Abstract
Non-fungitoxic concentrations of tricyclazole, pyroquilon, 4, 5, 6, 7-tetrachlorophthalide, PCBA (2, 3, 4, 5, 6-pentachlorobenzyl alcohol), coumarin, pp-389 (4, 5-dihydro-4-methyltetrazolo [1, 5-a] quinazolin-5-one), s-triazolo[4, 3-a] quinoline and N-methyl-2-quinolone inhibit melanin biosynthesis in Pyricularia oryzae. These compounds do not inhibit growth of P. oryzae in culture or conidial germination and appressorial formation on isolated Bryophyllum pinnatum epidermal strips, but block melanization of the appressoria and prevent penetration of the epidermal wall. The epidermal wall is penetrated by infection hyphae from 80 to 95 percent of control appressoria. Successful penetration is observed only when appressoria are melanized. All compounds prevent conversion of scytalone to melanin but not the conversion of vermelone to melanin by P. oryzae. This investigation indicates that these compounds act on the pathogen by a similar or an identical mechanism to protect plants by interfering with appressorial functions required for epidermal penetration.
