A single dominant gene for resistance to the soybean aphid in the soybean cultivar Dowling

The soybean aphid (Aphis glycines Matsumura), a new pest of soybean [Glycine max (L.) Merr.], rapidly spread throughout North America after its arrival in 2000 and caused millions of dollars in economic losses. At present, the application of insecticides is the only means to control the soybean aphid. However, genetic resistance to the aphid was recently discovered in soybean germplasm and the soybean cultivar Dowling was identified as having strong antibiosis-type aphid resistance. The objective of this study was to determine the inheritance of resistance to the soybean aphid in Dowling. Resistance in F-1, F-2, and F-2-derived F-3 (F-2:3) families from crosses between Dowling and the two susceptible soybean cultivars Loda and Williams 82 was analyzed. All F-1 plants were resistant to the aphid. Heterogeneity of segregation of F-2 plants in 14 Dowling x Loda F-2 families was nonsignificant (P = 0.16), and pooled F-2 data, with 132 resistant to 45 susceptible plants, fit a 3:1 ratio (P = 0.90). F-2 plants from Dowling x Williams 82 segregated 135 resistant to 44 susceptible, also fitting a 3:1 ratio (P = 0.89). Segregation among the F-2:3 families fit a 1:2:1 monogenic inheritance pattern. These results indicated that a single dominant gene named Rag1 controlled resistance in Dowling. The monogenic dominant nature of resistance will enable breeders to rapidly convert existing susceptible cultivars to resistant cultivars using backcrossing procedures.