Bacterial pustule is a major bacterial disease in most soybean-growing regions of Korea, resulting in soybean yield reductions of up to 60%. In this study, we aimed to understand the differences in disease severity caused by three strains of Xanthomonas citri pv. glycines, including two newly differentiated strains (K29 and K100) and the conventional representative strain, 8ra. Seventeen major soybean cultivars and 14 breeding lines were inoculated and compared for their reactions to the three strains of Xcg. The two new strains caused higher levels of disease severity, resulting in a greater number of susceptible cultivars. The landrace PI 547711, like Williams 82, was highly resistant to all Xcg strains; however, the other six cultivars that were resistant to 8ra, including Daepung2, were susceptible to the new strains (K29 and K100). In particular, the most widely grown cultivars, Daewon and Daepung2, were highly susceptible to K100. All of the breeding lines except two were also vulnerable to the new strains, K100 and K29. Of the breeding lines, SS05004-1-1-4-2-3-4 and SS05022-5-4-2-4-4-4 were resistant to the three Xcg strains, at similar levels to that of Williams 82. The breeding lines and cultivars evaluated in this study may be used to develop breeding materials resistant to new Xcg strains in the future. In addition, establishment of an improved disease evaluation system for bacterial pustule, by using multiple representative strains, is strongly recommended for breeding programs, to increase the efficiency and accuracy of selection for resistance as the pathogenic diversity of X. citri pv. glycines changes.

In this study, composition and agronomic traits, including yield-related traits, were investigated and compared among 35 Korean landrace germplasm for two years (2019 and 2020). The contents of 12 isoflavones were measured using high-performance liquid chromatography, and agronomic trait data were collected according to the Rural Development Administration criteria. Comparing isoflavone composition between the two years, all isoflavones, except glycitein, were generally higher in 2019. The values of yield-related and major agronomic traits decreased in most accessions in 2020. ANOVA showed highly significant differences (p<0.001) in genotypes, years, and genotype-by-year interaction for all isoflavones, the number of pods per plant, and 100-seed weight. The number of seeds per pod, days to flowering, and days to maturity also showed significant differences among genotypes, as well as between the two years. Correlation analysis revealed that daidzin and genistin were positively correlated with their malonylated form. Malonyl daidzin was also positively correlated with malonyl genistin levels. The accessions with the least variation in the total isoflavone content were IT 153844 (907.5 µg/g, 898.6 µg/g) and IT 252252 (663.2 µg/g, 636.4 µg/g). Some of the evaluated landraces will be a promising genetic source for developing soybean varieties with high levels of environmental stability in isoflavone content and agronomic traits.

Phytophthora root rot attributable to infection by the soil-borne oomycete Phytophthora sojae causes serious damage to susceptible soybeans grown in poorly drained soil. Management of this disease depends primarily on Rps (resistance to P. sojae) resistance genes. The
objective
of this study was to map resistance to two P. sojae isolates (40412 and 2457) in a Daepung×Socheong2 recombinant inbred line population. Of these two varieties, Socheong2 is resistant to the two isolates, whereas Daepung is susceptible. Single-marker analysis of variance and linkage analyses using a high-density genetic map identified different resistance loci for each isolate. A genomic region of 36.2~37.4 Mbp on chromosome 3 was identified as being associated with resistance to isolate 40412, explaining 18% of the phenotypic variance (PV), whereas, a 2.1~2.6-Mbp region on chromosome 18 was significantly associated with resistance to isolate 2457, accounting for approximately 26% of the PV. An additional region of 53.1~53.3 Mbp on chromosome 18 was also significantly associated with resistance to isolate 2457. All three loci coincide with genomic regions where an Rps gene or partial resistance have been mapped in previous studies. The respective locus showed significance for only one or the other of the isolates, indicating an isolate-specific interaction. From this finding, it can be inferred that isolates 40412 and 2457 are characterized by different avirulence genes, and that Socheong2 has at least two Rps genes that interact with each isolate. The finding of multiple Rps loci specific to an isolate within a single soybean genotype is a unique discovery. Socheong2 will accordingly be a useful genetic source for breeding resistance to multiple P. sojae isolates.