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  • 1990-1994  (1,578)
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  • 1
    ISSN: 1432-2242
    Keywords: Competition ; Coexistence ; Coevolution ; White clover ; Perennial ryegrass
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The role of competition, coexistence and co-evolution in the formation of plant communities is discussed, particularly in relation to the breeding of improved grass/legume mixtures. Competition occurs whenever the demand for a particular resource outstrips supply, with the pressures generated within a species expected to exceed those between species. These pressures must be withstood before populations can coexist within a community. This is accomplished by a process of niche diversification, arising from temporal or spatial differences between the populations, that enables them to draw on resources not readily available to their competitors. Coexistence is crucial to the success of any breeding programme designed to raise the productivity of grass/ legume pastures, because it enables components to adapt not only to the environment which they share, but also to each other. A strategy that improves the “general ecological combining ability” of one or both components by a process of recurrent or reciprocal recurrent unilateral adaptation may prove successful, particularly if existing niche differences are increased thereby. Although both processes may give rise to populations which have apparently coevolved, only those resulting from reciprocal recurrent selection will meet the criteria of specificity and reciprocity.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2242
    Keywords: Lycopersicon esculentum ; Asymmetric somatic hybrids ; Protoplast fusion ; Restriction fragment length polymorphism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Two somatic hybrid plants generated from a single fusion event between Lycopersicon esculentum and irradiated L. pennellii protoplasts have been analyzed at the molecular level. Over 30 loci have been analyzed using isozymes and RFLPs. All loci tested on chromosomes 2–10 were heterozygous, while those loci on chromosome 12 were homozygous L. pennellii in both somatic hybrids. In one of the somatic hybrids, 2850, loci on chromosome 1 were also homozygous L. pennellii. The other somatic hybrid, 28F5, was heterozygous at all chromosome 1 loci tested, but exhibited altered stoichiometry of parental bands as compared to the sexual hybrid. Loci on chromosome 2 from both somatic hybrids have altered stoichiometry, with L. pennellii alleles being four times more abundant than expected. Both somatic hybrids contain the L. esculentum chloroplast genome, while only L. pennellii polymorphisms have been detected in the mitochondrial genome.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical and applied genetics 79 (1990), S. 216-218 
    ISSN: 1432-2242
    Keywords: Extra chromosome ; Trisomies ; Plantago lagopus ; Telotrisomics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In the progenies of the crosses between disomics and trisomies, two plants were isolated which carried an extra chromosome that was unlike any in the standard complement. The plants were not alike; while one carried a metacentric, the other had a telocentric extra chromosome. Their detailed structure and possible modes of origin are discussed.
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  • 4
    ISSN: 1432-2242
    Keywords: Secale ; Secalin loci ; Mapping ; Rearrangements ; Chromosome 1R
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Linkage relationships were established between the secalin loci, Sec 1 (40-K gamma and omega secalins, homologous to the wheat gliadins) and Sec 3 (HMW = high-molecular-weight secalins, homologous to the wheat HMW glutenin subunits), and five chromosomal rearrangements involving chromosome 1R of rye (Secale cereale L.). These were: interchanges T273W (1RL/5RS), T306W (1RS/5RL), and T850W (1RS/ 4RL), Robertsonian centromere split Rb1RW and the interchanged Robertsonian split Rb2R/248W. The analysis established the linkage relationships between the secalin loci and the breakpoints of the rearrangements, in addition to the quantitative effects of the rearrangements on the linkage. Sec-1 is located in the satellite at a position at least 2.5 cMorgan from the proximal border of the terminal C-band, and about 30 cMorgan from the nucleolar organizing region (NOR). The locus is also physically closer to the terminal C-band than to the NOR, but not as much as corresponds with the map distances. Similarly, the physical distance between Sec-3 and the centromere is greater than corresponds with the recombination frequency (0%–9%). Although overall recombination in 1RL remains the same, recombination between the centromere and Sec-3 is greatly reduced in the Robertsonian split combined with the interchange. This is not the case with the single Robertsonian split.
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  • 5
    ISSN: 1432-2242
    Keywords: Tissue culture mutant selection ; Amino acid biosynthesis ; Lysine plus threonine resistance ; Aspartate kinase ; Maize
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Regenerable maize (Zea mays L.) tissue cultures were selected for ability to grow in the presence of inhibitory (1.0–1.5 mM) concentrations of L-lysine plus L-threonine. Testcross kernels from one regenerated plant (LT20) segregated for wild-type and high free threonine concentration in a 1∶1 ratio consistent with a single dominant gene for high free threonine. Free threonine concentrations (nmol/mg dry weight) increased an average of 29-fold in bulked F2 kernel samples from heterozygous mutant plants, and the total (free plus protein-bound) threonine concentration increased 68%. Increases in protein-bound methionine, lysine and glycine concentrations were also noted, suggesting a possible effect of the mutation on protein concentration and composition. Allelism tests with a previously selected mutant line, Ltr *19, showed that two unlinked, codominant genes conditioned the high free threonine phenotype. Based on a separate study of aspartate kinase feedback inhibition characteristics in the two mutant lines, we propose that the mutant alleles [gene and allele designations are according to guidelines for maize genetic nomenclature (Burnham et al. 1975)] be designated Ask-LT19 and Ask2-LT20 for the Ltr *19 and LT20 mutants, respectively.
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  • 6
    ISSN: 1432-2242
    Keywords: Linkage ; Epistasis ; Genetic covariances ; Inbred species
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Tests for linkage based on covariances among relatives in self-pollinated species are usually based upon an assumption that epistasis is not important. This study was conducted to determine the impact of epistasis on, and to investigate the sensitivity of, such tests. Thirty covariances were calculated for each of ten non-epistatic and ten epistatic genetic models with varying probabilities of recombination between two coupling or repulsion loci. Each set of covariances was tested for linkage by comparing covariances calculated for the model with those expected for an additive-dominance model with no linkage. Results showed that the test for linkage is quite insensitive to the effects of linkage due to the disproportionate influence of inbreeding. Repulsion linkages should be easier to detect than coupling linkages for all models. Epistasis was found to mimic or counteract the effects of linkage. Tests for linkage based on covariances within a hierarchical mating design appear to be insensitive to linkage and may confuse the effects of linkage and epistasis.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1432-2242
    Keywords: Three way data ; Clustering via mixtures ; Principal component analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The Australian Cotton Cultivar Trials (ACCT) are designed to investigate various cotton [Gossypium hirsutum (L.)] lines in several locations in New South Wales and Queensland each year. If these lines are to be assessed by the simultaneous use of yield and lint quality data, then a multivariate technique applicable to three-way data is desirable. Two such techniques, the mixture maximum likelihood method of clustering and three-mode principal component analysis, are described and used to analyze these data. Applied together, the methods enhance each other's usefulness in interpreting the information on the line response patterns across the locations. The methods provide a good integration of the responses across environments of the entries for the different attributes in the trials. For instance, using yield as the sole criterion, the excellence of the namcala and coker group for quality is overlooked. The analyses point to a decision in favor of either high yields of moderate to good quality lint or moderate yield but superior lint quality. The decisions indicated by the methods confirmed the selections made by the plant breeders. The procedures provide a less subjective, relatively easy to apply and interpret analytical method of describing the patterns of performance and associations in complex multiattribute and multilocation trials. This should lead to more efficient selection among lines in such trials.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1432-2242
    Keywords: Glycine spp. ; RFLP ; Taxonomy ; Wild perennial species
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Total DNA from callus tissue of 28 accessions representing seven wild perennial Glycine species was compared using recombinant genomic probes derived from G. max, the soybean. Using two probes, we show that this molecular approach both confirms and extends the model for the taxonomic relationships between the species derived from morphological and cytogenetic data, and that it provides clear evidence that RFLP analysis of genomic sequences has the potential for revealing the derivation of the member species of the wild perennial Glycine taxon. Although, in this preliminary report, the sample size for each species is small, it is clear that the greatest between-accession variation occurs in G. tabacina (B2B2) and G. clandestine (A1A1), suggesting that these may be the taxa from which further speciation occurred in the subgenus.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1432-2242
    Keywords: Triticum aestivum L. ; Genetic diversity ; Coefficient of kinship ; Genetic distance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In winter wheat (Triticum aestivum L.), the development of a methodology to estimate genetic divergence between parental lines, when combined with knowledge of parental performance, could be beneficial in the prediction of bulk progeny performance. The objective of this study was to relate F2 heterosis for grain yield and its components in 116 crosses to two independent estimates of genetic divergence among 28 parental genotypes of diverse origins. Genetic divergence between parents was estimated from (a) pedigree relationships (coefficients of kinship) determined without experimentation, and (b) quantitative traits measured in two years of field experimentation in Kansas and North Carolina, USA. These distances, designated (1 -r) and G, respectively, provided ample differentiation among the parents. The 116 F2 bulks were evaluated at four locations in Kansas and North Carolina in one year. Significant rank correlations of 0.46 (P = 0.01) and 0.44 (P = 0.01) were observed between G and grain yield and kernel number heterosis, respectively. Although (1 -r) was poorly associated with grain yield heterosis, G and midparent performance combined to account for 50% of the variation in F2 yields among crosses when (1 -r) was above the median value, whereas they accounted for only 9% of the variation among crosses when (1-r) was below the median. Midparent and (1 -r) had equal effects on F2 grain yield (R 2= 0.40) when G was greater than the median value. A breeding strategy is proposed whereby parents are first selected on the basis of performance per se and, subsequently, crosses are made between genetically divergent parents that have both large quantitative (G) and pedigree divergence (1 -r).
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical and applied genetics 79 (1990), S. 251-255 
    ISSN: 1432-2242
    Keywords: Species variability ; Western white pine ; Pinus monticola ; Heteroplasmic trees ; Chloroplast DNA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Within-species variability of a restriction site in the chloroplast (cp) DNA in Pinus monticola has been surveyed. Frequencies of two variants of the cp genome are significantly different in interior versus coastal populations. Paternal inheritance of the cp genome predominates, though some individuals have both variants of the genome. The presence of heteroplasmic individuals indicates occasional biparental inheritance.
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