Potential and limits to unravel the genetic architecture and predict the variation of Fusarium head blight resistance in European winter wheat (Triticum aestivum L.).

Genome-wide mapping approaches in diverse populations are powerful tools to unravel the genetic architecture of complex traits. The main goals of our study were to investigate the potential and limits to unravel the genetic architecture and to identify the factors determining the accuracy of prediction of the genotypic variation of Fusarium head blight (FHB) resistance in wheat (Triticum aestivum L.) based on data collected with a diverse panel of 372 European varieties. The wheat lines were phenotyped in multi-location field trials for FHB resistance and genotyped with 782 simple sequence repeat (SSR) markers, and 9k and 90k single-nucleotide polymorphism (SNP) arrays. We applied genome-wide association mapping in combination with fivefold cross-validations and observed surprisingly high accuracies of prediction for marker-assisted selection based on the detected quantitative trait loci (QTLs). Using a random sample of markers not selected for marker-trait associations revealed only a slight decrease in prediction accuracy compared with marker-based selection exploiting the QTL information. The same picture was confirmed in a simulation study, suggesting that relatedness is a main driver of the accuracy of prediction in marker-assisted selection of FHB resistance. When the accuracy of prediction of three genomic selection models was contrasted for the three marker data sets, no significant differences in accuracies among marker platforms and genomic selection models were observed. Marker density impacted the accuracy of prediction only marginally. Consequently, genomic selection of FHB resistance can be implemented most cost-efficiently based on low- to medium-density SNP arrays.

Relatedness severely impacts accuracy of marker-assisted selection for disease resistance in hybrid wheat.

The accuracy of genomic selection depends on the relatedness between the members of the set in which marker effects are estimated based on evaluation data and the types for which performance is predicted. Here, we investigate the impact of relatedness on the performance of marker-assisted selection for fungal disease resistance in hybrid wheat. A large and diverse mapping population of 1739 elite European winter wheat inbred lines and hybrids was evaluated for powdery mildew, leaf rust and stripe rust resistance in multi-location field trials and fingerprinted with 9 k and 90 k SNP arrays. Comparison of the accuracies of prediction achieved with data sets from the two marker arrays revealed a crucial role for a sufficiently high marker density in genome-wide association mapping. Cross-validation studies using test sets with varying degrees of relationship to the corresponding estimation sets revealed that close relatedness leads to a substantial increase in the proportion of total genotypic variance explained by the identified QTL and consequently to an overoptimistic judgment of the precision of marker-assisted selection.

Quantitative trait loci for adult-plant resistance to Mycosphaerella graminicola in two winter wheat populations.

Septoria tritici blotch (STB) is one of the most important leaf spot diseases in wheat worldwide. The goal of this study was to detect chromosomal regions for adult-plant resistance in large winter wheat populations to STB. Inoculation by two isolates with virulence to Stb6 and Stb15, both present in the parents, was performed and STB severity was visually scored plotwise as percent coverage of flag leaves with pycnidia-bearing lesions. 'Florett'/'Biscay' and 'Tuareg'/'Biscay', each comprising a cross of a resistant and a susceptible cultivar, with population sizes of 316 and 269 F(7:8) recombinant inbred lines, respectively, were phenotyped across four and five environments and mapped with amplified fragment length polymorphism, diversity array technology, and simple sequence repeat markers covering polymorphic regions of ≈1,340 centimorgans. Phenotypic data revealed significant (P < 0.01) genotypic differentiation for STB, heading date, and plant height. Entry-mean heritabilities (h(2)) for STB were 0.73 for 'Florett'/'Biscay' and 0.38 for 'Tuareg'/'Biscay'. All correlations between STB and heading date as well as between STB and plant height were low (r = -0.13 to -0.20). In quantitative trait loci (QTL) analysis, nine and six QTL were found for STB ratings explaining, together, 55 and 51% of phenotypic variation in 'Florett'/'Biscay' and 'Tuareg'/'Biscay', respectively. Genotype-environment and QTL-environment interactions had a large impact. Two major QTL were detected consistently across environments on chromosomes 3B and 6D from 'Florett' and chromosomes 4B and 6B from 'Tuareg', each explaining 12 to 17% of normalized adjusted phenotypic variance. These results indicate that adult-plant resistance to STB in both mapping populations was of a quantitative nature.

Marker-based introduction of three quantitative-trait loci conferring resistance to Fusarium head blight into an independent elite winter wheat breeding population.

Fusarium head blight (FHB) is one of the most important wheat diseases that causes yield and quality losses as well as contamination with deoxynivalenol (DON). This study aimed for marker-based introduction of three previously mapped QTLs from two German winter wheat resistance sources into an elite background unrelated to the mapping population. A double cross (DC) served as initial population that combined two resistance donor-QTL alleles from "Dream" (Qfhs.lfl-6AL, Qfhs.lfl-7BS) and one donor-QTL allele from "G16-92" on chromosome 2BL with two high yielding, susceptible elite winter wheats ("Brando", "LP235.1"). The initial population of 600 DC-derived F(1) lines was selected with SSR markers for the respective QTLs. After two marker-selection steps, each of eight marker classes was represented by 9-22 lines possessing the respective donor-QTL allele or all possible combinations thereof in the homozygous state. The effect of the QTLs was estimated by field tests at four locations inoculated with Fusarium culmorum. Resistance was measured as the mean of multiple FHB ratings (0-100%). Marker classes incorporating only one QTL were not significantly more resistant than the class without any QTL, the combination of two donor-QTL alleles reduced FHB significantly. On average, lines with Qfhs.lfl-6AL were significantly taller than lines without this QTL. A considerable variation for FHB resistance was found in all marker classes. Marker-based introduction of two QTLs enhanced mean FHB rating by about 40 percentage points, the selected plants, however, were, on average, significantly taller. Both findings strongly support a phenotypic selection following after marker-based introduction of effective QTLs.

Stacking quantitative trait loci (QTL) for Fusarium head blight resistance from non-adapted sources in an European elite spring wheat background and assessing their effects on deoxynivalenol (DON) content and disease severity.

Fusarium head blight (FHB) is a devastating disease in wheat that reduces grain yield, grain quality and contaminates the harvest with deoxynivalenol (DON). As potent resistance sources Sumai 3 and its descendants from China and Frontana from Brazil had been analysed by quantitative trait loci (QTL) mapping. We introgressed and stacked two donor QTL from CM82036 (Sumai 3/Thornbird) located on chromosomes 3B and 5A and one donor QTL from Frontana on chromosome 3A in elite European spring wheat and estimated the effects of the three individual donor QTL and their four combinations on DON, Fusarium exoantigen content, and FHB rating adjusted to heading date. One class with the susceptible QTL alleles served as control. Each of the eight QTL classes was represented by 12-15 F(3)-derived lines tested in F(5) generation as bulked progeny possessing the respective marker alleles homozygously. Traits were evaluated in a field experiment across four locations with spray inoculation of Fusarium culmorum. All three individual donor-QTL alleles significantly reduced DON content and FHB severity compared to the marker class with no donor QTL. The only exception was the donor-QTL allele 3A that had a low, but non-significant effect on FHB severity. The highest effect had the stacked donor-QTL alleles 3B and 5A for both traits. They jointly reduced DON content by 78% and FHB rating by 55% compared to the susceptible QTL class. Analysis of Fusarium exoantigen content illustrates that lower disease severity is associated with less mycelium content in the grain. In conclusion, QTL from non-adapted sources could be verified in a genetic background of German elite spring wheat. Within the QTL classes significant (P<0.05) genotypic differences were found among the individual genotypes. An additional phenotypic selection would, therefore, be advantageous after performing a marker-based selection.

Molecular mapping of Fusarium head blight resistance in the winter wheat population Dream/Lynx.

Fusarium head blight (FHB), mainly caused by Fusarium graminearum and F. culmorum, can significantly reduce the grain quality of wheat (Triticum aestivum L.) due to mycotoxin contamination. The objective of this study was to identify quantitative trait loci (QTLs) for FHB resistance in a winter wheat population developed by crossing the resistant German cultivar Dream with the susceptible British cultivar Lynx. A total of 145 recombinant inbred lines (RILs) were evaluated following spray inoculation with a F. culmorum suspension in field trials in 2002 in four environments across Germany. Based on amplified fragment length polymorphism and simple sequence repeat marker data, a 1,734 cM linkage map was established assuming that the majority of the polymorphic parts of the genome were covered. The area under disease progress curve (AUDPC) was calculated based on the visually scored FHB symptoms. The population segregated quantitatively for FHB severity. Composite interval mapping analysis for means across the environments identified four FHB resistance QTLs on chromosomes 6AL, 1B, 2BL and 7BS. Individually the QTLs explained 19%, 12%, 11% and 21% of the phenotypic variance, respectively, and together accounted for 41%. The QTL alleles conferring resistance on 6AL, 2BL and 7BS originated from cv. Dream. The resistance QTL on chromosome 6AL partly overlapped with a QTL for plant height. The FHB resistance QTL on 7BS coincided with a QTL for heading date, but the additive effect on heading date was of minor importance. The resistance QTL on chromosome 1B was associated with the T1BL.1RS wheat-rye translocation of Lynx.

Epinephrine and sodium bicarbonate during CPR following asphyxial cardiac arrest in rats.

Although high-dose epinephrine during CPR improves coronary perfusion pressure (CoPP) and rate of return of spontaneous circulation (ROSC) in some models, its impact on long term outcome (> or = 72 h) has not been evaluated. Previous studies of sodium bicarbonate (NaHCO3) therapy during CPR indicate that beneficial effects may be dependent on epinephrine (EPI) dose. We hypothesized that EPI and NaHCO3 given during CPR have a significant impact on long term outcome. One hundred male Sprague-Dawley rats were prospectively studied in a block randomized placebo controlled trial. Rats were anesthetized, paralyzed, mechanically ventilated, instrumented, and each underwent 10 min of asphyxia, resulting in 6.8 +/- 0.4 min of circulatory arrest. Resuscitation was performed by mechanical ventilation and manual external chest compressions. EPI 0.0 (placebo), 0.01, 0.1, or 1.0 mg/kg IV was given at the onset of CPR, followed by NaHCO3 0.0 (placebo) or 1.0 mEq/kg IV. Successfully resuscitated rats were monitored and ventilated for 1 h without hemodynamic support. Neurologic deficit scores (NDS), cerebral histopathologic damage scores (CHDS) and myocardial histopathologic damage scores (MHDS) were determined in rats that survived 72 h. EPI improved CoPP and ROSC in a dose-dependent manner up to 0.1 mg/kg. Rats receiving EPI 0.1 and 1.0 mg/kg during CPR exhibited prolonged post-ROSC hypertension and metabolic acidemia, increased A-a O2 gradient, and an increased incidence of post-ROSC ventricular tachycardia or fibrillation. Overall survival was lower with EPI 0.1 and 1.0 mg/kg compared to 0.01 mg/kg. Although NDS was significantly less with EPI 0.1 mg/kg compared to placebo, there was no difference in CHDS between groups. In contrast, MDS was significantly higher with EPI 0.1 mg/kg compared to placebo or EPI 0.01 mg/kg. There was an overall trend toward improved survival at 72 h in rats that received NaHCO3 which was most evident in the EPI 0.1 mg/kg group. We conclude that (1) EPI during CPR has a biphasic dose/response curve in terms of survival, when post-resuscitation effects are left untreated and (2) NaHCO3 doses greater than 1.0 mEq/kg may be necessary to treat the side-effects of high-dose EPI. Further work is needed to determine if treating the immediate post-resuscitation effects of high-dose EPI can prevent detrimental effects on long-term outcome.