Isolation and characterization of two nonaflatoxigenic classes of morphological variants of Aspergillus parasiticus [Aflatoxin production]

Serial transfer of mycelial macerates of aflatoxigenic strains of Aspergillus parasiticus produced 2 morphological variants. The “fan” variant type showed flat growth, a gradient of sporulation density, absence of mycelial pigmentation and deep furrows on the back of the colony. The “fluff” variants displayed abundant aerial mycelium, sparse sporulation, absence of mycelial pigmentation and furrows on the reverse of the colony. Neither “fan” nor “fluff” produced detectable aflatoxin. In a marked mutant strain, the appearance of “fan” and “fluff” and their concomitant loss of aflatoxin production occurred whereas spore color and auxotrophic markers were retained. A parasexual diploid synthesized from the mutant strain with the “fan” phenotype produced high levels of aflatoxin whereas a parasexual diploid containing the “fluff” pheno‐type produced low levels of aflatoxin. The unusual mode of isolation, the differential retention of aflatoxin and other genetic markers in a mutant strain, and the different levels of aflatoxin production in parasexual diploids with “fan” and “fluff” imply an unusual genetic mechanism for the control of the aflatoxin pathway.