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  • 1
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    Bifurcation Analysis of a Class of Parametrized Two-Point Boundary Value Problems (2000)
    Springer
    Details
    Publikationsdatum: 2000-10-01
    Print ISSN: 0938-8974
    Digitale ISSN: 1432-1467
    Thema: Mathematik , Physik
    Publiziert von Springer
    Standort Signatur Erwartet Verfügbarkeit
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    AKTUELLE ARTIKEL
  • 2
    Digitale Medien
    Digitale Medien
    Variance component estimations and allocation of resources for breeding sweetpotato under East African conditions (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Plant breeding 123 (2004), S. 0 
    Details
    ISSN: 1439-0523
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: In Africa, average sweetpotato storage root yields are low and breeding is considered to be an important factor in increasing production. The objectives of this study were to obtain variance component estimations for sweetpotato in this region of the world and then use these to determine the efficiency of variety trials and breeding systems. From an incomplete series of variety trials in Kenya and Uganda (comprising 15 genotypes, three locations, two crop durations and three seasons) variance components were estimated - using the REML method - for the following traits: storage root yield, biomass production, harvest index, storage root dry matter and the Elston index which was used to aggregate all four traits. The storage root yield of clones across all 12 environments ranged from 15.2 to 33.0 t/ha. The variance components were significant for all traits, except the genotype by season interactions for storage root dry matter. The efficiency of selection systems was determined for total test capacities of 450 and 900 plots and using not more than five locations. Two-stage selection was 17-81% more efficient than one-stage selection after two seasons of testing. Two-stage selection was optimized under the restriction of using at least two locations at step 1. Trials with two locations and one replication at step 1 and five locations and two replications at step 2 were appropriate both for selecting for storage root yield and for simultaneously selecting for storage root yield, biomass production, harvest index and storage root dry matter content by using the Elston index. There are indications that such an allocation of resources for breeding sweetpotato is also appropriate for other regions in Sub-Saharan Africa.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1439-0523.2004.01000.x
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  • 3
    Digitale Medien
    Digitale Medien
    Expression of stylar incompatibility in the Andean clonal tuber crop oca (Oxalis tuberosa Mol., Oxalidaceae) (2000)
    Springer
    Sexual plant reproduction 13 (2000), S. 105-111 
    Details
    ISSN: 1432-2145
    Schlagwort(e): Key words Oca ; Oxalis tuberosa ; Floral heteromorphy ; Self-incompatibility ; Pollen fertility
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract  Long-, mid-, and short-styled clonal accessions of oca (Oxalis tuberosa) were intercrossed in a complete diallelic design. Pollen tube growth in styles was monitored in all diallelic crosses. Pollen fertility was estimated by two tests: staining of pollen grains with aceto-carmine and detection of β-galactosidase activity by the substrate X-Gal. The two methods of pollen fertility estimation were equally useful to detect fertility levels. Pollen originating from short stamens had the highest fertility (85%) and pollen from long stamens had the lowest fertility (70%). Pollen fertility was high throughout, but its degree varied with the stylar morph on which the pollen was formed. Long-styled accessions had the highest rates of fertile pollen. Differences in pollen fertility at different anther levels in the same style morph were also apparent. Pollen grain diameter of the six morph-anther level combinations was inversely correlated with pollen fertility. Pollen grains from long stamens were the largest and pollen grains from short stamens were the smallest. Neither pollen fertility nor pollen grain size had an influence on pollen tube growth in the style or on fruit and seed set. Pollen tubes growing within the styles were inhibited at a different level for each of the 18 cross combinations in the diallel. Although legitimate crosses had greatest pollen tube growth, some of the illegitimate inter- and intramorph crosses had equally high scores. Of all illegitimate crosses, mid-styled seed parents had the lowest level of stylar incompatibility. Fruit and seed set were highly correlated with the extent of pollen tube growth in the style. The number of pollen tubes entering ovules in a flower was in good agreement with the number of seeds produced per fruit. Therefore, it is concluded that stylar incompatibility is the major determinant of limited seed formation in oca even in the most successful legitimate cross combinations.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004970000040
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  • 4
    Digitale Medien
    Digitale Medien
    The Influence of Previous Experience and Starvation on Aphid Feeding Behavior (2000)
    Springer
    Journal of insect behavior 13 (2000), S. 699-709 
    Details
    ISSN: 1572-8889
    Schlagwort(e): feeding behavior ; previous experience ; starvation ; stylet ; xylem ingestion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract It was hypothesized that (1) previous experience of aphids on a host plant leads to differences in their feeding behavior relative to aphids without previous experience on it and that (2) a change in the physiological state of the aphid modifies their experience-induced behavior. Using electronic recording, the feeding behavior of the aphid Sitobion fragariae (Walker) on wheat Triticum aestivum L. and oat Avena sativa L. was examined, comparing aphids with or without previous experience on a given host and with or without a period of starvation before assessing probing behavior. All comparisons were performed within a single aphid clone to minimize the effect of genetic variation. Feeding behavior on wheat was significantly affected by previous experience and starvation. The effect of previous experience interacted with the host plant where feeding behavior was tested. Aphids feeding on wheat following previous experience on wheat showed a longer time and a higher number of pathway activities and less time in waveform F (i.e., mechanical stylet work and penetration difficulties) than did aphids feeding on wheat after a previous experience on oat. No differences in the time from the beginning of the recording until the first salivation into the sieve elements were found. When aphids were subjected to a period of starvation, the time devoted to xylem ingestion increased compared with that of nonconstrained aphids. These results are discussed in terms of factors affecting foraging decisions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1007844027368
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  • 5
    Digitale Medien
    Digitale Medien
    Bifurcation Analysis of a Class of Parametrized Two-Point Boundary Value Problems (2000)
    Springer
    Journal of nonlinear science 10 (2000), S. 507-531 
    Details
    ISSN: 1432-1467
    Schlagwort(e): Key words. bifurcation, equivariance, nonlinear boundary value problem, shell equations
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik , Physik
    Notizen: Summary. In this paper, we study the solution manifold M of a class of nonlinear parametrized two-point boundary value problems. Typical representatives of this class are the shell equations of Bauer, Reiss, Keller [2] and Troger, Steindl [29]. The boundary value problems are formulated as an abstract operator equation T(x,λ)=0 in appropriate Banach spaces. By exploiting the equivariance of T , we obtain detailed information about the structure of M. Moreover, we show how these theoretical results can be used to compute efficiently interesting parts of M with numerical standard techniques. Finally, we present numerical results for the shell equations given in [2] and [29].
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s003320010004
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  • 6
    Digitale Medien
    Digitale Medien
    Pseudoreplication and Its Frequency in Olfactometric Laboratory Studies (2000)
    Springer
    Journal of chemical ecology 26 (2000), S. 1423-1431 
    Details
    ISSN: 1573-1561
    Schlagwort(e): Pseudoreplication ; experimental design ; olfactometer ; wind tunnel ; semiochemical ; statistical independence
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Abstract The evaluation of behavioral responses of an organism to a particular stimulus normally implies the design of a bioassay. Measurements of the response in a number of replicates are necessary to perform inferential statistics and therefore accept or reject a hypothesis about the effect of the stimulus on the behavior of the organism under study. In the present article, we address the importance of pseudoreplication in studies of chemical ecology, particularly in laboratory experiments on olfactory responses of insects to semiochemicals in olfactometers and wind tunnels. Pseudoreplication may be caused by lack of independence in the stimulus or the experimental device, the reutilization of test insects, or the use of groups of test insects, without adequate statistical analysis addressing such dependency. Each and all of the cases reviewed (N = 105) lacked information in at least one of the factors listed above; hence no cases could be said with certainty to be free of pseudoreplication. Forty-nine cases (46.7%) contained explicit information revealing that pseudoreplication existed in terms of one or more of the criteria listed above; in only three of these cases did the authors address statistically the stated dependence of the samples. Pseudoreplication due to different factors ranged from 2% to 30% of the cases, with an average of 13%. The most frequent sources of pseudoreplication were the reuse of the device and the use of groups of test insects. The analysis showed the low importance given to obtaining independent replicates in bioassays involving olfactometric responses of insects to semiochemicals.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1005583624795
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  • 7
    Digitale Medien
    Digitale Medien
    Effect of Two Wheat Cultivars Differing in Hydroxamic Acid Concentration on Detoxification Metabolism in the AphidSitobion avenae (2000)
    Springer
    Journal of chemical ecology 26 (2000), S. 2725-2736 
    Details
    ISSN: 1573-1561
    Schlagwort(e): Sitobion avenae ; aphids ; hydroxamic acids ; DIMBOA ; detoxification ; cytochrome P-450 monooxygenases ; NADPH cytochrome c reductase ; glutathione S-transferases ; esterases ; catalase
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Abstract Hydroxamic acids (Hx) are wheat secondary metabolites conferring resistance for cereals against aphids. The activity of five enzymatic systems were evaluated in the aphid Sitobion avenae reared on the high-Hx wheat cultivar Chagual and the low-Hx wheat cultivar Huayún for 10 generations. Enzyme solutions were prepared from aphid homogenates and assayed for mixed function oxidases (including cytochrome P-450 monooxygenases and NADPH cytochrome c reductase), glutathione S-transferases, esterases, and catalase. Specific activities per aphid individual of cytochrome P-450 monooxygenases, NADPH cytochrome c reductase, glutathione S-transferases, and esterases were significantly increased in wheat cultivars relative to oat (only marginal increase of esterases in Chagual). Aphids fed on cv. Huayún showed an overall higher induction of enzymatic systems than those fed on cv. Chagual. Comparison of these results with reported effects of Hx on detoxifying enzymes in other insects, including aphids, support the hypothesis that these enzymatic pathways play an important role in the detoxification of toxic host-plant secondary metabolites.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1026481524896
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  • 8
    Digitale Medien
    Digitale Medien
    Effect of wheat resistance, the parasitoid Aphidius rhopalosiphi, and the entomopathogenic fungus Pandora neoaphidis, on population dynamics of the cereal aphid Sitobion avenae (2000)
    Springer
    Entomologia experimentalis et applicata 97 (2000), S. 109-114 
    Details
    ISSN: 1570-7458
    Schlagwort(e): Sitobion avenae ; Aphidius rhopalosiphi ; Pandora neoaphidis ; Entomophthorales ; tritrophic effects ; wheat resistance ; natural enemies
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The influence of wheat (Triticum aestivumL.) resistance, the parasitoid Aphidius rhopalosiphiDe Stephani-Perez (Hymenoptera: Braconidae) and the entomopathogenic fungus Pandora neoaphidis(Remaudière et Hennebert) Humber (Zygomycetes: Entomophthorales) on the density and population growth rate of the cereal aphid Sitobion avenae(F.) (Hemiptera: Aphididae) was studied under laboratory conditions. Partial wheat resistance was based on hydroxamic acids, a family of secondary metabolites characteristic of several cultivated cereals. The partial resistance of wheat cultivar Naofén, the action of the parasitoid and the joint action of the parasitoid and fungus, reduced aphid density. The lowest aphid densities were obtained with the combination of the parasitoid and the fungus, but wheat resistance under these circumstances did not improve aphid control. Significant reductions of population growth rate (PGR) of aphids were obtained with the joint action of wheat resistance and natural enemies. In particular, the combined effects of parasitoids and fungi showed significantly lower PGR than the control without natural enemies in both wheat cultivars. Our results support the hypothesis that wheat resistance and the utilization of biological control agents could be complementary strategies in an integrated pest management program against cereal aphids.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1004048600899
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