Water potential and time of Pyrenophora tritici-repentis inoculation in wheat seeds

Wheat seeds infected with Pyrenophora tritici-repentis, the causal agent of tan spot, are partially responsible for outbreaks caused by this pathogen. Seed lots with a high incidence of P. tritici-repentis must be rapidly acquired for transmission and pathogen-control studies. Therefore, the aim of this study was to determine whether changes in water potential of culture medium and variations in inoculation time might favor the infection of wheat seeds by P. tritici-repentis without compromising seed viability. Colonies of P. tritici-repentis were grown on potato-dextrose-agar (PDA) culture medium, adjusted to a water potential of -0.36 MPa, under water stress induced by mannitol at potentials of -0.4, -0.6, -0.8, -1.0, and -1.2 MPa. Analyses were carried out to determine mycelial growth index and seed exposure time to the culture medium to start germination as a function of water potential. Afterwards, wheat seeds were placed in contact with colonies of P. tritici-repentis for 24, 48, and 72 hours at potentials of -0.4, -0.6, -0.8, -1.0, and -1.2 MPa. The experiment was arranged in a completely randomized design, in a factorial scheme (water potential × inoculation time). Rates of germination, seedling emergence in soil, and seed infection were assessed. Mycelial growth was stimulated at lower water potentials, which germinated faster. A 24-hour inoculation time and a -0.4 MPa water potential were efficient to infect wheat seeds with P. tritici-repentis, without hindering seedling germination and emergence under laboratory conditions.