Screening and assessment of phenotypic diversity in nontoxigenic strains of Aspergillus flavus in pistachio orchards of Iran

The use of nontoxigenic strains of Aspergillus flavus as an effective biological method to reduce aflatoxin is being developed in different countries. Nontoxigenic strains are able to compete with toxigenic strains by substrate occupation, which reduces the toxigenic population and the amount of aflatoxin in the substrate. The aim of study was to investigate the morphological diversity in the nontoxigenic population of A. flavus. To isolate nontoxigenic strains from 225 fruit and pistachio soil samples obtained from different provinces, AFPA culture medium and dilution series method were used. Primary nontoxigenicity screening was performed by ammonia vapor method in coconut agar medium and thin layer chromatography was used for result confirmation. Isolates were identified molecularly using FLAVIQ1/FlaQ2 species-specific primers. In order to identify the macromorphological and micromorphological features of 56 obtained strains, four culture media including CYA (Czapek yeast agar), MEA (malt extract agar), CY20S (Czapek yeast 20% sucrose) and CZ (Czapek) were used. Investigation of macro-micromorphological features, classified A. flavus strains into five groups. Colony growth pattern on CYA25 cultural media has shown good differentiation between isolates. The results showed that there is a great variety among nontoxigenic A. flavus isolates obtained from different agro ecological zones due to the presence of different species in the A. flavus complex.