Mapping and confirmation of the 'Hyuuga' red-brown lesion resistance gene for Asian soybean rust

Asian soybean rust (ASR), caused by Phakopsora pachyrhizi Syd., is a widespread disease of soybean [Glycine max (L.) Merr.] with the potential to cause serious economic losses. The objective of this study was to genetically map red-brown lesion type resistance from the cultivar Hyuuga. A population of 117 recombinant inbred lines (RILs) from the cross of Dillon (tan lesion) x Hyuuga (red-brown [RB] lesion) was rated for ASR lesion type in the field and inoculated with P. pachyrhizi in the greenhouse. The RB resistance gene mapped between Satt460 and Satt307 on linkage group (LG)-C2. When field severity and lesion density in the greenhouse were mapped, the Rpp?(Hyuuga) locus explained 22 and 15% of the variation, respectively (P < 0.0001). The RB lesion type was associated with lower severity, fewer lesions, and reduced sporulation when compared to the tan lesion type. A population from the cross of Benning x Hyuuga was screened with simple sequence repeat (SSR) markers in the region on LG-C2 flanked by Satt134 and Satt460. Genotype at these markers was used to predict lesion type when the plants were exposed to P. pachyrhizi. All the lines selected for the Hyuuga markers in this interval had the RB lesion type and they averaged approximately 50% fewer lesions compared to lines with tan lesions. Sporulation was only detected in 6% of the RB lines compared with 100% of the tan lines. Marker-assisted selection can be used to develop soybean cultivars with the Rpp?(Hyuuga) gene for resistance to ASR.