the groups of lines derived from Cycle 0. Allelic variation within each group of lines, however, decreased just slightly with the elite lines capturing almost 75 and 67% of the allelic variation present in the progenitor lines of BSSS and BSCB1, respectively. The results of this study confirm the long-term potential of this RRS program and the importance of the choice of broadly based progenitor materials.This article is published as Hagdorn, Sandra, Kendall R. Lamkey, Matthias Frisch, Paulo EO Guimaraes, and Albrecht E. Melchinger. "Molecular genetic diversity among progenitors and derived elite lines of BSSS and BSCB1 maize populations." Crop Science 43, no. 2 (2003): 474-482. doi: 10.2135/cropsci2003.4740. Posted with permission.</p
PISM glacial cycle sensitivity experiments of the Antarctic Ice Sheet
No full textThis dataset contains PISM simulation results (http://www.pism-docs.org) of the Antarctic Ice Sheet based on code release v1.0-paleo-ensemble (https://doi.org/10.5281/zenodo.3574033). PISM is the open-source Parallel Ice Sheet Model developed mainly at UAF, USA and PIK, Germany.
With the help of added python scripts, all figures can be reproduced as in the journal publication:
- Albrecht et al., 2020, doi:10.5194/tc-14-599-2020.
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Data:
Find PISM results as netCDF data. See 'README.md' for a list of all performed experiment.
All forcing input data for the experiments and plots can be downloaded and remapped via https://github.com/pism/pism-ais. Some of the original input data files are freely available, for others please contact the author or the corresponding data publisher.
Figure plotting scripts (jupyter notebook based on python, see https://jupyter.org) in 'plot_scripts' access the uploaded PISM results in 'model_data' and save the plots to 'final_figures'. Jupyter notebook can be run in the browser and shared, see https://nbviewer.jupyter.org/url/www.pik-potsdam.de/~albrecht/notebooks/paleo_paper/paleo_paper_final.ipynb.
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Contact:
Albrecht, Torsten ([email protected]) ; Potsdam-Institute for Climate Impact Research (PIK), Potsdam, German
pism/pik/paleo_07dev: PISM version as used in Kingslake, Scherer, Albrecht et al. Nature publication
No full text<p>This is a code release of the Parallel Ice Sheet Model (PISM) used for paleo simulations of the Antarctic Ice Sheet as discussed in</p>
<p><a href="https://doi.org/10.1038/s41586-018-0208-x">Kingslake, J., Scherer, R.P., Albrecht, T., Coenen, J., Powell, R.D., Reese, R., Stansell, N.D., Tulaczyk, S., Wearing, M.G. and Whitehouse, P.L., 2018. Extensive retreat and re-advance of the West Antarctic Ice Sheet during the Holocene. <em>Nature</em>, <em>558</em>(7710), p.430</a>.</p>
<p>For input data and plotting scripts please contact the author ([email protected]).</p>
Una nota su Albrecht Dürer e Vitruvio = A Note on Albrecht Dürer and Vitruvius
No full textIn questo saggio l’autore propone una riconsiderazione globale del rapporto di Albrecht Dürer con il De Architectura di Vitruvio, prestando costante attenzione alle fonti rimaste. Inoltre, l’autore indaga anche un aspetto trascurato di questo rapporto, che riguarda la significativa accoglienza dei trattati di Dürer tra i traduttori e i commentatori di Vitruvio tra il XVI e il XVII secolo.AbstractIn this essay the author proposes an overall reconsideration of Albrecht Dürer’s relationship with Vitruvius’ De Architectura, paying constant attention to the surviving sources. Furthermore, the author also investigates an overlooked aspect of this relationship that concerns the significant reception of Dürer’s treatises among Vitruvius’ translators and commentators between the XVIth and the XVIIth centuries
Entwicklung und Anwendungen von Plabsoft : ein Computerprogramm zur populationsgenetischen Datenanalyse und Simulation in der Pflanzenzüchtung
No full textMarker-assisted breeding approaches are promising tools for enhancement of the conventional plant breeding process. They have been successfully applied in many areas such as plant variety protection, classification of germplasm, assessment of genetic diversity, mapping of genes underlying important agronomic traits, and using the mapping information for selection decisions. Powerful and flexible bioinformatic tools are urgently required for a better integration of molecular marker applications and classical plant breeding methods. The objective of my thesis work was to develop and apply Plabsoft, a computer program for population genetic data analyses and simulations in plant breeding.
The assumption of Hardy-Weinberg equilibrium is a cornerstone of many concepts in population and quantitative genetics. Therefore, tests for Hardy-Weinberg equilibrium are of crucial importance, but the assumptions underlying asymptotic chi-square tests are often not met in datasets from plant breeding programs. I developed and implemented in Plabsoft a new algorithm for exact tests of Hardy-Weinberg equilibrium with multiple alleles. The newly derived algorithm has considerable computational advantages over previously described algorithms and extends substantially the range of problems that can be tested.
Knowledge about the amount and distribution of linkage disequilibrium (LD) in breeding populations is of fundamental importance to assess the prospects for gene mapping with whole-genome association studies. To analyze LD in breeding populations, I implemented various LD measures in Plabsoft and developed a new significance test for these LD measures. The routines were employed to analyze LD in 497 elite maize lines from a commercial hybrid breeding program, which were fingerprinted by 81 simple sequence repeat (SSR) markers covering the entire genome. Strong LD was detected and, therefore, whole-genome association studies were recommended as promising. However, LD between unlinked loci will most likely result in a high rate of false positives.
The prediction of hybrid performance with DNA markers facilitates the identification of superior hybrids. The single marker models used so far do not take into account the correlation between allele frequencies at linked markers. To overcome this problem, the concept of haplotype blocks was proposed. I developed and implemented in Plabsoft three alternative algorithms for haplotype block detection suitable for plant breeding. The algorithms were applied for the haplotype-based prediction of the hybrid performance of 270 hybrids, the parents of which were fingerprinted with 20 amplified fragment length polymorphism (AFLP) primer combinations. Employing haplotypes resulted in an improved prediction of hybrid performance compared with single marker models. Consequently, haplotype-based prediction methods have a high potential to improve substantially the efficiency of hybrid breeding programs.
Computer simulations can be employed to solve population genetic problems in plant breeding, for which the simplifying assumptions underlying the classical population genetic theory do not hold true. However, before the start of my thesis no flexible simulation software was available. I developed algorithms for simulation of single breeding steps and entire plant breeding programs and implemented these in Plabsoft. The routines allow the simulation of plant breeding programs as they are conducted in practice.
The simulation routines of Plabsoft were validated by simulating two marker-assisted backcross programs in rice conducted by the International Rice Research Institute (IRRI). In the simulations, the frequency distributions of the proportion of recurrent parent genome in the backcross populations were assessed. The simulation results were in good agreement with the experimental data. Therefore, computer simulations are a useful tool for pre-test estimation of selection response in marker-assisted backcrossing.
The application of Plabsoft was exemplified by two studies in maize. In the first study, the expected LD decay in the intermating generations of two recurrent selections programs was determined with simulations. This application demonstrates the use of Plabsoft to solve problems for which analytical results are not available. In the second study, the forces generating and maintaining LD in a hybrid maize breeding program were investigated with computer simulations. This application demonstrates the capability of modeling complex long-term breeding programs as performed in practice.
The studies of my thesis provide an example for the broad range of possible applications of Plabsoft. In addition to the presented studies, Plabsoft has so far been employed in about 40 further studies, which corroborates the usefulness of Plabsoft for integrating new genomic tools in applied plant breeding programs.DNA Marker werden in der Pflanzenzüchtung zum Erkennen von Sortenplagiaten, zur Gruppierung von Zuchtmaterial, zur Überwachung der genetischen Diversität, zur Kartierung von Genen, die für die Ausprägung wichtiger agronomischer Merkmale verantwortlich sind, sowie zur marker-gestützten Selektion eingesetzt. Um die Markertechnologie in die Methodik der klassischen Pflanzenzüchtung zu integrieren, werden dringend flexible und leistungsfähige bioinformatische Konzepte und darauf basierende Computerprogramme benötigt. Das Ziel dieser Arbeit war es, Plabsoft, ein Computerprogramm zur populationsgenetischen Datenanalyse und Simulation von Pflanzenzüchtungsprogrammen, zu entwickeln und anzuwenden.
Die Annahme, dass sich eine Population im Hardy-Weinberg Gleichgewicht befindet, liegt vielen Konzepten der Populationsgenetik und der quantitativen Genetik zugrunde. Deswegen sind statistische Tests auf Hardy-Weinberg Gleichgewicht von großer Bedeutung. In Datensätzen aus Pflanzenzüchtungsprogrammen treffen die statistischen Annahmen, welche den oft verwendeten Chi-Quadrat-Tests zugrunde liegen, häufig nicht zu. Aus diesem Grund wurde in dieser Arbeit ein neuer Algorithmus für einen exakten Test auf Hardy-Weinberg Gleichgewicht mit multiplen Allelen entwickelt und in Plabsoft umgesetzt. Der neu implementierte Algorithmus ist deutlich schneller als alle vorher beschriebenen Algorithmen und erlaubt somit eine bedeutende Erweiterung für den Anwendungsbereich exakter Hardy-Weinberg Tests.
Die genaue Kenntnis der Höhe und Verteilung von Gametenphasenungleichgewicht (linkage disequilibrium, LD) in pflanzenzüchterischen Populationen ist von großer Bedeutung, um die Erfolgsaussichten genomweiter Assoziationsstudien abschätzen zu können. Zu diesem Zweck wurde die Berechnung der wichtigsten LD Maße in Plabsoft implementiert und ein neuer Signifikanztest für die LD Maße entwickelt. Die neu entwickelten Routinen wurden zur Analyse des LD in einem kommerziellen Hybridmaiszüchtungsprogramm verwendet. Hierzu wurden 497 Inzuchtlinien mit 81 SSR (simple sequence repeat, Mikrosatelliten) Markern genotypisiert und ein hohes Ausmaß an LD detektiert, so dass genomweite Assoziationskartierungsansätze vielversprechend erscheinen. Jedoch ist zu erwarten, dass aufgrund des hohen Ausmaßes an LD zwischen ungekoppelten Markerloci viele falsch positive Assoziationen beobachtet werden.
Eine markergestützte Vorhersage der Hybridleistung vereinfacht die Identifizierung überlegener Kreuzungskombinationen. Bisher wurden hierfür nur Vorhersagemodelle verwendet, die auf einzelnen Markerloci basieren und die Korrelationsstruktur zwischen Allelen an benachbarten Markerloci nicht berücksichtigen. In der Humangenetik wurde vorgeschlagen, benachbarte Markerloci zu sogenannten Haploblöcken zusammenzufassen, um das Problem der Multikolinearität zu lösen. Im Rahmen dieser Arbeit wurden drei unterschiedliche Algorithmen zur Detektion von Haploblöcken im Zuchtmaterial erarbeitet und in Plabsoft umgesetzt. Die Routinen wurden für eine haplotyp-basierte Vorhersage der Leistung von 270 Hybriden verwendet, deren Eltern mit 20 AFLP (amplified fragment length polymorphism) Primerkombinationen untersucht wurden. Die Vorhersage der Hybridleistung konnte durch die Verwendung von Haploblöcken verbessert werden. Folglich haben haplotyp-basierte Vorhersagemethoden ein großes Potential, die Effizienz von Hybridzuchtprogrammen zu steigern.
Computersimulationen können in der Pflanzenzüchtung zur Lösung populationsgenetischer Fragestellungen auch dann angewendet werden, wenn die Annahmen, welche der klassischen populationsgenetischen Theorie zugrunde liegen, nicht erfüllt sind. Vor Beginn dieser Arbeit stand jedoch keine Software zur Verfügung, welche auf flexible Art und Weise Simulationen pflanzenzüchterischer Fragestellungen ermöglicht hätte. Aus diesem Grund wurden Algorithmen entwickelt, die die Simulation einzelner Züchtungsschritte sowie kompletter Pflanzenzüchtungsprogramme ermöglichen. Die entwickelten Algorithmen wurden im Computerprogramm Plabsoft umgesetzt, so dass es jetzt möglich ist, komplexe Pflanzenzüchtungsprogramme praxisnah zu simulieren.
Die Simulationsroutinen von Plabsoft wurden an einem experimentellen Datensatz zur markergestützten Introgression eines Überflutungstoleranzgens in Reis validiert. Hierzu wurde das gesamte Zuchtprogramm, wie es in der Praxis durchgeführt wurde, simuliert. In den Simulationen wurde die Häufigkeitsverteilung des rekurrenten Eltergenomanteils in den Rückkreuzungspopulationen erfasst. Die Simulationsergebnisse stimmten nahezu vollständig mit den experimentell beobachteten Daten überein. Dies belegt, dass Computersimulationen ein äußerst effektives Hilfsmittel sind, um den Selektionserfolg bei der markergestützten Rückkreuzung abzuschätzen.
Die Anwendung der Simulations- und Analysesoftware Plabsoft wurde exemplarisch an zwei Studien dargestellt. In der ersten Studie wurde mit Hilfe von Simulationen der zu erwartende Abfall an LD in den Durchkreuzungsgenerationen bei zwei rekurrenten Selektionsprogrammen in Mais bestimmt. Diese Studie demonstriert die Anwendung von Plabsoft zur Lösung von Fragestellungen, für welche keine analytische Lösungen zur Verfügung stehen. In der zweiten Studie wurden mit Hilfe von Computersimulationen die Ursachen untersucht, welche in einem Hybridmaiszuchtprogramm LD generieren und aufrecht erhalten. Hiermit wurde gezeigt, dass mit Plabsoft komplexe praktische Zuchtprogramme modelliert werden können.
Die Studien dieser Arbeit geben einen Überblick über das breite Anwendungsspektrum der entwickelten Simulations- und Analysesoftware Plabsoft. Darüber hinaus wurde Plabsoft bis jetzt in vierzig weiteren Studien verwendet, womit die Nützlichkeit von Plabsoft für die Integration neuer genomischer Werkzeuge in die angewandte Züchtungsforschung zweifelsfrei belegt wird
Genetische Analyse der Resistenz gegen Kolbenfusarium und Mykotoxinkontamination in Europäischem Mais
No full textMaize is affected by a number of diseases. Among the various ear rots of maize, Gibberella ear rot (GER) caused by Fusarium graminearum is prevalent in Central Europe. This fungal pathogen produces secondary metabolites (mycotoxins), which adversely affect the health of humans and animals. Two important mycotoxins are the immunosuppressant deoxynivalenol (DON) and the mycoestrogen zearalenone (ZEA). The most efficient method to reduce mycotoxin contamination in maize is cultivation of resistant varieties. However, resistance breeding using classical phenotypic selection is laborious and time-consuming. Therefore, marker-assisted selection (MAS) may be a promising alternative to classical selection. Furthermore, for setting up a breeding program, knowledge about the relevance of the different modes of gene action and genotypic correlations among resistance and agronomic traits is required.
The objectives of this study were to (1) estimate quantitative genetic parameters for GER severity and mycotoxin concentration in connected populations of doubled haploid (DH) lines, (2) map quantitative trait loci (QTL) for GER resistance and reduced mycotoxin contamination in these populations, (3) examine the congruency of QTL in these populations, (4) evaluate the prospects of using MAS to breed for GER resistance and reduced mycotoxin contamination, (5) estimate the genotypic correlation between the resistance of DH lines per se and the resistance of their testcrosses, (6) evaluate the influence of selection for increased resistance on agronomic performance of hybrids and (7) examine the relevance of different modes of gene action involved in the expression of the resistance in flint maize.
Three field experiments were conducted, each of which comprised a different set of plant material. Experiment I comprised five DH line populations derived from the following F1 crosses among elite flint inbred lines: D152×UH006, D152×UH007, UH007×UH006, UH009×UH006 and UH009×UH007. Experiment II comprised testcross progenies of 94 DH lines and a dent single cross tester. Experiment III comprised the five F1 crosses, from which the DH populations had been derived, the F2 and the first backcross generations to the parents (BC1-P1, BC1-P2) as well as the two parent lines of each cross. Plants were artificially infected with spores of F. graminearum shortly after mid-silking using the silk channel inoculation technique. The DH lines were genotyped with simple sequence repeat (SSR) DNA markers, genetic linkage maps were constructed and QTL analyses were performed for resistance to GER, DON and ZEA contamination.
Estimates of genotypic and genotype-by-environment interaction variances in Experiment I for GER severity and mycotoxin concentration were significant and heritabilities were moderately high to high in all populations. Thus, differences among DH lines for the resistance traits were mainly caused genetically and the resistance response varied depending on the environment. Owing to the effectiveness of artificial inoculation, the prospects are good to improve line resistance using a small number of test environments.
QTL were detected in the four largest populations. Depending on the population, the mapped QTL together explained 21-51% of the genotypic variance for GER severity and 19-45% for DON concentration and 52% for ZEA concentration. Additive gene action was more important than digenic interactions of QTL, as indicated by the number of QTL having significant additive effects, their relative contributions to the total genotypic variance explained and the magnitude of their effects.
Colocalized QTL for resistance to GER and mycotoxin contamination were identified in each mapping population. This was in agreement with strong genotypic correlations among these traits. QTL located at similar positions were detected across three populations in two chromosomal regions and across two populations in additional two regions. The results of this study indicated that a combination of classical phenotypic selection and MAS is a promising strategy for resistance breeding.
In Experiment II, significant genotypic variation for resistance in lines and testcrosses showed that selection will be successful in both groups. Owing to low genotypic correlations between lines and testcrosses, however, resources should be mainly allocated to the evaluation of GER in testcrosses. Correlations of resistance with agronomic traits were weak or not significant. Therefore, selection for resistance and better agronomic performance can be carried out simultaneously.
In Experiment III, generation means analysis indicated a prevalence of additive gene action for resistance. Significant dominance effects were found in only one cross for resistance to GER, but in four crosses for resistance to DON contamination. Owing to prevalence of additive gene action, the prospects are good to improve the resistance of the flint germplasm and to accumulate more favorable gene combinations in future breeding lines. Comparing the hybrid performance of flint×flint crosses of Experiment II and flint×dent crosses of Experiment III with their corresponding mid-parent performances indicated mid-parent heterosis for resistance. Therefore, prediction of hybrid performance based on performance of their parents will be possible only to a very limited extent.
Future research should focus on fine mapping and validating of the detected QTL. For an efficient use of the QTL in a marker-assisted breeding program, knowledge about their effects in different genetic backgrounds is needed. Of particular importance are thereby the QTL effects in flint×dent crosses, which represent the preferred type of hybrid in Central European maize breeding programs.Mais wird von zahlreichen Krankheiten befallen, wobei die Kolbenfusariosen von besonderer Bedeutung sind. In Mitteleuropa ist Fusarium graminearum der wichtigste Erreger dieser Krankheit. Dieser pilzliche Schaderreger produziert sekundäre Metabolite (Mykotoxine), die gesundheitsschädlich für Menschen und Tiere sind. Zwei wichtige Mykotoxine sind das immunsuppressiv wirkende Deoxynivalenol (DON) und das Mykoöstrogen Zearalenon (ZEA). Der effizienteste Weg Mykotoxinkontaminationen zu vermeiden ist der Anbau resistenter Sorten. Allerdings ist die Resistenzzüchtung mittels klassischer phänotypischer Selektion arbeits- und zeitaufwendig. Daher könnte die Marker-gestützte Selektion eine vielversprechende Alternative zur klassischen Selektion darstellen. Darüber hinaus sind für die Planung eines Zuchtprogrammes Kenntnisse über die Bedeutung verschiedener Genwirkungsweisen und über genotypische Korrelationen zwischen der Resistenz und agronomischen Merkmalen notwendig.
Die Ziele der vorliegenden Arbeit waren, (1) quantitativ-genetische Parameter für Kolbenfusariumbefall und Mykotoxinkonzentration in verbundenen Populationen doppelt-haploider (DH) Linien zu schätzen, (2) sog. quantitative trait loci (QTL) für Fusariumresistenz und reduzierte Mykotoxinkontamination in diesen Populationen zu kartieren, (3) die Übereinstimmung der QTL in diesen Populationen zu untersuchen, (4) die Aussichten der Marker-gestützten Selektion für die Züchtung auf Fusariumresistenz und reduzierte Mykotoxinkontamination zu bewerten, (5) die genotypische Korrelation zwischen der Resistenz von DH-Linien per se und deren Testkreuzungen zu schätzen, (6) die Auswirkung der Selektion auf verbesserte Resistenz auf agronomische Eigenschaften von Hybriden zu bewerten und (7) die Bedeutung verschiedener Genwirkungsweisen auf die Expression der Resistenz in Flint-Mais zu untersuchen.
Drei Feldexperimente wurden durchgeführt, in denen jeweils unterschiedliches Pflanzenmaterial geprüft wurde. In Experiment I wurden fünf DH-Populationen untersucht, die aus folgenden F1-Kreuzungen von Elite-Flint-Inzuchtlinien erstellt wurden: D152×UH006, D152×UH007, UH007×UH006, UH009×UH006 und UH009×UH007. In Experiment II wurden die Testkreuzungsnachkommen von 94 DH-Linien und einer Dent-Einfachkreuzung, die als Tester fungierte, untersucht. In Experiment III wurden neben den fünf F1-Kreuzungen, aus denen die DH-Populationen abgeleitet wurden, deren F2- und erste Rückkreuzungsgenerationen zu beiden Eltern (BC1-P1, BC1-P2) sowie die zwei Elternlinien jeder Kreuzung untersucht.
Die Versuchspflanzen wurden kurz nach dem Erscheinen der Narbenfäden künstlich mit Sporen von F. graminearum infiziert. Die DH-Linien wurden mit sog. simple sequence repeat (SSR) DNA-Markern genotypisiert, genetische Kopplungskarten wurden erstellt und QTL für die Resistenz gegen Kolbenfusarium und Mykotoxinbelastung kartiert.
Die genotypischen Varianzen und Genotyp-Umwelt-Wechselwirkungsvarianzen für Kolbenfusariumbefall und Mykotoxinkonzentrationen waren in Experiment I signifikant und die Heritabilitäten waren mäßig hoch bis hoch. Somit waren die Unterschiede zwischen den DH-Linien hauptsächlich genetisch bedingt. Aufgrund der Effizienz künstlicher Inokulation sind die Aussichten günstig, die Linienresistenz mit einer geringen Anzahl an Test-Umwelten zu verbessern.
QTL wurden in den vier größeren Populationen gefunden. Je nach Population erklärten die kartierten QTL zusammen 21-51% der genotypischen Varianz für Kolbenfusariumbefall, 19-45% für DON- und 52% für ZEA-Konzentration. In Übereinstimmung mit den engen genotypischen Korrelationen wurden kolokalisierte QTL für die Resistenz gegen Kolbenfusarium und Mykotoxinkontamination in jeder Kartierungspopulation gefunden. Die Ergebnisse deuteten darauf hin, dass eine Kombination von klassischer phänotypischer und Marker-gestützter Selektion eine vielversprechende Strategie für die Resistenzzüchtung ist.
In Experiment II waren die genotypischen Varianzen für die Resistenz in den Linien und Testkreuzungen signifikant. Dies zeigt, dass in beiden Gruppen erfolgreich selektiert werden kann. Jedoch sollten aufgrund der geringen genotypischen Korrelationen zwischen Linien und Testkreuzungen die vorhandenen Ressourcen größtenteils zur Prüfung von Testkreuzungen verwendet werden. Die Korrelationen zwischen der Resistenz und den agronomischen Merkmalen waren schwach oder nicht signifikant. Dadurch kann problemlos auf Resistenz und verbesserte agronomische Eigenschaften selektiert werden.
In Experiment III zeigten Generationsmittelwertanalysen eine vornehmliche Bedeutung additiver Genwirkung auf die Resistenz. Die Aussichten sind gut, die Resistenz im Flint-Material zu verbessern und günstige Genkombinationen in zukünftigen Zuchtlinien anzureichern. Vergleiche der Flint×Flint-Hybridkreuzungen aus Experiment II und der Flint×Dent-Hybridkreuzungen aus Experiment III mit den jeweiligen Elternmittelwerten deuteten auf eine Überlegenheit der Nachkommen gegenüber dem Elternmittel aufgrund von Heterosis hin. Aufgrund dessen wird es nur eingeschränkt möglich sein, die Resistenz von Hybriden aufgrund der Resistenz ihrer Eltern vorherzusagen.
Zukünftige Forschungsarbeiten sollten sich auf die Feinkartierung und Validierung der gefundenen QTL konzentrieren. Um die QTL effizient zu nutzen, sind Kenntnisse über deren Effekte in unterschiedlichen genetischen Hintergründen notwendig. Dabei sind die QTL-Effekte in Flint×Dent-Hybridkreuzungen von besonderer Bedeutung, da diese den bevorzugten Hybrid-Typ in Mitteleuropäischen Maiszüchtungsprogrammen darstellen
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