Mycotoxigenic potential ofAspergillus flavus strains isolated from groundnuts growing in Israel

Two hundred strains of the Aspergillus flavus group isolated from groundnuts (peanuts) growing in Israel were examined for their ability to produce mycotoxins in potato dextrose (PD) broth. Almost 77% of the isolates produced aflatoxin; aflatoxins B₁ and B₂ were formed by most of the isolates. Simultaneous production of aflatoxins of groups B and G was detected in only 0.5% of the isolates. Microscopic examination revealed that 98% of the isolates wereA. flavus and only 2%A. parasiticus. Cyclopiazonic acid (CPA) was detected in 22.5% of the isolates, including 3.5% that produced only CPA. Sterigmatocystin was detected in only 2% of the isolates and only one isolate produced aflatoxin simultaneously with CPA and sterigmatocysin. The dry weight (DW) of mycelium, 7 days after inoculating the medium, was between 71–110 mg/30 ml medium in more than 70% of the isolates. A general decrease in the pH was observed and 75% of the isolates reduced the pH to 4.5 or below. After 14 days, a small increase in DW and an increase in the pH toward neutrality was observed. On PD agar, 30% of the isolates produced sclerotia, including 5% that produced them profusely. No correlation between mycelial growth, changes in pH of the medium, sclerotium formation, and aflatoxin accumulation could be observed. The mycotoxigenic potential of theA. flavus strains isolated from groundnuts seems to be relatively high and may present a potential threat to human and animal health.Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan 50250, Israel. No. 3559-E.