Plant & Animal Genome VI Conference

P25

BAC CONTIG ANCHORED IN A SOYBEAN POPULATION SEGREGATING FOR DISEASE RESISTANCE GENES

1. Agronomy Department, Iowa State University, Ames, IA 50011-1010
2. USDA-ARS/Agronomy Department, Iowa State University, Ames, IA 50011-1010
3. Horticulture and Crop Science, Ohio State University, Wooster, OH 44691-4096

The soybean genes for resistance to Phytophthora soja (Rps2) and powdery mildew (Rmd) and the ineffective nodulation gene Rj2 were genetically mapped in the segregating population L76-1988 x L82-2024. The three genes are closely linked and three polymorphic RFLP markers anchor these loci into the lower portion of linkage group J on the Glycine max (A81-356-022) x Glycine soja (PI-468-916) map. We constructed a BAC contig in this region on linkage group J using fingerprint analysis of a disease resistance candidate gene family (identified using degenerate primers designed from conserved motifs in cloned plant disease resistance genes). We have expanded this contig to 800 kb by screening our BAC library using primers designed from BAC-end sequence obtained from direct sequencing of candidate BACs. Sequencing of PCR product from candidate BACs in addition to analysis of fingerprints confirmed the physical placement of the BACs in the contig. This contig is anchored in the L76-1988 x L82-2024 population by two BAC-end PCR based markers. We have added eight AFLP and two BAC-end markers to this region in L76-1988 x L82-2024. The segregating population used for the original mapping contained 200 individuals. We have expanded the population to 1000 individuals and are in process of using PCR markers flanking the disease resistance region to identify a sub-population of recombinant individuals for fine-scale mapping.