Submitted to: Theoretical and Applied Genetics
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/21/2007
Publication Date: 12/7/2007
Citation: Zhu, S., Walker, D.R., Boerma, H.R., All, J.N., Parrott, W.A. 2007. Effects of Defoliating Insect Resistance QTLs and a crylAc Transgene in Soybean Near-Isogenic Lines. Theoretical and Applied Genetics. 16:455-463. Interpretive Summary: Bacillus thuringiensis (Bt) transgenes such as cry1Ac that are genetically engineered into plants to provide high levels of resistance to certain insect pests, but precautions are needed to prevent pests from quickly overcoming this resistance. Native insect resistance was identified in three Japanese plant introductions (PIs) almost 40 years ago, but efforts to transfer this resistance to high-yielding cultivars have been only moderately successful. Three quantitative trait loci (QTLs) with genes conditioning insect resistance in PI 229358 have been genetically mapped and tagged with DNA markers which were used to transfer the resistance genes into the soybean cultivar Benning. Two of these QTLs reduced feeding damage and/or the larval weights of two major soybean pests, corn earworm and soybean looper. The third QTL did not confer resistance directly, but was found to enhance resistance through interaction with genes at the other two loci. These results support findings from earlier experiments indicating that combining one or more of the QTLs in the same genetic background as a cry1Ac transgene may prolong the effectiveness of the Bt gene against insect pests. This information will be useful to plant breeders, entomologists, and other scientists interested in host plant resistance to insects.
Technical Abstract: Additional sources of resistance would be desirable to manage defoliating insect resistance to crystal proteins coded by transgenes from Bacillus thuringiensis (Bt) and to sustain the deployment of Bt crops. The objective of this study was to evaluate the effects and interactions of three soybean (Glycine max [L.] Merr.) insect resistance quantitative trait loci (QTLs; QTL-M, QTL-H, and QTL-G) originating from the Japanese PI 229358, and a Bt cry1Ac gene in a ‘Benning’ genetic background. A set of 16 BC6F2-derived near isogenic lines (NILs) was developed using marker-assisted backcrosses and evaluated against soybean looper (SBL, Pseudoplusia includens [Walker]) and corn earworm (CEW, Helicoverpa zea [Boddie]) in field cage, greenhouse, and detached leaf assays. Both Bt and QTL-M had a significant effect on reducing defoliation by both SBL and CEW and larval weight of CEW in the Benning genetic background. The antibiosis QTL-G had a significant effect on reducing CEW larval weight, and also a significant effect on reducing defoliation by SBL and CEW in some assays. The antixenosis QTL-H had no main effect, but it appeared to function through interaction with QTL-M and QTL-G. Adding QTL-H and QTL-G further enhanced the resistance of the Bt and QTL-M combination towards CEW in the field cage assay. These results should help guide the development of strategies for effective management of insect pests and for sustainable deployment of Bt genes.