INFECTION OF WHEAT SEED BY PYRENOPHORA-TRITICI-REPENTIS

The seed infection process of Pyrenophora tritici-repentis, incitant o f tan spot of wheat, was investigated, as were several influencing fac tors. Following inoculation of the wheat spike, P. tritici-repentis ga ined access to the seed by first colonizing the glume, lemma, or palea . Seed infection was first observed 3 d after inoculation, and infecti on incidence increased with time and with inoculum concentration. Whea t seeds were susceptible to infection by this fungus throughout most o f their development, although inoculation at the milk stage resulted i n the highest percentage of infected seeds. Susceptibility to foliar i nfection by P. tritici-repentis was not a good predictor of susceptibi lity to seed infection in four wheat cultivars tested in a glasshouse experiment, except perhaps in 'BR 8', which was significantly less sus ceptible than the other cultivars at early and late stages of seed dev elopment. In a field experiment, wheat seed infection by P. tritici-re pentis occurred primarily after the early dough stage and was positive ly correlated with tan spot severity on the flag leaf shortly after an thesis.