Initial tests of two‐hybrid switch in Phytophthora infestans. (A) Shown from top to bottom are the linearized maps of plasmids expressing the GAL4 DBD‐EcR chimera, VP16‐RXR fusion and β‐glucuronidase (GUS) reporter. Not shown are the neomycin phosphotransferase II (nptII) cassettes. (B) Histochemical staining of GUS in transformants (T2, T13, T92) obtained using the three plasmids, a negative control transformant containing the GUS reporter alone (NC) and a strain expressing GUS from the Ham34 promoter (CC). Cultures were grown as described in Fig. 3 with 0, 0.01 or 1 mm inducer. (C) Specific activity of GUS in transformants grown for 24 h in rye–sucrose broth containing 10 μm methoxyfenozide or the dimethylsulphoxide (DMSO) solvent alone. Numbers above the bars represent the fold induction by methoxyfenozide.