Time ofAspergillus flavus infection and aflatoxin formation in ripening of figs

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Abstract
Figs in an orchard were inoculated with an aflatoxigenicAspergillus flavus strain in two ways by spore injection or by dusting at three maturation stages: firm ripe, shrivelled, and dried. Fruits were individually examined for fungal development and analyzed for aflatoxin B1 (AF B1) after 2, 4, 6, 8 and 10 days. Fruit injected at the first stage showed fungal development and AF B1 contamination within two days. The toxin level increased sharply to 1 ppm after 10 days. The mean level of AF B1 (284.75 ng/g) was significantly higher than those observed in other conditions. Figs dusted at the first stage showed only a tiny fungal growth even after 10 days. AF B1 appeared after 6 days with a low frequency (35%), mean level (7.6 ng/g) and a great variation among figs (0.22–15 ng/g). Among fruits inoculated during the shrivelled fig and dried fruit stages, no fungal growth was observed and AF B1 was detected with a lower incidence in association with low mean levels (less than 1.25 ng/g). Methods of prevention of aflatoxin contamination at the critical step, the firm ripe stage, are discussed.