Bacillus thuringiensis (Bt) crops require a high dosage of Bt toxin to delay development of insect resistance, in particular, when the refuge strategy is applied. This strategy is threatened by plant developmental and environmental factors that might reduce Bt toxin concentration and Bt efficacy in Bt crops. Growth of Bt (Cry1Ac) cotton under prolonged, moderate water deficit as a single stress factor was evaluated. Bt cotton plants were analysed for physiological performance, Bt toxin concentration and Bt efficacy. For performance analysis, leaf and total plant dry weight and leaf area were measured. Bt toxin concentration was determined by an immuno‐assay. Effects of Bt toxin on growth and mortality of African cotton bollworm, Helicoverpa armigera, larvae were measured in different plant organs. Leaves from young plants exposed for 30 days to moderate water deficit had both higher Bt toxin concentrations and were more effective against larvae than leaves, flowers or bolls from mature flowering plants exposed to 60 days of moderate water deficit. Although growth of Bt cotton plants under moderate water‐deficit conditions decreased Bt concentrations in leaves, flowers and bolls, this had no effect on efficacy against first‐instar cotton bollworm larvae. No significant evidence was found that moderate water deficit, as a single stress factor, decreases Bt efficacy in Bt cotton.
In the framework of a gene flow assessment, we investigated the natural hybridization rate between Gossypium hirsutum (AADD genome) and G. herbaceum (AA genome). The latter species, a diploid progenitor of G. hirsutum, is spontaneously present in South Africa. Reciprocal crosses were performed without emasculation between G. herbaceum and G. hirsutum. Neither examination of the morphological characteristics nor flow cytometry analysis of the 335 plants resulting from the G. hirsutum × G. herbaceum cross showed any hybrid features. Of the 148 plants produced from the G. herbaceum × G. hirsutum cross, three showed a hybrid phenotype, and their hybrid status was confirmed by SSR markers. Analysis of DNA content by flow cytometry and morphological traits clearly showed that two of these plants were triploid (AAD). The third plant had a flow cytometry DNA content slightly higher than G. hirsutum. In addition, its morphological characteristics (plant architecture, presence and size of petal spots, leaf shape) led us to conclude that this plant was AAAD thus resulting from fertilization with an unreduced AA gamete of the female G. herbaceum parent. Fluorescent In Situ Hybridization (FISH) and meiotic behavior confirmed this hypothesis. To the best of our knowledge, this is the first description of such gametes in G. herbaceum, and it opens new avenues in breeding programs. Furthermore, this plant material could provide a useful tool for studying the expression of genes duplicated in the A and D cotton genome.
Si l'utilisation du coton génétiquement modifié (CGM) en Afrique du Sud, depuis 1996-1997, est le plus souvent présentée comme un succès d'adoption d'OGM par les petits paysans de pays en développement, c'est une présentation qui occulte le fait que la production cotonnière est d'abord celle des fermiers blancs. Le succès du CGM dans ce pays est aussi tout relatif car la production continue à décliner et la part des petits paysans noirs reste toujours aussi faible. Le cas de l'Afrique du Sud montre que la seule introduction d'une technologie nouvelle ne suffit pas pour assurer la progression de la production à l'échelle du pays. Des facteurs d'ordre institutionnel interviennent, mais la focalisation exclusive sur le CGM les occulte. Nos travaux fondés sur une enquête récente mettent en évidence une mauvaise rentabilité dans une année défavorable sur le plan climatique et institutionnel. Dans des conditions plus favorables, la rentabilité est meilleure, mais avec un risque financier accru. Rares sont les pays de l'Afrique Zone Franc présentant aujourd'hui une stabilité institutionnelle favorable à l'introduction du CGM. Celle-ci nécessite préparation notamment pour négocier des conditions économiques favorables de transfert de la biotechnologie et pour une réorganisation de la distribution de semences préservant les intérêts des paysans. Les difficultés associées à cette préparation mettent en garde contre une adoption précipitée. Beaucoup d'études récentes démontrent l'efficacité et la rentabilité des variétés génétiquement modifiées en agriculture (EDEN, SLINSKY, LARSON, ROBERTS et * CIRAD-UPR 10, TA 72/09.
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