The oomycete Pythium oligandrum expresses putative effectors during mycoparasitism of Phytophthora infestans and is amenable to transformation

► Stable transformation of the oomycete Pythium oligandrum was achieved for the first time. ► Use of the GFP reporter gene shows parasitism of Phytophthora infestans by P. oligandrum. ► Novel P. oligandrum transcripts were identified along with those similar to plant-pathogenic oomycetes. ► Putative effectors were expressed during mycoparasitism.