Action mechanism of the novel rice blast fungicide tolprocarb distinct from that of conventional melanin biosynthesis inhibitors

The target site of tolprocarb, a novel systemic fungicide used for controlling rice blast, was investigated. Tolprocarb decolorized the mycelia of Magnaporthe grisea; the decolorization was reversed by adding scytalone or 1,3,6,8-tetrahydroxynaphthalene (1,3,6,8-THN). This result suggested that the target site of tolprocarb was polyketide synthase (PKS), which regulated polyketide synthesis and pentaketide cyclization in melanin biosynthesis. Further, we produced a transgenic Aspergillus oryzae, which possessed the PKS gene of M. grisea, and performed in vitro assays of PKS using membrane fractions from the transgenic A. oryzae. Compared with some conventional melanin biosynthesis inhibitors (cMBIs), tolprocarb only inhibited PKS activity in vitro. These results indicated that tolprocarb's target protein in M. grisea was PKS, which differentiates this fungicide from other cMBIs. Pesticide Science Society of Japan