Home About us Contact
|
Home About us Contact | ||
|
|
||
Bt Cotton (bt + cotton)
Kinds of Bt Cotton Selected AbstractsIs Bt Cotton a Pro-Poor Technology?JOURNAL OF AGRARIAN CHANGE, Issue 4 2010A Review, Critique of the Empirical Record Policy makers, journalists and other commentators have hailed genetically modified (GM) crops as a ,pro-poor' success in the developing world. Their confidence appears to be justified by the encouraging conclusions reached by academic studies on the performance and impacts of GM crops, which seem to provide convincing evidence of substantial benefits for smallholders in developing countries. However, a detailed, critical examination of studies on transgenic, insect-resistant cotton in China, India and South Africa demonstrates that the technology's impacts have been evaluated and represented in selective and misleading ways. The performance and impacts of GM crops have in fact been highly variable, socio-economically differentiated and contingent on a range of agronomic, socio-economic and institutional factors. The shortcomings of the GM crop-impacts literature have done a disservice to public and policy debates about GM crops in international development and impeded the development of sound, evidence-based policy. [source] Effects of Elevated Carbon Dioxide on the Growth and Foliar Chemistry of Transgenic Bt CottonJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 9 2007Gang Wu Abstract A field study was carried out to quantify plant growth and the foliar chemistry of transgenic Bacillus thuringiensis (Bt) cotton (cv. GK-12) exposed to ambient CO2 and elevated (double-ambient) CO2 for different lengths of time (1, 2 and 3 months) in 2004 and 2005. The results indicated that CO2 levels significantly affected plant height, leaf area per plant and leaf chemistry of transgenic Bt cotton. Significantly, higher plant height and leaf area per plant were observed after cotton plants that were grown in elevated CO2 were compared with plants grown in ambient CO2 for 1, 2 and 3 months in the investigation. Simultaneously, significant interaction between CO2 level × investigating year was observed in leaf area per plant.Moreover, foliar total amino acids were increased by 14%, 13%, 11% and 12%, 14%, 10% in transgenic Bt cotton after exposed to elevated CO2 for 1, 2 or 3 months compared with ambient CO2 in 2004 and 2005, respectively. Condensed tannin occurrence increased by 17%, 11%, 9% in 2004 and 12%, 11%, 9% in 2005 in transgenic Bt cotton after being exposed to elevated CO2 for 1, 2 or 3 months compared with ambient CO2 for the same time. However, Bt toxin decreased by 3.0%, 2.9%, 3.1% and 2.4%, 2.5%, 2.9% in transgenic Bt cotton after exposed to elevated CO2 for 1, 2 or 3 months compared with ambient CO2 for same time in 2004 and 2005, respectively. Furthermore, there was prominent interaction on the foliar total amino acids between the CO2 level and the time of cotton plant being exposed to elevated CO2. It is presumed that elevated CO2 can alter the plant growth and hence ultimately the phenotype allocation to foliar chemistical components of transgenic Bt cotton, which may in turn, affect the plant-herbivore interactions. [source] Bias from Farmer Self-Selection in Genetically Modified Crop Productivity Estimates: Evidence from Indian DataJOURNAL OF AGRICULTURAL ECONOMICS, Issue 1 2007Benjamin Crost Q12; D81 Abstract In the continuing debate over the impact of genetically modified (GM) crops on farmers of developing countries, it is important to accurately measure magnitudes such as farm-level yield gains from GM crop adoption. Yet most farm-level studies in the literature do not control for farmer self-selection, a potentially important source of bias in such estimates. We use farm-level panel data from Indian cotton farmers to investigate the yield effect of GM insect-resistant cotton. We explicitly take into account the fact that the choice of crop variety is an endogenous variable which might lead to bias from self-selection. A production function is estimated using a fixed-effects model to control for selection bias. Our results show that efficient farmers adopt Bacillus thuringiensis (Bt) cotton at a higher rate than their less efficient peers. This suggests that cross-sectional estimates of the yield effect of Bt cotton, which do not control for self-selection effects, are likely to be biased upwards. However, after controlling for selection bias, we still find that there is a significant positive yield effect from adoption of Bt cotton that more than offsets the additional cost of Bt seed. [source] Variability of Endotoxin Expression in Bt Transgenic CottonJOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 1 2007H. Z. Dong Abstract Transgenic cotton expressing Bt (Bacillus thuringiensis) toxins is currently cultivated on a large commercial scale in many countries, but observations have shown that it behaves variably in toxin efficacy against target insects under field conditions. Understanding of the temporal and spatial variation in efficacy and the resulting mechanisms is essential for cotton protection and production. In this review, we summarize current knowledge on variability in Bt cotton efficacy, in particular on the induced variability by environmental stresses. We also discuss the resulting mechanisms and the countermeasures for the inconsistence in efficacy in Bt cotton. It is indicated that insecticidal protein content in Bt cotton is variable with plant age, plant structure or under certain environmental stresses. Variability in Bt cotton efficacy against target insect pests is mainly attributed to the changes in Bt protein content, but physiological changes associated with the production of secondary compounds in plant tissues may also play an important role. Reduction of Bt protein content in late-season cotton could be due to the overexpression of Bt gene at earlier stages, which leads to gene regulation at post-transcription levels and consequently results in gene silencing at a later stage. Methylation of the promotor may be also involved in the declined expression of endotoxin proteins. As a part of total protein, the insecticidal protein in plant tissues changes its level through inhibited synthesis, degradation or translocation to developing plant parts, particularly under environmental stresses, thus being closely correlated to N metabolism. It can be concluded that developing new cotton varieties with more powerful resistance, applying certain plant growth regulators, enhancing intra-plant defensive capability, and maintenance of general health of the transgenic crop are important in realizing the full transgenic potential in Bt cotton. [source] Spatial and temporal variability in host use by Helicoverpa zea as measured by analyses of stable carbon isotope ratios and gossypol residuesJOURNAL OF APPLIED ECOLOGY, Issue 3 2010Graham Head Summary 1.,A high dose/refuge strategy has been adopted in the USA to manage the risk of Bacillus thuringiensis (Bt) resistance in target pests such as the cotton bollworm (CBW), Helicoverpa zea (Boddie) in transgenic Bt cotton Gossypium hirsutum L. Structured refuges, consisting of non-Bt cotton, have been a mandated part of this strategy to produce non-selected insects that are temporally and spatially synchronous with insects from the Bt crop, diluting Bt resistance alleles through mating. However, the bollworm is highly polyphagous and exploits a large number of crop and weedy hosts concurrently with Bt cotton. 2.,A study was carried out in five major US cotton-producing states during 2002 and 2003 using the ratios of 13C to 12C in bollworm moths to estimate the proportions of the population originating from C3 or C4 plants. A separate study measured gossypol residues in moths from four states in 2005 and 2006, enabling the identification of moths whose natal hosts were cotton rather than other C3 hosts. 3.,C4 hosts served as the principal source of bollworm moths from mid-to-late June to early September, depending on the state. Beginning in late August/early September and lasting 1,4 weeks, the majority of moths exhibited isotopic compositions characteristic of C3 hosts. During this period, however, the minimum percentage of moths that developed as larvae on C4 hosts was typically >25%. By mid-September and through October and November, the majority of the bollworm population exhibited C4 isotopic compositions. 4.,Between late June and early August, cotton-derived bollworm moths (moths with gossypol residues) comprised <1% of moths in all states, and remained below this level throughout the season in North Carolina. In other states, cotton-derived moths increased between early August and early September to peak at an average of 19·1% of all moths. 5.,Synthesis and applications.,Data on 13C/12C ratios and gossypol residues in CBW moths were used to assess the importance of structured non-Bt cotton refuges for the management of Bt resistance risk in H. zea. Weekly estimates of bollworm breeding on cotton, C3 plants other than cotton and C4 plants showed that, throughout the season, the majority of bollworm moths caught in pheromone traps adjacent to cotton fields did not develop as larvae on cotton. This result implies that management practices in cotton such as the use of structured cotton refuges will play a relatively minor role , particularly compared with maize Zea mays L. , in managing potential resistance to Bt cotton in populations of the CBW in the US Cotton Belt. [source] Response of multiple generations of beet armyworm, Spodoptera exigua (Hübner), feeding on transgenic Bt cottonJOURNAL OF APPLIED ENTOMOLOGY, Issue 2 2009G. Wu Abstract Development, reproduction and food utilization of three successive generations of beet armyworm, Spodoptera exigua (Hübner), fed on transgenic and non-transgenic Bt cotton were examined. Significantly longer larval life-span and lower pupal weight were observed in three successive generations of S. exigua fed on transgenic Bt cotton compared with non-transgenic Bt cotton. Significantly higher survival rate and adult fecundity of S. exigua were found in three successive generations of S. exigua fed on transgenic Bt cotton compared with non-transgenic Bt cotton. The survival rate and adult fecundity of S. exigua were occurred significant increase in the third generation compared with the first generation after feeding on transgenic Bt cotton. Significantly lower consumption, frass and relative growth rate (RGR) were observed in three successive generations of S. exigua fed on transgenic Bt cotton compared with non-transgenic Bt cotton. Cotton variety significantly affected all indices of larval consumption and utilization in three successive generations of S. exigua, except for efficiency of conversion of ingested food. However, beet armyworm generation only significantly affected RGR of S. exigua. The results of this study indicated food quality on the diet-utilization efficiency of S. exigua was different along with beet armyworm generation. Measuring multigenerational development and food utilization of S. exigua at individual and population level in response to Bacillus thuringiensis (Bt) can provide a more meaningful evaluation of long-term population dynamics than experiments on a single generation. It is imperative to develop an appropriate multigenerational pest management tactic to monitor the field population dynamics of non-target pests (e.g., beet armyworm) in agricultural Bt cotton ecosystem. [source] Effects of Bt-toxin Cry1Ac on Propylaea japonica Thunberg (Col., Coccinellidae) by feeding on Bt-treated Bt-resistant Helicoverpa armigera (Hübner) (Lep., Noctuidae) larvaeJOURNAL OF APPLIED ENTOMOLOGY, Issue 4 2006S.-Y. Zhang Abstract:,Propylaea japonica is an important predatory insect of common cotton pests. To assess the ecological effects of transgenic Bt cotton, expressing Cry1Ac toxin, on this predator, we examined the life history parameters of P. japonica for two generations by feeding them with Bt-resistant Helicoverpa armigera. After ingesting Bt-treated Bt-resistant H. armigera larvae in the third and fourth instar, the body mass and body length of adult P. japonica decreased, a combined effect of poor prey quality and Cry1Ac Bt-toxin may account for these effects. However, larval survivorship and development in these two instars, pupal mortality, fecundity and adult longevity of P. japonica were not affected in both the generations. These results suggest that ingesting Bt-toxin Cry1Ac-treated pests in advanced larval stage might have no significant effect on the fitness of predator P. japonica. [source] Modelling the spatial configuration of refuges for a sustainable control of pests: a case study of Bt cottonJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 3 2003C. Vacher Abstract The ,high-dose-refuge' (HDR) strategy is widely recommended by the biotechnology industry and regulatory authorities to delay pest adaptation to transgenic crops that produce Bacillus thuringiensis (Bt) toxins. This involves cultivating nontoxic plants (refuges) in close proximity to crops producing a high dose of Bt toxin. The principal cost associated with this strategy is due to yield losses suffered by farmers growing unprotected, refuge plants. Using a population genetic model of selection in a spatially heterogeneous environment, we show the existence of an optimal spatial configuration of refuges that could prevent the evolution of resistance whilst reducing the use of costly refuges. In particular, the sustainable control of pests is achievable with the use of more aggregated distributions of nontransgenic plants and transgenic plants producing lower doses of toxin. The HDR strategy is thus suboptimal within the context of sustainable agricultural development. [source] Expression of Bacillus thuringiensis Cry1Ac protein in cotton plants, acquisition by pests and predators: a tritrophic analysisAGRICULTURAL AND FOREST ENTOMOLOGY, Issue 3 2006Jorge B. Torres Abstract 1.,Studies have shown that Cry proteins of the bacterium Bacillus thuringiensis expressed in transgenic plants can be acquired by nontarget herbivores and predators. A series of studies under field and controlled conditions was conducted to investigate the extent to which Cry1Ac protein from Bt transgenic cotton reaches the third trophic level and to measure the amount of protein that herbivores can acquire and expose to predators. 2.,Levels of Cry1Ac in Bt cotton leaves decreased over the season. Among herbivores (four species), Cry1Ac was detected in lepidopteran larvae and the amount varied between species. Among predators (seven species), Cry1Ac was detected in Podisus maculiventris and Chrysoperla rufilabris. 3.,In the greenhouse, only 14% of the Cry1Ac detected in the prey (Spodoptera exigua larvae) was subsequently found in the predator P. maculiventris. Detection of Cry1Ac protein in Orius insidiosus, Geocoris punctipes and Nabis roseipennis was probably limited by the amount of prey consumed that had fed on Bt cotton. 4.,Purified Cry1Ac was acquired by the small predatory bug G. punctipes but at much higher concentration than found in plants or in lepidopteran larvae. 5.,Bt protein was shown to move through prey to the third trophic level. Predatory heteropterans acquired Cry1Ac from prey fed Bt cotton, but acquisition was dependent on the concentration of Cry1Ac conveyed by the prey and the amount of prey consumed. The type and availability of prey capable of acquiring the protein, coupled with the generalist feeding behaviour of the most common predators in the cotton ecosystem, probably constrain the flow of Cry1Ac through trophic levels. [source] Effects of Elevated Carbon Dioxide on the Growth and Foliar Chemistry of Transgenic Bt CottonJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 9 2007Gang Wu Abstract A field study was carried out to quantify plant growth and the foliar chemistry of transgenic Bacillus thuringiensis (Bt) cotton (cv. GK-12) exposed to ambient CO2 and elevated (double-ambient) CO2 for different lengths of time (1, 2 and 3 months) in 2004 and 2005. The results indicated that CO2 levels significantly affected plant height, leaf area per plant and leaf chemistry of transgenic Bt cotton. Significantly, higher plant height and leaf area per plant were observed after cotton plants that were grown in elevated CO2 were compared with plants grown in ambient CO2 for 1, 2 and 3 months in the investigation. Simultaneously, significant interaction between CO2 level × investigating year was observed in leaf area per plant.Moreover, foliar total amino acids were increased by 14%, 13%, 11% and 12%, 14%, 10% in transgenic Bt cotton after exposed to elevated CO2 for 1, 2 or 3 months compared with ambient CO2 in 2004 and 2005, respectively. Condensed tannin occurrence increased by 17%, 11%, 9% in 2004 and 12%, 11%, 9% in 2005 in transgenic Bt cotton after being exposed to elevated CO2 for 1, 2 or 3 months compared with ambient CO2 for the same time. However, Bt toxin decreased by 3.0%, 2.9%, 3.1% and 2.4%, 2.5%, 2.9% in transgenic Bt cotton after exposed to elevated CO2 for 1, 2 or 3 months compared with ambient CO2 for same time in 2004 and 2005, respectively. Furthermore, there was prominent interaction on the foliar total amino acids between the CO2 level and the time of cotton plant being exposed to elevated CO2. It is presumed that elevated CO2 can alter the plant growth and hence ultimately the phenotype allocation to foliar chemistical components of transgenic Bt cotton, which may in turn, affect the plant-herbivore interactions. [source] | |||||||||||||