Genetic mapping of loci underlying field resistance to soybean sudden death syndrome (SDS)

Sudden death syndrome (SDS) is a fungal disease of soybean [Glycine max (L.) Merr.], caused by Fusarium solani (Mart.) Sacc. f. sp. phaseoli (Burk.) Snyd. & Hans., type A (FSA), that reduces crop yields in the USA. Quantitative partial resistance to SDS does exist; therefore, one method of controlling the disease is to select cultivars with genetic resistance. The objective of this study was to use molecular markers to identify and locate alleles of chromosomal segments associated with field resistance to SDS in adapted soybean genotypes, Seventy polymorphic DNA markers were compared with SDS response among 100 F-5:9 recombinant inbred lines derived from a cross between SDS-resistant 'Forrest' and SDS-susceptible 'Essex', SDS disease incidence (DI), disease severity (DS), and yield were determined in replicated, FSA-infested test sites during 4 yr encompassing five locations with recombinant inbred lines from the F-5:7 to F-5:11. Two separate chromosomal segments identified by two RAPD markers, OO05(250) and OC01(650), were found to be associated with mean SDS response across five locations as well as within each of the five locations. These two quantitative trait loci (QTL) jointly accounted for 34% of total phenotypic variability in mean DI, OC01(650) was significantly associated with mean DS and yield and was putatively assigned to linkage group N. The beneficial allele was derived from the resistant parent Forrest. OO05(250) was not significantly associated with mean DS or yield and was putatively assigned to linkage group C. The beneficial allele was derived from the susceptible parent Essex. Molecular markers can be used to define alleles of chromosomal segments conferring resistance to SDS in several environments and may allow efficient selection of resistant genotypes with good yield potential for FSA-infested fields.