Aflatoxin Production by Aspergillus flavus and A. parasiticus on Visibly Sound Rehydrated Peanut, Corn and Soybean Seed1

Abstract

Peanut, corn and soybean seed were inoculated with 14 isolates of Aspergillus flavus Link and A. parasiticus Speare. The seeds were hand sorted to remove all visibly damaged seeds and were fumigated under vacuum (-95.25 k Pa Hg) with 2.2% cyano (methylmercuri) guanidine at 37 C for 48–96 hours. All fumigated seed had a minimum of 95% germination and a maximum of 5% residual contamination by fungi and bacteria. Corn and peanut samples (100 g/flask) were rehydrated to 28% moisture and inoculated with all isolates; soybean samples (100 g/flask) were rehydrated to 28% moisture and inoculated with four A. flavus and two A. parasiticus isolates. Samples were incubated for 10 days at 30 C and analyzed for aflatoxins. Aspergillus parasiticus isolates produced aflatoxin B1, B2, G1 and G2 while A. flavus isolates produced aflatoxin B1 and B2. Mean B1 production for 12 isolates was 34 mg/kg in peanut seed and 3.6 mg/kg in corn seed. Two A. flavus isolates produced 3.8 to 5.4 mg/kg B1 in peanut seed, and 2.2 mg/kg in corn seed. Overall, the mean B1 production was about 10 times higher on peanut seed than on corn seed. However, more G1 was produced on soybean seed than B1. The isolate and the substrate are apparent limiting factors in aflatoxin production. Peanut seed accumulated more aflatoxin than corn or soybean seed when inoculated with the same isolates and incubated under similar conditions.