Aphis glycines Matsumura (Hemiptera: Aphididae) can reduce the yield of aphidsusceptible soybean (Glycine max (L.) Merrill) cultivars. The Rag1 and Rag2 genes confer resistance to some biotypes of A. glycines. These genes individually can limit population growth of A. glycines and prevent yield loss. The impact of these genes when combined is not known. We compared the development of A. glycines on soybean with Rag1 alone (R1/S2), Rag2 alone (S1/R2), both genes combined (R1/R2), or neither gene (S1/S2). In addition, we determined the impact of different levels of aphid infestation on seed yield. The genotypes were grown in cages and artificially infested with A. glycines to achieve five treatment levels: aphid-free, 675 aphids per plant, 25,000 cumulative aphid days (CAD) (25K), 50,000 CAD (50K), and 75,000 CAD (75K). The S1/S2 line reached the 50K treatment, but did not reach the 75K treatment. Aphid development on R1/S2 and S1/R2 soybeans after two infestations reached a maximum of 25K. The maximum treatment reached on R1/R2 was only 675 aphids per plant after two infestations, at which there was no significant yield reduction when compared with the aphid-free treatment. The maximum yield reduction of S1/S2 was 27% at 50K treatment compared with 2% for R1/S2 and 12% for S1/R2 at the 25K treatment. Our results indicated that for A. glycines used in our study, cultivars with both Rag1 and Rag2 had less aphid exposure and less yield reduction than soybeans with only one resistant gene.
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