Zymoseptoria tritici is the causal agent of Septoria leaf blotch of wheat. On the leaf, spores of this fungus germinate to form hyphae, which extend across the leaf surface and penetrate the leaf via stomata. However, in contrast to other plant pathogens, spores of Z. tritici germinate very asynchronously and hyphae spend a long and variable period exploring the leaf surface. Many isolates undergo microcycle conidiation on the leaf surface, reproducing via yeast-like budding. This behaviour can be seen in compatible interactions where disease ensues, as well as in incompatible interactions where stomatal entry is prevented by the host plant. In the Fones lab, we study the period of epiphytic (leaf surface) growth by Z. tritici, seeking to understand how it obtains nutrients and survives in an environment where drying, UV, and fungicide stressors are all present. We are interested in understanding how this extended period of leaf surface growth and reproduction affects the population genetics of the pathogen, including its effects upon the evolution of virulence on resistance wheat and the emergence of fungicide resistance, a key challenge in this fungus. We have discovered that Z. tritici is able to form biofilms which show increased resistance to fungicides and drying, and that some of these biofilms include cross-kingdom interactions with bacteria. We are currently investigating biofilm formation and the interactions of Z. tritici with a library of leaf-surface microbes from field-grown wheat, with a view to identifying ways to manipulate the microbiome for disease control.