Next generation transgenic IR products in soybeans

Intacta RR2 Pro®, the first transgenic insect-protected soybean product, was commercialized in Brazil and Argentina by Monsanto in 2013. This product provides season-long control of several key lepidopteran soybean pests, including Anticarsia gemmatalis (Hübner) and Chrysodeixis includens (Walker), through expression of a synthetic, Cry1A-like protein from Bacillus thuringiensis. Despite the level of control provided against these pests, the use of a single insecticidal protein requires that a “high-dose/refuge” insect resistance management (IRM) strategy be implemented to lower the chance that insects will develop resistance to the product. In addition, the Cry1A protein expressed by Intacta provides little control of Spodoptera spp., which can occasionally reach economically damaging levels in soybean. To further minimize the risk that insects will develop resistance and to expand the spectrum of pests controlled, Monsanto is developing a second-generation transgenic insect-protected soybean that expresses two additional Cry proteins from B. thuringiensis. The proteins have modes-of-action that are different from each other and from the Cry1A protein in Intacta, making them useful in a “stacked toxin” IRM strategy that reduces reliance on structured refuge. Second-generation soybean by itself and in breeding stacks with Intacta has exhibited a high degree of protection from a wide variety of lepidopteran pests in artificially-infested screenhouses and naturally-infested field trials in the U.S. and Argentina across multiple seasons. The spectrum of pests controlled includes several Spodoptera spp. that are not well-controlled by Intacta alone. Diet dilution bioassays using lyophilized leaf tissues from second-generation soybean, soybean plants expressing single proteins, and breeding stacks with second-generation soybean and Intacta showed no evidence of substantial synergistic or antagonistic effects among co-expressed proteins that could compromise their activity against key target pests and, thus, reduce the effectiveness of a stacked toxin IRM strategy. Second-generation insect-protected soybean has the potential to not only further reduce applications of chemical insecticides, but also offer increased durability by further minimizing the risk that insects will develop resistance.