Regulation of in vitro Ptr‐toxin Production by Pyrenophora tritici‐repentis Isolates by Environmental Parameters and Accumulation of Ptr‐toxin in Culture over Time

Abstract Previous work has demonstrated the production of a low molecular weight toxin (designated Ptr‐toxin) by isolates of Pyrenophora tritici‐repentis (Died.) Drechs., the cause of tan spot of wheat ( Triticum aestivum ). Before the mechanisms by which Ptr‐toxin is produced are understood, conditions for optimal toxin production must be identified. This study defined glucose concentration, light and temperature for optimal fungal growth and accumulation of Ptr‐toxin in a defined mineral salts‐glucose liquid medium. The accumulation of Ptr‐toxin in culture was monitored over a 21‐day period. The growth of six P. tritici‐repentis isolates increased significantly over the range of 0.05–5.0% glucose; however, the greatest accumulation of Ptr‐toxin was observed at 1 and 2% glucose. Significant increases in fungal dry weights were observed at 23 and 30°C, although the effect of temperature on toxin production remains questionable. No significant influence of light on growth and Ptr‐toxin production was observed. Ptr‐toxin continues to accumulate in culture over the 21‐day period tested in this study. The results of the present study reveal much about the specific isolates included but little information upon which generalizations may be based. As such, screening numerous P. tritici‐repentis isolates for Ptr‐toxin production under one set of conditions appears to be unreliable.