Reaction of Soybean Rust-Resistant Lines Identified in Paraguay to Mississippi Isolates of Phakopsora pachyrhizi

Phakopsora pachyrhizi is the causal agent of Asian soybean rust (ASR). Since the discovery of ASR in North America in 2004, evaluation of soybean [Glycine max (L.) Merr.] lines with U.S. isolates has become an important objective to identify resistance sources to the pathogen. In this study, 10 plant introductions (PIs) previously identified as resistant in Paraguay were evaluated using three ASR isolates from Mississippi. Soybean cultivars Williams 82 and Freedom, and four PIs with known single genes for resistance to P. pachyrhizi also were included as susceptible and resistant checks, respectively. Replicated experiments were conducted in growth chambers at the USDA-ARS Stoneville Research Quarantine Facility in Mississippi. Soybean line PI 567102B was identified as the most resistant line among the 10 resistant PIs identified in Paraguay. It had the lowest severity rating, no sporulation, and near immune/hypersensitive reaction to isolate MS07-2, and red-brown (RB) reactions to isolates MS06-1 and MS07-1. In addition, reaction of PI 567102B to ASR differed from that of four PIs with known resistance genes. PI 200492 (Rpp1) had immune reaction to all three Mississippi isolates, while PI 230970 (Rpp2), PI 462312 (Rpp3), and PI 459025B (Rpp4) had RB lesions with different sporulation ratings. Soybean lines having resistant reactions to both U.S. and Paraguay isolates may be important sources for developing elite cultivars with broad resistance to ASR.