Evaluation location: Maryland, United States
Greenhouse study. Soybean accessions were spray inoculated between the first and second trifoliate stage using a mixture of urediniospores (60,000 spores per ml) from four Phakopsora pachyrhizi isolates, incubated overnight in a dew chamber at 22-25 C, and placed a greenhouse at 20-25 C for 14 days. Disease severity was evaluated on the first trifoliate leaves for most accessions, however the unifoliate leaves were evaluated for a few accessions with slow germination. A disease severity scale, based on symptom and lesion development on 1 to 5 scale, was used where 1 = no visible symptoms, 2 = light infection with few lesions present, 3 = light to moderate infection, 4 = moderate to severe infection, and 5 = severe infection. TAN, RB, or mixed lesion types were also recorded. The TAN lesion type is a susceptible reaction, while the RB or "reddish-brown" lesion type has been associated with resistance in the known single genes. The mixed reaction was recorded when both RB and TAN lesions were observed on the same leaf.