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Identification of quantitative trait loci for Fusarium head blight (FHB) resistance from different sources and pyramiding them into cultivars could provide effective protection against FHB. The objective of this study was to characterize a soft red winter wheat (SRWW) breeding population that has been subjected to intense germplasm introduction and alien introgression for FHB resistance in the past. The population was evaluated under misted FHB nurseries inoculated with Fusarium graminearum-infested corn spawn for two years. Phenotypic data included disease incidence (INC), disease severity (SEV), Fusarium damaged kernels (FDK), FHB index (FHBdx), and deoxynivalenol concentration (DON). Genome-wide association studies using 13,784 SNP markers identified 25 genomic regions at -logP ≥ 4.0 that were associated with five FHB-related traits. Of these 25, the marker trait associations that explained more than 5% phenotypic variation were localized on chromosomes 1A, 2B, 3B, 5A, 7A, 7B, and 7D, and from diverse sources including adapted SRWW lines such as Truman and Bess, and unadapted common wheat lines such as Ning7840 and Fundulea 201R. Furthermore, individuals with favorable alleles at the four loci Fhb1, Qfhb.nc-2B.1 (Q2B.1), Q7D.1, and Q7D.2 showed better FDK and DON scores (but not INC, SEV, and FHBdx) compared with other allelic combinations. Our data also showed while pyramiding multiple loci provides protection against FHB disease, it has a significant trade-off with grain yield.

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is one of the most devastating diseases of common wheat (Triticum aestivum L.). The wheat line 92145E8-9 is immune to Bgt isolate E09. Genetic analysis reveals that the powdery mildew resistance in 92145E8-9 is controlled by a single dominant gene, temporarily designated Ml92145E8-9. Bulked-segregant analysis (BSA) with simple sequence repeat (SSR) markers indicates that Ml92145E8-9 is located on chromosome 2AL. According to the reactions of 92145E8-9, VPM1 (Pm4b carrier), and Lankao 906 (PmLK906 carrier) to 14 Bgt isolates, the resistance spectrum of 92145E8-9 differs from those of Pm4b and PmLK906, both of which were previously localized to 2AL. To test the allelism among Ml92145E8-9, Pm4b and PmLK906, two F2 populations of 92145E8-9 × VPM1 (Pm4b) and 92145E8-9 × Lankao 906 (PmLK906) were developed in this study. Screening of 784 F2 progeny of 92145E8-9 × VPM1 and 973 F2 progeny of 92145E8-9 × Lankao 906 for Bgt isolate E09 identified 37 and 19 susceptible plants, respectively. These findings indicated that Ml92145E8-9 is non-allelic to either Pm4b or PmLK906. Thus, Ml92145E8-9 is likely to be a new powdery mildew resistance gene on 2AL. New polymorphic markers were developed based on the collinearity of genomic regions of Ml92145E8-9 with the reference sequences of the International Wheat Genome Sequencing Consortium (IWGSC). Ml92145E8-9 was mapped to a 3.6 cM interval flanked by molecular markers Xsdauk13 and Xsdauk682. This study also developed five powdery mildew-resistant wheat lines (SDAU3561, SDAU3562, SDAU4173, SDAU4174, and SDAU4175) using flanking marker-aided selection. The markers closely linked to Ml92145E8-9 would be useful in marker-assisted selection for wheat powdery mildew resistance breeding. Keywords: Marker-assisted selection, Ml92145E8-9, Powdery mildew, Triticum aestivum L.

Comprehensive information of a breeding population is a necessity to design promising crosses. This study was conducted to characterize a soft red winter wheat breeding population that was subject of intensive germplasm introductions and introgression from exotic germplasm. We used genome‐wide markers and phenotypic assessment to identify signatures of selection and loci controlling agronomic traits in a soft red winter wheat population. The study of linkage disequilibrium (LD) revealed that the extent of LD and its decay varied among chromosomes with chromosomes 2B and 7D showing the most extended islands of high‐LD with slow rates of decay. Four sub‐populations, two with North American origin and two with Australian and Chinese origins, were identified. Genome‐wide scans for selection signatures using FST and hapFLK identified 13 genomic regions under selection, of which five loci (LT, Fr‐A2, Vrn‐A1, Vrn‐B1, Vrn3) were associated with environmental adaptation and two loci were associated with disease resistance genes (Sr36 and Fhb1). Genome‐wide association studies identified major loci controlling yield and yield related traits. For days to heading and plant height, major loci with effects sizes of 2.2 days and 5 cm were identified on chromosomes 7B and 6A respectively. For test weight, number of spikes per square meter, and number of kernels per square meter, large effect loci were identified on chromosomes 1A, 4B, and 5A, respectively. However, for yield alone, no major loci were detected. A combination of selection for large effect loci for yield components and genomic selection could be a promising approach for yield improvement.

Fungal disease meets its matchFusariumhead blight (FHB), caused by a fungus, reduces wheat crop yield and introduces toxins into the harvest. From the assembly of the genome ofThinopyrum elongatum, a wild relative of wheat used in breeding programs to improve cultivated wheat, Wanget al.cloned a gene that can address both problems (see the Perspective by Wulff and Jones). The encoded glutathioneS-transferase detoxifies the trichothecene toxin and, when expressed in wheat, confers resistance to FHB.Science, this issue p.eaba5435; see also p.822

Wheat lines with shortened Th. ponticum chromatin carrying Fhb7 and molecular markers linked to Fhb7 will accelerate the transfer of Fhb7 to breeding lines and provide an important resource for future map-based cloning of this gene. Fusarium head blight is a major wheat disease globally. A major FHB resistance gene, designated as Fhb7, derived from Thinopyrum ponticum, was earlier transferred to common wheat, but was not used in wheat breeding due to linkage drag. The aims of this study were to (1) saturate this FHB resistance gene region; (2) develop and characterize secondary translocation lines with shortened Thinopyrum segments carrying Fhb7 using ph1b; (3) pyramid Fhb7 and Fhb1 by marker-assisted selection. Fhb7 was mapped in a 1.7 cM interval that was flanked by molecular markers XsdauK66 and Xcfa2240 with SSR, diversity arrays technology, EST-derived and conserved markers. KS24-2 carrying Fhb7 was analyzed with molecular markers and genomic in situ hybridization, confirming it was a 7DS.7el2L Robertsonian translocation. To reduce the Thinopyrum chromatin segments carrying Fhb7, a BC1F2 population (Chinese Spring ph1bph1b*2/KS24-2) was developed and genotyped with the markers linked to Fhb7. Two new translocation lines (SDAU1881 and SDAU1886) carrying Fhb7 on shortened alien segments (approximately 16.1 and 17.3 % of the translocation chromosome, respectively) were developed. Furthermore, four wheat lines (SDAU1902, SDAU1903, SDAU1904, and SDAU1906) with the pyramided markers flanking Fhb1 and Fhb7 were developed and the FHB responses indicated lines with mean NDS ranging from 1.3 to 1.6 had successfully combined Fhb7 and Fhb1. Three new molecular markers associated with Fhb7 were identified and validated in 35 common wheat varieties. The translocation lines with shortened alien segments carrying Fhb7 (and Fhb1) and the markers closely linked to Fhb7 will be useful for improving wheat scab resistance.

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.

Fusarium graminearum Schwabe (Fusarium head blight, FHB) and Puccinia triticina Eriks (leaf rust) are two major fungal pathogens posing a continuous threat to the wheat crop; consequently, identifying resistance genes from various sources is always of importance to wheat breeders. We identified tightly linked single nucleotide polymorphism (SNP) markers for the FHB resistance quantitative trait locus (QTL) Qfhs.pur-7EL and the leaf rust resistance locus Lr19 using genotyping-by-sequencing (GBS) in a wheat–tall wheatgrass introgression-derived recombinant inbred line (RIL) population. One thousand and seven hundred high-confidence SNPs were used to conduct the linkage and QTL analysis. Qfhs.pur-7EL was mapped to a 2.9 cM region containing four markers within a 43.6 cM segment of wheatgrass chromosome 7el2 that was translocated onto wheat chromosome 7DL. Lr19 from 7el1 was mapped to a 1.21 cM region containing two markers in the same area, in repulsion. Five lines were identified with the resistance-associated SNP alleles for Qfhs.pur-7EL and Lr19 in coupling. Two SNP markers in the Qfhs.pur-7EL region were converted into PCR-based KASP markers. Investigation of the genetic characteristics of the parental lines of this RIL population indicated that they are translocation lines in two different wheat cultivar genetic backgrounds instead of 7E–7D substitution lines in Thatcher wheat background, as previously reported in the literature.

Septoria tritici blotch (STB) is one of the most destructive foliar diseases in many of the wheat (Triticum aestivum) growing regions of the world. Gene Stb2, derived from cultivar ‘Veranopolis’, provides effective resistance against STB. In our attempts to refine the map location of this resistance gene we could not confirm a previous report that Stb2 is on wheat chromosome 3BS. Instead, based on characterization of the same doubled-haploid population used for the original mapping derived from a cross between Veranopolis and susceptible line RAC875-2, and linkage analysis of the resistance phenotype to previously mapped SSR loci, we report that Stb2 is located on the short arm of wheat chromosome 1B, flanked by microsatellite loci Xwmc406 and Xbarc008 (with Xwmc230 closely located) at map distances of 6 and 5 cM, respectively. Presence of the markers on chromosome arm 1BS was confirmed by analysis of nullisomic-tetrasomic lines. These three co-dominant markers can be used in wheat breeding programs to facilitate combining Stb2 with genes of interest. Other STB resistance genes, including Stb11, have been reported on wheat chromosome arm 1BS, with locus Xbarc008 as a diagnostic marker. Whether Stb2, Stb11 and the previously identified Stb11-like genes are the same, allelic, or different but closely linked has not been determined. In addition to STB, numerous genes for resistance to many other fungal pathogens have been reported on wheat chromosome arm 1BS, including those for yellow (or stripe) rust, leaf rust and common bunt. The approximate locations for all of these genes were added onto the Stb2 map based on published distances from common markers to provide a rough guide for future wheat improvement.

Unlike most documented plant-insect interactions, Hessian fly-resistance [Mayetiola destructor (Say)] in wheat (Triticum aestivum L.) is initiated by a gene-for-gene recognition event in which plants carrying a specific R gene recognize salivary effectors encoded by a corresponding larval avirulence gene. However, dual infestation resulting from oviposition by virulent insects from 5 d before to 3 d after oviposition by avirulent insects on the same host plant, lead to systemic induced susceptibility, obviation of resistance, and ultimately the survival of both virulent and genetically avirulent progeny to adulthood. Simultaneous oviposition allowed greater survival of avirulent progeny than ovipositions separated by larger intervals. Because of the induction of plant resistance, hatch of avirulent larvae before virulent was more detrimental to rate of development than hatch of virulent before avirulent larvae. Obviation of resistance was not localized to the leaf being attacked by the virulent larvae, but also functioned across spatial distance into younger leaves. This research suggests that virulent Hessian fly larvae directly suppress the defense response of wheat, thus providing a refuge for avirulent genotypes, preserving diversity in field populations and increasing durability of deployed resistance genes.

Within the United States, end-use quality of soft wheat (Triticum aestivum L.) is determined by several genetically controlled components: milling yield, fl our particle size, and baking characteristics related to fl our water absorption. In 2007 and 2008, we measured the soft wheat quality of 187 soft winter wheat cultivars, released from 1801 to 2005, for the eastern United States. Wheat cultivars were grown in nine eastern United States environments. Quality traits included test weight, fl our yield, softness equivalent (an estimator of break fl our yield), fl our protein concentration, solvent retention capacity (SRC) of fl our, and sugarsnap cookie quality. All of the traits had large variance components due to genotype. Flour milling characteristics had the largest ratio of genotype variance to genotype × environment interaction variance. Based on multivariate analysis of the trait correlation structure, breeders should focus on milling yield, fl our softness equivalent, and sucrose SRC, as they predict long-fl ow fl our milling performance and have value for commercial milling and baking. These traits also have large genetic variance relative to genotype × environment interactions and represent distinct aspects of quality. Although some improvement in soft wheat milling and baking quality has been observed over the past 200 yr, the dominant effect of selection appears to be a stable standard of quality that is associated with the soft wheat classes of the eastern United States. E.J. Souza and A. Sturbaum, USDA-ARS, Soft Wheat Quality Laboratory, Wooster, OH 44691; C. Sneller and M.J. Guttieri, The Ohio State Univ., Ohio Agricultural Research and Development Center, Wooster, OH 44691; C. Griff ey, Crop and Soil Environmental Sciences Dep., Virginia Tech, Blacksburg, VA 24061; M. Sorrells, Dep. of Plant Breeding, Cornell Univ., Ithaca, NY 14861; H. Ohm, Dep. of Agronomy, Purdue Univ., West Lafayette, IN 47907; D. Van Sanford, Dep. of Plant & Soil Sciences, Univ. of Kentucky, Lexington, KY 40540. Received 18 Feb. 2011. *Corresponding author (edward.souza@Bayer.com). Abbreviations: AACC, American Association of Cereal Chemists; ARS, Agricultural Research Service; ESI, endosperm separation index; PC, principal component; QTL, quantitative trait locus; SRC, solvent retention capacity; SWQL, Soft Wheat Quality Laboratory. Published in Crop Sci. 52:21–31 (2012). doi: 10.2135/cropsci2011.02.0090 Published online 4 Oct. 2011. © Crop Science Society of America | 5585 Guilford Rd., Madison, WI 53711 USA All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.

To identify resistance to Fusarium head blight (FHB), cereal yellow dwarf virus (CYDV), stem rust (Sr), and powdery mildew (Pm) in 24 common wheat (Triticum aestivum)-Leymus multicaulis addition/translocation lines that were developed cytogenetically and to verify the authenticity of these lines using microsatellite (SSR) DNA markers. Resistance to FHB was identified in the wheat-L. multicaulis addition lines, Line 9 and Line 26, which both contained L. multicaulis-specific fragments as shown by SSR markers. The translocation line, Trans 1, and the addition lines, Line 5 and Line 29, have resistance to stem rust (IT 0). Resistance to CYDV was evaluated based on virus titers measured by enzyme linked immunosorbent assay (ELISA). The addition line, Line 23, showed low virus titer (0.15), indicating resistance to CYDV. The segregation distribution of CYDV resistance in 98 F2 plants of Line 23/CS showed a significant deviation from 3:1. Inoculation with a set of 14 differential Blumeria graminis f. sp. tritici (Bgt) isolates did not detect powdery mildew resistance in translocation line Trans 1, addition line Line 9 and the amphiploid of wheat-L. multicaulis. However, Line 26 exhibited the resistance response pattern of Kavkaz, which carries Pm8, indicating that Line 26 most likely has the powdery mildew resistance gene Pm8 inherited from its parent lines Feng Kang 7 or Feng Kang 10. Twelve SSR markers, distributed on different homeologous chromosome groups of wheat, which distinguished L. multicaulis addition/translocation chromosomes, were used to verify the presence of L. multicaulis chromatin in the putative wheat-L. multicaulis addition/translocation lines. Of the 24 addition/translocation lines investigated using the 12 polymorphic SSR markers, 18 wheat-L. multicaulis derivatives showed the expected L. multicaulis-specific fragments, indicating that all of these 18 addition/translocation lines would most likely have the introgressed L. multicaulis chromosome(s). Chromosomal rearrangements also were detected in some of the wheat-L. multicaulis introgression lines.

Identification and genetic mapping of loci conferring resistance to polycyclic pathogens such as the rust fungi depends on accurate measurement of disease resistance. We converted an absolute quantification assay of Puccinia coronata DNA to a relative assay by adding a TaqMan® primers/probe set specific to the oat β-actin gene to simplify and improve quantification of fungal infection. The new multiplex assay estimates the amount of fungal DNA in a sample relative to the amount of host DNA and requires fewer and less labour-intensive steps than previous assays. The relative fungal DNA assay (RFDNA) reliably detected and quantified both host and pathogen DNA over five orders of magnitude and was at least as sensitive as either digital image analysis (DLA) or absolute estimation of fungal DNA (AFDNA) in repeated greenhouse studies using 12 oat cultivars with different resistance responses to P. coronata isolate LGCG. Measuring crown rust resistance to LGCG using DLA, AFDNA and RFDNA in a P8669/P941...

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.

Endosperm texture, i.e., the hardness or softness of the grain, is an important trait because it determines many end-use properties of wheat (Triticum aestivum L.). It is primarily controlled by the puroindoline genes (Pina and Pinb) at the Hardness (Ha) locus, mapped on the short arm of chromosome 5D. The introgression of functional Pin genes from diploid wheat Triticum monococcum L. chromosome 5Am into hexaploid wheat resulted in softer grains, suggesting that this translocation might be useful for soft wheat breeders. However, the translocated segment includes a large portion of the 5Am short arm and may carry detrimental genes for agronomic performance. In this study we have generated a backcross (BC) population of 210 individuals where 5A-5Am homeologous recombination was induced by the ph1b mutation to recover individuals with a reduced translocated segment. A map of this region was constructed using specific sequence tagged site (STS) markers for the three T. monococcum Ha-related genes, the completely linked BGGP gene, three wheat ESTs (BG606847, BF474606, and BQ168958), and two microsatellite markers. Eight plants with recombination events between XBggp and the closest proximal locus BG606847 were identified. Of these, four have the desired T. monococcum allele at the Ha locus. These plants carry a 6.3-cM segment of T. monococcum chromatin proximal to the Ha locus. This germplasm, which will be publicly available, and the molecular markers developed in this study will be valuable tools for soft wheat breeding programs. © Crop Science Society of America.

SUMMARY The gene-for-gene interaction triggering resistance of wheat against first-instar Hessian fly larvae utilizes specialized defence response genes not previously identified in other interactions with pests or pathogens. We characterized the expression of Hfr-3, a novel gene encoding a lectin-like protein with 68-70% identity to the wheat germ agglutinins. Within each of the four predicted chitin-binding hevein domains, the HFR-3 translated protein sequence contained five conserved saccharide-binding amino acids. Quantification of Hfr-3 mRNA levels confirmed a rapid response and gradual increase, up to 3000-fold above the uninfested control in the incompatible interaction 3 days after egg hatch. Hfr-3 mRNA abundance was influenced by the number of larvae per plant, suggesting that resistance is localized rather than systemic. In addition, Hfr-3 was responsive to another sucking insect, the bird cherry-oat aphid, but not to fall armyworm attack, wounding or exogenous application of methyl jasmonate, salicylic acid or abscisic acid. Western blot analysis demonstrated that HFR-3 protein increased in parallel to mRNA levels in crown tissues during incompatible interactions. HFR-3 protein was detected in both virulent and avirulent larvae, indicating ingestion. Anti-nutritional proteins, such as lectins, may be responsible for the apparent starvation of avirulent first-instar Hessian fly larvae during the initial few days of incompatible interactions with resistant wheat plants.

A variety of diseases of wheat (Triticum aestivum L.) occurs every year in the U.S. leading to significant grain yield losses. Stagonospora nodorum blotch (SNB), fusarium head blight (FHB) and stem rust (SR) are caused by the fungi Stagonospora nodorum, Fusarium graminearum and Puccinia graminis, respectively. These diseases penalize both grain yield and quality. Three resistance factors, Qsng.sfr-3BS, Fhb1 and Sr2 conferring resistance, respectively, to SNB, FHB and SR, each from a unique donor wheat parent line, have been mapped to chromosome 3BS of wheat and are believed to be closely linked. Based on previously published analyses, Sr2 is on the distal end, Fhb1 is on the proximal end and Qsng.sfr-3BS is in the middle of Sr2 and Fhb1 in the 3BS wheat genome. Thus, the objectives of this project are to determine the gene order of Qsng.sfr-3BS, Fhb1 and Sr2, in a linkage block on chromosome 3BS and combining them in coupling. The linkage relationships were determined through analysis of a three-way cross between parental lines Arina, Alsen and Ocoroni86, containing the resistance genes Qsng.sfr-3BS, Fhb1 and Sr2, respectively. A total of 1,600 F2 plants was screened, along with the parental lines, using KASPar genotyping technology via single-nucleotide polymorphism markers to identify the recombinant progeny. Phenotypic screening for SNB was performed on the entire F2 population. Knowing the positional order of these resistance genes will enable the development of a wheat line with three genes in coupling to provide durable and broad-spectrum resistance against three major diseases of wheat.

Genetic similarities between plant interactions with microbial pathogens and wheat interactions with Hessian fly larvae prompted us to investigate defense and counterdefense mechanisms. Plant oxidative burst, a rapid increase in the levels of active oxygen species (AOS) within the initial 24 h of an interaction with pathogens, commonly is associated with defenses that are triggered by gene-for-gene recognition events similar to those involving wheat and Hessian fly larvae. RNAs encoded by Hessian fly superoxide dismutase (SOD) and catalase (CAT) genes, involved in detoxification of AOS, increased in first-instar larvae during both compatible and incompatible interactions. However, mRNA levels of a wheat NADPH oxidase (NOX) gene that generates superoxide (O2¯) did not increase. In addition, inhibiting wheat NOX enzyme with diphenyleneiodonium did not result in increased survival of avirulent larvae. However, nitro blue tetrazolium staining indicated that basal levels of O2¯ are present in both uninfested and infested wheat tissue. mRNA encoded by wheat genes involved in detoxification of the cellular environment, SOD, CAT, and glutathione-S-transferase did not increase in abundance. Histo-chemical staining with 3,3-diaminobenzidine revealed no increases in wheat hydrogen peroxide (H2O2) during infestation that were correlated with the changes in larval SOD and CAT mRNA. However, treatment with 2′,7′-dichlorofluorescin demonstrated the presence of basal levels of H2O2 in the elongation zone of both infested and uninfested plants. The accumulation of a wheat flavanone 3-hydroxylase mRNA did show some parallels with larval gene mRNA profiles. These results suggested that larvae encounter stresses imposed by mechanisms other than an oxidative burst in wheat seedlings.

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 much of the variation for resistance. The cloning of candidate disease-resistance genes for FHB QTLs on chromosome 3B can provide further elucidation of the mechanisms that control resistance. However, rearrangements and divergence during plant genome evolution often hampers the identification of sequences with similarity to known disease-resistance genes. This study focuses on the use of wheat expressed sequence tags (ESTs) that map to the region on chromosome 3B containing the QTL for FHB resistance and low-stringency BLAST searching to identify sequences with similarity to known disease-resistance genes. One EST rich with leucine repeats and low similarity to a protein kinase domain of the barley Rpg1 gene was identified. Genetic mapping using a Ning894037 × Alondra recombinant inbred (RI) population showed that this EST mapped to the QTL on the short arm of chromosome 3B and may represent a portion of a newly diverged gene contributing to FHB resistance. The EST is a new marker suitable for marker-assisted selection and provides a starting point to begin map-based cloning for chromosome walking and investigate new diverged genes at this locus.Key words: Fusarium head blight resistance, expressed sequence tags, quantitative trait loci, Rpg1, wheat.

La mouche de Hesse est un important ravageur de blé (Triticum spp.) et le biotype L de cette mouche est reconnu comme le plus virulent des biotypes connus. L'héritabilité de la résistance au biotype L de la mouche de Hesse a été étudiée à l'aide de croisements entre, d'une part, une lignée résistante de Triticum monococcum et, d'autre part, deux lignées sensibles de T. monococcum et une lignée sensible de T. boeoticum, tous des blés diploïdes. Les familles de plante F2 ou issues de rétrocroisements ont été évaluées au stade de semis par leur réaction à la mouche de Hesse et les ratios de ségrégation génétique des familles résistantes ou ségréguées par rapport aux familles sensibles ont été analysés par des tests d'ajustement du chi-carré. Il a été découvert que l'héritabilité est simple et sous le contrôle d'un ou deux gènes. Ceci est la première mention de l'héritabilité de la résistance à la mouche de Hesse chez les blés diploïdes de génome A et son contrôle génétique simple suggère la possibilité de transférer ce caractère aux blés cultivés., Hessian fly (Mayetiola destructor) is a serious pest of wheat (Triticum spp.) and of the reported biotypes of Hessian fly, biotype L is described as the most virulent. Inheritance of resistance to Hessian fly biotype L was investigated in crosses of a resistant accession of Triticum monococcum, and two susceptible accessions of T. monococcum and one susceptible accession of T. boeoticum, all diploid wheats. F2 and testeross (backeross) families were classified for reaction to Hessian fly in the seedling stage and analysed by Chi-square goodness-of-fit tests for genetic segregation ratios of resistant or segregating families to susceptible families. Resistance was found to be simply inherited, controlled by one or two genes. This is the first report on the inheritance of resistance to Hessian fly in A-genome diploid wheats, and simple genetic control indicates possibility of transfer of this trait to cultivated wheats.

Wheat (Triticumaestivum) relatives are sources of useful genes for disease resistance. Chromosomally segregating populations of intergeneric hybrids between wheat and its distantly related species provide opportunity to study and introgress multiple disease resistance. While introgressing resistance to barley yellow dwarf virus (BYDV) from Thinopyrum into wheat, which is susceptible to BYDV, we scored powdery mildew (Erysiphaegraminis) and leaf rust (Pucciniatriticina) resistance, and chromosome numbers in second and third backcrosses (BC2 and BC3) of intergeneric hybrids of wheat with Thinopyrum ponticum and Thinopyrumintermedium. The frequency of multiple resistance to all the three diseases was low or became low when selection was applied for BYDV resistance and low chromosome numbers. Selection for fewer alien chromosomes while maintaining BYDV resistance was more effective in wheat x T. intermedium than in the wheat x T. ponticum cross. Mean chromosome numbers were significantly different in BC3 generation between BYDV resistant and susceptible plants in both crosses. Significant negative correlations between chromosome numbers and enzyme-linked immunosorbent assay (ELISA) values showed that as the critical Thinopyrum chromosome(s) were eliminated, susceptibility to BYDV increased. Results indicated that it is unlikely that genes for full resistance to all three diseases can be transferred simultaneously from Thinopyrum to wheat., Les espèces proches du blé (Triticumaestivum) sont à l’origine de gènes utiles pour la résistance aux maladies. Les populations à ségrégation chromosomique d’hybrides intergénériques entre le blé et des espèces peu apparentées nous offrent la chance de procéder à l’étude et à l’introgression de la multirésistance aux maladies. Alors que nous introgressions la résistance au virus de la jaunisse nanisante de l’orge (BYDV) de Thinopyrum dans le blé, qui est sensible au BYDV, nous avons coté la résistance à l’oïdium (Erysiphaegraminis) et à la rouille des feuilles (Pucciniatriticina), et compté le nombre de chromosomes dans les deuxième et troisième rétrocroisements (BC2 et BC3) d’hybrides intergénériques entre le blé et le Thinopyrum ponticum ou le Thinopyrumintermedium. Le taux de multirésistance aux trois maladies était bas ou est devenu bas lorsqu’une sélection a été faite pour la résistance au BYDV et pour un faible nombre de chromosomes. La sélection pour un plus faible nombre de chromosomes étrangers tout en maintenant la résistance au BYDV a été plus efficace pour le croisement de blé x T. intermedium que pour celui de blé x T. ponticum. À la génération du BC3, pour les deux croisements, le nombre moyen de chromosomes était significativement différent entre les plantes résistantes et celles sensibles au BYDV. Des corrélations négatives significatives entre le nombre de chromosomes et les valeurs du test immunoenzymatique ELISA ont démontré qu’à mesure que le ou les chromosomes déterminants du Thinopyrum étaient éliminés, la sensibilité au BYDV augmentait. Les résultats montrent qu’il est peu probable que les gènes conférant une résistance complète aux trois maladies puissent être transférés simultanément du Thinopyrum au blé.

Cowpea, Vigna unguiculata (L.) Walp., is an important grain legume grown in tropical and subtropical regions, primarily Africa. The parasitic weed Striga gesnerioides (Willd.) Vatke is one of the most important constraints to cowpea production. Host plant resistance is the only practical control method. Five virulence genotypes (races) of S. gesnerioides have been identified in different regions of Africa. Several host resistance genes have also been identified that are effective against specific races of S. gesnerioides. The rapid spread of this parasitic weed creates an urgent need for cowpea varieties with multiple resistance genes. A recently identified cowpea breeding line, IT93K-693-2, has resistance to all known races. The objective of this research was to develop DNA markers that are useful for marker-assisted selection (MAS) in breeding cowpea for resistance to S. gesnerioides. An F 2 population developed from the cross between IT93K-693-2 and the susceptible cultivar IAR1696 was characterized for resistance against race 3 of S. gesnerioides for genetic analysis and molecular mapping. IT93K-693-2 was found to have a single dominant gene for resistance. Four amplified fragment length polymorphism (AFLP) markers, designated E-ACT/M-CTC 115 , E-ACT/M-CAC 115 , E-ACA/M-CAG 108 and E-AAG/E-CTA 190 , were identified and mapped 3.2, 4.8, 13.5 and 23.0 cM, respectively, from Rsgl, a gene in IT93K-693-2 that gives resistance to race 3 (or Nigerian strain) of S. gesnerioides. The first two markers were validated in a second F 2 population developed from crossing the same resistant parent with 'Kamboinse local', a different susceptible cultivar. The AFLP fragment from marker combination E-ACT/M-CAC, which is linked in coupling with Rsgl was cloned, sequenced, and converted into a sequence characterized amplified region (SCAR) marker named SEACTMCAC83/85, which is codominant and useful in breeding programs.

The objective of this research was to identify Fusarium head blight (FHB) resistance in wheat ( Triticum aestivum)- Lophopyrum genetic lines that might complement FHB resistance in common wheat; and to identify DNA markers that can be used to tag the resistance gene in the alien chromatin (E or el(2) genome) for the development of improved wheat cultivars. FHB resistance was evaluated in 19 Chinese Spring- Lophopyrum elongatum (EE) substitution lines, two Thatcher -L. ponticum (el(1) and el(2)) substitution lines, and four Thatcher- L. ponticum translocation lines. Significant resistance was identified in the substitution lines 7E(7A), 7E(7B), and 7E(7D). The homoeologous chromosome, 7el(2),()also showed resistance in the Thatcher genetic background. Both the Thatcher-7el(1) substitution and translocation lines were susceptible, like Thatcher, indicating that there is no resistance gene on the 7el(1) chromosome. Simple sequence repeat (SSR) and cleaved amplified polymorphic sequences (CAPS) in homoeologous group 7 chromosomes were used to identify DNA markers located on 7E and 7el(2). As expected, the transferability of wheat SSR markers to Lophopyrum is low. Of the 52 SSR markers that we tested, only five were found to be co-dominant on 7E of L. elongatum versus 7A, 7B, and 7D, one of which is also positive on 7el(2). A CAPS marker, derived from the RFLP probe PSR129, can serve as a dominant marker for 7el(2) chromatin.

Barley yellow dwarf virus (BYDV) is the most serious viral disease affecting wheat and genes for BYDV resistance have not been found in wheat. BYDV-resistant alien addition and alien substitution lines produced from a wheat × Thinopyrum intermedium (species of Agropyron complex) cross were characterized. Chromosome pairing in the hybrids between two substitution lines showed that they had the same Th. intermedium chromosome. Likewise, two addition lines involved the same alien chromosome. In situ hybridization of chromosomes, confirmed that line P29 is a disomic substitution line. Double monosomic seeds and self-pollinated seeds from monosomic addition plants were irradiated to induce translocations between wheat and Th. intermedium chromosomes. Putative translocations were selected on the basis of BYDV resistance and studied by chromosome analysis, Southern hybridization using Thinopyrum specific probe and RFLP markers. A BYDV-resistant translocation was identified.

Wheatgrass (Thinopyrum intermedium) possesses a high level of resistance to barley yellow dwarf virus (BYDV) subgroup I and subgroup II strains. A wheat line (P29), in which the 7D chromosome has been substituted with a group 7 chromosome from T. intermedium, was examined for the level of resistance to two subgroup I and two subgroup II BYDV strains. In P29 plants inoculated with the subgroup I PAV strains, the titer of virus in leaf and stem tissue was typically reduced 42 to 52% when compared with the BYDV-susceptible cv. Abe. P29 and ‘Abe’ had the same content of PAV in roots. These results and the absence of detectable virus in inoculated T. intermedium plants indicate that the complete resistance to subgroup I possessed by the wheatgrass has not been introgressed into P29. In contrast, P29 was completely resistant throughout the plant to the subgroup II strains, NY-RPV and NY-RMV, demonstrating that the complete resistance to subgroup II in T. intermedium was incorporated into P29. Further analysis of this resistance to NY-RPV showed that NY-RPV can replicate in mesophyll protoplasts of P29 and ‘Abe’, suggesting that this resistance is not operating at the single-cell level. Molecular marker analysis confirmed that the T. intermedium chromosome present in P29 is a different group 7 wheatgrass chromosome than that present in L1, a wheat line with BYDV resistance properties similar to those of P29.

Fourteen populations of Hessian fly, Mayetiola destructor (Say), from Arkansas, Georgia, Illinois, North Carolina, and Virginia were evaluated for biotype composition, and two Arkansas populations were tested for response to Hessian fly resistance genes or gene combinations H3, H5, H6, H7H8, and H9 to H19 in wheat. The biotype composition of Hessian fly populations was estimated by confining individual gravid females on the four wheat differential cultivars ‘Monon’ (H3), ‘Magnum’ (H5), ‘Caldwell’ (H6), and ‘Seneca’ (H7H8). The response of Arkansas fly populations to resistance genes was evaluated in replicated tests with wheat germplasm lines or cultivars homozygous for these genes. Hessian fly populations from Arkansas were predominately biotype L, with low levels of biotypes F, G, J, M, and O, depending upon population. Biotype L was predominant in the Illinois, North Carolina, and Virginia populations, although biotype D was present in populations from extreme southwestern Illinois and Virginia and North Carolina. Biotypes G, J, L, M, and O were identified from the west-central Georgia population collected at Griffin, while only biotypes M and O were identified from the southwestern Georgia population, collected at Plains. All fly populations were virulent to resistance genes H3, H5, and H6, while the southwestern Georgia population was avirulent to H7H8. Plants with single resistance genes H9 to H19 varied significantly (P ≤ 0.05) in their resistance to the two Arkansas populations. Plants with single resistance genes H9, H10, H13, H14, and H16 to H19 conditioned resistance (88 to 100%) to both populations, while plants with single genes Hll, H12, or H15 were susceptible to one or both populations. Wheat germplasm lines developed in the Purdue/USDA program that carry single gene resistances H9, H13, H14, and H16 to H19 should provide useful sources of resistance for developing improved wheat cultivars adapted to the mid-south and southeastern United States.

The pyramiding of genes that confer race- or biotype-specific resistance has become increasingly attractive as a breeding strategy now that DNA-based marker-assisted selection is feasible. Our objective here was to identify DNA markers closely linked to genes in wheat (Triticum aestivum L.) that condition resistance to Hessian fly [Mayetiola destructor (Say)]. We used a set of near-isogenic wheat lines, each carrying a resistance gene at 1 of 11 loci (H3, H5, H6, H9, H10, H11, H12, H13, H14, H16 or H17) and developed by backcrossing to the Hessian fly-susceptible wheat cultivar ‘Newton’. Using genomic DNA of these 11 lines and ‘Newton’, we have identified 18 randomly amplified polymorphic DNA (RAPD) markers linked to the 11 resistance genes. Seven of these markers were identified by denaturing gradient gel electrophoresis and the others by agarose gel electrophoresis. We confirmed linkage to the Hessian fly resistance loci by cosegregation analysis in F2 populations of 50–120 plants for each different gene. Several of the DNA markers were used to determine the presence/absence of specific Hessian fly resistance genes in resistant wheat lines that have 1 or possibly multiple genes for resistance. The use of RAPD markers presents a valuable strategy for selection of single and combined Hessian fly resistance genes in wheat improvement.

A physically anchored consensus map is foundational to modern genomics research; however, construction of such a map in oat (Avena sativa L., 2n = 6x = 42) has been hindered by the size and complexity of the genome, the scarcity of robust molecular markers, and the lack of aneuploid stocks. Resources developed in this study include a modified SNP discovery method for complex genomes, a diverse set of oat SNP markers, and a novel chromosome-deficient SNP anchoring strategy. These resources were applied to build the first complete, physically-anchored consensus map of hexaploid oat. Approximately 11,000 high-confidence in silico SNPs were discovered based on nine million inter-varietal sequence reads of genomic and cDNA origin. GoldenGate genotyping of 3,072 SNP assays yielded 1,311 robust markers, of which 985 were mapped in 390 recombinant-inbred lines from six bi-parental mapping populations ranging in size from 49 to 97 progeny. The consensus map included 985 SNPs and 68 previously-published markers, resolving 21 linkage groups with a total map distance of 1,838.8 cM. Consensus linkage groups were assigned to 21 chromosomes using SNP deletion analysis of chromosome-deficient monosomic hybrid stocks. Alignments with sequenced genomes of rice and Brachypodium provide evidence for extensive conservation of genomic regions, and renewed encouragement for orthology-based genomic discovery in this important hexaploid species. These results also provide a framework for high-resolution genetic analysis in oat, and a model for marker development and map construction in other species with complex genomes and limited resources.

Ten populations of Hessian fly, Mayetiola destructor (Say), from the eastern United States were evaluated for binotype composition and response to Hessian fly resistance genes H9-H19 in wheat. The binotype composition of Hessian fly populations was estimated by confining individual gravid females on wheat ‘Manon’ (H3), ‘Magnum’ (H5), ‘Caldwell’ (H6), and ‘Seneca’ (H7H8). The response of Hessian fly populations and laboratory mistypes to resistance genes from the Purdue/USDA program were evaluated in replicated tests with wheat lines homozygous for these genes. Hessian fly populations from northwestern Florida and southwestern South Carolina were predominantly mistypes E, G, M, and 0 and were virulent to H7H8. Fly populations from northeastern and northwestern South Carolina had a low percentage of binotype E, but contained H7H8-virulent mistypes J and L in varying frequency. Populations from north central Arkansas and Indiana were predominantly binotype L. In tests with genes H9-H19 with laboratory-reared mistypes GP, B, C, D, E, and L, H9 was susceptible to binotype C, HI2 to binotype E, and H11 and H15 to binotype L. Genes HI6 and H17 were resistant to all Hessian fly mistypes and populations, and the remaining genes varied in response to fly sources. The resistance of genes H9-H19 to the 10 Hessian fly populations, in descending order of effectiveness, was HI6 = H17> H9 = H13 = H14 > H10 = H18 > H12 = H15 = H19 > H11. The number of Hessian fly populations virulent to the respective genes were H16, H17 = 0; H9, H13, H14 = 1; H10, H18 = 2; H12, H15, H19 = 3; H11 = 7. Research demonstrated the importance of continuing to sample field populations. Changes in frequency of virulent genotypes and the response of genotypes to specific resistance genes should be monitored in order to develop deployment strategies to improve the durability of resistance in wheat cultivars.

Septoria glume blotch, caused by Stagonospora nodorum, is an important disease of wheat (Triticum aestivum). Separate genetic mechanisms were found to control flag leaf and spike resistance. Genes for resistance to S. nodorum were located on different chromosomes in the few wheat cultivars studied. These studies only partially agree on the chromosome locations of gene in wheat for resistance to S. nodorum, and chromosomal arm locations of such genes are not known. The objectives of this study were to determine the chromosome and chromosomal arm locations of genes that significantly influence resistance to S. nodorum in wheat cultivar Cotipora. Monosomic analysis showed that flag leaf resistance was controlled by genes on chromosomes 3A, 4A, and 3B whereas the spike resistance was controlled by genes on chromosomes 3A, 4A, 7A, and 3B (P=0.01). Additionally, genes on chromosomes 6B and 5A influenced the susceptibility of the flag leaf and spike reactions, respectively (P=0.01). Telocentric analysis showed that genes on both arms of chromosome 3A, and the long arms of chromosomes 4A and 3B were involved in the flag leaf resistance whereas genes on both arms of chromosome 4A, the short arm of chromosome 3A, and the long arm of chromosome 3B conferred spike resistance.

Hessian fly [Mayetiola destructor (Say)] is a serious pest of wheat (Triticum ssp.) in many wheat growing areas of the world. A number of genes (H1-H26) that confer resistance to Hessian fly have been described. The linkage relationships of many of these genes, which are useful in breeding wheat for resistance to Hessian fly, are unknown. Testcross analyses were made in tetraploid durum wheat (Triticum turgidum L.) and tested to biotype D of Hessian fly to determine the linkage relationships among genes H9, H10, H12, H14, H15, H16 and H17, all conferring resistance to biotype D. Also, monosomic 5A plants of susceptible cultivar Chinese Spring were crossed as seed parents to Purdue wheat (T. aestivum L. em Thell.) lines carrying gene H10 or H12. Testcross analyses indicated that six of these genes appear to occupy a single linkage block on wheat chromosome 5A in the order H9 to H15, H10, H17, H16, and H12. Gene H14 did not appear to be within the linkage block H9 to H12. Additionally, F 2 plants derived from 41-chromosome F 1 plants and F 3 families derived from F 2 resistant plants were tested against biotype D. F 2 segregation deviated significantly from 3 resistant : 1 susceptible and F 3 families from resistant F 2 plants deviated significantly from 1 resistant : 2 segregating for both crosses involving H10 and H12. Thus, monosomic analyses provided additional evidence that genes H10 and H12 are likely on chromosome 5A. Linkage between these genes would not seriously limit efforts to pyramid them in breeding for resistance to the Hessian fly because the linkage values are more than 20 centimorgans.

Twenty-eight Hessian fly, Mayetiola destructor (Say), populations from 15 states in soft winter wheat area of the eastern United States were evaluated for biotype composition and response to 14 Hessian fly resistance genes. The biotype composition of each Hessian fly population was estimated by confining individual gravid females on the wheat differentials ‘Seneca’ (H7H8), ‘Monon’ (H3), ‘Abe’ or ‘Magnum’ (H5), and ‘Caldwell’ (H6). The response of Hessian fly populations to resistance genes not deployed in the eastern United States was evaluated in replicated tests with wheat containing H9, H10, H12, H13, H14H15, H17, H18, and H19+ genes and two Purdue germplasm lines with unknown sources of resistance (’ACC 1566-1-1-IX’ and ‘Giorgio 331-39-10’). Based on biotype determinations, H7H8 was resistant or moderately resistant to populations from the South and Southeast, H3 and H5 were resistant to populations from East Texas, H6 was susceptible to all but the ML-TX population, and no deployed genes were resistant to populations from most locations in the Midwest and in the Mid-Atlantic region and the Northeast. Predominant biotypes in Florida, Georgia, and South Carolina were E, G, and O, respectively. Biotype L was predominant in populations from the Midwest and some states of the Mid-Atlantic region. Texas populations were predominantly GP and A. The most resistant undeployed genes or gene combinations were H9, H13, H14H15, and H17, but Hessian fly virulence was found to all genes except H17. Continued monitoring of biotype frequency in Hessian fly populations is required for optimal deployment and management of resistance genes.

Incorportion of resistance to septoria glume blotch, caused by Stagonospora nodorum (Berk.) Castellani & E.C. 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 Cotipera and the susceptible Purdue line, P83179A1-1-6. Populations of parents, F 1 , F 2 , BCF 1 , and BCF 2 were inoculated with a conidial suspension of the pathogen containing 2.5×10 6 spores mL -1 and given a moist period of 52 h (.)

The introduction of molecular biology methodologies to plant improvement programs offers an invaluable opportunity for extensive germplasm characterization. However, the detection of adequate DNA polymorphism in self-pollinating species remains on obstacle. We have optimized a denaturing-gradient-gel electrophoresis (DGGE) system which, when used in combination with random amplified polymorphic DNA (RAPD) analysis, greatly facilitates the detection of reproducible DNA polymorphism among closely related plant lines. We have used this approach to estimate pedigree relationships among a spectrum of plant materials in wheat, barley and oat. Based on analysis with one or two primers, we were able to distinguish soft from hard winter wheat, and 2-rowed from 6-rowed barley. Further analysis with additional primers allowed resolution of polymorpisms even among closely related lines in highly selected populations. We placed 17 cultivars of oat into two distinct clusters that differed significantly from previous oat pedigree assessments. We believe that DGGE-RAPD is a superior method for detecting DNA polymorphism when compared to RFLP, agarose-RAPD, or polyacrylamide-RAPD methods.

The leaf rust resistance gene Lr19 and Fusarium head blight (FHB) resistance quantitative trait loci (QTL) derived from the wild wheatgrass Lophopyrum ponticum have been located on chromosome 7E. The main objectives of the present study were to develop a genetic map of chromosome 7E and map the two resistance loci using a population of 237 F(7:8) recombinant inbred lines (RILs) derived from a cross between two Thatcher-L. ponticum substitution lines, K11463 (7el(1)(7D)) and K2620 (7el(2)(7D)). 532 G-SSR, E-SSR and STS markers from wheat chromosome group 7 were screened in the parent lines. Of these, 118 markers were polymorphic, with a polymorphism frequency of 22.2%. A genetic map of L. ponticum chromosome 7E was constructed with 64 markers, covering 95.76 cM, with an average genetic distance of 1.47 cM between markers. The major FHB resistance locus, temporarily assigned as FhbLoP, was mapped to the very distal region of the long arm of chromosome 7E within a 3.71 cM interval flanked by Xcfa2240 and Xswes19, which accounts for 30.46% of the phenotypic variance. Lr19 was bracketed by Xwmc273 and XBE404744, with a map distance of 1.54 and 1.43 cM from either side, respectively. The closely linked markers identified in this study will be helpful for marker-assisted introgression of the L. ponticum-derived FhbLoP and Lr19 genes into elite cultivars of wheat, and the development of a genetic map will accelerate the map-based cloning of these two genes.

Twenty genes in wheat, Triticum spp ., for resistance to Hessian fly, Mayetiola destructor (Say), have been previously designated H1 to H20 . The location on wheat chromosomes of some of the genes is known, but several have not yet been assigned to specific chromosomes. Four wheat differential cultivars have been used to identify 16 possible biotypes of Hessian fly; biotypes were designated GP and A–O. If an additional differential host genotype were added, it is apparent that there are not enough letters in the alphabet to designate all of the biotypes. Therefore, a new system of biotype designation is proposed. Three differential cultivars or lines are assigned to a set. Sets are designated A, B, C, and so on. There are eight combinations of resistant and susceptible reactions within a set. These are coded 1 to 8 for each set. Three sets are proposed to begin biotype designation. Abiotype avirulent to all differentials in three sets is coded 111. If set C were not used, a zero (untested) replaces the digit. In the above case, the biotype is designated 110. The biotype designation system provides flexibility for the addition of new sets as new genes are identified and for the deletion of sets no longer deemed useful.

A sequence encoding a putative type-1 lipid transfer protein from wheat ( Triticum aestivum L. em Thell) was identified through ‘GeneCalling’, an mRNA profiling technology. The mRNA for the Hfr-LTP (Hessian fly-responsive lipid transfer protein) gene decreased in abundance (196-fold) in susceptible wheat plants over the first eight days of attack by virulent Hessian fly larvae ( Mayetiola destructor Say). Hfr-LTP encodes a putative protein containing eight cysteine residues that are conserved among plant LTPs and are responsible for correct protein folding through formation of disulfide bridges. Twelve hydrophobic amino acids in addition to arginine, glycine, proline, serine, threonine and tyrosine, plus an LTP signature sequence were present in conserved positions. A highly conserved signal peptide sequence was also present. Although attack by one virulent larva was sufficient to cause a decrease in Hfr-LTP mRNA abundance, higher infestation levels led to near silencing of the gene. Hfr-LTP transcript levels were not affected by other biotic factors (feeding by bird cherry-oat aphid, Rhopalosiphum padi L., and fall armyworm larvae, Spodoptera frugiperda Smith) or abiotic factors tested (mechanical wounding or treatment with abscisic acid, methyl jasmonate, or salicylic acid). Comparison to a previously described Hessian fly-responsive wheat LTP gene, TaLTP3 , confirmed an initial increase in TaLTP3 mRNA in resistant plants. However, when quantified through eight days after egg hatch, responsiveness to infestation level and a marked decrease in susceptible plant TaLTP3 mRNA abundance were detected, as was seen for Hfr-LTP . Possible functions of LTP gene products in wheat–Hessian fly interactions are discussed.

Discussions and simulation models have been used by others to develop strategies for deploying genes in wheat ( Triticum spp. ) for resistance to the Hessian fly, Mayetiola destructor (Say). Effects of deploying genes one at a time in sequence and redeploying a gene after a 10-yr absence from the commercial crop in Indiana during 1955–1989 are presented. Three genes, H3, H6 , and H5 , were deployed in 1955, 1962, and 1971, respectively, and H6 was redeployed in 1981. A reduction in infestation levels of Hessian fly occurred for 6–8 yr after each deployment. Redeployment of H6 , after a 10-yr absence in commercial use, was highly effective. Other methods of deploying resistance genes in conjunction with cultural practices should be considered for control of Hessian fly. When considering the pyramiding of genes for resistance, one must evaluate the time required to develop new productive cultivars. Efficient methods to determine that all of the pyramided genes are present in a line are important for the successful use of pyramided genes. Wheat cultivars are seldom grown for more than 8–10 yr, but the same pyramided genes might be used in subsequent cultivars.

Three cultivars of soft red winter wheat were evaluated to determine the relationship between the incidence and time of infection by Barley yellow dwarf virus (BYDV) and yield. Wheat was planted in 1995, 1996, and 1997 in a split-plot design with six replicates at sites in Indiana and Illinois. Yield plots were infested with different amounts of viruliferous aphids, and the incidence of BYDV in each plot was measured. In a 2-year study in Illinois with cv. Clark and the PAV-IL isolate of BYDV, yields were assessed following aphid infestation in fall, early spring, and late spring. Early spring infections resulted in larger yield reductions than late spring infections in both years and larger than fall infections in one year. Regression analyses to relate incidence of infection and yield with data from fall and early spring infections provided R2 values of 0.89 and 0.51 for the 1996 to 1997 and 1997 to 1998 seasons, respectively. An additional study at the same site in the 1996 to 1997 season compared the yield responses of cvs. Clark, Y88-3e, and PT8935b. Increases in the incidence of BYDV correlated with decreases in yield, with R2 values of 0.80, 0.78, and 0.90 for the three cultivars, respectively. Estimated yield losses in both studies and all cultivars ranged from 27 to 45 kg/ha or 0.34 to 0.55% for each percent increase in virus infection. In a third study over a 2-year period in Indiana with the same three wheat genot ypes and a second BYDV isolate (PAV-P), BYDV treatments resulted in significant reductions in yield, but yield loss and the incidence of BYDV were not linearly correlated. Given the differences in yield reductions caused by the two BYDV isolates, PAV-P may be an attenuated strain of BYDV and may cross-protect plants from naturally occurring strains of the virus.

A number of technologies are available to increase the abundance of DNA markers and contribute to developing high resolution genetic maps suitable for genetic analysis. The aim of this study was to expand the number of Diversity Array Technology (DArT) markers on the wheat array that can be mapped in the wheat genome, and to determine their chromosomal location with respect to simple sequence repeat (SSR) markers and their position on the cytogenetic map. A total of 749 and 512 individual DArT and SSR markers, respectively, were identified on at least one of four genetic maps derived from recombinant inbred line (RIL) or doubled haploid (DH) populations. A number of clustered DArT markers were observed in each genetic map, in which 20-34% of markers were redundant. Segregation distortion of DArT and SSR markers was also observed in each mapping population. Only 14% of markers on the Version 2.0 wheat array were assigned to chromosomal bins by deletion mapping using aneuploid lines. In this regard, methylation effects need to be considered when applying DArT marker in genetic mapping. However, deletion mapping of DArT markers provides a reference to align genetic and cytogenetic maps and estimate the coverage of DNA markers across the wheat genome.