Factors affecting aflatoxin contamination of cottonseed. I. Contamination of cottonseed with Aspergillus flavus at harvest and during storage

Examination of cottonseed production has shown that boll weevils ( Anthonomus grandis ), boll rots, and improper handling and storage conditions are critical factors in Aspergillus flavus contamination of cotton‐seed. A. flavus cultures were isolated from both field‐collected and laboratory emerged boll weevils, as well as from boll weevil emergence holes. Diseased cotton bolls have been found to contain A. flavus conidia. Infection by A. flavus was limited to the surface of cottonseeds collected from gin and from the gin blower. Seeds improperty stored outside the gin were infected internally with A. flavus . Observation of bright greenish‐yellow fluorescence was not useful as a diagnostic procedure to detect contaminated seeds. Aflatoxin‐producing potential of A. flavus isolates is being investigated. When A. flavus conidia were artifically inoculated onto the surface of the seeds, 87% of the seeds from Athens, GA, were internally infected whereas only 29% of the seeds from Macon, GA, were internally infected. A. flavus invade the cottonseed embryo through the chalazal region, the micropylar region, or cracks developed in the seed coat during ginning. Invasion of cottonseed by A. flavus was predominant at 28, 30, and 37 C while at 15 and 20 C other fungi dominated in surface and internal invasions of cottonseed. At relative humidities of 75% and 80%, Chaetomium spp. successfully competed in growth on the surface, while at a relative humidity of 90% and above, fungi belonging to the order Mucorales outgrew A. flavus .