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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.

Six hundred thirty five oat ( L.) lines and 4561 single-nucleotide polymorphism (SNP) loci were used to evaluate population structure, linkage disequilibrium (LD), and genotype-phenotype association with heading date. The first five principal components (PCs) accounted for 25.3% of genetic variation. Neither the eigenvalues of the first 25 PCs nor the cross-validation errors from = 1 to 20 model-based analyses suggested a structured population. However, the PC and = 2 model-based analyses supported clustering of lines on spring oat vs. southern United States origin, accounting for 16% of genetic variation ( < 0.0001). Single-locus -statistic () in the highest 1% of the distribution suggested linkage groups that may be differentiated between the two population subgroups. Population structure and kinship-corrected LD of = 0.10 was observed at an average pairwise distance of 0.44 cM (0.71 and 2.64 cM within spring and southern oat, respectively). On most linkage groups LD decay was slower within southern lines than within the spring lines. A notable exception was found on linkage group Mrg28, where LD decay was substantially slower in the spring subpopulation. It is speculated that this may be caused by a heterogeneous translocation event on this chromosome. Association with heading date was most consistent across location-years on linkage groups Mrg02, Mrg12, Mrg13, and Mrg24., (Copyright © Her Majesty the Queen in Right of Canada, as represented by the Minister of Agriculture and Agri-Food Canada.)