Temporal Expression of Cry1Ab/c Protein in Bt-Cotton Varieties, their Efficacy against Helicoverpa armigera (Lepidoptera: Noctuidae) and Population Dynamics of Sucking Arthropods on Them (original) (raw)
Related papers
The quantitative levels of Cry1Ac and the seasonal decline in expression differed significantly among the eight commercial Bollgard hybrids tested. The Cry1Ac expression was found to be variable among the hybrids and also between different plant parts. The leaves of Bt-cotton plants were found to have the highest levels of Cry1Ac expression followed by squares, bolls and flowers. The toxin expression in the boll-rind, square bud and ovary of flowers was clearly inadequate to confer full protection to the fruiting parts. Increasing levels of Helicoverpa armigera survival were correlated with the toxin levels decreasing below 1.8 µ µg/g in the plant parts. Genotype-independent seasonal decline of the Cry1Ac toxin levels was observed in all the hybrids. Cry1Ac expression decreased consistently as the plant aged. The decline in Cry1Ac was more rapid in some hybrids compared to others. The choice of parental background appeared to be crucial for sustainable expression of the cry1Ac transgene. The implications of variability in Cry1Ac expression and the seasonal decline on bollworm management are discussed.
Journal of Economic Entomology, 2008
Cry1Ac protoxin (the active insecticidal toxin in both Bollgard and Bollgard II cotton [Gossypium hirsutum L.]), and Cry2Ab2 toxin (the second insecticidal toxin in Bollgard II cotton) were bioassayed against Þve of the primary lepidopteran pests of cotton by using diet incorporation. Cry1Ac was the most toxic to Heliothis virescens (F.) and Pectinophora gossypiella (Saunders), demonstrated good activity against Helicoverpa zea (Boddie), and had negligible toxicity against Spodoptera exigua (Hü bner) and Spodoptera frugiperda (J. E. Smith). Cry2Ab2 was the most toxic to P. gossypiella and least toxic to S. frugiperda. Cry2Ab2 was more toxic to S. exigua and S. frugiperda than Cry1Ac. Of the three insect species most sensitive to both Bacillus thuringiensis (Bt) proteins (including H. zea), P. gossypiella was only three-fold less sensitive to Cry2Ab2 than Cry1Ac, whereas H. virescens was 40-fold less sensitive to Cry2Ab2 compared with Cry1Ac. Cotton plants expressing Cry1Ac only and both Cry1Ac and Cry2Ab2 proteins were characterized for toxicity against H. zea and S. frugiperda larvae in the laboratory and H. zea larvae in an environmental chamber. In no-choice assays on excised squares from plants of different ages, second instar H. zea larvae were controlled by Cry1Ac/Cry2Ab2 cotton with mortality levels of 90% and greater at 5 d compared with 30 Ð 80% mortality for Cry1Ac-only cotton, depending on plant age. Similarly, feeding on leaf discs from Cry1Ac/Cry2Ab2 cotton resulted in mortality of second instars of S. frugiperda ranging from 69 to 93%, whereas exposure to Cry1Ac-only cotton yielded 20 Ð 69% mortality, depending on plant age. When cotton blooms were infested in situ in an environmental chamber with neonate H. zea larvae previously fed on synthetic diet for 0, 24, or 48 h, 7-d ßower abortion levels for Cry1Ac-only cotton were 15, 41, and 63%, respectively, whereas for Cry1Ac/Cry2Ab2 cotton, ßower abortion levels were 0, 0, and 5%, respectively. Cry1Ac and Cry2Ab2 concentrations were measured within various cotton tissues of Cry1Ac-only and Cry1Ac/Cry2Ab2 plants, respectively, by using enzyme-linked immunosorbent assay. Terminal leaves signiÞcantly expressed the highest, and large leaves, calyx, and bracts expressed signiÞcantly the lowest concentrations of Cry1Ac, respectively. Ovules expressed signiÞcantly the highest, and terminal leaves, large leaves, bracts, and calyx expressed signiÞcantly (P Ͻ 0.05) the lowest concentrations of Cry2Ab2. These results help explain the observed differences between Bollgard and Bollgard II mortality against the primary lepidopteran cotton pests, and they may lead to improved scouting and resistance management practices, and to more effective control of these pests with Bt transgenic crops in the future.
Journal of Chemical Ecology, 2009
Larvae of the bollworm Helicoverpa zea (Boddie) show some tolerance to Bacillus thuringiensis (Bt) Cry1Ac, and can survive on Cry1Ac-expressing Bt cotton, which should increase resistance development concerns. However, field-evolved resistance has not yet been observed. In a previous study, a population of H. zea was selected for stable resistance to Cry1Ac toxin. In the present study, we determined in laboratory bioassays if larvae of the Cry1Ac toxin-resistant H. zea population show higher survival rates on field-cultivated Bt cotton squares (= flower buds) collected prebloom-bloom than susceptible H. zea. Our results show that Cry1Ac toxin-resistant H. zea cannot complete larval development on Cry1Ac-expressing Bt cotton, despite being more than 150-fold resistant to Cry1Ac toxin and able to survive until pupation on Cry1Ac toxin concentrations greater than present in Bt cotton squares. Since mortality observed for Cry1Ac-resistant H. zea on Bt cotton was higher than expected, we investigated whether Cry1Ac interacts with gossypol and or other compounds offered with cotton powder in artificial diet. Diet incorporation bioassays were conducted with Cry1Ac toxin alone, and with gossypol and 4% cotton powder in the presence and absence of Cry1Ac. Cry1Ac toxin was significantly more lethal to susceptible H. zea than to resistant H. zea, but no difference in susceptibility to gossypol was observed between strains. However, combinations of Cry1Ac with gossypol or cotton powder were synergistic against resistant, but not against susceptible H. zea. Gossypol concentrations in individual larvae showed no significant differences between insect strains, or between larvae fed gossypol alone vs. those fed gossypol plus Cry1Ac. These results may help explain the inability of Cry1Ac-resistant H. zea to complete development on Bt cotton, and the absence of field-evolved resistance to Bt cotton by this pest.
Journal of Economic Entomology, 2005
The insertion of genes encoding insecticidal Cry1A ␦-endotoxins from the bacterium Bacillus thuringiensis Berliner variety kurstaki (Bt) into varieties of cotton (Gossypium spp.) was undertaken to assist in the control of a range of lepidopteran pests. In Australia, where Helicoverpa armigera (Hü bner) and Helicoverpa punctigera (Wallengren) are major pests, the level of control is useful, but not complete, because efÞcacy declines as the crop matures. Fluctuations in the efÞcacy of Bt cotton, to the extent that some insects survive, provide opportunities for H. armigera to develop resistance to the Bt toxin. Therefore, variations in the efÞcacy of Bt cotton need to be understood if we are to plan rational resistance management strategies to retard the rate of the development of resistance. We measured the changes in efÞcacy associated with plant development over the growing season, in the Þeld and glasshouse. In addition, the levels of Cry1Ac protein toxin and cry1Ac RNA were determined. In this Þrst demonstration of the relationship between these three factors, we found that the developmental decline in bioefÞcacy in Þeld-grown plants was associated with reduced cry1Ac transcript levels and Bt toxin levels in postsquaring cotton. In addition, changes in plant chemistry associated with the maturation of the cotton plant were observed to contribute to changes in the efÞcacy of Bt toxin. Results from the Þeld and glasshouse suggested that variations in efÞcacy within the growing season and between seasons also may be inßuenced by environmental factors.
Current Science, 2005
The quantitative levels of Cry1Ac and the seasonal decline in expression differed significantly among the eight commercial Bollgard hybrids tested. The Cry1Ac expression was found to be variable among the hybrids and also between different plant parts. The leaves of Bt-cotton plants were found to have the highest levels of Cry1Ac expression followed by squares, bolls and flowers. The toxin expression in the boll-rind, square bud and ovary of flowers was clearly inadequate to confer full protection to the fruiting parts. Increasing levels of Helicoverpa armigera survival were correlated with the toxin levels decreasing below 1.8 µ µg/g in the plant parts. Genotype-independent seasonal decline of the Cry1Ac toxin levels was observed in all the hybrids. Cry1Ac expression decreased consistently as the plant aged. The decline in Cry1Ac was more rapid in some hybrids compared to others. The choice of parental background appeared to be crucial for sustainable expression of the cry1Ac transgene. The implications of variability in Cry1Ac expression and the seasonal decline on bollworm management are discussed.
Bt cotton : A boon against insect resistance
2019
The cultivation of transgenic cotton is increased in a large scale since from its introduction globally. Bacillus thuringiensis is produced crystalline proteins, these proteins were used in transgenic cotton to control insect pest. Resistance in insects is a major problem in transgenic cotton growing regions in all over the world especially, pink boll worm developed resistance in all major cotton regions in India. It was noticed in our studies that the expression levels of Cry1Ac in different plant parts such as upper leaves, lower leaves, sepals and boll bracts was increased while increasing refuge percentage. Planting refuge with alternatively with Bt cotton also increase the Cry1Ac expression levels compare with border refuge. An optimized unique combination of refuge crop viz., 75% Bt with 25% nBt showed higher expression level of Cry1Ac and highest yield was also achieved. This combination is useful to counter insect resistance and the staking of two toxin Cry proteins in same ...
Advance generations of different transgenic lines of locally approved cotton cultivar CIM-482 expressing two insecticidal genes (Cry1Ac and Cry2A) were confirmed for the integration and expression of insectidal genes, evaluated for the resistance against cotton boll worms especially american boll worm (Heliothis armerigera) under field condition for three consecutive years. Homozygous lines showing high insect resistance, morphological and agronomic characteristics were selected, risk assessment studies of these transgenic lines were also undertaken. Laboratory biotoxicity assays were performed to calculate the mortality %age of Heliothis larvae as a result of expression of insecticidal genes. Most of the transgenic lines showed up to 70-100% resistance against targeted insect pests. After artificial infestation of targeted insects, transgenic lines showed significant resistance levels. Data were recorded in terms of boll damage percentage. Morphological and yield data analysis were recorded. All the characters were stably inherited in advance generations. Experiments conducted to evaluated potential risk of transgenic lines on non target insects and soil organisms showed that these lines have no significant effect on non target insects (insects belonging to orders other than Lepidoptera). No any evidence of transgene flow was found from crop to soil organisms.
Emirates Journal of Food and Agriculture, 2011
The progenies of transgenic lines Bt-14 and Bt-17 developed as an independent transformation event from a local cotton variety CIM-482 harboring two insecticidal genes (cry1Ac & cry2a) were evaluated to determine resistance against lepidopterans, mainly Helicoverpa armigera L. under field conditions. The standard molecular techniques, i.e. polymerase chain reaction (PCR), enzyme-linked immunosorbent assay (ELISA) and western dot blot were used to confirm gene presence and expression level of transformed Bt gene, and its transfer pattern to further progeny. PCR confirmed integration of insecticidal gene in most of the plants in transgenic progeny, while expression of Bt gene quantified by ELISA and western dot blot showed variation in cry1Ac expression levels but interestingly, it conferred full protection against targeted insect pests. The leaf bioassays were conducted to determine the effectiveness of Bt genes against Helicoverpa armigera by calculating the mortality percentage of larvae. Most of the transgenic lines showed 70-100% mortality % age of Helicoverpa armigera. The agronomic characteristics of the transgenic lines were also recorded along with non transgenic control variety CIM-482. Morphological, agronomic and fibre data of these transgenic lines was recorded and analyzed statistically. Our results show that these transgenic lines (especially Bt-17 line) are promising cotton germplasm to be used in an efficient breeding programme.
Brazilian Archives of Biology and Technology, 2020
Development of transgenic Bt crops with stable and high level of Bt protein expression over generations under different environmental conditions is critical for successful deployment at field level. In the present study, progenies of transgenic cotton Coker310 event, CH12 expressing novel cry2AX1 gene were evaluated in T3 generation for stable integration, expression and resistance against cotton bollworm, Helicoverpa armigera. The cry2AX1 gene showed stable inheritance and integration in the T3 progeny plants as revealed by PCR and Southern blot hybridization. The expression of Cry2AX1 protein on 90 days after sowing (DAS) was in the range of 1.055 to 1.5 μg/g of fresh leaf tissue except one plant which showed 0.806 μg/g of fresh leaf tissue and after 30 days (i.e., on 120 DAS) three plants recorded in between 0.69 to 0.82 μg/g and other plants are in range of 0.918 to 1.058 μg/g of fresh leaf tissue. Detached leaf bit bioassay in T3 progeny on 110 DAS recorded mortality of 73.33 t...
Expression and Segregation of Genes Encoding CryIA Insecticidal Proteins in Cotton
Crop Science, 1998
Epistatic and environmental effects on foreign gene expression in cotton (Gossypium hirsutum L.) could influence the breeding, stability and, in the case of pest resistance, efficacy and durability of the foreign gene. This study was undertaken to characterize the expression and segregation of two foreign crylA genes in a range of insect-resistant cotton lines derived in three backgrounds. The crylA genes encoded insecticidal proteins from the bacterium Bacillus thuringiensis spp. kurstaki.