Root and stem rot is one of the major diseases of soybean. It is caused by the oomycete pathogen Phytophthora sojae. A series of resistance genes (Rps) have been providing soybean with reasonable protection against this pathogen. Among these genes, Rps8, which confers resistance to most P. sojae isolates, recently has been mapped. However, the most closely linked molecular marker was mapped at about 10 cM from Rps8. In this investigation, we attempted to develop a high-density genetic map of the Rps8 region and identify closely linked SSR markers for marker-assisted selection of this invaluable gene. Bulk segregant analysis was conducted for the identification of SSR markers that are tightly linked to Rps8. Polymorphic SSR markers selected from the Rps8 region failed to show cosegregation with Phytophthora resistance. Subsequently, bulk segregant analysis of the whole soybean genome and mapping experiments revealed that the Rps8 gene maps closely to the disease resistance gene-rich Rps3 region.

Disease resistance is an important crop trait that protects yield and farmers' incomes. The objective of the soybean breeding program for disease resistance at Iowa State University (ISU) is to develop germplasm lines for Iowa. AR10SDS (Reg. No. GP-391, PI 669816) is the irst sudden death syndrome (SDS) partially resistant line released by ISU, Project nos. 4403 and 0159 (Agronomy and Plant Pathology departments), ISU Research Foundation (ISURF) Docket #03264. AR10SDS is partially resistant to Fusarium virguliforme which causes SDS, and resistant to soybean cyst nematode (SCN) phenotypic race 3 (HG types 0 and 7) caused by Heterodera glycines. AR10SDS is a bulk of 60 F 3:8 plants uniform in plant and seed traits. The parentage is 'Ripley' × 'IA1008'. Ripley is resistant to SDS. IA1008 is resistant to SCN. The cross and generations advances were made in Puerto Rico beginning in 2000, ISU research site at the Isabela Substation, University of Puerto Rico, Isabela, PR. Yield was evaluated from 2003 to 2006 in Iowa and in the northern U.S. regions. From 2003 to 2011, SDS resistance was evaluated under greenhouse conditions and in SDS-infested ield soil. Soybean cyst nematode screening was conducted in 2005 to 2006 under greenhouse conditions. Three SDS resistance quantitative trait loci (QTLs) were inherited from Ripley, and two SCN resistance QTLs from IA1008. Seed yield is similar to IA1008 and signiicantly (P = 0.05) better than 'Parker' and 'Freeborn'. It is of early-to mid-maturity group I and adapted from 40 to 42° N latitude. AR10SDS may serve breeding programs for its dual disease resistance.

Genetically resistant crops are effective strategies for crop production and the soybean [Glycine max (L.) Merr.] program against pathogens at Iowa State University (ISU) breeds germplasm possessing resistance to Iowa pests. Sudden death syndrome (SDS) caused by Fusarium virguliforme, soybean cyst nematode (SCN; Heterodera glycines Ichinoe), and iron deficiency chlorosis (IDC) are Iowa yield deterrents. AR11SDS (Reg. No. GP‐399, PI 675224) was developed at ISU, Project 4403, Agronomy Department, ISU Research Foundation (ISURF) Docket # 3999. AR11SDS is an F3–derived bulk of 60 F8:9 plants from the cross ‘Ripley’ × ‘IA2036’. Ripley resistance to SDS and IA2036 resistance to SCN were crossed in Iowa. Generations were advanced at the ISU research site, University of Puerto Rico, PR. From 2003 to 2006, AR11SDS yield was evaluated. Resistance to SDS and SCN was screened in greenhouses and on SCN‐infested fields. Calcareous soils were used to screen IDC. Five SDS resistance quantitative trait loci (QTLs) were from Ripley, and one SCN QTL was from IA2036. Average seed yield on SCN‐infested soil (3891 kg ha−1) was similar to the high‐yielding SDS‐susceptible ‘IA2068’ (3658 kg ha−1) although lower on non‐SCN soil, similar in yield to SDS‐susceptible ‘IA2065’, and superior to SDS‐susceptible ‘Dwight’. AR11SDS is of early‐mid maturity group II, adapted to 40 to 42° N latitude, and is highly resistant to SDS, resistant to SCN (Race 3, HG Type 0, and 7), and moderately resistant to IDC (score 2.4). These traits and its yield and agronomic performances make AR11SDS a unique source for SDS breeding in the northern US soybean region.

Soybean [Glycine max (L.) Merr.] yields will be protected by introgressing pathogen resistance, an objective of soybean breeding for pathogen resistance at Iowa State University (ISU). Germplasms AR4SCN (Reg. No. GP‐410, PI 684651), AR5SCN (Reg. No. GP‐411, PI 684652), AR6SCN (Reg. No. GP‐412, PI 684653), AR7SCN (Reg. No. GP‐413, PI 684654), and AR8SCN (Reg. No. GP‐414, PI 684655), are resistant to soybean cyst nematode (SCN, Heterodera glycines [HG] Ichinohe) HG type 0 (Race 3) and HG type 1.3.6.7 (Race 14). In 2007, ISU Projects 3722 of the Agronomy Department and Project 3384 of the Plant Pathology Department, the Iowa Agricultural and Home Economics Experiment Station, and the ISU Research Foundation released the lines. Each line is an F12:13 bulk of 60 agronomically uniform plants from the cross of the genetically diverse SCN parents PI 88788 and ‘Columbia’. The cross made at the Isabela Substation, Puerto Rico, underwent generation advances in Puerto Rico and Iowa. Phenotyping/molecular characterizations of lines at Arelli's, Cianzio's and Diers’ labs confirmed the presence of high copy numbers of the full‐length sequence repeat of the highly important major PI 88788‐type rhg1‐b gene, conferring high levels of SCN resistance on each germplasm. In Iowa, average seed yield of the maturity group (MG) II line AR4SCN was 57% of the check ‘Dwight’. For MG III lines (AR5SCN, AR6SCN, AR7SCN, AR8SCN), yield was 77% of ‘Macon’. The germplasms will serve in the development of SCN‐resistant genotypes adapted to northern US regions where SCN HG type 0 and/or 1.3.6.7 may be prevalent. Lines may also serve as research genetic stocks.