International Journal of Agriculture and Environmental Research

The effects of osmotic and matric water potential on mycelial growth, production and germination of conidia, and production and maturation of pseudothecia of Pyrenophora triticirepentis (PTR), the cause of tan spot of wheat, were examined on clarified V8 juice agar amended with KCl or polyethylene glycol 8000 (PEG8000). Patterns of the growth responses of three isolates to decreasing osmotic and matric potentials were similar for KCl and PEG8000, respectively. Compared with growth on non-amended CV8 agar (-0.24 MPa), growth of all isolates significantly decreased as osmotic and matric potentials reduced to -4.0 MPa and -2.0 MPa, respectively. Conidia production and germination decreased in response to the reduction in osmotic and matric potentials. All isolates produced pseudothecia on wheat straw at all water potentials created by PEG8000 over the range of -0.29 to -2.0 MPa. Mycelial growth, conidia production, germination and pseudothecia production were not completely inhibited at any of the osmotic and matric potentials used in this study. In additional experiments, treatment with various concentrations of PEG8000 was used to simulate water stress on the wheat cultivar TAM105 in the second week after planting, followed by inoculation with PTR when three leaves were fully expanded. Increasing water stress on TAM105 was associated with a greater susceptibility to tan spot.