Laboratory and Field Evaluations of Transgenic Soybean Exhibiting High-Dose Expression of a Synthetic Bacillus thuringiensis cry1A Gene for Control of Lepidoptera

Abstract

Transgenic lines of soybean, Glycine max (L.) Merrill, expressing a synthetic cry1A gene (tic107) from Bacillus thuringiensis (Bt), were evaluated in screenhouse and conventional field trials for efficacy against lepidopteran pests. In screenhouse trials, Bt soybean and negative checks (isogenic segregants and parental lines) were evaluated against Anticarsia gemmatalis Hübner and Pseudoplusia includens (Walker) in the United States and against A. gemmatalis, Epinotia aporema (Walsingham), Rachiplusia nu (Guenée), and Spilosoma virginica (F.) in Argentina. Bt soybean exhibited virtually complete efficacy against each of these pests, whereas negative checks suffered significant damage. Bt soybean and negative checks also were evaluated in conventional trials against native populations of A. gemmatalis and P. includens in the southeastern United States. Each of these insects caused significant damage to negative checks in one or more locations, whereas Bt soybean exhibited virtually complete efficacy against these pests. In the laboratory, lyophilized leaf tissues from Bt soybean incorporated in artificial diet at a concentration representing a 25-fold dilution of fresh tissue caused complete mortality of A. gemmatalis and near complete mortality of P. includens neonates after 11 d, whereas mortality on negative checks did not exceed 10% for either insect. Average TIC107 expression approached or exceeded 50 microg/g fresh weight at V3 stage of growth and 200 microg/g by R6 stage of growth. These results demonstrate that expression of TIC107 in soybean can not only achieve highly efficacious control of several lepidopterans under field conditions but also provide a high dose for effective insect resistance management.

Genetically modified soybean expressing insecticidal protein (Cry1Ac): Management risk and perspectives

“…The Cry1Ac protein is expressed in leaves, pollen/anthers, seeds, and pods, but not roots. The high-dose expression (25 times the amount required to kill 99% of a susceptible population) and concentration in the leaves can reach approximately 450 μg/g of the dry weight (MacRae et al 2005). …”

Resistance to Anticarsia gemmatalis Hübner (Lepidoptera, Noctuidae) in transgenic soybean (Glycine max (L.) Merrill Fabales, Fabaceae) cultivar IAS5 expressing a modified Cry1Ac endotoxin

“…It has been reported that a transgenic line of the soybean cultivar Jack expressing high levels of synthetic cry1Ac killed all A. gemmatalis larvae and significantly reduced the survival and feeding of the soybean looper (Pseudoplusia includens) and the corn earworm (Helicoverpa zea) in laboratory bioassays (Stewart et al, 1996) and in artificially infested field cages (Walker et al, 2000). More recently, Macrae et al (2005) evaluated transgenic soybean lines (based on cultivar A5547) expressing synthetic cry1A for resistance against several lepidopteran pests in screenhouse and conventional field trials carried out in the United States and Argentina and found that the Bt lines exhibited virtually complete efficacy against all the pests evaluated.…”

“…The velvetbean caterpillar (Anticarsia gemmatalis Hübner) is a major soybean pest, mainly occurring in soybean growing regions of North and South America (Panizzi and Corrêa-Ferreira, 1997;Macrae et al, 2005), causes extremely high levels of defoliation when infestation is heavy and can severely damage axillary meristems, with a single caterpillar being able to consume up to 110 cm 2 of soybean foliage (Walker et al, 2000). However, various authors have reported that A. gemmatalis can be controlled by the delta-endotoxin (δ-endotoxin) produced by some strains of Bacillus thuringiensis (Stewart et al,1996;Walker et al, 2000;Macrae et al, 2005).…”

Genetic Study on Resistance to the Common Cutworm and Other Leaf-eating Insects in Soybean

“…The search for resistant germplasms and investigation of their resistance mechanisms preceded such studies in Japan. Although transgenic crops are generally accepted in the United States, the effects of the transgene alone is not always sufficient for effective pest management 33,34,48 . Because these researchers believed that very high production of the Bt protein was needed to prevent the development of Bt-resistant insects, the native resistance of soybeans is also being used in breeding programs as a means of preventing the development of Bt resistance 51,52 .…”