Effect of pentachloronitrobenzene, pentachloroaniline, and albinism on epidermal penetration by appressoria of Pyricularia

Abstract

Pentachloroaniline or pentachloronitrobenzene at concentrations between 0.5 and 5 μg/ml blocked appressorial melanization and appressorial penetration of onion epidermal cell walls by Pyricularia oryzae, strain P-2, without affecting conidial germination or appressorial formation. Among polyphenol oxidase inhibitors, salicylhydroxamic acid, and phenylthiourea at 100 μg/ml inhibited appressorial penetration of onion epidermis without affecting appressorial melanization, whereas sodium diethyldithiocarbamate and 2,3-naphthalenediol did not affect either process at 1.0 μg/ml but inhibited conidial germination and appressorial formation at 10 μg/ml. EDTA was without effect on either melanization or penetration at 100 μg/ml. The melanized appressoria of Pyricularia grisea, strain BL-3, penetrated onion epidermal cell walls, whereas nonpigmented appressoria of an albino mutant (AL-3) of this fungus did not. Melanization and penetration ability of AL-3 appressoria were restored by adding melanin biosynthesis intermediates scytalone or 1,8-dihydroxynaphthalene (1,8-DHN). Tricyclazole blocked melanization and epidermal penetration by AL-3 appressoria treated with scytalone but not by those treated with 1,8-DHN. Scytalone (20 μg/ml) increased the effectiveness of tricyclazole in blocking penetration by appressoria of BL-3. Tricyclazole was about 10 times more effective in inhibiting penetration by P-2 appressoria than by BL-3 appressoria.