Wheat seed colonized with atoxigenic Aspergillus flavus: Characterization and production of a biopesticide for aflatoxin control

Biocontrol of aflatoxin contamination using atoxigenic Aspergillus flavus t o competitively exclude aflatoxin-producing strains has previously been rep orted and is currently in the third year of commercial-scale tests (treatin g 50-200 ha per annum). Wheat seed colonized with atoxigenic A. flavus has been used in the commercial trials. Requirements Sor production of this col onized wheat seed are described and the spore yield of wheat is compared to other substrates. The study suggests that the most cost-effective inoculum production would require colonization of wheat (10(6) conidia kg(-1) of wh eat seed) at 25% (w/w) moisture for 18 h at 31 degrees C. To prevent fungal growth and associated wheat aggregation in storage, seed had to be dried b elow, 15% (w/w) moisture, although a moisture content of 35% (w/w) did not reduce viability in sealed containers stored at 18-25 degrees C over an 8-m onth period. The dry biopesticide had multi-year stability without refriger ation and withstood temperatures of 70 degrees C for 20 min. Sporulation of the product occurred within 3 days at 31 degrees C and 100% relative humid ity with yields averaging 4.9 x 10(9) conidia g(-1) by day 7.