ABSTRACT

Racemic, (—)-, and (+)-gossypol were evaluated over a concentration range of 0 to 400 µg per mL for effects on several Aspergillus flavus growth parameters. In the concentration range tested, racemic gossypol did not stimulate conidial germination on water agar alone. In a germination stimulatory environment (potato dextrose medium), racemic gossypol concentrations of ≥ 200 µg per mL decreased the number of germinated conidia, germ tube length and conidiophore development, and increased frequency of hyphal branching. (—)-Gossypol elicited the same fungal responses as racemic gossypol, but at lower concentrations (≥ 50 µg/mL). (+)-Gossypol was less active than racemic gossypol. Activity differences exhibited by the different enantiomers of gossypol were quantitative in nature and activity of racemic gossypol equaled the sum of activities of the individual optical isomers. The observed inhibitory effects on A. flavus development were temporal, and were partially reversed with longer incubation. Thus, A. flavus appeared to adapt to the presence of gossypol to overcome its inhibitory growth effects.