The associated effects of the soybean aphid resistance locus rag1 on soybean yield and other agronomic traits
The soybean aphid (Aphis glycines Matsumura) is a new invasive soybean [Glycine max (L.) Merr.] insect pest first identified in North America in 2000. A major aphid resistance gene Rag1 was identified and mapped from the maturity group VIII cultivar Dowling, and the gene has been introgressed into Midwest-adapted germplasm. The objective of this study was to test the associated effects of Rag1 on yield and several important agronomic traits in two elite Midwest-adapted soybean backgrounds. To do this, we tested two backcross populations that segregate for Rag1 with simple sequence repeat markers linked to the gene in field tests conducted in multiple environments with no detectable soybean aphid infestations. Across environments, Rag1 had no significant (P = 0.05) associated effects on yield, plant height, and lodging score in either population. However, Rag1 was significantly associated with a 2-d delay in maturity in one population. This delay in maturity is likely caused by linkage drag between Rag1 and gene(s) that delayed maturity. These results indicate that breeders can incorporate Rag1 into Midwest-adapted backgrounds without an associated yield reduction.