Aflatoxin in Arizona cottonseed: increase in toxin formation during field drying of bolls

Aflatoxin assays and moisture determinations were made on locks from bolls inoculated with Aspergillus flavus 30-32 days from flower and harvested after additional periods of 5, 7, 9, 11, 13 and 15 days. Inoculated locks were always tight but had moisture contents comparable to those in non-inoculated locks on the same bolls. Lowest toxin concentrations were in seeds from bolls still green at harvest with moisture contents > 50%; highest concentrations were in bolls with fully fluffed locks and moisture contents < 10%. The greatest increase in toxin concentrations occurred in bolls following suture opening, at the initiation of boll dry-down. Toxin concentrations were comparable for bolls that fluffed in 11 days from inoculation and those requiring 15 days for fluffing. A boll fluffing 11 days from inoculation had the highest level of toxin detected, ca 400 mu g/g. The ripening and drying processes rather than the duration of fungal/plant interaction per se seems critical for maximum toxin formation.