ASSOCIATION OF LOCI UNDERLYING FIELD-RESISTANCE TO SOYBEAN SUDDEN-DEATH SYNDROME (SDS) AND CYST-NEMATODE (SCN) RACE-3

Coinheritance of field resistance of soybean [Glycine max (L.) Merr.] to sudden death syndrome (SDS) [caused by the fungus Fusarium solani ( Mart.) Sacc. f. sp. phaseoli (Burk.) Snyd. & Hans.] and soybean cyst n ematode (SCN) race 3 (caused by Heterodera glycines Ichinohe) sometime s occurs in crosses among adapted cultivars. Our objective was to char acterize the loci underlying this coinheritance. One hundred thirty DN A markers were compared with SDS disease response and SCN score among 100 recombinant inbred lines (RILs) derived from a cross between SDS a nd SCN resistant 'Forrest' and SDS and SCN susceptible 'Essex'. SDS di sease incidence (DI) was determined in replicated sites during 4 yr en compassing five locations. The SCN score was determined in the greenho use from naturally infested held soil samples. Two separate genomic re gions identified by random amplified polymorphic DNA (RAPD) markers OI 03(450) and OW15(400) were associated with mean SCN score (P = 0.0001) and jointly accounted for about 47% of variability in SCN score, OI03 (450) identified a QTL for resistance to SCN (R-2 = 14%) within a geno mic region that was strongly associated with SDS DI (R-2 = 20%), partl y explaining the coinheritance of the two traits. This locus could be assigned to the region of linkage group G already known to encompass t he major SCN resistance locus.