The influence of temperature and external water potential on mycelial growth, production of pseudothecia and maturation of ascospores by P. tritici-repentis was examined. In the range 10°–30 °C, mycelial growth was optimal at 20°–25°, but pseudothecial production was not temperature dependent. Ascospores developed most quickly at 15°. Mycelial growth and pseudothecial numbers declined as the external water potential decreased. Pseudothecia were not produced at water potentials lower than −1.7 MPa. Ascospores did not develop when the external water potential was less than −2.8 MPa. The production of pseudothecia on naturally infected wheat, barley and oat straw also was examined. Pseudothecia developed on all straw types in equivalent numbers, and production was not correlated with the reaction of the living host to infection.
