From the soils of soybean fields in Cotton Branch Station (CBS) and Pine Tree Station (PTS), Arkansas, USA, various single spore isloates of sudden death syndrome (SDS) pathogen were obtained on modified Nash ＆ Snyder's medium (MNSM) with dilution plating technique and transferred to potato dextrose agar (PDA) medium to identify the cultural colony shape. The colony shapes of these isolates resembled F. solani isolate 171 which was white and chalky shaped on MNSM and most of them had unique form of morphology which produced white margin and blue center colony on PDA. Although, some of these isolates had more dark blue or showed slightly different color, all isolates that were selected randomly for green-house inoculation assay produced typical foliar symptoms on leaves of soybean, Hartz 6686. To determine the genetic differences among the isolates, mitochondrial DNA restriction fragment length polymorphism (RFLP) was conducted with fourty isolates from both fields, using mtDNA probes, 2U18 and 4U40, derived from Colletotrichum orbiculare. We obtained distinctive RFLPs in each treatment of restriction enzyme, EcoRI and HaeⅢ. Isolates, 11-2-5 and 14-3-1-1, from CBS and isolates, 104-3-1-2 and 701-1-5-1, from PTS showed different band patterns from 171 in both or in either treatment of restriction enzymes. Even if some of these isolates showed heterogeneous, they were more closer to 171 than PN603. And, also, rest of the thirty-six isolates had exactly same polymorphisms as 171 in each treatment of restriction enzyme. Although, some of the isolates showed the different morphological shape on PDA and slightly different band patterns on RFLPs, all of the isolates selected on MNSM due to their distinctive colony shape from other fungi produced the typical foliar symptoms on soybean leaves in greenhouse inoculation assay. It might be suggested that these isolates were not genetically different from check isolate 171 and they were unique strain of F. solani

In order to identify the responses of Korean soybean cultivars to sudden death syndrome (SDS), forty-two Korean cultivars and three check cultivars (Hartwig and PI 520733 are resistant; Hartz 6686 is susceptible) were tested with sorghum seed inoculum infested with Fusarium solani f. sp. glycines isolate 171 in the greenhouse. This isolate has blue pigment cultural shape on potato dextrose agar (PDA) medium. All Korean cultivars inoculated with F. solani isolate 171 showed the typical SDS symptoms and disease severity on soybean leaves in each cultivar varied at 4 weeks after inoculation. Nine cultivars were included in the most SDS susceptible group and six cultivars were included in the most susceptible group based on Duncan＇s multiple range tests (P~leq 0.05). In results of the LSD analysis for SDS the resistant group, a total of twenty-five Korean cultivars were included in the same SDS resistant group as PI 520733 or Hartwig and fourteen Korean cultivars were included in the same SDS susceptible group as Hartz 6686. In the second experiment, ten Korean cultivars, ten U.S. cultivars, and one introduced line were compared in the same way as the first experiment Disease severity ranking of check cultivars, Hartwig, PI 520733, and Hartz 6686, were the same as in the first experiment. Within Korean cultivars, seven cultivars showed the consistent severity proportions of leaf symptoms. Disease rankings of these cultivars in this experiment were the same as those in the first experiment. Three US cultivars: Hartwig, Hartz 5454, and Forrest, three Korean cultivars： Keunolkong, Myeongjunamulkong, and Jinpumkong 2, and one introduced line, PI 520733, were included in the highest SDS resistant group. Shinphaldalkong 2, Milyang 87, and Samnamkong consistently showed the highest SDS susceptibility in both experiments. Average disease severity in the first and the second experiment were 49.56% and 45.39%, respectively.