A soybean restriction fragment length polymorphism (RFLP) map (ISU/USDA‐ARS‐FCR, Ames, IA) was derived from an interspecific cross of Glycine max (L.) Merr. × G. soja Siebold & Zucc. using early maturity group genotypes. We characterized the feasibility of the application of this map to physiologically distant soybean genotypes mainly maturity group (MG) V to IX. A total of 108 genotypes of G. max were surveyed. Germplasm represented ancestral genotypes, breeding lines and elite cultivars. The RFLP markers (83 probes) used in this research spanned fifteen major linkage groups at an average distance of 26 centimorgans (cM). Fifty‐four percent of the probes were non informative. Thirty‐five percent had a probability of detecting polymorphism between any two random genotypes with a frequency above 0.3. The RFLP probes detecting polymorphism with high frequency were identified. Restriction fragment length polymorphism was associated with cultivar pedigree and relation to ancestral genotypes. The majority of genotypes showed molecular similarities to ‘Ralsoy’, ‘Dorman’, ‘Dunfield’, and ‘Ogden’ germplasms; a smaller group of genotypes showed molecular similarities to S‐100. Genotypic similarities were observed among most genotypes. However, genotypes of MG VI and VII retained potentially valuable levels of genetic diversity. Soybean cyst nematode and bacterial pustule resistance were present in many different genetic backgrounds and no association with donor genotypes was observed in principal components analysis. The set of identified RFLP probes with high frequency of polymorphism detection should serve as a core of molecular markers for initiating mapping of agronomic traits and detection of gene linkages across a wide range of maturity groups of cultivated soybean. Genomic diversity described by the principal components analysis may be useful in germplasm selection to develop populations for genome mapping in soybean.

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The soybean cyst nematode (SCN), Heterodera glycines Ichinohe, is the foremost pest of soybean (Glycine max L. Merr.). The rhg1 allele on linkage group (LG) G and the Rhg4 allele on LG A2 are important in conditioning resistance. Markers closely linked to the Rhg4 locus were used previously to screen a library of bacterial artificial chromosome (BAC) clones from susceptible 'Williams 82' and identified a single 150-kb BAC, Gm_ISb001_056_G02 (56G2). End-sequenced subclones positioned onto a restriction map provided landmarks for identifying the corresponding region from a BAC library from accession PI 437654 with broad resistance to SCN. Seventy-three PI 437654 BACs were assigned to contigs based upon HindIII restriction fragment profiles. Four contigs represented the PI 437654 counterpart of the 'Williams 82' BAC, with PCR assays connecting these contigs. Some of the markers on the PI 437654 contigs are separated by a greater physical distance than in the 'Williams 82' BAC and some primers amplify bands from BACs in the mid-portion of the connected PI 437654 BAC contigs that are not amplified from the 'Williams 82' BAC. These observations suggest that there is an insertion in the PI 437654 genome relative to the 'Williams 82' genome in the Rhg4 region.

Soybean [Glycine max (L.) Merr.] germplasm PI 437654 exhibits broad resistance to soybean cyst nematode (Heterodera glycines Ichinohe, SCN). Probes derived from PI 437654 bacterial artificial chromosome (BAC) clone 15G19 at the Rhg4 locus detected a restriction fragment length polymorphism (RFLP) between resistant and susceptible germplasms. Detailed RFLP analysis using restriction fragments from BAC clone 15G19 associated the polymorphism with an 8‐kb BamHI fragment containing the promoter region and partial coding sequence of a novel soybean subtilisin‐like protease, GmSUB1 Complete sequence of GmSUB1 was determined (GenBank ). Regulatory elements for root gene expression, pathogen response, coordinated multiple‐gene expression, and a novel 90‐bp direct repeat were identified. GmSUB1 shows 74% similarity to Arabidopsis thaliana AIR3. Hybridization analyses indicate that PI 437654 contains only full‐length copies of GmSUB1, whereas susceptible germplasm ‘Williams 82’ contains both full‐length and truncated copies of the gene. A 4‐fold increase in GmSUB1 copy number, and a corresponding 2‐ to 3‐fold increase in steady state GmSUB1 mRNA levels, was observed in PI 437654 compared with Williams 82. Localization and polymorphism of GmSUB1 within the Rhg4 resistance region, and increases in GmSUB1 gene copy number and expression in PI 437654 compared with Williams 82 infers a functional role in the pathogen response. GmSUB1 is believed to be secreted into the extracellular matrix, and may function in reorganization of cell wall components during plant development and in the defense response.

naling and cellular response to provide resistance to the specific pathogen. The complexity of this system is Soybean [Glycine max (L.) Merr.] germplasm PI 437654 exhibitsrepresented by the large number of genes whose activity broad resistance to soybean cyst nematode (Heterodera glycines Ichinohe, SCN). Probes derived from PI 437654 bacterial artificial chro-