Cytochalasins in Diaporthe longicolla from Soybean ( Glycine max L.): Insights from Untargeted Metabolomics and Implications for Animal Health

Species of Diaporthe cause soybean (Glycine max L.) diseases in the United States, including stem canker, pod and stem blight, and seed decay. Among different species of Diaporthe, Diaporthe longicolla, the causal agent of pod and stem blight and seed decay, is associated with the production of cytochalasin compounds. In this study, untargeted metabolomic profiling was conducted on two isolates of D. longicolla (16-OP-SB-DIA-52 and 14-OP-PHO-SD-19) recovered from soybean plants affected by pod and stem blight to identify both known and previously uncharacterized metabolites. Axenic cultures were established in potato dextrose broth (PDB) for metabolite characterization. Among the top 150 significantly upregulated metabolites compared to the PDB control, nitro-phenoxy cytochalasin (P = 0.009) and ortho-phenoxy cytochalasin (P = 0.002) were putatively identified. For 14-OP-PHO-SD-19, cytochalasin B (P = 0.021) and the nitro-phenoxy cytochalasin (P = 0.002) were detected. In addition, metabolomic analysis detected fumonisin B2 [16-OP-SB-DIA-52 (P = 0.001); 14-OP-PHO-SD-19 (P = 0.009)] and zearalanone [16-OP-SB-DIA-52 (P = 0.0002); 14-OP-PHO-SD-19 (P = 0.01)], which were significantly upregulated and among the top 400 metabolites putatively identified in the two isolates. Interestingly, cytochalasin compounds, fumonisins, and zearalanone have been previously implicated in detrimental effects on livestock health (e.g., sheep, horses, and pigs). While incorporating soybean meal into livestock diets underscores the potential relevance of D. longicolla-associated metabolites to feed safety, the present study was designed as a proof-of-concept metabolomics investigation. Consequently, any implications for animal health should be considered preliminary and require confirmation through metabolite quantification, feed analyses, and toxicity studies.