In August 2025, symptomatic soybean (Glycine max L. Merr.) plants at the Fisher Delta Research Center, in New Madrid County, Missouri, exhibited leaf yellowing, wilting, and red discoloration at the stem base. Plants were collected and placed in a moist chamber. After a 7-day incubation, orangish-red perithecia developed on stems and roots. A crushed perithecium contained asci with 8 two-celled, striate ascospores, consistent with the morphology of Fusarium neocosmosporiellum O’Donnell & Geiser (≅ Neocosmospora vasinfecta E. F. Sm.) (Geiser et al. 2013). A pure isolate was obtained from placing one perithecium on one-fourth strength potato dextrose agar (PDA). Genomic DNA was extracted using DNeasy Plant Mini Kit (Qiagen, Hilden, Germany). Similar to Jimenez Madrid et al. (2023), part of the internal transcribed spacer (ITS) region, translation elongation factor 1-alpha (EF1-alpha), and calmodulin (CAL) genes were amplified by PCR with primer pairs ITS5/ITS4, EF-1/EF-2, and CAL-228F/CAL2Rd (Groenewald et al. 2013), respectively. The PCR products were sequenced, and consensus sequences were deposited in GenBank under accession numbers PX901390 (ITS), PX919729 (EF1-alpha), and PX919728 (CAL). NCBI BLAST analysis revealed that the ITS sequence shared 99.4% similarity with isolate SSLNV18 (KF662733), the EF1-alpha sequence showed 99.4% similarity with HF33 (PQ632685), and the CAL sequence showed 99.5% similarity with culture NFCCI:2972 (OM960789). To complete Koch’s postulates, F. neocosmosporieullm was cultured on one-third strength PDA in the dark at 24°C for 3 weeks. Williams 82 soybean seed were germinated and three seedings were planted in a 15cm diameter plastic pot. A total of six pots (18 plants total) were placed in a greenhouse at 26°C and under a 14-hour photoperiod. After two weeks, the top layer of soil was removed from every pot until the first lateral root was visible on each plant. In three pots, two 5mm plugs with mycelial growth and perithecia were placed next to the stem at the first lateral root of each plant. As a control, two 5mm non-inoculated plugs of one-third strength PDA were placed next to the stem at the lateral roots of plants in the other three pots. Soil was carefully placed back into the pots (Bish et al. 2025). After 4 weeks, non-inoculated plants remained asymptomatic while inoculated plants showed stem browning without foliar symptoms. Plants were then removed from pots and stems were split and incubated in a moist chamber. After 21 days, orangish-red perithecia developed on the stems. Ascospore morphology matched the above description. The fungus was successfully re-isolated from the symptomatic plants. This is the first report of F. neocosmoporiellum causing Neocosmospora stem rot in Missouri. This pathogen was previously reported to cause disease in soybean in Alabama (Gray et al. 1980), Arkansas (Greer et al. 2015), Georgia (Philips 1972), and Mississippi (Jimenez Madrid et al. 2022). F. neocosmosporiellum was also observed causing foot rot-induced wilting in peanuts in Texas (Obasa 2023). This pathogen poses a threat to Missouri soybean and peanut production. The perithecia were similar in appearance to those of Calonectria ilicicola (the causal agent of Red Crown Rot of soybean), first reported in Missouri in 2024 (Bish et al. 2025), and this report emphasizes that observation of perithecia alone is insufficient for diagnosis.
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