Recovery of Appressorial Penetration by Some Melanin Precursors in Pyricularia oryzae Treated with Tricyclazole and in a Melanin Deficient Mutant

Abstract

Spores of Pyricularia oryzae treated with tricyclazole [5-methyl-1, 2, 4-triazolo(3, 4-b)benzothiazole] at concentrations higher than 0.1μM produced hyaline appressoria on cellulose membrane. The appressoria lacked the ability to penetrate the membrane. The inhibitory effect of tricyclazole (0.2μM) was nullified completely by the addition of 3, 4-dihydroxyphenyl alanine (DOPA) (10μM) and partially by the addition of 1, 8-dihydroxynaphthalene (1, 8-DHN) (50μM) but not by that of scytalone. DOPA and 1, 8-DHN also colored hyaline appressoria of a melanin deficient mutant with no ability to penetrate cellulose membrane isolated from a wild type P. oryzae and the melanized appressoria recovered the ability to penetrate cellulose membrane. The results presented in this paper suggest that it is the lack of melanization in appressoria that caused failure of penetration from appressoria in P. oryzae treated with tricyclazole and in its melanin deficient mutant.