Fusarium pseudograminearum Isolates Show Enhanced Growth and Na+ Uptake but Suppressed Mycotoxin Production After Exposure to NaCl at Different Temperatures

Several Fusarium species have demonstrated the ability to thrive in saline soils and to tolerate or prefer high salt concentrations. In this context, the potential halophilic or halotolerant lifestyle of Fusarium pseudograminearum was investigated. Four isolates (3B, PVS-Fu 7, ColPat-1, and CBS 109956) were grown at different temperatures (10, 15, 20, 25, 30, and 35 °C) and NaCl concentrations (0, 7, 14, 21, and 28 g L−1), and daily growth, mycotoxin production, and K+ and Na+ accumulation within hyphae were assessed. All F. pseudograminearum isolates exhibited strong adaptability to saline conditions, with significantly enhanced growth in the presence of NaCl. All isolates accumulated Na+ within their hyphae while retaining K+. The production of deoxynivalenol (DON) and zearalenone (ZEA) was generally suppressed following NaCl exposure, consistent with the known inhibitory effect of reduced water activity on mycotoxin biosynthesis. However, at 22 °C, two isolates, 3B and CBS 109956, showed no significant differences in ZEA production between the control (no salt) and the medium containing the lowest NaCl concentration tested (7 g L−1). Notably, isolate 3B, obtained from the halophyte Salicornia europaea, retained the highest levels of both Na+ and K+ within hyphae and showed the greatest overall adaptation to salinity. These results confirm the hypothesis that the ability of F. pseudograminearum to colonize and infect a halophytic host is indicative of a halophilic lifestyle. In the context of increasing soil salinization, these findings help identify conditions that permit pathogen persistence without hazardous mycotoxin accumulation.