Isotensor Dibaryon in the pp→ppπ

Exclusive measurements of the quasifree pp→ppπ^{+}π^{-} reaction have been carried out at WASA@COSY by means of pd collisions at T_{p}=1.2 GeV. Total and differential cross sections have been extracted covering the energy region T_{p}=1.08-1.36 GeV, which is the region of N^{*}(1440) and Δ(1232)Δ(1232) resonance excitations. Calculations describing these excitations by t-channel meson exchange are at variance with the measured differential cross sections and underpredict substantially the experimental total cross section. An isotensor ΔN dibaryon resonance with I(J^{P})=2(1^{+}) produced associatedly with a pion is able to overcome these deficiencies.

New quantitative trait loci in wheat for flag leaf resistance to Stagonospora nodorum blotch.

Stagonospora nodorum blotch (SNB) is a significant disease in some wheat-growing regions of the world. Resistance in wheat to Stagonospora nodorum is complex, whereby genes for seedling, flag leaf, and glume resistance are independent. The aims of this study were to identify alternative genes for flag leaf resistance, to compare and contrast with known quantitative trait loci (QTL) for SNB resistance, and to determine the potential role of host-specific toxins for SNB QTL. Novel QTL for flag leaf resistance were identified on chromosome 2AS inherited from winter wheat parent 'P92201D5' and chromosome 1BS from spring wheat parent 'EGA Blanco'. The chromosomal map position of markers associated with QTL on 1BS and 2AS indicated that they were unlikely to be associated with known host-toxin insensitivity loci. A QTL on chromosome 5BL inherited from EGA Blanco had highly significant association with markers fcp001 and fcp620 based on disease evaluation in 2007 and, therefore, is likely to be associated with Tsn1-ToxA insensitivity for flag leaf resistance. However, fcp001 and fcp620 were not associated with a QTL detected based on disease evaluation in 2008, indicating two linked QTL for flag leaf resistance with multiple genes residing on 5BL. This study identified novel QTL and their effects in controlling flag leaf SNB resistance.

Molecular markers show a complex mosaic pattern of wheat-Thinopyrum intermedium translocations carrying resistance to YDV.

Thinopyrum intermedium translocations derived from the wheat (Triticum aestivum L.) substitution line P-29 were previously characterized by RFLP. We have further analyzed these lines and additional related germplasm with publicly available STS and SSRs. Primers which showed a polymorphism between wheat and P-29, were tested in all recombinant and nulli-tetrasomic lines confirming their position on chromosome 7D. The resulting 7D/7E chromosome maps appeared as a mosaic of wheat and Th. intermedium chromatin sections. To verify the composition of the translocation lines suggested by the RFLP-PCR map, F(2) progeny of two crosses (CS/216-1 and CS/260-1) were analyzed with molecular markers. Both populations gave an unexpectedly diverse number of recombinant individuals, suggesting that interstitial translocations occur more frequently than previously thought. This analysis also showed that there is a wide range in the number and position of the interstitial translocations within a given line such as the mosaic chromosome in recombinant line 260-1/CS-26, which has four Th. intermedium chromosome segments. Phenotypic data of the two populations suggested the presence of one gene which we have called Bdv3 to differentiate it from the previously reported orthologous gene Bdv2. Using the PCR-based molecular markers identified in this study, 5 out of 12 elite lines that showed good yields and no YDV symptoms contained Th. intermedium chromatin. Due to the multiple components involved in the YDV disease complex, combining selection for YDV resistance with the molecular markers and maps identified in this study will increase the efficiency of introgressing Th. intermedium chromatin containing YDV resistance or other beneficial traits into elite wheat germplasm.

Observation of an "ABC" Effect in proton-proton collisions.

The cross section for inclusive multipion production in the pp-->ppX reaction was measured at COSY-ANKE at four beam energies, 0.8, 1.1, 1.4, and 2.0 GeV, for low excitation energy in the final pp system, such that the diproton quasiparticle is in the 1S0 state. At the three higher energies, the missing-mass M_{X} spectra show a strong enhancement at low M_{X}, corresponding to an Abashian-Booth-Crowe effect that moves steadily to larger values as the energy is increased. Despite the missing-mass structure looking very different at 0.8 GeV, the variation with M_{X} and beam energy are consistent with two-pion production being mediated through the excitation of two Delta(1232) isobars, coupled to S and D states of the initial pp system. There is no sign of any resonancelike structure in the energy dependence of the type recently observed for the pn-->dpi;{0}pi;{0} total cross section.

Precision study of the eta3He system using the dp--> 3Heeta reaction.

The differential and total cross sections for the dp--> 3Heeta reaction have been measured in a high precision high statistics COSY-ANKE experiment near threshold using a continuous beam energy ramp up to an excess energy Q of 11.3 MeV with essentially 100% acceptance. The kinematics allowed the mean value of Q to be determined to about 9 keV. Evidence is found for the effects of higher partial waves for Q >or= 4 MeV. The very rapid rise of the total cross section to its maximum value within 0.5 MeV of threshold implies a very large eta3He scattering length and hence the presence of a quasibound state extremely close to threshold.

Precision measurement of the quasifree pn-->dvarphi reaction close to threshold.

The quasifree pn-->dvarphi reaction has been studied at the Cooler Synchrotron COSY-Jülich, using the internal proton beam incident on a deuterium cluster-jet target and detecting a fast deuteron in coincidence with the K+K- decay of the varphi meson. The energy dependence of the total and differential cross sections are extracted for excess energies up to 80 MeV by determining the Fermi momentum of the target neutron on an event-by-event basis. Though these cross sections are consistent with s-wave production, the kaon angular distributions show the presence of p waves at quite a low energy. Production on the neutron is found to be stronger than on the proton but not by as much as for the eta meson.

Near-threshold production of phi mesons in pp collisions.

The pp-->ppphi reaction has been studied at the Cooler Synchrotron COSY-Jülich, using the internal beam and ANKE facility. Total cross sections have been determined at three excess energies epsilon near the production threshold. The differential cross section closest to threshold at epsilon=18.5 MeV exhibits a clear S wave dominance as well as a noticeable effect due to the proton-proton final-state interaction. Taken together with data for ppomega production, a significant enhancement of the phi/omega ratio of a factor 8 is found compared to predictions based on the Okubo-Zweig-Iizuka rule.

Measurement of the analyzing power in p-->d-->(p p)n with a fast forward 1S0 proton pair.

A measurement of the analyzing power A(y) of the p-->d--> (p p) + n reaction was carried out at the ANKE spectrometer at COSY at beam energies of 0.5 and 0.8 GeV by detection of a fast forward proton pair of small excitation energy E(pp) < 3 MeV. The S-wave dominance in the fast diproton is experimentally demonstrated in this reaction. While at T(p) = 0.8 GeV the measured analyzing power almost vanishes, it rises to nearly unity at T(p) = 0.5 GeV for neutrons emitted at theta(c.m.)(n) = 167 degrees. The results are compared with a model taking into account one-nucleon exchange, single scattering, and Delta(1232) excitation in the intermediate state. The model describes fairly well the unpolarized cross section obtained earlier and the analyzing power at 0.8 GeV; it fails to reproduce A(y) at 0.5 GeV.

DNA markers associated with low Fusarium head blight incidence and narrow flower opening in wheat.

Fusarium head blight (FHB) of wheat, caused by Fusarium graminearum, is an important fungal disease in many wheat-growing areas of the world. The objectives of this study were to determine the relationship between width and duration of flower opening and incidence of FHB in wheat, and to identify DNA markers associated with narrow flower opening and low FHB incidence. It was hypothesized that wheat lines whose flowers open briefly and narrowly have a reduced risk of infection. To test the hypothesis, we crossed wheat cultivars Patterson and Goldfield to generate a population of 100 random F(2)-derived recombinant inbred lines (RILs). Florets of Patterson open wide; florets of Goldfield tend to stay closed. The population of RILs was characterized for FHB incidence and flower opening width (FOW) and duration in the F(7:9) and F(7:10) generations. Of the 305 simple sequence repeat primer pairs screened on the parents, 79 amplified polymorphic DNA bands. Pooled DNA from each of the two bulks was tested with these 79 SSR primer pairs. Four markers were found to have significant marker-trait association with low FHB incidence and narrow flower opening. The major QTL effect associated with narrow flower opening and low FHB incidence was found between the map interval Xbarc200-Xgwm210, explaining 29% of the phenotypic variation for FHB incidence averaged over six replicated tests in Indiana in 2002 and 2003. This adds credence to the hypothesis that narrow flower opening is responsible for low FHB incidence in this population. Breeding wheat lines for both morphological avoidance, such as narrow flower opening, and physiological resistance to FHB may be valuable in future breeding research to reduce crop production and grain quality losses in wheat due to FHB.

Molecular mapping of Stb1, a potentially durable gene for resistance to septoria tritici blotch in wheat.

Septoria tritici blotch (STB), caused by the ascomycete Mycosphaerella graminicola (anamorph Septoria tritici), was the most destructive disease of wheat in Indiana and adjacent states before deployment of the resistance gene Stb1 during the early 1970s. Since then, Stb1 has provided durable protection against STB in widely grown wheat cultivars. However, its chromosomal location and allelic relationships to most other STB genes are not known, so the molecular mapping of Stb1 is of great interest. Genetic analyses and molecular mapping were performed for two mapping populations. A total of 148 F1 plants (mapping population I) were derived from a three-way cross between the resistant line P881072-75-1 and the susceptible lines P881072-75-2 and Monon, and 106 F6 recombinant-inbred lines (mapping population II) were developed from a cross between the resistant line 72626E2-12-9-1 and the susceptible cultivar Arthur. Bulked-segregant analysis with random amplified polymorphic DNA (RAPD), amplified fragment length polymorphism (AFLP), and microsatellite or simple-sequence repeat (SSR) markers was conducted to identify those that were putatively linked to the Stb1 gene. Segregation analyses confirmed that a single dominant gene controls the resistance to M. graminicola in each mapping population. Two RAPD markers, G7(1200) and H19(520), were tightly linked to Stb1 in wheat line P881072-75-1 at distances of less than 0.68 cM and 1.4 cM, respectively. In mapping population II, the most closely linked marker was SSR Xbarc74, which was 2.8 cM proximal to Stb1 on chromosome 5BL. Microsatellite loci Xgwm335 and Xgwm213 also were proximal to Stb1 at distances of 7.4 cM and 8.3 cM, respectively. The flanking AFLP marker, EcoRI-AGC/ MseI-CTA-1, was 8.4 cM distal to Stb1. The two RAPD markers, G7(1200) and H19(520), and AFLP EcoRI-AGC/ MseI-CTA-1, were cloned and sequenced for conversion into sequence-characterized amplified region (SCAR) markers. Only RAPD allele H19(520) could be converted successfully, and none of the SCAR markers was diagnostic for the Stb1 locus. Analysis of SSR and the original RAPD primers on several 5BL deletion stocks positioned the Stb1 locus in the region delineated by chromosome breakpoints at fraction lengths 0.59 and 0.75. The molecular markers tightly linked to Stb1 could be useful for marker-assisted selection and for pyramiding of Stb1 with other genes for resistance to M. graminicola in wheat.

a+0 (980)-resonance production in pp-->dK+K-0 reactions close to threshold.

The reaction pp-->dK+K(-)0 has been investigated at an excess energy of Q=46 MeV above the K+K(-)0 threshold with ANKE at the cooler synchrotron COSY-Jülich. From the detected coincident dK(+) pairs, about 1000 events with a missing K(-)0 were identified, corresponding to a total cross section of sigma(pp-->dK+K(-)0)=[38+/-2(stat)+/-14(syst)] nb. Invariant-mass and angular distributions have been jointly analyzed and reveal s-wave dominance between the two kaons, accompanied by a p wave between the deuteron and the kaon system. This is interpreted in terms of a(+)0 (980)-resonance production.

Phenotypic assessment and mapped markers for H31, a new wheat gene conferring resistance to Hessian fly (Diptera: Cecidomyiidae).

A new source of resistance to the highly virulent and widespread biotype L of the Hessian fly, Mayetiola destructor (Say), was identified in an accession of tetraploid durum wheat, Triticum turgidum Desf., and was introgressed into hexaploid common wheat, Triticum aestivum L. Genetic analysis and deletion mapping revealed that the common wheat line contained a single locus for resistance, H31, residing at the terminus of chromosome 5BS. H31 is the first Hessian fly-resistance gene to be placed on 5BS, making it unique from all previously reported sources of resistance. AFLP analysis identified two markers linked to the resistance locus. These markers were converted to highly specific sequence-tagged site markers. The markers are being applied to the development of cultivars carrying multiple genes for resistance to Hessian fly biotype L in order to test gene pyramiding as a strategy for extending the durability of deployed resistance.

Detection of Fusarium head blight resistance QTL in a wheat population using bulked segregant analysis.

A population of 218 recombinant inbred lines (RILs) was developed from the cross of two wheat (Triticum aestivum L.) cultivars, 'Ning 894037' and 'Alondra'. Ning 894037 has resistance to Fusarium head blight (FHB) and Alondra is moderately susceptible. Response of the RILs and their parental lines to FHB infection was evaluated with point inoculation in four experiments both in greenhouse and in field conditions. Distribution of disease severity in the population is continuous, indicating quantitative inheritance of resistance to FHB. Bulked segregant analysis and QTL mapping based on simple sequence repeat (SSR) markers revealed three chromosome regions that are responsible for FHB resistance. A chromosome region on 3BS accounted for 42.5% of the phenotypic variation for FHB resistance. Additional QTLs were located on chromosomes 2D and 6B. These three QTLs jointly accounted for 51.6% of the phenotypic variation. SSR markers linked to the QTLs influencing resistance to FHB have potential for use in breeding programs.

Mapping QTL for popping expansion volume in popcorn with simple sequence repeat markers.

Popping expansion volume is the most important quality trait in popcorn ( Zea mays L.), but its genetics is not well understood. The objectives of this study were to map quantitative trait loci (QTLs) responsible for popping expansion volume in a popcorn x dent corn cross, and to compare the predicted efficiencies of phenotypic selection, marker-based selection, and marker-assisted selection for popping expansion volume. Of 259 simple sequence repeat (SSR) primer pairs screened, 83 pairs were polymorphic between the H123 (dent corn) and AG19 (popcorn) parental inbreds. Popping test data were obtained for 160 S(1) families developed from the [AG19(H123 x AG19)] BC(1) population. The heritability ( h(2)) for popping expansion volume on an S(1) family mean basis was 0.73. The presence of the gametophyte factor Ga1(s) in popcorn complicates the analysis of popcorn x dent corn crosses. But, from a practical perspective, the linkage between a favorable QTL allele and Ga1(s) in popcorn will lead to selection for the favorable QTL allele. Four QTLs, on chromosomes 1S, 3S, 5S and 5L, jointly explained 45% of the phenotypic variation. Marker-based selection for popping expansion volume would require less time and work than phenotypic selection. But due to the high h(2) of popping expansion volume, marker-based selection was predicted to be only 92% as efficient as phenotypic selection. Marker-assisted selection, which comprises index selection on phenotypic and marker scores, was predicted to be 106% as efficient as phenotypic selection. Overall, our results suggest that phenotypic selection will remain the preferred method for selection in popcorn x dent corn crosses.

Development of STS markers linked to Hessian fly resistance gene H6 in wheat.

Hessian fly is one of the world's most destructive insect pests of wheat Triticum aestivum L. We have used the combination of near-isogenic lines (NIL) and random amplified polymorphic DNA (RAPD) analysis to screen up to 2,000 primers to identify DNA markers that are linked to gene H6 that confers resistance to biotype B of the insect. This screen produced six primers that show polymorphic fragments associated with resistance by H6. We have screened 440 F(2) individuals from a cross of the susceptible cultivar Newton and a NIL that contains H6 to verify the linkage between these markers and the resistance gene. A high-resolution genetic map was constructed based on recombination frequency. Two of the markers were tightly linked to the gene with no recombination observed, three were within 2.0 cM, and one was 11 cM from the gene. Three of the six markers were successfully converted to sequence tagged site (STS) markers. Both RAPD and STS primers were used to screen for the presence or absence of the resistance gene in wheat varieties. The identification of markers and construction of the genetic high resolution map provide the first steps toward localization of this resistance gene.

Physical location of a HSP70 gene homologue on the centromere of chromosome 1B of wheat ( Triticum aestivum L.).

Cereal centromeres consist of a complex organization of repetitive DNA sequences. Several repetitive DNA sequences are common amongst members of the Triticeae family, and others are unique to particular species. The organization of these repetitive elements and the abundance of other types of DNA sequences in cereal centromeres are largely unknown. In this study, we have used wheat-rye translocation lines to physically map 1BL.1RS centromeric breakpoints and molecular probes to obtain further information on the nature of other types of centromeric DNA sequences. Our results, using the rye-specific centromeric sequence, pAWRC.1, indicate that 1BL.1RS contains a small portion of the centromere from 1R of rye. Further studies used molecular markers to identify centromeric segments on wheat group-1 chromosomes. Selected RFLP markers, clustered around the centromere of wheat homoeologous group-1S chromosomes, were chosen as probes during Southern hybridization. One marker, PSR161, identified a small 1BS segment in all 1BL.1RS lines. This segment maps proximal to pAWRC.1 in 1BL.1RS and on the centromere of 1B. Sequence analysis of PSR161 showed high homology to HSP70 genes and Northern hybridization showed that this gene is constitutively expressed in leaf tissue and induced by heat shock and light stimuli. The significance of this work with respect to centromere organization and the possible significance of this HSP70 gene homologue are discussed.

Identification and characterization of wheat-wheatgrass translocation lines and localization of barley yellow dwarf virus resistance.

Stable introgression of agronomically important traits into crop plants through wide crossing often requires the generation and identification of translocation lines. However, the low efficiency of identifying lines containing translocations is a significant limitation in utilizing valuable alien chromatin-derived traits. Selection of putative wheatgrass-wheat translocation lines based on segregation ratios of progeny from gamma-irradiated seed using a standard phenotypic analysis resulted in a low 4% success rate of identifying barley yellow dwarf virus (BYDV) resistant and susceptible translocation lines. However, 58% of the susceptible progeny of this irradiated seed contained a Thinopyrum intermedium chromosome-specific repetitive sequence, which indicated that gamma-irradiation-induced translocations occurred at high rate. Restriction fragment length polymorphism (RFLP) analysis of susceptible lines containing alien chromatin, their resistant sister lines and other resistant lines showed that more than one third of the progeny of gamma-irradiated double monosomic seeds contained wheatgrass-wheat translocations. Genomic in situ hybridization (GISH) analysis of selected lines confirmed that these were wheatgrass-wheat translocation lines. This approach of initially identifying BYDV susceptible deletion lines using an alien chromosome-specific repetitive sequence followed by RFLP analysis of their resistant sister lines efficiently identified resistant translocation lines and localized the BYDV resistance to the distal end of the introgressed Th. intermedium chromosome.

Biotype composition of Hessian fly (Diptera: Cecidomyiidae) populations from the southeastern, midwestern, and northwestern United States and virulence to resistance genes in wheat.

Twenty-three Hessian fly, Mayetiola destructor (Say), populations collected in the southeastern (Alabama and Mississippi), midwestern (Indiana), and northwestern (Idaho and Washington) United States from 1995 to 1999 were evaluated for biotype composition based on response to Hessian fly resistance genes H3, H5, H6, and H7H8 in wheat, Triticum aestivum L. Biotypes L and O, combined, made up at least 60% of all Alabama populations. Biotype L was predominant in the northern third of Alabama and biotype O in the southern two-thirds of the state. Based on biotype data, wheat cultivars with H7H8 resistance should be highly effective in central and southern Alabama. Fifty-four percent of the Mississippi population consisted of biotype L, and the remaining virulent biotypes (B, D, E, G, J, and O) ranged in frequency from 1 to 17%. The Mississippi population also contained 4% of the avirulent biotype GP. Only biotypes D and L were found in Indiana populations, but biotype L was predominant. Hessian fly populations from Idaho and Washington contained one or more of the virulent biotypes D-H, J, and L-O; however, only biotypes E, F, and G occurred at frequencies > 12%. The avirulent biotype GP made up 25-57% of Idaho and Washington populations, a much higher percentage than found in populations from the eastern United States. Although the highest level of virulence in Idaho and Washington populations was found to resistance genes H3 and H6, the frequency of biotype GP would indicate that the currently deployed gene H3 would provide a moderate to high level of resistance, depending on location. Nine of the populations, plus populations collected from the mid-Atlantic state area in 1989 and 1996, also were tested against the wheat cultivar 'INW9811' that carries H13 resistance to Hessian fly biotype L and two Purdue wheat lines with unidentified genes for resistance. The H13 resistance in INW9811 was highly effective against all populations tested from the eastern and northwestern U.S. wheat production areas, except Maryland and Virginia. Population studies also indicated that wheat line CI 17960-1-1-2-4-2-10 likely carries the H13 resistance gene, based on the similarity of its response and that of INW9811 to eight fly populations. Continued monitoring of biotype frequency in Hessian fly populations is required for optimal deployment and management of resistance genes in all wheat production areas.

Yield Effects of Barley yellow dwarf virus in Soft Red Winter Wheat.

ABSTRACT 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 R(2) 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 R(2) 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.

Characterization of wheatgrass-derived barley yellow dwarf virus resistance in a wheat alien chromosome substitution line.

ABSTRACT 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.