2 MICROSATELLITE MARKERS THAT FLANK THE MAJOR SOYBEAN CYST-NEMATODE RESISTANCE LOCUS

The use of resistant cultivars is the most effective method for contro lling soybean cyst nematode (Heterodera glycines Ichinoe; SCN) on soyb ean [Glycine max (L.) Merrill]. However, resistance to SCN is oligogen ic, making inheritance patterns complex and breeding difficult. One ma jor partial-resistance locus for SCN resistance is located on molecula r Linkage group (MLG) 'G'. This locus controls more than 50% of variat ion associated with response to SCN and resistant alleles are present in many important sources of SCN resistance, including PI 209332, PI 8 8788, PI 90763, PI 437654, and 'Peking'. Restriction fragment length p olymorphisms (RFLPs) Linked to the major SCN resistance alleles on MLG G have proven effective in tracking the alleles and predicting SCN re sponse. These RFLPs are much more efficient in terms of time and labor than greenhouse assays for SCN. Nevertheless, more efficient DNA mark ers are needed to screen the many lines required for marker-assisted s election. Polymerase chain reaction-based markers, such as microsatell ites (simple sequence repeats), have been sought because they are fast er, less expensive, more polymorphic, and require less labor than RFLP s. In this study, we report two microsatellites, BARC-Satt038 and BARC -Satt130, that flank the major SCN resistance locus on MLG G. These mi crosatellites efficiently identify the chromosome fragment carrying th e resistance allele and are also good predictors of SCN phenotype resp onse.