• Vol. 2026, 44(1)
• Phytopathological Note

In vitro effect of pydiflumetofen against Fusarium virguliforme and Sclerotinia sclerotiorum isolates from soybean in Iowa, USA

By Edgar H Nieto Lopez, Austin Bierl, Desiree Chang Villatoro, Parbati Joshi, José F González Acuña, Stith Wiggs, Daren Mueller*

*Corresponding Author.

Received: 05/May/2025 – Published: 31/October/2025
DOI: https://doi.org/10.18781/R.MEX.FIT.2505-2

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  • Nieto-Lopez EH, Bierl- A, Chang-Villatoro D, Joshi- P, González-Acuña JF, Wiggs- S, Mueller- D. 2026. In vitro effect of pydiflumetofen against Fusarium virguliforme and Sclerotinia sclerotiorum isolates from soybean in Iowa, USA. Mexican Journal of Phytopathology 44(1):97. https://doi.org/10.18781/R.MEX.FIT.2505-2
  • Nieto-Lopez, EH, Bierl-, A, Chang-Villatoro, D, Joshi-, P, González-Acuña, JF, Wiggs-, S y Mueller-, D (2026). In vitro effect of pydiflumetofen against Fusarium virguliforme and Sclerotinia sclerotiorum isolates from soybean in Iowa, USA. Mexican Journal of Phytopathology 44(1):97. https://doi.org/10.18781/R.MEX.FIT.2505-2
  • Edgar Nieto-LopezH, Austin Bierl-, Desiree Chang-Villatoro, Parbati Joshi-, José González-AcuñaF, Stith Wiggs- y Daren Mueller-. 2026. In vitro effect of pydiflumetofen against Fusarium virguliforme and Sclerotinia sclerotiorum isolates from soybean in Iowa, USA. Mexican Journal of Phytopathology 44(1):97. https://doi.org/10.18781/R.MEX.FIT.2505-2

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Abstract Background/Objective. Sudden death syndrome caused by Fusarium virguliforme (Fv) and White mold caused by Sclerotinia sclerotiorum (Ss) are the most important soybean disease in regards to yield loss in the Northern USA. Few studies have estimated for Fv and Ss isolates from Iowa, the EC₅₀ mycelial growth of the fungicide pydiflumetofen for Fv and Ss; likewise, the EC₅₀ sclerotial production for Ss.

Experimental development. Potato dextrose agar (PDA) at 1/3 strength was amended with Saltro® (pydiflumetofen 41.7%) at 0.0008, 0.0042, 0.0083, 0.0417, 0.0834, 0.8340, and 834 ppm from serial dilutions. Isolates were incubated in darkness at 25 °C. Fv isolates were evaluated at 7 days and Ss isolates at 48 h after inoculation, measuring the radial growth. The sclerotia number and dried-weight were measured after 21 days of incubation.

Results. Pydiflumetofen absolute EC₅₀ values for mycelial growth Fv were 0.045 and 0.048 ppm. The Fv contemporary isolate (FV-RD-0024; collected in year 2024), and the historical isolate (NE205; collected in year 2006—years before pydiflumetofen introduction in the market), both presented EC50 mycelial growth in the range of the baseline (0.04–0.24 ppm) in the USA. EC₅₀ values for the mycelial growth of Ss contemporary isolates ranged from 0.011 to 0.046 ppm, which fall in the baseline from soybean and non-soybean hosts from China. Concentrations of 0.834 and 834 ppm were statistically different (no sclerotia production) than the control, which showed 14.6 sclerotia and 0.066 g.

Conclusion. The EC₅₀ mycelial growth of F. virguliforme Iowa isolates fall in the range of previous reported for the USA. The EC₅₀ mycelial growth of S. sclerotiorum Iowa isolates fall in the range previous reported outside the USA. Pydiflumetofen has the potential to diminish the sclerotial production but more studies are needed

Keywords: EC₅₀ mycelial growth, EC₅₀ number sclerotia, EC₅₀ dried-weight sclerotia, MIC

Table 1. Isolates of Fusarium virguliforme (Fv) and Sclerotinia sclerotiorum (Ss) used in the study including their background information and their absolute EC₅₀ estimated per variable on petri plates amended with pydiflumetofen fungicide (Saltro®; Syngenta) at 0.0008, 0.0042, 0.0083, 0.0417, 0.0834, 0.8340, and 834 ppm through standard serial dilutions. The isolate Ss2 (#630) shows one model since it did not produce sclerotia in the control.

Table 2. Average of number and dried-weight of sclerotia produced of Sclerotinia sclerotiorum isolates Ss1 (WM-2024) and Ss4 (WM-CO-0024) incubated for 21 days in darkness 25 °C. Petri plates amended with pydiflumetofen fungicide. Metrics between both isolates were combined.

Figure 1. Fusarium virguliforme isolates on 1/3 strength PDA petri plates incubated for 7 days after inoculation (DAI) at 25 °C dark. Petri plates amended with pydiflumetofen fungicide through standard serial dilutions. A) Fusarium virguliforme isolate Fv1 (NE305); B) Fusarium virguliforme isolate Fv3 (FV-RD-0024).

Figure 2. Mycelial growth and sclerotia production of Sclerotinia sclerotiorum isolates petri plates incubated at 25 °C dark. Petri plates amended with pydiflumetofen fungicide serial dilutions. A) Boxplot. B) Image in which a same isolate lays on each panel, with different concentrations increase from left to right along the row. Panels B-I to B-III: Mycelial growth at 48 hours after inoculation (HAI); B-I) Sclerotinia sclerotiorum isolate Ss1 – labeled WM1 (WM-2024); B-II) Sclerotinia sclerotiorum isolate Ss2 – labeled WM2 (#630); B-III) Sclerotinia sclerotiorum isolate Ss4 – labeled WM4 (WM-CO-0024); Panel B-IV: Sclerotia production at 21 days of incubation (DAI); B-IV) Sclerotinia sclerotiorum isolate Ss4 (WM-CO-0024).