Technical Abstract: In 2009, Soybean Phomopsis seed decay (PSD) caused over 12 million bushels of yield loss in 16 southern states. This disease severely affects soybean seed quality due to the reduction of seed viability, oil content, and alteration of seed composition, and it may also increase moldy and/or split seed potentially leading dockage at the point of sale. The disease is primarily caused by Phomopsis longicolla along with other Phomopsis and Diaporthe spp. To identify new sources of resistance to PSD, 45 maturity group V soybean germplasm lines from 28 countries were field screened by natural infection along with PSD resistant and susceptible checks in 2009 at Kibler, AR, Stoneville, MS and Portageville, MO. Planting dates for AR, MS, and MO were June 5, May 20, and May 21, respectively. The experimental design was a randomized complete block with four replications. Seeds were harvested from each plot when the plants were mature. Seeds from each plot were tested for percent seed infected by Phomopsis spp., percent seed germination, and visual quality. Hot and humid environments, especially from pod fill to harvest in AR, MS, and MO favored pathogen growth and disease development. Significant differences in seed infection by Phomopsis spp. were observed among soybean lines with some lines having no infection while others had levels as high as 83%. These differences between lines were reflected in visual seed quality and seed germination. Soybean lines PI507690, 5002T, and V01-1702 were among the lines with low percentages of seed infection at each location. PI417567 and PI381659 had the lowest percentage of seed infection in Mississippi, while PI471942 had the lowest percentage of seed infection in Arkansas but was very susceptible to PSD in Mississippi and Missouri. Of 45 lines tested in Missouri, 43 lines had over 30% of seed infection. Soybean lines with low infection incidences, good visual quality, and high germination rates at all locations will be tested in 2010 field trials.