| Wheat Fusarium head blight, caused primarily by Fusarium graminearum, is one of themost devastating diseases worldwide, especitally in the region of humid and semi humid area.FHB causes significant reductions in both grain yield and quality through Fusarium-damagedkernels (FDK) and mycotoxins, especially deoxynivalenol (DON), produced in harvestedgrain infected by the pathogen, and DON contamination is a serious health concern to humansand livestock. To date, various cultural control measures and fungicides can reduce diseasedamage, but they could not be used to prevent FHB epidemics. Growing resistant cultivars isan effective method to control Fusarium head blight (FHB) caused by Fusarium graminearum.Recent years, Fusarium head blight rapidly spread in U.S. Great Plains for winter wheat.Therefore, the evaluation of FHB resistance indicators, exploitation FHB resistance germplasmand utilization of association mapping method for locating resistant QTLs or gene will beimperative in improving FHB resistance of U.S. native wheat lines, reduce the threat of thisdisease and minimize economic losses. This study used363significant representative hard andsoft winter wheats as materials, by repeatdly syring inoculation method in greenhouseexperiments and spray and syring inoculation in field experiments, screening FHB resistancewheat accessions, assessing associated trats of FHB diease; by using different evaluation anddetection methods to test FHB traits and comparing their correlations to ensure the properevaluation methods; then based on207wheat accessions, evulating the genetic structure, diversityand linkage disequilibrium of U.S. winter wheat by using polymorphic markers from the wholegenome; finally, to detect significant markers or QTLs in winter wheat associated with percentageof symptomatic spikelets and percentage of damage kernels, using9K SNP and145SSR and STSto analyse165accessions by association mapping method. Result as show:1. To characterize FHB resistance in U.S. wheat germplasm,363U.S. winter wheataccessions were repeatedly evaluated for FHB resistance. A high correlation (r=0.73, P <0.001) for mean percentages of symptomatic spikelets (PSS) was observed betweengreenhouse and field experiments. The majority of tested accessions were either moderatelyor highly susceptible;22accessions showed a high level of resistance in the greenhouse and field experiments, such as Lyman, Harry, T154, Heyne, Everest, Freedom, Roane and Bess.Mean PSS for19accessions that carry markers for Fhb1, a major quantitative trait locus(QTL) from ‘Sumai3’, are29.8%in the greenhouse and25.1%in the field experiments.Accessions without Fhb1that showed consistent resistance in both field and greenhouseexperiments may be good sources for pyramiding native resistance QTLs from U.S. wheatwith Fhb1.2. FHB infection results in Fusarium-damaged kernels (FDK) and deoxynivalenol (DON)that dramatically reduce grain yield and quality. More effective and accurate diseaseevaluation methods are imperative for successful identification of FHB-resistant sources andselection of resistant cultivars. To determine the relationships among different types ofresistance,363U.S. winter wheat accessions were repeatedly evaluated for FDK and DONconcentration in greenhouse and field experiments. Single kernel near-infrared(SKNIR)-estimated FDK and DON were compared with visually estimated FDK and gaschromatography-mass spectroscopy-estimated DON. High correlation coefficients also wereobserved between visually scored FDK and PSS (r=0.62, P <0.001), SKNIR-estimated FDK(r=0.72, P <0.001) and SKNIRestimated DON (r=0.68, P <0.001); Significant correlations(r=0.95, P <0.001) were detected between SKNIR-estimated FDK and SKNIRestimatedDON. Therefore, both visual scoring and SKNIR methods are useful for estimating FDK andDON in breeding programs. Four parental cultivars used in the Fhb1backcross projectshowed different levels of FHB infection, including Wesley, Trego, Clark, and Harding. AllWesleyFhb1, ClarkFhb1and TregoFhb1resistant NILs had significantly lower DONconcentrations and FDK than their recurrent parent. Therefore, Fhb1significantly reducesboth FDK and DON concentration in U.S. winter wheat genetic backgrounds.3. Using168wheat genomic polymorphic markers throughout the whole genome toanalyse the population structure of207U.S. winter wheat accessions, which were divided intofour subgroups. The analysis of Genetic diversity showed a lower level in U.S. winter wheat,and the genetic distance between H1and H2, H3and H4being the smallest, indicating largedifference of genetic background were usually accompanied with larger genetic distance. Themethods of UPGMA cluster and Principal components analysis (PCA) verified it wasreasonable that the wheat population was classified into four subgroups associated withgenetic background and geographic factors. A short LD decay distance less than10cM wasobserved in U.S. winter wheat, therefore, for further research on U.S. winter wheat, increasingthe density of molecular markers was necessary.4. Genome-wide association mapping was conducted to analyse a panel of165winter wheat accessions, majority were HWW accessions. The panel was repeatedly evaluated forpercentage of symptomatic spikelets (PSS) and Fusarium damaged kernels (FDK) afterinoculation with Fusarium graminearum in greenhouses, and genotyped with145SSR andSTS markers and9,000iSelect Beadchip Assay.4SSR (Xgwm261(2D), Xgwm493(3B),Xbarc102(3B), Xwmc273(7B)) and1STS (Xumn10(3B)) markers were significantlyassociated with FHB resistance as reflected by low PSS and FDK at q <0.1. Two SNP(IWA5426(3B) and IWA92(3B)) and one SNP (IWA2493(3B)) were associated with lowlevel of PSS and FDK, respectively. A QTL in Fhb1region on3BS was highly significantwith both low PSS and FDK, whereas QTL on2D was significant only in southern GreatPlains area and QTL on chromosome7B was highly associated with low PSS and FDK inboth north and south Great Plains. SNP marker IWA2493was significantly correlated with theQTL spanned in Fhb1region responding low FDK ratings. These SNP should be useful formarker assisted selection in U.S. winter wheat breeding programs. |
