Mycopathologia 127: 29-33, 1994. © 1994 Kluwer Academic Publishers. Printed in the Netherlands. Time of Aspergillus flavus infection and aflatoxin formation in ripening of figs Hamid Boudra, Joseph Le Bars, Pierette Le Bars & Jacques Dupuy Station de Phamacologie-ToxicoIogie, Institut National de la Recherche Agronomique, Toulouse, France Received 17 March 1993; acceptedin revised form 22 March 1994 Abstract. Figs in an orchard were inoculated with an aflatoxigenic Aspergillus 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 B~ (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 i ppm after 10 days. The mean level of AF Bx (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 Bx 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 B~ was detected with a lower incidence in association with low mean levels (less than 1.25 rig/g). Methods of prevention of aflatoxin contamination at the critical step, the firm ripe stage, are discussed. Key words: Aflatoxin, Aspergillus flavus, Figs, Orchard Introduction Dried figs are considered susceptible to aftatoxin B1 (AF B1) contamination [1, 2] since the first report of this in 1974 [3]. Despite the practice of industrial sorting based on the Bright Green Yellow Fluorescence (BGY-F) appearing under UV light (360 nm), contamination of figs by afla- toxin remains an important problem reported from England [4], France [5], Italy [6], Sweden [7], Switzerland [7, 8] and Turkey [9, 10]. To re- duce the risk of fig contamination requires knowl- edge of the moment and mechanisms of fig infec- tion by Aspergillus flavus. Buchanan et al. [1] have shown that the immature green fig did not support colonization and AF B1 production by A. flavus but became susceptible when ripe. Nev- ertheless the precise stage of fig maturation con- ducive to fungal growth and AF contamination is not known. The present work was thus designed (1) to determine the critical period in fig develop- ment for A. flavus with subsequent toxinogenesis; (2) to determine the main way of infection, whether internal or external. Materials and methods Experimental procedure. An aflatoxigenic isolate of A. flavus recently isolated from algerian wal- nuts, was cultured on malt agar Petri dishes. After 10 days of incubation, the spores were har- vested in two ways (1) spores suspension in 0.1% of Tween solution, (2) talc mixture. The experi- ment was done on figs on the tree in an orchard close to Algiers. The variety concerned (Tagh- limt) provides dry figs. Fruit partially dried on the tree, was collected and sun-dried on clay for 7-10 days. Trees and fruits were not chemically