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Abstract: Fusarium head blight (FHB), caused by the fungi Fusarium graminearum and Fusarium culmorum, is a worldwide disease of wheat (Triticum aestivum L.). The Chinese cultivar Ning 7840 is one [...]

Abstract: Fusarium head blight (FHB) is a major disease in the wheat growing regions of the world. A quantitative trait locus (QTL) on the short arm of chromosome 3B controls [...]

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.

Abstract Background Genomic discovery in oat and its application to oat improvement have been hindered by a lack of genetic markers common to different genetic maps, and by the difficulty of conducting whole-genome analysis using high-throughput markers. This study was intended to develop, characterize, and apply a large set of oat genetic markers based on Diversity Array Technology (DArT). Results Approximately 19,000 genomic clones were isolated from complexity-reduced genomic representations of pooled DNA samples from 60 oat varieties of global origin. These were screened on three discovery arrays, with more than 2000 polymorphic markers being identified for use in this study, and approximately 2700 potentially polymorphic markers being identified for use in future studies. DNA sequence was obtained for 2573 clones and assembled into a non-redundant set of 1770 contigs and singletons. Of these, 705 showed highly significant (Expectation < 10E-10) BLAST similarity to gene sequences in public databases. Based on marker scores in 80 recombinant inbred lines, 1010 new DArT markers were used to saturate and improve the 'Kanota' × 'Ogle' genetic map. DArT markers provided map coverage approximately equivalent to existing markers. After binning markers from similar clones, as well as those with 99% scoring similarity, a set of 1295 non-redundant markers was used to analyze genetic diversity in 182 accessions of cultivated oat of worldwide origin. Results of this analysis confirmed that major clusters of oat diversity are related to spring vs. winter type, and to the presence of major breeding programs within geographical regions. Secondary clusters revealed groups that were often related to known pedigree structure. Conclusion These markers will provide a solid basis for future efforts in genomic discovery, comparative mapping, and the generation of an oat consensus map. They will also provide new opportunities for directed breeding of superior oat varieties, and guidance in the maintenance of oat genetic diversity.

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]

Hessian fly [ Mayetiola destructor (Say)] is one of the major insect pests of wheat ( Triticum aestivum L.) worldwide. Hessian fly (Hf)-resistance genes H16 and H17 were reported to condition resistance to Hf biotype L that is prevalent in many wheat-growing areas of eastern USA, and both of them were previously assigned to wheat chromosome 5A by their linkage to H9. The objectives in this study were to (1) map H16 and H17 independent of their linkage with H9 and (2) identify DNA markers that co-segregate with H16 or H17, and that are useful for selection of these genes in segregating populations and to combine these genes with other Hf-resistance genes in wheat cultivars. Contrary to previously reported locations, H16 and H17 did not show linkage with the molecular markers on chromosome 5A. Instead, both of them are linked with the molecular markers on the short arm of chromosome 1A (1AS). The simple sequence repeat (SSR) marker Xpsp2999 and EST-derived SSR (eSSR) marker Xwem6b are two flanking markers that are linked to H16 at genetic distances of 3.7 and 5.5 cM, respectively. Similarly, H17 is located between markers Xpsp2999 and Xwem6b at genetic distances of 6.2 and 5.1 cM, respectively. Five other SSR and eSSR markers including Xcfa2153, Xbarc263, Xwem3a, Xwmc329, and Xwmc24 were also linked to H16 and H17 at close genetic distances. These closely linked molecular markers should be useful for pyramiding H16 and H17 with other Hessian fly resistance genes in a single wheat genotype. In addition, using Chinese Spring deletion line bin mapping we positioned all of the linked markers and the Hf-resistance genes ( H16 and H17) to the distal 14% of chromosome 1AS, where Hf-resistance genes H9, H10, and H11 are located. Our results together with previous studies suggest that Hf-resistance genes H9, H10, H11, H16, and H17 along with the pathogen resistance genes Pm3 and Lr10 appear to occupy a resistance gene cluster in the distal region of chromosome 1AS in wheat. [ABSTRACT FROM AUTHOR]

Fusarium head blight (FHB), caused by the fungi Fusarium graminearum and Fusarium culmorum, is a worldwide disease of wheat (Triticum aestivum L.). The Chinese cultivar Ning 7840 is one of a few wheat cultivars with resistance to FHB. GeneCalling™, an open-architecture mRNA-profiling technology, was used to identify differentially expressed genes induced or suppressed in spikes of Ning 7840 after infection by F. graminearum. One hundred and twenty-five cDNA fragments representing transcripts differentially expressed in wheat spikes were identified. Based on BLASTN and BLASTX analyses, putative functions were assigned to some of the genes: 28 were assigned functions in primary metabolism and photosynthesis, 7 were involved in defense response, 14 were involved in gene expression and regulation, 24 encoded proteins associated with structure and protein synthesis, 42 lacked homology to sequences in the database, and 3 were similar to cloned multidrug resistance or disease resistance proteins. Of particular interest in this study were genes associated with resistance and defense against pathogen infection. Real-time quantitative reverse-transcription PCR indicated that of 51 genes tested, 19 showed 2-fold or greater induction or suppression in infected Ning 7840 in comparison with the water-treated control. The remaining 32 genes were not significantly induced or suppressed in infected Ning 7840 compared with the control. Subsequently, these 19 induced or suppressed genes were examined in the wheat line KS24-1, containing FHB resistance derived from Lophopyrum elongatum, and Len, an FHB-susceptible wheat cultivar. The temporal expression of some of these sequences encoding resistance proteins or defense-related proteins showed FHB (resistance specific) induction, suggesting that these genes play a role in protection against toxic compounds in plant–fungus interactions. On the basis of comprehensive expression profiling of various biotic or abiotic stress response genes revealed by quantitative PCR in this study and other supporting data, we hypothesized that the plant–pathogen interactions may be highly integrated into a network of diverse biosynthetic pathways. La fusariose de l’épi, causée par les champignons Fusarium graminearum et Fusarium culmorum, est une maladie répandue mondialement chez le blé (Triticumaestivum L.). Le cultivar chinois Ning 7840 est l’un des rares cultivars de blé montrant une résistance à la fusariose. La technologie GeneCalling™, une technologie transcriptomique à architecture ouverte, a été employée pour identifier des gènes induits ou réprimés chez des épis du blé Ning 7840 suite à l’infection par le F. graminearum. Cent vingt-cinq fragments de cDNA individuels représentant des transcrits exprimés de manière différentielle dans les épis ont été identifiés. Sur la base d’analyses BLASTN et BLASTX, des fonctions possibles ont été assignées à certains des gènes : 28 sont postulés avoir une fonction dans le métabolisme primaire ou la photosynthèse, 7 seraient impliqués dans les réactions de défense, 14 dans l’expression ou la régulation de l’expression génique, 24 codent pour des protéines associées à la synthèse ou à la structure des protéines, 42 ne présentaient pas d’homologie aux séquences contenues dans la banque de séquences et 3 sont semblables à des protéines de résistance à plusieurs drogues ou de résistance aux maladies. Les gènes associés à la résistance ou aux réactions de défense contre les pathogènes présentaient un intérêt particulier dans le cadre de ce travail. Des amplifications RT-PCR en temps réel ont indiqué que des 51 gènes testés, 19 montraient une induction ou répression de deux fois ou plus chez le cultivar Ning 7840 par rapport au témoin inoculé avec de l’eau. Les autres 32 gènes n’étaient pas induits ou réprimés de manière significative chez Ning 7840 par rapport au témoin. Subséquemment, les 19 gènes induits ou réprimés ont été examinés chez le blé KS24-1, lequel possède une résistance à la fusariose provenant du Lophopyrum elongatum, et Len, un cultivar sensible. L’expression de certaines de ces séquences codant pour des protéines de défense ou impliquées dans la défense affichaient une induction (spécifique à la résistance) face à la fusariose, ce qui suggère que ces gènes joueraient un rôle dans la protection contre les composés toxiques produits lors des interactions plante–champignon. Sur la base d’une analyse exhaustive des profils d’expression de divers gènes impliqués dans la réponse aux stress biotiques ou abiotiques, les auteurs proposent que les interactions plante–pathogène seraient intimement intégrées à un réseau formé de plusieurs sentiers biosynthétiques. [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]