Identification of Novel Genes Conferring Resistance to Phytophthora sojae in Soybean

Joshua C Fitzgerald, Purdue University

Abstract

Phytophthora root and stem rot (PRSR), caused by the soil-borne pathogen, Phytopthora sojae, is a debilitating disease of soybean [ Glycine max (L.) Merr.] throughout the world. The most effective, yet environmentally friendly way to combat the disease is through the deployment of race-specific genes that impart resistance to Phytopthora sojae (Rps). Three soybean landrace varieties, USDA 112, USDA 203 and USDA 052, were found to carry excellent resistance to a wide variety of P. sojae isolates, including two races (race 17 and race 25), together which are virulent to all soybean germplasm carrying currently known Rps genes. Additionally, these landraces possess resistance to several isolates of P. sojae capable of defeating the most widely used Rps genes, such as Rps1-k, Rps1-c, and Rps3-a, found in the majority of U.S. soybean breeding programs. A mapping population consisting of 59 F2 individuals and 189 F2:3 families derived from a cross between USDA 112 and the susceptible cultivar ‘Williams’ was used to characterize the resistance inheritance pattern found in USDA 112. The resistance was found to be from a single Rps gene, designated Rps1-das, initially defined to a ∼3 Mb genomic region along chromosome 3 defined by bulked segregant analysis (BSA) with a single nucleotide polymorphism (SNP) chip comprised of 7,039 SNP markers. Furthermore, simple sequence repeat (SSR) markers in the defined target region were used to genotype the F2:3 mapping population and map Rps1-das to a 185.3-kb genomic region flanked by SSR markers BARCSOY_03_0250 and BARCSOY_03_0266. A second mapping population consisting of 59 F2 individuals and 110 F2:3 families derived from a cross between USDA 203 and the susceptible cultivar ‘Williams’ was used to characterize the resistance inheritance pattern found in USDA 203. The resistance was also found to be from a single Rps gene, designated Rps1-f, initially defined to ∼5 Mb genomic region along chromosome 3 defined by BSA coupled with a SNP chip comprised of 7,039 SNP markers. SSR markers in the defined target region were used to genotype the F2:3 mapping population and map Rps1-f to a 277.4-kb genomic region flanked by SSR markers BARCSOY_03_0232 and BARCSOY_03_0242. A third mapping population consisting of 57 F2 individuals and 104 F 2:3 families derived from the cross between USDA 052 and the susceptible cultivar ‘Williams’ was used to characterize the resistance inheritance pattern found in USDA 052. The first source of resistance to race 1 was found to be from a single Rps gene, designated Rps2-das, initially defined to ∼2 Mb genomic region along the end of chromosome 16 defined by BSA coupled with SNP Chip comprised of 7,039 SNP markers. SSR markers within the target region were used to genotype the F2:3 families and map Rps2-das to a 454.6-kb genomic region between BARCSOY_16_1288 and Sat_395. Another source of resistance identified to race 17 was found to be from a single Rps gene, designated Rps1-g, initially defined to a large genomic region of chromosome 3 by BSA and SNP chip comprised of 7,039 SNP markers. SSR markers linked to the previous locations defined in USDA 112 and USDA 203 were used to genotype the F 2:3 families and map Rps1-g to a 185.3-kb genomic region on chromosome 3. A preliminary search of each of the Rps loci identified in this study indicates the presence of genes encoding the NBS-LRR type class of proteins in these gene-rich regions. The markers flanking each of the identified Rps loci can be used to aid in marker-assisted selection (MAS), gene stacking and future fine mapping studies to narrow the defined regions in an effort to clone these individual alleles.

Degree

Ph.D.

Advisors

Ma, Purdue University.

Subject Area

Agronomy

COinS