Effect of Pyroquilon, an Inhibitor of Melanin Synthesis, on Sporulation and Secondary Infection of Magnaporthe grisea

Abstract The effect of pyroquilon. an inhibitor of meianin synthesis. on the sporulation and secondary infection of Magnaporthe grisea spores was investigated. Spore formation of M. grisea was significantly inhibited on the pyroquilon‐containing medium. but mycelial growth was not impaired. Moreover, although the colour of the spore suspension obtained from control medium without pyroquilon was black, the suspension prepared from spores which had grown on the pyroquilon‐containing medium was red‐brown. The cell walls of the spores consisted of two layers. the outer of which was highly electron‐dense and saw‐like in cross section, regardless of treatment. Both the outer and the inner layers of the cell walls of spores which had grown on pyroquilon‐containing medium were thin compared with those of control spores. When M. grisea spores which had formed on the pyroquilon‐containing medium were inoculated onto rice leaf sheaths, red brown appressoria were formed. Compared with the control, appressorial penetration and hyphal growth in the host cells were inhibited. The inhibitory effect pyroquilon exerted upon the infection behavior of M. grisea spores was dependent on the dose of the chemical.