Plant Genome IV Conference Plant Genome IV Conference
Soybean cyst nematode (SCN; Heterodera glycines) is the most important disease problem of soybeans today. SCN resistance is oligogenic and complex, so conventional breeding for SCN remains difficult. DNA markers can locate and characterize partial SCN resistance genes and provide valuable information for selection and breeding. We have used RFLPs to examine SCN resistance in four different lines, PI 209332, PI 88788, Peking1 and PI 90763. For each resistance source, F2:F3 (or RIL) populations of 98 - 120 individuals were constructed by crossing with the susceptible cultivar Evans1. These populations were assayed for SCN disease response using three SCN races, and the disease phenotypes were contrasted with DNA genotypes at 70 - 100 RFLP loci. One partial resistance locus near the top of linkage group G1 was most significant in all lines and against all races. This locus explained as much as 50% of total variation in SCN disease response in PI 209332 and PI 90763. By examining an PI 209332 x Evans recombinant inbred population, this partial resistance locus could be treated qualitatively and pinpointed to a specific location on the genome. Other genomic regions significant against SCN were found on linkage groups D1, J1, L1 and N1, as well as a second locus at the opposite end linkage group of linkage group G1. In many cases genomic regions were significant in all or most of the resistant lines, though some regions, like the loci on J1 and L1, were significant in only two of the lines.