Novel strains of Non-toxigenic Aspergillus flf lavus and their Potential to Control Fungal Growth and Af lflatoxin B1 Production in Maize

Abstract

Aspergillus spp. were isolated from soil and agricultural product of 25 provinces across Thailand by soil dilution spread plate technique and agar plate method using DG18 medium. The isolates were identified for morphological character using microscopy. The Aspergillus spp. found in this study were A. flavus (602 isolates), A. tamarii (97 isolates) and A. nomius (20 isolates). Strains of A. flavus were preliminary screened for aflatoxin production strains using coconut agar method. After 5 days of incubation in the dark, plates were examined under UV light at 365 nm. Plate contained aflatoxin-producing strains showed luminescent blue colour. One hundred and seven strains which did not show blue colour were selected. The strains were re-checked for their ability to produce aflatoxin using YES medium. Only 2 isolates did not produce aflatoxin. Two non-aflatoxin producing strains (No. 400 and 561) were tested for antagonistic efficacy to control aflatoxin-producing strains (A. flavus No. A39) by competition plate method. Strains No. 400 and 561 could suppress A39 strain which resulted to reduction of AFB₁contents for 100 and 99.1%, respectively. These two strains were genetically identified as A. flavus.. before being applied to maize for controlling aflatoxin-producing strains. Maize confined with A. flavus No. 400 and 561 contained AFB₁ concentrations lower than control group for 83.92 and 97.43 %. The result indicated that A. flavus No. 400 and 561 could be a novel strain of non-toxigenic fungi found in Thailand to repress aflatoxin-producing strain of A. flavus resulting to low contamination of aflatoxin in maize.