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PubMed2004

The epidemiology of Wheat dwarf virus in relation to occurrence of the leafhopper Psammotettix alienus in Middle-Germany.

Occurrence of the leafhopper Psammotettix alienus Dahlb. and its infectivity with Wheat dwarf virus (WDV) were studied in cereal crops in Saxony-Anhalt (Middle-Germany) in 2000 and 2001. The leafhoppers were collected with a sweep net and/or a cage trap and their WDV infectivity was determined by transmission to test plants. In 2000, adult leafhoppers were caught from the second week of May to the third week of December, whereas in 2001 they were trapped from the fourth week of May to the second week of December. Nymphs and adults were caught in spring in young actively growing crops and in summer in maturing crops and also in self-sown cereal stands. However, only adults were found in autumn in newly sown crops. The peak population density of adult leafhoppers was in self-sown cereal plants in September when there were 25 individuals per m(2) in 2000 and 15 in 2001. The proportion of leafhoppers that were infective with WDV when transferred to barley test plants ranged from 5 to 79% in 2000 and from 0 to 56% in 2001. Two leafhoppers collected in June 2000 in a crop of maturing winter barley each infected both barley and wheat plants with WDV. It is concluded that the same leafhoppers are able to acquire both virus strains and transmit them to cereals.

Animals↗

PubMed1995

Effect of protein supplementation on forage intake and nitrogen balance of lambs fed freshly harvested wheat forage.

Wether lambs (mean BW = 32 kg) fed wheat forage freshly harvested daily (Exp. 1, n = 28; Exp. 2, n = 25) were used to evaluate the effects of supplemental energy and protein on forage intake, diet digestibility, and N retention. Experiment 1 was conducted in the winter of 1988 and the four treatments were 1) CONTROL, no supplement; 2) ENERGY, low-protein corn-based supplement; 3) CSM, 22% CP supplement with cottonseed meal; and 4) CGM, 22% CP supplement with corn gluten meal. Experiment 2 was conducted in the spring of 1989, and the five treatments were 1) CONTROL; 2) ENERGY; 3) CSM, 23% CP with cottonseed meal; 4) FTM, 25% CP supplement with feather meal and corn gluten meal; and 5) BM, 25% CP supplement with blood meal and corn gluten meal. All supplements were isoenergetic and composed 22 and 24% of total DMI in Exp. 1 and 2, respectively. In Exp. 1, forage intake was not affected but total and digestible DMI were increased (P < .01) by energy and protein supplementation. Protein supplements did not (P > .10) increase total and digestible DMI compared to ENERGY supplementation but tended (P < .10) to increase N retention (g/d). In Exp. 2, digestible DMI and N retention did not differ among the five treatments. Results suggest that lambs consuming wheat forage in the vegetative stage (Exp. 1) will have greater digestible DMI if supplemental energy or protein is provided. When more mature wheat forage was fed (Exp. 2), energy seemed to limit animal performance.

Animal Feed↗

PubMed2002

Genomic analysis of cultivated barley (Hordeum vulgare) using sequence-tagged molecular markers. Estimates of divergence based on RFLP and PCR markers derived from stress-responsive genes, and simple-sequence repeats (SSRs).

Three types of molecular markers have been compared for their utility in evaluating genetic diversity among cultivars of Hordeum vulgare. Restriction fragment length polymorphisms at 71 sites were scored with the aid of probes corresponding to stress-responsive genes from barley and wheat, coding for a low-molecular-weight heat shock protein, a dehydrin, an aldose reductase homolog, and a 18.9-kDa drought-induced protein of unknown function. Indexes of genetic diversity computed in the total sample and within groups of cultivars (two-rowed and six-rowed, winter and spring varieties) indicated high values of genetic differentiation ( F (ST) >15%). A second assessment of genetic diversity was performed by PCR amplification of genomic DNA using as primers 13 arbitrary oligonucleotides derived from sequences of the same stress-responsive genes. A high degree of polymorphism was uncovered using these markers also, but they yielded low values for F (ST) (<7%) among groups of cultivars. Finally, 15 different simple-sequence repeats (AC or AG) were amplified with primers based on unique flanking sequences. Levels of polymorphism and differentiation between groups of cultivars revealed by these markers were quite high. Ordination techniques applied to measures of genetic distance among cultivars demonstrated a remarkable ability of the RFLPs associated with stress-responsive genes to discriminate on the basis of growth habit. The correlation with production data for the cultivars in different environments was also significant. This "functional genomics" strategy was therefore as informative as the "structural genomics" (SSR-based) approach, but requires the analysis of fewer probes.

Base Sequence↗

PubMed1997

Denervation-induced sprouting of intact peripheral afferents into the cuneate nucleus of adult rats.

In adult monkeys with dorsal rhizotomies extending from the second cervical (C2) to the fifth thoracic (T5) vertebrae, cortex deprived of its normal inputs regained responsiveness to inputs conveyed by intact peripheral afferents from the face [T.P. Pons, P.E. Garraghty, A.K. Ommaya, J.H. Kaas, E. Taub, M. Mishkin, Massive reorganization of the primary somatosensory cortex after peripheral sensory deafferentation, Science 252 (1991) 1857-1860]. It has been suggested that the extent of this massive topographic reorganization may be due to the establishment of novel connections between intact afferents and neurons denervated after dorsal rhizotomy [P.E. Garraghty, D.P. Hanes, S.L. Florence, J.H. Kaas, Pattern of peripheral deafferentation predicts reorganizational limits in adult primate somatosensory cortex, Somatosens. Motor Res. 11 (1994) 109-117]. Using adult rats with comparably extensive dorsal rhizotomies, we employed anatomical tracing techniques to address this possibility. Subcutaneous hindpaw injections of horseradish peroxidase conjugated to either wheat germ agglutinin or cholera toxin subunit B revealed aberrant expansions of gracile projections into the cuneate and, in one case, external cuneate nucleus within three months of the deafferentation. It seems plausible that such modest sprouting of ascending projections at the level of the brainstem may form functional connections which, through divergence, ultimately drive a larger population of neurons in cortex. This new growth may well account for both the substantial cortical reorganization observed in the 'Silver Spring monkeys' [T.P. Pons, P.E. Garraghty, A.K. Ommaya, J.H. Kaas, E. Taub, M. Mishkin, Massive reorganization of the primary somatosensory cortex after peripheral sensory deafferentation, Science 252 (1991) 1857-1860] and the 'referred sensation' phenomena (see J.P. Donoghue, Plasticity of adult sensorimotor representations, Curr. Opin. Neurobiol., 5 (1995) 749-754 for review) reported to follow proximal limb amputations in humans.

Afferent Pathways↗

PubMed2006

Evolutionary conservation of the FLOWERING LOCUS C-mediated vernalization response: evidence from the sugar beet (Beta vulgaris).

In many plant species, exposure to a prolonged period of cold during the winter promotes flowering in the spring, a process termed vernalization. In Arabidopsis thaliana, the vernalization requirement of winter-annual ecotypes is caused by the MADS-box gene FLOWERING LOCUS C (FLC), which is a repressor of flowering. During the vernalization process, FLC is downregulated by alteration of its chromatin structure, thereby permitting flowering to occur. In wheat, a vernalization requirement is imposed by a different repressor of flowering, suggesting that some components of the regulatory network controlling the vernalization response differ between monocots and dicots. The extent to which the molecular mechanisms underlying vernalization have been conserved during the diversification of the angiosperms is not well understood. Using phylogenetic analysis, we identified homologs of FLC in species representing the three major eudicot lineages. FLC homologs have not previously been documented outside the plant family Brassicaceae. We show that the sugar beet FLC homolog BvFL1 functions as a repressor of flowering in transgenic Arabidopsis and is downregulated in response to cold in sugar beet. Cold-induced downregulation of an FLC-like floral repressor may be a central feature of the vernalization response in at least half of eudicot species.

Arabidopsis↗

PubMed2000

Identification of AFLP markers on the satellite region of chromosome 1BS in wheat.

The satellite region on the short arm of chromosome 1B in wheat (Triticum aestivum L., 2n = 6x = 42) carries many agronomically important genes; i.e., genes conferring fungal disease resistance, seed storage proteins, and fertility restoration. To find molecular markers located on the satellite region, we applied the fluorescent AFLP (amplified fragment length polymorphism) technique to aneuploids and deletion stocks of the cultivar T. aestivum 'Chinese Spring'. Out of 6017 fragments amplified with 80 primer combinations in normal 'Chinese Spring', 24 were assigned to 1BS. Twelve of them clustered within a small region of the satellite known to be rich in RFLP (restriction fragment length polymorphism) markers. AFLPs in 1BS and in the whole genome were calculated between 'Chinese Spring' and T. spelta var. duhamelianum. The polymorphism rates in the satellite region (58.3%) and in the 1BS arm (45.8%) were much higher than the average rate for the whole genome (10.7%). Seven of the 12 AFLP markers in the satellite region were revealed to be specific to 'Chinese Spring' and could potentially be useful for genetic mapping in a segregation population of 'Chinese Spring' x T. spelta.

Aneuploidy↗

PubMed1999

Postweaning performance of calves from Angus, Brahman, and reciprocal-cross cows grazing endophyte-infected tall fescue or common bermudagrass.

Data from 403 Polled Hereford-sired calves from Angus, Brahman, and reciprocal-cross cows were used to evaluate the effects of preweaning forage environment on postweaning performance. Calves were spring-born in 1991 to 1994 and managed on either endophyte-infected tall fescue (E+) or common bermudagrass (BG) during the preweaning phase. After weaning, calves were shipped to the Grazinglands Research Laboratory, El Reno, OK and stratified to one of two winter stocker treatments by breed and preweaning forage; stocker treatments were winter wheat pasture (WW) or native range plus supplemental CP (NR). Each stocker treatment was terminated in March, calves grazed cool-season grasses, and calves were then moved to a feedlot phase in June. In the feedlot phase, calves were fed to approximately 10 mm fat over the 12th rib and averaged approximately 115 d on feed. When finished, calves were weighed and shipped to Amarillo, TX for slaughter. Averaged over calf breed group, calves from E+ gained faster during the stocker phase (P<.10), had lighter starting and finished weights on feed (P< .01), lighter carcass weights (P<.01), and smaller longissimus muscle areas (P<.05) than calves from BG. Calves from E+ were similar to calves from BG in feedlot ADG, percentage kidney, heart, and pelvic fat, fat thickness over 12th rib, yield grade, marbling score, and dressing percentage. Maternal heterosis was larger in calves from E+ for starting weight on feed (P<.01), finished weight (P<.10), and carcass weight (P<.16). These data suggest that few carryover effects from tall fescue preweaning environments exist, other than lighter, but acceptable, weights through slaughter. These data further suggest that the tolerance to E+ in calves from reciprocal-cross cows, expressed in weaning weights, moderated postweaning weight differences between E+ and BG compared to similar comparisons in calves from purebred cows.

Animal Feed↗

PubMed1995

Genetic and physical characterization of the LR1 leaf rust resistance locus in wheat (Triticum aestivum L.).

The objective of this study was to characterize the leaf rust resistance locus Lr1 in wheat. Restriction fragment length polymorphism (RFLP) analysis was performed on the resistant line Lr1/6* Thatcher and the susceptible varieties Thatcher and Frisal, as well as on the segregating F2 populations. Seventeen out of 37 RFLP probes mapping to group 5 chromosomes showed polymorphism between Lr1/6* Thatcher and Frisal, whereas 11 probes were polymorphic between the near-isogenic lines (NILs) Lr1/6* Thatcher and Thatcher. Three of these probes were linked to the resistance gene in the segregating F2 populations. One probe (pTAG621) showed very tight linkage to Lr1 and mapped to a single-copy region on chromosome 5D. The map location of pTAG621 at the end of the long arm of chromosome 5D was confirmed by the absence of the band in the nulli-tetrasomic line N5DT5B of Chinese Spring and a set of deletion lines of Chinese Spring lacking the distal part of 5DL. Twenty-seven breeding lines containing the Lr1 resistance gene in different genetic backgrounds showed the same band as Lr1/6* Thatcher when hybridized with pTAG621. The RFLP marker was converted to a sequence-tagged-site marker using polymerase chain reaction (PCR) amplification. Sequencing of the specific fragment amplified from both NILs revealed point mutations as well as small insertion/deletion events. These were used to design primers that allowed amplification of a specific product only from the resistant line Lr1/6* Thatcher. This STS, specific for the Lr1 resistance gene, will allow efficient selection for the disease resistance gene in wheat breeding programmes. In addition, the identification of a D-genome-specific probe tightly linked to Lr1 should ultimately provide the basis for positional cloning of the gene.

Alleles↗

PubMed2002

Winter-annual pasture as a supplement for beef cows.

In each of two experiments, 120 pregnant beef cows were stratified by body condition score, BW, breed, and age, randomly divided into six groups of 20, and assigned to one of six 5.1-ha bermudagrass (Cynodon dactylon [L.] Pers.) pastures (two replicates/ treatment) in early January to evaluate the use of winter-annual pasture as a supplement. All cows in Exp. 1 and 2 had ad libitum access to bermudagrass/dallisgrass (Paspalum dilatatum Poir.) hay plus three treatments: 1) a concentrate-based supplement fed 3 d/wk, 2) limit grazing on winter-annual pasture 2 d/wk (7 hr/ d; 0.04 ha x cow(-1) x grazing d(-1)), or 3) limit grazing on winter-annual pasture 3 d/wk (7 hr/d; 0.04 ha x cow(-1) x grazing d(-1)) sod-seeded into a portion of the pasture until mid-May. The seeded portion of pastures in Exp. 1 was planted with a mixture of wheat (Triticum aestivum L.) and rye (Secale cereale L.), but annual ryegrass (Lolium multiflorum Lam.) was added to the seed mixture in Exp. 2. In mid-May, cows were blocked by treatment and the previous sorting factors, randomly assigned to six new groups of 20, and placed on the six perennial pastures until calves were weaned. Groups of cows were exposed to a bull for 60 d beginning in mid-May. In Exp. 1 and 2, limit-grazing winter-annual pasture compared to the concentrate-based supplement or limit grazing 2 vs 3 d/wk did not affect (P > 0.15) cow BW. In Exp. 1, cows limit grazed on winter-annual pasture had a lower (P = 0.05) body condition score than cows fed the concentrate-based supplement in the early spring. However, in Exp. 2, cows limit grazed on winter-annual pasture had higher (P < or = 0.07) body condition score than cows fed the concentrate-based supplement. The conception rate of cows in Exp. 1 and 2 did not differ (P > 0.22) between cows fed concentrate-based supplements and cows limit grazed on winter-annual pasture. In Exp. 2, cows limit grazed 2 d/wk tended to have a greater (P = 0.10) conception rate than cows limit grazed 3 d/wk. In Exp. 1 and 2, birth weight, total gain, BW, and ADG of calves were not affected (P > 0.15) by treatment. We conclude that wheat and rye pasture is a marginal supplement for lactating beef cows. However, cows limit grazed 2 d/wk on winter-annual pasture of wheat, rye, and annual ryegrass as a supplement maintained BW and body condition score as well as cows fed the concentrate-based supplement. But, grazing pasture 3 vs 2 d/wk did not seem to affect performance of cows.

Animal Feed↗

PubMed2002

[Effect of earthworm inoculation on soil carbon and nitrogen dynamics and on crop yield with application of corn residues].

This study was carried out in the Experimental Station of Nanjing Agricultural University, which is in a subtropical monsoon region characterized by a warm-wet spring and a hot-dry summer. The annual average temperature, precipitation and evaporation are 15.6 degrees C, 1010 mm and 1560 mm, respectively. In 1999, the experimental plots (2.8 m x 1.0 m x 0.6 m) were established by concrete frame. Soil in the plots was orthic aquisols collected from Rugao County, Jiangsu Province. Crop rotation was upland rice and winter wheat. At the beginning of the first crop (rice) season, earthworms (Pheretima sp.) were inoculated at a density of 10.m-2 and 20.m-2, respectively, in the plots with an application of corn residues at the rate of 1500 g.m-2(750 g.m-2 in the following seasons). The responses of soil carbon and nitrogen and crop yield to earthworm activity were investigated from 1999 to 2001. The results showed that earthworms had no significant influences on total soil carbon and nitrogen content, which implied that there was no depletion of soil carbon and nitrogen pools in the presence of earthworms. The maintenance of soil carbon might be explained by low assimilation efficiency of organic matter by earthworms, and by the compensation of carbon returning from plant production enhancement. Soil mineral nitrogen, soil microbial biomass carbon and microbial biomass nitrogen were increased, and nitrogen mineralization was strengthened by earthworm activities, which was more obvious at jointing/booting and heading stages. In comparison with no-worm treatments, the yield of rice wheat increased by 9.3% and 5.1%, respectively, in the treatments inoculated with earthworms. It was concluded that earthworm was very important in promoting nitrogen recycling of crop residues and plant productivity, and in keeping the balance of soil carbon pool as well.

Agriculture↗

PubMed1999

Effect of Detarium microcarpum (Dm) and Mucuna flagellipes (Mf) gums on the quality of white bread.

Incorporation of Detarium Microcarpum (Dm) and Mucuna flagellipes (Mf) water soluble polysaccharides (gums) at 0.0 to 0.5% levels in wheat flour was studied to evaluate their effect on the rheological properties of wheat flour dough and white bread quality. At all levels of incorporation, there were increases (p < or = 0.05) in water absorption of the dough. Doughs containing gums had higher (p < or = 0.05) mixing tolerance index than the control. Set back viscosities decreased by 4.0 RVU and 9.0 RVU with increased levels of Dm and Mf gum incorporation, respectively. Significantly (p < or = 0.05) higher oven spring occurred in all the gum substituted white bread when compared to the control. The 0.5% gum substituted breads had a significantly (p < or = 0.05) higher sensory score for crumb grain, texture but lower (p < 0.05) crumb firmness than the control as determined instrumentally. Textural analysis after 5 days storage revealed that Dm and Mf gums improved moisture retention properties of the bread and reduced crumb firming tendency.

Bread↗

PubMed2003

Integration, expression and inheritance of transgenes in hexaploid oat (Avena sativa L.).

Two oat varieties, Melys (spring variety) and Bulwark (winter variety) were transformed by particle bombardment of primary embryogenic callus using either a ubi-bar-ubi-gus co-integration vector or co-transformed (Melys) with a ubi-bar plasmid together with one of three plasmids containing the beta-glucuronidase (gus) gene under the control of either a rice actin promoter, a CaMV35S promoter or a wheat high molecular weight glutenin promoter. Morphologically normal and fertile transgenic plants were regenerated following callus selection with glufosinate ammonium. Evidence for the integration and functioning of the selectable (bar) and reporter (gus) genes in T0 and T1 plants was confirmed by PCR, Southern hybridisation, fluorescence in situ hybridisation (FISH), histochemical assays, and by progeny analysis. Transformation rates varied from 0.2 to 5.0 lines/plate of callus bombarded, with co-transformation frequencies of 83 to 100%, and co-expression frequencies of 60 to 100%. Copy numbers for the bar and gus gene varied from 3 to 17 and from 2 to 20 respectively. Cell and tissue specific expression of the gus gene was evident from the different promoters, with the HMW glutenin promoter showing endosperm specific expression in T1 seed. No expression of the gus gene under the CaMV35S promoter was detected in any tissues. Progeny analysis provided evidence of Mendelian inheritance of the introduced genes suggesting either one or two unlinked integration sites. This was confirmed by fluorescence in situ hybridisation to chromosome spread preparations. No segregation of the gus gene from the bar gene was observed in any of the progeny derived from co-transformation.

Avena↗

PubMed2003

Effectiveness of predators and parasitoids for the natural control of Diuraphis noxia (Homoptera: Aphididae) on barley in central Ethiopia.

The Russian wheat aphid, Diuraphis noxia (Kurdj.), is a serious threat for the production of barley, Hordeum vulgare L., in Ethiopia. The pest can cause up to 100% yield losses in years of heavy infestation. Natural control of D. noxia by using predators and parasitoids might be the best alternative both from economical and ecological point of view. In this regard, a field investigation was conducted during the 2001 spring cropping season at Fitche, central Ethiopia to determine abundance of D. noxia and associated natural enemies and evaluate their effectiveness as natural control agents for this pest. In addition, the data collected during the 1995-1997 spring and summer cropping seasons at Chacha was analysed and presented. There was a highly significant difference (P < 0.01) on the population density of D. noxia between spring and summer and among sampling dates. The average aphid density was 23.1 and 0.7 aphids per tiller during spring and summer, respectively. The quantitative analyses based on predator units (PU) showed a highly significant difference (P < 0.01) among the predator groups, coccinellids and syrphids being more important, however, the coccinellid beetle, Hippodamia variegata Goeze, was the dominant species from all predator species or groups. Moreover, syrphid fly larvae were the only predators consistently found feeding on aphids within D. noxia rolled leaves. The polyphagous predators: Chrysopids, spiders and staphylinids were found to have less effect on D. noxia populations. Only two primary parasitoid species were recorded both during spring and summer cropping seasons: Aphidius colemani Vier. and Aphidius spp. Of these, A. colemani was more abundant in both seasons. The rate of parasitism was also generally low during the season. In general, the population build up of these natural enemies is slow and maximum population size is reached after the aphid population peaks and the crop has already been damaged. Further extensive work is necessary to maximize the effectiveness of natural enemies against this pest.

Animals↗

PubMed2002

Structural organization of the group-1 chromosomes of two bread wheat sister lines.

Eureka and Renan are two French bread wheat cultivars derived from a 4-way cross. Using molecular markers (essentially RFLPs), we studied the structure of the group-1 chromosomes of these two genotypes, their parents and a doubled-haploid (DH) population derived from their F(1). Using the DH population (102 lines), a molecular map of the three homoeologous group-1 chromosomes was produced and compared with the map established on another intervarietal cross: Courtot x Chinese Spring (Cadalen et al. 1997). The polymorphic markers were mapped on the DH population and characterized on the four grand-parents, allowing us to compare the structural organization of the group-1 chromosomes of Eureka and Renan and determine their origin. These chromosomes were very different, except for small regions (1AL proximal and 1BL distal) which were identical.

Biological Evolution↗

PubMed2000

Phenology and spatial pattern of Typhaea stercorea (Coleoptera: Mycetophagidae) infesting stored grain: estimation by pitfall trapping.

The hairy fungus beetle, Typhaea stercorea (L.), occurs frequently in stored grain, often in large numbers. Populations infesting stored barley in Minnesota, corn in South Carolina, and wheat in Florida were sampled by means of grain probe traps. Spatial distribution of the species was examined by contour analysis of trap catch. In South Carolina, corn was sampled at 2 locations over 2 storage seasons, and temperature, moisture content, and malathion residues were measured. These data were used to examine phenology as well as spatial distribution, and showed peak trap catch shortly after harvest in the fall, and in the spring. This pattern followed seasonal changes in grain temperature, but there was no apparent relationship of trap catch to either grain moisture content or malathion residue. The populations of T. stercorea were not distributed randomly, but were largely concentrated in 1 or very few aggregations associated with the "spoutline," a region high in foreign material and broken grain that forms near the center of a bin as it is loaded. However, the spatial patterns were dynamic, even on a very small time scale (week to week). Numbers of insects in aggregations rose and fell, the areas involved expanded and contracted, the centers shifted, and secondary centers appeared and disappeared. These changes were apparently in response to changing patterns of grain temperature and moisture content. Secondary centers of aggregation often formed in warmer grain along bin walls.

Animals↗

PubMed2004

Occurrence and distribution of pesticides in the province of Bologna, Italy, using honeybees as bioindicators.

Samples of honeybees (Apis mellifera, n = 92) from 14 beehive monitoring stations located in 3 townships in the province of Bologna were analyzed from April to October 2000. The concentration of 32 organophosphorus pesticides and 5 carbamates was determined through liquid-liquid extraction followed by gas chromatography with a nitrogen-phosphorus detector and liquid chromatography coupled to mass spectrometry using atmospheric pressure chemical ionization in positive and negative ion modes. The most contaminated samples were from Granarolo Emilia where cereals (wheat, sorghum, and corn), sugar beets, and potatoes are the main agriculture products. Thirty-five pesticides were detected, with organophosphorus being the most abundant ones. Malathion was detected in 58% of the samples (mean level 0.360 mg/kg) followed by fenithrothion in 53% of the samples (mean level 0.544 mg/kg) and pirimiphos methyl in 48% of the samples (mean level 0.006 mg/kg). Temporal trends showed that the maximum detection frequency occurred in late spring and was associated with the use of treatment products and less rainfall. The obtained results demonstrated the feasibility of using honeybees for assessing pesticide exposure in agriculture settings.

Agriculture↗

PubMed2002

Resistance gene-analog polymorphism markers co-segregating with the YR5 gene for resistance to wheat stripe rust.

The Yr5 gene confers resistance to all races of the stripe rust pathogen ( Puccinia striiformis f. sp. tritici) of wheat in the United States. To develop molecular markers for Yr5, a BC(7):F(3) population was developed by backcrossing the Yr5 donor ' Triticum spelta album' (TSA) with the recurrent parent 'Avocet Susceptible' (AVS). Seedlings of the Yr5 near-isogenic lines (AVS/6* Yr5), AVS, TSA, and the BC(7):F(3) lines were tested with North American races of P. striiformis f. sp. tritici under controlled greenhouse conditions. The single gene was confirmed by a 1:2:1 segregation ratio for homozygous-resistant, heterozygous and homozygous-susceptible BC(7):F(3) lines. Genomic DNA was extracted from the parents (the Yr5 near-isogenic line and AVS) and 202 BC(7):F(3) lines. The resistance gene-analog polymorphism (RGAP) technique was used to identify molecular markers. The parents and the homozygous-resistant and homozygous-susceptible BC(7):F(3) bulks were used to identify putative RGAP markers for Yr5. Association of the markers with Yr5 was determined using segregation analysis with DNA from the individual BC(7):F(3) lines. Of 16 RGAP markers confirmed by segregation analysis with 109 BC(7):F(3) lines, and nine of the markers confirmed with an additional 93 BC(7):F(3) lines, three markers co-segregated with the resistance allele and three markers co-segregated with the susceptibility allele at the Yr5 locus. The other four markers were tightly linked to the locus. Analysis of a set of Chinese Spring nulli-tetrasomic lines with three markers that co-segregated with, or were linked to, the susceptibility allele confirmed that the Yr5 locus is on chromosome 2B. Of five RGAP markers that were cloned and sequenced, markers Xwgp-17 and Xwgp-18 that co-segregated with the Yr5 locus were co-dominant and had 98% homology with each other in both DNA and translated amino-acid sequences. The two markers had 97% homology with a resistance gene-like sequence from Aegilops ventricosa and had significant homology with many known plant resistance genes, resistance gene analogs and expressed sequence tags (ESTs) from wheat and other plant species. The markers Xwgp-17 and Xwgp-18 also had significant homology with the NB-ARC domain that is in several genes for plant resistance to diseases, nematode cell death and human apoptotic signaling. These markers should be useful to clone Yr5 and combine Yr5 with other genes for durable and superior resistance for the control of stripe rust.

Amino Acid Sequence↗

PubMed1998

Position effects of ribosomal RNA multigene loci on meiotic recombination in wheat.

Homeologous wheat chromosome arms that differ by the presence or absence of a Nor locus or greatly differ in the numbers of copies of rRNA genes per Nor locus show conspicuous differences in the distribution of recombination. To assess directly the position effects of Nor loci on recombination across chromosome arms, a Triticum monococcum Nor9 haplotype was substituted for Triticum aestivum Nor9 haplotypes on two T. aestivum 1A chromosomes in the isogenic background of cv Chinese Spring. The numbers of rRNA genes in the 1A Nor9 haplotypes are greatly reduced relative to the T. monococcum haplotype. The substitution resulted in reduced recombination rate in the vicinity of the Nor9 locus. An intra-arm compensatory increase was observed in the proximal region of the arm so that the genetic length of the chromosome arm was unchanged. These findings suggest that Nor loci suppress recombination in their vicinity and change recombination patterns in Nor-bearing chromosome arms.

Chromosomes↗