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  • 1
    ISSN: 1432-2242
    Keywords: Key wordsCCN ; RFLP ; Hordeum vulgare ; Heterodera avenae ; Genetic mapping
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  The cereal cyst nematode (CCN), Heterodera avenae Woll., is an economically damaging pest of barley in many of the world’s cereal-growing areas. The development of CCN-resistant cultivars may be accelerated through the use of molecular markers. A number of resistance genes against the pest are well known; one of them, the single dominant Ha 2 resistance gene, has been shown to be effective against the Australian pathotype and maps to chromosome 2 of barley. Segregation analysis identified two restriction fragment length polymorphism (RFLP) markers flanking the resistance gene in two doubled-haploid populations of barley. AWBMA 21 and MWG 694 mapped 4.1 and 6.1 cM respectively from the Ha 2 locus in the Chebec×Harrington cross and 4.0 and 9.2 cM respectively in the Clipper×Sahara cross. Analysis of a further seven sources of CCN resistance in the form of near-isogenic lines (NILs) indicates that all available sources of resistance to the Australian pathotype of CCN in barley represent the Ha 2 locus.
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  • 2
    ISSN: 1432-2242
    Keywords: Key words Hordeum vulgare ; Disease resistance ; Genetic mapping ; RFLP ; QTL
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Spot form of net blotch (SFNB) (Pyrenophora teres f maculata) is an economically damaging foliar disease of barley in many of the world’s cereal growing areas. The development of SFNB-resistant cultivars may be accelerated through the use of molecular markers. A screen for SFNB resistance in 96 lines identified four new sources of resistance, including a feed variety, ‘Galleon’, for which a fully mapped doubled haploid population was available. Segregation data indicated SFNB resistance was conferred by a single gene in the ‘Galleon’בHaruna Nijo’ cross, positioned on the long arm of chromosome 7H. This gene is designated Rpt4 and is flanked by the RFLP loci Xpsr117(D) and Xcdo673 at distances of 6.9 cM and 25.9 cM, respectively. The marker Xpsr117(D) was validated using another population segregating for Rpt4, correctly predicting SFNB resistance with more than 90% accuracy.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-2242
    Keywords: Key words Boron toxicity ; Boron tolerance ; Mapping ; Wheat ; Marker-assisted selection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Boron is an essential plant micro-nutrient which can be phytotoxic to plants if present in soils in high concentration. Boron toxicity has been recognised as an important problem limiting production in the low rainfall areas of southern Australia, West Asia and North Africa. Genetic variation for boron toxicity tolerance in wheat has been well-characterised. The efficiency of breeding for boron toxicity tolerance could be greatly enhanced by the development of molecular markers associated with QTLs for tolerance in wheat. A population of 161 doubled haploids from a cross between the tolerant cultivar Halberd and the moderately sensitive cultivar Cranbrook was used to identify chromosomal regions involved in boron tolerance. A combined RFLP and AFLP linkage map of the Cranbrook x Halberd population was used to identify chromosomal regions involved in the boron tolerance traits measured. Regions on chromosome 7B and 7D were associated with leaf symptom expression. The region on chromosome 7B was also associated with the control of boron uptake and with a reduction in the effect of boron toxicity on root-growth suppression. RFLP markers at the chromosome 7B and 7D loci were shown to be effective in selecting for improved boron tolerance in an alternative genetic background. Halberd alleles at the chromosome 7B locus were associated with the concentration of boron in whole shoots and grain. The concentration of boron in whole shoots and in grain were both related to grain yield in a field trial conducted on soil containing toxic levels of boron. Implications relating to marker-assisted selection for boron toxicity tolerance in wheat are discussed.
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  • 4
    ISSN: 1432-2242
    Keywords: Key words RFLP analysis ; Triticum aestivum ; Genetic diversity ; Genetic similarity estimates ; Cluster analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Restriction fragment length polymorphisms (RFLPs) have been used to characterise the genetic diversity of wheat (Triticum aestivum) germplasm. One hundred and twenty-four accessions comprising all major Australian wheat varieties and lines important for breeding purposes were assayed for RFLPs with clones of known genetic location and selected to give uniform genome coverage. The objectives of this study were to determine RFLP-based genetic similarity between accessions and to derive associations between agronomically significant traits and RFLP phenotypes. Ninety-eight probes screened against genomic DNA digested with five restriction endonucleases detected a total of 1968 polymorphic fragments. Genetic similarity (GS) calculated from the RFLP data ranged from 0.004 to 0.409 between accessions, with a mean of 0.18. Cluster analysis based on GS estimates produced four groupings that were generally consistent with available pedigree information. Comparisons of the RFLP phenotypes of accessions containing disease resistance genes present on introgressed alien segments enabled the identification of specific alleles characteristic of these regions. Associations were derived for a range of stem-rust, leaf-rust and yellow-rust resistance genes. These results suggest that RFLP analysis can be used for the characterisation and grouping of elite breeding material of wheat and RFLP profiling can identify chromosome segments associated with agronomic traits.
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  • 5
    ISSN: 1432-2242
    Keywords: Key words Boron toxicity ; Boron tolerance ; RFLP mapping ; Barley
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Boron toxicity has been recognised as an important problem limiting production in the low-rainfall regions of southern Australia, West Asia and North Africa. Genetic variation for boron toxicity tolerance in barley has been characterised but the mode of inheritance and the location of genes controlling tolerance were not previously known. A population of 150 doubled-haploid lines from a cross between a boron toxicity tolerant Algerian landrace, Sahara 3771, and the intolerant Australian cultivar Clipper was screened in four tolerance assays. An RFLP linkage map of the Clipper×Sahara population was used to identify chromosomal regions associated with boron tolerance in barley. Interval regression-mapping allowed the detection of four chromosomal regions involved in the boron tolerance traits measured. A region on chromosome 2H was associated with leaf-symptom expression, a region on chromosome 3H was associated with a reduction of the affect of boron toxicity on root growth suppression, a region on chromosome 6H was associated with reduced boron uptake, and a region on chromosome 4H was also associated with the control of boron uptake as well as being associated with root-length response, dry matter production and symptom expression. The benefits and potential of marker-assisted selection for boron toxicity tolerance are discussed.
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  • 6
    ISSN: 1432-1424
    Keywords: platelet surface membrane ; lipid bilayer ; anion channel ; ion selectivity ; block
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary We have investigated the basic properties of a predominantly anion-selective channel derived from highly purified human platelet surface membrane. Single channels have been reconstituted into planar phospholipid bilayers by fusion of membrane vesicles and recorded under voltage-clamp conditions. The channel is found to have the following properties: (i) Channel activity occurs in bursts of openings separated by long closed periods. (ii) The current-voltage relationship is nonlinear. Channel current is seen to rectify, with less current flowing at positive than at negative voltages. Rectification may be due to asymmetric block by HEPES/Tris buffers. In 450mm KCl, 5mm HEPES/Tris, pH 7.2 the single channel conductance at −40 mV is ∼160 pS and at +40 mV is ∼90 pS. (iii) The conductanceconcentration relationship follows a simple saturation curve. Half maximal conductance is achieved at a concentration of ∼1000mm KCl, and the curve saturates at a conductance of ∼500 pS. (iv) Reversal potentials interpreted in terms of the Goldman-Hodgkin-Katz equation indicate a Cl∶K permeability ratio of 4∶1. (v) The channel accepts all of the halides as well as a number of other anions. The following sequence of relative anion permeabilities (in the presence of K+) is obtained: F−〈acetate−〈gluconate−〈Cl−〈Br−〈I−〈NO 3 − 〈SCN−. (vi) Cations as large as TEA+ are permeant. (vii) Current through the channel is blocked in the presence of DIDS, SITS and ATP, but not by Zn2+.
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