Pyramiding Bt genes for increasing resistance of cotton to two major lepidopteran pests: Spodoptera litura and Heliothis armigera
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Spodoptera litura
Bacillus thuringiensis
Cry1Ac
Cry1Ac
Bacillus thuringiensis
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Bacillus thuringiensis
Cry1Ac
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Abstract Polycalin has been confirmed as a binding protein of the Cry toxins in a few Lepidoptera insects, but its function in the action mechanism of Cry1Ac and whether it is involved in resistance evolution are still unclear. In this study, Ligand blot and enzyme‐linked immunosorbent assays showed that Helicoverpa armigera polycalin could specifically interact with Cry1Ac with a high affinity ( K d = 118.80 nM). Importantly, antisera blocking polycalin in H. armigera larvae decreased the toxicity of Cry1Ac by 31.84%. Furthermore, the relative gene and protein expressions were lower in Cry1Ac‐resistant strain (LF60) than that in Cry1Ac‐susceptible strain (LF). These findings indicated that H. armigera polycalin was a possible receptor of Cry1Ac and may be contributed to the resistance to Cry1Ac.
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ABSTRACT Four subpopulations of a Plutella xylostella (L.) strain from Malaysia (F 4 to F 8 ) were selected with Bacillus thuringiensis subsp. kurstaki HD-1, Bacillus thuringiensis subsp. aizawai , Cry1Ab, and Cry1Ac, respectively, while a fifth subpopulation was left as unselected (UNSEL-MEL). Bioassays at F 9 found that selection with Cry1Ac, Cry1Ab, B. thuringiensis subsp. kurstaki , and B. thuringiensis subsp. aizawai gave resistance ratios of >95, 10, 7, and 3, respectively, compared with UNSEL-MEL (>10,500, 500, >100, and 26, respectively, compared with a susceptible population, ROTH). Resistance to Cry1Ac, Cry1Ab, B. thuringiensis subsp. kurstaki , and B. thuringiensis subsp. aizawai in UNSEL-MEL declined significantly by F 9 . The Cry1Ac-selected population showed very little cross-resistance to Cry1Ab, B. thuringiensis subsp. kurstaki , and B. thuringiensis subsp. aizawai (5-, 1-, and 4-fold compared with UNSEL-MEL), whereas the Cry1Ab-, B. thuringiensis subsp. kurstaki -, and B. thuringiensis subsp. aizawai -selected populations showed high cross-resistance to Cry1Ac (60-, 100-, and 70-fold). The Cry1Ac-selected population was reselected (F 9 to F 13 ) to give a resistance ratio of >2,400 compared with UNSEL-MEL. Binding studies with 125 I-labeled Cry1Ab and Cry1Ac revealed complete lack of binding to brush border membrane vesicles prepared from Cry1Ac-selected larvae (F 15 ). Binding was also reduced, although less drastically, in the revertant population, which indicates that a modification in the common binding site of these two toxins was involved in the resistance mechanism in the original population. Reciprocal genetic crosses between Cry1Ac-reselected and ROTH insects indicated that resistance was autosomal and showed incomplete dominance. At the highest dose of Cry1Ac tested, resistance was recessive while at the lowest dose it was almost completely dominant. The F 2 progeny from a backcross of F 1 progeny with ROTH was tested with a concentration of Cry1Ac which would kill 100% of ROTH moths. Eight of the 12 families tested had 60 to 90% mortality, which indicated that more than one allele on separate loci was responsible for resistance to Cry1Ac.
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The temporal susceptibility of neonates of the American bollworm, Hellcoverpa armigera to Bacillus thuringiensis (Bt) var. kurstaki HD-73 or its Cry1Ac toxin in the artificial diet assays was investigated for the populations of four different locations. The insect populations, collected post-Bt cotton introduction, showed less susceptibility to Cry1 Ac/HD-73 in the artificial diet assays. The larval susceptibiilty to Cry1Ac in the cotton leaf dip assays was higher than in the artificial diet assays, possibly due to the synergism of Cry1Ac with cotton leaf allelochemicals. The toxicity of Bt cotton leaves to neonates of H. armigera remained high during the course of studies from 2204–2000. The absence of resistance to Bt cotton in H. armigera is discussed in relation to Bt resistance traits and current management practices.
Cry1Ac
Bacillus thuringiensis
Bt Cotton
Bollworm
Pink bollworm
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Cry1Ac
Bacillus thuringiensis
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ABSTRACT A laboratory strain (GY) of Helicoverpa armigera (Hübner) was established from surviving larvae collected from transgenic cotton expressing a Bacillus thuringiensis var. kurstaki insecticidal protein (Bt cotton) in Gaoyang County, Hebei Province, People's Republic of China, in 2001. The GYBT strain was derived from the GY strain through 28 generations of selection with activated Cry1Ac delivered by diet surface contamination. When resistance to Cry1Ac in the GYBT strain increased to 564-fold after selection, we detected high levels of cross-resistance to Cry1Aa (103-fold) and Cry1Ab (>46-fold) in the GYBT strain with reference to those in the GY strain. The GYBT strain had a low level of cross-resistance to B. thuringiensis var. kurstaki formulation (Btk) (5-fold) and no cross-resistance to Cry2Aa (1.4-fold). Genetic analysis showed that Cry1Ac resistance in the GYBT strain was controlled by one autosomal and incompletely recessive gene. The cross-resistance pattern and inheritance mode suggest that the Cry1Ac resistance in the GYBT strain of H. armigera belongs to “mode 1,” the most common type of lepidopteran resistance to B. thuringiensis toxins. A cadherin gene was cloned and sequenced from both the GY and GYBT strains. Disruption of the cadherin gene by a premature stop codon was associated with a high level of Cry1Ac resistance in H. armigera . Tight linkage between Cry1Ac resistance and the cadherin locus was observed in a backcross analysis. Together with previous evidence found with Heliothis virescens and Pectinophora gossypiella , our results confirmed that the cadherin gene is a preferred target for developing DNA-based monitoring of B. thuringiensis resistance in field populations of lepidopteran pests.
Cry1Ac
Bacillus thuringiensis
Strain (injury)
Heliothis virescens
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Spodoptera litura
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Bt cotton expressing Cry1Ac can efficiently control Helicoverpa armigera, but field-evolved Bt resistance reduces its efficacy. Susceptibility of H. armigera field populations to Cry1Ac protein has been monitored since Bt cotton was commercialized in 1997 in China. Here we report the results of our continued monitoring from 2005 to 2017 to provide important guidelines for sustainably growing cotton.From 13 provinces and regions, 221 populations were sampled and measured. IC50 values (concentration producing 50% inhibition of larval development to third instar) among different strains ranged from 0.004 to 0.212 µg mL-1 , the percentage survival at a diagnostic concentration (IC99 , 1.0 µg mL-1 ) (SUR) ranged from 0% to 22.2%, and the percentage of field populations yielding survivors at diagnostic concentration (PSD) increased from 0 in 2006 and 2007 to 80% in 2015.Compared to resistance level from 1998 to 2004 and the geographic baseline in different places of China in 1997, Bt resistance of H. armigera field populations to Cry1Ac protein has increased significantly, but failure of Bt cotton has not yet been detected. © 2018 Society of Chemical Industry.
Cry1Ac
Bt Cotton
Insecticide Resistance
Bacillus thuringiensis
Gossypium
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