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 nematode (SCN) race 3 (caused by Heterodera glycines Ichinohe) sometimes occurs in crosses among adapted cultivars. Our objective was to characterize the loci underlying this coinheritance. One hundred thirty DNA markers were compared with SDS disease response and SCN score among 100 recombinant inbred lines (RILs) derived from a cross between SDS and SCN resistant 'Forrest' and SDS and SCN susceptible 'Essex'. SDS disease incidence (DI) was determined in replicated sites during 4 yr encompassing five locations. The SCN score was determined in the greenhouse from naturally infested held soil samples. Two separate genomic regions identified by random amplified polymorphic DNA (RAPD) markers OI03(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 genomic region that was strongly associated with SDS DI (R-2 = 20%), partly explaining the coinheritance of the two traits. This locus could be assigned to the region of linkage group G already known to encompass the major SCN resistance locus.