Charaterization of toxigenic and atoxigenicAspergillus spp. strains isolated from corn fields in Thailand

Abstract

Aspergillus flavus is morphologically similar to other species of the section Flavi. A facile method to distinguish these species based on cultural characteristics is reported. Several A. flavus and some related strains in section Flavi including A. parasiticus, A. nomius, and A. tamarii were isolated, and characterized from corn fields in different areas of Thailand. Aspergillus section Flavi produced a wide range of color in reverse on Apergillus flavus and parasiticus agar (AFPA) at 30°C for 7 days in the dark including dark yellow orange {A. flavus, A. parasiticus, and A.oryzae), pale yellow (A. parasiticus, and A. nomius), and pale or dark brown (A. tamarii, and A. pseudotamarii). Only A. flavus produced columnar shape of conidiophores in V8 medium. All isolated strains in Aspergillus section Flavi produced kojic acid in modified rice medium. Only A. flavus produced synnemata on modified Czapek medium containing (20-1,000 1/L) Avid®. This novel, yet readily prepared, culture medium permits differentiation of A. flavus from related species in section Flavi. Aflatoxins producing strains were identified to be A. flavus, A. parasiticus, and A. nomius. Isolated fungi in Aspergillus section Flavi differently produced aflatoxins including A. parasiticus produced aflatoxin B more than G, A. nomius produced aflatoxin G more than B, and A. flavus widely produced range of aflatoxins. Twenty three stains of atoxigenic strains of A. flavus were observed in the isolates. Some aflatoxin producing strains of A. flavus were obtained from some areas without more com cultivation, produced high quantity of aflatoxin yields. So high level of com cultivation areas did not specific to find aflatoxin producing strains of A. flavus in Thailand. Inhibition of aflatoxins production from toxigenic strains A. flavus by the same strain of atoxigenic involves solution factors more than living cell of fungi (mycelial network, or touching).