DNA MARKER ANALYSIS OF LOCI UNDERLYING RESISTANCE TO SOYBEAN CYST-NEMATODE (HETERODERA-GLYCINES ICHINOHE)

Inheritance of resistance to soybean cyst nematode (SCN, Heterodera glycines Ichinohe) is oligogenic and complex. DNA markers, such as restriction fragment length polymorphisms (RFLPs), can be used to identify loci associated with complex genetic characters, including SCN resistance. To uncover these associations, 56 F-2 lines from a cross between a susceptible (M83-15) and a resistant (M85-1430) soybean [Glycine mar (L.) Merr.] inbred line were mapped for DNA marker polymorphisms. F-3 lines derived from these F-2 individuals were assayed for SCN disease response in the greenhouse to a field isolate of SCN from Minnesota that tested as Race 3. The F-2 genotypic classes for each of 43 DNA markers were then contrasted with SCN disease response to identify marker loci associated with SCN resistance. Two unlinked RFLP markers, pA85 and pB32, were found to be significantly associated with SCN disease response, together ac counting for 51.7% of total phenotypic variation. Based on RFLP analysis, individual F-2:3 lines that retained either one or both resistance loci were identified. Lines that possess both resistance loci could be valuable in developing resistant soybean lines free of linkage drag, while lines that have just one of the resistance loci may be useful as single-gene differentials for SCN race determination.