Soybean aphid resistance in soybean germplasm accessions of maturity group I

Soybean aphid (SA; Aphis glycines Matsumura) is a major pest of soybean [Glycine max (L.) Merr.] in North America, particularly the northern United States. Identification of SA resistance in early-maturing soybeans will facilitate development of aphid-resistant cultivars for this region. In this study, 330 soybean germplasm accessions from Maturity Group (MG) I, along with 11 resistant or susceptible checks, were evaluated against SA in greenhouse by caged (no-choice) and noncaged tests. Germplasm accessions that showed resistance in these tests were then tested in the field under natural infestations supplemented by artificial inoculation. In the greenhouse tests, accessions PI 189946, PI 153214, and PI 437075 exhibited low SA levels (<50 aphids plant^-11 in caged test and SA score of 1.3 or less in noncaged test) similar to those on resistant checks. Six accessions (PI 378663, PI 603587A, PI 567250A, PI 603326, PI 603339A, and PI 603546A) showed moderate aphid resistance with <135 aphids plant^-11 in caged and SA score of 2.3 or less in noncaged test. In the field, PI 567250A and PI 603339A performed similar to resistant checks, and PI 153214 and PI 437075 showed moderate aphid resistance. Across all three tests, PI 567250A and PI 603339A exhibited consistently low levels of aphid infestation and thus may be useful in soybean breeding as newly identified sources of SA resistance.