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Aflatoxin and Sclerotial Production by Aspergillus flavus: Influence of pH. P. J. Cotty, Research plant pathologist, Southern Regional Research Center, U.S. Department of Agriculture, Agricultural Research Service, New Orleans, LA 70179; Phytopathology 78:1250-1253. Accepted for publication 22 April 1988. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1988. DOI: 10.1094/Phyto-78-1250.

Sodium nitrate and ammonium sulfate have different influences on aflatoxin and sclerotial production when used as sole nitrogen sources in solid media. The effects are attributable, at least in part, to pH. Ammonium-based media became acidified during culture, while aflatoxin production increased, and sclerotial production was totally inhibited. Sclerotia were produced on buffered ammonium media. Sclerotial production increased with increased pH on buffered ammonium media while aflatoxin production declined; aflatoxin was not produced after sclerotial maturation (5 days of incubation). Aflatoxin B1 concentrations declined in acidic ammonium media, whereas aflatoxin B2 remained stable. Nitrate-based media pH increased with fungal growth and production of large quantities of sclerotia and low concentrations of aflatoxin. Lowering nitrate media pH during culture with exogenous HCl totally inhibited sclerotial production and increased aflatoxin production 10-fold. Sclerotia produced on nitrate media contained less aflatoxin than those produced on ammonium media. Results suggest a pH-mediated, interrelated regulation of sclerotial morphogenesis, and aflatoxin biosynthesis.