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Fusarium head blight (FHB) of wheat (Triticum aestivum L.) is a devastating disease in wheat production worldwide. Identifying resistance genes and understanding the genetic basis of resistance to FHB are prerequisites to developing cultivars that can avoid losses from FHB. This investigation of quantitative trait loci (QTL) was performed in a recombinant inbred (RI) population derived from a cross between the FHB-moderately susceptible cv. Patterson and the FHB-resistant line Fundulea 201R (F201R). Bulk DNAs from the 11 most resistant and 12 most susceptible lines of the phenotypic distribution of the RI population, together with the parental lines, were screened with simple sequence repeat (SSR) markers. Regional QTL mapping identified four interval regions, located on chromosomes 1B, 3A, 3D, and 5A, that conferred resistance to FHB. The QTLs located on chromosomes 1B and 3A, contributed by F201R, had large effects and were consistently expressed in three environments. The four QTLs together accounted for 32.7% of the phenotypic variation, or 43.0% of the genotypic variation. The QTL on chromosome 3A is located in the same region as a QTL that was detected in wild tetraploid wheat T. dicoccoides (Koern. ex Asch. & Graebner) Aarons. The possibility that the FHB resistance QTLs of F201R and that of T. dicoccoides on chromosome 3A have the same origin is discussed., WHEAT IS A STAPLE FOOD CROP in the USA and worldwide. In the past decade, there have been epidemics of FHB in many areas where the flowering period coincides with [...]

The barley yellow dwarf viruses (BYDVs) constitute an important group of plant viruses of cultivated cereal crops in which only tolerance and/or low levels of resistance are known. High levels of resistance, which we here define as low concentrations of virus in plant tissues, have been discovered in Thinopyrum spp. (formerly Agropyron). In this study we have characterized such resistance in [BC.sub.2] and [BC.sub.3] populations, derived by crossing cultivated wheat (Triticum aestivum L. emend. Thell.) with Th. ponticum (Podp.) Barkw. & D.R. Dewey Agropyron Elongatum [Syn (Host) P. Beauv.] and backcrossing to wheat. The objectives were to evaluate the levels of resistance genetically transferable to wheat lines using both enzyme-linked immunosorbent assay (ELISA) and cDNA dot-blot hybridization for the detection of low levels of virus in plant tissues. Uniformity in results using both techniques depends on procedural uniformity, but a high correlation (0.93) between ELISA values and densitometry scans was obtained. A range in resistance was observed among the BC[sub2] and BC[sub3] populations from highly resistant to moderately resistant to susceptible. Lines classified as resistant had densitometry absorbance values of 0.25 to 0.60 and ELISA values from 0.03 to 0.30. The low values .for both ELISA and dot-blot assays indicate that significant resistance can be maintained in more advanced generations. Such low virus levels also suggest that inhibition of virus replication or cell to cell movement may occur in resistant Thinopyrum spp.

Incorporated of resistance to septoria glume blotch, caused by Stagonospora nodorum (Berk.) Castellani & E.G. Germano, into wheat (Triticum aestivum L.) is complex because resistance is quantitatively inherited. The Brazilian wheat |Cotipora' expresses a high level of resistance to this pathogen. Crosses were made between Cotipora and the susceptible Purdue line, P831791A1-1-6. Populations of parents, [F.sub.1], [F.sub.2] [BCF.sub.1], and [BCF.sub.2] were inoculated with a conidial suspension of the pathogen containing 2.5 x [10.sup.6] spores [mL.sup.-1] and given a moist period of 52 h. Percentage of diseased tissue was estimated on the spikes and flag leaves four times over a 20-d period, and an area under disease progress curve (AUDPC) was calculated. Correlations between AUDPCs of spike and flag leaf in the [F.sub.2] and [BCF.sub.1] populations were 0.312 and 0.283, respectively, indicating that resistance is at least partially controlled by different genes in these two plant organs. Resistance was partially dominant in the [F.sub.1] generation in both the spike and flag leaf. In the [F.sub.2] [BCF.sub.1], and [BCF.sub.2] generations, however, dominant gene action was not evident. The gene number estimate for the spike reaction was 3.16. Broad sense heritability estimates were 0.51 and 034 for the spike and flat leaf reactions to S. nodorum, respectively. Cotipora is a valuable source of S. nodorum resistance because of its high level of resistance expressed in the spike and flag leaves.

Fusarium head blight (FHB) is one of the most damaging wheat (Triticum aestivum L.) diseases in humid and semihumid regions around the world. Breeding efforts have focused on resistance mechanisms that limit the spread once a spike is infected--type II resistance. But resistance to initial infection, type I resistance, is an important trait that could be combined with other modes of resistance. The objective of this project was to identify and map the locations of previously unknown quantitative trait loci (QTL) that reduce the incidence of initial infection. A mapping population of 198 recombinant inbred lines (RILs) was evaluated for type I resistance in both the field and greenhouse. A two-enzyme genotyping-by-sequencing (GBS) approach was applied to construct a 1883-cM linkage map yielding single-nucleotide polymorphism (SNP) markers. Composite interval mapping analysis detected a QTL on chromosome 1AS under greenhouse conditions and three other QTL on chromosomes 1BL, 2BL, and 3AS in field environments. Each QTL explained between 7.44 and 12.20% of the total phenotypic variation. Sixteen RILs were identified with markers for all three QTL on chromosomes 1BL, 2BL, and 3AS exhibiting significantly improved type I resistance (a mean of 33.06% improvement) over RILs with none of the three markers in field experiments. Our results also confirmed that types I and II FHB resistance were controlled by different loci in the wheat RIL population and could be used in combination to provide multiple layers of defense for cultivar development through marker-assisted selection. [ABSTRACT FROM AUTHOR]

Fusarium head blight (FHB) of wheat (Triticum aestivum L.) is a devastating disease in wheat production worldwide. Identifying resistance genes and understanding the genetic basis of resistance to FHB are prerequisites to developing cultivars that can avoid losses from FHB. This investigation of quantitative trait loci (QTL) was performed in a recombinant inbred (RI) population derived from a cross between the FHB-moderately susceptible cv. Patterson and the FHB-resistant line Fundulea 201R (F201R). Bulk DNAs from the 11 most resistant and 12 most susceptible lines of the phenotypic distribution of the RI population, together with the parental lines, were screened with simple sequence repeat (SSR) markers. Regional QTL mapping identified four interval regions, located on chromosomes 1B, 3A, 3D, and 5A, that conferred resistance to FHB. The QTLs located on chromosomes 1B and 3A, contributed by F201R, had large effects and were consistently expressed in three environments. The four QTLs together accounted for 32.7% of the phenotypic variation, or 43.0% of the genotypic variation. The QTL on chromosome 3A is located in the same region as a QTL that was detected in wild tetraploid wheat T. dicoccoides (Koern. ex Asch. & Graebner) Aarons. The possibility that the FHB resistance QTLs of F201R and that of T. dicoccoides on chromosome 3A have the same origin is discussed. [ABSTRACT FROM AUTHOR]