Selecting soybean cultivars for dual resistance to soybean cyst nematode and sudden death syndrome using two DNA markers

DNA markers for genes conditioning resistance to soybean [Glycine max (L.) Merr.] root infection by [Fusarium solani (Mart.) Sacc. f. sp. glycine (Burk.)] (Rfs1), sudden death syndrome (SDS), and soybean cyst nematode (SCN; Heterodera glycines Ichinohe; Rhg4 and rhg1 ) were previously identified in 'Essex' x 'Forrest'. This study tests the effectiveness of those markers in selecting for disease resistance among recombinant inbred lines from 'Flyer' x 'Hartwig'. A total of 535 among 739 lines were scored by two markers, providing four genotypes. A stratified random sample of 50 lines was evaluated for SDS by F. solani root infection severity at two locations and SCN race 3 index of parasitism in the greenhouse. Selection with BLT65 identified 281 among 671 lines with the genomic region that underlies Rhg4-derived SCN resistance. Selection with Satt038 identified 230 among 613 lines containing the genomic region that underlies resistance to SDS (rfs1) and rhg1-derived SCN resistance. A total of 93 out of 535 lines had genomic regions that underlie resistance to both SDS and SCN in Essex x Forrest. Segregation of both markers was not random (P < or = 0.05). Infection severity means for genotypes with the Hartwig allele at Satt038 (28-29%) were lower (P = 0.0001, R(2) = 28%) than with the Flyer allele (31-42%); irrespective of maturity group. BLT65 was not associated with infection severity. Mean SCN index of parasitism was lower (P < or = 0.05) only for genotypes carrying the Hartwig allele at both Satt038 and BLT65. Therefore, alleles conferring resistance to SDS and SCN in Essex x Forrest are transferable to other populations.