Monday, November 13, 2006 - 11:15 AM

Mapping and Confirmation of the 'Hyuuga' Red-Brown Lesion Resistance Gene for Asian Soybean Rust.

Maria J. Monteros1, Ali M. Missaoui1, Daniel V. Phillips2, David R. Walker3, and H. Roger Boerma1. (1) Center for Applied Genetic Technologies, 111 Riverbend Rd. #202, Athens, GA 30602, (2) Univ of Georgia, 214 Redding Bldg, Griffin, GA 30223, (3) USDA-ARS Soybean/Maize Germplasm, Pathology and Genetics Unit, 232 National Soybean Research Center, 1101 W. Peabody Drive, Urbana, IL 61801

Asian soybean rust (ASR), caused by Phakopsora pachyrhizi, is a widespread disease of soybean [Glycine max (L.) Merr.], and has the potential to cause serious economic losses.  The objective of this study was to genetically map red-brown lesion type resistance from the Japanese cultivar ‘Hyuuga’.  A population of 117 RILs from the cross of ‘Dillon’ (tan lesion type) × Hyuuga (red-brown lesion type, RB) was rated for ASR lesion type in the field at Attapulgus, GA, and fingerprinted using SSR markers.  The RB resistance gene was mapped close to Satt460 on LG-C2.  The Dillon × Hyuuga RILs were also inoculated with P. pachyrhizi in the greenhouse to confirm the RB-lesion phenotype.  Using the greenhouse data, the resistance gene mapped between Satt460 and Satt307 on LG-C2.   When field severity rating and lesion density in the greenhouse were mapped as quantitative traits, the Rpp?(Hyuuga) locus explained 22% and 15% of the variation, respectively (P < 0.0001).  The RB lesion type was associated with fewer lesions and reduced sporulation when compared to the tan lesion type.  A population of F5:6 lines from the cross of Benning × Hyuuga was screened with SSR markers in the 4 cM 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 RB lesions and they averaged approximately 50% fewer lesions compared to F5:6 lines with tan lesions.  Sporulation could only be detected in 6% of the RB lines compared with 100% in the tan lines.   SSR markers associated with lesion type can be used by soybean breeders to develop cultivars with the Rpp?(Hyuuga) gene for resistance to ASR.