Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/10/2003
Publication Date: 3/1/2003
Citation: Mellon, J.E., Cotty, P.J., Dowd, M.K. 2003. Effects of optically active gossypol on conidia germination and growth of Aspergillus flavus. Proceedings of National Cotton Council Beltwide Cotton Conference. p. A29-A32. Interpretive Summary: Aflatoxin is a very potent carcinogen and toxin that is produced by the fungus Aspergillus flavus. When this fungus infects cotton plants, the developing seed can become contaminated with this toxin, rendering the product unusable for food or feed. Cottonseed contains up to 1.5 percent (by weight) gossypol, a plant derived chemical that helps protect the plant from insect predation. The fungus can potentially encounter high levels of gossypol during seed invasion. An investigation was undertaken to determine the effects of gossypol on fungal growth; a bioassay was designed to test the effects of two different chemical forms (optical isomers) of gossypol on fungal growth. Gossypol was found to inhibit germination of vegetative spores (conidia), as well as inhibit fungal growth in general. One optical isomer was about three times more active than a mixture of the two isomers (1:1 ratio); the other optical isomer was less active than the 1:1 mixture. However, the fungus was able to adapt to the presence of gossypol; it had less effect with increased time. This research will benefit cotton producers and pathologists, and will aid in the formulation of methods to prevent aflatoxin contamination of food and feedstuffs.
Technical Abstract: Racemic, (-)- and (+)- gossypol were evaluated over a concentration range of 0 to 400 ug 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 equal to or greater than 200 ug 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 (equal to or greater than 50 ug/mL). (+)-Gossypol was less active than racemic gossypol. Activity differences exhibited by the different enantiomers of gossypol were quantitative in nature. The biological activity exhibited by racemic gossypol with A. flavus appeared to be the sum of activities of the individual optical isomers. These inhibitory effects on A. flavus development were temporal, and were partially reversed at longer incubation times. Thus, A. flavus appeared to adapt to the presence of gossypol to overcome its inhibitory effects on fungal growth.