Mapping and Confirmation of a New Allele at Rpp1 from Soybean PI 594538A Conferring RB Lesion–Type Resistance to Soybean Rust

Soybean rust, caused by Phakopsora pachyrhizi (H. Sydow & Sydow), is a destructive soybean [ Glycine max (L.) Merr.] disease and identification of new resistance genes is essential for effective rust management. Our research objectives were to map and confirm the location of resistance gene(s) in PI 594538A using a population of 98 F 3:4 lines from a cross between PI594538A (reddish‐brown [RB] lesions) and the susceptible cultivar Loda (tan [TAN] lesions). The lines were inoculated with the P. pachyrhizi isolate ZM01‐1 from Zimbabwe. The RB resistance in PI 594538A mapped on linkage group G as a single dominant gene. This gene is likely an allele of Rpp1 or a new closely linked gene because it mapped within 1 cM of Rpp1 and ZM01‐1 produced RB lesions on PI 594538A and TAN lesions on PI 200492, the original source of Rpp1 The mapping of the new Rpp1 allele, named Rpp1‐b , was confirmed in a second population.