Inheritance of Barley yellow dwarf virus resistance in maize

Barley yellow dwarf (BYD) is one of the economically most important virus diseases in cereals. Due to increasing winter temperatures it is expected that BYD will become an increasing problem in maize cultivation. In earlier studies, it was reported that BYD has a negative impact on plant performance of maize. BYD virus (BYDV) is transmitted by aphids and the best control of the virus is the development of resistant maize cultivars. Therefore, the first objectives of my thesis research were to (i) determine phenotypic and genotypic variation in five segregating populations and in a broad germplasm set of maize with respect to BYDV tolerance and resistance as well as to (ii) quantify the influence of BYDV infection on the plant traits plant height, ear height, and flowering time. I observed a negative impact of BYDV infection on maize plant traits which shows that the development of resistant maize cultivars is of high importance for maize cultivation. Furthermore, in the connected biparental populations as well as in the association mapping population, I observed a high genotypic variance with regard to BYDV resistance which is the requirement for successful breeding and the identification of genome regions which contribute to BYDV resistance. The evaluation of BYDV resistance by the inoculation with BYDV and by double antibody sandwich enzyme-linked immunosorbent assay (DASELISA) is dificult to be included in the breeding process. Therefore, molecular markers are of high importance for the improvement of BYDV resistance by breeding. Therefore, the objective of this study was the (iii) identification of genome regions which are involved in the BYDV resistance by a genome wide association study (GWAS). For the BYDV resistance traits, significantly (α=0.01) associated SNPs were identified in the GWAS on chromosome 10 and 4. The SNPs identified for virus extinction on chromosome 10 explained in a simultaneous fit 25% of the phenotypic variance and were located in gene regions which were in other plants described to be involved in resistance mechanisms. This suggests that BYDV resistance is inherited oligogenically and that genes involved in general resistance mechanisms are also involved in BYDV resistance in maize. GWAS has the advantage that a large number of alleles per locus can be surveyed simultaneously, and because historical recombinations can be used, the mapping resolution is higher compared to classical linkage mapping. Nevertheless, genes contributing to phenotypic variation which show a low allele frequency can remain undetected. Due to a balanced allele frequency in segregating populations, linkage mapping has the advantage of higher QTL detection power compared to GWAS. Therefore, the objective of this study was to (iv) validate the genome regions with a linkage analysis in connected biparental crosses. The genome region on chromosome 10 which was identified in the GWAS to be linked to BYDV resistance could be validated in the linkage mapping study with connected populations as well as in the single populations. Furthermore, the QTL on chromosome 10 colocalized with the QTL identified in controlled greenhouse conditions. In earlier studies, QTL for other virus resistances were identified on chromosome 10. This suggests that these genes are involved in multiple virus resistances. The identified genome regions explain 45% of the phenotypic variance and are, therefore, promising for the use in MAS. The broad genotypic variation with regard to BYDV resistance, observed in my thesis research, provided a good basis for the successful identification of molecular markers which are associated with BYDV resistance in maize. The markers identified in my study by GWAS were validated by a linkage mapping approach and are promising for the use in marker assisted selection on BYDV resistance in maize breeding.Die Gerstengelbverzwergung (Barley yellow dwarf, BYD) gehört wirtschaftlich zu den wichtigsten Viruskrankheiten im Getreide. Aufgrund steigender Wintertemperaturen wird auch in Mais erwartet, dass die BYD in Zukunft ein wachsendes Problem wird, zumal aus bisherigen Studien bekannt ist, dass die BYD einen negativen Einfluss auf Mais hat. Die effektivste Methode zur Bekämpfung des BYD Virus (BYDV), welches von Aphiden übertragen wird, ist die Züchtung von resistenten Maissorten. Deshalb waren die ersten Ziele meiner Doktorarbeit (i) die Erfassung der genotypischen Variation für die BYDV-Resistenz in fünf spaltenden Populationen und in einem diversen Mais-Set, sowie (ii) die Beobachtung des Einflusses der BYDV-Infektion auf die Pflanzenmerkmale, Pflanzenhöhe, Kolbenhöhe und den Blühzeitpunkt. In der aktuellen Studie wurde beobachtet, dass eine BYDV-Infektion einen negativen Einfluss auf Pflanzenmerkmale von Mais hat - was die Relevanz einer Verbesserung der BYDV-Resistenz hervorhebt. Des Weiteren wurde sowohl in den verbundenen spaltenden Populationen als auch in der Assoziationskartierungspopulation eine hohe genotypische Variation für die BYDV Resistenz beobachtet. Diese stellt eine wichtige Voraussetzung für eine erfolgreiche Assoziationskartierung dar. Die Evaluierung hinsichtlich der BYDV-Resistenz ist schwer in den Züchtungsprozess zu integrieren, da die Virus-Inokulation mit Blattläusen und die Bestimmung des Virusgehalts durch DAS-ELISA sehr aufwändig sind. Für die züchterische Verbesserung der BYDV-Resistenz sind molekulare Marker von gröer Bedeutung. Deshalb war ein weiteres Ziel der Arbeit (iii) in einer genomweiten Assoziationskartierung (GWAS) Genomregionen zu identifizieren, die an der BYDV-Resistenz in Mais beteiligt sind. In der GWAS wurden signifikante (α=0.01) SNPs auf Chromosom 4 und 10 für die BYDV-Resistenzmerkmale identifiziert. Die SNPs die auf Chromosom 10 für die Virusextinktion identifiziert wurden, erklären zusammen 25% der phänotypischen Varianz. Dieser Genombereich wurde schon in anderen Pflanzen als für Resistenzmechanismen zuständig beschrieben. Die Ergebnisse der aktuellen Studie lassen deshalb vermuten, dass die BYDV-Resistenz oligogen vererbt wird und, dass Gene, die in generelle Resistenzmechanismen involviert sind, auch an der BYDV-Resistenz in Mais beteiligt sind. Die GWAS hat den Vorteil, dass eine groβe Anzahl von Allelen pro Locus gleichzeitig untersucht werden können. Da in verbundenen Populationen eine höhere Rekombination stattgefunden hat, ist die Auflösung, verglichen zur klassischen quantitative trait locus (QTL) Kartierung, höher. Trotzdem können Gene, die zu einer gröen phänotypischen Variation füuhren, unentdeckt bleiben, wenn sie eine niedrige Allel Frequenz aufweisen. Durch die ausgeglichene Allelfrequenz in biparentalen Populationen hat die klassische QTL-Analyse eine höhere Power weitere QTL zu detektieren als eine GWAS. Deshalb war ein weiteres Ziel dieser Arbeit (iv) die Validierung der Genomregionen in einer QTL-Analyse mit verbundenen Populationen. Die Genomregion auf Chromosom 10, die in der GWAS identifiziert wurde, konnte in der QTL-Analyse mit verbundenen Populationen und in QTL- Analysen mit Einzel-Populationen validiert werden. Darüber hinaus kolokalisieren diese QTL mit den QTL, die in kontrollierten Gewächshausbedingungen identifiziert wurden. Auβerdem lassen die Ergebnisse vermuten, dass die Gene auch an der Ausprägung anderer Virus-Resistenzen beteiligt sind. Da diese Genomregionen 45% der phänotypischen Varianz erklären, sind sie vielversprechend für die Marker-gestützte Selektion. Die hohe genotypische Varianz, die in meiner Arbeit beobachtet wurde, stellte eine gute Gundlage für die Identifizierung von molekularen Markern dar, die mit der BYDV Resistenz assoziiert sind. Diese Marker, welche mit einer GWAS identifiziert wurden, konnten mit einer QTL Kartierung verifiziert werden und sind vielversprechend für die markergestützte Selektion auf BYDV Resistenz in der Maiszüchtung

Natural variation for BYDV resistance in maize

With increasing winter temperatures, Barley yellow dwarf virus (BYDV) is expected to become a prominent problem also in maize cultivation. Breeding for resistance is the best alternative to control the disease and break the transmission cycle of the virus. The objectives of our study were to (I) determine phenotypic and genotypic variation in five segregating populations of maize with respect to BYDV tolerance or resistance as well as (II) quantify the influence of BYDV infection on plant performance traits. In 2011, five segregating populations with a total of 445 genotypes were grown at two locations in Germany. Plants were inoculated with BYDV-PAV transmitted by aphids of the species Rhopalosiphum padi. We observed considerable genotypic variance for the traits virus concentration as measured by double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) as well as expression of symptoms. Furthermore, heritabilities were high for the plant performance traits ear height and plant height. Correlation coefficients between all pairs of traits were significantly different from 0 (P < 0.05). Genotypes of the inoculated variant were reduced in plant height by 3 cm, ear height by 6 cm, and flowered 3 days earlier compared to genotypes of the non-inoculated variant. The results of our study suggested a high potential for breeding of BVDY resistant / tolerant maize

Linkage mapping of Barley yellow dwarf virus resistance in connected populations of maize

BACKGROUND: With increasing winter temperatures, Barley yellow dwarf virus (BYDV) is expected to become an increasing problem in maize cultivation in Germany. Earlier studies revealed that BYDV has a negative impact on maize performance. Molecular markers would accelerate the development of BYDV resistant maize. Therefore, the objectives of this study were (i) the identification of quantitative trait loci (QTL) for BYDV resistance in five connected segregating maize populations in a field experiment and (ii) their comparison with the QTL detected under greenhouse conditions. RESULTS: In linkage analyses of the traits virus extinction, infection rate, and the symptom red edges, a highly associated major QTL was identified on chromosome 10. This QTL explained 45% of the phenotypic variance for the traits virus extinction and infection rate and 30% for the symptom red edges. CONCLUSION: We could show that BYDV resistance traits are oligogenically inherited. The QTL on chromosome 10 could be observed in the connected linkage analyses and in the single population analyses. Furthermore, this QTL could also be confirmed in the greenhouse experiment. Our results let suggest that this QTL is involved in multiple virus resistance and the markers are promising for marker assisted selection. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12870-015-0420-x) contains supplementary material, which is available to authorized users

“Uninformed consent” in clinical trials with cancer patients: A qualitative analysis of patients’ and support persons’ communication experiences and needs

Objective Cancer patients are often overwhelmed when being informed about clinical trials. However, there is a lack of evidence-based strategies to improve physician-patient communication in this area. This study assessed the experiences and needs of cancer patients and their support persons (SPs) during the informed consent (IC) process prior to participation in clinical trials. Methods 17 semi-structured interviews with cancer patients and their SP were conducted and analysed using a framework analysis. Results Most respondents reported feeling well informed about the clinical trial. However, core aspects of the study were often not understood highlighting a dissonance between perceived and actual recall and understanding. Many participants trusted that the trial recommended was the best available care and only skimmed the consent form or did not read it at all. Conclusions This is the first German study to analyse both cancer patients’ and SPs’ perspectives on IC processes. Although many feel well informed, our results suggest a significant gap in recall and understanding of core components of clinical trials which hinders IC. Practice implications Further interventional research is required to improve the consent processes prior to clinical trials in order to provide optimal, patient-centred care

A paired-kidney allocation study found superior survival with HLA-DR compatible kidney transplants in the Eurotransplant Senior Program

The Eurotransplant Senior Program (ESP) has expedited the chance for elderly patients with kidney failure to receive a timely transplant. This current study evaluated survival parameters of kidneys donated after brain death with or without matching for HLA-DR antigens. This cohort study evaluated the period within ESP with paired allocation of 675 kidneys from donors 65 years and older to transplant candidates 65 years and older, the first kidney to 341 patients within the Eurotransplant Senior DR-compatible Program and 334 contralateral kidneys without (ESP) HLA-DR antigen matching. We used Kaplan-Meier estimates and competing risk analysis to assess all cause mortality and kidney graft failure, respectively. The log-rank test and Cox proportional hazards regression were used for comparisons. Within ESP, matching for HLA-DR antigens was associated with a significantly lower five-year risk of mortality (hazard ratio 0.71; 95% confidence interval 0.53-0.95) and significantly lower cause-specific hazards for kidney graft failure and return to dialysis at one year (0.55; 0.35-0.87) and five years (0.73; 0.53-0.99) post-transplant. Allocation based on HLA-DR matching resulted in longer cold ischemia (mean difference 1.00 hours; 95% confidence interval: 0.32-1.68) and kidney offers with a significantly shorter median dialysis vintage of 2.4 versus 4.1 yrs. in ESP without matching. Thus, our allocation based on HLA-DR matching improved five-year patient and kidney allograft survival. Hence, our paired allocation study suggests a superior outcome of HLA-DR matching in the context of old-for-old kidney transplantation.</p

Prospective observational cohort study on grading the severity of postoperative complications in global surgery research

Background The Clavien–Dindo classification is perhaps the most widely used approach for reporting postoperative complications in clinical trials. This system classifies complication severity by the treatment provided. However, it is unclear whether the Clavien–Dindo system can be used internationally in studies across differing healthcare systems in high- (HICs) and low- and middle-income countries (LMICs). Methods This was a secondary analysis of the International Surgical Outcomes Study (ISOS), a prospective observational cohort study of elective surgery in adults. Data collection occurred over a 7-day period. Severity of complications was graded using Clavien–Dindo and the simpler ISOS grading (mild, moderate or severe, based on guided investigator judgement). Severity grading was compared using the intraclass correlation coefficient (ICC). Data are presented as frequencies and ICC values (with 95 per cent c.i.). The analysis was stratified by income status of the country, comparing HICs with LMICs. Results A total of 44 814 patients were recruited from 474 hospitals in 27 countries (19 HICs and 8 LMICs). Some 7508 patients (16·8 per cent) experienced at least one postoperative complication, equivalent to 11 664 complications in total. Using the ISOS classification, 5504 of 11 664 complications (47·2 per cent) were graded as mild, 4244 (36·4 per cent) as moderate and 1916 (16·4 per cent) as severe. Using Clavien–Dindo, 6781 of 11 664 complications (58·1 per cent) were graded as I or II, 1740 (14·9 per cent) as III, 2408 (20·6 per cent) as IV and 735 (6·3 per cent) as V. Agreement between classification systems was poor overall (ICC 0·41, 95 per cent c.i. 0·20 to 0·55), and in LMICs (ICC 0·23, 0·05 to 0·38) and HICs (ICC 0·46, 0·25 to 0·59). Conclusion Caution is recommended when using a treatment approach to grade complications in global surgery studies, as this may introduce bias unintentionally