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 mar (L,) Merr.] root infection by [Fusarium solani (Mart.) Sacc. f. sp. glycine (Bur k.)] (Rfs1), sudden death syndrome (SDS), and soybean cyst nematode (SCN; H eterodera 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 hom 'Flyer' x 'Hartwig'. A total of 535 among 739 lines were scored by two markers, pr oviding four genotypes. 4 stratified random sample of 50 lines was evaluate d for SDS by F, solani root infection severity at two locations and SCN rac e 3 index of parasitism in the greenhouse, Selection,vith BLT65 identified 281 among 671 Lines with the genomic region that underlies Rhg4-derived SCN resistance. Selection with Satt038 identified 230 among 613 lines containi ng the genomic region that underlies resistance to SDS (rfs1) and rhg1-deri ved 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 less than or equal to 0.05), Infection seve rity means for genotypes with the Hartwig allele at Satt038 (28-29%) were l ower (P = 0.0001, R-2 = 28%) than with the Fiver allele (31-42%); irrespect ive of maturity group. BLT65 was not associated with infection severity. Me an SCN index of parasitism was lower (P less than or equal to 0.05) only fo r genotypes carrying the Hartwig allele at both Satt038 and BLT65. Therefor e, alleles conferring resistance to SDS and SCN in Essex x Forrest are tran sferable to other populations.