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Linus U. Ogbuji - One of the best experts on this subject based on the ideXlab platform.

  • Pest-Resistance in SiC/BN/SiC composites
    Journal of the European Ceramic Society, 2003
    Co-Authors: Linus U. Ogbuji
    Abstract:

    Abstract State-of-the-art non-oxide ceramic-matrix composites (consisting of SiC fibers, cvi -BN interphase coating, and mi -SiC matrix) exhibit excellent mechanical properties at room temperature, as well as above ∼1000 °C (where oxidation easily seals flaws with silica); but they are prone to Pest degradation at intermediate temperatures in an oxidizing environment, and especially so in the fast, moist flame of a jet engine. Two modes of Pest may be distinguished in these composites. The more severe type of Pest is promoted by extraneous factors, like a layer of elemental carbon underlying the BN interphase and undermining its intrinsic oxidation Resistance. It is shown that, when care is taken to exclude such a carbon layer, SiC/BN/SiC composite can easily survive a 100-h exposure in a burner rig without noticeable loss of strength or strain to fracture.

Martha A Mutschler - One of the best experts on this subject based on the ideXlab platform.

  • Marker-assisted transfer of acylsugar-mediated Pest Resistance from the wild tomato, Lycopersicon pennellii , to the cultivated tomato, Lycopersicon esculentum
    Molecular Breeding, 1997
    Co-Authors: Darlene M. Lawson, China F. Lunde, Martha A Mutschler
    Abstract:

    Acylsugars exuded from type IV trichomes mediate the multiple Pest Resistance found in the wild tomato species, Lycopersicon pennellii. A marker-assisted selection breeding program was used to attempt the transfer of the ability to accumulate acylsugars to cultivated tomato. RFLP and PCR-based markers were used through three backcross generations to select plants containing 5 target regions associated by QTL analysis with acylsugar accumulation. The BC1F1 plant selected possessed all 5 target regions and accumulated acylsugars at a moderate level similar to that of the interspecific F1 control. The BC2F1 and BC3F1 selections contained complementary subsets of the 5 target regions and did not accumulate acylsugars. BC3F1 plants with complementary subsets of the 5 target regions were intermated to produce populations segregating for the 5 target regions. From 1000 BC3F1-intermated plants, three plants were found which accumulated acylsugars at low levels and contained 3 to 5 of the target regions. The recovery of acylsugar accumulation in progeny of the intermated BC3F1 plants supports the involvement of at least some of the 5 target regions in acylsugar biosynthesis. However, since the levels of acylsugars accumulated by these plants were lower than that of the interspecific F1, it is likely that another, as of yet unidentified, region is necessary for accumulation of higher levels of acylsugars.

  • Breeding for Acylsugar-mediated Multiple-Pest Resistance in Cultivated Tomato, Lycopersicon esculentum
    Hortscience, 1995
    Co-Authors: Martha A Mutschler, Edward D. Cobb, Barbara E. Liedl, Joseph A. Shapiro
    Abstract:

    Acylsugar mediates the Resistance of Lycopersicon pennellii LA716 to several important insect Pests of cultivated tomato, including potato aphid, green peach aphid, leaf miner, fruitworm, armyworm, and silverleaf whitefly. Incorporation of acylsugar-mediated multiple Pest Resistance could result in a significant reduction in the use of Pesticidal sprays in cultivated tomato. Development of a reliable assay for acylsugar production and confirmation of the association between the Resistance and acylsugars allowed us to try to breed for the trait by selecting for acylsugar-producing plants. The breeding cycle allows us to progress by one backcross generation per year. The breeding program was faced by several challenges, including interference in gene transfer by interspecific crossing barriers, and the oligogenic nature of the acylsugar-mediated Resistance trait. Despite these challenges, the breeding program has produced BC3F2 plants that produce effective levels of acylsugars, are tomato-like in vine appearance, and produce seed-bearing fruit in the field without manual pollination. The current status of the program and future plans will be discussed.

N Mcnamara - One of the best experts on this subject based on the ideXlab platform.

  • foliar insect Pest management on cowpea vigna unguiculata walpers in simulated varietal mixtures ii Pest Resistance management implications
    Field Crops Research, 2002
    Co-Authors: A Ward, Stephen Morse, I Denholm, R Thompson, N Mcnamara
    Abstract:

    Field experiments were established in which cowpea (Vigna unguiculata Walpers) was treated with a series of partial insecticide (carbofuran) application treatments to simulate (susceptible/resistant) varietal mixtures and a series of inter-crops with soybean (Glycine max). Treatments were sampled for damage by the foliage Pests Ootheca mutabilis Sahlberg and Aphis craccivora Koch and for flower production. The soybean is likely to have provided both a mechanical barrier to Pest movement and disruption to O. mutabilis through volatile allelochemicals. The comparison between the two treatment types would suggest whether similar mechanisms were the cause of Pest reductions observed in partial insecticide applications on cowpea. The results suggested that the inter-cropping with soybean was not as effective in managing Pest populations as a partial insecticide application and could even increase Pest numbers. Further examination of the data from the partial insecticide application treatments appeared to show that the Pest infestation was lower on the untreated plants closest to the insecticide-treated plants. This could be as a result of Pest redistribution onto insecticide-treated plants after initial colonisation. The implications of this, in terms of Pest Resistance management are discussed.

Darlene M. Lawson - One of the best experts on this subject based on the ideXlab platform.

  • Marker-assisted transfer of acylsugar-mediated Pest Resistance from the wild tomato, Lycopersicon pennellii , to the cultivated tomato, Lycopersicon esculentum
    Molecular Breeding, 1997
    Co-Authors: Darlene M. Lawson, China F. Lunde, Martha A Mutschler
    Abstract:

    Acylsugars exuded from type IV trichomes mediate the multiple Pest Resistance found in the wild tomato species, Lycopersicon pennellii. A marker-assisted selection breeding program was used to attempt the transfer of the ability to accumulate acylsugars to cultivated tomato. RFLP and PCR-based markers were used through three backcross generations to select plants containing 5 target regions associated by QTL analysis with acylsugar accumulation. The BC1F1 plant selected possessed all 5 target regions and accumulated acylsugars at a moderate level similar to that of the interspecific F1 control. The BC2F1 and BC3F1 selections contained complementary subsets of the 5 target regions and did not accumulate acylsugars. BC3F1 plants with complementary subsets of the 5 target regions were intermated to produce populations segregating for the 5 target regions. From 1000 BC3F1-intermated plants, three plants were found which accumulated acylsugars at low levels and contained 3 to 5 of the target regions. The recovery of acylsugar accumulation in progeny of the intermated BC3F1 plants supports the involvement of at least some of the 5 target regions in acylsugar biosynthesis. However, since the levels of acylsugars accumulated by these plants were lower than that of the interspecific F1, it is likely that another, as of yet unidentified, region is necessary for accumulation of higher levels of acylsugars.

Marion Desquilbet - One of the best experts on this subject based on the ideXlab platform.

  • The Dynamics of Pest Resistance Management: The Case of Refuge Fields forBtCrops
    Canadian Journal of Agricultural Economics Revue canadienne d'agroeconomie, 2016
    Co-Authors: Marion Desquilbet, Markus Herrmann
    Abstract:

    We examine the optimal time-variant refuge policy to manage Pest Resistance to Bacillus thuringiensis (Bt) crops in a finite, discrete-time horizon model. We identify analytically the intertemporal effects of refuge fields on the Pest population and its susceptibility. The shape of the optimal refuge policy and whether or not Pest susceptibility should be exhausted completely at the end of the time horizon depend crucially on the values of a cost premium of Bt seeds and the fitness cost of Resistance (over mortality of resistant Pests) and are addressed via numerical simulations. We demonstrate the importance of modeling the dynamics of the biological system accurately, of defining a diploid (and not haploid) biological model, and of using a discrete-time (rather than continuous-time) framework.

  • Pest Resistance management: an economic perspective
    2012
    Co-Authors: Marion Desquilbet
    Abstract:

    This presentation gives a perspective on the main findings of the economic literature dealing with Pest Resistance management and on questions for future research. Resistance to Pest damage is embedded in some crop varieties, which thereby have an economic advantage over their conventional non-resistant counterparts. But this advantage may be lost over time, as selection pressure causes Pest populations to adapt to this Resistance. The economic literature has mainly illustrated the examples of Resistance to a chemical Pesticide or to an insect-resistant transgenic variety (as well as the related case of weed adaptation to a herbicide-tolerant transgenic crop variety on which a total herbicide may be applied). It has explored how to best design the use of Pest-toxic varieties over time, which involves an intertemporal trade-off between controlling the Pest population now and preserving its susceptibility to the Pest-toxic crop in the future. It has also analyzed how to regulate this use, with regulation being motivated by the common-pooled nature of Pest population and Pest Resistance, two detrimental resources exploited by farmers under open access. Besides, it has tackled the issue of how the interest of a social planner in preserving the Resistance of a Pest-toxic variety compares with that of a monopolist selling the crop variety with patent rights. At last, the literature has looked into the question of possible increasing returns to adoption in disfavor or in favor on Pest-toxic varieties. Vanloqueren and Baret (2008) illustrate path-dependent processes and lock-in factors playing against the diffusion of multi-resistant wheat cultivars. In the case of herbicide-tolerant transgenic varieties, which allow the use of a total herbicide to combat weeds, on the contrary, some weed scientists warn on some path-dependence factors that play in favor of increased herbicide use over time to control weeds with herbicide-tolerant varieties (Mortensen et al., 2012).

  • An assessment of bioeconomic modeling of Pest Resistance with new insights into dynamic refuge fields
    2012
    Co-Authors: Marion Desquilbet, Markus Hermann
    Abstract:

    We examine the optimal time-variant refuge policy to manage Pest Resistance to Bt crops in afinite-horizon discrete-time model. We identify analytically the intertemporal effects of refuge fields on the Pest population and its susceptibility. The shape of the optimal refuge policy and whether or not Pest susceptibility should be exhausted completely at the end of the time horizon depend crucially on the values of a cost premium of Bt seeds and the fitness cost of Resistance (over-mortality of resistant Pests) and are addressed via numerical simulations. We demonstrate the importance of modeling the dynamics of the biological system accurately, of defining a diploid (and not haploid) biological model, and of using a discrete-time (rather than continuous-time) framework.

  • Regulation of a Spatial Externality: Refuges versus Tax for Managing Pest Resistance
    Environmental and Resource Economics, 2011
    Co-Authors: Stefan Ambec, Marion Desquilbet
    Abstract:

    We examine regulations for managing Pest Resistance to Pesticide varieties in a temporally and spatially explicit framework. We compare the performance of the EPA’s mandatory refuges and a tax (or subsidy) on the Pesticide variety under several biological assumptions on Pest mobility and the heterogeneity of farmers’ Pest vulnerability. We find that only the tax (or subsidy) restores efficiency if Pest mobility is perfect within the area. If Pest mobility is imperfect and when farmers face identical Pest vulnerability, only the refuge might restore efficiency. With simulations we illustrate that complex outcomes may arise for intermediate levels of Pest mobility and farmers’ heterogeneity. Our results shed light on the choice of regulatory instruments for common-pool resource regulations where spatial localization matters.

  • Pest Resistance Regulation and Pest Mobility
    2006
    Co-Authors: Stefan Ambec, Marion Desquilbet
    Abstract:

    We use a spatially-explicit analytical framework to compare mandatory refuges and a tax on the resistant variety as regulation instruments for Pest Resistance management. Because the extraction of the common-pool Pest susceptibility resource depends on the spatial pattern of Pest dispersal, we find that the usual preference for market-based environmental instruments does not necessarily apply to Pest Resistance management. Mandatory refuges are preferred to a tax on the resistant variety for some assumption sets on heterogeneity between farms and Pest dispersal distances.